Phosphinothioic halides

When diphenylphosphinodithioic acid is heated at 170 °C for an extended period, a loss of H2S occurs with the formation of the anhydrosulphide. Related compounds are also easily prepared by the reactions between salts of dithioic acids (these are more reactive than salts of phosphinic acids) and phosphinothioic halides obviously, this procedure is capable, in principle, of providing unsymmetrical anhydrosulphides (equation 46), but these tend to disproportionate into a mixture of symmetrical compounds ... 

Phosphinodithioic acids, R2P(S)SH, (9.433a) can be made in up to 90% yields by the action of secondary phosphines on sulphur in dilnte ammonia. The ammonium salts so obtained can then be converted into the corresponding acids with HCl (9.434). Phosphinodithioic adds can in some instances be obtained from phosphinothioic halides and sodium hydrosulphide (9.435). They may also be made by a Friedel-Crafts-type reaction with benzene (9.436). Metal salts may be produced directly by the action of sulphur and alkali sulphide, or sulphur and metal, on diphosphine disulphides (Figure 9.23). 

A study has been made of the kinetics of epoxidation of allylphosphinates and of the addition of C-benzoyl-iV-phenylnitrone to vinyl- and allyl-phosphonates. Boron trifluoride stabilizes phosphorus(v) thiocyanates, preventing their isomerization to isothiocyanates. Cleavage of the phosphinothioic methanesulphonic anhydride (97) with aluminium halides yields the phosphinic halide with retained chirality. ... 

The (5 p)-phosphinothioate (287) can be separated in pure, crystalline, form from the oily racemic mixture the addition to it of selenium yields the phosphonoselenothioic ester, oxidation of which, by iodine in water, affords the (i p/ p)-diselenide (288). ° Reactions between (carbon tetrahalides CX4 (X = Cl or Br)-Et3N yield the thiophosphonic halides (289), evidently with retention of configuration at phosphorus, since the anilide derived from them has a configuration known to be (S p). ... 

The alkylation, with the more reactive of alkyl halides, of the sodium salts of monoes-terified phosphonothioic acids (equation 22) (see also Scheme 11) or of the disodium salts 107 results in preferential S-alkylation, and the same situation obtains for the salts of phosphinothioic acid " methylation can also be carried out with dimethyl sulphate. Alkylations may also be performed under phase-transfer conditions. From both practical and theoretical perspectives, the subject is more complex, since the course of alkylation reactions depends on the nature of the alkylating agent, on the polarity of solvent and whether this is protic or non-protic and on the concentrations of reactants a study of these features has been the subject of two reports In non-polar or weakly polar aprotic media, or in EtOH, alkylation occurs almost exclusively on sulphur, but in dipolar aprotic solvents, O-alkylation also takes place. The relative yields of sulphur- and oxygen-substituted derivatives, [Qs/Qol depends, for a given solvent, on the nature of substituents on phosphorus, i.e. essentially, whether the substrate is a thiophosphoric, thiophosphonic or thiophosphinic acid. With alkyl tosylates as alkylating agents at 0.02 m in hmpt, the alkylation of sodium 0,0-dialkyl or diphenyl phosphorothioates results in 100% overall conversions with [Qs/Qo] 5 the overall yields for sodium diphenyl- or diisopropyl-phosphinothioates are lower (50-100%) with [Qs/Qo] 1 ... 

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