5020-21-3Relevant articles and documents
Kinetics and mechanism of the isomerization of 1H-indene-1-carboxylic acid to 1H-indene-3-carboxylic acid in aqueous solution and determination of their keto-enol equilibrium constants and acid dissociation constants of the keto and enol forms. Implication on the photolysis of diazonaphthoquinones
Andraos,Kresge,Popik
, p. 961 - 967 (2007/10/02)
Rates of isomerization of 1H-indene-1-carboxylic acid to 1H-indene-3-carboxylic acid were measured in dilute aqueous solutions of HClO4, NaOH, and CH3CO2H and H2PO4-, (CH3)3CPO3H-, and HCO3- buffers. This gave a rate profile which, together with the occurrence of general base catalysis and sizable primary kinetic isotope effects, indicates that the isomerization takes place through an enolization-reketonization reaction sequence. The equilibrium constant of the isomerization reaction is K = [indene-3-carboxylic acid]/[indene-1-carboxylic acid] = 200 in aqueous acid solution and K = 100 in base. The ratio of products formed by ketonization of the indenecarboxylic acid enol intermediate generated in the photolysis of 2-diazo-1 (2H)-naphthalenone is R = [indene-3-carboxylic acid]/[indene-1-carboxylic acid] = 0.47 in aqueous acid solution and R = 20 in base. The failure of previous investigations of the photolysis reaction to detect any indene-1-carboxylic acid as the product is attributed to the facile isomerization of this substance to indene-3-carboxylic acid and the preponderance of the latter at equilibrium. The enol intermediate of this isomerization reaction was also generated by flash photolysis of 2-diazo-1 (2H)-naphthalene and rates of its ketonization were measured in dilute aqueous HClO4 solutions. Analysis of the data gave the enol acidity constant pKaE = 2.09. The results, in combination with those for the isomerization reaction, also provided carbon acid acidity constants (KaK) and keto-enol equilibrium constants (KE) for the two acids: pKaK = 9.35 and pKE = 7.26 for indene-1-carboxylic acid and pKaK = 11.69 and pKE = 9.60 for indene-3-carboxylic acid.