WO2025051570A1 - Polymerisation inhibitors - Google Patents

Abstract

The present invention relates to a mixture containing at least one 1,2,3,4-tetrahydroquinoxaline and at least one polymerisable carbonyl compound.

Description

Polymerization inhibitors

The present invention relates to a mixture containing at least one substituted 1,2,3,4-tetrahydroquinoxaline and at least one polymerizable carbonyl compound.

Chemical compounds that contain one or more ethylenically unsaturated groups have a pronounced tendency toward radical polymerization. Such compounds are therefore also referred to as polymerizable compounds. Due to their tendency toward radical polymerization, these compounds are used as monomers for the production of polymers. However, the pronounced tendency of these compounds toward radical polymerization is disadvantageous in that unwanted, spontaneous radical polymerization can occur during storage and transport, as well as during chemical and/or physical processing, such as distillation or rectification, particularly under the influence of energy, such as heat and/or light. Such uncontrolled polymerizations can lead to the gradual formation of polymer deposits, for example, on heated surfaces, which makes removal of the polymer deposits necessary and thus often leads to a reduction in operating times. The uncontrolled polymerizations can even be explosive.

It is therefore common practice to add compounds that inhibit or at least slow down unwanted, spontaneous radical polymerization to ethylenically unsaturated compounds that have a tendency toward radical polymerization, or to mixtures containing such compounds, both during storage and transport and during chemical and/or physical processing. Such substances are referred to as polymerization inhibitors.

Polymerization inhibitors can be used as individual chemical compounds or as mixtures of compounds. Depending on the application, the polymerization inhibitor must meet specific requirements. For a polymerization inhibitor to be suitable as a transport and/or storage stabilizer for ethylenically unsaturated compounds, it is important that its efficiency, i.e., the extent of polymerization inhibition, can be regulated. Under the storage and/or transport conditions of the ethylenically unsaturated compounds, the polymerization inhibitor should sufficiently inhibit or slow down unwanted, spontaneous radical polymerization, while allowing the desired radical polymerization of the ethylenically unsaturated compounds under appropriate polymerization conditions without the need to first separate the polymerization inhibitor used during storage and/or transport. If the stabilizer used during storage and/or transport is not separated during the desired polymerization, it is important that it does not adversely affect the polymerization during the desired polymerization, for example by acting unintentionally as a regulator.

Measured by global production volume, acrylic acid is certainly one of the most important ethylenically unsaturated compounds. Acrylic acid is normally stored and/or transported at 0.018 up to 0.022 wt. % hydroquinone monomethyl ether (MEHQ), based on the amount of acrylic acid, stabilized against unwanted, spontaneous radical polymerization. For adequate stabilization of acrylic acid against unwanted, spontaneous radical polymerization by means of MEHQ, it is necessary that oxygen is dissolved in the acrylic acid in sufficient quantities. Sufficient quantities of oxygen are generally dissolved in the acrylic acid when acrylic acid is stored and/or transported under an atmosphere containing 5 to 21 vol. % oxygen. During the deliberate polymerization of acrylic acid, the oxygen content dissolved in the acrylic acid is reduced, whereby the effectiveness of MEHQ in inhibiting polymerization is reduced to such an extent that acrylic acid can be polymerized in the presence of MEHQ.

In addition to its use as a polymerization inhibitor during storage and/or transport of acrylic acid, MEHQ is also used as a polymerization inhibitor during storage and/or transport of methacrylic acid, acrylic acid esters and/or methacrylic acid esters or mixtures containing one or more of the aforementioned compounds.

Due to its wide use, MEHQ is one of the most important storage and/or transport stabilizers for polymerizable compounds, especially for acrylic acid, methacrylic acid, acrylic acid esters and methacrylic acid esters.

Polymerizable compounds are stored in suitable, permanently installed containers, such as storage tanks or storage containers (see, for example, Acrylic Acid, A Summary of Safety and Handling, 4th Edition 2013, 7 Bulk Storage Facilities and Accessories). It is preferred that the polymerizable compounds remain in the respective containers for at least one minute during storage, more preferably at least 10 minutes, and most preferably at least 60 minutes. Although the storage period is theoretically unlimited under appropriate conditions, the storage period is generally reduced to a minimum for economic reasons. It is preferred that the polymerizable compounds remain in the respective containers for a maximum of 180 days, more preferably for a maximum of 90 days, and most preferably for a maximum of 30 days. Particularly preferred ranges result from any combination of the aforementioned lower and upper limits.

The transport of polymerizable compounds is usually carried out in suitable, transportable containers such as tanks or containers by ship, railcar and/or truck (see, for example, Acrylic Acid, A Summary of Safety and Handling, 4th Edition 2013, 9 Safe Transport of Acrylic Acid). Of course, the transportable containers can also be permanently installed on the corresponding means of transport, for example ship tanks or rail tank cars. It is also possible for the containers to be stored at a specific location for a certain period of time before being transported to another location. The transport of polymerizable compounds can also take place in pipelines or hoses, for example, after purification of the polymerizable compounds to the storage tank, during loading from the storage tank to a transportable container and/or during loading from one transportable container to another. It is preferred that the polymerizable compounds are present in the respective containers for at least 10 seconds, preferably at least one minute, more preferably at least 10 minutes, and most preferably at least 60 minutes during transport. Although the duration is theoretically unlimited under appropriate conditions, the duration is generally reduced to a minimum for economic and safety reasons. It is preferred that the polymerizable compounds are present in the respective containers for a maximum of 180 days during transport, more preferably for a maximum of 90 days, and most preferably for a maximum of 30 days. Particularly preferred ranges result from any combination of the aforementioned lower and upper limits.

It was the object of the present invention to provide mixtures containing at least one polymerizable carbonyl compound, in particular acrylic acid, methacrylic acid, acrylic acid esters, and/or methacrylic acid esters, and at least one polymerization inhibitor. The polymerization inhibitors are intended to ensure sufficient stabilization of the polymerizable compounds against unwanted radical polymerization. However, in the case of desired radical polymerization, there should be no need to separate the polymerization inhibitors from the mixture prior to polymerization. The polymerization inhibitors should therefore not act as polymerization regulators and/or polymerization inhibitors in the case of desired radical polymerization.

wobei The object is achieved by mixtures containing at least one compound of the general formula (I)

where

R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxy or halide,

R ⁵ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl,

R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxy or halide and

wobei R ¹⁰ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, or a compound of the general formula (II)

where

R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxy or halide,

R ¹⁵ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl,

R ¹⁶ and R ¹⁷ are independently H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxy or halide and

R ¹⁸ is H, C 1 -C 20 -alkyl, C 1 -C 20 -acyl, or aryl, and at least one polymerizable carbonyl compound, wherein the total amount of the polymerizable carbonyl compound in the mixture is at least 30 wt. %, based on the total weight of the mixture. The polymerizable carbonyl compounds are among the polymerizable compounds. The polymerizable carbonyl compounds are preferably ethylenically unsaturated carbonyl compounds.

The alkyl groups can be straight, branched and/or cyclic, whereby branched and cyclic alkyl compounds would only be possible from Ce-alkyl onwards.

Preferably, R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 8 -alkyl, C 1 -C 8 -alkoxy, hydroxyl or halide, R ⁵ is H or C 1 -C 8 -alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, C 1 -C 8 -alkyl, C 1 -C 8 -alkoxy, hydroxyl or halide and R ¹⁰ is H or C 1 -C 8 -alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 -C 8 -alkyl, C 1 -C 8 -alkoxy, hydroxyl or halide, R ¹⁵ is H or C 1 -C 8 -alkyl, R ¹⁶ and R ¹⁷ are independently H, C 1 -C 8 -alkyl, C 1 -C 8 -alkoxy, hydroxyl or halide and R ¹⁸ is H or C 1 -C 8 -alkyl.

More preferably, R ¹ , R ² , R ³ and R ⁴ are each independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy, R ⁵ is H or C 1 -C 2 -alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are each independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy and R ¹⁰ is H or C 1 -C 2 -alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are each independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy, R ^{15 is} H or C 1 -C 2 -alkyl, R ¹⁶ and R ¹⁷ are each independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy and R ^{18 is} H or C 1 -C 2 -alkyl. Particularly preferably, R ¹ , R ² , R ³ and R ⁴ are independently H, Ci- to C alkyl or Ci- to C ikoxy, R ⁵ is H or Ci- to Cs-alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, Ci- to C alkyl or Ci- to C ikoxy and R ¹⁰ is H or Ci- to Cs-alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, Ci- to C alkyl or Ci- to C ikoxy, R ¹⁵ is H or Ci- to Cs-alkyl, R ¹⁶ and R ¹⁷ are independently H, Ci- to C alkyl or Ci- to C ikoxy and R ¹⁸ is H or Ci- to Cs-alkyl.

