Purification of tetrahydrodibenzo[b,d]pyrans from crude synthetic mixtures

A process for the isolation of a compound of the formula:

• ##STR3## in which R is hydrogen or C.sub.1 -C.sub.10 alkyl from a crude synthetic mixture, comprising the steps of:
• (a) esterifying at least a portion of the components of said mixture to form perfluorinated alkanoic acid esters thereof,
• (b) removing low-boiling components and non-volatile components from said mixture,
• (c) passing said mixture through a first preparative gas chromatographic column containing a packing consisting essentially of a slightly polar phenyl-substituted silicone oil on a porous, inert solid support to separate said mixture into a plurality of substantially discrete portions, and recovering therefrom the portion containing the highest proportion of the perfluorinated alkanoic acid ester of said compound, or a substantial fraction of said portion,
• (d) passing said recovered portion or fraction through a second preparative gas chromatographic column containing a packing consisting essentially of a non-phenyl-substituted silicone oil on a porous, inert solid support to further separate said portion or fraction into a plurality of substantially discrete subportions, and recovering therefrom the subportion containing the highest proportion of the perfluorinated alkanoic acid ester of said compound, or a substantial subfraction of said subportion,
• (e) hydrolyzing said recovered subportion or subfraction to convert the perfluorinated alkanoic ester moieties contained therein to hydroxyl groups, and
• (f) recovering said compound from said hydrolyzed subportion or subfraction.