A NEW APPROACH TO THE ANALYSIS OF THE UV ABSORPTION-SPECTRA OF KETONES IN AQUEOUS SULFURIC-ACID

Using the measured UV absorption spectra of 2-pentanone and cyclopentanone (33,000-53,000 cm-1) in 0-99% H2SO4 (w/w) as an example, a new approach to the analysis of ketone UV absorption spectra in aqueous strong acid solutions has been suggested. According to this approach, in 0-65% H2SO4 the changes in the ketone spectra are due mainly to the H-bond strengthening [GRAPHICS] and may be quantitatively interpreted by the increase in the medium electrophilicity (DELTA-E). In more concentrated acid solutions the H-bond strengthening continues to occur but the protonation of the carbonyl group predominates. Applying a nonlinear least squares iteration method, all the parameters needed to describe changes in the set of measured spectra were obtained. Also among them were the estimated values of the basicity constant pK(BH+) and slope parameter m*: pK(BH+) = -5.51, m* = 0.76 for 2-pentanone; and pK(BH+) = -5.88, m* = 0.77 for cyclopentanone.