Amberlyst-15 catalysed oxidative esterification of aldehydes using a H2O2 trapped oxidant as a terminal oxidant

Article abstract of DOI:10.1039/c6nj03831j

A simple and efficient method has been developed for the selective oxidative esterification of aldehydes using commercially available Amberlyst-15 as a catalyst. H₂O₂ released from a clathrate structured 4Na₂SO₄·2H₂O₂·NaCl oxidant serves as an efficient source of terminal oxidants. Various aromatic, heteroaromatic, and aliphatic aldehydes undergo selective esterification to give good to excellent yield. The heterogeneous catalyst, Amberlyst-15, exhibits high reactivity and can be recycled over several runs. The 4Na₂SO₄·2H₂O₂·NaCl oxidant was found to be superior to commonly used oxidizing agents providing an anhydrous, easy to handle and stable form of H₂O₂

Full text of DOI:10.1039/c6nj03831j

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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NEW JOURNAL OF CHEMISTRY
ARTICLE
Amberlyst-15 catalysed oxidative esterification of aldehydes using
H O trapped Oxidant as terminal oxidant
2
2
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
Eknath M. Gayakwad , Vilas V. Patil , and Ganapati S. Shankarling *
DOI: 10.1039/x0xx00000x
Abstract
www.rsc.org/
A simple efficient method has been developed for the selective oxidative esterification of aldehyde using commercially
2 2 2 4 2 2
available Amberlyst-15 as a catalyst. The H O released from clathrate structured 4Na SO .2H O .NaCl oxidant serves as an
efficient source of terminal oxidant. Various aromatic, heteroaromatic, and aliphatic aldehydes undergo selective
esterification to give good to excellent yield. The heterogeneous catalyst, Amberlyst-15 exhibit high reactivity and can be
2 4 2 2
recycled over several runs. The 4Na SO .2H O .NaCl oxidant was found to be superior to commonly used oxidizing agents
providing anhydrous, eassily handled and stable form of H
2
2
O .
3
3
3
TEMPO-TBAB, In(TfO) with Oxone , sodium perborate, and
3
4
Introduction
2 2 2
sodium percarbonate , and [IrCl(Cod)] and [CpIrCl ] /MAE
35
1
Esters are important compounds because of their fragrances ,
with acetone as hydrogen acceptor under basic conditions .
Although, most of the above protocols offer good yield with
good TON, reaction suffer certain shortcomings such as use of
toxic and costly transition metal catalysts, required longer
2
biological activities , and readily conversion to other useful
3
classes of compounds Due to such versatile characteristics,
esters are considered as a compound of prime importance in
2
8,29,36–38
4
5
6,7
reaction time (12 to 24 h)
and higher temperature
perfumery , chemical, polymer , medicinal and many more
fields. The conventional esterification process involves
nucleophilic acyl substitution reaction of alcohol with acid in
(
100-120 °C), use of magnesium sulphate as a dehydrating
39
agent for selective esterification and excess use of oxidants.
Aerobic oxidation serves as an environmentally benign as
8
9
the presence of dehydrating agents , or with activated form
1
of acid such as acid chloride
0–12
13
and acid anhydride . The pre-
well as efficient alternative utilizing molecular O
or air along
2
40
with metal catalysts such as gold on oxide support , CoNP,
functionalization of the acids leads to addition of extra steps
and use of additional reagents that in turn affects the yield and
1
economy of the process .
