A process for purifying monoterpenes, including the steps of: providing a monoterpene comprising alpha terpinene of about 90% or greater purity and comprising an oxygen-containing impurity compound selected from the group consisting of 1,8-cineole, 1,4,-cineole, and mixtures thereof; providing an activated silica gel preparative chromatographic column; contacting the monoterpene with the column, wherein the oxygen-containing impurity compounds are retained on the column; recovering monterpenes depleted of oxygen-containing impurity compounds from the column by applying a pressure above atmospheric from a gas source without the use of a solvent; and removing the oxygen-containing impurity compounds by contacting the column with an alcohol.