Equilibrium constants for bisulfite addition to benzaldehyde and its derivatives were determined by a spectrophotometric method developed by Kokesh and Hall. The concentration of the benzaldehyde derivative was monitored by UV as aliquots of a bisulfite solution are added to a buffered solution of the aldehyde. Additional data on ΔH° and ΔS° for the reactions were derived from the temperature variation of the equilibrium constants. For benzaldehyde, the reaction had an equilibrium constant at 25°C of 6.2 x 103 M-1, a ΔH° of -54.3 kJ/mol, and a ΔS° of -111 J/Mol·K. o-Tolualdehyde exhibited a lower Keq of 2.4 x 103 M-1, ΔH° of -39.5 kJ/mol and ΔS° of -67.3 J/Mol·K. Similarly, the reaction with o-anisaldehyde had a Keq of 2.6 x 103 M-1, ΔH° of -38.2 kJ/mol and ΔS° of -62.9 J/Mol·K. The reaction involving salicyladehyde exhibited a much lower Keq of 6.9 x 102 M-1, and ΔH° of -38.5 kJ/Mol and ΔS° of -76.1 J/Mol·K
