Abstract
A range of hemiacetal esters were synthesized by the reaction between carboxylic acids and butyl vinyl ether using n-dodecyl dihydrogen phosphate as catalyst. Specifically, nonanoic, propionic, acrylic, sebacic, and fumaric acids were used as substrates to prepare the corresponding hemiacetal esters. These compounds were used as model molecules to demonstrate the ability of hemiacetal ester functional groups to undergo the exchange reaction in the presence of weak carboxylic acids without any catalyst. Kinetics studies examined the eect of the carboxylic acid concentration on the exchange rate, and revealed that the exchange reaction proceeds through an associative mechanism.
Highlights
Hemiacetal esters, called acylated hemiacetals, possess a very interesting functional group, which has yet to be fully studied
The ability of n-dodecyl dihydrogen phosphate to catalyze the reaction of carboxylic acids, including diacids, with butyl vinyl ether to form hemiacetal esters, and without undesirable cationic vinyl ether polymerization, was demonstrated
This synthesis proceeded to high conversion in 6–24 h at ambient temperature for a selection of mono and dicarboxylic acids
Summary
Hemiacetal esters, called acylated hemiacetals, (see Scheme 1), possess a very interesting functional group, which has yet to be fully studied It can be synthesized by a number of methods, such as through the addition of a carboxylic acid onto a vinyl ether [1], through Baeyer–Villiger oxidation of a cyclic ketone bearing a vicinal methoxy group [2], or through reaction of a ketone or acetaldehyde with β-hydroxy acids [3]. In a first publication [4], they showed that hemiacetals formed from carboxylic acids bearing unsaturated groups have a lower dissociation temperature than their saturated aliphatic analogs due to inductive and mesomeric electronic effects These authors showed that cyclic aliphatic acids led to even higher dissociation temperature. In a second publication [5], they demonstrated that vinyl ethers with higher inductive donor effects (such as tert-butyl vinyl ether compared to cyclohexyl vinyl ether) led to lower dissociation temperature
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