EP1619273A1 - Process for the synthesis of 2 Alkyne-1-acetales - Google Patents

Abstract

Preparation of 2-alkyne-1-acetal compounds (I) comprises electro-chemically oxidizing alcohol compounds (II) in the presence of 1-6C alkyl alcohol (A) or substance. Preparation of 2-alkyne-1-acetal compounds of formula (I) comprises electro-chemically oxidizing alcohol compounds (II) of formula (R 1>-C?=C-CH 2-OH) in the presence of 1-6C alkyl alcohol (A) or substance. R 1>1-20C alkyl, 2-20C alkenyl, 2-20C alkenyl, 3-12C cycloalkyl, 4-20C cycloalkyl-alkyl, 4-10C aryl (all optionally substituted with hydroxy, halo, 1-6C alkoxy, (1-6C alkoxy)-carbonyl, carboxyl or nitrile) or H; and R 2>, R 3>1-6C alkyl or a group of formula (R 1>-C?=C-CH 2-). [Image].

Description

The present invention relates to a process for the preparation of 2-alkyne-1-acetals.

Non-electrochemical processes for the preparation of 2-alkyne-1-acetals are e.g. from US 2879305, wherein 2-alkyne-1-aldehydes are acetalated with an alcohol.

From Journal of Electroanalytical Chemistry (1994), 371 (1-2), 167-77 and Electrochimica Acta (1993), 38 (10), 1337-44, electrochemical processes in aqueous solution are known in which a 2-alkyne-1 -ol is oxidized. A targeted formation of the acetal is not described.

From Chemical Reports (1954), 87, 668-76 and Surface Science (2000), 457 (1-2), 178-184; DE-A1-2409117 discloses electrochemical processes in which a 2-alkyn-1-ol is oxidized. There, the formation of the corresponding aldehydes, acids or CO _{2 is} described.

It is known to use a saturated alcohol (methanol) (see Bulletin of the Chemical Society of Japan (1991), 64 (3), 796-800; Journal of Organic Chemistry (1991), 56 (7), 2416-21; Synlett (1990), (1), 57-8 (with Mediator)) or an allyl ether alcohol (see Tetrahedron, 43, 24 (1987), 5797-5806) to oxidize to an acetal in an electrochemical process.

The object underlying the invention was to provide an electrochemical process in order to produce 2-alkyne-1-acetals economically and in particular in high product yields and with high selectivity.

wobei die Reste die folgende Bedeutung haben
R¹: Wasserstoff, C₁- bis C₂₀-Alkyl, C₂- bis C₂₀-Alkenyl, C₂- bis C₂₀-Alkinyl, C₃- bis C_12-Cycloalkyl, C₄- bis C₂₀-Cycloalkyl-alkyl, C₄- bis C₁₀-Aryl, wobei diese Reste ggf. durch Hydroxy-, Halogen, C₁- bis C₆-Alkoxy, (C₁- bis C₆-Alkoxy)-Carbonyl, Carboxyl- oder Nitrilgruppen substituiert sein können
R²: C₁- bis C₆-Alkyl oder ein Rest der allgemeinen Formel II

Accordingly, a process for the preparation of 2-alkyne-1-acetals of general formula I,

where the radicals have the following meaning
R ¹ : hydrogen, C ₁ - to C ₂₀ -alkyl, C ₂ - to C ₂₀ -alkenyl, C ₂ - to C ₂₀ -alkynyl, C ₃ - to C ₁₂ -cycloalkyl, C ₄ - to C ₂₀ -cycloalkyl- alkyl, C ₄ - to C ₁₀ -aryl, these radicals being optionally substituted by hydroxyl, halogen, C ₁ - to C ₆ -alkoxy, (C ₁ - to C ₆ -alkoxy) -carbonyl, carboxyl or nitrile groups can
R ² : C ₁ - to C ₆ -alkyl or a radical of the general formula II

in which R ^{1 has} the abovementioned meaning
R ³ : has the same meaning as the radical R ² ,
by giving a compound of general formula III

in which the radical has the same meaning as in the general formula I,
in the presence of C ₁ - to C ₆ -alkyl alcohols (alcohol A) or in substance electrochemically oxidized.

In general, those compounds of general formula I are prepared in which the radicals R ² and R ^{3 have} the same meaning.

In the case of the compounds of the general formula I in which R ^{2 is} a radical of the general formula II, R ³ is preferably a radical of the general formula II.

