An expedient esterification of aromatic carboxylic acids using sodium bromate and sodium hydrogen sulfite

Article abstract of DOI:10.1016/S0040-4020(03)00812-3

Treatment of aromatic carboxylic acids and substituted toluenes with a mixture of sodium bromate and sodium hydrogen sulfite in a two-phase system gave the corresponding esters in good yield. The intermediate α-brominated toluene was formed by the in situ generated hypobromous acid. The α-bromotoluene underwent an intermolecular nucleophilic substitution reaction with aromatic carboxylic acids present in the reaction mixture to afford the corresponding esters.

Full text of DOI:10.1016/S0040-4020(03)00812-3

Tetrahedron 59 (2003) 5549–5554
An expedient esterification of aromatic carboxylic acids using
sodium bromate and sodium hydrogen sulfite
*
Khalid Mohammed Khan, Ghulam Murtaza Maharvi, Safdar Hayat, Zia-Ullah,
M. Iqbal Choudhary and Atta-ur-Rahman
International Center for Chemical Sciences, H.E.J. Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan
Received 5 November 2002; revised 28 April 2003; accepted 22 May 2003
Abstract—Treatment of aromatic carboxylic acids and substituted toluenes with a mixture of sodium bromate and sodium hydrogen sulfite
in a two-phase system gave the corresponding esters in good yield. The intermediate a-brominated toluene was formed by the in situ
generated hypobromous acid. The a-bromotoluene underwent an intermolecular nucleophilic substitution reaction with aromatic carboxylic
acids present in the reaction mixture to afford the corresponding esters. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
also reported. More recently, we have reported the
conversion of o-alkylbenzoic acids into the corresponding
g-lactones by using this reagent.20 In continuation of our
study to extend the scope of the NaBrO3/NaHSO3 reagent in
organic synthesis, we have found that the conversion of
aromatic carboxylic acids with substituted toluenes into its
corresponding esters can proceed using the NaBrO3/
NaHSO3 reagent. To the best of our knowledge this is the
first report of a one pot direct conversion of alkylbenzenes to
the corresponding esters at room temperature.
Esterification of carboxylic acids by reaction with alkyl
halides is a fundamental transformation in synthetic organic
and medicinal chemistry.1–3 Potassium and cesium salts are
effectively used for this purpose.4 Clark et al. in their
extensive studies, revealed KF to be effective, but
unfortunately the reaction usually requires high tempera-
tures (110–130 8C).4,5 Carboxylic esters have also been
employed as key intermediates for the synthesis of a number
of natural products.6 Therefore, the synthesis of carboxylic
esters is a very important transformation in organic
chemistry. A number of reports7–13 have been published
to achieve this conversion, however, some of these require
expensive reagents and tedious reaction work-up. More
recently, the esterification of carboxylic acids with alkyl
halides has been accomplished by employing CsF-Celite/
CH3CN.14
2. Results and discussion
The NaBrO3/NaHSO3 reagent system appears to be most
reactive, versatile, selective and useful for the conversion of
aromatic carboxylic acids to their corresponding esters
without affecting other susceptible functionalities.
The present study describes a convenient and efficient one
pot method for the esterification of substituted aromatic
carboxylic acids with substituted toluenes by using the
NaBrO3/NaHSO3 reagent at ambient temperature under a
two-phase system.
In a typical experiment, to a two-phase system comprised of
a solution of benzoic acid (1a) and toluene (2a) in ethyl
acetate and aqueous NaBrO3 (3 equiv.), aqueous NaHSO3
(3 equiv.) was added over a period of about 15 min and
stirred at room temperature for 40 h. The benzylbenzoate
(3a) was obtained in 95% yield. However, the increase in
reaction time from 40 to 60 h produced little increase in
yield of product 3a (from 95 to 99%). The yields using this
two-phase system are generally higher than in a homo-
genous solution in acetonitrile, where 3a is obtained only in
a yield of 28%. Using the above procedure, the esters shown
in Scheme 1 were prepared in very high yield.
The chemistry of the NaBrO3/NaHSO3 reagent has been
widely studied. It can serve as an effective bromohydroxyl-
ation reagent and can react with olefins,15 alkynes and
allylic alcohols.16 The oxidation of primary alcohols,17
diols, ethers18 and a-bromination of alkyl benzenes19 was
Keywords: aromatic carboxylic acids; substituted toluene; sodium bromate;
sodium hydrogen sulfite; esters.
