Metal-Free Dehomologative Oxidation of Arylacetic Acids for the Synthesis of Aryl Carboxylic Acids

Article abstract of DOI:10.1021/acs.joc.7b00242

A novel I₂-promoted direct conversion of arylacetic acids into aryl carboxylic acids under metal-free conditions has been described. This remarkable transformation involves decarboxylation followed by an oxidation reaction enabled just by using DMSO as the solvent as well as an oxidant. Notably, aryl carboxylic acids are isolated by simple filtration technique and obtained in good to excellent yields. This protocol is free from chromatographic purification, which makes it applicable for large-scale synthesis.

Full text of DOI:10.1021/acs.joc.7b00242

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Article
Metal-Free Dehomologative Oxidation of Arylacetic
Acids for the Synthesis of Aryl Carboxylic Acids
Hanuman Popat Kalmode, Kamlesh S. Vadagaonkar, Suresh L. Shinde, and Atul C. Chaskar
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b00242 • Publication Date (Web): 03 Mar 2017
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Metal-Free Dehomologative Oxidation of Arylacetic Acids for the Synthesis of
Aryl Carboxylic Acids
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Hanuman P. Kalmode,*† Kamlesh S. Vadagaonkar,† Suresh L. Shinde‡ and Atul C. Chaskar*†,‡
†Department of Dyestuff Technology, Institute of Chemical Technology, Mumbai 400019, India
‡National Centre for Nanosciences and Nanotechnology, University of Mumbai, Mumbai,
400098, India, E-mail: achaskar25@gmail.com; Tel.: +91-22-33612706; Fax: +91-22-3361
1020.
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TOC/Abstract Graphics
ABSTRACT:
A novel I2-promoted direct conversion of arylacetic acids into aryl carboxylic acids under
metal-free conditions has been described. This remarkable transformation involves
decarboxylation followed by oxidation reaction enabled just by using DMSO as the solvent as
well as an oxidant. Notably, aryl carboxylic acids are isolated by simple filtration technique and
obtained in good to excellent yields. This protocol is free from chromatographic purification
which makes it applicable for the large scale synthesis.
INTRODUCTION
Aryl carboxylic acid is an important structural unit in organic chemistry, ubiquitous in various
natural products, pharmaceuticals, dyes, polymers, agricultural and bioactive molecules.1 Besides
this, aryl carboxylic acids are key synthetic building blocks owing to their further facile
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transformation into esters, amides, acid chlorides and heterocycles. Thus, the development of
novel methods for their synthesis is of great interest to organic chemists. Conventionally, benzoic
acid is prepared via partial oxidation of toluene using cobalt or manganese naphthenates as
catalysts.2 The global production capacity of aryl carboxylic acids was estimated to be 480,000
tons in 2014 and is likely to exceed 620,000 tons by 2023 with gains of over 3.2% from 2016 to
2023.3 Due to the increasing demand of benzoic acid and its derivatives various oxidizing
methods have been developed for their synthesis.
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Figure 1. Methods for the preparation of aryl carboxylic acid
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The most widely used method involves direct oxidation of methylarenes or aldehydes to aryl
carboxylic acids. Stoichiometric amounts4 of metal oxidants such as KMnO4, Na2Cr2O7, CrO3,
CeO2, TiO2, or NaIO4 and catalytic amounts5a-5j of Co(OAc)2, Cu–Fe, ZnO, MnCO3, AlBr3,
FeCl3, NiII(TPA), RuCl3, CuCl and Bi salts have been successfully employed for these oxidative
processes. Domínguez et al.5k have developed expedient and viable protocol for the aerobic
oxidation of phenylacetic acid through oxygen-mediated cleavage of C–C bond to aryl
carboxylic acids by using 1,2,4-triazole-type ligands and nickel(II) bromide. In addition, non-
metal oxidants such as urea, hydrogen peroxide, HNO3, HBr, and CBr4–PPh3 have also been
used.6 Aryl carboxylic acids have also been prepared from various starting materials (Figure
1).2,4,7 Recently, Wu et al. have reported novel protocol for the preparation of aryl carboxylic
acids via palladium-catalyzed hydroxycarbonylation of aryl halides.7g However, inherent
drawback of either environmental pollution or difficulty in metal reagent separation from the
products are associated with the stoichiometric use of metallic oxidants. Furthermore, metal-free
reagents8 such as Oxone, porphyrin sensitizer, NHC, biomimetic-flavin have also been used to
achieve this transformation. Most of these methods suffer from limitations of toxicity or harsh
reaction conditions. Hence the search for novel and more efficient methods which involve the
use of cheap and biodegradable reagents is highly desirable.