Particularly preferably, R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 - C 2 alkyl or C 1 - C 2 alkoxy, R ⁵ is H or C 1 - C 2 alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, C 1 - C 2 alkyl or C 1 - C 2 alkoxy and R ¹⁰ is H or C 1 - C 2 alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 - C 2 alkyl or C 1 - C 2 alkoxy, R ¹⁵ is H or C 1 - C 2 alkyl, R ¹⁶ and R ¹⁷ are independently H, C 1 - C 2 alkyl or C 1 - C 2 alkoxy and R ¹⁸ is H or C 1 - C 2 alkyl.

Suitable compounds of the general formula (I) are, for example, 1,2,3,4-tetrahydroquinoxaline, 1-methyl-1,2,3,4-tetrahydroquinoxaline, 2-methyl-1,2,3,4-tetrahydroquinoxaline, 5-methyl-1,2,3,4-tetrahydroquinoxaline, 6-methyl-1 ,2,3,4-Tetrahydroquinoxaline, 1-Ethyl-1,2,3,4-Tetrahydroquinoxaline, 2-Ethyl-1,2,3,4-Tetrahydroquinoxaline, 5-Ethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Ethyl-1,2,3,4-Tetrahydroquinoxaline, 1-propyl-1,2,3,4-tetrahydroquinoxaline, 2-propyl-1,2,3,4-tetrahydroquinoxaline, 5-propyl-1,2,3,4-tetrahydroquinoxaline, 6-propyl-1,2,3,4-tetrahydroquinoxaline, 1-Butyl-1,2,3,4-Tetrahydroquinoxaline, 2-Butyl-1,2,3,4-Tetrahydroquinoxaline, 5-Butyl-1,2,3,4-Tetrahydroquinoxaline, 6-Butyl-1,2,3,4-Tetrahydroquinoxaline,

1-phenyl-1,2,3,4-tetrahydroquinoxaline, 2-phenyl-1,2,3,4-tetrahydroquinoxaline, 5-phenyl-1,2,3,4-tetrahydroquinoxaline, 6-phenyl-1,2,3,4-tetrahydroquinoxaline, 1-benzyl-1 ,2,3,4-Tetrahydroquinoxaline, 2-Benzyl-1,2,3,4-Tetrahydroquinoxaline, 5-Benzyl-1,2,3,4-Tetrahydroquinoxaline, 6-Benzyl-1,2,3,4-Tetrahydroquinoxaline,

2,2-Dimethyl-1,2,3,4-tetrahydroquinoxaline, 2,2-diethyl-1,2,3,4-tetrahydroquinoxaline, 2,2-dipropyl-1,2,3,4-tetrahydroquinoxaline, 2,2-dibutyl-1,2,3,4-tetrahydroquinoxaline, 2,3-dimethyl-1 ,2,3,4-tetrahydroquinoxaline, 2,3-diethyl-1,2,3,4-tetrahydroquinoxaline, 2,3-dipropyl-1,2,3,4-tetrahydroquinoxaline, 2,3-dibutyl-1,2,3,4-tetrahydroquinoxaline, 2,5-dimethyl-1 ,2,3,4-Tetrahydroquinoxaline, 2,5-diethyl-1,2,3,4-tetrahydroquinoxaline, 2,5-dipropyl-1,2,3,4-tetrahydroquinoxaline, 2,5-dibutyl-1,2,3,4-tetrahydroquinoxaline, 2,6-dimethyl-1,2,3,4-tetrahydroquinoxaline, 2,6-diethyl-1 ,2,3,4-tetrahydroquinoxaline, 2,6-dipropyl-1, 2,3,4-tetrahydroquinoxaline, 2,6-dibutyl-1, 2,3,4-tetrahydroquinoxaline, 2, 7-dimethyl-1,2,3,4-tetrahydroquinoxaline, 2,7-diethyl-1 ,2,3,4-Tetrahydroquinoxaline, 2,7-Dipropyl-1,2,3,4-tetrahydroquinoxaline, 2,7-dibutyl-1,2,3,4-tetrahydroquinoxaline, 2,8-dimethyl-1,2,3,4-tetrahydroquinoxaline, 2,8-diethyl-1,2,3,4-tetrahydroquinoxaline, 2,8-dipropyl-1 ,2,3,4-Tetrahydroquinoxaline, 2,8-Dibutyl-1,2,3,4-Tetrahydroquinoxaline,

1,2-Dimethyl-1,2,3,4-tetrahydroquinoxaline, 1,2-diethyl-1,2,3,4-tetrahydroquinoxaline, 1,2-dipropyl-1,2,3,4-tetrahydroquinoxaline, 1,2-dibutyl-1,2,3,4-tetrahydroquinoxaline, 1,3-dimethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1,3-diethyl-1,2,3,4- Tetrahydroq uinoxalin, 1, 3-D ipropyl-1, 2, 3, 4-Tetrahydroq uinoxal in, 1, 3-D ibuty I- 1, 2, 3, 4-Tetrahydroq uinoxal in, 1,4-dimethyl-1,2,3,4-tetrahydroquinoxaline, 1,4-diethyl-1,2,3,4-tetrahydroquinoxaline, 1,4-dipropyl-1,2,3,4-tetrahydroquinoxaline, 1,4-dibutyl-1,2,3,4-tetrahydroquinoxaline, 1,5-dimethyl-1,2,3,4-tetrahydroquinoxaline, 1 ,5-diethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1, 5-Dipropyl- 1,2,3,4-Tetrahydroquinoxaline, 1, 5-Dibutyl-1,2,3,4-Tetrahydroquinoxaline, 1,6-Dimethyl-

1.2.3.4-Tetrahydroquinoxaline, 1,6-diethyl-1,2,3,4-tetrahydroquinoxaline, 1,6-dipropyl-1,2,3,4-tetrahydroquinoxaline,

1,6-Dibutyl-1,2,3,4-tetrahydroquinoxaline, 1,7-dimethyl-1,2,3,4-tetrahydroquinoxaline, 1,7-diethyl-1,2,3,4-tetrahydroquinoxaline, 1, 7-dipropy I-1,2,3,4-tetrahydroquinoxaline, 1, 7-Dibutyl-1,2,3,4-Tetrahydroquinoxaline, 1,8-Dimethy 1-1,2,3,4-Tetrahydroquinoxaline, 1,8-diethyl-1,2,3,4-Tetrahydroquinoxaline, 1,8-Dipropyl-1,2,3,4-Tetrahydroquinoxaline, 1,8-Di- butyl-1 ,2,3,4-Tetrahydroquinoxaline,

1,2,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3-triethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3-tripropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3-tributyl-1,2,3,4-tetrahydroquinoxaline, 1 ,2,3,4-Tetramethyl-1,2,3,4-Tetrahydroquinoxaline,

1.2.3.4-Tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4-tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4-tetrabutyl-

1.2.3.4-Tetrahydroquinoxaline. 1,2,3,4,5-Pentamethyl-1,2,3,4-Tetrahydroquinoxaline, 1, 2,3,4, 5-Pentaethyl-1, 2,3, 4-Tetrahydroquinoxaline, 1,2,3,4,5-Pentapropyl-1,2,3,4-Tetrahydroquinoxaline, 1 ,2,3,4,5-Pentabutyl-1,2,3,4-Tetrahydroquinoxaline, 1,2,3,4,5,6-Hexamethyl-1,2,3,4-Tetrahydroquinoxaline, 1,2,3,4,5,6-Hexaethyl-1,2,3,4-Tetrahydroquinoxaline,

1.2.3.4.5.6-Hexapropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4,5,6-hexabutyl-1,2,3,4-tetrahydroquinoxaline,

1.2.3.4.5.6.7-Heptamethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4,5,6,7-heptaethyl-1,2,3,4-tetrahydroquinoxaline,

1.2.3.4.5.6.7-Heptapropyl-1,2,3,4-Tetrahydroquinoxaline, 1,2,3,4,5,6,7-Heptabutyl-1,2,3,4-Tetrahydroquinoxaline,

1.2.3.4.5.6.7.8-Octamethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4,5,6,7,8-octaethyl-1,2,3,4-tetrahydroquinoxaline,

1.2.3.4.5.6.7.8-Octapropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,3,4,5,6,7,8-octabutyl-1,2,3,4-tetrahydroquinoxaline,

1.2.2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2-triethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2-tripropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2-tributyl-1,2,3,4-tetrahydroquinoxaline, 1 ,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline,

