Novel synthesis of flavour quality γ ‐lactones

The cyclization of 3‐alkenoic acids with 80% sulphuric acid in the synthesis of γ ‐lactones is always associated with fumes of sulphur dioxide gas and traces of cyclopentenones. The cyclopentenones formed during the reaction give off‐odours to the γ ‐lactones formed. Two catalysts, p ‐toluene sulphonic acid and o ‐phosphoric acid, with a catalytic amount of perchloric acid, were tried in the lactonization reaction to obtain γ ‐lactones in high yields, and the reaction was free from sulphur dioxide gas fumes and cyclopentenones. A comparison of these catalysts with 80% sulphuric acid in the synthesis of γ ‐lactones was also made. Copyright © 2006 John Wiley & Sons, Ltd.