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Although several diverse approaches have been reported for the synthesis of substituted aryl
carboxylic acids, development of practical and sustainable synthetic method still serve to be an
attractive goal for synthetic organic chemist. In this context, based on the literature reports and
our endeavours for the exploration of simple and green methods for the synthesis of biologically
important compounds,9 we herein wish to report a convenient and metal-free process for the
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synthesis of aryl carboxylic acids from easily available arylacetic acids via dehomologative
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oxidation (Scheme 1).
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Scheme 1. Dehomologative oxidation of arylacetic acids to aryl carboxylic acids
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RESULTS AND DISCUSSION
Inspired by recently developed iodine-mediated oxidative C-H functionalization reactions by
using DMSO as a solvent as well as an oxidant,10 we envisaged that halide-containing reagent
could be used as the promoter for the functionalization of C−H bond in arylacetic acids. Initially,
we studied the influence of the different catalysts or promoters, oxidants and solvents on the
oxidative dehomologation reaction of phenylacetic acid (1a). Phenylacetic acid (1a) with varying
concentration of I2 (0.2-1.0 eq., Table 1, entries 1-4) and TBHP (5.0 eq.) as an oxidant at 100 oC
offered benzoic acid 2a in low yields (12-22%) while slightly better yield (29%) of the product
o
was obtained at 120 C (Table 1, entry 5). A slight drop in the yield (23%) was observed when
1.5 eq. of I2 was used (Table 1, entry 6). With a view to improve the yield of the product, various
oxidants such as DTBP, TBPB, CHP, DCP, H2O2 (Table 1, entries 7-11) were screened for this
reaction but these oxidants afforded product 2a in low yields (17-26%). The reaction without the
use of molecular iodine failed to produce desired product, this implied the importance of iodine
as a promoter for this reaction (Table 1, entry 12).
Various promoters such as NIS, KI, CuI, and TBAI were also used instead of iodine for this
reaction. But, these promoters could afford product 2a in low yields (14–28%) (Table 1, entries
13–16). We also tried the reaction of phenylacetic acid (1a) with 1.0 eq. of I2 in DMSO. To our
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delight, benzoic acid (2a) was obtained in 68% (Table 1, entry 17). Inspired with this
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observation, we performed this reaction by using 1.5 eq. of I2 in DMSO at 120 C for 28 h and
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surprisingly enhancement in the yield upto 87% was observed (Table 1, entry 18). In order to
check the possibility of further increase in the yield of 2a, various solvents such as water,
DMSO, DMF, CH3CN and 1,4-dioxane were also used in combination with TBHP (5.0 eq.)
(Table 1, entries 19-23). Use of water as a solvent resulted in 13% yield of the product 2a (Table
1, entry 19) whereas in the case of DMSO also lower yield was obtained (35%) (Table 1, entry
20). Trace amount of product formation was observed in DMF, CH3CN and 1,4-dioxane (Table
1, entries 21-23). Albeit, the use of I2 (1.5 eq.) as a promoter, DMSO as an oxidant as well as a
solvent at 120 oC was found to be the best reaction condition.
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Table 1. Optimization of reaction conditionsa
entry catalyst / promoter (eq.)
