Patent GB-790611-A (GB)
Title: A process for the manufacture of unsaturated aldehydes
Filed: 1955-08-16
Abstract: A process for the manufacture of unsaturated aldehydes of the general formula: <FORM:0790611/IV (b)/1> wherein X stands for the group -CH = O or -CH = CH-CH = O or <FORM:0790611/IV (b)/2> and acetals thereof comprise brominating an aldehyde of the general formula: <FORM:0790611/IV (b)/3> in which X has the significance already given, or an acetal thereof by a Wohl-Ziegler reaction and heating the product with a tertiary amine and, if desired, hydrolysing or partially hydrolysing any acetal group present in said product. Preferably N-bromo-succimide or N-bromo-acetamide in an inert organic solvent, carbon tetrachloride, chloroform, benzene or methylene chloride, is used for the bromination, which is accelerated by the addition of dibenzoyl peroxide or irradiation.  When N-bromosuccinimide is used sodium bicarbonate and calcium hydroxide are suitably added to the brominated mixture. Bromo-aldehydes of the general formula: <FORM:0790611/IV (b)/4> wherein X has the significance already given, and acetals thereof are the products of the first stage of the process.  Tertiary amines employed in the second step include quinoline, pyridine, dimethyl aniline or collidine.  The product may be treated with ice-cold dilute acid and extracted with organic solvent, e.g. petroleum ether.  Where the product is an acetal and it is desired to minimize hydrolysis the organic solvent may be added before the treatment with dilute acid. Where it is desired to hydrolyse the acetal group the product is treated with an acid, e.g. acetic acid preferably with the addition of sodium acetate.  The retrodehydro-C14- and C16-aldehydes and their acetals may be converted to the retrodehydro-C16- and C19-aldehydes by the processes of Specifications 790,613 and 790,612.  In examples, retrodehydro-C14-aldehyde is obtained by treating 4-[21,61,61-trimethyl-cyclohexen - (1) - yl] - 2 - methyl - buten - (2) - al - (1) in the presence of methylene chloride, sodium bicarbonate and calcium oxide with N-bromo-succinimide, heating the product with quinoline and extracting with petroleum ether (1); a mixture of retrodehydro-C16-aldehyde isomers is similarly obtained from 6-[21,61,61-trimethyl-cyclohexen - (11) - yl] - 4 - methyl - hexadien-(2,4) - ol - 1 (2), retrodehydro - C19 - aldehyde is similarly obtained from 8-[21,61,61-trimethyl cyclohexen - (11) - yl] - 2,6 - dimethyl - octatrien-(2,4,6) - al - 1 (3); retrodehydro - C14 - aldehyde is also obtained by converting 4-(21,61,61-tri - methyl - cyclohexen - (11) - yl] - 2 - methyl-1,1 - diethoxy - butene - (2) to retrodehydro-C14-aldehyde-diethyl acetal by a similar process and heating the product with sodium acetate, acetic acid and water to effect hydrolysis (4).  4 - [21,61,61 - Trimethyl - cyclohexen - (1) - yl]-2 - methyl - buten - (2) - al - (1) employed as starting material is obtained by reacting b -ionone and chloracetic acid in a glycide ester synthesis and treating the product with alkali.  6 - [21,61,61 - trimethyl - cyclohexen - (11) - yl]-4 - methyl - hexadien - (2,4) - al - 1 is obtained from 4 - [21,61,61 - trimethyl - cyclohexen - (11)-yl - 2 - methyl - buten - (2) - ol - (1). 8 - [21,6,61 - trimethyl - cyclohexen - (11) - yl]-2,6 - dimethyl - octatrien - (2,4,6) - al - (1) is ob-tained by treating the latter with orthoformic acid ethyl ester in the presence of p-toluene-sulphonic acid, condensing the resulting diethyl acetal with ethyl propenyl ether in the presence of zinc chloride and heating the 8-[21,61,61-tri methyl - cyclohexen - (11) - yl] - 2,6 - dimethyl-1,1,3 - triethoxy - octadien - (4,6) with acetic acid and sodium acetate to hydrolyse the acetal group and split off the elements of ethyl alcohol.  The above aldehydes may be converted to acetals for use as starting materials, e.g. by treatment with orthoformic ethyl ester in the presence of p-toluene-sulphonic acid. Specifications 753,552 and 753,559 also are referred to.