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Crawford, John (1965) Quantitative studies of the transesterification of some phosphorus esters. Doctoral thesis, Sir John Cass College.
The transesterification of phosphorus esters catalysed by alkoxide ion has been studied. Under suitable conditions all the alkoxy groups of the ester can be displaced successively. The distribution of products suggest that the net displacement is athermal. The alternative nucleophilic attack at carbon is noticeably less in phosphonate and phosphinate esters than it is in phosphate esters.
The initial transesterification reaction of a homomorphic series of pentavalent phosphorus esters has been studied in alcohol and in the less polar media iso-octane/alcohol. The kinetic results are strongly influenced by medium effects which have been ascribed largely to electrostatic catalysis. Pseudo first order rate constants for the initial transesterification step show the order of reactivity to be phosphate phosphinate. phosphonate per ethoxy group. This cannot be interpreted in terms of electronic influences within the ester molecule.
A measure of the relative excess free energy of solution of phosphorus esters in a solvent containing polar groups has been obtained from G.L.C. retention data. The lower electrophilic reactivity of the phosphonate ester is paralleled by a lower excess free energy of solution.
Analyses of the phosphorus esters were by quantitative G.L.C. Precision limits were of the order +- 2% or better at high concentrations of ester, or +- 10% or better at low concentrations of ester in solvent.
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