Polyethylene glycol (PEG) mediated green synthesis of 2,5-disubstituted 1,3,4-oxadiazoles catalyzed by ceric ammonium nitrate (CAN)

Figures & data

short-legendScheme 1. Synthesis of 2,5-disubstituted oxadiazoles.

Figure 1.  Synthesis of 2,5-disubstituted oxadiazoles in various solvents.^a

^aReaction conditions: carboxylic acid (1 mmol), benzhydrazide (1 mmol); temperature 80°C; solvent.

^bIsolated and unoptimized yields.

Figure 2.  Catalytic activity evaluation of CAN for the synthesis of 2,5-disubstituted oxadiazoles.^a

^aReaction conditions: carboxylic acid (1 mmol), benzhydrazide (1 mmol); temperature 80°C; PEG 400.

^bIsolated and unoptimized yields.

Table 1. Screening of various Lewis acids for the synthesis of 2,5-disubstituted oxadiazoles.^a

Entry	Catalyst	Time (h)	Yield^b (%)
1	InCl3	11	87
2	CuO	8.5	79
3	NbCl5	9	82
4	FeCl3	9.5	73
5	I2	7	76
6	CuSO4	8	83
7	CAN	5	98
^aReaction conditions: carboxylic acid (1 mmol), benzhydrazide (1 mmol), catalyst (5 mol%); solvent PEG 400; temperature 80°C.
^bIsolated and unoptimized yields.

Figure 3.  Recycling yields.

Note: Reaction conditions: carboxylic acid (1 mmol), benzhydrazide (1 mmol), CAN (5 mol%); solvent PEG 400; temperature 80°C.

^aIsolated and unoptimized yields.

Table 2. Synthesis of various 2,5-disubstituted oxadiazoles.^a

Entry	3	R	Time (h)	Yield (%)^b	M.P (°C)	Lit M.P (°C)
1	3a	C6H5	5	98	132–133	132–133^18
2	3b	2-NH2C6H5	6	96	161–163	161–163^19
3	3c	4-OHC6H5	6	91	165–166	165–166^20
4	3d	4-CH3C6H5	6	95	132–135	132–135^18
5	3e	4-Cl C6H5	5	97	157–159	157–159^18
6	3f	4-OCH3C6H5	6	98	148–149	148–150^21
7	3g	3-OCH3C6H5	6	98	152–154	154–157^22
8	3h	4-NO2C6H5	5	95	200–203	200–204^23
9	3i	Furyl	5	78	84–85	84–85^18
10	3j	Pyridinyl	5	84	131–132	133–136^21
^aReaction conditions: carboxylic acid (1 mmol), benzhydrazide (1 mmol), CAN (5 mol%); solvent PEG 400; temperature 80°C.
^bIsolated and unoptimized yields.