86302-40-1Relevant articles and documents
The 4,4,4-trifluoroacetoacetic acid keto-enol system in aqueous solution. Generation of the enol by hydration of trifluoroacetylketene
Chiang,Kresge,Meng,Morita,Yamamoto
, p. 8345 - 8351 (1999)
Trifluoroacetylketene was generated in aqueous solution by flash photolysis of 2,2-dimethyl-6-trifluoromethyl-4H-1,3-dioxin-4-one and its spiro analogue, 4-trifluoromethyl-1,5-dioxaspiro[5.5]undec-3-en-2-one, and rates of hydration of the ketene to 4,4,4-trifluoroacetoacetic acid enol as well as subsequent ketonization of the enol were measured in this solvent across the acidity range [H+] = 10-1-10-12 M. Analysis of the rate profile produced by these data provides the acidity constants pQa,E = 1.85 for the carboxylic acid group of the enol and pQEa = 9.95 for its enolic hydroxyl group, which make these groups 2 and 3 orders of magnitude more acidic, respectively, than the corresponding groups in the parent unfluorinated acetoacetic acid enol. Rates of enolization of the keto group of 4,4,4-trifluoroacetoacetic acid were also measured, by bromine scavenging, and these, together with a value of the equilibrium constant for hydration of the keto group to its gem-diol derivative based upon a free energy relationship, Kh = 2900, provide an estimate of the keto-enol equilibrium constant for this system: pKE = 0.28. This is greater, by 2 orders of magnitude, than the keto-enol equilibrium constant for the unfluorinated acetoacetic acid.
