Stopped-flow spectrophotometric measurements on the reaction of isobutyraldehyde with methylamine in water at 35°over the pH range 10.1-11.5 gave a value of 8.5 ± 0.5 M-1 for the equilibrium constant for addition of the amine to the aldehyde, and a value of 6.2 ± 0.7 sec-1 for kc, the rate constant for dehydration of the carbinolamine to N-isobutylidenemethylamine. Kinetic studies of methylammonium chloride catalysis of the oximation of isobutyraldehyde at pH 8.5-9.8 gave values of kcKc* in agreement with the stopped-flow measurement, but at pH 7.6 larger values were obtained, suggesting acid catalysis of the dehydration of the carbinolamine. The equilibrium constant for the addition of hydroxylamine to isobutyraldehyde was found to be 105 ± 11 M~\ and the rate constant for dehydration of the adduct to give oxime fit the equation kd = (6.5 X 105[H+] + 3.2 X 10~12/ [H+] + 4.6 X 10-3) sec-1. A kinetic study of the hydration of isobutyraldehyde in the presence of N-methylmorpholine buffers showed that the reaction was fast enough that the hydration-dehydration equilibrium could be treated as continually established throughout the studies of the reaction of isobutyraldehyde. Structural effects on equilibrium constants for addition to isobutyraldehyde are discussed.

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