GB898307A - A method of preparing disubstituted chlorinated benzene derivatives - Google Patents

Abstract

Para-chlorinated benzene derivatives, in particular, p-dichlorobenzene and p-chlorotoluene, are prepared by passing gaseous chlorine into-the compound-to-be-chlorinated in the liquid state, the chlorination being carried out in the presence of a chlorination catalyst dissolved or dispersed in the liquid and in the presence of a "para orientation catalyst", such as a mixture of sulphuric acid, a sulphonic acid and a small proportion of water, which is capable of constituting a separate phase. After chlorination the mixture is allowed to separate into two liquid layers, and the appropriate layer is worked up to separate the desired para-chlorinated derivative from the isomers and from higher chlorinated products. Suitable chlorination-catalysts are: antimony sulphide, chloride or chloro-sulphide, and ferric acid. In an example, antimony trichloride and sulphur are dissolved in dry benzene; and chlorine is passed into the solution, with stirring, for 45 minutes. A mixture of sulphuric acid, benzene sulphonic acid and water is then added; and the stirring and addition of chlorine are continued, while the temperature is maintained at about 20 DEG C. The temperature is then allowed to rise to 50 DEG C. to prevent p-dichlorobenzene from crystallizing out: and the two liquid layers are decanted. The chlorobenzene layer is washed with dilute hydrochloric acid, neutralized, dried and distilled. The product contains over 90% dichlorobenzene in which the para : ortho ratio is 5 to 6.5. The product also contains 5% to 10% of monochlorobenzene, and only 0.2% of higher chlorinated derivatives. Another example relates to the production of ortho- and para-chlorotoluene from toluene. In other examples, toluene sulphonic acid, p-chlorobenzene sulphonic acid, and a mixture of benzene and dodecylbenzene sulphonic acids, are used, together with sulphuric acid and water, as "orientation catalysts".