Patent GB-605208-A (GB)
Title: A process for the manufacture of pentaenes
Filed: 1945-11-05
Abstract: Pentaenes are obtained by heating with a small proportion of iodine, e.g. between 1-2 per cent and preferably in an inert solvent, 1 - hydroxy - 3 : 7 - dimethyl - 6 - hydroxy - 9 - (21 : 61 : 61 - trimethyl - cyclohexene - (11) - yl) - nonetriene-2 : 4 : 7 or an ether thereof which is preferably obtained by condensing 4-(21 : 61 : 61-trimethyl-cyclohexene-(11)-yl) -2-methyl-butene-2-al-1 with a Grignard component of 1-hydroxy-3-methyl-pentene-2-yne-4- or an ether thereof to produce 1-hydroxy-3 : 7-dimethyl-6-hydroxy-9-(21 : 61 : 61-cyclohexene-(11)-yl-nonadiene-2 : 7-yne-(4)- or an ether thereof which is hydrogenated in the presence of a hydrogenation catalyst until 1 mol. of hydrogen has been added to the triple bond thereof. Anti-oxidants, e.g. tocophenols, should also preferably be present during the reaction.  In examples: (1) 4-(21 : 61 : 61 - trimethyl - cyclohexene - (11) - yl) - 2 - methyl-butene-(2)-al-(1) is condensed by means of 1 mol. of ethyl magnesium bromide with 1 - methoxy - 3 - methyl - pentene - 2 - yne - (4) to produce 1-methoxy-3 : 7-dimethyl-6-hydroxy-9-(21 : 61 : 61 - trimethyl - cyclohexene - (11) - yl) - nonadiene-(2 : 7)-yne-(4) which is hydrogenated using palladised charcoal on which quinoline had been previously adsorbed to produce 1-methoxy-3 : 7-dimethyl-6-hydroxy-9-(21 : 61 : 61-cyclohexene-(11)-yl)-nonatriene-2 : 4 : 7 which is boiled in xylol in the presence of iodine; a concentrate of vitamin A methyl ether is obtained from the residue by chromatographic adsorption; (2) vitamin A methyl ether is obtained as in (1) except that the 1-methoxy-3 : 7 - dimethyl - 6 - hydroxy - 9 - trimethyl - cyclo - hexenyl-nonatriene-2 : 4 : 7 is boiled in petroleum ether instead of xylol; (3) vitamin A butyl ether is obtained as in (2) using 1-butoxy-3-methyl-pentene-(2)-yne-(4) instead of 1-methoxy-3-methyl-pentene-2-yne-(4); (4) vitamin A phenyl ether is obtained as in (2) using 1-phenoxy-3-methyl-pentene-(2)-yne-(4) and boiling the 1-phenoxy-3 : 7-dimethyl-6-hydroxy-9-trimethyl-cyclohexenyl-nonatriene-2 : 4 : 7 with toluene instead of petroleum ether.  A sample has been furnished under Sect. 2 (5) of vitamin A alcohol prepared similarly from 1-hydroxy-3-methyl-pentene-(2)-yne-(4).  4 - (21 : 61 : 61 - Trimethyl - cyclohexene - (11) - yl) - 2 - methyl - butene - (2) - al - (1) is obtained from b -ionone by glycide ester synthesis, saponification of the glycide ester formed and decarboxylation of the glycide ester in vacuo in the presence of copper powder; or according to the Provisional Specification, by the cyanohydrin synthesis of dihydro-b -ionone, splitting of water or hydrogen halide, respectively, and reduction of the resulting 4-(21 : 61 : 61-trimethyl-cyclohexene - (11) - yl) - butenyl - cyanide - (2) by way of the imide chloride.  1 - Hydroxy - 3 - methyl - pentene - (2) - yne-(4) and its ethers. The alkyl ethers are obtained by reacting 3-hydroxy-3-methyl-pentene-(1)-yne-(4) (the condensation product of methyl vinyl ketone and acetylene) with acid and alcohol (e.g. sulphuric acid and methyl alcohol), the hydroxyl group being simultaneously etherified and shifted thereby or alternatively by halogenating 3-hydroxy-3-methyl-pentene-(1)-yne-(4) with phosphorous halides and reacting the primary halide thus formed with a sodium alcoholate.  The phenyl ether may be obtained from the primary bromide by boiling with phenol in acetone in the presence of potassium carbonate.