Mechanism Arbusov reaction

The mechanism of the Arbusov reaction has been the subject of some study. Intermediates (4), isolated at low temperatures from the reaction of phosphonites with alkyl halides, show n.m.r. chemical shifts in the region of — 95 p.p.m. in a wide variety of solvents. ... 

A kinetic study of the previously reported substitution of aromatic nitro groups by tervalent phosphorus has established an aromatic 5n2 mechanism. Similarities in values of activation energies, and in relative reactivities of phosphite and phosphonite esters, between this displacement and the Arbusov reaction suggest a related mechanism (31), while the lack of reactivity of p-dinitrobenzene is attributed to the need for intramolecular solvation (32). The exclusive formation of ethyl nitrite, rather than other isomers, is confirmed from the decomposition of triethoxy-(ethyl)phosphonium fluoroborate (33) in the presence of silver nitrite. A mechanism involving quinquevalent phosphorus (34) still seems applicable, particularly in view of the recent mechanistic work on the Arbusov reaction. ... 

The mechanism of the reaction of tertiary phosphites with halogeno-acetylenes has been investigated by two groups of workers. - Initial attack of phosphite could be on carbon to give the anion (78), which can eliminate halide, or on halogen to give the ion pair (79) which leads to the same intermediate (80). In both cases an Arbusov reaction would give the isolated product (81). 

Bodkin, C.L. and Simpson, P., The role of pentaco-ordinate species in the mechanism of the Arbusov reaction, /. Chem. Soc., Perkin II, 2049, 1972. 

In the area of trivalent phosphorus acid chemistry some very unusual reactions have been reported from combinations of 4-dimethylamino-pyridine (DMAP) with phosphorus trichloride. In one case a phosphide and free chlorine are claimed to be formed The extreme nucleofugicity of a tervalent phosphorus atom bearing two DMAP groups also stimulates an unprecedented Arbusov reaction of a tervalent derivative. Another surprise is that, although the reaction is certainly acid-catalysed, the mechanism of substitution at phosphoramidites does not involve either P- or N-protonated species. A final surprise in this area is the preparation, by Russian chemists, of some tervalent phosphorus compounds which apparently contain P-OH groups. 

It is known that triethyl phosphite reacts with carbon tetrachloride to give ethyl chloride and diethyl (trichloroethyl)phosphonate. Ionic and radical mechanisms have been suggested to account for this remarkable reaction. According to the most reasonable, fundamental one (61), the reaction is initiated by a nucleophilic attack on chlorine (not an Arbusov reaction) followed by formation of the phosphonium salt [71] (Atkinson et al., 1969). 

The reaction of orthophosphorous acid, H3PO8, with vanadium(v) in the presence of silver(i) yields a rate law that is zero-order with respect to the concentration of vanadium(v). This is not thought to involve a rate-determining formation of the tautomer P(OH)3 from HP(0)(0H)2, but instead a mechanism involving the formation of complexes between H3PO3 and vanadium(v) is favoured. Phosphite esters are involved in the Arbusov reaction, and there has been work on the mechanism of the reactions between trimethyl phosphite and a-halogenoacetophenones. 

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