oxidant
solvent
temp. (oC) yield (%)
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I2 (0.2)
I2 (0.3)
I2 (0.5)
I2 (1.0)
I2 (1.0)
I2 (1.5)
I2 (1.0)
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
DTBP
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120
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120
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I2 (1.0)
I2 (1.0)
I2 (1.0)
I2 (1.0)
-
TBPB
CHP
-
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120
120
120
120
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20c
21c
22c
23c
DCP
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H2O2
TBHP
TBHP
TBHP
TBHP
TBHP
-
-
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-
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NIS (1.0)
KI (1.0)
CuI (1.0)
TBAI (1.0)
I2 (1.0)
I2 (1.5)
I2 (1.0)
I2 (1.0)
I2 (1.0)
I2 (1.0)
I2 (1.0)
-
-
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14
-
18
-
28
DMSO
DMSO
H2O
68
-
87
TBHP
TBHP
TBHP
TBHP
TBHP
13
DMSO
DMF
CH3CN
1,4-dioxane
35
Trace
Trace
Trace
aReaction conditions: phenylacetic acid 1a (1.0 mmol), catalyst (0.2-0.5 mmol) or
promoter (1.0-1.5 mmol) and oxidant (5.0 mmol) or solvent (3 mL) were heated at 100-
o
b
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120 C for 28 h in sealed tube. in the absence of I2. I2 (1.0 mmol), 70% aq. TBHP (5.0
mmol) and solvent (3 mL). TBHP = tert-butyl hydroperoxide, DTBP = di-tert-butyl
peroxide, TBPB = tert-butyl peroxybenzoate, CHP = cumene hydroperoxide, DCP =
dicumyl peroxide, H2O2 = hydrogen peroxide.
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In order to explore the generality of this protocol for the synthesis of substituted benzoic acids,
various arylacetic acids (1) were examined under the optimized reaction condition (Table 2). The
protocol is highly robust and can tolerate a variety of electron-withdrawing, electron-donating
and halogen substituents in all positions. The reactions of phenylacetic acids with electron-
withdrawing substituents such as 3-nitro- and 4-nitro- proceeded smoothly to afford the
corresponding products 2b and 2c in 86% and 90% yield, respectively. Phenylacetic acids with
methyl group were easily tolerated under the optimized reaction condition and were selectively
converted into the corresponding benzoic acids 2d and 2e in moderate yields. The substrate
scope was also extended to various halogen substituted phenylacetic acids, which can offer the
possibility of further synthetic elaboration. The reaction of phenylacetic acids with halogen
substituents (2-Cl, 2-I, 4-F, 4-Br and 4-bromo-1,3-phenylenediacetic acid) proceeded efficiently
to give the corresponding benzoic acids in good yields (2f-2j, 83-89%). Under optimized
reaction condition 1,2- and 1,3-phenylenediacetic acid were successfully converted into phthalic
acid (2k) and isophthalic acid (2l), respectively, in excellent yields.
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Table 2. Substrate scope with various arylacetic acidsa
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aReaction conditions: arylacetic acid
heated at 120 oC in sealed tube.
1
(1.0 mmol), I2 (1.5 mmol) and DMSO (3 mL) were
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The electron rich phenylacetic acids such as 2-hydroxy, 2,6-dihydroxy, 2,4-dihydroxy, 2,6-
dimethoxy, 3,4-dimethoxy and 4-methoxy underwent dehomologative oxidation reaction
successfully to afford the corresponding benzoic acids (2m-2r) in good yields. Naphthalene-1-
acetic acid was also easily transformed into the 1-naphthoic acid (2s) in 88% yield.
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The scope of this reaction was extended to various heterocyclic arylacetic acids such as furan-
2-acetic acid and pyridine, thiophene-3-acetic acid. The reaction of furan-2-acetic acid furnished
the furan-2-carboxylic acid (2t) in 65% yield whereas thiophene- and pyridine-3-acetic acid
offered corresponding carboxylic acids 2u and 2v in 62% and 57% yield, respectively. Amino,
alcohol and thiol substituents on the phenyl ring of arylacetic acid were not tolerated under the
standard reaction condition.
In view of the broad substrate scope and environmentally benign approach the present method
was evaluated for the gram scale synthesis of benzoic acid (2a). Gratifyingly, 5 g of phenylacetic
acid produced 3.9 g of benzoic acid (87%) under the optimized reaction condition. Thus, this
protocol can be applied for the gram scale synthesis of benzoic acids.
Scheme 2. Control experiments
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To understand the mechanism of this reaction, we performed some control experiments. To
confirm the formation of benzaldehyde (1ac) as an intermediate in this transformation, the
reaction of benzaldehyde (1ac) under the standard condition was carried out which afforded
benzoic acid (2a) in 76% yield (Scheme 2a). This result clearly indicated that the benzaldehyde
(1ac) was the intermediate in dehomologative oxidation reaction. Further to affirm the role of
DMSO as an oxidant, a reaction was performed by using 1.5 eq. of iodine and N,N-dimethyl
formamide (DMF) as a solvent, which failed to give the product 2a (Scheme 2b). For additional
support, we have also tried the reaction of phenyl acetic acid under optimized reaction condition
in N2 and argon atmosphere. In both the cases, the formation of benzoic acid was observed in
78% and 80% respectively (Scheme 2c). These results clearly highlighted the key dual role of
DMSO.