4
1
Pd/C under microwave irradiation . But the reaction requires
to be performed under O pressure with high temperature and
longer reaction time. Thus, as continuation of our work to
4
2
The oxidative esterification of aldehyde offers a potentially
useful alternative for the synthesis of ester functionality. This
transformation was performed by various oxidizing agents
4
2–45
develop mild and selective oxidation protocols
herein we
report an efficient, transition metal free approach for selective
oxidative esterification of aldehydes by using Amberlyst-15 as
catalyst. The oxidizing agent reported is clathrate structure
1
5
16
17
such as PhI(OAc),-I
2 3 2 2 3
, [Bmim]N , TsNBr -K CO . The use of
oxidant with transition metal catalyst was also employed for
4
6
adduct of H O prepared from non-toxic, easily available,
2
2
oxidative esterification for instance, use of H
2
O
2
with various
4
7
1
8
inexpensive Na
2
SO and NaCl . The 4Na SO .2H O .NaCl is
4 2 4 2 2
catalysts
phosphotungstates (PW12
pyridine dichromate, methyltrioxorhenium
such
as
Mn-phthalocyanine ,
anchored
20
1
9
neutral in nature, easy to prepare as well as handle, stable at
room temperature and provides anhydrous condition to the
3
) /MCM-41 , manganese oxide ,
2
1,22
, supported iron
, nickel , rhodium , and Ag catalysts. The other
2
3,24
25
26
reaction medium. On other hand, Amberlyst-15 is
sulfonated, crosslinked polystyrene resin, available
commercially and exhibits good catalytic activity and
a
oxide
protocols used are Amberlyst-15 with m-CPBA and DBU ,
27
2
potassium iodide , (ClO
8
29
4 2 3
) and InBr , Cu-quinolate with
4
8
3
tetra-butyl ammonium bromide , and copper bromide with
0
recyclability .
3
1
tert-Butyl hydroperoxide , peroxovanadium with
32
H
2
O
2
,
Result and discussion
Benzaldehyde 1a was selected as key substrate to investigate
the reaction conditions for the oxidative transformation of
aldehyde to ester. The effect of various reaction parameters
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ARTICLE
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were examined for oxidative esterification of 1a (Table 1). The oxidative esterification reaction proceeds through
5
1–53
2 4 2 2
Initially, optimization of 4Na SO .2H O .NaCl oxidant was done
hemiacetal formation
which further undergo oxidation in
by taking 1a (0.94 mmol), Amberlyst-15 (20% w/w) in
methanolic medium (2 mL) under reflux conditions at 70 °C
(Table 1, entries 1-4). The oxidant equivalent study
demonstrated that the maximum yield of 90% was obtained
for 3a when 1.5 equivalents of oxidant were used in 4 h (Table
1, entry 3). The reaction temperature optimization study
shows that rate of reaction increases as we increase the
reaction temperature from room temperature to 70 °C (Table
presence of oxidizing agent to yield ester. The presence of
water in this reaction is detrimental towards ester
39 54
formation , . If Water is present in the system reverts back
the unstable intermediate hemiacetal to starting aldehyde.
Hence it is essentially important to remove the already present
or water that is formed during the course of reaction to
accelerate the reaction in forward direction. The adduct used
1
, entries 5-7). Further increase in the temperature had no here provides anhydrous form of oxidant, additionally it
significant effect on the yield of 3a as well as reaction time comprises of a dehydrating agent i.e. sodium sulphate which
(
Table 1, entry 8). The influence of catalyst loading on reaction takes care of the water formed during the reaction. Further,
4
6
rate and yield of 3a was investigated by varying catalyst
loading from 15% (w/w) to 22.5% (w/w) (Table 1, entries 9-11).
When 15% of Amberlyst-15 was used, only 59% yield of 3a was
obtained in 10 h (Table 1, entry 9), whereas increasing the
Amberlyst-15 loading to 22.5% (w/w) gives 88% yield of 3a in 4
h (Table 1, entry 11). When the reaction was performed in the
absence of Amberlyst-15, only 28% yield of 3a was obtained in
2 2
the adduct has a clathrate structure in which H O is trapped
that prevents its decomposition at higher temperature. Thus
the overall combined effect results in higher esters selectivity
with good yields.
a
Table-1 Optimization of reaction parameters
10 h (Table 1, entry 12).