The versatility of the reaction was demonstrated by its
application to a wide range of structurally different aromatic
carboxylic acids 1a–1j. The reaction of 1b with an alkyl
*
Corresponding author. Tel.: þ92-21-924-3227; fax: þ92-21-924 3190-
91; e-mail: hassaan2@super.net.pk
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00812-3

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K. M. Khan et al. / Tetrahedron 59 (2003) 5549–5554
Scheme 1.
benzene such as toluene (2a) or 3-ethoxytoluene (2b) using
NaBrO3/NaHSO3 in ethyl acetate/water at room tempera-
ture, led to the formation of the 3b and 3l in excellent yields
(90 and 82%), respectively. Similarly, 4-hydroxybenzoic
acid (1c) was converted with toluene (2a) and 3-ethoxy-
toluene (2b) into 3c and 3m in good yields (85 and 84%),
respectively. Furthermore, 2-nitrobenzoic acid (1d), 3,4,5-
trimethoxybenzoic acid (1e) and 4-methoxybenzoic acid
(1f) were reacted with toluene (2a) using NaBrO3/NaHSO3
reagent under a two-phase system to form the corresponding
3d,3e and 3f products by this procedure in satisfactory
yields. The compounds 1d,1e and 1f were also treated with

K. M. Khan et al. / Tetrahedron 59 (2003) 5549–5554
5551
3-ethoxytoluene (2b) using this reagent under two-phase
system (method A) in ethyl acetate/water for 40 h to obtain
compounds 3n, 3o and 3p, respectively.
3. Conclusion
The convenient, efficient, simple, highly selective and high
yielding esterification of aromatic carboxylic acids with
toluene using NaBrO3/NaHSO3 reagent under two-phase
system at ambient temperature, described in this paper,
serves as a useful synthetic tool to obtain valuable esters.
Products obtained were pure in most cases with no C-, S- or
N-alkylation or quaternary salt formation being detected.
The reaction protocol described is promising in the sense
that it offers an easy access to ester structures which
frequently occur in natural products.
The compounds 1g–1j, which are not sufficiently soluble in
ethyl acetate, gave under these conditions, the esters in
lower yield 17–18%. However, when these reactions were
carried out under homogeneous conditions (method B)
using CH3CN as a solvent the corresponding esters were
obtained in 61–68% yields, which indicates the versatility
of the reagent. On the basis of these results, nicotinic acid
(1g) and isonicotinic acid (1h) were treated with toluene
(2a) in the presence of NaBrO3/NaHSO3 reagent under
homogeneous conditions using acetonitrile as the solvent to
form compounds 3g and 3h, respectively. Similarly, the
reaction of 1g and 1h with 3-ethoxytoluene (2b) gave 3q
and 3r products in satisfactory yields. Moreover, benzyl
2-thiophenecarboxylate (3i) and benzyl 2-naphthoate (3j)
were synthesized by treatment of toluene (2a) in acetonitrile
with 1i and 1j, respectively in the presence of NaBrO3/
NaHSO3 reagent. The synthesis of 3s and 3t were also
accomplished by the treatment of 3-ethoxytoluene (2b) with
1i and 1j respectively using NaBrO3/NaHSO3 reagent
under homogeneous conditions in satisfactory yield (68
and 66%). The results and spectroscopic data of the all
esters were collected in Section 4. The reaction was found to
be highly selective as only aromatic carboxylic acids are
converted to esters in moderate to high yield, whereas
aliphatic carboxylic acids did not yield esters even after
four days stirring in CH3CN at room temperature
(Scheme 2). The chemoselectivity of this reagent
system has been illustrated in the case of 1c, where the
carboxylic acid group alone has been converted to its ester
form 3c and 3m without effecting OH group present in the
molecule.
