Optimization of the reaction conditions for the synthesis of 5-phenyl-1H-tetrazole.

Entry	Solvent	Catalyst (mol%)	Temp. (°C)	Time (min)	Yielda (%)
1	Water	0.4	80	15	98
2	EtOH	0.4	Reflux	60	40
3	CH3CN	0.4	Reflux	30	55
4	DMF	0.4	80	30	80
5	Neat	0.4	80	120	20
6	Water	No catalyst	80	240	0
7	Water	0.2	80	45	70
8	Water	0.6	80	15	98
9	Water	—b	80	180	Trace
10	Water	—c	80	180	35
11	Water	—d	80	180	55
12	Water	—e	80	60	75
13	Water	0.4	R.T.	90	10
14	Water	0.4	40	60	60
15	Water	0.4	50	45	82
16	Water	0.4	60	15	97
17	Water	0.4	70	15	98
18	Water	0.4	90	15	95

^aReaction conditions: aldehyde (1.0 mmol), hydroxylamine (1.2 mmol), and sodium azide (1.5 mmol). The catalyst was prepared using 0.4 mol% catalyst, as explained in the experimental section.

^bReaction was performed in the presence of Fe₃O₄ as the catalyst.

^cReaction was performed in the presence of Fe₃O₄@NFC as the catalyst.

^dReaction was performed in the presence of Cu(OAc)₂ as the catalyst.

^eReaction was performed in the presence of [(5-Cl-Saloph)Cu(ii)]CO₂H as the catalyst.