Investigation of effect of other sulphonic acid containing
catalysts such as Amberlite IR-120, sulphated zirconia, Indion-
130, sulphated tungstate, and p-toluene sulphonic acid (PTSA)
on oxidative esterification of 1a under optimized conditions
showed poor to moderate yield of 3a in 10 h (Table 2, entries
Catalyst
conc.
%,
Isolated
yield
%)
Oxidant
equiv.
Time
(h)
Temp
(°C)
1-6). The lowest yield of 47% was obtained for Amberlite IR-
Entry
Catalyst
(
(
120 whereas for PTSA 73% yield of 3a was obtained in 10 h.
w/w)
Oxidant equivalent study
This confirmed that the Amberlyst-15 plays vital role in
enhancing the reaction rate as well as yield of 3a. Thus, the
reaction parameters were finalized as oxidant (1.5 equiv),
Amberlyst-15 (20%, w/w) at 70 °C temperature.
Amberlyst-
1
20
0.5
10
70
64
15
2
3
20
20
20
1
1.5
2
10
4
4
70
70
70
81
90
91
We have also calculated acidic sites for all the catalysts studied
here (except P-Toluene sulphonic acid) that corresponds to
acidic sites available with 20% w/w of Amberlyst-15 (Table 2,
entries 1-6). The reactions were performed by taking those
quantities of the catalysts. The results obtained are
summarized in Table 2. After performing reaction with new
quantities of catalyst loading the yield of 3a was found to be
increased in all the cases. In the case of Amberlite-IR and
Indion-130 moderate yield was obtained for 3a. It is noticeable
4
Temperature study
Amberlyst-
5
20
1.5
10
30-32
33
15
6
7
8
20
20
20
1.5
1.5
1.5
10
10
4
50
60
80
57
76
89
Catalyst equivalent study
Amberlyst-
9
15
1.5
10
70
59
15
4
9
10
17.5
22.5
1.5
1.5
10
4
70
70
77
88
that in the case of Sulphated zirconia and Sulphated
1
1
5
0
tungstate comparative yields were obtained but due to the
lower active sites, excess catalyst is required. Additionally,
reaction requires more time to get respective yields. Thus,
from these results it is confirmed that the catalyst Amberlyst-
No
Catalyst
1
2
-
1.5
10
70
28
a
Reaction conditions: 1a (0.94 mmol, 1 equiv), methanol: 2 mL; RT: room
temperature.
15 is superior over other catalysts for the present work.
a
Table-2 Study with other catalysts
In order to investigate the efficacy of oxidant, oxidative
esterification of 1a was performed by using other oxidizing
agents (Table 3, entries 1-7). It was noticeable that, with 50%
H O , sodium perborate, and sodium percarbonate traces of
Entry
Catalyst
Active
sites
Oxidant
eq.
Temp
( C)
Time
(h)
Isolated Yield
(Base on)
o
(
mmol/g)
2
2
20
Active
%w/w
sites
3a
formation was observed in 10 h (Table 3, entries 1-3).
Whereas, Oxone gives moderate yield of 3a in 10 h (Table 3,
entry 4). In case of, urea hydrogen peroxide (UHP), m-CPBA,
and 70%
Amberlite IR-
1
4.4
1.5
70
10
47
58
1
20
b
Sulphated
Zirconia
Indion- 130
Sulphated
tungstate
PTSA
2
2.07
4.8
0.65
-
1.5
1.5
1.5
1.5
70
70
70
70
10
10
10
10
56
70
69
73
82
72
87
69
tert-utyl hydrogen peroxide (TBHP) poor yield of 3a was
obtained in 10 h (Table 3, entries 5-7).
3
b
4
5
2
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6
Amberlyst-15
4.7
1.5
70
4
90
90
a
Reaction conditions: 1a: (0.94 mmol, 1 equiv); Oxidant: (1.5 equiv), Methanol: 2
b
a
mL,Temperature: 70 °C,PTSA : p-toluene sulphonic acid; Acids sites are
determined by potentiometric titration.
