Acetylene → HCID 21483752, compound

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Reaction Steps

The acetylenic ketones HC≡CCOCR2R3 (CH2)pQ can be prepared by several alternate routes analogous to those described for preparation of the corresponding vinyl ketones. For example (Method 1) propiolaldehyde is treated with the ##STR236## Grignard reagent derived from Q(CH2)pCR2R3X where X is halogen, preferably chlorine, affording an acetylenic carbinol which in turn is oxidized with chromic acid to the acetylenic ketone. Care must be taken that the aldehyde be added very slowly to cold Grignard reagent lest the aldehyde undergo extremely vigorous decomposition or polymerization. Method (2) involves addition of excess acetylene to an acyl chloride in the presence of a Friedel-Crafts catalyst such as aluminum chloride. Finally, in Method (3) sodium acetylide is allowed to react with a suitable aldehyde to afford an acetylenic carbinol, which in turn is oxidized by chromic acid to give the acetylenic ketone. Of these three methods (2) and (3) are usually the most satisfactory. Thus 6,6,6 trifluorohexanoic acid chloride (prepared via adipic acid monomethyl ester and SF4) reacts smoothly as its complex with aluminum chloride in nitromethane with excess acetylene (Method 2) to give a good yield of 8,8,8-trifluoro-1-octyn-3-one. Likewise, the acid chloride of 4 (p-chlorophenyl)butyric acid gives 6-(p-chlorophenyl)-1-hexyn-3-one. Hexaldehyde readily reacts with acetylene in glyme in the presence of powdered KOH to give an acetylenic carbinol which in turn is oxidized by a solution of CrO3 in water and sulfuric acid to 1-octyn-3-one (Method 3).

Provenance & Evidence