CA1309724C

CA1309724C - Diisocyanates and a process for their preparation

Info

Publication number: CA1309724C
Application number: CA000562122A
Authority: CA
Inventors: Hans J. Scholl; Alfons Klein
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1987-03-25
Filing date: 1988-03-22
Publication date: 1992-11-03
Anticipated expiration: 2009-11-03
Also published as: DE3709781A1; DE3863207D1; EP0283884A1; EP0283884B1; JPS63255256A

Abstract

NEW DIISOCYANATES AND A PROCESS FOR THEIR PREPARATION

ABSTRACT OF THE DISCLOSURE
Alkyl-substituted diisocyanatotoluene(s) is (are) produced by (a) heating diaminotoluene(s) in the presence of an Al/Zn alloy and aluminum chloride until evolution of hydrogen ceases, (b) reacting the diamino-toluene(s) with at least one 1-alkene having 8 to 18 carbon atoms at elevated temperature and pressure and (c) phosgenating the resultant alkyl-substituted diaminotoluene(s). These alkyl-substituted diiso-cyanatotoluenes are liquids having low vapor pressures and are useful in the production of polyurethanes,

Description

1 ~ r' ~
Mo-3019 LeA 25,142 NEW DIISOCYANATES AND A PROCESS FOR THEIR PREPARATION
. ~, . . ......
BACK&ROUND OF THE INVENTION
This invention relates to new alkyl-substituted diisocyanatotoluenes, optionally in the form of homologous and/or isGmeric mixtures and to a process for their preparation.
Diisocyantobenzenes containing higher alkyl substituents are particularly interesting starting materials for the production of polyurethanes. These lo diisocyanates are liquids with a low vapor pressure which are physiologically much less problematic than, for example, the homologous diisocyanatotoluenes. They have the added advantage that the alkyl substituents impart not only to the diisocyanates but also to the intermediate products produced from them (e.g. the isocyanate prepolymers obtained from the diisocyanates) improved solubility in comparatively nonpolar solvents.
Diisocyanatobenzenes of this type containing higher alkyl groups as substituents and a process for their preparation are described, for example, in DE-AS
1,123,662 (GB 852,988; U.S. 2,986,576). The alkyl substituted diaminobenzene of the process described in this prior publication is prepared according to U.S.

2,934,571 by dinitration of the corresponding alkyl benzene and hydrogenation of the resulting alkyl-sub-stituted dinitrobenzene. One disadvantage of this disclosed procedure is that dinitration of the alkyl benzenes carried out according to U.S. 2,934,571 does not go to completion even when a mixture of fuming nitric acid and fuming sulphuric acid is used as nitrating acid. It is therefore virtually impossible to obtain diisocyanates which are strictly difunctional.

Mo-3019 LeA 25 142-US

1 7 !~ ~ ~7 ~
J, J I ,' This di~ficulty in achieving exclusively difunctional diisocyanates is discussed in some detail in EP-B-00 58 368. The authors of this prior publication made it their task to overcome the above-mentioned disadvantages of the methods described inDE~AS 1,123,662 and U.S. 2,934,571. They achieved this by using special alkyl benzenes in the form of homologous mi~tures as the starting material for the nitration. These homologous mixtures of alkyl benzenes used as starting materials must have a boiling range of 10 to 50C, preferably 20 to 30C within the temperature range of from 270C to 330C at 1013 mbar and the alkyl substituents are saturated, straight chained aliphatic hydrocarbon groups with 8 to 15, preferably 10 to 13 carbon atoms. Such homologous mixtures of alkyl benzenes must be prepared in a separate process by the alkylation of benzene with the appropriate straight chained olefin mixtures which in turn are obtained by oligomerization of ethylene. Therefore, although the diisocyanates according to EP-B-00 58 368 are technically interesting starting materials for the polyurethane chemist, their preparation is technically complicated.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide new substituted diisocyanatobenzenes which would to a large extent be equivalent in their properties to the diisocyanates according to EP-B-00 58 368 but would be technically more easily available from inexpensive starting materials.
This and other objects which will be apparent to those skilled in the art are accomplished by orthoalkylating diaminotoluenes in the presence of an Al/Zn alloy and aluminum chloride to orm diamono-toluenes which are alkyl substituted on the nucleus.These diaminotoluenes are then phosgenated to form diisocyanates corresponding to a specified formula.
Mo-3019 2 -1 ~ r !~ 7 ~
i / i ,, s DETAILED DESCRIPTION OF THE INVENTION
r The present invention relates to diisocyanates, optionally in the form of isomeric and/or homologous mixtures corresponding to the formula f~3 s ~--~CO
I~CO
in which R represents an alkyl group with 8 to 18 carbon atoms.
The present invention also relates to a process for the preparation of these diisocyanates. In this lo process, diamonotoluenes, optionally in the form of isomeric mixtures, are heated with an Al/Zn alloy and aluminum chloride. When evolution of hydrogen has ceased, the compounds are reacted at elevated pressures and temperatures with l-alkenes containing 8 to 18 carbon atoms, which alkenes are optionally homologous mixtures~ The resulting alkyl-substituted diamino-toluenes are converted into the corresponding diisocyanates by phosgenation.
The heating of diaminotoluenes in the presence of Al/Zn alloys and aluminum chloride and subsequent reaction with l-alkenes after evolution of hydrogen has ceased has been described for the low alkenes, ethene and propene, in DE-OS 3,402,983. It has also been disclosed in the literature (Angew. Chem. 69 (1957) page 131) that the reactivity for this alkylating reaction decreases with increasing molecular weight of the alkenes. Consequently, higher olefins have hitherto not been used for such orthoalkylating reactions. It must therefore be regarded as surprising that the reaction carried out in the first stage of the process of the present invention proceeds smoothly and with high yields.

