methanol (10 mL) were added vanadium pentoxide (0.2 mmol)
and sodium perborate (SPB) or sodium percarbonate (SPC) (17.5
mmol). To this heterogeneous mixture was added 70% perchloric
acid (21.5 mmol for SPB and 43 mmol for SPC) over a period of
1
h, and the progress of the reaction was monitored by TLC and
GC. After completion of the reaction, the reaction mixture was
concentrated in vacuo and the residue was redissolved in ethyl
acetate (20 mL). The organic layer was first washed with 5%
sodium bicarbonate solution (2 × 5 mL) (except in the case of
phenolic benzaldehydes) and then with water (2 × 5 mL), dried
over anhydrous sodium sulfate, and concentrated. Further
purification was achieved by vacuum distillation or by passing
through a short column of silica gel, and products were identified
by comparison of their NMR, IR, GC, and GC co-injection with
authentic samples prepared by known methods.
Meth od B. To an ice-cooled and stirred solution of aldehyde
(
(
5 mmol) in methanol (10 mL) were added vanadium pentoxide
0.2 mmol) and 70% perchloric acid (21.5 mmol for SPB and 43
mmol for SPC). To this heterogeneous mixture was added
sodium perborate (SPB) or sodium percarbonate (SPC) (17.5
mmol) over a period of 1 h, and the progress of the reaction was
monitored by TLC and GC. After completion of the reaction,
further workup and purification were done as in method A.
4
-Allyloxyben zoic a cid m eth yl ester (17a ): 1H NMR (300
MHz, CDCl
H), 6.93 (d, 2H, J ) 8.94 Hz), 7.98 (d, 2H, J ) 8.94 Hz);
NMR (75 MHz, CDCl ) δ 166.8, 162.3, 132.6, 131.5, 122.7, 118.0,
14.3, 68.8, 51.8.
-Ben zyloxyben zoic a cid eth yl ester (12b): 1H NMR (400
3
) δ 3.88 (s, 3H), 4.58 (m, 2H), 5.39 (m, 2H), 6.10 (m,
13
1
C
3
1
4
MHz, CDCl
3
) δ 1.37 (t, 3H), 4.33 (q, 2H), 5.11 (s, 2H), 6.96 (d,
2
H, J ) 14.4 Hz), 7.31-7.53 (m, 5H), 7.99 (d, 2H, J ) 14.8 Hz).
F IGURE 1. 1H and 13C NMR spectra of di(ethylene glycol)
monobenzoate 1e.
1
4
-Br om oben zoic a cid 2-h yd r oxyeth yl ester (19c):
H
NMR (300 MHz, CDCl
3
) δ 2.80 (brs, 1H), 3.94 (t, 2H), 4.44 (t,
1
3
2
H), 7.56 (d, 2H, J ) 8.49 Hz), 7.90 (d, 2H, J ) 8.49 Hz);
C
NMR (75 MHz, CDCl
60.9.
3
) δ 166.1, 131.6, 131.1, 128.6, 128.2, 66.6,
dehyde with di(ethylene glycol) resulted di(ethylene
1
13
glycol) monobenzoate (28%, 3 h). The H and C NMR
spectra of di(ethylene glycol) monobenzoate 1e are shown
in Figure 1. Formation of diesters was not observed by
this method for any of the diols. To the best of our
knowledge, this is the first successful monoesterification
of diols in one pot directly from diols and aldehydes.
In conclusion, the method represents a simple, rapid
way to oxidize a variety of aldehydes to a wide range of
esters, including an efficient preparation of monoesters
from diols. The simplicity and convenience of this oxida-
tion procedure are appealing, the fact that the reaction
proceeds in high yields, and in particular, its use in
aqueous media hold promise as the basis for this process,
which is environmentally safe, and economical. The high
catalytic turnover number combined with inexpensive,
easily available reagents and innocuous side products in
the reaction makes it a suitable practical alternative.
Ben zoic a cid 3-h yd r oxyp r op yl ester (1d ): 1H NMR (300
MHz, CDCl
H), 7.40-7.60 (m, 3H), 8.04 (m, 2H); C NMR (75 MHz, CDCl
δ 167.0, 133.0, 130.0, 129.6, 128.4, 61.8, 59.2, 31.9.
