Novel acetylenic compounds and a process for the manufacture and conversion thereof

摘要

The invention comprises acetylenic compounds of the general formula in which R1 and R2 each represent a hydrogen atom or the acyl residue of a carboxylic acid, and also 3,7-dimethylocten-(1)-diol-3,7. The novel acetylamic compounds are produced by treating the compound with an aqueous mineral acid and, if desired, converting the product into a carboxylic diester. The preferred mineral acid is sulphuric acid but other acids, e.g. phosphonic, nitric or a hydrohalic acid may be used. The compound in which both R1 and R2 represent hydrogen may be converted to 3,7-dimethyl-7-hydroxyoctanal-(1) (hydroxy-citronellal) as follows: (a) it is partially hydrogenated in the presence of a hydrogenation catalyst to produce 3,7-dimethylocten-(1)-diol, 3,7; this diol is then oxidized to 3,7-dimethyl-7-hydroxy-octen-(2)-al-(1) either directly, e.g. by chromic acid or in two stages by first treating the dol with a halogenating agent to give 1-halo-3,7-dimethyl-7-hydroxy-octene-(2) and oxidizing this with nitromic acid; the a ,b -unsaturated hydroxyaldehyde is then hydrogenated, e.g. using palladium on charcoal as catalyst, to give hydroxy-citronellal. An acetylenic diester is converted to hydroxy-citronellal as follows: (a) it is first converted to the corresponding 3,7 - dimethyl - 7 - acyloxy - octen - (2) - al-(1) by re-arranging it, in the presence of a rearrangement catalyst (e.g. silver carbonate, silver acetate, silver trifluoroacetate, silver nitrate, silver fluoroborate, silver perchlorate, copper powder or copper acetate), to the allenic diester 3,7-dimethyl-1,7-diacyloxy-octadiene-(1,2) which is partially saponified; (b) the a ,b -unsaturated monoacyloxy-aldehyde so obtained is catalytically hydrogenated, e.g. in methanoline solution using a palladium on charcoal catalyst to give a mixture of a 3,7-dimethyl - 7 - acyloxy - octanal - (1) and its dimethyl acetal; and (c) completing the acetal conversion and hydrolysing the product first in alkaline medium to give 1,1-dimethoxy-3,7-dimethyl-7-hydroxy-octane and then in acidic medium to give hydroxy-citronellal.