Quasi-phosphonium salts

Phosphonium (and quasi-phosphonium) salts generate phosphines under electrolytic reduction (Table 7). Mercury, lead, platinum, tin, copper and aluminium172 cathodes were tried, mercury being the most often used173. Product dependence on cathode material, current, density and solvent has been observed174. In the case of unsymmetrical... 

Aminophosphines, phosphinites and phosphonites from quasi-phosphonium salts with alkyl halides in normal 5 n reactions. The aminophosphonium salts and the salts derived from aryl phosphinites and diaryl phosphonites are stable, but the majority of the quasi-phosphonium salts which contain alkoxy groups are dealkylated during the reaction with the alkyl halide (the Arbuzov reaction, see below). Thio analogues of phosphinites and... 

The new trinorborn-l-yl phosphite (7) has been prepared and shown to give quasi-phosphonium salts which are even more stable than those derived from trineopentyl phosphite thus the salt with methyl iodide had a half-life of more than 100 h in deuterochloroform at 150 C, compared to less than 2 h at 33 C for the neopentyl analogue. Although phenacyl chloride gave mainly the Arbuzov intermediate (8), with p-nitrophenacyl chloride a stable Perkow intermediate (9) could be isolated and its X-ray crystal structure studied. Trifluoroiodomethane with tris(dialkylamino)phosphines gave the normal trifluoromethylphosphonium salts (10) in the absence... 

The thermal stability of phosphonium salts (except quasi-phosphonium species) indicates following stability order for those containing an alkenyl substituent157 ... 

The potentials in Table 2 are referred to Ag/AgI in a medium of dmf + Bu4NI. While both the peaks are reversible or quasi-reversible in the cyclic voltammetric scans, the electrochemical reduction is carried out at the first peak, where an anion is generated. Dianion formation occurs at a more negative potential but is at a lower potential than the phosphonium salt. On controlling the potential of the electrode at the first reduction of the probase and carrying it to 2 F mol" the ylide is produced. 

Organo-phosphonium salts can be regarded as derived from the parent tetrahedral phosphonium cation, PH J and can be represented as (6.359), where R, R, etc. can be H, halogen, alkyl, aryl, acyl alkoxy, amino, etc., and X can be halogen or other anionic group. When four different groups are attached to the P atom, enantiomorphic forms are possible (Chapter 14.2). The term quasi-phospho-nium is sometimes used to describe species in which one or more of the atoms directly bonded to phosphorus is neither C or H. 

From tertiary phosphine sulphides and alkyl halides, quasi phosphonium compounds are formed (9.411). If trialkyl phosphites are reacted with sulphenyl chlorides in the presence of SbCls, thiophosphonium salts can be isolated (9.489). Reaction (9.490) occurs spontaneously and goes to completion in a few days. 

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