Mo-3019 - 3 -1 7 .~7~
The diamonotoluenes used in the process of the present invention are generally 2,~-diaminotoluene or commercial mixtures thereof with up to 35 wt. 7O~ based on the mixture, of 2,6-diaminotoluene. Mixtures of 2,4-and 2,6-diaminotoluene in proportions by w~ight within the range of from 80:20 to ~5:35 are particularly preferred.
The 1 alkenes used in the process of the present invention are ethylene oligomers containing 8 to 18 carbon atoms. These l-alkenes may be obtained on a technical scale by the oligomerization of ethylene and which are marketed e.g. as "Shop Olefine" by Shell. The alkenes used for the process according to the invention may be technically pure compounds or mixtures of homolo~ues with different chain lengths within the range of 8 to 18 carbon atoms.
The Al/Zn alloys may have a zinc content of about 2 to 30 wt. %, preferably 5 to 20 wt. ~. The aluminum content accordingly amounts to about 70 to 98 wt. ~., preferably 80 to 95 wt. %. The alloys may be put into the process in the form of turnings, granules, fine grains or powder.
The quantity of Al/Zn alloy used may vary and depends upon the proportion of Zn in the Al/Zn alloy.
Generally amounts o~ about 0.5 to 4 wt. %, preferably 1 to 2 wt. % of Al/Zn alloy, based on the m-phenylene diamine which is to be alkylated are employed.
The quantity of aluminum chloride to be put into the process is generally about 1 to 7 wt. ~, preferably 2.5 to 4 wt. ~, based on the tolylenediamine to be alkylated.
In the process of the present invention, the diaminotoluene which is to be orthoalkylated is firs~
heated with an Al/Zn alloy and the aluminum chloride tanhydrous) at temperatures of about 150 to 250C, preferably 170 to 220C until no more evolution of Mo-3019 - 4 -,~ r~ f ~ 7 ~ fl 1, ,, ,,. i-hydrogen can be observed. The mixture is then reacted with the alkene in an autoclave at temperatures of about 250 to 330C, preferably at 280 to 310C. The pressures are about 5 to S0 bar, preferably 10 to 30 bar. The reaction is allowed to continue for some time after the absorption of alkene has ceased. The reaction mixture is then worked up after release of the pressure.
Working up of the reaction mixture is carried out in known manner by the addition of water or aqueous lo sodium hydroxide solution to t~e reaction mixture to decompose the catalyst. The organic phase may then be subjected to vacuum distillation or worked up by other conventional methods of purification.
The diamines thus obtained are subjected to a phosgenation reaction. Phosgenation procedures are known to those skilled in the art. Phosgenation may also be carried out, for example, by dissolving the diamine in an auxiliary solvent SUCh as chlorobenzene and adding the resulting solution dropwise to a solution of phosgene in chlorobenzene with stirring and cooling at -20 to + 5C, preferably -10 to 0C (cold phosgenation). The reaction mixture is then heated with continued stirring and introduction of phosgene to a final temperature of 80 to 160C, preferably 100 to 140C so that the carbamic acid chloride initially formed is converted into the required diisocyanate (hot phosgenation). The reaction mixture is then worked up in known manner. Conversion of the diamines into the diisocyanates of the present invention may, of course, also be carried out by any other known phosgenation method.
The diisocyanates of the present invention are liquid substances which show no tendency to crystallize.
Due to their low vapor pressure, they are virtually odorless at room temperature. Further 9 due to the method by which they have been prepared, they cGntain no Mo-3019 - 5 ~

