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Abstract
The results of the kinetic study of the Horner-reaction between m- and p-substituted benzaldehydes and two 2-carbethoxymethyl-substituted phosphinates (III and IV), and corresponding phosphine oxides (V and VI) in ethanolic sodium ethoxide are reported. The kinetics of the reactions are overall third order, first order in aldehyde, ethoxide and phosphinate, or phosphine oxide.
The rates of the reaction are found to be increased by electron-withdrawing substituents in the benzaldehydes, in accordance with a rate-determining addition of the phosphoryl stabilized carbanion to the carbonyl group in the aldehydes. Phosphinate (III) are found to react about 35 times faster than the analogous phosphine oxide (V), in spite of the nearly equal p K-values of the two compounds. This rate effect is discussed in terms of their ability, in the reactions with aldehydes, to form a pentacoordinated intermediate. Within each group of compounds, the rate of the reaction is found to increase with increasing basicity of the phosphoryl stabilized carbanion.