Polyvinylsulfonic acid as a novel Brønsted acid catalyst for the synthesis of bis(indolyl)methanes

Figures & data

short-legendScheme 1. PVSA-catalyzed bis(indolyl)methane synthesis.

Figure 1.  XRD profile of Na-PVSA.

Figure 2.  FT-IR spectrum of Na-PVSA.

Table 1. Optimization of reaction conditions of indole and benzaldehyde.^a

Entry	Catalyst	Mol%	Solvent	Temperature (°C)	Yield%^b
1	PVSA	20	CH3OH	RT	90
2	PVSA	20	H2O	RT	30
3	PVSA	20	C2H5OH	RT	90
4	PVSA	20	ACN	RT	52
5	PVSA	20	CHCl3	RT	NR^c
6	PVSA	15	C2H5OH	RT	92
7	PVSA	10	C2H5OH	RT	93
8	PVSA	10	No solvent	RT	86
9	No catalyst	–	C2H5OH	RT	NR^c
10	PVSA	10	C2H5OH	50	81
11	PVSA	10	C2H5OH	80	56
12	PTSA	10	C2H5OH	RT	87
13	MSA	10	C2H5OH	RT	90
14	Indion 225	10	C2H5OH	RT	NR^c
15	H2SO4	10	C2H5OH	RT	93
16	Sulfamic acid	10	C2H5OH	RT	84
^aAll reactions were carried out using 2:1 mol ratio of indole and benzaldehyde.
^bIsolated yield.
^cNR, no reaction.

Table 2. PVSA catalyzed synthesis of bis(indolyl)methanes.^a

Table 3. Catalyst recyclability.^a

Entry	Catalyst recycle no.	Yield^b
1	0	93
2	1	85
3	2	80
4	3	78
^aReactions were performed with indole (2 mmol), aldehyde (1 mmol) using 10 mol% of PVSA catalyst and solvent of 1 ml ethanol at room temperature for 2 h.
^bIsolated yield.