Kinetics of the condensation of acetaldehyde with formaldehyde in aqueous alkaline solutions at 5–20°

Abstract

The kinetics of the early stages of the condensation of acetaldehyde with formaldehyde to form β-hydroxypropionaldehyde and bishydroxymethylacetaldehyde (precursors to pentaerythritol) have been investigated in aqueous alkaline solutions at 5–20°. The rate of monohydroxymethylation of acetaldehyde is expressed as v=k₁k₂[CH₃CHO][CH₂O]·[base]/(k_–1+k₂[CH₂O]). β-Hydroxypropionaldehyde, the product of monohydroxymethylation of acetaldehyde, is prepared in good yield from acetaldehyde and formaldehyde. The rate of hydroxymethylation of β-hydroxypropionaldehyde fits the rate equation analogous to that for the monohydroxymethylation of acetaldehyde. The results show that the rate of hydroxymethylation for one hydrogen atom of β-hydroxypropionaldehyde is four times that of monohydroxymethylation of acetaldehyde. The apparent energy and entropy of activation are 22·1 kcal. mole^–1 and 14 e.u. for hydroxymethylation of acetaldehyde and 22·9 kcal. mole^–1 and 17 e.u. for hydroxymethylation of β-hydroxypropionaldehyde. A probable mechanism involving an attack of conjugate base of acetaldehyde on free formaldehyde is suggested and discussed.