Table-4 Substrate scope
a
Table-3 Comparison with other oxidizing agents
Time
h)
Isolated
Yield (%)
Entry
Substrate
Product
(
Catalyst
conc.
Oxidizing
agent
Oxidant
equiv
Time
(h)
Temp
( °C)
Isolated
yield (%)
Entry
(
%,w/w)
1
4 h
90
1
2
50% H
2
O
2
20
1.5
1.5
10
10
70
70
Traces
Traces
Sodium
perborate
20
Sodium
percarbonate
2
3
2h
2h
85
82
3
4
20
20
1.5
1.5
10
10
70
70
Traces
70
Oxone
Urea
hydrogen
peroxide
5
6
20
20
1.5
1.5
10
10
70
70
40
40
m-CPBA
7
0% tert.
Butyl
hydrogen
peroxide
7
20
1.5
10
70
20
4
5
6
2 h
89
84
87
5
0
a
Reaction conditions: 1a (0.94 mmol, 1 equiv), methanol: 2 mL.
min
5
0
Various aromatic, hetero-aromatic and aliphatic aldehydes
were verified under the optimized reaction conditions (Table
min
4
). The esterification of unsubstituted benzaldehyde 1a was a
sluggish reaction compared to substituted benzaldehyde
derivatives and takes to give 90% yield of the
corresponding methyl benzoate 3a (Table 4, entry 1). Whereas
electron donating (-CH and withdrawing (-NO -Cl)
5
min
0
7
8
9
86
92
69
50
4
h
1.75 h
3
)
2
,
substituents readily undergo esterification to give desired
esterification that in turn reduces the yield. (Table 4, entries
1 h
9
-11). The 4-methoxy 1i and 4-hydroxy benzaldehyde 1j gives
only 69% and 50% yield of respective esters (Table 4, entries 9,
0). The 2-hydroxy benzaldehyde 1k selectively gives 90% yield
1
5
min
0
1
0
of catechol 3k (Table 4, entry 11). Hetero-aromatic aldehydes
such as thiophene-2-carbaldehyde 1l and furan-2-
carbaldehyde 1m also promptly undergo oxidative
esterification to give 88% yield of 3l and 90% yield of 3m
c
50
min
11
90
88
(
Table 4, entries 12, 13). On the other hand, aliphatic
aldehydes (table 4, entries 14, 15) gives moderate yield of
desired ester under optimized conditions. Butyraldehyde 1n
gives 70% yield of 3n (Table 4, entry 14) and heptanal 1m gives
12
2.5 h
60% yield of 3m in 4 h (Table 4, entry 15).
1
3
2.15 h
90
After investigating various aldehydes under optimized
conditions, the effect of alcohol chain (straight chain,
branched, and aromatic) on oxidative esterification of 1a was
investigated (Table 5, entries 1-7). It was observed that the
1
1
4
5
4
4
70
60
yield and the rate of formation of
type of alcohol used. As the alcohol chain increased from
ethanol 2b to n-butanol 2d
3 was dependent on the
,
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a
Reaction conditions: 1 (1 equiv); Oxidant: (1.5 equiv), Amberlyst-15: (20% w/w),
Methanol: 2 mL, Temperature: 70 °C
.
5
6
12 h
60
NR
NR
24 h
24 h
-
-
reaction time for the esterification was also increases from 5 h
to 8 h (Table 5, entries 1-3). Ethanol 2b on reaction with 1a
gives 89% yield of 3p in 5 h (Table 5, entry 1) whereas n-
butanol gives 86% yield of 3q in 8 h (Table 5, entry 3).
7
a
Reaction conditions: 1a (0.94 mmol, 1 equiv); 4Na
equiv), Amberlyst-15: (20% w/w), Alcohol: 2 mL, Temperature: 70 C.