4. Experimental
4.1. General
Ultraviolet spectra were recorded in methanol on a Hitachi
U-3200 spectrophotometer. Infrared (IR) spectra were
measured on a Shimadzu IR 460 spectrophotometer in
CHCl3. Electron impact mass spectra were determined with
a Finnigan MAT-312 or Varian MAT-112 double focusing
mass spectrophotometer connected to a PDP 11/34 (DEC)
computer system. Elemental analyses were carried out on a
Perkin–Elmer 2400 CHN Elemental Analyzer. The 1H
NMR spectra were recorded in CDCl3 or CD3OD with
Bruker AM 400 spectrophotometers operating at 400 MHz.
1H NMR chemical shifts are reported in d (ppm) and
coupling constants in Hz. Reactions were monitored by
TLC using silica gel type 60F254 of E. Merck for preparing
TLC plates and visualized with ultra violet light at 254 and
366 nm and spraying with iodine vapors.
4.2. Materials
NaBrO3/NaHSO3 present in aqueous phase in situ
generates HOBr which delivers a Br-radical in the
aqueous solution19 and the radical moves to the ethyl
acetate phase, where 1 and 2 are dissolved, subsequently by
intermolecular nucleophilic attack, the esters 3 form
(Scheme 1).
All substituted benzoic acids, toluene (2a) and 3-ethoxy-
toluene (2b) are commercially available (Fluka, Aldrich).
All reagents NaBrO3, NaHSO3, Na2S2O3 and MgSO4 are
also available from Aldrich. The acetonitrile, ethyl acetate
and diethyl ether were purchased from Merck and used
without purification.
The advantages of NaBrO3/NaHSO3 method over other
existing procedures for this transformation are: (1) It is a
direct one pot method of esterification of aromatic
carboxylic acids by reaction with substituted toluenes. (2)
The reaction takes place at room temperature. (3) In situ
generation of arylhalides takes place, so it may be a useful
method for preparation of those aryl halides which may
unstable.2,10,14
4.3. General procedure for the preparation of 3a-3t
Method A. To a solution of 1 (1 mmol) and substituted
toluene 2 (1 mmol) in ethyl acetate (5 mL) was added a
solution of NaBrO3 (3 mmol) in H2O (3 mL). To this
mixture NaHSO3 (3 mmol) in H2O (6 mL) during a period
of 15 min was added and the mixture was stirred at room
temperature for 40 h. The mixture was extracted with
Scheme 2.

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K. M. Khan et al. / Tetrahedron 59 (2003) 5549–5554
diethyl ether (25£3 mL). Then the combined organic
layer was washed with aqueous Na2S2O3 and dried over
MgSO4. After filtration, the solvent was evaporated (under
vacuum) to leave the crude material. The crude product was
purified by column chromatography over silica gel using
n-hexane/ethyl acetate (9:1) as an eluent to afford pure
esters 3.
s, ArCH2); m/z 302 (25Mþ), 211 (100), 195 (43), 167 (32),
287 (9), 27 (7), 91 (15), 74 (19), 54 (8%).
4.3.6. Benzyl 4-methoxybenzoate (3f).23,25 Yield: 0.19 g
(80%); oily compound; [Found: C, 74.41; H, 5.78.
C15H14O3 requires C, 74.36; H, 5.82%]; Rf¼0.61 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 267 (1¼4.56) nm; nmax
(CHCl3) 3028, 2916, 2824, 1721, 1493, 1128, 764,
684 cm21; dH (400 MHz, CDCl3) 7.79 (2H, d, J¼8.1 Hz,
H-2/H-6), 7.27–7.05 (5H, m, Ar-H), 6.81 (2H, d, J¼8.1 Hz,
H-3/H-5), 5.31 (2H, s, ArCH2), 3.83 (3H, s, OCH3); m/z 242
(41Mþ), 151 (100), 135 (56), 107 (31), 91 (23), 76 (9), 54
(8%).
Method B. To a solution of 1 (1 mmol) and substituted
toluene 2 (1 mmol) in acetonitrile (10 mL) was added a
solution of NaBrO3 (3 mmol) in H2O (6 mL). To this
mixture NaHSO3 (3 mmol) in H2O (12 mL) during a period
of 15 min was added and the mixture was stirred at ambient
temperature for 40 h. The product was worked up as
described above.