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A plausible mechanistic pathway of this dehomologative oxidation of phenylacetic acid (1a)
into benzoic acid by using molecular iodine as a promoter with dimethyl sulfoxide (DMSO) in
the dual role is depicted in Scheme 3. Initially, iodination11 of phenylacetic acid occurs in the
presence of molecular iodine to afford iodo-(α-iodophenyl)-acetate (1aa). Intermediate 1aa on
decarboxylative Kornblum oxidation12 gives benzaldehyde (1ac), which was confirmed by using
TLC, GC-MS, and 1H NMR analysis. Benzaldehyde (1ac) on oxidation forms benzoic acid 2a.
Scheme 3. Proposed reaction mechanism
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Conclusion
In summary, we have developed an efficient and unique I2-promoted synthesis of aryl
carboxylic acids via C-H functionalization of arylacetic acids followed by decarboxylative
oxidation. This protocol is highly green and practical due to the use of inexpensive DMSO as an
oxidant as well as solvent with easy workup procedure. Metal-free condition, broad substrate
scope with diverse substitution pattern and operational simplicity are noteworthy features of this
protocol.
EXPERIMENTAL SECTION
General Information
Chemical reagents were purchased from commercial suppliers and all reactions were
performed in a sealed tube. The reaction progress was monitored by using TLC performed on
aluminium plates (0.25 mm, E. Merck) precoated with silica gel Merck 60 F-254. Developed
TLC plates were visualized under a short-wavelength UV lamp. Reactions were conducted under
atmospheric condition in solvents such as water, DMSO, DMF, CH3CN and 1,4-dioxane. Yields
refer to spectroscopically (1H NMR) homogeneous material obtained after acid-base treatment
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followed by filtration. Infrared spectra were recorded using an FT/IR spectrometer with ATR
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PRO450-S and the absorption is expressed in cm-1. H NMR spectra were obtained using 500,
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400 and 200 MHz NMR spectrometers, respectively. Chemical shifts (δ) are reported in parts per
million (ppm) downfield from tetramethylsilane and is referenced to the solvent peak: DMSO-d6
(δ 2.50 for 1H NMR). The number of protons (n) for a given resonance is indicated by nH. Peak
multiplicities are designated by the following abbreviations: s, singlet; d, doublet; t, triplet; m,
multiplet; dd, doublet of doublet; td, triplet of doublet; dt, doublet of triplet; tt, triplet of triplet;
ddd, doublet of doublet of doublet; br, broad; J, coupling constant in Hz. High resolution mass
spectra were obtained by using negative electrospray ionization (ESI) by time of flight (TOF)
method. Melting points were recorded on a standard melting point apparatus and are uncorrected.
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General experimental procedure for the synthesis of aryl carboxylic acids:
A sealed tube equipped with a magnetic stirrer bar was charged with arylacetic acid 1 (1.0
mmol), I2 (350-755 mg, 1.5 mmol) and DMSO (3 mL). The reaction vessel was stirred at 120 oC
for 24-30 h. After disappearance of the reactant, monitored by TLC, the reaction mass was
cooled to room temperature, quenched with 10% aq. Na2S2O3 solution and diluted with saturated
NaHCO3 solution. The resulting mixture was then extracted with ethyl acetate to remove organic
impurities. The aqueous layer was then acidified with ice cooled 2 M HCl until the reaction
mixture was strongly acidic by pH paper. This on simple filtration and washing with ice cooled
water resulted in pure benzoic acids 2a-2v.
Product characterization data
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Benzoic acid (2a):7a Yield 87% (195 mg); Colorless solid; mp 122-124 ℃; IR (ATR) ṽ (cm-1):
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3441, 2912, 1718, 1698, 1456, 1279, 933, 711; H NMR (400 MHz, DMSO-d6):  12.96 (bs,
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1H), 7.95 (distorted dd, J = 8.4, 1.6 Hz, 2H), 7.62 (tt, J = 7.6, 1.2 Hz, 1H), 7.50 (distorted t, J =
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8.0, 7.6, 1.6 Hz, 2H); C{1H}NMR (50 MHz, DMSO-d6): δ 167.5, 132.9, 130.9, 129.4 (2C),
128.6 (2C); HRMS (ESI): calc. for [C7H5O2]- [M-H]- 121.0289, found 121.0291.
