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Tetraphosphorus Heptasulphide, P4S7

Tetraphosphorus Heptasulphide or Phosphorus Tetritaheptasulphide, P4S7, was first obtained during the distillation of P4S6 in a vacuum, and was separated by heating under pressure with carbon disulphide in which, as distinguished from P4S3, it was only sparingly soluble. In the methods of preparation which have been described the phosphorus should be in slight excess over that required for P4S7. The ingredients may be heated together in a sealed tube and the product recrystallised from carbon disulphide in pale yellow crystals.

The melting-point was 310° C. and the boiling-point 523° C. A maximum melting-point corresponding to P4S7 was found on the thermal diagram of P4S6 and P4S10. The solubility in carbon disulphide was 0.0286 gram per 100 grams solvent at 17° C.

A compound having the empirical formula PS2 was said to be formed by heating together the elements in the proportions theoretically required, or by distillation or heating with carbon disulphide in a sealed tube at 210° C. Other methods include the exposure to sunlight of P4S3 (1 part) with sulphur (2 parts) dissolved in carbon disulphide, or a solution of phosphorus and sulphur with a little iodine in carbon disulphide. Pale yellow transparent needles of the compound are deposited.

The molecular weight deduced from the vapour density was P4S8 or P3S6. The melting-point was 248° to 249° C. or 290° to 298° C. The boiling-point is given as 516° to 519° C.

The chemical properties are similar to those of the other sulphides of phosphorus, but the compound is less stable, and easily decomposes, giving P4S3 with separation of sulphur.

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