2
SO
4
.2H
2
O
2
.NaCl: (1.8 mole, 1.5
In the case of branched chain alcohols such as isopropyl 2e and
isobutyl alcohol 2f rate as well as yield of ester reduced
significantly (Table 5, entries 4, 5). The present protocol failed
for sterically hindered alcohols such as tert. butyl alcohol 2g
and benzyl alcohol 2h as only starting material was observed
o
a
Table-6 Selective mono esterification with diols
even after keeping reaction for 24 h (Table 5, entry 6, 7). This
confirms that the present protocol was selective for primary
and secondary alcohols whereas sterically hindered alcohols
and benzylic alcohols remain unaffected under optimized
conditions.
Isolate
d yield
Time
Entry
-R
Alcohol
Product
(h)
(
%)
The present protocol was found to give selective mono-
esterification with diols. The ethylene glycol 2h on treatment
with an aldehyde under optimized conditions selectively gives
mono-ester product (Table 6, entries 1-3). The unsubstituted
benzaldehyde 1a on reaction with 2h gives 88% yield of 3u
1
5
88
2
3
5
5
80
50
(
Table 6, entry 1), whereas benzaldehyde with electron
donating substituent 1d (4-CH ) gives 80% yield of 3v in 5 h
Table 6, entry 2). Unlike 1d, the benzaldehyde with electron
withdrawing substituent 1i (4-NO ) gives a moderate yield of
in 5 h (Table 6, entry 3). When ethanolamine 2i was
3
(
2
3w
treated with 1a under optimized conditions, instead of ester,
formation of 2-(benzylidineamino) ethanol 3x (an imine
product of 2i) was obtained with 20% yield (Table 6, entry 4).
4
5
20
a
2 4 2 2
Reaction conditions: Aldehyde, (1 equiv); 4Na SO .2H O .NaCl: (1.8 mole, 1.5
0
equiv), Amberlyst-15: (20% w/w), Alcohol: 2 ml, Temperature : 70 C.
a
Table-5 Effect of carbon chain of alcohol on rate of esterification
Recyclability study of Amberlyst-15
After successful oxidative esterification of various aldehydes,
we investigated the recyclability of Amberlyst-15 by taking 1a
(1.8 mmol, 1 equiv), 4Na SO .2H O .NaCl (2.8 mmole, 1.5
Reacti
on
Time
2
4
2 2
Isolated yield
(%)
Entry
Alcohol
Product
equiv), Amberlyst-15 (20% w/w), methanol: 2 ml, and
(
h)
temperature was kept at 70 °C. After completion of the
reaction, the solid residue containing oxidant remains and
Amberlyst-15 was filtered and water was added to it (3 mL).
The insoluble Amberlyst-15 was filtered off from the aqueous
phase and treated with 0.1 N HCl. It was dried at 60-65 °C for
1
5 h
8 h
89
84
2
3
4
3
0 min and used for the successive cycles. As depicted in
Figure 1, there was no significant loss in the catalytic activity of
Amberlyst-15 even after fifth cycle.
8 h
86
58
12 h
4
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Conclusions
Yield of Methylbenzoate 3a
91 90
In summary, we have developed an efficient, metal-free
catalytic system for selective esterification of various aromatic,
hetero-aromatic and aliphatic aldehydes. The addition of
Amberlyst-15 resulted into increase in the rate esterification
9
0
89
87
86
and
Na SO
than H
demonstrated
.2H .NaCl oxidant exhibits superior oxidizing property
and other commonly used oxidants under present
excellent
recyclability.
The
2
4
2 2
O
2 2
O
conditions. Aldehyde possessing methoxy and hydroxy
substituents showed the formation of Dakin product along
with ester. In the case of ethylene glycol selective mono-ester
formation was observed.