3-Nitrobenzoic acid (2b):7h Yield 86% (199 mg); Light yellow solid; mp 140–142 oC; IR (ATR)
ṽ (cm-1): : 3448, 1715, 1695, 1216, 721; 1H NMR (400 MHz, DMSO-d6):  13.71 (bs, 1H), 8.61
(d, J = 0.8 Hz, 1H), 8.46 (dd, J = 8.0, 1.2, 0.8 Hz, 1H), 8.34 (dd, J = 7.6, 0.8 Hz, 1H), 7.81 (t, J =
8.0 Hz, 1H); C{1H}NMR (125 MHz, DMSO-d6): δ 165.5, 147.9, 135.4, 132.5, 130.5, 127.3,
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123.7; HRMS (ESI): calc. for [C7H4NO4]- [M-H]- 166.0140, found 166.0143.
4-Nitrobenzoic acid (2c):7a Yield 90% (208 mg); Colorless solid; mp 236-238 C; IR (ATR) ṽ
o
(cm-1): 3445, 1719, 1696, 1452, 1213, 749; H NMR (400 MHz, DMSO-d6):  13.68 (bs, 1H),
1
8.32 (d, J = 9.2 Hz, 2H), 8.16 (d, J = 9.2 Hz, 2H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 165.9,
150.0, 136.5, 130.7 (2C), 123.7 (2C); HRMS (ESI): calc. for [C7H4NO4]- [M-H]- 166.0140,
found 166.0141.
2-Methylbenzoic acid (2d):13a Yield 85% (193 mg); Colorless solid; mp 104-106 oC; IR (ATR)
ṽ (cm-1): 3450, 1717, 1652, 1454, 1505, 1107, 729; 1H NMR (400 MHz, DMSO-d6):  12.82 (bs,
1H), 7.81 (dd, J = 7.6, 1.2 Hz, 1H), 7.44 (td, J = 7.6, 7.2, 1.2 Hz, 1H), 7.30-7.25 (m, 2H), 2.51 (s,
3H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 168.9, 139.2, 131.8, 131.6, 130.6, 130.4, 125.9,
21.4; HRMS (ESI): calc. for [C8H7O2]- [M-H]- 135.0445, found 135.0444.
4-Methylbenzoic acid (2e):4g Yield 84% (190 mg); Colorless solid; mp 180–182 ℃; IR (ATR) ṽ
(cm-1): 3442, 1712, 1655, 1386, 724; 1H NMR (400 MHz, DMSO-d6):  12.79 (bs, 1H), 7.83 (d,
J = 8.0 Hz, 2H), 7.29 (d, J = 8.0 Hz, 2H), 2.36 (s, 3H); C{1H}NMR (125 MHz, DMSO-d6): δ
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167.4, 143.1, 129.4 (2C), 129.2 (2C), 128.2, 21.2; HRMS (ESI): calc. for [C8H7O2]- [M-H]-
135.0445, found 135.0448.
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9
o
2-Chlorobenzoic acid (2f):7a Yield 83% (190 mg); Light brown solid; mp 142–144 C; IR
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(ATR) ṽ (cm-1): 2983, 2867, 1697, 1462, 1311, 924, 735; H NMR (400 MHz, DMSO-d6): 
13.40 (bs, 1H), 7.78 (distorted dd, J = 8.0, 1.2 Hz, 1H), 7.55-7.50 (m, 2H), 7.45-7.40 (m, 1H);
13C{1H}NMR (100 MHz, DMSO-d6): δ 166.9, 132.6, 131.8, 131.5, 130.9, 130.7, 127.3; HRMS
(ESI): calc. for [C7H4ClO2]- [M-H]- 154.9900, found 154.9902.
2-Iodobenzoic acid (2g):13b Yield 87% (206 mg); White solid; mp 162–164 C; IR (ATR) ṽ
o
(cm-1): 3441, 1711, 1682, 1543, 1509, 751; H NMR (400 MHz, DMSO-d6):  13.32 (bs, 1H),
1
7.98 (dd, J = 8.0, 0.8 Hz, 1H), 7.71 (dd, J = 8.0, 7.6, 1.6, 1.2 Hz, 1H), 7.48 (td, J = 7.6, 7.2, 1.2,
0.8 Hz, 1H), 7.23 (td, J = 8.0, 7.6, 1.6, 1.2 Hz, 1H); 13C{1H}NMR (100 MHz, DMSO-d6): δ
168.2, 140.6, 136.9, 132.5, 130.1, 128.2, 94.2; HRMS (ESI): calc. for [C7H4IO2]- [M-H]-
246.9255, found 246.9252.
