Quasiphosphonium intermediates. Part 3. Preparation, structure, and reactivity of alkoxyphosphonium halides in the reactions of neopentyl diphenylphosphinite, dineopentyl phenylphosphonite, and trineopentyl phosphite with halogenomethanes and the effect of phenoxy-substituents on the mechanism of alkyl–oxygen fission in Michaelis–Arbuzov reactions
- 1 January 1983
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 9,p. 1363-1368
- https://doi.org/10.1039/p29830001363
Abstract
The reactions of neopentyl diphenylphosphinite with chloro-, bromo-, or iodo-methane and of dineopentyl phenylphosphonite with bromo- or iodo-methane yield crystalline alkoxyphosphonium halides. In deuteriochloroform these intermediates decompose by a first-order process which involves rate-determining collapse of the phosphonium halide ion-pair with SN2-type fission of the alkyl–oxygen bond. Rates for chloride, bromide, and iodide are similar. In a more ionising medium (deuterioacetonitrile) dissociation leads to stabilisation of the intermediates and to deviation from first-order decomposition. Previously determined X-ray diffraction data for the bromides, together with relative rates of decomposition in deuteriochloroform for intermediates in the series Phn(RO)3–n[graphic omitted]MeX–(n= 0, 1, or 2) suggest that the stability and reactivity of alkoxyphosphonium intermediates are determined largely by inductive rather than mesomeric effects of ligands. The presence of phenoxy-substituents on phosphorus may cause a tendency towards SN1-type fission of the alkyl–oxygen bond in certain circumstances.Keywords
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