Table 2.

Apparent 2^nd order rate constants (M^{− 1} min^{− 1}) for different ortho proton donor nucleophilic catalysts.^a

catalyst	2nd order rate constant	rel. to uncat. rxn.
(none)	0.10 ± 0.01	1
	1.1 ± 0.1	11
	4.7 ± 0.3	46
	5.0 ± 0.7	49
	8.5 ± 0.5	83
	5.4 ± 0.7	53

^aConditions: 18 µM NBD Hydrazine, 1 mM 4-nitrobenzaldehyde, 1 mM catalyst in 10:1 PBS (pH 7.4):DMF, 23 °C.