4-Fluorobenzoic acid (2h):7f Yield 88% (199 mg); Colorless solid; mp 182–184 C; IR (ATR)
o
ṽ (cm-1): 3443, 1715, 1685, 1544, 1509, 748; 1H NMR (400 MHz, DMSO-d6):  13.03 (bs, 1H),
8.09–7.92 (m, 2H), 7.39–7.21 (m, 2H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 166.5, 165.0 (d, J
= 248.9 Hz), 132.2 (d, J = 9.4 Hz), 127.5 (d, J = 2.6 Hz), 115.7 (d, J = 21.8 Hz); HRMS (ESI):
calc. for [C7H4FO2]- [M-H]- 139.0195, found 139.0191.
4-Bromobenzoic acid (2i):7f Yield 89% (208 mg); Pale yellow solid; mp 252–254 oC; IR (ATR)
ṽ (cm-1): 3414, 1712, 1688, 1389, 644; H NMR (400 MHz, DMSO-d6):  13.14 (bs, 1H), 7.86
1
(d, J = 7.4 Hz, 2H), 7.69 (d, J = 7.5 Hz, 2H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 166.8, 131.7
(2C), 131.4 (2C), 130.3, 126.9; HRMS (ESI): calc. for [C7H4BrO2]- [M-H]- 198.9394, found
198.9398.
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4-Bromoisophthalic acid (2j):13c Yield 88% (197 mg); White solid; mp 298–300 C; IR (ATR)
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6
7
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ṽ (cm-1): 3444, 1714, 1686, 1389, 742; H NMR (400 MHz, DMSO-d6):  13.55 (bs, 2H), 8.23
8
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(d, J = 1.6 Hz, 1H), 7.92 (distorted dd, J = 8.4, 2.0 Hz, 1H), 7.86 (d, J = 8.0 Hz, 1H);
13C{1H}NMR (100 MHz, DMSO-d6): δ 166.7, 166.1, 134.6, 133.8, 132.8, 131.4, 130.4, 125.3;
HRMS (ESI): calc. for [C8H4BrO4]- [M-H]- 242.9292, found 242.9291.
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Phthalic acid (2k):13d Yield 90% (192 mg); White solid; mp 210-212 °C (dec.); IR (ATR) ṽ (cm-
1): 3454, 1714, 1689, 1392, 752; 1H NMR (200 MHz, DMSO-d6):  13.06 (bs, 2H), 7.66 (dt, J =
13
6.5, 3.6 Hz, 2H), 7.58 (dt, J = 5.1, 3.5 Hz, 2H); C{1H}NMR (100 MHz, DMSO-d6): δ 168.8
(2C), 132.9 (2C), 130.9 (2C), 128.4 (2C); HRMS (ESI): calc. for [C8H5O4]- [M-H]- 165.0187,
found 165.0188.
o
Isophthalic acid (2l):7f Yield 87% (186 mg); White solid; mp 341–343 C; IR (ATR) ṽ (cm-1):
3448, 1718, 1687, 1385, 765; 1H NMR (200 MHz, DMSO-d6):  13.25 (bs, 2H), 8.48 (d, J = 1.5
Hz, 1H), 8.16 (dd, J = 7.7, 1.6 Hz, 2H), 7.63 (t, J = 7.7 Hz, 1H); 13C{1H}NMR (100 MHz,
DMSO-d6): δ 167.1 (2C), 133.8 (2C), 131.5 (2C), 130.3, 129.6; HRMS (ESI): calc. for [C8H5O4]-
[M-H]- 165.0187, found 165.0185.
o
2-Hydroxybenzoic acid (2m):13e Yield 84% (191 mg); Colorless solid; mp 158-160 C; IR
1
(ATR) ṽ (cm-1): 3213, 3078, 2633, 2579, 1625, 1581, 1477, 1373, 963; H NMR (400 MHz,
DMSO-d6):  11.32 (bs, 2H), 7.79 (dd, J = 7.6, 1.6 Hz, 1H), 7.51 (distorted td, J = 8.4, 7.6, 2.0
13
Hz, 1H), 6.95 (dd, J = 8.8, 1.2 Hz, 1H), 6.91 (dd, J = 8.4, 7.6, 1.2 Hz, 1H); C{1H}NMR (100
MHz, DMSO-d6): δ 172.1, 161.3, 135.8, 130.4, 119.3, 117.2, 112.9; HRMS (ESI): calc. for
[C7H5O3]- [M-H]- 137.0240, found 137.0244.