4.3.7. Benzyl nicotinate (3g).26 Yield: 0.12 g (61%); oily
compound; [Found: C, 73.27; H, 5.16; N, 6.61. C13H11NO2
requires C, 73.22; H, 5.20; N, 6.57%]; Rf¼0.51 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 265 (1¼4.73) nm; nmax
(CHCl3) 3011, 2925, 1719, 1487, 1311, 1135, 829 cm21; dH
(400 MHz, CD3OD) 9.19–7.83 (4H, m, pyridine-H), 7.48–
7.16 (5H, m, Ar-H), 5.36 (2H, s, ArCH2); m/z: 213 (43Mþ),
122 (100), 106 (21), 91 (17), 78 (19), 55 (9%).
4.3.1. Benzyl benzoate (3a).21,23,25 Yield: 0.20 g (95%);
oily compound; [Found: C, 79.29; H, 5.66. C14H12O2
requires C, 79.22; H, 5.70%] Rf¼0.69 (hexane/ethyl acetate,
5:2); lmax (MeOH) 256 (1¼3.92) nm; nmax (CHCl3) 2913,
1721, 1135, 1083, 761, 663 cm21; dH (400 MHz, CDCl3)
7.92–7.49 (5H, m, Ar-H), 7.45–7.19 (5H, m, Ar-H), 5.31
(2H, s, ArCH2); m/z 212 (28Mþ), 121 (100), 105 (32), 91
(52), 77 (19), 56 (11%).
4.3.8. Benzyl isonicotinate (3h).26,27 Yield: 0.13 g (61%);
oily compound; [Found: C, 73.29; H, 5.17; N, 6.55.
C13H11NO2 requires C, 73.22; H, 5.20; N, 6.57%];
Rf¼0.53 (hexane/ethyl acetate, 5:2); lmax (MeOH) 258
(1¼4.16) nm; nmax (CHCl3) 3013, 2926, 1724, 1496, 1315,
1136, 832 cm21; dH (400 MHz, CD3OD) 8.91 (2H, d,
J¼8.4 Hz, H-2/H-6), 7.92 (2H, d, J¼8.4 Hz, H-3/H-5),
7.47–7.15 (5H, m, Ar-H), 5.35 (2H, s, ArCH2); m/z 213
(39Mþ), 122 (100), 106 (23), 91 (19), 77 (18), 56 (11%).
4.3.2. Benzyl 4-bromobenzoate (3b).22,24 Yield: 0.26 g
(90%); oily compound; [Found: C, 57.81; H, 3.77; Br,
27.53. C14H11BrO2 requires C, 57.76; H, 3.81; Br, 27.45%];
Rf¼0.65 (hexane/ethyl acetate, 5:2); lmax (MeOH) 257
(1¼3.97) nm; nmax (CHCl3) 2898, 1723, 1248, 1145, 836,
745, 663 cm21; dH (400 MHz, CDCl3) 7.96 (2H, d,
J¼8.1 Hz, H-2/H-6), 7.49 (2H, d, J¼8.1 Hz, H-3/H-5),
7.41–7.13 (5H, m, Ar-H), 5.34 (2H, s, ArCH2); m/z 293
(19Mþþ2), 291 (21Mþ), 211 (11), 200 (100), 184 (31), 156
(13), 91 (25), 76 (21), 55 (12%).
4.3.9. Benzyl 2-thiophenecarboxylate (3i). Yield: 0.14 g
(63%); oily compound; [Found: C, 66.07; H, 4.67; S, 14.62.
C12H10O2S requires C, 66.03; H, 4.62; S, 14.69%]; Rf¼0.55
(hexane/ethyl acetate, 5:2); lmax (MeOH) 244 (1¼3.87) nm;
nmax (CHCl3) 3015, 2861, 1721, 1256, 1035, 811,
648 cm21; dH (400 MHz, CDCl3) 7.08–6.79 (3H, m,
thiophene-H), 7.46–7.16 (5H, m, Ar-H), 5.27 (2H, s,
ArCH2); m/z 218 (33Mþ), 127 (100), 111 (21), 91 (19), 83
(25), 46 (9%).
4.3.3. Benzyl 4-hydroxybenzoate (3c).21,23 Yield: 0.19 g
(85%); oily compound; [Found: C, 73.72; H, 5.36.
