| 摘要 |
The process of the parent Specification for the production of cresol by vapour phase hydrogenation of chlorocresol is carried out in the presence of a chromite catalyst consisting of an oxide of chromium associated with at least one of the following metals or their oxides: zinc, cadmium, iron, cobalt, nickel, manganese, aluminium, barium, calcium, magnesium, copper or silver. A suitable temperature is 250-550 DEG C., preferably 300-400 DEG C., the molar ratio of hydrogen to chloro-cresol being up to 5:1 for a good yield of cresol. The catalyst is preferably jacketed with a heat exchange medium to prevent any local rise in temperature. The process is particularly applicable to the production of o-cresol from 6-chloro-o-cresol, an example of this being given using a zinc-iron-chromium oxide catalyst. The reaction may form part of a cyclic process for the production of 2-methyl-4-chlorophenoxyacetic acid as in the parent Specification.ALSO:Catalysts for the hydrogenation of chloro-cresol to cresol comprise an oxide of chromium in association with at least one of the following metals or their oxides:-zinc, cadmium, iron, cobalt, nickel, manganese, aluminium, barium, calcium, magnesium, copper or silver. They may be made by precipitation of the hydrated oxides from solutions of their salts, followed by drying and calcining, or by the process of Specification 301,806 [Class 1(1)]. In the example a solution of zinc nitrate, ferric nitrate and chromium trioxide is precipitated with ammonia and the hydrated oxides dried, calcined, ground and pelleted, giving a product containing the metals in proportion 4:1:5.
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