MXPA97008836A - Preparation of esters 2-cyan-3,3-diarilacrili - Google Patents

Abstract

A process for preparing the 2-cyano-3,3-diarylacrylic esters of the general formula I, wherein R 1 and R 2 are hydrogen, C 1 -C 12 alkyl groups, C 1 -C 12 alkoxy groups or dialkyl (C 1 -C 4) groups amino and R3 is a C4-C18 alkyl group which can be interrupted by oxygen atoms which function as the ether, by reacting a benzophenone imine of the general formula II, with a cyanoacetic ester of the general formula III, wherein the reaction is carried out from 20 to 60 ° C and, during this, the released ammonia is continuously removed from the reaction mixture with the help of a gas stream or by reducing the pressure from 900 to 100 mb

Description

PREPARATION OF 2-CYANO-3, 3-DIARI ACRYLIC ESTERS The present invention relates to an improved process for preparing 2-cyano-3,3-diarylacrylic esters of the general formula. wherein R1 and R2 are hydrogen, C1-C alkyl groups, C1-C4 alkoxy groups or dialkyl (C1-C4) amino groups and R3 is a C4-Cli alkyl group which can be interrupted by functional oxygen atoms as an ether, reacting the appropriate benzophenone imines with the appropriate 2-cyanoacetic esters. The 2-cyano-3,3-diarylacrylic esters are highly effective absorbers of UV rays which are used in particular as light stabilizers in plastics and cosmetic products. It is generally known to prepare the compounds of type I from benzophenones by reaction with cyanoacetic esters (see, for example, EP-A 1 430 023, US-A 3 215 724 and DE-AI 43 14 035).

Although this reaction requires relatively high temperatures from 70 to 130 ° C, it takes place slowly and therefore requires the use of a catalyst, which must subsequently be removed from the product. In addition, unwanted concomitant substances are produced and, for this reason, the reaction must follow elaborate purification steps. In addition, it is known (Bull. Chem. Soc. Fr. (1993) 1576 (G. Charles)) the preparation of ethyl 2-cyano-3, 3-diphenyl acrylate from benzophenone i ina and ethyl 2-cyanoacetate from 70 to 120 ° C, but this reaction has the disadvantage that colorful by-products are produced at the reaction temperatures, and the released ammonia reacts to a degree to interfere with the ester portion of the molecule to give the corresponding amide. that is, the elaborate purification steps are also necessary in this case, especially to make the product suitable for use in cosmetic products. An object of the present invention is to make the compounds I available in a simpler and cheaper way than the current one.

