DK155001B - PROCEDURE FOR THE PREPARATION OF UNSATURED CARBOXYLIC ACIDS - Google Patents

Description

DK 155001 B

The present invention relates to a process for the preparation of novel unsaturated carboxylic acids which are valuable chemical intermediates.

The present invention relates to the preparation of unsaturated carboxylic acids of general formula I

R1

HOOC -CH -C -CH - CHo I

1> 2 10 X R 2 where X represents cyano or alkoxycarbonyl, and and R 2 each represent alkyl, or a salt of such an acid.

The process of the invention is characterized in that an enolate salt of an ester of the general formula II

15 R1 0

C = CH - CH2OC-CH2X II

R2, where X, R * and R2 have the meaning set forth above, is thermally rearranged at a temperature between 100 ° C and 150 ° C and the acid, if desired, is released from the salt thus formed by acidification.

The enolate salt is preferably an alkali metal or alkaline earth metal salt which can be formed by reaction of the ester with the metal itself or a basic compound thereof, e.g. hydride. Particularly preferred is the sodium salt, which can be conveniently formed by reacting the ester with sodium hydride.

The thermal rearrangement is carried out as indicated at a temperature between 100 and 1500C. There may also be an inert solvent, e.g. a liquid aromatic compound such as toluene, xylene or chlorobenzene.

The product of the thermal rearrangement is a salt of the acid of the formula

DK 155001 B

2 I from which the acid is released by acidification with e.g. a strong mineral acid such as hydrochloric acid, preferably under aqueous conditions.

As stated above, the compounds of formula I can be used as intermediates, especially for the preparation of pesticides. Thus, the 2-5 cyano-4-pentenoic acid derivatives can be used for the preparation of esters of 2- (2,2-dichlorovinyl) cyclopropane carboxylic acids which have interesting insecticidal properties, cf. Dutch Patent Application No. 7,307,130.

The invention is further illustrated by the following examples in which the NMR spectra are measured at 60 MHz in deuterochloroform solution; the absorbances are given relative to a tetramethylsilane standard.

EXAMPLE 1

A solution of 30 g (0.2 mole) of 3-methyl-2-butenyl cyanoacetate in 50 ml of a mixture of xylenes (bp 137-143 ° C) is stirred over 15 minutes to a suspension of 5.0 g (0.2 mole) of sodium hydride in the 150 ml xylene mixture. The suspension of the enolate salt formed is diluted to 500 ml with additional xylene mixture and then stirred at 130 ° C for 2 1/2 hours. The suspension is then cooled to 22 ° C and extracted three times with 150 ml of water each time. The aqueous extract is sieved to pH 1 with aqueous hydrochloric acid solution, and the precipitate formed is extracted three times with 150 ml of diethyl ether each time. The extracts are dried over sodium sulfate and the ether is evaporated under reduced pressure to give the desired 2-cyano-3,3-dimethyl-4-pentenoic acid in the form of a viscous oil in a yield of 86% of theory.

The NMR spectrum of the compound shows the following absorptions: 8 = 1.30 ppm (singlet,> C (CH 3) 2) 8 = 3.41 ppm (singlet,> CHCN) 8 - 5.17 ppm (double doubled, = 0¾ 8 = 5.95 ppm (double doubled, -CH =) 8 = 10.1 ppm (singlet, -COOH).

EXAMPLE 2

DK 155001 B

3

Proceed as described in Example 1 using toluene as the diluent, a reaction temperature of 110 ° C and a reaction time of 3 hours. The yield of acid is 80% of the theoretical.

EXAMPLE 3

Proceed as described in Example 1 using metallic sodium instead of sodium hydride. The yield of acid is 40% of theory.

EXAMPLE 4 10 Proceed as described in Example 1 using chlorobenzene as diluent and a reaction time of 1 hour. The yield of acid is 68% of the theoretical.

EXAMPLE 5

Proceed as described in Example 1 using 3-methyl-2-butenyl-ethyl malonate as starting material. The product, 2-ethoxycarbonyl-3,3-dimethyl-4-pentenoic acid, is formed as a viscous oil in a yield of 40% of theory.

The NMR spectrum of this compound shows the following absorbances: δ 6 = 6.05 ppm (double doubled, HC =) δ = 5.05 ppm (double doubled, = CH 2) δ δ 4.2 ppm (quartet, -0¾-O ) C00 δ - 3.3 ppm (singlet, -CH) C00 δ = 1.28 ppm (singlet on triplet, three CH3 groups).

Claims (3)

A process for preparing unsaturated carboxylic acids of general formula I R 1 In HOOC -CH -C -CH - CHo I 1> 2 X R 2 where X represents cyano or alkoxycarbonyl, and R 2 - and R 2 are each 10 alkyl, or a salt of such an acid, characterized in that a enolate salt of an ester of the general formula II R1O C - CH - CH 2 OC-CH 2 X II R 2 where X, R 2 - and R 2 have the meaning given above, are thermally rearranged at a temperature between 100 ° C and 150 ° C and the acid, if desired, is released from the salt thus formed. by acidification. Process according to claim 1, characterized in that the enolate salt is the sodium salt. Process according to claim 1 or 2, characterized in that the thermal rearrangement is carried out in the presence of a liquid aromatic compound.