Shaterian & Rigi
FULL PAPER
Scheme 1
obtained at 80 ℃ and 0.07 g (3.5 mol%) of the cata-
lyst.
R1
HO
HO
OH
OH
R1 O
O
O R1
O R2
Cellulose sulfuric acid
Solvent-Free, 80 oC
Using these optimized reaction conditions, the scope
and efficiency of these procedures were explored for a
wide variety of substituted aldehydes and ketones de-
rivatives (Table 1). Ketones show less reactivity than
aldehydes for this reaction, for example dibenzalpen-
taerythritol (Table 1, Entry1) was obtained in 96% yield
in 15 min, whereas acetophenone (Table 1, Entry 16)
provided 85% yield of product in 22 min. Aromatic al-
dehydes with stronger electron-donor groups such as
methoxy and methyl (Table 1, Entries 4, 10) showed
less reactivity and give lower yields, whereas elec-
tron-withdrawing substituents enhanced the rate of
acetal formation. So, nitro and chloro derivatives of
benzaldehyde (Table 1, Entries 2, 3, 11—14) reacted
faster than the other aldehydes. Alkyl aldehydes are
converted to their respective acetals such as aryl alde-
hydes in excellent yield. (Table 1, Entries 6—9).
In order to show the accessibility of the present work
in comparison with the reported results in the litera-
ture,[7,8,12,13] we summarized some of the results for
acetalizaton of carbonyl compounds in Table 2, which
shows that CellSA is the most efficient catalyst with
respect to the reaction time and temperature and exhibits
broad applicability in terms of yield.
We also studied the reusability of the catalysts in the
reaction of benzaldehyde and pentaerythritol under sol-
vent-free conditions at 80 ℃. In this procedure, after
completion of the reaction, the reaction mixture was
cooled to room temperature, and the crude solid was
dissolved in hot ethanol. The mixture was filtered for
separation of the catalyst. The catalyst was washed with
hot ethanol (5 mL×2). The recovered catalyst was
dried in 60 ℃ and used for the subsequent catalytic
runs. The recovered catalyst was reused four times
without any loss of its activities (Figure 1).
O
R2
R2
R1 = R2 = H, Alkyl, Aryl
Experimental
All reagents were purchased from Merck and Al-
drich and used without further purification. All yields
refer to isolated products after purification. CellSA was
preapared according to the literature.[22] The NMR spec-
tra were recorded on a Bruker Avance DPX 300 MHz
instrument. Elemental analyses for C, H and N were
performed using a Heraeus CHN-O-Rapid analyzer. IR
spectra were recorded on a JASCO FT-IR 460 plus
spectrophotometer. Mass spectra were recorded on an
Agilent technologies 5973 network mass selective de-
tector (MSD) operating at an ionization potential of 70
eV. TLC was performed on silica-gel Poly Gram SIL
G/UV 254 plates.
General procedure for the preparation of penta-
erythritol diacetals and diketals
Pentaerythritol (1 mmol), aldehydes or ketones (2
mmol), and CellSA (0.07 g, 3.5 mol %) were added at
80 ℃ under solvent-free conditions. The completion of
reaction is monitored by TLC. After completion, the
reaction mass was cooled to 25 ℃, then the solid resi-
due was dissolved in hot EtOH and the catalyst was fil-
tered off. The filtrate solution was concentrated and the
solid product was purified by recrystallization in aque-
ous EtOH (25%). Some selected spectroscopic data for
known products are given below.
1
1: H NMR (CDCl3, 300 MHz) δ: 7.55—7.60 (m,
2H), 7.24—7.30 (m, 2H), 6.91—6.96 (m, 2H), 6.83 (d,
J=8.2 Hz, 2H), 5.79 (s, 2H), 4.87 (d, J=11.5 Hz, 2H),
3.27—3.87 (m, 10H), 3.61 (d, J=11.5 Hz, 2H); IR
(KBr) ν: 2980, 2900, 2850, 1610, 1470, 1400, 1250,
-
1
1070, 1030, 760 cm .
2: 1H NMR (CDCl3, 300 MHz) δ: 7.50 (d, J=8.4 Hz,
4H), 7.26 (d, J=8.4 Hz, 4H), 4.40 (d, J=11.5, 2H),
3.54 (d, J=11.5 Hz, 2H), 3.17 (s, 4H), 1.46 (s, 6H); IR
(KBr) ν: 2970, 2920, 2850, 1610, 1460, 1400, 250, 1070,
-
1
1040, 708 cm .
Results and Discussion
To choose optimum conditions, first we tried to per-
form acetatalization of carbonyl compound from the
reaction of benzaldehyde (2 mmol) and pentaerythritol
(1 mmol) as a model under solvent-free conditions at
different temperatures (60, 70, 80, 100 ℃) in the pres-
ence of CellSA (0.05 g, 0.5 mol%). The best result was
obtained at 80 ℃. Next, the model was examined at
different amount of CellSA (0.05, 0.06, 0.07, 0.08 g) at
80 ℃. The highest yield and short reaction time was
Figure 1 Reusability of the catalyst.
Conclusions
We have developed a green and straightforward
protocol for acetalization of carbonyl compounds as
biscyclic acetals derivatives via the reaction of alde-
hydes and pentaerythritol using CellSA as a bio-
696
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2012, 30, 695—698