The efficient palladium-catalyzed selective t synthesis of benzenesulfonic acids

Article abstract of DOI:10.1080/00397911.2010.502991

Palladium-catalyzed synthetic methodology has been developed for the synthesis of 2-aminobenzenesulfonic acids from benzothiazoles in good to excellent yields using chloramine-B in alkaline (pH 12) acetonitrile/water (1:1) at 80C.

Full text of DOI:10.1080/00397911.2010.502991

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The Efficient Palladium-Catalyzed
Selective t Synthesis of Benzenesulfonic
Acids
Rajenahally V. Jagadeesh a , Y. Sree Sandhya a , P. Karthikeyan a , S.
Sudhakar Reddy a , P. Pradeep Kumar Reddy a , M. Viniod Kumar a
K. T. Prabhu Charan a , R. Narender a & P. R. Bhagat a
a Division of Organic Chemistry, School of Advanced Sciences, VIT
University , Vellore , India
,
Published online: 14 Jun 2011.
To cite this article: Rajenahally V. Jagadeesh , Y. Sree Sandhya , P. Karthikeyan , S. Sudhakar
Reddy , P. Pradeep Kumar Reddy , M. Viniod Kumar , K. T. Prabhu Charan , R. Narender & P. R. Bhagat
(2011) The Efficient Palladium-Catalyzed Selective t Synthesis of Benzenesulfonic Acids, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:16, 2343-2349, DOI: 10.1080/00397911.2010.502991
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Synthetic Communications1, 41: 2343–2349, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.502991
THE EFFICIENT PALLADIUM-CATALYZED SELECTIVE
t SYNTHESIS OF BENZENESULFONIC ACIDS
Rajenahally V. Jagadeesh, Y. Sree Sandhya, P. Karthikeyan,
S. Sudhakar Reddy, P. Pradeep Kumar Reddy,
M. Viniod Kumar, K. T. Prabhu Charan,
R. Narender, and P. R. Bhagat
Division of Organic Chemistry, School of Advanced Sciences, VIT University,
Vellore, India
GRAPHICAL ABSTRACT
Abstract Palladium-catalyzed synthetic methodology has been developed for the synthesis
of 2-aminobenzenesulfonic acids from benzothiazoles in good to excellent yields using
chloramine-B in alkaline (pH 12) acetonitrile/water (1:1) at 80 ꢀC.
Keywords 2-Aminobenzenesulfonic acids; benzothiazoles; chloramine-B; palladium
catalyst
INTRODUCTION
The importance of aminobenzenesulfonic acids resides in their widespread use
in the syntheses of various organic dyes[1] and heterocyclic compounds. The amide
derivatives of aminobenzenesulfonic acids and certain related substitutes have sig-
nificant medicinal importance as sulfa drugs. Because of the versatile properties
and pharmaceutical applications of aminobenzenesulfonic acids, synthesis of these
compounds using convenient and efficient methodologies is an important task.
In synthetic methodology, as the building block of organic synthesis, research-
ers continuously seek new reagents, better reaction conditions, and more efficient
and selective methods. In this regard, a large group of compounds, sodium
N-haloarenesulfonamidates (organic haloamines), are widely used in fine organic
synthesis.[2–4] Sodium N-haloarenesulfonamidates, because of their versatile proper-
ties, have proved to be valuable reagents for a variety of functional group transfor-
mations.[2,3] N-Haloamines act as good oxidants and reagents both in alkaline and
acidic media and have been widely used for the oxidation and synthesis of a variety
Received February 16, 2010.
Address correspondence to Rajenahally V. Jagadeesh, Division of Organic Chemistry, School of
Advanced Sciences, VIT University, Vellore 632014, India. E-mail: rvjdeesh@yahoo.com
2343