1.3.3-Triethy I- 1,2,3,4-Tetrahydroquinoxaline, 1,3,3-Tripropyl-1,2,3,4-Tetrahydroquinoxaline, 1,3,3-Tributyl-1,2,3,4-Tetrahydroquinoxaline, 1,2,2,4-Tetramethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1,2,2,4-Tetraethyl-1,2,3,4-Tetrahydroquinoxaline,

1.2.2.4-Tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,4-tetrabutyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,3,4-pentamethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,3,4-Pentaethyl-1,2,3,4-Tetrahydroquinoxaline, 1,2,2,3,4-Pentapropyl-

1.2.3.4-Tetrahydroquinoxaline, 1,2,2,3,4-pentabutyl-1,2,3,4-tetrahydroquinoxaline, 1, 2, 2,3,3, 4-hexamethyl-1, 2,3,4-tetrahydroquinoxaline, 1,2,2,3,3,4-hexaethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1,2, 2,3,3, 4-hexapropyl-1, 2,3, 4-tetrahydroquinoxaline, 1,2,2,3,3,4-hexabutyl-1,2,3,4-tetrahydroquinoxaline,

1.2.2.5-Tetramethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,5-tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,5-tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1 ,2,2,5-Tetrabutyl-1 ,2,3,4-Tetrahydroquinoxaline, 1,2,2,6-Tetramethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1 , 2, 2, 6-Tetraethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1 ,2,2,6-Tetrapropyl-1 ,2,3,4-Tetrahydroquinoxaline,

1.2.2.6-Tetrabutyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,7-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,7-tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,7-tetrapropyl-1 ,2,3,4-Tetrahydroquinoxaline, 1, 2,2, 7-Tetrabutyl-1, 2,3,4- Tetrahydroquinoxaline, 1,2,2,8-tetramethyl-l,2,3,4-tetrahydroquinoxaline, 1,2,2,8-tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,8-tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1,2,2,8-Tetrabutyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,5-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,5-tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1, 3,3, 5-tetrapropyl-1, 2,3,4-Tetrahydroquinoxaline, 1 ,3,3,5-Tetrabutyl-1 ,2,3,4-Tetrahydroquinoxaline, 1 ,3,3,6-Tetramethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1 ,3,3,6-Tetraethyl-1 ,2,3,4-Tetrahydroquinoxaline, 1 ,3,3,6-Tetrapropyl-1 ,2,3,4-tetrahydroquinoxaline, 1,3,3,6-tetrabutyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,7-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 1, 3,3, 7-tetraethyl-1, 2,3,4-

Tetrahydroquinoxaline, 1,3,3,7-tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,7-tetrabutyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,8-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 1 ,3,3,8-tetraethyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,8-tetrapropyl-1,2,3,4-tetrahydroquinoxaline, 1,3,3,8-tetrabutyl-1,2,3,4-tetrahydroquinoxaline,

1-Ethyl-2,2-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 1-Ethyl-3,3-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 1,4-Diethyl-2,2-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 1 ,4-Diethyl-2,2,3-Trimethyl-1,2,3,4-Tetrahydroquinoxaline, 1,4-Diethyl-

2.2.3.3-Tetramethyl-1,2,3,4-tetrahydroquinoxaline,

5-methoxy-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1,2,3,4-tetrahydroquinoxaline, 5-propoxy-1 ,2,3,4-tetrahydroquinoxaline, 6-propoxy-1,2,3,4-tetrahydroquinoxaline,

5-methoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 7-methoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 8-methoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 5-Ethoxy-1-methyl-1, 2,3,4-tetrahydroquinoxaline, 6-ethoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 8-ethoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 5-Propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 6-propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 7-propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 8-propoxy-1-methyl-1, 2,3,4-tetrahydroquinoxaline,

5-Methoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-methoxy-1-ethyl-

1.2.3.4-tetrahydroquinoxaline, 8-methoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1-ethyl-1 ,2,3,4-tetrahydroquinoxaline, 8-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 5-propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-propoxy-1-ethyl-1 ,2,3,4-tetrahydroquinoxaline, 8-propoxy-1-ethyl-1 ,2,3,4-tetrahydroquinoxaline,

5-methoxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-2,2-diethyl-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-2,2-diethyl-1 ,2,3,4-Tetrahydroquinoxaline, 5-Methoxy-1,2,2-tri-methyl-1,2,3,4-tetrahydroquinoxaline, 6-Methoxy-1, 2,2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-Methoxy-1, 2,2-trime- thyl-1,2,3,4-tetrahydroquinoxaline, 8-Methoxy-1,2,2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1,2,2-trimethyl-

1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1,2,2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1,2,2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 8-ethoxy-1,2,2-trimethyl-1 ,2,3,4-tetrahydroquinoxaline, 5-methoxy-1,3,3-trimethyl-1,2,3,4- tetrahydroquinoxalin, 6-methoxy-1,3,3-trimethyl-1, 2, 3,4-tetrahydroquinoxalin, 7-methoxy-1, 3,3-trimethyl-1,2,3,4-tetra-hydroquinoxaline, 8-methoxy-1, 3,3-trimethyl-1, 2, 3,4-tetrahy d roq uinoxaline, 5-ethoxy-1,3,3-trimethy 1-1, 2, 3,4-tetrahydroquinoxaline, 6-ethoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1,3,3-trimethyl-l ,2,3,4-tetrahydroquinoxaline, 8-Ethoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline,

5-Methoxy-1,4-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Methoxy-1,4-diethyl-1,2,3,4-Tetrahydroquinoxaline, 5-Ethoxy-

1,4-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Ethoxy-1,4-diethyl-1,2,3,4-Tetrahydroquinoxaline,

5-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 7-methoxy-1,2,2,4-tetramethyl-1 ,2,3,4-Tetrahydroquinoxaline, 8-Methoxy-1,2,2,4-Tetramethyl-1,2,3,4-Tetra-hydroquinoxaline, 5-Ethoxy-1,2,2,4-Tetramethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Ethoxy-1, 2,2, 4-Tetramethyl-1, 2,3,4-Tetrahydroquinoxaline, 7-Ethoxy-1 ,2,2,4-Tetramethyl-1,2,3,4-Tetrahydroquinoxaline, 8-Ethoxy-1,2,2,4-Tetramethyl-

1.2.3.4-Tetrahydroquinoxaline,

5-Hydroxy-1, 2, 3,4-tetrahydroq ui noxal in, 6-Hydroxy-1, 2, 3, 4-tetrahy d roqui noxal I n, 5-Ethoxy-1, 2, 3, 4-tetrahydroqu I noxalin, 6-Ethoxy-1,2,3,4-tetrahydroquinoxaline, 5-propoxy-1,2,3,4-tetrahydroquinoxaline, 6-propoxy-1,2,3,4-tetrahydroquinoxaline,

5-Hydroxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 6-hydroxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 7-hydroxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 8-hydroxy-1-methyl-1 ,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1-methyl-1, 2,3,4-tetra-hydroquinoxaline, 6-ethoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1-methyl-1, 2,3,4-tetrahydroquinoxaline, 8-ethoxy-1-methyl-1 ,2,3,4-tetrahydroquinoxaline, 5-propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 6-Propoxy-1-methyl-

1.2.3.4-tetrahydroquinoxaline, 7-propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline, 8-propoxy-1-methyl-1,2,3,4-tetrahydroquinoxaline,

5-Hydroxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-Hydroxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-hydroxy-1-ethyl-

1,2,3,4-tetrahydroquinoxaline, 8-hydroxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-Ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 8-ethoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 5-propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 6-propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 7-Propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline, 8-Propoxy-1-ethyl-1,2,3,4-tetrahydroquinoxaline,

5-Hydroxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoxaline, 6-hydroxy-2,2-diethyl-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-2,2-diethyl-1 ,2,3,4-Tetrahydroquinoxaline, 5-Hydroxy-1,2,2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-Hydroxy-1,2, 2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-Hydroxy-1,2, 2-trimethy I-

1,2,3,4-tetrahydroquinoxaline, 8-hydroxy-1,2, 2-trimethy 1-1,2,3,4-tetrahydroquinoxaline, 5-ethoxy-1,2, 2-trimethy 1-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1,2, 2-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1,2, 2-trimethy 1-1,2,3,4-tetrahydroquinoxaline, 8-ethoxy-1,2, 2-trimethy I-1,2,3,4-tetrahydroquinoxaline, 5-hydroxy-1,3, 3-trimethy I-1,2,3,4- tetrahydroqu i noxal in, 6-Hydroxy-1, 3, 3-trimethy I-1,2, 3, 4-tetrahydroqu i noxal in, 7-Hy d roxy-1, 3,3-trimethyl-1, 2, 3,4-tetra-hydroquinoxaline, 8-Hy d roxy-1, 3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-ethoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 7-ethoxy-1 ,3,3-trimethyl-1,2,3,4-tetrahydroquinoxa- lin, 8-ethoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline,

5-Hydroxy-1,4-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Hydroxy-1,4-diethyl-1,2,3,4-Tetrahydroquinoxaline, 5-Ethoxy-

1,4-Dimethyl-1,2,3,4-Tetrahydroquinoxaline, 6-Ethoxy-1,4-diethyl-1,2,3,4-Tetrahydroquinoxaline,

5-Hydroxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 6-hydroxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline, 7-hydroxy-1,2,2,4-tetramethyl-1 ,2,3,4-tetrahydroquinoxaline, 8-hydroxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline.

