Flash photolytic generation of two keto tautomers of 1-naphthol in aqueous solution: kinetics and equilibria of enolization

• Published in: Photochemical & photobiological sciences Vol. 9; no. 7; pp. 901 - 907
• Main Authors: Gut, Ivo Glynne, Scheibler, Lukas C., Wirz, Jakob
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.01.2010
• Subjects: Biochemistry; Biomaterials; Chemistry; Physical Chemistry; Plant Sciences
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c0pp00034e

Benzo[ b ]cyclohexa-2,4-dien-1-one ( 4 ) and benzo[ b ]cyclohexa-2,5-dien-1-one ( 5 ), the two most stable keto tautomers of 1-naphthol ( 1 ), were generated in aqueous solution by Norrish Type II fission of 4- and 2-phenacyl-1-tetralone, respectively, and the pH–rate profiles of their enolization were measured by flash photolysis. Several isotopic exchange rates of 1 were measured in aqueous acid to determine the corresponding rate constants of ketonization. The resulting equilibrium constants for enolization are p K E ( 4 ) = −7.1 and p K E ( 5 ) = −6.2. The acidity constants of the carbon acids 4 and 5 , p K a ( 4 ) = 2.1 and p K a ( 5 ) = 3.0, were then obtained from a thermodynamic cycle using p K a ( 1 ) = 9.25.