264 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

SOME INVESTIGATIONS OF THE CHEMISTRY OF CARENE Table III Products % from heating (q-)-cis-caran-cis-$-ol (formula 26) with acetic acid at various temperatures 265 . Formulae Temperature øC (43) (44) (31) 180 71.7 12.2 16.7 210 74.5 13.3 11.6 300 61.8 21.7 3.4 (14.4%). The ultraviolet spectrum of (+)-p-mentha-2,4(8)-diene (formula 41 R, CH3) showed a maximum at 244 nm (log e 3.93) (35) and at 731 cm-1 (cis CH =CH) (36) in the infra-red. Signals at • 9.02 (d, J 7Hz, 3H, CH 3-7), 8.29 Is, 6H, (CH 3)2 C=Cl, 4.55 (d, J 11Hz, H2) and 3.68 (d, J 11Hz, H3) in the nmr spectrum are in complete agreement with its struc- ture. m-Mentha-l,3(8)-diene (formula 42) likewise showed a conjugated diene maximum at 245 nm (log e 4.11) in the ultraviolet, and at 1 630 cm-• in the infra-red. Its nmr spectrum showed peaks at • 8.29 (s, 9H, vinylic CH 3 groups) and at 3.9 (s, 1H, H2), in agreement with its structure. We portray the formation of these dienes, which is acid catalysed, in the following manner. o, Hf • '--•-(40)(41 R,CHz,) ""/ H+ • b '•+.• -H+ • (42) ( q- )-cis-Caran-cis-$-ol We next pyrolysed (q-)-cis-caran-cis-5-ol (formula 26), without catalyst, at about 480øC, in the vapour phase, with the object of obtaining other menthadienes. In the event the product consisted largely of (--)-cis-m- mentha-4, 8-diene (formula 43) (80%) (17) and the previously unknown (q-)-m-mentha-3(8), 4-diene (formula 44). When the caran-5-ol (formula 26) was heated with a catalytic amount of acetic acid (Table III), the dienes (formulae 43 and 44) were formed along with (--)-cis-m-menth- 4-en-8-ol (formula 31) (8). This is an interesting result for unlike the