Silica supported orthophosphoric acid (H₃PO₄. SiO₂): a green, heterogeneous catalyst for solvent-free oxathioacetalization of aldehydes

Figures & data

Figure 1.  SEM images of (a) SiO₂, (b) H₃PO₄.SiO₂.

short-legendScheme 1. Chemoselective oxathioacetalization of aldehyde (GC yields).

short-legendScheme 2. Oxathioacetalization of aldehyde.

Table 1. Table 1. Optimization of reaction conditions.

No	Solvent	Catalyst	Yield ^a
1	Ethyl acetate	H3PO4. SiO2, 50mg	21
2	[bmim]BF4	H3PO4. SiO2, 50mg	56
3	[bmim]PF6	H3PO4. SiO2, 50mg	61
4	THF	H3PO4. SiO2, 50mg	20
5	Acetonitrile	H3PO4. SiO2, 50mg	80
6	Chloroform	H3PO4. SiO2, 50mg	82(78)
7	–	H3PO4. SiO2, 50mg	92(86)
8	–	H3PO4. SiO2, 100	90(81)
9	–	H3PO4. SiO2, 40mg	89(80)
10	–	SiO2	0
11	–	No catalyst	0
^a% GC yields;% isolated yields are in parenthesis; reactions were carried out at r.t. with 2mmol of benzaldehyde; [bmim]BF4, butyl methyl imidazolium tetrafluoroborate and [bmim]PF6, butyl methyl imidazolium hexafluorophosphate.

Table 2. Oxathioacetalization of aldehydes.

^aIsolated yields.

Table 3. Comparison of some recent results with present protocol.

Catalyst	Solvent	Catalyst quantity	Time (min)	Yield (%)a	Ref.
SiO2.H3PO4	–	50mg	60	78	–
SiO2.HClO4	–	40mg	30	65	10
^SiO 2 ^.HBF 4	–	20mg	25	78	18
SiO2.PPA	C2H2Cl2	1g	30	82	22
Sn(HPO4)2.H2O	CH2Cl2	5mole%	50	88	25
^aIsolated yields based on reaction of 4-Nitro benzaldehyde (2mmol) and mercaptoethanol (2.4mmol).

Table 4. Reusability of the catalyst.

Run	Conversion (%)a
1	92
2	88
3	84
4	82
^aGC yields for oxathioacetalization of benzaldehyde.

Khan , A.T. ; Pravin , T. ; Choudhury , L.H. Synthesis 2006 , 15 , 2497 – 2502 .

 Web of Science ®Google Scholar

Aoyama , T. ; Takido , T. ; Kodomari , M. Synlett 2004 , 13 , 2307 – 2310 .

 Web of Science ®Google Scholar

Ali , M.H. ; Gomes , M.G. Synthesis 2005 , 1326 – 1332 .

 Web of Science ®Google Scholar

Hazarika , P. ; Sharma , S.D. ; Konwar , D. Catal. Commun . 2008 , 9 , 2398 – 2402 .

 Web of Science ®Google Scholar