C14H12O3 requires C, 73.67; H, 5.30%]; Rf¼0.59 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 261 (1¼4.32) nm; nmax
(CHCl3) 3311, 2906, 1721, 1156, 1047, 834, 732 cm21; dH
(400 MHz, CDCl3) 7.89 (2H, d, J¼8.3 Hz, H-2/H-6), 6.83
(2H, d, J¼8.3 Hz, H-3/H-5), 7.39–7.16 (5H, m, Ar-H), 5.29
(2H, s, ArCH2); m/z 228 (18Mþ), 211 (8), 137 (100), 121
(41), 93 (12), 91 (31), 75 (17), 55 (9%).
4.3.10. Benzyl 2-naphthoate (3j).25,28 Yield: 0.17 g (65%);
oily compound; [Found: C, 82.46; H 5.33. C18H14O2
requires C, 82.42; H, 5.38%]; Rf¼0.56 (hexane/ethyl
acetate, 5:2); lmax (MeOH) 272 (1¼4.69) nm; nmax
4.3.4. Benzyl 2-nitrobenzoate (3d).23 Yield: 0.21 g (81%);
oily compound; [Found: C, 65.31; H, 4.36; N, 5.49.
C14H11NO4 requires C, 65.37; H, 4.31; N, 5.44%];
Rf¼0.67 (hexane/ethyl acetate, 5:2); lmax (MeOH) 263
(1¼4.35) nm; nmax (CHCl3) 2905, 1719, 1585, 1210, 1055,
735, 665 cm21; dH (400 MHz, CDCl3) 8.12–7.56 (4H, m,
Ar-H), 7.45–7.18 (5H, m, Ar-H), 5.32 (2H, s, ArCH2); m/z
257 (31Mþ), 211 (11), 166 (100), 150 (17), 122 (31), 91
(15), 76 (22), 54 (9), 46 (8%).
(CHCl3) 2895, 1719, 1408, 1263, 1134, 732, 678 cm21
;
dH (400 MHz, CD3OD) 8.51–7.76 (7H, m, naphthol-H),
7.45–7.18 (5H, m, Ar-H), 5.33 (2H, s, ArCH2); m/z 262
(34Mþ), 171 (100), 155 (21), 127 (24), 91 (18), 76 (9), 75
(14), 52 (13%).
4.3.11. 3-Ethoxy benzylbenzoate (3k). Yield: 0.22 g
(88%); oily compound; [Found: C, 74.93; H, 6.33.
C16H16O3 requires C, 74.98; H, 6.29%]; Rf¼0.75 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 254 (1¼3.91) nm; nmax
(CHCl3) 2913, 1722, 1138, 1083, 763, 662 cm21; dH
(400 MHz, CDCl3) 7.92–7.45 (5H, m, Ar-H), 7.34–6.76
(4H, m, Ar-H), 5.33 (2H, s, ArCH2), 3.82 (2H, q, J¼7.4 Hz,
CH2), 1.31 (3H, t, J¼7.4 Hz, CH3); m/z 256 (23Mþ), 227
(14), 211 (21), 122 (100), 105 (31), 91 (43), 77 (17), 56
(9%).
4.3.5. Benzyl 3,4,5-trimethoxybenzoate (3e).24 Yield:
0.26 g (86%); oily compound; [Found: C, 67.59; H, 5.95.
C17H18O5 requires C, 67.54; H, 6.00%]; Rf¼0.68 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 263 (1¼4.58) nm; nmax
(CHCl3) 2892, 1723, 1411, 1144, 1026, 818, 742 cm21; dH
(400 MHz, CDCl3) 7.56–7.21 (5H, m, Ar-H), 7.09 (2H, s,
Ar-H), 3.85 (6H, s, 2OCH3), 3.81 (3H, s, OCH3), 5.28 (2H,

K. M. Khan et al. / Tetrahedron 59 (2003) 5549–5554
5553
4.3.12. 3-Ethoxybenzyl 4-bromobenzoate (3l). Yield:
0.27 g (82%); oily compound; [Found: C, 57.37; H, 4.56;
Br, 23.79. C16H15BrO3 requires C, 57.33; H, 4.51; Br,
23.84%]; Rf¼0.72 (hexane/ethyl acetate, 5:2); lmax
(MeOH) 259 (1¼3.99) nm; nmax (CHCl3) 2889, 1721,
1241, 1146, 837, 746, 661 cm21; dH (400 MHz, CDCl3)
7.93 (2H, d, J¼8.4 Hz, H-2/H-6), 7.41 (2H, d, J¼8.4 Hz,
H-3/H-5), 7.31–6.67 (4H, m, Ar-H), 5.31 (2H, s, ArCH2),
3.79 (2H, q, J¼7.5 Hz, CH2), 1.29 (3H, t, J¼7.5 Hz, CH3);
m/z 337 (18Mþ þ 2), 335 (19Mþ), 306 (21), 290 (16), 201
(100), 184 (32), 156 (15), 91 (43), 76 (13), 55 (9%).
