HRGC separation of hydroperoxides formed during the photosensitized oxidation of (R)—(+)‐Limonene

(R)—(+)‐Limonene was photooxidized in the presence of Rose Bengal as catalyst. After TLC isolation, the hydroperoxides formed were separated directly by HRGC and analyzed by MS (El; Cl). Each hydroperoxide isomer was then isolated by HPLC for structure determination which after reduction of the HOO group with sodium borohydride was performed by ¹H‐NMR and ¹³C‐NMR. Six hydroperoxide isomers formed by oxidation of the endocyclic double bond were identified. The compounds eluted from the HRGC column in the following order (proportions are given in brackets) I (40.1%) (1S, 4R)‐p‐mentha‐2, 8‐diene 1‐hydroperoxide; II (5.8%) (1R, 4R)‐p‐mentha‐2, 8‐diene 1‐hydroperoxide; III (20.6%) (2R, 4R)‐p‐mentha‐[1(7), 8]‐diene 2‐hydroperoxide; IV (8.5%) (2R, 4R)‐p‐mentha‐6, 8‐diene 2‐hydroperoxide; V (4%) (2S, 4R)‐p‐mentha‐6, 8‐diene 2‐hydroperoxide; and VI (21.0%) (2S, 4R)‐p‐mentha‐[1(7), 8]‐diene 2‐hydroperoxide. Direct HRGC separation of the limonene hydroperoxides offers, inter alia, the possibility of determining their flavor qualities by HRGC/effluent sniffing.