Patent GB-831051-A (GB)
Title: Improvements in or relating to production of polychlorobenzene compounds
IPC: C07C51/08
Filed: 1957-02-28
Abstract: A benzene compound having the formula <FORM:0831051/IV (b)/1> p wherein A is COCl, COOR, CONH2, CONHR, CONR2 or CN, (R being an alkyl group containing 1-5 carbon atoms), and wherein Y and Z may be H or Cl in an ortho or meta position relative to A, is subjected to a nuclear chlorination process so as to produce a compound or mixture of compounds having 3 or 4 chlorine atoms in the nucleus.  The product of the chlorination may be subjected to hydrolysis to convert the group A into a carboxylic acid group. Thus trichlorobenzoic and tetrachlorobenzoic acids including their various isomers and mixtures may be obtained.  Benzoyl chloride may be mono or dichlorinated and thereafter, further chlorinated to obtain the trichloro or tetrachlorobenzoyl chloride.  The o- or m-chlorobenzoyl chloride, or the 2,3- or 2,5-dichloro compound may be subjected to further chlorination.  Specified esters which may be subjected to the chlorination are ethyl and butyl benzoates, and specified amides are benzamide, N-methyl-, N-isopropyl- and N,N-dimethyl-benzamide. Preferably the chlorination is carried out in presence of a nuclear chlorination catalyst such as ferric chloride, iron, aluminium chloride, iodine, boron fluoride, and thallium chloride.  Hydrolysis of the tri- or tetra-chlorobenzoyl chloride may be effected with an alkali metal hydroxide such as sodium hydroxide and the salt which is formed may be acidified, e.g. with sulphuric or hydrochloric acid to form the polychlorobenzoic acid.  Hydrolysis of the polychlorinated benzoic esters may be effected with hydriodic acid, or with an alkali such as sodium hydroxide, followed by acidification.  The alkali treatment also hydrolyses any acid chloride groups which may have been formed from the ester groups during the chlorination.  When benzonitrile is used as starting material and subjected to the nuclear chlorination, the product may be converted to polychlorobenzoic acid by a two-step process comprising partial hydrolysis with aqueous mineral acid to form a polychlorobenzamide and hydrolysis of that compound with nitrous acid or a salt thereof to form a polychlorobenzoic acid.  During the chlorination there is a tendency for chlorine to react with the CN group so as to form polychlorobenzylimino chloride as well as polychlorobenzonitrile. Treatment with strong sulphuric acid converts both these compounds into polychloro benzoic acid.  The polychlorinated benzamides may be hydrolysed to the corresponding acids with strong sulphuric acid.  In examples: (1) chlorine is passed through a mixture of o-chlorobenzoyl chloride and ferric chloride for 2 1/2 hours at 20-50 DEG  C., and then after addition of more ferric chloride the chlorination is continued at 90 DEG  C. to obtain a reaction product from which mixed isomers of tetrachlorobenzoyl chloride are obtained by distillation under reduced pressure, and the acid chloride product is converted into a tetrachlorobenzoic acid containing mainly the 2,3,5,6-tetrachloro isomer with some 2,3,4,5-isomer, together with isomers of trichlorobenzoic acid, by hydrolysis with caustic soda solution and acidification with hydrochloric acid; (2) tetrachlorobenzoic acid containing mainly the 2,3,5,6-tetrachloro isomer is obtained by chlorinating benzoyl chloride in presence of ferric chloride first at 30-50 DEG  C. and then at 90-110 DEG  C., distilling the product under reduced pressure, hydrolysing with caustic soda solution, and acidifying; (3) polychlorobenzoic acid is obtained by chlorinating benzonitrile in presence of ferric chloride at 25-100 DEG  C. to obtain a product consisting of a mixture of tri- and tetrachloro isomers in which the side chain CN has been partially chlorinated and then hydrolysing it by means of sulphuric acid; (4) ethyl benzoate is chlorinated to form a product, containing mainly the tri-chloro compound, which is subjected to hydrolysis to form a polychlorobenzoic acid; (5) N,N-dimethyl-benzamide is chlorinated at 50 DEG  C. in presence of ferric chloride and the product is fractionated to separate the dichlorinated and tetrachlorinated compounds from the trichloro-N,N-dimethylbenzamide which may be converted to trichloro benzoic acid by hydrolysis with sulphuric acid.  The mixed isomers of tetrachlorobenzoic acid containing the 2,3,5,6-isomer, and the trichlorobenzoic acid containing the 2,3,6-isomer, and mixtures of these, may be used as insecticides. Reference has been directed by the Comptroller to Specification 785,989.