Suitable compounds of general formula (II) are, for example, 3,4-dihydroquinoxalin-2(1 H)-one, 1-methyl-

3.4-di hydroquinoxal in-2(1 H)-one, 3-Methyl-3, 4-dihydroquinoxal in-2(1 H)-one, 4-Methy i-3, 4-dihydroquinoxali n-2(1 H)-one,

5-Methy l-3,4-dihydroquinoxali n-2(1 H)-one, 6-Methyl-3, 4-di hydroquinoxal in-2(1 H)-one, 7-Methy l-3,4-di hydroquinoxalin- 2(1 H)-one, 8-Methyl-3,4-dihydroquinoxalin-2(1 H)-one, 1-Ethyl-3,4-dihydroquinoxalin-2(1H)-one, 3-Ethyl-3,4-dihydroquinoxali n-2(1H)-one, 4-Ethy I-3, 4-dihy d roqui noxali n-2(1 H)-one, 5-Ethy l-3,4-dihy d roqu i noxal i n-2 (1 H)-one, 6-Ethy l-3,4-dihy d- roqui noxal in-2(1 H)-one, 7-Ethyl-3,4-di hydroqui noxal in-2(1 H)-one, 8-Ethy i-3, 4-di hydroqui noxali n-2(1 H)-one,

1-Phenyl-3,4-dihydroquinoxalin-2(1H)-one, 3-phenyl-3,4-dihydroquinoxalin-2(1H)-one, 4-phenyl-3,4-dihydroquinoxalin-2(1H)-one, 5-Pheny i-3, 4-dihydroquinoxali n-2(1H)-one, 6-Pheny i-3, 4-di hydroquinoxal in-2(1 H)-one, 7-Pheny l-3,4-dihydro- qui noxali n-2(1 H)-one, 8-Pheny l-3,4-di hydroquinoxal in-2(1 H)-one, 1 -Benzy i-3, 4-dihydroquinoxali n-2(1 H)-one, 3-Benzyl-

3.4-dihydroqui noxal in-2(1 H)-one, 4-Benzy i-3, 4-dihydroquinoxali n-2(1 H)-one, 5-Benzy l-3,4-di hydroqui noxal in-2(1 H)-one,

6-Benzyl-3, 4-dihydroquinoxali n-2(1 H)-one, 7-Benzy i-3, 4-di hydroquinoxal in-2(1 H)-one, 8-Benzy i-3, 4-di hydroquinoxalin- 2(1 H)-one,

1.3-D i methy i-3, 4-d i hydroqu i noxal i n-2 (1 H)-one, 1 , 4-D i methy i-3, 4-dihyd roq ui noxal i n-2(1 H)-one, 1 , 5-D i methy i-3, 4-di hydroquinoxalin-2(1 H)-one, 1,6-Dimethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,7-dimethyl-3,4-dihydroquinoxalin-2(1H)-one.

1,8-Dimethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3-Diethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,4-Diethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,5-Diethyl i-3, 4-dihydroqu i noxal i n-2 (1 H)-one, 1, 6-D iethy i-3, 4-d I hydroqu I noxal I n-2 (1 H)-one, 1,7-Diethy i-3, 4-di hydroqu i noxal i n-2 (1 H)-one. 1, 8-D i ethy l-3,4-dihyd roq uinoxal in-2(1 H)-one,

3.3-Dimethyl-3,4-dihydroquinoxalin-2(1H)-one, 3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 3,3,4-Trimethyl-3,4-dihydroquinoxalin-2(1H)-one,

3.3.4-Triethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,4-tetramethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,4-tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,5-Tetramethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,5-tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,6-tetramethyl-3,4-dihydroquinoxalin-2(1H)-one, 1 ,3,3,6-Tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,7-Tetramethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,7-Tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,8-Tetramethyl-3,4-dihydroquinoxalin-2(1H)-one, 1 ,3,3,8-Tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 1, 3,3,4, 5-pentamethyl-3,4-dihydroquinoxalin-2(1H)-one, 1, 3,3, 4, 5-Pentaethy I-3, 4-dihydroqu i noxalin-2 (1 H)-one, 1 , 3,3, 4, 6-Pentaethy l-3, 4-dihydroqu i noxal i n-2(1 H)-one, 1 , 3, 3, 4, 6-Pentaethy l-3,4-di hydroq ui noxal i n-2(1 H)-one, 1 , 3, 3, 4, 7-Pentamethy I-3, 4-di hydroqu i noxal i n-2(1 H)-one,

1.3.3.4.7-Pentaethyl-3,4-dihydroquinoxalin-2(1H)-one, 1,3,3,4,8-pentamethyl-3,4-dihydroquinoxalin-2(1H)-one,

1.3.3.4.8-Pentaethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-methoxy-3, 4-dihydroquinoxali n-2(1 H)-one, 6-methoxy-3, 4-dihydroquinoxali n-2(1 H)-one, 7-methoxy-3,4-dihydroquinoxalin-2(1 H)-one, 8-methoxy-3, 4-dihydroquinoxali n-2(1 H)-one, 5-Ethoxy-3,4-di hydroquinoxal in-2(1 H)-one, 6-Ethoxy-3,4- di hydroquinoxal in-2(1 H)-one, 7-Ethoxy-3, 4-dihydroquinoxal in-2(1 H)-one, 8-Ethoxy-3, 4-di hydroquinoxal in-2(1 H)-one,

5-Methoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 6-methoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 7-methoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 8-methoxy-1-methyl-3,4-dihydroquinoxalin-2(1 H)-one, 5-ethoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 6-ethoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 7-ethoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 8-Ethoxy-1-methyl-3,4-dihydroquinoxalin-2(1H)-one, 5-Methoxy-3-methyl-3,4-dihydroquinoxal i n-2 ( 1 H)-one, 6-Methoxy-3-methy i-3, 4-d i hydroq u i noxal i n-2( 1 H)-one, 7-methoxy-3-methyl-3, 4-d I hydroqu I noxal I n- 2(1 H)-one, 8-Methoxy-3-methy i-3, 4-dihydroquinoxalin-2(1 H)-one, 5-ethoxy-3-methyl-3, 4-dihydroquinoxal in-2(1 H)-one, 6-ethoxy-3-methy i-3, 4-dihyd roq ui noxali n-2(1 H)-one, 7-ethoxy-3-methy i-3, 4-di hyd roqu I noxal I n-2(1H)-one, 8-Ethoxy-3-methy i-3, 4-di hydroquinoxal in-2(1 H)-one, 5-methoxy-4-methyl-3,4-di hydroquinoxal in-2(1 H)-one, 6-Methoxy-4-methyl-3, 4-di hydroquinoxal in-2(1 H)-one, 7-Methoxy-4-methy i-3, 4-dihydroquinoxali n-2(1 H)-one, 8-methoxy-4-methy i-3, 4-dihydroquinoxalin-2(1 H)-one, 5-ethoxy-4-methyl-3,4-di hydroquinoxali n-2(1 H)-one, 6-ethoxy-4-methy i-3, 4-dihydroquinoxal in-2(1H)-one, 7-Ethoxy-4-methyl-3, 4-di hydroquinoxalin-2(1H)-one, 8-ethoxy-4-methyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Methoxy-3, 3-dimethy i-3, 4-di hydroquinoxal in-2(1 H)-one, 6-Methoxy-3,3-dimethy i-3, 4-dihydroqui noxali n-2(1 H)-one, 7-Methoxy-3,3-di methyl l-3,4-dihydroquinoxalin-2(1 H)-one, 8-Methoxy-3,3-di methy i-3, 4-di hydroquinoxalin-2(1 H)-one, 5- Methoxy-3,3-diethy i-3, 4-dihydroquinoxal in-2(1 H)-one, 6-Methoxy-3, 3-diethy i-3, 4-dihydroqui noxali n-2(1 H)-one, 7-Me- thoxy-3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-methoxy-3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Methoxy-1, 3, 3-trimethy i-3, 4-di hydroq uinoxalin-2( 1 H)-one, 6-Methoxy-1, 3, 3-trimethy i-3, 4-di hydroqu i noxal i n-2 ( 1 H)-one, 7-Methoxy-1, 3, 3-trimethy i-3, 4-di hydroq uinoxalin-2( 1 H)-one, 8-methoxy-1, 3, 3-trimethy i-3, 4-di hydroqu i noxal i n-2 ( 1 H)-one, 5-methoxy-1, 3, 3-triethy i-3, 4-di hyd roqu i noxal i n-2(1 H)-one, 6-Methoxy-1, 3, 3-triethy i-3, 4-dihyd roqui noxal i n-2(1 H)-one, 7-Methoxy-1, 3, 3-triethy I -3, 4-dihyd roq ui noxal i n-2(1 H)-one, 8-Methoxy-1, 3, 3-triethy I -3, 4-dihyd roq ui noxali n-2(1H)-one, 5-methoxy-3,3,4-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 6-methoxy-3,3,4-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 7-methoxy-3,3,4-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-Methoxy-3,3,4-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 5-Methoxy-3, 3, 4-triethy I-3, 4-di hydroquinoxal in-2(1 H)-one, 6-Methoxy-3, 3, 4-triethy I-3, 4-di hydroquinoxal in-2(1 H)-one, 7-

Methoxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-methoxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Methoxy-1, 3, 3,4-tetramethyl-3, 4-dihydroqu i noxal i n-2(1 H)-one, 6-Methoxy-1, 3, 3, 4-tetramethy I-3, 4-di hyd roqu i noxal i n-2(1 H)-one, 7-Methoxy-1, 3, 3,4-tetramethy I-3, 4-d i hydroquinoxalin-2 (1 H)-one, 8-methoxy-1, 3, 3, 4-tetramethy I-3, 4-d i hydro-quinoxalin-2(1 H)-one, 5-methoxy-1,3,3,4-tetraethyl-3,4-dihydroquinoxalin-2(1 H)-on, 6-methoxy-1,3,3,4-tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 7-methoxy-1,3,3,4-tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-methoxy-1,3,3,4-tetra-ethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Ethoxy-3,3-dimethy l-3,4-dihydroquinoxali n-2(1 H)-one, 6-ethoxy-3, 3-di methyl-3, 4-di hydroquinoxal in-2(1 H)-one, 7-ethoxy-3, 3-di methy i-3, 4-di hydroqui noxal in-2(1 H)-one, 8-Ethoxy-3, 3-dimethy i-3, 4-di hydroquinoxal in-2(1 H)-one, 5- Ethoxy-3, 3-diethyl l-3,4-di hydroquinoxal in-2(1 H)-one, 6-ethoxy-3, 3-diethyl-3, 4-dihydroquinoxali n-2(1 H)-one, 7-ethoxy-

3.3-diethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-ethoxy-3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Ethoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 6-ethoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 7-ethoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-ethoxy-1 ,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one, 5-ethoxy-1,3,3-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 6-ethoxy-1,3,3-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 7- Ethoxy-1,3,3-triethyl-3,4-dihydroquinoxaline-2(1 H)-one, 8-ethoxy-1,3,3-triethyl-3,4-dihydroquinoxalin-2(1 H)-one, 5-ethoxy-3, 3,4-trimethy i-3, 4-dihydroquinoxalin-2(1 H)-one, 6-ethoxy-3,3, 4-trimethoxy i-3, 4-di hydroquinoxalin-2(1 H)-one, 7-ethoxy-3, 3,4-tri methyl i-3, 4-dihydroquinoxalin-2(1 H)-one, 8-ethoxy-3,3, 4-trimethoxy i-3, 4-di hydroquinoxalin-2(1 H)-one, 5- ethoxy-3, 3, 4-triethy i-3, 4-di hydroquinoxal in-2(1H)-one, 6-ethoxy-3, 3, 4-triethy i-3, 4-di hydroquinoxal in-2(1 H)-one, 7-ethoxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1 H)-one, 8-ethoxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1 H)-one,

5-Ethoxy-1, 3, 3,4-tetramethy i-3, 4-dihydroqu i noxal i n-2(1 H)-one, 6-ethoxy-1, 3, 3,4-tetramethy i-3, 4-di hyd roqu i noxal i n-2(1 H)-one, 7-ethoxy-1, 3, 3,4-tetramethy i-3, 4-d i hydroqu i noxal i n-2 ( 1 H)-one, 8-ethoxy- 1 , 3, 3, 4-tetramethy i-3, 4-di hyd roqu i- noxal i n-2(1 H)-one, 5-ethoxy- 1 , 3, 3,4-tetraethy i-3, 4-d i hydroqu i noxal in-2(1H)-one, 6-ethoxy-1, 3, 3, 4-tetraethyi-3, 4-dihydroquinoxalin-2(1H)-one, 7-ethoxy-1,3,3,4-tetraethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-Ethoxy-1,3,3,4-tetraethyl-3,4-di hydroquinoxal in-2(1H)-one,

5-Hydroxy-3, 4-d I hydroqu I noxal I n-2 (1 H)-one, 6-Hyd roxy-3, 4-d I hydroqu I noxal I n-2(1 H)-one, 7- Hydroqu I noxal I n-2(1 H)-one, 7- Hydroqu I noxal I n-2(1 H)-one, 8-Hydroxy-3,4-dihydroquinoxalin-2(1H)-one,

5-Hydroxy-1 -methyl-3, 4-dihydroquinoxalin-2(1H)-one, 6-hydroxy-1 -methyl-3, 4-dihydroquinoxalin-2(1H)-one, 7-hydroxy-1-methyl-3, 4-dihydroquinoxalin-2(1H)-one, 8-hydroxy-1 -methyl-3, 4-dihydroquinoxalin-2(1H)-one, 5-hydroxy-3-methyl-

3.4-dihydroqui noxal in-2(1 H)-one, 6-hydroxy-3-methy i-3, 4-di hydroqui noxal in-2(1 H)-one, 7-hydroxy-3-methyl-3,4-di hydroquinoxal in-2(1 H)-one, 8-hydroxy-3-methy i-3, 4-di hydroquinoxalin-2(1H)-one, 5-hydroxy-4-methyl-3,4- di hydroquinoxalin-2(1H)-one, 6-hydroxy-4-methyl-3, 4-dihydroquinoxalin-2(1H)-one, 7-hydroxy-4-methyl-3,4-dihydroquinoxalin-2 (1H)-one, 8-hydroxy-4-methy I-3, 4-dihydroquinoxalin-2 ( 1 H)-on,

5-Hyd roxy-3,3-dimethy I-3, 4-dihydroq u i noxal i n-2 (1 H)-one, 6-Hyd roxy-3, 3-di methy I-3, 4-dihy droq u i noxal i n-2 (1 H)-one, 7-Hyd roxy-3, 3-d i methy I-3, 4-di hydroqui noxal in-2(1H)-one, 8-hydroxy-3, 3-dimethyl-3, 4-dihydroquinoxali n-2(1H)-one, 5-hydroxy-3, 3-diethyl-3, 4-dihydroquinoxali n-2(1H)-one, 6-hydroxy-3,3-diethy i-3, 4-dihydroquinoxal in-2(1H)-on, 7-hydroxy-3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-hydroxy-3,3-diethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Hydroxy-1, 3, 3-trimethy i-3, 4-d i hydroqu i noxal in-2 (1 H)-one, 6-hydroxy-1, 3,3-trimethyl-3, 4-d i hydroqu i noxal i n-2 (1 H)-one, 7-hydroxy-1, 3, 3-trimethyl-3, 4-d i hydroqu i noxal in-2 ( 1 H)-one, 8-hydroxy-1, 3,3-trimethyl-3, 4-d i hydroqu i noxal i n-2 (1 H)-one, 5-hydroxy-1, 3, 3-triethy I -3, 4-dihy d roq ui noxali n-2(1 H)-one, 6-Hydroxy-1, 3, 3-triethyl-3, 4-di hyd roq ui noxal i n-2(1H)-one, 7-Hydroxy-1, 3,3-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-Hydroxy-1, 3,3-triethyl-3,4-dihydroquinoxalin-2 (1H)-one, 5-Hydroxy-3, 3, 4-trimethyl l-3,4-dihydroquinoxalin-2(1H)-one, 6-hydroxy-3, 3, 4-trimethyl-3, 4-dihydroquinoxali n-2(1H)-one, 7-hydroxy-3, 3, 4-trimethyl l-3,4-dihydroquinoxalin-2(1H)-one, 8-Hyd roxy-3, 3, 4-trimethyl-3, 4-dihydroquinoxali n-2(1 H)-one, 5- hydroxy-3,3,4-triethy I-3, 4-di hydroquinoxal in-2(1 H)-one, 6- hydroxy-3, 3, 4-triethy l-3,4-di hydroquinoxalin-2(1 H)-one, 7- Hydroxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1H)-one, 8-hydroxy-3,3,4-triethyl-3,4-dihydroquinoxalin-2(1H)-one,

