Thermal Stability of Phosphorus Sulphides

The order of thermal stability of the common varieties is P4S3 P4S7 P4S10 P4S5. 

The tri- and heptasulphides show no appreciable decomposition up to 700°C, but the pentasul-phide decomposes at its melting point to give tri- and heptasulphide (4.92). 

Similarly, the disulphide decomposes according to the reversible reaction (4.93), which can also be used for its preparation. In air, P4S3 ignites at 100°C and P4S10 at 142°C. 

Tetraphosphorus decasulphide, P4S10, decomposes a few degrees above its boiling point, but its decomposition is reversible since the compound can be purified by distillation. If this compound is melted and re-solidified, some decomposition occurs and the product consists of a mass of crystalline P4S10 embedded in a mixture of P4S9 and S. 

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