~ 7~
, / , ; .. , signifîcant residues of unwanted monoisocyanates.
Depending upon the nature of the starting materials from which they were produced, the diisocyana~es may be chemically substantially uniform products or they may be isomeric and/or homologous mixtures of diisocyanates corresponding to the general formula indicated above.
The diisocyanates of the present invention are valuable starting materials for the production of polyurethane resins by the isocyanate polyaddition 0 process. The diisocyanates of the present invention may be used for this purpose instead of the known aromatic diisocyanates used. This means that the diisocyanates of the present invention are eminently suitable, for example, for the production of polyurethane foams, elastomers, adhesives, dispersions, coatings or lacquers by known processes using known reactants and auxiliary substances. The diisocyanates of this invention are also eminently suitable for the preparation of polyurethane preliminary products such as isocyanate prepolymers or known modified polyisocyanates used in polyurethane chemistry, in particular polyisocyanates containing isocyanurate groups obtainable by the partial trimerization of isocyanate groups. The diisocyanates of the present invention are very suitable for the preparation of isocyanato-isocyanurates, by a known trimerization reaction, either as the only starting diisocyanates or as mixtures with other diisocyanates (for example, with 2,4-diisocyanatotoluene). The mixed trimers of the diisocyanates of the present invention with 2,4-diisocyanatotoluene have lower viscosity, for example, than the corresponding mixed trimers of the alkyl substituted diisocyanates according to EP-B-00 58 368 with 2,4-diisocyanatotoluene.
The diisocyanates of the present invention are also valuable intermediate products for the production of pest control agents.
Mo-3019 - 6 -7 r~ 1'1 7 7 .~
., / ! / 'i The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLE
a) Orthoalkylation of aminotoluene.
200 g of a mixture of 80 parts by weight of 2,4-diaminotoluene and 20 parts by weight of 2,6-diaminotoluene, 4.7 g of an aluminum/zinc alloy (ratio by weight Al:Zn = 90:10) and 8.3 g of anhydrous aluminum chloride were introduced into a 0.7 liter stainless steel autoclave. The mixture was then stirred at 200C for 1.5 hours, during which a pressure of 9 bar was established due to the evolution of hydrogen. After cooling to 140C, the pressure was released and 275 g of l-dodecene which had been pre-heated to 130C were added. Stirring was then continued at 300C for 12 hours, during which a pressure of 10 bar was established. The reaction mixture plus 150 g of 10% sodium hydroxide solution was then heated to boiling with stirring for one hour to decompose the catalyst. The reaulting organic phase was then separated and subjected to fractional distillation. 137 g of a dodecyl-substituted diaminotoluene isomeric mixture boiling in the range of 190 to 205C/1.0 mbar were obtalned. The first runnings were unreacted starting material (173 g of l-dodecene and 109 g of diaminotoluene), b) Phosgenation:
500 g of anhydrous chlorobenzene were introduced into a 2 liter 4 necked flask equipped with stirrer, thermometer, gas inlet tube and reflux condenser.
About 200 g of phosgene were incorporated by condensation under conditions of stirring and cooling (-10C). 150 g of a crude amine mixture Mo-3019 - 7 -1 7r r~ 7'~1 from (a) dissolved in 150 g of chlorobenzene were then added dropwise with cooling at -10 to -5C. As phosgene continued to be introduced without further cooling, the temperature of the solution rose to about 30~C. When the evolution of heat had ceased, the temperature was gradually raised to 125C and phosgene continued to be introduced (~otal 400 g) until the evolution of hydrogen chloride ceased.
The excess phosgene was blown out with nitrogen and the solution was concentrated by evaporation in vacuo. 175 g of a crude isocyanate mixture having an isocyanate content of 23% (theoretical:
24.6%) were obtained. The resulting diisocyanate according to the invention could be used as starting material for the production of polyurethanes without further purification. It was however subjected to an additional purification by distillation as described below.
150 g of the diisocyanate mixture were distilled at reduced pressure. 132 g of a virtually colorless mixture of diisocyanates corresponding to the formula ~H3 R ~ ~ NCO
~5 OCN
distilled off at a pressure of 1.2 mbar within the temperature range of 188 to 206C. This diiso-cyanate mixture showed no tendency to undergo crystallization even when cooled to -50C.

Mo-3019 - 8 -1,, '2 The compositional analysis of the product was as follows:
Analysis (%) -found: 24.2 74.~ 9.0 7.9 S _ .
Theoretical: 24.6 73.7 8.8 8.2 (based on C21H30N22) Although the invention has been descrlbed in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Mo-3019 - 9 -

Claims

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. A process for the production of a diiso-cyanate or mixture of diisocyanates corresponding to the formula in which R represents an alkyl group having 8 to 18 carbon atoms comprising (a) heating a mixture of diaminotoluene or mixture of diaminotoluenes, an Al/Zn alloy and aluminum chloride, (b) reacting the mixture of (a) with at least one 1-alkene containing 8 to 18 carbon atoms at elevated temperature and pressure after evolution of hydrogen has ceased to produce an alkyl-substituted diaminotoluene or mixture of alkyl-substituted diaminotoluenes and (c) phosgenating the alkyl-substituted diamino-toluene or mixture thereof to form the corresponding diisocyanate or mixture of diisocyanates.

Mb-3019 - 10 -