Acetal Metathesis: Mechanistic Insight

Published as part of the Cluster Metathesis beyond Olefins

Abstract

The origins and recent applications of acetal metathesis are discussed in the context of synthesizing polyacetals via acetal metathesis polymerization (AMP). A kinetic study of the acid-catalyzed acetal metathesis reaction suggests the rate = k[H⁺][acetal]², with MeOCH₂OMe and EtOCH₂OEt interchanging to yield MeOCH₂OEt, achieving the statistical 1:2:1 equilibrium distribution in 4 hours at 80 °C and in 1 hour at 90 °C. Upon heating 1,10-decanediol and diethoxymethane, polydecylene acetal is formed with sequential distillation of ethanol, followed by diethoxymethane. A full mechanism for this polymerization is proposed, which begins with a transacetalization sequence to convert the diol into a bisacetal, followed by acetal metathesis to yield a high-molecular-weight polymer.

Key words

acetal - metathesis - transacetalization - polyacetal - acid catalysis - kinetic study - nucleophilicity

• References and Notes

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• 28 Protocol for the Bisacetal SynthesisA 1 liter round-bottom flask was charged with 17.43 g (0.100 mol, 1 equiv) of 1,10-decanediol, 208.30 g (2.00 mol, 20 equiv) of diethoxymethane, 0.190 g (1 mol%) of para-toluenesulfonic acid, and 100 mL of toluene. Ethanol was exhaustively removed via distillation over 24 h, followed by refluxing for 48 h. Workup, as described in the Supporting Information, afforded the bisacetal as a colorless oil in 72% yield (21.03 g).