Benzylic quaternary phosphonium salts

The benzylation of a wide variety of aHphatic, aromatic, and heterocycHc amines has been reported. Benzyl chloride is converted into mono-, di-, and tribenzyl amines by reaction with ammonia. Benzylaniline [103-32-2] results from the reaction of benzyl chloride with aniline. Reaction with tertiary amines yields quaternary ammonium salts with trialkylpbospbines, quaternary phosphonium salts and with sulfides, sulfonium salts are formed. 

The quaternary phosphonium salt is prepared by refluxing for 12 hours or longer a mixture of 4.5 g of benzyl chloride and 13 g of triphenylphosphine in 70 ml of xylene. On cooling to approx. 60°, colorless crystals of benzyltriphenylphosphonium chloride can be filtered off, washed with xylene (approx. 50 ml) and dried. The yield is virtually quantitative, mp 310-311°. 

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). 

The results of the pulse radiolysis in aqueous solution of substituted phosphonium ions have been investigated38 in addition to those of the electrode reduction of benzyl triphenyl-phosphonium ion39 and quaternary phosphonium salts with hydrated electrons40-42. The radiolysis of methyltriphenylphosphonium, dimethyldiphosphonium and trimethyl-phenylphosphonium ions in neutral aqueous solutions leads to phosphoranyl radicals... 

Synthesis. Polymers containing the vinyl-benzyl phosphonium unit can be made by either direct synthesis of the monomers and subsequent polymerization or phosphonation of chloromethyl styrene containing polymers. The latter is preferred due to the difficulty of obtaining the vinyl benzyl phosphonium monomer in good yield and purity without spontaneous polymerization. In either case, synthesis of elastomers containing quaternary phosphonium salts have not been reported to date. 

In the reactions characterized in the general sense above, phenyl and benzyl were the organic residues bound to phosphorus. It is not clear which of these groups is removed in the LAH dealkylation step. It should also be noted that as tetraquaternary phosphonium salts, these species do not qualify as crown analogs in the strictest sense because of the absence of lone pair electrons on phosphorus. Furthermore, the quaternary phosphorus can resist oxidation much better than secondary or tertiary phospho-... 

Phase-transfer catalysts are used to facilitate reactions between reagents that are in two different phases (e.g., 1-bromooctane in toluene with aqueous potassium iodide to form 1-iodooctane). They are usually quaternary ammonium or phosphonium salts or crown ethers. They can complicate the workup of the reaction and may be difficult to recover for reuse. When they are insoluble polymeric ones, workup and recycle can be done by simple filtration.192 The process is called triphase catalysis. In favorable cases, their activity can be comparable with that of their lower molecular weight analogues. They are often based on cross-linked polystyrene, for which spacers between the aromatic ring and the quaternary onium salt can increase activity two- to fourfold. Copolymerization of 4-vinylben-zyl chloride with styrene or N, N- d i m e Ihy I a c ry I a m i d e, followed by treatment with tri-/ -butylphosphine produced catalysts that were used in the reaction of benzyl chloride with solid potassium acetate (5.43).193... 

Mixed tert. amines and phosphines as well as mixed quaternary ammonium and phosphonium salts can be conveniently prepared by successive alkylations and reductions because of the varying ease with which the groups are removed. The benzyl group is most easily removed. F. e., also with a polished Pb-cathode, s. L. Horner and A. Mentrup, A. 646, 49, 65 (1961) optically active phosphines from phosphonium salts s. Tetrah. Let. 1961, 161 optically active arsines cf. Tetrah. Let. 1962, 203. 

In a recent modification of the oxone-type oxidation, the quaternary salt benzyl-triphenyl phosphonium peroxymonosulfate PhCH2Ph3P" HS05 was employed (Eq. (8.4)). No overoxidation to sulfone was detected, according to the authors. 

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