Silica immobilized sulfuric acid ([3-(propyl)sulfanyl]propyl]ester and N-propylsulfamic acid as recyclable catalysts for chemoselective synthesis of 1,1-diacetates

Figures & data

Figure 1.  The structure of catalysts I and II.

short-legendScheme 1. Synthesis of 1,1-diacetate derivatives catalyzed by I or II.

Table 1. Conversion of p-methylbenzaldehyde to the corresponding diacetate with acetic anhydride in the presence of different amounts of catalysts I and II under solvent-free conditions and at room temperature.^a

Entry	Catalyst loading (g)	Ac2O (mmol)	Time (min)	Yield %^b
1	No catalyst	15	12 h	0
2	0.01	15	10 (10)	80 (79)
3	0.03	15	7 (7)	96 (92)
4	0.03	1	7 (7)	70 (67)
5	0.03	3	7 (7)	70 (68)
6	0.03	6	7 (7)	76 (73)
7	0.03	10	7 (7)	83 (80)
8	0.03	12	7 (7)	88 (85)
9	0.05	15	5 (5)	95 (93)
^aThe time and yield in parenthesis are related to catalyst II.
^bIsolated yield.

Table 2. Conversion of p-methylbenzaldehyde to the corresponding diacetate in different solvents and under solvent-free conditions in the presence of I and II (0.03 g).

Entry	Solvent^a,b	Time (min)	Yield^c
1	H2O	30 (30)	10 (10)
2	EtOH	30 (30)	25 (25)
3	CH2Cl2	7 (7)	90 (87)
4	n-hexane	40 (40)	82 (80)
5	MeCN	10 (10)	85 (83)
6	Solvent-free^d	7 (7)	96 (92)
^aThe reaction was carried out in 5 mL of solvent at room temperature.
^bThe time and yield in parenthesis are related to catalyst II.
^cIsolated yield.
^dThe reaction was carried out with 15 mmol of Ac2O at room temperature.

Table 3. Preparation of various acylals in the presence of I and II under solvent-free conditions at room temperature.^a,b

Entry	Ar (1)	Product 2	Time (min)	Yield (%)^c	Melting point (°C)	Lit. melting point (°C)
a	C6H5−		5 (5)	83 (86)	44–45	45^34
b	4-Me–C6H4−		7 (7)	96 (92)	79–81	80–81^35
c	4-O2N–C6H4−		3 (3)	90 (85)	123–125	125^32
d	4-Cl–C6H4−		3 (3)	89 (87)	81–83	82^32
e	2-MeO–C6H4−		3 (3)	89 (89)	75–77	76^32
f	4-Br–C6H4−		3 (4)	85 (92)	90–93	92–95^22
g	4-F–C6H4−		2 (3)	86 (87)	51–53	51^32
h	4-NC–C6H4−		4 (3)	82 (83)	99–101	100–102^31
i	2,4-(Cl)2-C6H3−		3 (3)	84 (87)	99–101	100–102^34
j	2,6-(Cl)2-C6H3−		3 (3)	80 (80)	87–89	88–89^31
k	2-HO–C6H4−		3 (3)	83 (80)	99–101	100–102^31
l	2-O2N–C6H4−		3 (3)	87 (82)	84–86	85^32
m	3-OHC–C6H4−		3 (3)	81 (80)	108–110	108–110^7
n	4-OHC–C6H4−		4 (4)	85 (86)	172–174	174–175^34
o	2-thienyl-		4 (4)	76 (75)	67–68	66–67^21
p	Me(CH2)4–		3 (3)	70 (69)	Boiling point 127–129 (2 mm)	Boiling point 128–129 (2 mm)^12a
^aReaction conditions: aromatic aldehyde (1 mmol), acetic anhydride (15 mmol), catalyst I or II (0.03 g), room temperature, solvent-free.
^bThe time and yield in parenthesis are related to catalyst II.
^cIsolated yield.

Table 4. Competitive acylal formation from aldehydes in the presence of ketones using I or II under solvent-free conditions.^a

Entry	Substrates		Product (selectivity%)^b
1
			(100%)	(0%)
2
			(100%)	(0%)
^aReaction conditions: Substrate (1 mmol each), acetic anhydride (15 mmol), catalyst (0.03 g), 5 min at room temperature.
^bConversion.

Table 5. Comparison of the efficiency of I and II with some of the reported procedure on the reaction of 4-chlorobenzaldelyde with acetic anhydride.

Catalyst	Catalyst load (mmol)	Time (min)	Yield (%)^a	Reference
H2NSO3H	0.4	10	92	(14–17)
HClO4/SiO2	0.005	2	98	(38)
CPTS-HOAc	–^b	150	92	(40)
H3PW12O40-supported MCM-41	0.3 g (20 wt%)	240	91	(42)
PEG-SO3H	0.1	30	94	(43)
SBSSA	0.0017	3	85	(45)
Fe(CH3SO3)2.4H2O	0.45	360	92	(46–50)
CoBr2	0.1	25	93	(51–55)
I (II)	0.009	3 (3)	89 (87)	Present work
^aIsolated yield.
^b0.045 mmol of CPTS and 12 mmol of HOAC were used.

Figure 2.  Recyclability of I (0.03 g) in the reaction of p-methylbenzaldehyde (1 mmol) and acetic anhydride (15 mmol) at room temperature. Reaction time=7 min.

Figure 3.  Recyclability of II (0.03 g) in the reaction of p-methylbenzaldehyde (1 mmol) and acetic anhydride (15 mmol) at room temperature. Reaction time=7 min.