MODIFIED PHOTOBEHAVIOR OF CARBOXYLIC ACID DERIVATIVES INDUCED BY PROTONATION

Article abstract of DOI:10.1016/S0040-4020(01)90028-6

A series of carboxylic acid derivatives 1-6 containing a second interacting function have been converted into the corresponding O-protonated species or acylium ions upon treatment with 96percent sulfuric acid or oleum, respectively, at room temperature.The resulting stable cations have been spectroscopically characterized and submitted to irradiation.Cis-trans photoisomerization was observed in the ionic species derived from trans-crotonic, fumaric and maleic acids, and maleic anhydride.By contrast protonated crotonolactone 5a was found to be photostable.Finally, protonated α-bromobutyrolactone 6a was clean and efficiently dehydrohalogenated to 5a upon irradiation.Since the normal n ?^* photoreactions of the uncharged carboxylic acid and their derivatives are inhibited under these conditions, protonation can be envisaged as a chemical selective method for photoprotection of the carboxy group.