Researches on acetylenic compounds. Part LXVII. Base-catalysed isomerisation of hepta-2,4-diynoic, hepta-2,5-diynoic, hepta-4,5-dien-2-ynoic, and hepta-2,3-dien-5-ynoic acids

Abstract

In aqueous sodium hydroxide (1N) at 65° hepta-2,4-diynoic acid is isomerised to hepta-3,5-diynoic acid. A number of possible intermediates in this isomerisation: hepta-4,5-dien-2-ynoic, hepta-2,5-diynoic, and hepta-2,3-dien-5-ynoic acid have been synthesised and shown to isomerise to hepta-3,5-diynoic acid at rates which progressively increase in the order given. From a kinetic and spectroscopic study of the isomerisations it is concluded that the main route for the conversion involves the sequence hepta-2,4-diynoic acid → hepta-4,5-dien-2-ynoic acid → hepta-2,3,4,5-tetraenoic acid → hepta-3,5-diynoic acid.