The isomerization of 3-methyl-l-penten-4-yne-3-ol into trans-3-methy-2-penten-4-yne-1-ol and an isomer assumed to be the cis form has been studied. The problem of determining whether or not the arbitrarily assumed isomer is a geometrical isomer or an ordinary isomer has been brought forward in industry in the course of a synthesis of Vitamin A. Qualitative tests on the questionable isomer were without result because of the activity that the unsaturated bonds exhibited when reagents were used to test it. AU possible isomers of the compound were reviewed and the following chemical means were employed to prove that the isomer was the geometric one. A total hydrogenation of both isomers was carried out which, in both cases, gave 3-methyl-1-pentanol. The 3,5-dinitro benzoate derivatives of both isomers were made, which proved that the structures were similar. The isomer possibility was thus limited to two forms. The structure of the geometrical isomer was shown by adding one mole of hydrogen to cis-3-methyl-2-penten-4-yne-1-ol which produced 3-methyl-2,4-pentadien-1-ol. This resultant diene was reacted with maleic anhydride and the adduct formed was recrystallized from water to give a gamma lactone. As further proof, the same diens was reacted with acetylene dicarboxylic ester, The adduct was oxidized with chloranil and the product was further oxidized with potassium permanganate. This yielded a compound containing a benzene ring with two carboxylic groups and one anhydride group:(3,6-dicarboxy phthalic anhydride).
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