In the case of the compounds of the general formula I in which R ² and R ^{3 are} a radical of the general formula II, the radical R ¹ which occurs 3 times therein has preferably the same meaning. The preparation is carried out in bulk, ie, no alcohol A is used but the starting compound of general formula III occurs in terms of their function in place of the alcohol A, which acetalizes the oxidation product of the compound of general formula III.

Particular preference is given to preparing those compounds of the general formula I in which the radicals R ² and R ^{3 are} methyl. Accordingly, methanol is then used as alcohol A.

With regard to the radical R ¹ , preferred compounds of the general formula I are those in which hydrogen, C ₁ - to C ₆ -alkyl radical or a C ₁ - to C ₆ -alkyl radical substituted by a hydroxyl group. Correspondingly, the compounds of general formula II used are those in which the radical R ^{1 is} hydrogen, C ₁ - to C ₆ -alkyl radical or a C ₁ - to C ₆ -alkyl radical substituted by a hydroxyl group.

Very particular preference is given to preparing the compounds of general formula I in which R ^{1 is} hydrogen and R ² and R ^{3 are} methyl. The starting materials used as the compound of general formula III 2-propyn-1-ol and as alcohol A methanol.

A further very particularly preferably prepared compounds of general formula I is 1,1,4,4-tetramethoxybut-2-yn. The starting materials used as compound of the general formula III are 2-butyne-1,4-diol and, as alcohol A, methanol.

In the electrolyte, the alcohols A and the compound of general formula III are generally bisequimolar, based on the alcoholic hydroxyl groups contained in the compound of formula III used or alcohol A is used in excess and then serves as a solvent or diluent for the compound of the general formula III and the compound of the general formula I.

Preferably, when using a compound of general formula III, which carries 2 or more alcoholic hydroxyl groups, per mole of hydroxyl groups, which carries the compound of general formula III, more than 2 moles (preferably 5 to 20 mol) of the alcohol A is used to a To avoid oligomerization.

Optionally, the electrolysis solution is added to customary cosolvents. These are the inert solvents generally used in organic chemistry with a high oxidation potential. Examples include dimethyl carbonate or propylene carbonate.

In principle, water is also suitable as a cosolvent; the proportion of water in the electrolyte is preferably less than 20% by weight.

Conducting salts which are contained in the electrolysis solution are generally alkali metal, tetra (C ₁ - to C ₆ -alkyl) ammonium, preferably tri (C ₁ - to C ₆ -alkyl) -methylammonium salts. Suitable counterions are sulfate, bisulfate, alkyl sulfates, aryl sulfates, halides, phosphates, carbonates, alkyl phosphates, alkyl carbonates, nitrate, alcoholates, tetrafluoroborate or perchlorate.

Furthermore, the acids derived from the aforementioned anions may be considered as conductive salts, e.g. Sulfuric acid, sulfonic acids and carboxylic acids.

In addition, suitable electrolyte salts are ionic liquids. Suitable ionic liquids are described in "Lonic Liquids in Synthesis", ed. Peter Wasserscheid, Tom Welton, Verlag Wiley VCH, 2003, Chap. 1 to 3.

The process according to the invention can be carried out in all customary divided or undivided types of electrolytic cell. Preferably, one works continuously with undivided flow cells.

Particularly suitable are bipolar switched capillary gap cells or plate stacked cells, in which the electrodes are designed as plates and are arranged plane-parallel (see Ullmann's Encyclopedia of Industrial Chemistry, 1999 electronic release, Sixth Edition, VCH-Verlag Weinheim, Volume Electrochemistry, Chapter 3.5 cell designs and Chapter 5, Organic Electrochemistry, Subchapter 5.4.3.2 Cell Design). As the electrode material, graphite is preferable.

When the process is carried out continuously, the feed rate of the starting materials is generally selected such that the weight ratio of the compounds of general formula II used to the compounds of general formula I formed in the electrolyte is 10: 1 to 0.05: 1.

The current densities at which the process is carried out are generally 1 to 1000, preferably 10 to 100 mA / cm ² . In general, working at atmospheric pressure. Higher pressures are preferably used when operating at higher temperatures to avoid boiling of the starting compounds or the solvent.

Suitable anode materials are, for example, noble metals such as platinum or metal oxides such as ruthenium or chromium oxide or mixed oxides of the type Ruo _x Tio _x and diamond electrodes. Preference is given to graphite or carbon electrodes.

As cathode materials, for example, iron, steel, stainless steel, nickel or precious metals such as platinum and graphite or carbon materials and diamond electrodes into consideration. Preferably, the system is graphite as the anode and cathode and graphite as the anode and nickel, stainless steel or steel as the cathode.

