Application of open-tubular gas-liquid chromatography in an investigation of the stability of pristanic and phytanic acids towards alkaline treatment of their methyl or [-] menthyl esters.

Comparison between GLC separation of the (--) menthyl and methyl esters of two diastereoisomeric isoprenoid acids of geological interest showed that a 46 m x 0.25 mm ID butanediol succinate column gives effective separation of 2S,6R,10R- and 2R,LR,10R-isomers of (--) menthyl pristanate (2,6,10,14-tetramethylpentadecanoate), but inferior separation of the corresponding methyl ester mixture. With the latter, a small proportion (2%) of 2S,6R,10R-isomer is well resolved from the major 2R,6R,10R-component on a 92 m column. Use of the methyl esters in such analyses thus avoids the cumbersome preparation of the menthyl esters. No epimerization at the 2-methyl carbon of pristanic acid and its methyl or (--) menthyl esters was detected after treatment in 1N aqueous or methanolic NaOH under reflux for 1 hr or at 120 degrees (sealed tube) for 24 hr. Similarly no 3-methyl carbon epimerization was observed inphytanic (3R,7R,11R,15-tetramethylhexadecanoic) acid and its methyl ester after the same treatments.