2,6-Dihydroxybenzoic acid (2n):13f Yield 82% (188 mg); Off-white solid, mp 164-166 °C
(dec.); IR (ATR) ṽ (cm-1): 3224, 2665, 1677, 1608, 1532, 1424, 1352, 1132, 758; 1H NMR (400
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MHz, DMSO-d6):  8.64 (bs, 3H), 7.24 (dt, J = 16.4, 8.2 Hz, 1H), 6.37 (dd, J = 16.3, 8.2 Hz,
2H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 172.4, 160.7 (2C), 135.0, 107.2 (2C), 102.2; HRMS
(ESI): calc. for [C7H5O4]- [M-H]- 153.0187, found 153.0184.
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2,4-Dihydroxybenzoic acid (2o):13g Yield 83% (190 mg); White solid, mp 208-212 oC (dec.); IR
1
(ATR) ṽ (cm-1): 3220, 2664, 1678, 1605, 1530, 1420, 1350, 1128, 765; H NMR (400 MHz,
DMSO-d6):  13.40 (bs, 1H), 11.42 (bs, 1H), 10.37 (bs, 1H), 7.61 (d, J = 8.8 Hz, 1H), 6.34 (dd, J
= 8.8, 2.0 Hz, 1H), 6.26 (d, J = 2.0 Hz, 1H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 172.2, 164.3,
163.7, 132.2, 108.2, 104.6, 102.5; HRMS (ESI): calc. for [C7H5O4]- [M-H]- 153.0190, found
153.0193.
o
2,6-Dimethoxybenzoic acid (2p):13h Yield 84% (195 mg); White solid; mp 184-186 C; IR
1
(ATR) ṽ (cm-1): 3023, 2982, 2625, 1711, 1696, 1396, 1311, 1074, 644; H NMR (400 MHz,
DMSO-d6):  12.72 (bs, 1H), 7.31 (t, J = 8.4 Hz, 1H), 6.68 (d, J = 8.4 Hz, 2H), 3.75 (s, 6H);
13C{1H}NMR (125 MHz, DMSO-d6): δ 166.7, 156.1 (2C), 130.4, 114.4, 104.2 (2C), 55.8 (2C);
HRMS (ESI): calc. for [C9H9O4]- [M-H]- 181.0500, found 181.0503.
o
3,4-Dimethoxybenzoic acid (2q):13i Yield 83% (193 mg); Light yellow solid; mp 180-182 C;
1
IR (ATR) ṽ (cm-1): 3020, 2627, 1696, 1522, 1436, 1375, 1364, 1195, 927, 773; H NMR (400
MHz, DMSO-d6):  12.68 (bs, 1H), 7.56 (dd, J = 8.4, 2.0 Hz, 1H), 7.43 (d, J = 1.6 Hz, 1H), 7.04
13
(d, J = 8.8 Hz, 1H), 3.82 (s, 3H), 3.79 (s, 3H); C{1H}NMR (100 MHz, DMSO-d6): δ 167.2,
152.7, 148.4, 123.3, 123.0, 111.9, 111.0, 55.7, 55.5; HRMS (ESI): calc. for [C9H9O4]- [M-H]-
181.0500, found 181.0501.
4-Methoxybenzoic acid (2r):7h Yield 85% (195 mg); Colorless solid; mp 182-184 oC; IR (ATR)
1
ṽ (cm-1): 3442, 1718, 1648, 1381, 956, 760; H NMR (400 MHz, DMSO-d6):  12.64 (bs, 1H),
7.89 (d, J = 9.2 Hz, 2H), 7.01 (d, J = 8.8 Hz, 2H), 3.82 (s, 3H); 13C{1H}NMR (125 MHz,
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DMSO-d6): δ 167.1, 162.9, 131.4 (2C), 123.0, 113.8 (2C), 55.4; HRMS (ESI): calc. for
[C8H7O3]- [M-H]- 151.0394, found 151.0395.