5-Hydroxy-1, 3, 3,4-tetramethyl-3, 4-dihydroqu i noxal i n-2(1 H)-one, 6-Hydroxy-1, 3,3, 4-tetramethy I -3, 4-dihy d roqui noxal i n- 2(1 H)-one, 7-Hydroxy-1, 4-d i hydroqu i noxal i n-2 ( 1 H)-one, 6-hydroxy-1,3,3, 4-tetraethyl-3, 4-dihydroqu i noxal i n-2(1 H)-one, 7-hydroxy-1, 3, 3, 4-tetraethyl l-3,4-dihy d roq uinoxal i n-2(1 H)-one, 8-hydroxy-1,3, 3, 4-tetra- ethyl-3,4-dihydroquinoxalin-2(1H)-one.

The compound of general formula (I) is preferably 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1, 2, 2, 4-tetramethyl-1,2,3,4-tetrahydroquinoxaline or 7-Methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline. The compound of the general formula (II) is preferably 3, 3-dihydroquinoxalin-2(1H)-one, 7-methoxy-3, 3-dimethoxyI-3, 4-dihydroquinoxalin-2(1H)-one, 6-methoxy-3, 3-dimethoxyI-3, 4-di hyd roq uinoxali n-2(1 H)-one, 7-methoxy-1, 3, 3-trimethy I-3, 4-d i hydroqu i noxal i n-2 (1 H)-one or 6-methoxy-1, 3, 3-trimethyl-3, 4-d i hydroqu i noxal i n-2 (1 H)-one.

In the mixture, the total amount of the compounds of the general formula (I) or (II) is preferably from 0.0001 to 0.1000 wt.%, preferably from 0.0002 to 0.0750 wt.%, particularly preferably from 0.0005 to 0.0500 wt.%, very particularly preferably from 0.0010 to 0.0250 wt.%, in each case based on the total amount of polymerizable carbonyl compounds.

It is conceivable that a mixture of compounds of general formula (I) and/or (II) is used in the mixture according to the invention. The indication of the total amount of the compounds of general formula (I) or (II) then refers to the total amount of the mixture of compounds of general formula (I) and/or (II). For example, a mixture of 7-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one (each general formula II) or a mixture of 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline and 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline (each general formula I) can be used.

In the mixture, the total amount of polymerizable carbonyl compounds is preferably at least 50% by weight, preferably at least 80% by weight, particularly preferably at least 98% by weight, very particularly preferably at least 99% by weight, in each case based on the total weight of the mixture.

Polymerizable carbonyl compounds are preferably mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acids, mono-, di- or triethylenically unsaturated C3- to Cs-aldehydes, mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acid esters having 1 to 20 carbon atoms in the ester groups, mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acid amides, mono-, di- or triethylenically unsaturated C3- to Cs-nitriles, mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acid anhydrides, vinyl esters of saturated C2- to C2o-carboxylic acids, vinyl ethers of saturated C1- to C20-alcohols, vinyl aromatics, vinyl heteroaromatics, vinyl lactams having 3 to 10 Carbon atoms in the ring, open-chain N-vinylamide compounds and N-vinylamine compounds, vinyl halides, aliphatic, optionally halogenated hydrocarbons having 2 to 8 carbon atoms and 1 or 2 ethylenic double bonds, vinylidenes or any mixtures of two or more of the aforementioned compounds.

Particularly preferred are mono-, di- or triethylenically unsaturated C3- to C5-carboxylic acids, for example acrylic acid, methacrylic acid, dimethacrylic acid, ethacrylic acid, citraconic acid, methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid, itaconic acid and maleic acid, mono-, di- or triethylenically unsaturated C3- to C5-carboxylic acid esters having 1 to 20 carbon atoms in the ester groups, for example acrylic acid esters with C1- to C20-alkyl, methacrylic acid esters with C1- to C20-alkyl, dimethacrylic acid esters with C1- to C20-alkyl, ethacrylic acid esters with C1- to C20-alkyl, citraconic acid esters with C1- to C20-alkyl, methylenemalonic acid esters with C1- to C20-alkyl, crotonic acid esters with C1- to C20-alkyl, fumaric acid esters with C1- to C20-alkyl, mesaconic acid esters with Ci- to C2o-alkyl, itaconic acid esters with Ci- to C20-alkyl and maleic acid esters with Ci- to C2o-alkyl, mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acid amides, for example acrylamide, methacrylamide, dimethacrylamide, ethacrylamide, citraconic acid amide, methylenemalonic acid amide, crotonic acid amide, fumaric acid amide, mesaconic acid amide, itaconic acid amide and maleic acid amide, mono-, di- or triethylenically unsaturated C3- to Cs-nitriles, for example acrylonitrile and methacrylonitrile, and mono-, di- or triethylenically unsaturated C3- to Cs-carboxylic acid anhydrides, for example acrylic acid anhydride, methacrylic acid anhydride, itaconic acid anhydride and maleic acid anhydride. Very particular preference is given to acrylic acid, methacrylic acid, acrylic acid esters with Ci- to Cs-alkyl, such as methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, and methacrylic acid esters with Ci- to Cs-alkyl, such as methyl methacrylate.

Other suitable polymerizable carbonyl compounds are dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, glycerol triacrylate, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, butanediol monoacrylate, dicyclopentadienyl acrylate, 2-dimethylaminoethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate.

With acrylic acid as the polymerizable carbonyl compound, the total amount of the compounds of the general formula (I) or (II) in the mixture is preferably from 0.0050 to 0.1000 wt.%, preferably from 0.0100 to 0.0750 wt.%, particularly preferably from 0.0120 to 0.0500 wt.%, very particularly preferably from 0.0150 to 0.0250 wt.%, in each case based on acrylic acid.

With methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate as polymerizable carbonyl compound, the total amount of the compounds of the general formula (I) or (II) in the mixture is preferably from 0.0001 to 0.0100 wt.%, preferably from 0.0002 to 0.0075 wt.%, particularly preferably from 0.0005 to 0.0050 wt.%, very particularly preferably from 0.0010 to 0.0020 wt.%, in each case based on the total amount of methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate.

The mixture according to the invention preferably contains less than 0.0001 wt. % of a manganese salt, a copper salt, a 2,2,6,6-tetramethylpiperidine compound, an N-oxyl compound and a nitroso compound, each based on the total amount of the mixture.

A further object of the present invention is the use of at least one compound of the general formula (I) or (II), as defined above, for inhibiting the polymerization of at least one polymerizable carbonyl compound.

In a preferred embodiment of the present invention, the compound of general formula (I) or (II) is used essentially as the sole polymerization inhibitor.

The present invention further provides a process for storing and/or transporting a mixture comprising at least one compound of general formula (I) or (II), as defined above, and at least one polymerizable carbonyl compound.

The mixture is usually stored and/or transported under an oxygen-containing atmosphere. The mixture is preferably stored in a container under an oxygen-containing atmosphere with an oxygen content of 5 to 10 vol.%, and the mixture is regularly circulated within the container, for example, by completely pumping the tank contents over at least once a week. The relatively low oxygen content prevents flammable gas mixtures in the container. Circulation replaces consumed dissolved oxygen in the liquid polymerizable compound.

Mixtures according to the invention with acrylic acid as the polymerizable carbonyl compound are particularly suitable for the production of water-swellable polyacrylic acids (superabsorbents) and water-soluble polyacrylic acids. The production of superabsorbents is described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, Volume 35, pages 73 to 93.

Mixtures according to the invention with methyl acrylate, ethyl acrylate, n-butyl acrylate or 2-ethylhexyl acrylate as polymerizable carbonyl compound are particularly suitable for the preparation of polymer dispersions.

The present invention further relates to a process for radical polymerization, wherein one of the mixtures described above is polymerized by means of a polymerization initiator, and to the use of one of the mixtures described above for radical polymerization by means of a polymerization initiator.

