Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids

The hydrolytic degradation of squaramides and squaramic acids, the product of partial hydrolysis of squaramides, has been evaluated by UV spectroscopy at 37 degrees C in the pH range 310. Under these conditions, the compounds are kinetically stable over long time periods (>100 days). At pH >10, the hydrolysis of the squaramate anions shows first-order dependence on both squaramate and OH . At the same temperature and [OH ], the hydrolysis of squaramides usually displays biphasic spectral changes (A -> B -> C kinetic model) with formation of squaramates as detectable reaction intermediates. The measured rates for the first step (k(1) approximate to 10(4) M-1 s(1)) are 23 orders of magnitude faster than those for the second step (k(2) approximate to 10(6) M-1 s(1)). Experiments at different temperatures provide activation parameters with values of Delta H-double dagger approximate to 918 kcal mol(1) and Delta S-double dagger approximate to -5 to -30 cal K-1 mol(1). DFT calculations show that the mechanism for the alkaline hydrolysis of squaramic acids is quite similar to that of amides.