GB2085429A

GB2085429A - Process for producing carboxylic acid chlorides

Info

Publication number: GB2085429A
Application number: GB8032771A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1980-10-10
Filing date: 1980-10-10
Publication date: 1982-04-28

Abstract

Carboxylic acid chlorides of the formula R-CH2-COCl in which R is an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen or the carboxyl group are prepared by reacting an alkali metal salt of a corresponding carboxylic acid in an inert solvent, in the presence of 0.5 to 10 per cent by weight of an N,N-dialkyl-substituted carboxylic acid amide, at 30-110 DEG C with essentially the stoichiometric amount of phosgene. The carboxylic acid chlorides produced by this process can be used as solvents or as intermediates, for example as intermediates for producing pesticidal compositions.

Description

SPECIFICATION Process for producing carboxylic acid chlorides The present invention relates to a process for producing carboxylic acid chlorides of the formula I R-CH2-COCI (I) in which R is an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen or the carboxyl group.

The alkyl groups as R or occurring in R can be straight-chain or branched-chain, and are in particular: methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl and isobutyl. Halogen embraces fluorine, chlorine, bromine and iodine, especially however chlorine and bromine.

Preferred meanings of R are methoxy and chlorine.

The carboxylic acid chlorides of the formula I are on the one hand solvents, and on the other hand intermediates for producing softeners, odoriferous substances, detergents, mordants and pesticidal compositions. To be emphasised as intermediates for producing pesticidal compositions are in particular the methoxyacetyl chloride and chloroacetyl chloride, since these can be converted, by reaction with N-alkyl-substituted anilines, into the corresponding acetanilides, which have an excellent fungicidal action.

The method of producing carboxylic acid chlorides by reaction of corresponding carboxylic acids with phosgene in the present of N,N-disubstituted carboxylic acid amides, especially N,N-dialkylformamides, such as N,Ndimethylformamide, is known. This method has the disadvantage that phosgene has to be used in excess in order to effect complete reaction of the acid. The result of this is either that phosgene losses occur, or that, if the phosgene is to be recovered, a costly processing of the gaseous by-products is necessary (see German Offenlegungsschrift No.

2,057,956). After separation of the phosgene, there remains a corrosive gaseous mixture consisting of carbon dioxide and hydrogen chloride, and separation of this gaseous mixture is a complicated process.

It is the object of the present invention to eliminate these disadvantages of the known process and to provide a process which renders possible the production of carboxylic acid chlorides in good yields using an essentially stoichiometric amount of phosgene, and which avoids the formation of a corrosive waste gas containing hydrogen chloride.

It has been found that carboxylic acid chlorides of the formula I are obtained in good yield by reacting an alkali metal salt of a corresponding carboxylic acid in an inert solvent, in the presence of 0.5 to 10 per cent by weight of an N,N-dialkyl-substituted carboxylic acid amide, at 30-110"C with the essentially stoichiometric amount of phosgene.

Suitable alkali metal salts are lithium, sodium and potassium salts, the sodium and potassium salts being preferably used. The sodium salts are particularly preferred.

Suitable inert solvents are aromatic, aliphatic or cycloaliphatic hydrocarbons, such as benzene, toluene, xylene, hexane and cyclohexane, and also aliphatic and aromatic halogenated hydrocarbons, such as carbon tetrachloride, 1,2-dichloroethane and chlorobenzene. Preferred solvents are toluene and xylene.

N, N-Dialkyl-substituted carboxylic acid amides which can be used are in particular N,Ndialkyl-substituted amides of lower aliphatic carboxylic acids. Suitable N,N-dialkyl-substituted carboxylic acid amides of this type correspond to the formula (II)

in which R1 is hydrogen, methyl, ethyl or propyl, R2 and R3 are identical or different and are each an alkyl group having 1 to 4 carbon atoms, or R2 and R3 together with the adjacent nitrogen atom from the pyrrolidino, piperidino or morpholino group. Among .the N,Ndialkylated carboxylic acid amides embraced by the formula (II), N,N-dimethylformamide is particularly preferred.

The N,N-dialkyl-substituted carboxylic acid amides of the formula II are preferably used in an amount of 1 to 2 per cent by weight, relative to the alkali metal salt of the carboxylic acid.

Within the given temperature range of 30-110"C, in which the process according to the invention can be performed, the temperature range of 50-110"C is preferred. The time necessary to perform the process is about 2-5 hours. In the majority of cases, the reaction of the sodium salt of carboxylic acid with the phosgene is completed in 3-4 hours.

By an essentially stoichiometric amount of phosgene is meant the stoichiometric amount or a slight excess. The amount preferably used according to the invention is 1.0-1.05 mols of phosgene per mol of alkali metal salt of the carboxylic acid.