By means of the radical polymerization according to the invention, for example, water-soluble and water-swellable polyacrylic acids and their sodium salts are obtainable.

Radical polymerization itself is well known and is usually carried out in solution. Suitable polymerization initiators include all compounds that can decompose into radicals under the chosen reaction conditions, for example, thermal initiators, redox initiators, and photoinitiators. Suitable thermal initiators are peroxomono- and disulfates, as well as peroxomono- and diphosphates. Suitable redox initiators are sodium peroxodisulfate/ascorbic acid, hydrogen peroxide/ascorbic acid, sodium peroxodisulfate/sodium hypophosphite, sodium peroxodisulfate/sodium bisulfite, and hydrogen peroxide/sodium bisulfite.

wobei Another object of the invention is a compound of general formula (I)

where

R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 20 -alkyl, C 1 -C 20 -acyl, C 1 -C 20 -acyloxy, C 1 -C 20 -alkoxy, aryl, aryloxy, benzyl, hydroxy, nitro, cyano, amino or halide, wherein at least one of R ¹ , R ² , R ³ or R ⁴ is not H,

R ⁵ is Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl,

R ⁶ and R ⁷ are independently of one another C 1 -C 2o -alkyl and R ⁸ and R ⁹ are independently of one another H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxyl or halide or R ⁶ and R ⁷ are independently of one another H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxyl or halide and R ⁸ and R ⁹ are independently of one another C 1 -C 2o -alkyl and R ¹⁰ is C 1 -C 2o -alkyl, C 1 -C 2o -acyl or aryl, preferably for polymerization inhibition.

Preferably, R ¹ , R ² , R ³ and R ⁴ are independently H, Ci- to C alkyl or Ci- to C alkoxy, R ⁵ is Ci- to C 3 alkyl, R ⁶ and R ⁷ are independently Ci- to C alkyl and R ⁸ and R ⁹ are independently H or Ci- to C 4 alkyl or R ⁶ and R ⁷ are independently H or Ci- to C alkyl and R ⁸ and R ⁹ are independently Ci- to C ₄ alkyl and R ¹⁰ is Ci- to C ₃ alkyl.

More preferably, R ¹ and R ⁴ are H, R ² and R ³ are independently C 1 -C ₄ alkoxy, R ⁵ is C 1 -C 2 alkyl, R ⁶ and R ⁷ are independently C 1 -C 4 alkyl and R ⁸ and R ⁹ are independently H or R ⁶ and R ⁷ are independently H and R ⁸ and R ⁹ are independently C 1 -C 4 alkyl and R ^{10 is} C 1 -C 2 alkyl.

Preferably, R ¹ , R ² and R ⁴ are H and R ³ is methoxy or R ¹ , R ³ and R ⁴ are H and R ² is methoxy, R ⁵ is methyl, R ⁶ and R ⁷ are H, R ⁸ and R ⁹ are methyl and R ¹⁰ is methyl.

Particularly preferably, R ¹ , R ² and R ⁴ are H, R ³ is methoxy, R ⁵ is methyl, R ⁶ and R ^{7 are} H, R ⁸ and R ⁹ are methyl and R ¹⁰ is methyl (6-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydrooxalin).

This disclosure regarding the compound of general formula (I) alone is not to be understood as a limitation of the disclosure regarding the compound of general formula (I) in the mixture according to the invention.

Examples

Preparation of 7-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1 H)-one and 6-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1 H)-one A solution of 4-methoxy-o-phenylenediamine (3.00 g, 21.7 mmol, 1.0 equiv), 1,1,1-trichloro-2-methyl-2-propanol (9.63 g, 54.3 mmol, 2.5 equiv), and benzyltriethylammonium chloride (0.50 g, 2.2 mmol, 0.1 equiv) was dissolved in 145 mL of dichloromethane and cooled to 0°C under nitrogen. Subsequently, a sodium hydroxide solution (50%, 2.86 mL) was added within two minutes. The reaction mixture was warmed to room temperature overnight. After two days at room temperature, 50 mL of water was added, the phases were separated, and the aqueous phase was extracted again with dichloromethane (2 x 50 mL). The combined organic phases were dried (MgSiCl), and the solvent was removed under reduced pressure. The crude product obtained was purified by column chromatography (silica gel, cyclohexane/ethyl acetate, gradient). A mixture of the two isomers 7-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1H)-one (ratio 70:30, 3.46 g, 16.8 mmol, 77%) was obtained as a yellow-orange solid.

Preparation of 7-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one

The mixture of the two isomers 7-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1H)-one (ratio 70:30, 1.00 g, 4.85 mmol, 1.0 equiv) was dissolved in DMF (19 mL). Subsequently, cesium carbonate (2.37 g, 7.3 mmol, 1.5 equiv) and methyl iodide (1.38 g, 9.7 mmol, 2.0 equiv) were added and stirred at room temperature for 3 hours. After addition of 25 mL of ethyl acetate and 25 mL of water, the phases were separated and the organic phase was washed with saturated sodium chloride solution. The organic phase was dried (MgSO4) and the solvent was removed under reduced pressure. The crude product obtained was purified by column chromatography (silica gel, cyclohexane/ethyl acetate, gradient). A mixture of the two isomers 7-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one (ratio 70:30, 0.88 g, 3.97 mmol, 82%) was obtained as an orange oil.

Preparation of 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline and 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline

Under nitrogen, a mixture of the two isomers 7-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one (ratio 70:30, 0.59 g, 2.7 mmol, 1.0 equiv) was dissolved in dichloromethane (27 mL). A solution of diisobutylaluminum hydride in toluene (1 mol/L, 10.7 mL, 10.7 mmol, 4.0 equiv) was then added dropwise, and the reaction mixture was stirred at room temperature. After 5 hours, the mixture was cooled to 0°C, and dichloromethane (20 mL) and sodium hydroxide solution (2 mol/L, 20 mL) were added. The phases were separated, and the aqueous phase was extracted with dichloromethane (2 x 20 mL). The combined organic phases were dried (Na2SO4), and the solvent was removed under reduced pressure. The crude product was purified by column chromatography (silica gel, cyclohexane/ Ethyl acetate, gradient). The two isomers could be isolated separately. The isomer 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline (0.29 g, 1.41 mmol, 52%) was obtained as a gray solid, and the isomer 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline (0.13 g, 0.63 mmol, 23%) was obtained as an orange oil.

Preparation of 6-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline

A mixture of the two isomers 7-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one and 6-methoxy-1,3,3-trimethyl-3,4-dihydroquinoxalin-2(1H)-one (ratio 70:30, 4.84 g, 22.0 mmol, 1.0 equiv) was dissolved in DMF (90 mL). Subsequently, cesium carbonate (2.37 g, 7.3 mmol, 1.5 equiv) and methyl iodide (1.38 g, 9.7 mmol, 2.0 equiv) were added and stirred at room temperature for 3 hours. After addition of 25 mL of ethyl acetate and 25 mL of water, the phases were separated and the organic phase was washed with saturated sodium chloride solution. The organic phase was dried (MgSO4) and the solvent was removed under reduced pressure. The crude product obtained was used in the next step without further purification.

The crude product from the previous reaction was dissolved in dichloromethane (220 mL). A solution of diisobutylaluminum hydride in toluene (1 mol/L, 88 mL, 88 mmol, 4.0 equiv) was then added dropwise, and the reaction mixture was stirred at room temperature. After 5 hours, the mixture was cooled to 0°C, and dichloromethane (200 mL) and sodium hydroxide solution (2 mol/L, 200 mL) were added. The phases were separated, and the aqueous phase was extracted with dichloromethane (2 x 200 mL). The combined organic phases were dried (Na2SO4), and the solvent was removed under reduced pressure. The crude product obtained was purified by column chromatography (silica gel, cyclohexane/ethyl acetate, gradient). The two isomers could be isolated separately. The product 6-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline (1.34 g, 6.1 mmol, 28%) was obtained as an orange oil. Furthermore, the isomer 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline (0.52 g, 2.52 mmol, 11%) and the isomer 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline (0.78 g, 3.8 mmol, 17%) were isolated.

Experiments on polymerization inhibition

The monomer used was distilled twice to remove the polymerization inhibitor MEHQ. The resulting monomer was then treated with the specified amount of the polymerization inhibitor.

0.5 ml of each mixture was filled into a 1.8 ml ampoule and stored in a circulating air drying cabinet at the specified temperature. In each test series, three ampoules of each mixture were filled and tested, with the time to complete polymerization being recorded visually. The average of the three recorded times is given.

