Mixed Phosphorus Thiotrihalides

Mixed Phosphorus Thiotrihalides, PSClBr₂ and PSCl₂Br, have been prepared by passing a mixture of PSCl₃ and HBr over pumice at 400° to 500° C., the products being separated by fractional distillation. Amongst these is also the starting material PSCl₃, which is formed in a sealed tube by the reaction:—

2PSCl₂Br = PSClBr₂ + PSCl₃

Thioiodides may be obtained by several methods:—

1. By the interaction of the elements, in their correct proportions, in carbon disulphide.
By the action of hydrogen sulphide on heated iodides of phosphorus, thus

2P₂I₄ + 3H₂S = P₄S₃I₂ + 6HI
2PI₃ + 2H₂S = P₂S₂I₂ + 4HI

These compounds are soluble in carbon disulphide, from which they may be obtained as orange or yellow crystals. They are only slightly soluble in other organic solvents such as benzene, chloroform, etc. They can be burnt in air, giving oxides of phosphorus, sulphur and iodine. They are decomposed by warm water or moist air, giving first phosphoric and hydriodic acids, then phosphoric acid and hydrogen sulphide.