GB768454A - A new phenothiazine complex - Google Patents

Abstract

The invention comprises a complex of equimolecular proportions of phenothiazine and sulphur dioxide. It may be prepared by allowing a solution of phenothiazine in sulphur dioxide to crystallize at a temperature below the transition temperature, i.e. below the temperature of coexistence of the complex, unsolvated phenothiazine, their saturated solution in liquid sulphur dioxide and gaseous sulphur dioxide. This temperature lies between -2 DEG and -8 DEG C. The complex may also be prepared by contacting phenothiazine with sulphur dioxide at temperatures below the transition point preferably in the presence of small quantities of a saturated solution of phenothiazine in liquid sulphur dioxide. Phenothiazine may be regenerated by allowing the sulphur dioxide to evaporate under reduced pressure or elevated temperature. The regenerated phenothiazine may be produced in a very finely-divided state by a mild grinding operation and the grinding may be simplified by mixing the regenerated phenothiazine or the reaction mixture with a surface-active agent. Non-ionic surface-active agents, such as ethylene oxide condensation products of alcohols or phenols, are particularly suitable. In the examples: (a) crude pheno thiazine and a condensation product of sperm oil alcohols and ethylene oxide are dissolved in liquid sulphur dioxide; the sulphur dioxide is evaporated by reducing the pressure above the solution until the temperature drops to - 10 DEG C.; a solid phenothiazine complex with sulphur dioxide crystallizes out; phenothiazine is regenerated from the complex by lowering the pressure and/or raising the temperature to atmospheric and when mixed with methylenebis - naphthalene - 2 - sulphonic acid can be ground to a powder easily dispersible in water; and (b) regenerated phenothiazine is prepared as in (a) in the absence of the ethylene oxide condensate and is then wet milled with the sodium salt of a methylene-bis-naphthalene-2-sulphonic acid to give a suspension which does not settle after 24 hours.