Oxohalides and thiohalides of phosphorus

The chlorination of phosphonic and phosphinic acids and esters are of considerable importance. PCI5 can also act as a Lewis acid to give 6-coordinate P complexes, e.g. pyPClf, and pyz-PCI5, where py = C5H5N (pyridine) and pyz = cyclo-1, 4-C4H4N2 (pyrazine).  

Paralleling the various phosphorus trihalides are numerous pseudohalides and mixed pseudohalide-halides of which the various isocyanates and isothiocyanates are perhaps the best known. Most are volatile liquids, e.g. 

The corresponding phosphoryl and thiophos-phoryl pseudohalides are also known, i.e. P0(NC0)3, PS(NC0)3, etc. Preparations are by standard procedures such as those on the diagram for PCI3 (p. 497). As indicated there, P(CN)3 has also been made it is a highly reactive white crystalline solid mp 203° which reacts violently with water to give mainly phosphorous acid and HCN. 

The propensity of phosphorus(III) compounds to oxidize to phosphorus(V) by formation of an additional P=0 bond is well illustrated by the 

Most of the phosphoryl and thiophosphoryl compounds are colourless gases or volatile liquids though PSBt3 forms yellow crystals, mp 37.8°, POI3 is dark violet, mp 53°, and PSI3 is red-brown, mp 48°. All are monomeric tetrahedral (C y) or pseudotetrahedral. Some physical properties are in Table 12.4. The P-O interatomic 

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