Reusability of the catalyst humic acid^a.

Run	1	2	3	4	5
Yieldb (%)	92	92	92	91	90

^aReaction condition: benzaldehyde (1 mmol), hydroxylamine hydrochloride (1.2 mmol), sodium azide (1.5 mmol), H₂O (2 mL), humic acid (0.1 g) at 100 °C for 4 h.

^bIsolated yield.