Patent GB-755667-A (GB)
Title: Improvements in or relating to treatment of substituted alpha-pinenes
Filed: 1954-04-06
Abstract: The invention comprises the new compounds 1.8 - p - menthadiene - 3 - ol, 1.8 - p - menthadiene - 3 - amines, the ethers of 1.8 - p-menthadiene - 3 - ol (other than the phenyl ethers), pseudocyclocitral, a -pseudotagetone and b -pseudotagetone.  They, with other products, are prepared by a process comprising pyrolysing a 4-substituted a -pinene from the group consisting of verbenone, verbenol, verbenyl amines and verbenyl ethers (other than phenyl ethers) to form a mixture containing a substituted p-menthadiene isomer of the starting material.  The pyrolysis may be carried out in the liquid or vapour phase at atmospheric pressure or above.  The preferred temperatures of pyrolysis are in the range 200-400 DEG  C. In the examples (a) verbenol is heated to give a substituted p-menthadiene isomer of verbenol; (b) trans-d-verbenol is heated to give a mixture from which the following fractions are separated; (i) hydrocarbons including verbene and its monocyclic isomers; (ii) pseudo-cyclocitral 4.6.6 - trimethyl - 3 - cyclohexene - 1 - aldehyde), oxidation of which produces the corresponding acid which on heating with selenium is converted to 2.4-dimethylbenzoic acid; on treating with methanol and hydrochloric acid the pseudocyclocitral is converted to the corresponding dimethyl acid; it condenses with acetone to yield the alkylidene acetone and on reduction it yields 4,4,6-trimethyl-3-cyclohexene-1-carbinol which on further reduction yields 2.2.4-trimethyl-cyclohexane carbinol; (iii) 2.6-dimethyl - 2.6 - octadiene - 4 - one (a  - pseudotagetone) which on hydrogenation yields 2.6-dimethyl - octane - 4 - one; (iv) 2.6-dimethyl-2.5 - octadiene - 4 - one (b  - pseudotagetone) which on hydrogenation yields 2.6-dimethyloctane-4-one; (v) a mixture of the cis- and trans - forms of limonene - 5 - ol (1.8 - p-menthadiene-5-ol) which on selective hydrogenation gives the cis- and trans-forms of carvo-menthene-5-ol which on further hydrogenation give isomenthol; (vi) trans-isopiperitenol (trans - 1.8 - p - menthene - 3 - ol) which on selective hydrogenation yields trans-piperitol and on complete hydrogenation yields isomenthol and menthol; on oxidation it yields isopiperitone; and (vii) citral; (c) trans-verbenol is heated to give a mixture of citral, pseudotagetones, pseudocyclocitral, isopiperitenol and limonene-5-ol; (d) cis-verbenol is heated to give menthone, trans-limonene-5-ol and citral; (e) verbenone is heated to give isopiperitenone and piperitenone; (f) verbenone is heated to give piperitenone and thymol; (g) verbenone and cymene are heated to give isopiperitenone, piperitenone and thymol; (h) verbenyl chloride is prepared by treating verbenol with dry HCl and is treated with dimethyl amine to give a mixture of 3-pinene-2-yl dimethyl amine and verbenyl dimethylamine; the verbenyl dimethyl amine is heated to give isopiperitenyl dimethylamine which on hydrolysis and hydrogenation gives a mixture of menthols; (j) verbenyl chloride is treated with ammonia and the resulting amine on heating yields isopiperitenyl amine; (k) 1-trans-verbenyl methyl ether is heated to give the isopiperitenyl methyl ether and a small amount of cymene; on refluxing with water the isopiperitenyl methyl ether yields alcohols which on oxidation yields isopiperitenone; (l) 1-transverbenyl methyl ether is heated to give a compound containing the group CH2 = C< which on hydrogenation gives isomenthyl methyl ether; and (m) verbenyl isopropyl ether (prepared from verbenol and isopropanol) is pyrolized to give isopiperitenyl isopropyl ether.