1135, 829 cm21; dH (400 MHz, CD3OD) 9.19–7.91 (4H, m,
pyridine-H), 7.35–6.78 (4H, m, Ar-H), 5.35 (2H, s, ArCH2),
3.81 (2H, q, J¼7.4 Hz, CH2), 1.31 (3H, t, J¼7.4 Hz, CH3);
m/z 257 (38Mþ), 228 (23), 212 (34), 123 (100), 106 (25), 91
(19), 78 (11), 55 (9%).
4.3.18. 3-Ethoxybenzyl isonicotinate (3r). Yield: 0.17 g
(65%); oily compound; [Found: C, 70.07; H, 5.83; N, 5.41.
C15H15NO3 requires C, 70.02; H, 5.88; N, 5.44%]; Rf¼0.63
(hexane/ethyl acetate, 5:2); lmax (MeOH) 254 (1¼4.09) nm;
nmax (CHCl3) 3011, 2921, 1716, 1479, 1311, 1138,
827 cm21; dH (400 MHz, CD3OD) 8.89 (2H, d, J¼8.5 Hz,
H-2/H-6), 7.93 (2H, d, J¼8.5 Hz, H-3/H-5), 7.36–6.79 (4H,
m, Ar-H), 5.37 (2H, s, ArCH2), 3.84 (2H, q, J¼7.6 Hz,
CH2), 1.34 (3H, t, J¼7.6 Hz, CH3); m/z 257 (41Mþ), 228
(19), 212 (31), 123 (100), 106 (25), 91 (16), 77 (17), 56
(9%).
4.3.13. 3-Ethoxybenzyl 4-hydroxybenzoate (3m). Yield:
0.23 g (84%); oily compound; [Found: C, 70.61; H, 5.88.
C16H16O4 requires C, 70.57; H, 5.92%]; Rf¼0.66 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 261 (1¼4.42) nm; nmax
(CHCl3) 3315, 2909, 1719, 1151, 1048, 835, 731 cm21; dH
(400 MHz, CDCl3) 7.85 (2H, d, J¼7.9 Hz, H-2/H-6), 6.83
(2H, d, J¼7.9 Hz, H-3/H-5), 7.39–6.72 (4H, m, Ar-H), 5.28
(2H, s, ArCH2), 3.83 (2H, q, J¼7.6 Hz, CH2), 1.31 (3H, t,
J¼7.6 Hz, CH3); m/z 272 (24Mþ), 243 (35), 227 (21), 138
(100), 121 (43), 93 (15), 91 (27), 75 (11), 55 (8%).
4.3.19. 3-Ethoxybenzyl 2-thiophenecarboxylate (3s).
Yield: 0.18 g (68%); oily compound; [Found: C, 64.15; H,
5.32; S, 12.25. C14H14O3S requires C, 64.10; H, 5.38; S,
12.22%]; Rf¼0.61 (hexane/ethyl acetate, 5:2); lmax
(MeOH) 239 (1¼3.91) nm; nmax (CHCl3) 3021, 2893,
1721, 1251, 1037, 811, 649 cm21; dH (400 MHz, CDCl3)
7.06–6.84 (3H, m, thiophene-H), 7.35–6.78 (4H, m, Ar-H),
5.29 (2H, s, ArCH2), 3.79 (2H, q, J¼7.1 Hz, CH2), 1.29 (3H,
t, J¼7.1 Hz, CH3); m/z 262 (35Mþ), 233 (21), 217 (19), 128
(100), 111 (22), 91 (9), 83 (21), 46 (11%).
