Process For Preparing Cyanoacetic Esters

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The invention relates to a process for preparing cyanoacetic esters of the general formula

in which R is Ci-io-alkyl, C^-io-alkenyl or aryl-Ci-^-alkyl. Here and hereinbelow, Ci-io~alkyl is to be understood as any linear or branched primary, secondary or tertiary alkyl group having 1 to 10 carbon atoms, in particular groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. Cs-io-alkenyl is to be understood as the corresponding groups having 3 to 10 carbon atoms and at least one C=C double bond, where the double bond is advantageously separated from the free valency by at least one saturated carbon atom. These include, in particular, groups such as allyl, methallyl, but-2-enyl (crotyl), but-3-enyl, etc. Aryl-Ci-fl-alkyl is to be understood as, in particular, phenyl-substituted Ci-^-alkyl groups such as, for example, benzyl, phenethyl or 3-phenylpropyl, where the phenyl group may also carry one or more identical or different substituents such as, for example, Ci-4-alkyl, C1-4-alkoxy or halogen. The customary synthesis of cyanoacetic esters is carried out by cyanidation of sodium chloroacetat^ in aqueous solution, followed by an acid-catalysed esterification with the appropriate alcohol, where the water formed is distilled off azeotropically. An essential disadvantage of this two-step process is the fact that the water has to be removed after cyanidation, since the subsequent esterification is only passible under substantially water-free conditions. On an industrial scale, this is usually carried out by evaporating the water.

Since the sodium cyanoacetate which is formed as intermediate is moreover highly water-soluble, a method for its esterification in water as the solvent is desirable. Accordingly, it was an object of the present invention to develop a process where the aqueous solution of sodium cyanoacetate which is obtained after cyanidation can be esterified directly. Accordingly the present invention provides a process for preparing cyanoacetic ester of the general formula:

in which R is Ci.io-alkyl, C3.io-alkeny| or ar)'-Ci.4-alkyl, characterized in that an alkali metal cyanoacetate is reacted in an aqueous/organic two-phase system in the presence of a phase-transfer catalyst with a halide of formula R-X (II), in which R is as defined above and X is chlorine, bromme or iodine. The organic phase used can be the halide (II) on its own or m a mixture with an organic solvent. The alkali metal cyanoacetate which is preferably used is sodium cyanoacetate. The sodium cyanoacetate is particularly preferably employed in the form of the aqueous solution obtained in the reaction of sodium chloroacetate with sodium cyanide. X is preferably chlorine or bromine. 3

The phase-transfer catalyst which is preferably employed is a quaternary ammonium salt. Particularly preferred quatemary ammonium salts are the tetra-n-C4_io -alkylammonium, benzyltri-n-Cj-s-alkylammonium or methylti'i-n-C4_io-alkylammonium halides, in particular the chlorides and bromides. Preference is also given to using tert-butyl methyl ether or chlorobenzene as solvent in the organic phase. The examples below illustrate the practice of the process according to the invention without limiting it. All —

reactions were carried out in an autoclave having an internal volume of about 250 ml. The yield was determined by^ gas chromatography with the aid of an internal standard. Exan^le 1 Methyl cyanoacetate 10.0 g (9.9 equivalents, 0.20 raol) of methyl chloride were introduced into a mixture of 1,70 g (0,02 mol) of cyanoacetic acid, 0.8 g (0.2 mol) of sodium hydroxide and 0.64 g (2.0 mmol) of tetrabutylammonium bromide in 15 ml of tert-butyl methyl ether/water 2:1. The reaction mixture was heated to an internal temperature of 100°C (oil bath temperature 110°C) over a period of 30 minutes, during which the pressure in the autoclave increased from 4 to 10 bar. After 3.5 h at lOCC, the autoclave was cooled and vented. The pH of the aqueous phase was adjusted from 2.9 to 5.9 using 3.10 g of 1 M aqueous sodium hydroxide solution, the organic phase was separated off and the aqueous phase was extracted with tsrt-butyl methyl ether (2x6 ml) . The combined organic phases were dried with sodium sulfate, admixed with dimethyl succinate (as internal standard) and analysed by gas chromatography. 1.36 g (68%) of methyl cyanoacetate were obtained. Comparative Exan^le 1 Methyl cyanoacetate The method described in Example 1 was repeated, but without addition of tetratautylammon i jn bromide. The yield of methyl cyanoacetate was only 13%. Example 2 Ethyl cyanoacetate A mixture of 1.70 g (0.02 ii'ol i of cyanoacetic acid, 0.8 g (0.02 raol) of sodium hydroxide, 10.90 g (0.10 mol, 5 equivalents) of ethyl oromide and 0.64 g (2.0 mmol) of tetrabutylammonium bromide in 15ml of chlorobenzene/water

(2:1) was heated to an internal temperature of 100°C over a period of 30 min and stirred at 100°C (oil bath temperature 110°C) for 3.5 h. The reaction mixture was then cooled, the phases were separated and the aqueous phase {pH = 6.85) was extracted with tert-butyl methyl ether (2x5 ml) . The combined organic phases were dried with sodium sulfate, admixed with dimethyl succinate (as internal standard) and analysed by gas chromatography. I.AS g (65%) of ethyl cyanoacetate were obtained. Exanple 3 Benzyl cyanoacetate A mixture of 1./ g (0.02 mol) of cyanoacetic acid, 0.8 g {0.02 mol) of sodium hydroxide, 7.60 g (0.06 mol, 3 equivalents) of benzyl chloride and 0.64 g (2.0 mmol) of tetrabutylammonium bromide in 15 ml of tert-butyl methyl ether/water (v:v - 2:1) was stirred at 100°C (oil bath temperature 110''C) for 3 h. The pH of the aqueous phase was then adjusted from 0.2 to 6.3 using 3, 15 g of 1 M aqueous sodium hydroxide solution, the organic phase was separated off and the aqueous phase was extracted with tert-butyl methyl ether (2x5 ml). The combined organic phases were dried with sodium sulfate and analysed by gas chromatography. 2.45 g (70%) of benzyl cyanoacetate were obtained.

WE CLAIM: 1. A process for preparing cyanoacetic ester of the general formula:

in which R is Ci_io-alkyl, Q.io-alkenyl or ary-C|.4-alkyl, characterized in that an alkali metal cyanoacetate is reacted in an aqueous/organic two-phase system in the presence of a phase-transfer catalyst with a halide of formuJa R.-X (11), in which R i*^ as defined above and X is chlorine, bromine or iodine. 2. The process according to claim 1, wherein the alkali metal cyanoacetate is sodium cyanoacetate. 3. The process according to claim 2, wherein the sodium cyanoacetate is used in the form of the aqueous solution obtained in the reaction of sodium chloroacetate with sodium cyanide, 4. The process according to any one of claims 1 to 3, wherein X is chlorine or bromine. 5. The process according to any one of claims 1 to 4, wherein the phase-transfer catalyst is a quaternary ammonium salt. 7

6. The process according to claim 5, wherein the quaternary ammonium salt is tetra-n-C4.]o-alkylammonium, benzyltri-n-Ci.s-alkylammonium or methyltri-n-Q-io-alkylammonium halide, preferably chloride or bromide. 7. The process according to any one of claims 1 to 6, wherein the organic phase comprises tert-butyl methyl ether or chlorobenzene as a solvent. 8. A process for preparing a cyanoacetic ester substantially as herein described and exemplified.