C. Stelt, W. Nauta
Sep 2, 2010
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Journal
Recueil des Travaux Chimiques des Pays-Bas
Abstract
Chlorination of 4-acetylaminobenzoic acid (III) afforded 4-acetylamino-3,5-dichlorobenzoic acid (IV, m.p. 237-238°), which could be saponified easily to 4-amino-3,5-dichlorobenzoic acid (II, m.p. 290°). Direct chlorination of 4-aminobenzoic acid (I) in a mixture of glacial acetic acid and hydrochloric acid afforded 3,4,4,6,6-pentachloro-1-cyclohexen-5-one-2-carboxylic acid (V, m.p. 178-180°), a compound already obtained by Zincke by the chlorination of 4-hydroxybenzoic acid (VI). Compounds with a higher content of chlorine could be prepared by the chlorination of the methyl ester of I (VIII). The reaction carried out in a neutral medium led to the nitrogen containing compound IX with m.p. 151-153° and gross formula C8H5NO2Cl8 to which the structure of a methyl 1,2,3,3,5,5,6-heptachloro-4-chloriminocyclohexane-1-carboxylate was attributed. Reduction with stannous chloride converted IX into methyl 4-amino-3,5-dichlorobenzoate (X), which can be used as a starting product for IX. Chlorination of VIII in a mixture of glacial acetic acid and hydrochloric acid yielded a compound XI with m.p. 129-131° and gross formula C8H5O3Cl7 as the main reaction product to which the structure of a methyl 1,2,3,3,5,5,6-heptachlorocyclohexan-4-one-1-carboxylate has been attributed. Acid hydrolysis converted IX into XI. From the same reaction mixture two other stereo-isomers of XI also were isolated, be it in minor quantities (XII m.p. 140–142°, XIII m.p. 213-215°). The stereoisomerism of the three compounds is caused by the different spatial arrangement of the chlorine atoms attached to carbon atoms 1, 2 and 6. Reduction converted the three isomers into methyl 3,5-dichloro-4-hydroxybenzoate (XIV). Chlorination of the methyl esters of VI and XIV also afforded amounts of XI. A fourth chlorination product could be isolated from the reaction mixture of VIII, viz. a compound with m.p. 199-200° and gross formula C8H6O4Cl6 (XVI). Reduction with stannous chloride converted it into a compound XVII with m.p. 121-122° and gross formula C8H8O4Cl2. Both compounds contain an extra hydroxyl group. Lack of material prevented further establishment of the structure. The infrared spectra of a number of polychloro-compounds are given.