Patent GB-886763-A (GB)
Title: Process for preparing organoleptic materials from 7,8-epoxy-2,6-dimethyl-octane-2-olor its ethers or esters
IPC: C07C45/00
Filed: 1958-05-07
Abstract: A process for the production of organoleptic compounds comprises hydrogenating a compound of the general formula <FORM:0886763/IV (b)/1> wherein X is <FORM:0886763/IV (b)/2> in which R is an alkyl radical containing not more than 5 carbon atoms, to convert the epoxy group to a hydroxy group attached to a carbon atom originally part of the oxirane ring and thereafter eliminating the radical X from the 2-position by boiling with an aqueous mineral acid or an organic acid or organic acid anhydride and separating the corresponding unsaturated secondary and primary alcohols from the conversion products after hydrolysis of the ester formed when an anhydride is used to eliminate X.  In a modification of the process before or after the radical X is eliminated the product is heated in either the vapour or liquid phase in the presence of a dehydrogenation catalyst to convert the p  hydroxy group attached to the terminal carbon atom originally involved in the oxirane ring to an oxo group. Hydrogenation may be effected in the presence of such catalysts as Raney nickel or cobalt, palladium or carbon or copper chromite.  The use of sodium to effect reduction is also described.  Acids specified for use in the dehydration include sulphuric oxalic and phosphoric acids. Dehydrogenation catalysts specified for use in the modified process include copper chromite, copper compounds which yield copper readily on heating in the presence of organic material, e.g. basic copper carbonate, cuprous and cupric oxides, nickel and cobalt.  The dehydrogenation may be conducted in the liquid or vapour phase.  In examples 7,8-epoxy-2,6-dimethyl octane-2-ol is hydrogenated in the presence of Raney nickel and methanol to produce among other compounds 2,6-dimethyl-octane-2,7- and 2,8-diols, the latter being refluxed with aqueous phosphoric acid to obtain citronellol; the dehydration of the 2,6-dimethyl octane-2,7-diol to 2,6-dimethyl-2,7-octadiene is also referred to (1); 7,8-epoxy-2,6-dimethyloctane-2-ol is hydrogenated in the presence of cobalt, nickel with and without the addition of sodium hydroxide, copper chromite and palladium or carbon catalysts to obtain mixtures of dimethyl octane-2-ol, 2,6-dimethyloctane-2,7- and 2,8-diols, the products are fractionated and the 2,6-dimethyl-octane-2,8-diol is dehydrated and the b -citronellol obtained is dehydrogenated by heating with copper chromite or copper to obtain b -citronellal (2); 7,8-epoxy-2,6-dimethyloctane-2-ol is reduced with isopropanol and sodium in boiling toluene to obtain 2,6-dimethyl-7-octene-2-ol and 2,6-dimethyloctane-2,7- and 2,8-diols and the 2,8-diol is dehydrated with aqueous phosphoric acid to a mixture of a - and b -citronellols or is refluxed with acetic anhydride and the product hydrolysed with methanolic potash to obtain a mixture of a - and b -citronellols which is converted to a mixture of a - and b -citronellals by boiling with copper chromite (3); the crude diol produced as in (1) is heated with copper chromite under reduced pressure to obtain hydroxycitronellal and 2,6-dimethyl-octane-7-one-2-ol and the latter is boiled with dilute phosphoric acid to obtain b  - citronellal and 2, 6 - dimethyl - 2 - octene - 7 - one (4); and a mixture of a - and b -citronellals is obtained by dehydrating the crude diol mixture produced as in (1) and dehydrogenating the resulting mixture of 2,6-dimethyl-(1)- and -(2)-octen-7-ols.  The starting materials employed in the process may be prepared by the process of Specification 859,567.