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1-Naphthoic acid (2s):7a Yield 88% (203 mg); Colorless solid, mp 158-160 oC; IR (ATR) ṽ (cm-
1): 3441, 1714, 1649, 1381, 783; 1H NMR (400 MHz, DMSO-d6):  13.17 (bs, 1H), 8.86 (d, J =
8.8 Hz, 1H), 8.15 (distorted dt, J = 7.6, 3.6, 1.2 Hz, 2H), 8.02 (d, J = 7.6 Hz, 1H), 7.66-7.57 (m,
3H); 13C{1H}NMR (100 MHz, DMSO-d6): δ 168.8, 133.5, 133.0, 130.8, 129.9, 128.7, 127.8,
127.6, 126.2, 125.6, 124.9; HRMS (ESI): calc. for [C11H7O2]- [M-H]- 171.0445, found 171.0447.
Furan-2-carboxylic acid (2t):7a Yield 65% (144 mg); White solid; mp 130-132 oC; IR (ATR) ṽ
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(cm-1): 3141, 2837, 2574 1674, 1581, 1470, 1423, 1295, 1190, 1017, 885, 754; H NMR (400
MHz, DMSO-d6):  13.08 (bs, 1H), 7.91 (dd, J = 1.6, 0.8 Hz, 1H), 7.21 (dd, J = 3.2, 0.8 Hz, 1H),
6.65 (dd, J = 3.2, 1.6 Hz, 1H); 13C{1H}NMR (50 MHz, DMSO-d6): δ 163.9, 134.6, 133.4, 128.0,
127.3; HRMS (ESI): calc. for [C5H3O3]- [M-H]- 111.0081, found 111.0084.
Thiophene-3-carboxylic acid
(
2u):13j Yield 62% (140 mg); White solid; mp 138-140 oC;
1
IR (ATR) ṽ (cm-1): 3106, 2873, 2628, 1668, 1522, 1437, 1274, 1109, 917, 820, 727; H
NMR (500 MHz, DMSO-d6):

12.68 (bs, 1H), 8.25 (dd, J = 3.0, 1.2 Hz, 1H), 7.60 (dd, J
13
= 5.0, 3.0 Hz, 1H), 7.42 (dd, J = 5.1, 1.2 Hz, 1H); C{1H}NMR (50 MHz, DMSO-d6): δ
159.6, 147.2, 145.1, 117.9, 112.3; HRMS (ESI): calc. for [C5H3O2S]- [M-H]- 126.9853,
found 126.9853.
o
Nicotinic acid (2v):13a Yield 57% (128 mg); White solid; mp 236-238 C; IR (ATR) ṽ (cm-1):
1
3089, 3074, 2830, 1710, 1696, 1492, 1322, 968, 747; H NMR (400 MHz, DMSO-d6):  13.44
(bs, 1H), 9.07 (dd, J = 2.0, 0.8 Hz, 1H), 8.79 (dd, J = 4.8, 2.0 Hz, 1H), 8.26 (dt, J = 8.0, 2.0 Hz,
1H), 7.54 (ddd, J = 8.0, 0.8 Hz, 1H); 13C{1H}NMR (100 MHz, DMSO-d6): δ 166.4, 153.3,
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150.3, 137.0, 126.6, 123.9; HRMS (ESI): calc. for [C6H4NO2]- [M-H]- 122.0241, found
122.0244.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: achaskar25@gmail.com
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The financial support from the Council of Scientific and Industrial Research, New Delhi
(sanction no. 01(2427)/10/EMR-II dated 28/12/2010 and pool scheme no. 8644-A), India, to
carry out this work is gratefully acknowledged. H.P.K. and K.S.V. thank Council of Scientific
and Industrial Research and University Grants Commission-Special Assistance Programme, New
Delhi respectively for award of research fellowships. A.C.C. thanks DST for offering Fast Track
Project SB/FT/CS-147/2013. The authors thank Prof. Prakash M. Bhate and Prof. A. K.
Srivastava for their generous support.
Supporting Information
1H and 13C NMR spectra of all aryl carboxylic acids. This material is available free of charge via
the Internet at http://pubs.acs.org
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