Fresh
First Second Third Fourth
Fifth
Number of Cycles
Experimental
Material and equipments
Fig.1 Recyclability study of Amberlyst-15
Common reagent grade chemicals were purchased from Alfa
Aesar, Spectrochem, Sigma Aldrich and Sd fine chemicals. FT-IR
spectra were recorded on a Bomen Hartmann and Braun MB-
Series FT-IR spectrometer. GC–MS was carried out with a GC–
Plausible reaction mechanism
5
1–53
The present reaction proceeds through hemiacetal
1
MS-QP 2010 instrument. The H NMR spectroscopic data was
formation (Fig.2). The catalyst plays an important role in
hemiacetal formation step. It protonates the carbonyl oxygen
of the aldehyde rendering the carbonyl carbon more electron
deficient and thus susceptible towards nucleophilic attack. In
order to confirm the hemiacetal formation, we performed a
separate reaction that generates hemiacetal and monitored it
by gas chromatography. Then we conducted an esterification
reaction and monitored it on gas chromatography. The
retention time of the intermediate formed during
esterification reaction is exactly the same as that of hemiacetal
formed in initial reaction. Thus it is confirmed that both the
catalyst and the oxidant plays an important role to shift the
reaction in forward direction.
3
recorded with Agilent 500 MHz spectrometer with CDCl as the
solvent. GC analysis was carried out with Thermo scientific,
column-TR-1, 30mX0.25mm, IDX0.25um film, FID detector and
sample size 0.1 l µl.
Experimental procedure for the synthesis of methyl benzoate (3a)
In a 25 ml round bottom flask was charged, benzaldehyde
(
0.94 mmol, 1 equiv), methanol (2 ml), Amberlyst-15 (20%,
w/w) and oxidant (1.4 mmol, 1.5 equiv) and stirred at 65-70 °C.
The progress of the reaction was monitored by TLC. After
reaction completion, the reaction mixture was filtered off to
separate insoluble oxidant residue and catalyst. The oxidant
residue was dissolved in water (5 mL) and the insoluble
catalyst was filtered off. Both the filtrates were combined and
extracted with ethyl acetate (3 X 5 mL). The ethyl acetate
extract was dried over anhydrous sodium sulphate and the
solvent was evaporated under vacuum to give the crude
product that was further purified by column chromatography
using hexane: ethyl acetate as an eluting system.
H
H
O
O+
O
H+
MeOH
H
O
H
R
H
HA
R
H
R
Aldehyde
MeOH
Oxonium intermidiates
-
HA
HA =
CHCH
2
( )
n
O
OH
[
O]
H
O
Spectral data
R
O
5
Methyl benzoate (3a): Colorless oil; Yield: 230 mg,
5
R
1.
Ester
1
hemiacetal
9
2
3
1
3
0%; H NMR (400 MHz, CDCl ) δ 8.07 (d, J = 7.0 Hz,
3
SO H
H), 7.58 (t, J = 7.0 Hz, 1H), 7.46 (t, J = 7.1 Hz, 2H),
+
.94 (d, J = 1.8 Hz, 3H). GC-MS (EI, 70 eV): m/z, [M] =
Fig.2 Plausible reaction pathway
36.
5
3
2.
Methyl 4-methyl benzoate (3d): white crystals;
0
1
Yield: 222 mg, 89%; mp 34-36 C H NMR (400 MHz,
CDCl ) δ 7.92 (d, J = 7.1 Hz, 2H), 7.20 (d, J = 7.6 Hz,
H), 3.87 (s, J = 1.0 Hz, 3H), 2.37 (s, 3H). GC-MS (EI, 70
3
2
+
eV): m/z, [M] = 150.
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Methyl 4-nitrobenzoate (3g): Light yellow solid;
3
3
.
4
5
A. A. Schleppnik, 1986.
0
1
Yield: 206 mg, 86%; mp 94 C H NMR (400 MHz,
CDCl ) δ 8.30 (d, J = 7.6 Hz, 2H), 8.23 (d, J = 7.5 Hz,
H), 4.00 (s, 3H). GC-MS (EI, 70 eV): m/z, [M] = 181.
