Preparation of Ketals. A Reaction Mechanism

Abstract

The use of orthoformates in the preparation of ketals is a standard operating procedure. Relatively few of the many preparations have employed orthoformates other than triethyl orthoformate. Post (1) has stated the yields decrease with an increase in size of the trialkyl part of the molecule. Dykstra (2) claimed good yields with the tripropyl and tributyl orthoformates although exact values were not given and the experimental details were not reported.

Reactions of Ortho Esters Which Result in Carbon-Oxygen and Carbon-Halogen Bond Formation

“…The diisopropyl acetal of acrolein and the di-rec-butyl acetal of acetaldehyde have been prepared in moderate yields by the orthoformate method, but the only ketal of a secondary alcohol reported in the literature is acetone dicyclohexyl ketal. Acetone and tri-sec-butyl orthoformate do not yield a ketal in isolable amounts (190).…”

“…Butyl cyclohexenyl ether was prepared in this manner from cyclohexanone, butanol, and triethyl orthoformate (190).…”

“…Discussions of the mechanism of reactions of carbonyl compounds with trialkyl orthoformates have been largely speculative (2,190,225,227,239). The reversibility of the reaction was established by Adkins and co-workers (59,220), who found that in the case of diethyl ketals, equilibrium mixtures contained the same amounts of ethyl formate whether equilibrium was approached from the ketone-ethyl orthoformate side or from the ketal-ethyl formate side.…”

“…The reversibility of the reaction was established by Adkins and co-workers (59,220), who found that in the case of diethyl ketals, equilibrium mixtures contained the same amounts of ethyl formate whether equilibrium was approached from the ketone-ethyl orthoformate side or from the ketal-ethyl formate side. No one has reported isolating an ortho ester from an equilibrium mixture prepared from a ketal and an alkyl formate, but in one case the ketone was isolated (190).…”

Acetalation of Pentaerithritol Catalyzed by an Al-Pillared Saponite

“…The commonly used acid catalysts include corrosive protic acids such as HCl, H 2 SO 4 and Lewis acids such as ZnCl 2 and FeCl 3 [23,24]. A series of diphosphine complexes have also been employed for the synthesis of acetals [25,26]. However, acetalation by afore mentioned methods require tedious work-up procedures, and the chemicals required for the synthesis of complexes are expensive.…”