The process according to the invention is advantageously performed by introducing, with stirring, into a suspension of the sodium salt of carboxylic acid in toluene or xylene, which suspension contains 1 to 2 per cent by weight of an N,N-dialkylated carboxylic acid amide of the formula II, particularly N,Ndimethylformamide, relative to the employed amount of sodium salt of the carboxylic acid, in the course of 2 hours at 50-110"C, 1.0-1.05 mols of phosgene per mol of the sodium salt of carboxylic acid; and completing the reaction by stirring the reaction mixture at 105-1 10"C within one hour. The mixture thus obtained can be used immediately for the further reaction with a suitable N-alkylaniline, for example N-(1 -methoxycarbonylethyl)-2,6dimethylaniline.

Compared with the known process, the process according to the invention has the advantage that a complete reaction of the introduced phosgene is achieved. This renders unnecessary not only the application of a larger excess of phosgene but also the recycling of unreacted phosgene. Furthermore, it is advantageous that there is obtained as waste gas merely carbon dioxide instead of a corrosive mixture of carbon dioxide and hydrogen chloride. The expensive processing of the waste gas is thus also eliminated. In consequence of the avoidance of waste-gas processing and phosgene recycling, the process according to the invention can be performed in comparatively simple multipurpose apparatus.

The preferred use according to the invention of the sodium salt has in the production of methoxyacetyl chloride moreover the advantage that the acid does not have to be firstly liberated from the sodium salt of methoxyacetic acid, which salt is obtained directly on reaction of chloroacetic acid with methanolic sodium hydroxide solution.

The fact that with the use of alkali metal salts of carboxylic acids the reaction with phosgene, in the presence of a catalytic amount of an N,N-dialkylated carboxylic acid amide of the formula (II), at temperatures of up to 11 0 C, occurs quantitatively using merely the essentially stoichiometric amount of phosgene to yield the corresponding acid chloride has to be considered surprising. A quantitative reaction of this kind cannot be obtained with use of the free carboxylic acids.

It is always necessary in this case to use a considerable excess of phosgene.

The process according to the invention is further illustrated by the following Example.

Example 1: After the addition of 1.1 g of dimethylformamide to a suspension of 11 2 g (1.0 mol) of the sodium salt of methoxyacetic acid in 300 9 of toluene, there is introduced at 90-100 C below the surface of the suspension, in the course of 2 hours, 104 g (1.05 mols) of phosgene. When the addition of phosgene has been completed, the reaction mixture is held at 100-1 1 0 C for one hour.

The solution obtained after separation of the sodium chloride contains 105.5 g (97.2% of theory) of methoxyacetyl chloride. The solution can be used directly for further reactions, for example for the reaction with N-(1-methoxycarbonylethyl)-2, 6-dimethylaniiine.

Claims

1. A process for producing carboxylic acid chlorides of the formula I R-CH2-COCI (I) in which R is an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, halogen or the carboxyl group, which process comprises reacting an alkali metal salt of a corresponding carboxylic acid in an inert solvent, in the presence of 0.5 to 10 per cent by weight of an N,N-dialkylsubstituted carboxylic acid amide, at 30-110"C with the essentially stoichiometric amount of phosgene.

2. A process according to Claim 1, wherein the employed alkali metal salt of the carboxylic acid is the lithium, sodium, or potassium salt.

3. A process according to Claim 1 or 2, wherein the inert solvent used is an aromatic, aliphatic or cycloaliphatic hydrocarbon, or an aliphatic or aromatic halogenated hydrocarbon.

4. A process according to any preceding claim, wherein the inert solvent used is benzene, toluene, xylene, hexane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane or chlorobenzene.

5. A process according to any preceding claim, wherein the inert solvent used is toluene or xylene.

6. A process according to any preceding claim, wherein the N, N-dialkyl-substituted carboxylic acid amide used is an N,N-dialkylsubstituted amide of a lower aliphatic carboxylic acid.

7. A process according to any preceding claim, wherein the N,N-dialkyl-substituted carboxylic acid amide used is a compound of the formula II

in which R, is hydrogen, methyl, ethyl or propyl, R2 and R3 are identical or different and are each an alkyl group having 1 to 4 carbon atoms, or R2 and R3 together with the adjacent nitrogen atom form the pyrrolidino-, piperidino or morpholino group.

8. A process according to any preceding claim, wherein the N,N-dialkylated carboxylic acid amide used is N,N-dimethylformamide.

9. A process according to any preceding claim, wherein the reaction of the sodium salt of the carboxylic acid with phosgene is performed within the temperature range of 50-1 10 C.

10. A process according to any preceding claim, wherein 1.0-1.05 mols of phosgene are used per mol of alkali metal salt of the carboxylic acid.

11. A process according to Claim 1.

which process comprises introducing, with stirring, into a suspension of the sodium salt of the carboxylic acid in toluene or xylene, which suspension contains 1 to 2 per cent by weight of N,N-dimethylformamide, relative to the employed amount of sodium salt of the carboxylic acid, in the course of 2 hours at 50-110"C, 1.0-1.05 mols of phosgene per mol of sodium salt of the carboxylic acid; and subsequently maintaining the reaction mixture for 1 hour at 105-110"C.

1 2. A process according to Claim 1, substantially as hereinbefore described, with reference to the foregoing Example.