Etude du mécanisme de la réaction des dérivés phosphométhyléniques et des phosphobétaïnes avec le benzaldéhyde

In the reaction between triphenyl phosphomethylene and benzaldehyde, the decomposition of the intermediate betaine is very slow compared with its rate of formation, and at 40° in chloroform, the dissociation of the betaine into the initial reactants can be followed. On the other hand, the first stage in the reaction between betaines of the type, Ph 3 PCHCOR, and benzaldehyde is the slow one. The rate of reaction is determined by the p Ka of the corresponding phosphonium salt according to the B RÖNSTED catalysis law.