We have found that this objective is achieved by an improvement in the process, defined at the outset, for preparing the compounds I, which comprises reacting a benzophenone of the general formula II. with a cyanoacetic ester of the general formula III H2C COOR3 (III) at a temperature of 20 to 60 ° C and, during this, continuously remove the ammonia released from the reaction mixture with the aid of a gas stream or by reducing the pressure to 90-100 mbar. The compounds I that are particularly important for the properties of use are those wherein R1 and R2 are hydrogen, ethyl or ethyl. The most preferred radicals R1 and R2 are methoxy, ethoxy and diethylamino. The light absorption reaction can be displaced in some way by choosing the substituents R1 and R2 so that the compounds I may be suitable for the specific light stabilization requirements. The corresponding benzophenone derivatives II are known or obtainable by known methods (see, for example, Bull. Chem. Spc. Cot. And German Patent Application P 44 42 138.9). Particularly suitable cyanoacetic esters are those with a relatively long chain alcohol component. Preferred cyanoacetic esters are the 2-ethylhexanol and n-octanol derivatives which are proven components of important light stabilizers. However, other alcohol residues, such as the various isomeric butanols, pentanols, hexanols, heptanols, nonanols, decanoles, dodecanols or alcohols derived from long-chain fatty acids can also be constituents of the cyanoacetic esters that can be used advantageously. Also suitable as R 3 are the various polyoxyethylene radicals such as -CH¿-CH¿-0-CH¿-CH¿, -CH ^ -CH ^ -O-CH / -CH / -0-CH / -CH ,, and their larger chain homologs, which give the compounds I solubility properties which are advantageous in particular for cosmetic formulations. The process according to the invention is particularly suitable for preparing liquid products I that can not be separated from the initial materials and by-products by crystallization. This applies in particular to the compounds I wherein R3 is a larger alkyl or polyoxyethyl radical [sic]. The reaction of the diarylketone imine with cyanoacetic ester is carried out from 20 to 60 ° C, preferably from 25 to 50 ° C, in particular from 30 to 40 ° C. The temperature will depend on the thermal stability and the melting point of the reactants in the reaction mixture. The reaction will tend to be carried out in the higher temperature range for the high melting point substances. To keep all the reagents in solution, in some circumstances a small amount of solvent will be used. It is important that the ammonia produced during the reaction be removed from the mixture immediately by a gas stream passing through the solution or by reducing the pressure to 900-100 mbar, preferably from 500 to 150 mbar. The preferred gases are inert gases such as nitrogen, but air can also be used. The reaction usually proceeds to a conversion of about 85% after about 2-6 hours. An advantageous process provides a subsequent treatment by distillation, for example, in a thin film or, in particular, in a falling film evaporator. The preferred distillation is carried out with a nitrogen countercurrent from 170 to 210 ° C with from 1 to 25 mbar. This brief exposure of the reaction mixture to the heat increases the conversion by another 10% approximately without the quality of the final product suffering in terms of color or the increasing amide content. The residues of the initial materials are separated during the distillation and can be reused for another reaction. The purity of the products prepared in this way is, as a general rule, more than 99%, as demonstrated by the analysis in gas chromatography. The process according to the invention can be carried out in batch form or continuously by the methods customary for these purposes. Example Preparation of (2-ethyl) hexyl (2-cyano-3,3-diphenylacrylate 905 g (5.0 mol) of benzophenone imine was slowly added to 992 g (5.0 mol) of (2-ethyl) hexyl cyanoacetate and the mixture it was stirred at room temperature while passing nitrogen for 3 h, then the volatile constituents were removed from the reaction mixture in a thin layer evaporator (Sambay, drying area 0.05 m2) with a yield of 800 g / h at 185 °. C with about 8 mbar The countercurrent of nitrogen during the process was around 5 1 / h The product of the lower part was filtered through active carbon around 80 ° C. The product produced in the distillate by subsequent reaction The product was obtained as a pale yellow oil with a purity, determined by gas chromatography, of 99.5% and a color number (GARDNER, measured com or a 10% solution by weight in toluene) of 2.

Claims (4)

CLAIMS A process for preparing the 2-cyano-3,3-diarylacrylic esters of the general formula I. wherein R 1 and R 2 are hydrogen, C 1 -C 12 alkyl groups, C 1 -C 1 alkoxy groups or dialkyl (C

1 -C 4) amino groups and R 3 is a C 1 8 alkyl group which can be interrupted by carbon atoms. oxygen that function as ether, reacting a benzophenone imine of the general formula II with a cyanoaceester of the general formula III CN H2C COOR3 (III) wherein the reaction is carried out from 20 to 60 ° C and, during this, the released ammonia is continuously removed from the reaction mixture with the aid of a gas stream or reducing the pressure from 900 to 100 mbar, and the reaction mixture is then treated by distillation in a thin film or falling film evaporator to increase the conversion and remove the residues of the starting materials and other volatile compounds. The process, according to claim 1, wherein the reaction is carried out in the absence of solvent. The process according to any of claims 1 or 2, which is applied to the reaction of benzophenone imine (R1 = R2 = H) with 2-ethylhexyl cyanoacetate. SUMMARY OF THE INVENTION A process for preparing the

2-cyano-3,

3-diarylacrylic esters of the general formula I. wherein R1 and R2 are hydrogen, C1-C12 alkyl groups, C? -C? alkoxy groups, > or dialkyl (C1-C4) amino groups and R3 is a C

4-C18 alkyl group which can be interrupted by oxygen atoms functioning as ether, by reacting a benzophenone imine of the general formula II with a cyanoaceester of the general formula III CN H2C ^ COOR3 (III) wherein the reaction is carried out from 20 to 60 ° C and, during this, the released ammonia is continuously removed from the reaction mixture with the aid of a gas stream or reducing the pressure from 900 to 100 mbar.