Mixed Phosphono and Phosphino Acids

A convenient method of producing alkyl hydrogen phosphinothionates is by heating a phosphinic ester with P4S10, or by reacting H2S with a phosphonamidite ester or a phosphonous ester. Further treatment of the new ester with sulphuryl chloride replaces the hydrogen with chlorine. 

Thermal isomerisation from the thiono form occnrs with some esters (9.473), and the thiolo form can also be obtained from phosphinous salts and alkyl esters (9.474). 

As in the case of inorganic phosphorothioate ions and salts of the type (RO)2POS M+, there arise three possible formnlae for salts of phosphinothioic acid R2POS M. It appears from spectroscopic evidence that thiono, thiolo or mesomeric structures may exist in different salts, as weU as arrangements in which the metal atom is covalently bound to either the O or the S atom. The electronegativity of the metal atom and steric effects from the group R are liable to influence this situation. 

In crystalline (Ph2POS)3Sb, only O atoms are coordinated to metal atoms, but in the cyclohexane complex Nd[(C6H )2POS]3 H20 2, both O and S atoms from some of the ligands are involved in coordination [15,16]. 

Under anhydrous conditions, phosphinothioUc esters are converted by chlorine to phosphinyl halides, bnt under aqueous conditions, phosphinic acids are obtained directly. 

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