Ben zoic a cid 2-(2-h yd r oxyeth oxy)eth yl ester /d i(eth yl-
3
) δ 2.02 (m, 2H), 2.40 (brs, 1H), 3.78 (t, 2H), 4.50 (t,
13
2
3
)
1
en e glycol) m on oben zoa te (1e): H NMR (400 MHz, CDCl
δ 2.00 (brs, 1H), 3.66 (m, 2H), 3.75 (m, 2H), 3.86 (m, 2H), 4.53
3
)
13
(
m, 2H), 7.40-7.62 (m, 3H), 8.09 (m, 2H); C NMR (100 MHz,
CDCl ) δ 133.1, 130.0, 129.7, 128.4, 72.48, 69.28, 64.05, 61.79.
4-Met h ylb en zoic a cid 2-(2-h yd r oxyet h oxy)et h yl est er
3
1
(8e): H NMR (300 MHz, CDCl
3
2
3
) δ 2.10 (brs, 1H), 2.41 (s, 3H),
.66 (m, 2H), 3.76 (m, 2H), 3.84 (m, 2H), 4.48 (m, 2H), 7.24 (d,
H, J ) 8.05 Hz), 7.94 (d, 2H, J ) 8.14 Hz); 13C NMR (75 MHz,
) δ 166.6, 143.7, 129.7, 129.1, 127.3, 72.4, 69.3, 63.8, 61.7,
CDCl
1.6.
Ben zoic a cid 4-h yd r oxybu t-2-en yl ester (1f): 1H NMR
(300 MHz, CDCl ) δ 3.1 (brs, 1H), 4.33 (d, 2H, J ) 6.52 Hz),
.93 (d, 2H, J ) 6.91 Hz), 5.74 (m, 1H), 5.89 (m, 1H), 7.30-7.60
m, 3H), 8.08 (m, 2H); 13C NMR (75 MHz, CDCl
) δ 166.6, 133.4,
33.0, 130.0, 129.5, 128.3, 125.5, 60.6, 58.3.
3
2
3
4
(
1
3
Exp er im en ta l Section
Ack n ow led gm en t. B.K.P. acknowledges the sup-
port of this research from DST New Delhi SP/S1/G-28/
98 and CSIR 01(1688)/00/EMR-II, and R.G. acknowl-
edges the financial support to the Institute. Thanks are
due to RSIC, Lucknow; IACS, Kolkata; IICT, Hydera-
bad; and IIT Kanpur for providing NMR spectra. We
are thankful to all reviewers for their valuable com-
ments and suggestions.
Su p p or tin g In for m a tion Ava ila ble: NMR spectra for the
following compounds: methyl ester of 17a , monoesters of diols
1f, and di(ethylene glycol) monoester of 8e. This material is
available free of charge via the Internet at http://pubs.acs.org.
All the reagents were commercial grade and purified according
to the established procedures. Organic extracts were dried over
anhydrous sodium sulfate. Solvents were removed in a rotary
evaporator under reduced pressure. Silica gel (60-120 mesh
size) was used for column chromatography. Reactions were
monitored by TLC on silica gel 60 F254 (0.25 mm). Gas liquid
chromatography was performed using a crossed-linked methyl
silicon gum capillary column (30 m × 0.32 mm × 0.25 µm) fitted
with FID. NMR spectra were recorded in CDCl
3
with tetram-
1
ethylsilane as the internal standard for H (300 and 400 MHz)
1
3
or CDCl
3
solvent as the internal standard for C (75 and 100
MHz). The following esters derived from parent aldehydes have
3
,11
been reported in the literature: methyl esters
1a -16a , and
J O0266902
1
1
1
8a ; ethyl esters 1b-3b, 6b, 8b-10b, and 18b; glycol mo-
16
noesters 1c, 7c, 8c, and 18c.
(
16) (a) Choudary, B. M.; Reddy, P. N. Synlett 1995, 959-960. (b)
Gen er a l P r oced u r e for P r ep a r a tion of Ester s. Meth od
A. To an ice-cooled and stirred solution of aldehyde (5 mmol) in
Chidambaram, N.; Bhat, S.; Chandrasekaran, S. J . Org. Chem. 1992,
57, 5013-5015.
J . Org. Chem, Vol. 68, No. 7, 2003 2947