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Studies on the Oxidation of cis- and trans-Pinane with molecular oxygen

1992; Wiley; Volume: 334; Issue: 5 Linguagem: Inglês

10.1002/prac.19923340506

0941-1216

Thomas Brose, W. Pritzkow, Gerda Thomas,

Radical Photochemical Reactions

The pinanes are preferably attacked at the tertiary C-H bond in 2-position, but products of the oxidative attack at the secondary C-H bonds in 3- and 4-position are also found. At 100°C cis-pinane is attacked more easily than trans-pinane (kcis : ktrans = 6.4), the relative rates of attack at the secondary C-H bonds in positions 3 and 4 with respect to the tertiary C-H bond in 2-position were also determined (in cis-pinane ksec: ktert = 0.027; in trans-pinane ksec : ktert = 0.20). After the attack at the 2-C-H bond the radical formed can either react with oxygen to form the corresponding cis- and trans-peroxy radicals and further to give cis- and trans-2-hydroperoxy pinane or fragmentate to the monocyclic radical derived from α-terpinene, giving as final products α-terpinene hydroperoxide and the bicyclic 8-hydroperoxy 4,4,8-trimethyl 2,3-dioxabicyclo[3.3.1]nonane. The corresponding alcohols were found after reduction with sodium sulphite. The oxidation at position 2 of the pinanes delivers not only the cis- and trans-hydroperoxide but also, as shortlived intermediates, the corresponding 2-pinanyloxy radicals. These radicals fragmentate forming a carbon radical with cyclobutane structure whose oxidation products were identified. Besides fragmentation of the 2-pinanyloxy radical also an intramolecular H-transfer from the methyl group in 9-position to the oxygen of the trans-2-pinanyloxy radical takes place leading to 9-hydroperoxy trans-pinane-2-ol.