K. J. Edgar, C. M. Buchanan, J. S. Debenham, P. A.
Rundquist, B. D. Seiler, M. C. Shelton and D. Tindall, Prog.
Polym. Sci., 2001, 26, 1605–1688.
3
+
2
5
6
4.
Methyl 4-chlorobenzoate (3h): white crystal; Yield:
6
7
8
O. Hromatka, 1938.
0
23 mg, 92%; mp 40-42 C H NMR (400 MHz, CDCl
1
2
3
) δ
Z. Hadidian, 1952.
7
.87 (d, J = 8.0 Hz, 2H), 6.78 (d, J = 19.2 Hz, 2H), 3.82
C. S. de Oliveira, B. F. Lira, V. dos Santos Falcão-Silva, J. P.
Siqueira-Junior, J. M. Barbosa-Filho and P. F. de Athayde-
Filho, Molecules, 2012, 17, 5095.
+
s, 3H). GC-MS (EI, 70 eV): m/z, [M] = 170.
(
5
Methyl 4-methoxybenzoate (3i): white solid; Yield:
7
5.
0
1
68 mg, 69%; mp 46-48 C H NMR (400 MHz, CDCl
1
8
3
3
) δ
9
B. Neises and W. Steglich, Angew. Chemie Int. Ed. English,
1978, 17, 522–524.
.01 (d, J = 7.6 Hz, 2H), 6.93 (d, J = 7.6 Hz, 2H), 3.90 (s,
+
H), 3.87 (s, 3H). GC-MS (EI, 70 eV): m/z, [M] = 166.
10
F. E. A. Van Waes, J. Drabowicz, A. Cukalovic and C. V
Stevens, Green Chem., 2012, 14, 2776–2779.
A. R. Hajipour and G. Mazloumi, Synth. Commun., 2002, 32
23–30.
5
8
6.
Catechol (3k): white crystal; Yield: 163 mg, 91 %, mp
0
04-106 C; H NMR (400 MHz, DMSO) δ 8.80 (s, 2H), 11
1
1
,
6
.76 (dd, J = 18.2, 13.1 Hz, 2H), 6.66 – 6.54 (m, 2H);
+
GC-MS (EI, 70 eV): m/z, [M] = 110.
12
F. Tamaddon, M. A. Amrollahi and L. Sharafat, Tetrahedron
Lett., 2005, 46, 7841–7844.
5
7
1
7.
Ethyl benzoate (3p): oil; Yield: 251 mg, 89%; H NMR
400 MHz, CDCl ) δ 7.97 (d, J = 7.1 Hz, 2H), 7.46 (t, J = 13
.9 Hz, 1H), 7.35 (t, J = 6.9 Hz, 2H), 4.35 – 4.24 (q, 2H),
(
3
A. Sakakura, K. Kawajiri, T. Ohkubo, Y. Kosugi and K.
Ishihara, J. Am. Chem. Soc., 2007, 129, 14775–14779.
6
1
+
.38 – 1.23 (t, 3H). GC-MS (EI, 70 eV): m/z, [M] = 150. 14
9
Z. Huang, J. E. Reilly and R. N. Buckle, Synlett, 2007, 2007
,
5
8.
Butyl benzoate(3r): Colourless oil; Yield: 288 mg,
1026–1030.
1
6%; H NMR (400 MHz, CDCl
8
2
4
1
3
) δ 8.07 (d, J = 7.7 Hz, 15
N. N. Karade, Arkivoc, 2006, 2006, 162–167.
H), 7.56 (t, J = 7.3 Hz, 1H), 7.45 (t, J = 7.3 Hz, 2H), 16
.35 (t, J = 6.4 Hz, 2H), 1.83 – 1.72 (m, 2H), 1.56 –
H. Valizadeh and M. Ahmadi, Comptes Rendus Chim., 2012,
15, 1077–1080.