After completion of the reaction, the electrolyte solution is worked up by general separation methods. For this purpose, the electrolysis solution is generally first distilled and recovered the individual compounds in the form of different fractions separately. Further purification can be carried out, for example, by crystallization, extraction, distillation or by chromatography.

Experimental part

Example of undivided driving:
An undivided plate stack cell with graphite anodes and steel cathodes was used. There were 160 g of 2-propyn-1-ol in 640 g of methanol with 5.3 g of sulfuric acid at a temperature of 20 ° C within 19 h. The electrolysis was carried out at 3.4 A / dm2 and it was a charge amount of 2 F based on the used 2-propyn-1-ol passed through the cell. 8.8% areal of 1,1-dimethoxy-2-propyne (conversion 49%, yield 30%) were obtained in the electrolysis discharge.

Example of shared driving:
A split parallel plate cell with graphite anode and steel cathode was used. There were 401 g of 2-propynol in 1400 g of methanol and 38 g of MTBS (Methyltributylammoniummethylsulfat) in the anode compartment and 941 g of methanol and 24 g MTBS in the cathode compartment at a temperature of 20 ° C within 38 h. The electrolysis was carried out at 3.1 A / dm ² and it was a charge amount of 2 F based on the used 2-propyn-1-ol passed through the cell. 8.3 GC area% of 1,1-dimethoxy-2-propyne (conversion 91%, yield 19%) were obtained in the anolyte.

Example of shared driving:
A split parallel plate cell with graphite anode and steel cathode was used. There were 13 g of 2-butyne-1,4-diol in 117 g of methanol and 3.8 g of MTBS (Methyltributylammoniummethylsulfat) in the anode compartment and 130 g of methanol and 3.8 g of MTBS in the cathode compartment at a temperature of 19 ° C within 14 h implemented. The electrolysis was carried out at 3.4 A / dm ² and it was an amount of charge of 4 F based on the 2-butyne-1,4-diol passed through the cell. After the electrolysis, anolyte and catholyte were combined to give a yield (GC area%) of 1,1-dimethoxy-2-butyn-4-ol of 53% and 1.1, with a conversion of 100%, 4,4-tetramethoxy-2-butyne of 20%.

Claims (7)

Process for the preparation of 2-alkyne-1-acetals of general formula I,

where the radicals have the following meaning
R ¹ : hydrogen, C ₁ - to C ₂₀ -alkyl, C ₂ - to C ₂₀ -alkenyl, C ₂ - to C ₂₀ -alkynyl, C ₃ - to C ₁₂ -cycloalkyl, C ₄ - to C ₂₀ -cycloalkyl- alkyl, C ₄ - to C ₁₀ -aryl, these radicals being optionally substituted by hydroxyl, halogen, C ₁ - to C ₆ -alkoxy, (C ₁ - to C ₆ -alkoxy) -carbonyl, carboxyl or nitrile groups can
R ² : C ₁ - to C ₆ -alkyl or a radical of the general formula II

in which R ^{1 has} the abovementioned meaning
R ³ : has the same meaning as the radical R ² ,
by giving a compound of general formula III

in which the radical R ^{1 has} the same meaning as in the general formula I,
in the presence of C ₁ - to C ₆ -alkyl alcohols (alcohol A) or in substance electrochemically oxidized. A process as claimed in claim 1, wherein 2-propyn-1-ol or 2-butyne-1,4-diol is used as the compound of general formula III and methanol is used as alcohol A. A process according to claim 1 or 2, wherein the process is carried out in an electrolyte containing sulfuric acid, sulfonic acids or carboxylic acids. A process according to any one of the preceding claims, wherein the process is carried out in an electrolyte containing less than 20% by weight of water. Process according to one of the preceding claims, wherein the process is carried out in an electrolyte containing as conductive salt one or more compounds selected from the group of sodium, potassium, lithium, iron, tetra (C ₁ to C ₆ alkyl ) ammonium salts with sulfate, hydrogen sulfate, alkyl sulfates, aryl sulfates, Halides, phosphates, carbonates, alkyl phosphates, alkyl carbonates, nitrate, alcoholates, tetrafluoroborate or perchlorate as counterion or ionic liquids. Method according to one of the preceding claims, wherein the method is carried out in a bipolar switched capillary gap cell or plate stack cell or in a divided electrolysis cell. A process as claimed in any one of the preceding claims, wherein, using a compound of general formula III which carries 2 or more alcoholic hydroxyl groups, at least 2 moles (preferably 5 to 20 moles) of the formula (III) per mole of hydroxyl groups carrying the compound of general formula III Alcohol A is used.