Phosphonium thiolate

Acylation of alkylidenetriphenylphosphoranes by thiocarboxylic 5-ethyl esters 456 The reactions are carried out in a Schlenk tube, as above. To a boiling solution (which need not be filtered) of a salt-free alkylidenephosphorane (0.022 mole) in anhydrous toluene is added an 5-ethyl thiocarboxylate (0.02 mole), and the mixture is boiled for 18 h. The phosphonium thiolate, that is initially precipitated as an oil, gradually redissolves. If an unfiltered ylide solution was used, the reaction solution must be filtered hot at this stage to remove sodium... 

Ahnliche Ergebnisse werden ausgehend von Arensulfenylchloriden und Triphenylphosphan erzielt, wobei die intermediar auftretenden Acyloxy-triphenyl-phosphonium-thiolate zu S-Estern und Triphenylphosphanoxid abreagieren65 ... 

Benzylic quaternary phosphonium and ammonium salts are dealky-lated by mild heating and/or nucleophilic anions, particularly iodide (9) and thiolate (10), but also hydroxide (11). Most N-benzyl-pyridinium or quaternary aryl ammonium compounds are particularly susceptible (12). Decompositions of this sort have seriously limited the usefulness of solid phase-transfer catalysts derived from (chloromethyl)polystyrene (13, 14). 

Mit Thiolen als Nukleophilen wird sogar direkt die Hydroxy-Gruppe bzw. die Methoxy-Gruppe in Hydroxymethyl-1163,1164 bzw. Methoxymethyl-imidazolen1165 ausgetauscht [(Alkylthio-methyl)-imidazole], Der Phosphonium-Rest der (Triphenylphosphoniono-methyl)-Gruppe kann durch Thiolate oder Alkanolate substituiert werden1166. 

The formation of a P=0 bond is the driving force in the reaction of thioalkoxy-phosphonium salts, having non-nucleophilic counter anions, with carboxylates or alcoholates, thereby cirumventing the inconvenience of using thiols or thiolates in the synthesis of thiol esters or sulphides the yields are fair to excellent433,781 (reaction 235). 

The suggested mechanism involves an attack of the nucleophilic phosphorus reagent on the anomeric oxygen to afford an anomeric phosphonium ion and a thiolate counterion, which then attacks in a Sn2 reaction the anomeric position to give the thioglycoside and triafkyl phosphate or trialkylphosphine oxide. 

Since the phosphonium and pentacovalent phosphorus are hard acceptors, it is not surprising that the secondary phosphine oxides are rapidly oxidized by alkali (115) at room temperature. On the other hand, sodium benzenethiolate effects the oxidative thiolation only very slowly at 70°. 

The method can be used preparatively. Other examples include the selective demethylation of triethylmethylammoniiun chloride with sodium benzenethiolate. A somewhat analogous reaction is observed in the reaction of alkoxytri(dimethylamine)phosphonium chloride (33) with thiolates forming a phosphine oxide and sulphide. ... 

The initial attack of PR3 on the disulphide bond is the rate-limiting step. Hydrolysis of the phosphonium salt is rapid and irreversible. The rate of reaction is enhanced by either dilute acid or dilute base at high pH hydrolysis of the phosphoium salt is rapid but at low pH the thiolate anion becomes protonated, thus suppressing the reverse reaction in the rate-limiting step. 

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