.42 (m, 2H), 1.01 (t, J = 7.2 Hz, 3H). GC-MS (EI, 70 17
+
eV): m/z, [M] = 178.
K. K. Rajbongshi, M. J. Sarma and P. Phukan, Tetrahedron
Lett., 2014, 55, 5358–5360.
3
6
1
9.
Isopropyl benzoate (3s): oil; Yield: 179 mg, 58% H 18
NMR (400 MHz, CDCl ) δ 8.06 (dt, J = 36.8, 21.0 Hz,
H), 7.63 – 7.52 (m, 1H), 7.51 – 7.29 (m, 2H), 5.36 – 19
.11 (m, 1H), 1.41 (dd, J = 10.4, 6.3 Hz, 6H). GC-MS 20
R. K. Sharma and S. Gulati, J. Mol. Catal. A Chem., 2012,
363–364, 291–303.
3
2
5
S. Singh and A. Patel, Catal. Letters, 2014, 144, 1557–1567.
B. E. Maki and K. A. Scheidt, Org. Lett., 2008, 10, 4331–
4334.
+
(
EI, 70 eV): m/z, [M] = 164.
6
0. 2-hydroxyethyl benzoate (3u): Yellowish oil; Yield: 21
0
1
R. Xie, X. Wang, J. Wang, J. Ye, M. Zhou and S. Zang, J.
Saudi Chem. Soc.
1
2
7
2
3
75 mg, 88%; H NMR (400 MHz, CDCl ) δ 8.09 (d, J =
.5 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1H), 7.47 (t, J = 7.4 Hz, 22
H), 4.54 – 4.43 (m, 2H), 3.97 (d, J = 15.6 Hz, 2H), 2.27
J. H. Espenson, Z. Zhu and T. H. Zauche, J. Org. Chem.,
1999, 64, 1191–1196.
(
s, 1H). GC-MS (EI, 70 eV): m/z, [M+1] = 167.
23
R. Kashyap, D. J. Talukdar and S. Pratihar, New J. Chem.,
2015, 39, 1430–1437.
6
1. 2-hydroxy ethyl 4-methyl benzoate (3v): Colourless
1
1
1
oil; Yield: 241 mg, 80 %; H NMR (400 MHz CDCl
3
) δ 24
.93 (d, J = 8.0 Hz, 2H), 7.23 (d, J = 8.8 Hz, 2H), 4.48 –
.39 (t, 2H), 3.94 (t, 2H), 2.39 (t, 3H), 2.05 (s, 1H). GC- 25
X.-F. Wu and C. Darcel, European J. Org. Chem., 2009,
2009, 1144–1147.
7
4
A. Patel, S. Pathan and P. Prakashan, RSC Adv., 2016,
51394–51402.
6,
MS (EI, 70 eV): m/z, [M-1] = 180.
2
6
R. Grigg, T. R. B. Mitchell and S. Sutthivaiyakit,
Tetrahedron, 1981, 37, 4313–4319.
6
2. 2-hydroxy ethyl 4-nitro benzoate (3w): Yellowish
2
1
0
1
solid; Yield: 140 mg, 50 % , mp 77-78 C; H NMR (400 27
MHz, CDCl ) δ 8.28 (d, J = 8.7 Hz, 2H), 8.22 (d, J = 8.6
Hz, 2H), 4.55 – 4.44 (t, 2H), 3.98 (t, J = 3.4 Hz, 2H), 28
.92 (s, 1H). GC-MS (EI, 70 eV): m/z, [M-1] = 211.
H. Rhee and J. Y. Kim, Tetrahedron Lett., 1998, 39, 1365–
1368.
3
K. R. Reddy, M. Venkateshwar, C. U. Maheswari and S.
Prashanthi, Synth. Commun., 2009, 40, 186–195.
W.-J. Yoo and C.-J. Li, Tetrahedron Lett., 2007, 48, 1033–
1
2
9
1
035.
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