GB297019A - Improvements relating to the manufacture of crystalline menthol - Google Patents

Abstract

297,019. Howards & Sons, Ltd., and Blagden, J. W. June 8, 1927. Menthol.-By subjecting synthetic menthol to partial esterification, separating the unesterified from the esterified portion, and saponifying the latter, the parent material is divided into fractions of different melting-point of which one is of higher melting-point than that of the starting material. A similar result is obtained by partially saponifying a menthol ester, separating the liberated menthol from the unsaponified ester, and saponifying the latter. The partial saponification and esterification may be effected in two or more stages, and both may be combined. The process is applicable both to crystalline menthol of melting-point about 34‹ C. and to crude synthetic menthol of lower melting-point; menthol prepared by the hydrogenation of thymol, piperitone and menthone, and particularly that prepared according to Specification 213,991 and 238,314, is specially mentioned. At other stages of the partial saponification or esterification, there may be produced a crystalline menthol of lower melting-point or a liquid menthol, and these may be again treated, together if desired with a further quantity of parent menthol; alternatively, they may be treated by the processes described in the aforementioned Specifications. The esterification may be effected with aliphatic or aromatic acids or anhydrides; when the acid is polybasic, e.g. phthalic acid, either a normal or an acid ester may be formed. The saponification is carried out by treatment with caustic alkali, but in the case of an acid ester steam distillation may also be employed. Examples are given.