The results are summarized in Tables 1 to 4:

Table 1 : Mixtures with acrylic acid

MEHQ: Hydroquinone monomethyl ether *) Comparative example

Table 2: Mixtures with methacrylic acid

MEHQ: Hydroquinone monomethyl ether *) Comparative example

MEHQ: HydrochinonmonomethyletherTable 3: Mixtures with ethyl acrylate

MEHQ: hydroquinone monomethyl ether

*) Comparison example Table 4: Mixtures with n-butyl acrylate

MEHQ: hydroquinone monomethyl ether

*) Comparison example

The polymerization inhibitors according to the invention have improved or at least comparable efficacy compared to MEHQ.

Polymerization experiments

Under a nitrogen atmosphere, 450 g of water were placed in a reaction vessel. The reaction mixture was heated to 95°C with stirring. Once the temperature reached 95°C, three streams were added while stirring and maintaining the temperature.

Stream 1 : Dosage over 5 h, 500 g acrylic acid

Stream 2: Dosage over 4.75 h, 15 g sodium hypophosphite in 35 g deionized water

Stream 3: Dosage over 5.25 h, 5 g sodium peroxodisulfate in 66.4 g deionized water After addition of the three streams, the reaction mixture was stirred for another hour at 95°C. The reaction mixture was then cooled to room temperature and 80 g of water were added.

The acrylic acid used in stream 1 was stabilized with 200 wt. ppm of 3,3-dimethyl-3,4-dihydroquinoxalin-2(1 H)-one or 0.02 wt.% MEHQ.

The obtained polymers were analyzed by GPC (calibration with Na-PAA standard, eluent 0.01 mol/l phosphate buffer, pH=7.4 in distilled water, with 0.01 M NaNa).

The results are summarized in Table 5:

Table 5: Polymerization of acrylic acid

MEHQ: hydroquinone monomethyl ether

*) Comparison example

The polymerization inhibitor according to the invention resulted in a polyacrylic acid with a comparable molecular weight.

Claims

Patent claims 1. Mixture containing at least one compound of general formula (I)

where R ¹ , R ² , R ³ and R ⁴ independently of one another are H, Ci- to C2o-alkyl, Ci- to C2o-acyl, Ci- to C2o-acyloxy, Ci- to C2o-alkoxy, aryl, aryloxy, benzyl, hydroxy, nitro, cyano, amino or halide, R ⁵ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, R ⁶ , R ⁷ , R ⁸ and R ⁹ independently of one another are H, Ci- to C2o-alkyl, Ci- to C2o-acyl, Ci- to C2o-acyloxy, Ci- to C2o-alkoxy, aryl, aryloxy, benzyl, hydroxy or halide and R ¹⁰ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, or a compound of the general formula (II)

R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 -C 2o -alkyl, C 1 -C 2o -acyl, C 1 -C 2o -acyloxy, C 1 -C 2o -alkoxy, aryl, aryloxy, benzyl, hydroxy, nitro, cyano, amino or halide, R ¹⁵ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, R ¹⁶ and R ¹⁷ are independently H, Ci- to C2o-alkyl, Ci- to C2o-acyl, Ci- to C2o-acyloxy, Ci- to C20-alkoxy, aryl, aryloxy, benzyl, hydroxy or halide and R ¹⁸ is H, Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, and at least one polymerizable carbonyl compound, wherein the total amount of polymerizable carbonyl compounds in the mixture is at least 30 wt.%, based on the total weight of the mixture. 2. Mixture according to claim 1, characterized in that R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, hydroxyl or halide, R ⁵ is H or C 1 -C 10 -alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, hydroxyl or halide and R ¹⁰ is H or C 1 -C 10 -alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, hydroxyl or halide, R ¹⁵ is H or C 1 -C 10 -alkyl, R ¹⁶ and R ¹⁷ are independently H, C 1 -C 10 -alkyl, C 1 -C 10 -alkoxy, hydroxyl or halide and R ¹⁸ H or Ci- to Cw-alkyl. 3. Mixture according to claim 1, characterized in that R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy, R ⁵ is H or C 1 -C 2 -alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy and R ¹⁰ is H or C 1 -C 2 -alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy, R ¹⁵ is H or C 1 -C 2 -alkyl, R ¹⁶ and R ¹⁷ are independently H, C 1 -C 2 -alkyl or C 1 -C 2 -alkoxy and R ¹⁸ is H or C 1 -C 2 -alkyl. 4. Mixture according to claim 1, characterized in that R ¹ , R ² , R ³ and R ⁴ are independently H, Ci- to C alkyl or Ci- to C 1koxy, R ⁵ is H or Ci- to C e alkyl, R ⁶ , R ⁷ , R ⁸ and R ⁹ are independently H, Ci- to C alkyl or Ci- to C 4 alkoxy and R ¹⁰ is H or Ci- to C e alkyl, and R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are independently H, Ci- to C 4 alkyl or Ci- to C 4 alkoxy, R ¹⁵ is H or Ci- to C e alkyl, R ¹⁶ and R ¹⁷ are independently H, Ci- to C 4 alkyl or Ci- to C 4 alkoxy and R ¹⁸ is H or Ci- to C e alkyl. 5. Mixture according to claim 1, characterized in that the compound of the general formula (I) is 7-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1,3,3-trimethyl-1,2,3,4-tetrahydroquinoxaline, 6-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline or 7-methoxy-1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinoxaline and the compound of the general formula (II) is 3,3-dimethyl-3,4-dihydroquinoxalin-2(1H)-one, 7-methoxy-3,3-dimethyl-3,4-dihydroquinoxalin-2(1 H)-one, 6-Methoxy-3,3-dimethy I-3, 4-di hydroquinoxal in-2(1H)-one, 7-Methoxy-1, 3, 3-trimethyl-3, 4-dI hydroqu i noxalin-2 (1H)-one or 6-Methoxy-1, 3, 3-trimethoxy i-3, 4-d i hydroq uinoxalin-2(1H)-one is. 6. Mixture according to one of claims 1 to 5, characterized in that the total amount of the compounds of the general formula (I) or (II) in the mixture is from 0.0001 to 0.1000 wt.%, based on the total amount of polymerizable carbonyl compounds. 7. Mixture according to one of claims 1 to 6, characterized in that the total amount of polymerizable carbonyl compounds in the mixture is at least 98% by weight, based on the total weight of the mixture. 8. Mixture according to one of claims 1 to 7, characterized in that the polymerizable carbonyl compound is acrylic acid and/or methacrylic acid. 9. Mixture according to claim 8, characterized in that the total amount of the compounds of general formula (I) or (II) in the mixture is from 0.0050 to 0.1000 wt.%, based on the total amount of acrylic acid and/or methacrylic acid. 10. Mixture according to one of claims 1 to 7, characterized in that the polymerizable carbonyl compound is methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate. 11. Mixture according to claim 10, characterized in that the total amount of the compounds of the general formula (I) or (II) in the mixture is from 0.0001 to 0.0100 wt.%, based on the total amount of methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate. 12. Use of at least one compound of general formula (I) or (II) according to any one of claims 1 to 5 for inhibiting the polymerization of at least one polymerizable carbonyl compound. 13. A method for storing and/or transporting a mixture according to any one of claims 1 to 11. 14. Compound of general formula (I)

where R ¹ , R ² , R ³ and R ⁴ are independently H, C 1 -C 20 -alkyl, C 1 -C 20 -acyl, C 1 -C 20 -acyloxy, C 1 -C 20 -alkoxy, aryl, aryloxy, benzyl, hydroxy, nitro, cyano, amino or halide, wherein at least one of R ¹ , R ² , R ³ or R ⁴ is not H, R ⁵ is Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl, R ⁶ and R ⁷ are independently of one another C 1 -C 20 -alkyl and R ⁸ and R ⁹ are independently of one another H, C 1 -C 20 -alkyl, C 1 -C 20 -acyl, C 1 -C 20 -acyloxy, C 1 -C 20 -alkoxy, aryl, aryloxy, benzyl, hydroxyl or halide or R ⁶ and R ⁷ are independently of one another H, C 1 -C 20 -alkyl, C 1 -C 20 -acyl, C 1 -C 20 -acyloxy, C 1 -C 20 -alkoxy, aryl, aryloxy, benzyl, hydroxyl or halide and R ⁸ and R ⁹ are independently of one another C 1 -C 20 -alkyl and R ¹⁰ is Ci- to C2o-alkyl, Ci- to C2o-acyl or aryl. 15. A compound according to claim 14, characterized in that R ¹ , R ² and R ⁴ is H, R ³ is methoxy, R ⁵ is methyl, R ⁶ and R ⁷ are H, R ⁸ and R ⁹ are methyl and R ¹⁰ is methyl.