4.3.14. 3-Ethoxybenzyl 2-nitrobenzoate (3n). Yield:
0.25 g (83%); oily compound; [Found: C, 63.76; H, 5.07;
N, 4.61. C16H15NO4 requires C, 63.78; H, 5.02; N, 4.65%];
Rf¼0.73 (hexane/ethyl acetate, 5:2); lmax (MeOH) 266
(1¼4.35) nm; nmax (CHCl3) 2909, 1721, 1588, 1211, 1056,
741, 665 cm21; dH (400 MHz, CDCl3) 8.15–7.52 (4H, m,
Ar-H), 7.35–6.73 (4H, m, Ar-H), 5.31 (2H, s, ArCH2), 3.84
(2H, q, J¼7.3 Hz, CH2), 1.33 (3H, t, J¼7.3 Hz, CH3); m/z
301 (23Mþ), 272 (16), 256 (13), 167 (100), 150 (21), 122
(33), 91 (14), 76 (9), 54 (8), 46 (11%).
4.3.20. 3-Ethoxybenzyl 2-naphthoate (3t). Yield: 0.20 g
(66%); oily compound; [Found: C, 74.45; H, 5.88.
C20H18O3 requires C, 74.41; H, 5.92%]; Rf¼0.63 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 281 (1¼5.11) nm; nmax
(CHCl3) 2896, 1724, 1411, 1261, 1134, 737, 672 cm21; dH
(400 MHz, CD3OD) 8.79–7.76 (7H, m, naphthol-H), 7.38–
6.76 (4H, m, Ar-H), 5.34 (2H, s, ArCH2), 3.81 (2H, q,
J¼7.3 Hz, CH2), 1.32 (3H, t, J¼7.3 Hz, CH3); m/z 306
(41Mþ), 277 (17), 261 (11), 172 (100), 159 (19), 127 (23),
91 (14), 76 (11), 75 (9), 52 (14%).
4.3.15. 3-Ethoxybenzyl 3,4,5-trimethoxybenzoate (3o).
Yield: 0.29 g (83%); oily compound; [Found: C, 65.92; H,
6.35. C19H22O6 requires C, 65.88; H, 6.40%]; Rf¼0.74
(hexane/ethyl acetate, 5:2); lmax (MeOH) 269 (1¼4.64) nm;
nmax (CHCl3) 2899, 1725, 1416, 1145, 1036, 816,
739 cm21; dH (400 MHz, CDCl3) 7.41–6.76 (4H, m, Ar-
H), 7.11 (2H, s, Ar-H), 5.29 (2H, s, Ar-CH2), 3.84 (6H, s,
2OCH3), 3.82 (3H, s, OCH3), 3.79 (2H, q, J¼7.5 Hz, CH2),
1.31 (3H, t, J¼7.5 Hz, CH3); m/z 346 (34Mþ), 317 (11), 301
(19), 212 (100), 195 (45), 167 (33), 287 (9), 271 (6), 91 (14),
74 (21), 54 (11%).
Acknowledgements
Dr K. M. Khan would like to acknowledge Third World
Academy of Sciences (TWAS), Italy, for financial
assistance grant no. 01-310 RG/CHE/AS.
4.3.16. 3-Ethoxybenzyl 4-methoxybenzoate (3p). Yield:
0.24 g (84%); oily compound; [Found: C, 71.38; H, 6.29.
C17H18O4 requires C, 71.31; H, 6.34%]; Rf¼0.71 (hexane/
ethyl acetate, 5:2); lmax (MeOH) 273 (1¼5.04) nm; nmax
(CHCl3) 3031, 2917, 2825, 1722, 1492, 1131, 765,
683 cm21; dH (400 MHz, CDCl3) 7.68 (2H, d, J¼7.7 Hz,
H-2/H-6), 7.27–6.84 (4H, m, Ar-H), 6.79 (2H, d, J¼7.7 Hz,
H-3/H-5), 5.33 (2H, s, ArCH2), 3.85 (3H, s, OCH3), 3.82
(2H, q, J¼7.5 Hz, CH2), 1.34 (3H, t, J¼7.5 Hz, CH3); m/z
286 (41Mþ), 257 (19), 241 (31), 151 (100), 135 (51), 107
(27), 91 (21), 76 (9), 54 (14%).
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