2344
R. V. JAGADEESH ET AL.
Scheme 1. Synthesis of 2-aminobenzenesulfonic acids.
of organic and biomolecules.[3,4] Chloramine-B (C6H5SO2NClNa ꢁ 1.5H2O or
PhSO2NClNa or CAB), the N-chloro derivative of sulfonamide, is gaining impor-
tance as oxidant and reagent for the synthesis of a variety of organic molecules.
Although the mechanistic aspects of many haloamine reactions have been well docu-
mented,[4–9] similar studies on chloramine-B are sparse. In view of this, there is con-
siderable scope for the study with CAB to get better insight into the speciation of
CAB reaction models and to understand its redox chemistry in solutions.
Palladium has been extensively used[4,8,10–12] as catalyst for a number of reac-
tions. In recent times, the studies on the use of palladium as catalyst in many redox
and synthetic reactions have been increasing. In continuation of our studies with pal-
ladium catalysts and the synthetic applications of 2-aminobenzenesulfonic acids, we
report herein a new and efficient method for the preparation of 2-aminobenzenesul-
fonic acids from benzothiazole using chloramine-B and palladium chloride as the
catalyst (Scheme 1).
RESULTS AND DISCUSSION
Synthesis of 2-aminobenzenesulfonic acid and substituted 2-aminobenzene-
sulfonic acids were achieved by using a catalytic amount of palladium chloride in
acetonitrile=water (1:1) at 80 ꢀC by chloramine-B with 1:5 substrate=chloramine-B
ratio in the presence of alkali. The products and the yields are summarized in
Table 1. In general, substrates containing electron-donating moieties were found to
be more reactive and required shorter reaction times compared to substrates contain-
ing electron-withdrawing groups. The effect of various solvents [acetonitrile, 1,2-
dichloromethane, ethanol, and acetonitrile=water (1:1) mixture] was studied using
benzothiazole as the model compound. The mixture of acetonitrile=water (1:1) was
found to be the best solvent system, perhaps because of the high dielectric constant
of water.
The reactions were found to be highly dependent upon the pH of the system. To
evaluate the effect of pH, a reaction with benzothiazole was carried out under similar
experimental conditions at different pH values. At neutral pH, the synthesis of 2-ami-
nobenzenesulfonic acid from benzothiazole was found to be very slow. Reaction rates
increase with increase in pH (addition of NaOH) and reaches a maximum at pH 12.
This behavior of the reaction is attributed to the dissociation of chloramine-B in an
aqueous medium by furnishing different oxidizing species[13–15] in which PhSO2NHCl
is the predominant species. In presence of alkali, the free acid, PhSO2NHCl, under-
goes dissociation[16,17] to furnish the species PhSO2NClꢂ as presented in Eq. (1):
PhSO2NHCl þ OHꢂ Ð PhSO2NClꢂ þ H2O
ð1Þ

AMINOBENZENESULFONIC ACIDS
2345
Table 1. Palladium-catalyzed synthesis of aminobenzenesulfonic acidsa
Entry
1
Substrate
Product
Yield
Mp (ꢀC)
85
298 (300)b
2
3
4
5
6
80
85
86
80
80
345 (340)
329 (328)
278 (273)
201 (197)
219 (220)
7
8
9
86
82
81
241 (239)
198 (197)
245 (243)
aSubstrate: 1 mmol, Chloramine-B ¼ 5 mmol, temperature ¼ 80 ꢀC, time ¼ 24–26 h.
bMps given in parentheses refer to authentic samples.
The species PhSO2NClꢂ furnished by chloramine-B in the presence of alkali enhances
the reaction, and thus the reactions proceed with increasing rates.
Palladium(II) chloride catalysis has been observed during various reactions and
exists as different complexes in alkaline solutions,[18–20] and the possible Pd(II) complex
species are [Pd(OH)Cl3]2ꢂ, [Pd(OH)2Cl2]2ꢂ, [Pd(OH)3Cl]2ꢂ, and [Pd(OH)4]2ꢂ. The spe-
cies [Pd(OH)3Cl]2ꢂ and [Pd(OH)4]2ꢂ are not commonly found as they are insoluble.
Further, the rate increases with increase in [OHꢂ], and lack of effect of [Clꢂ] on the rate
of reaction clearly rules out [Pd(OH)Cl3]2ꢂ as the reactive species. Hence, [Pd(OH)2Cl2]2ꢂ
complex ion has been assumed to be the reactive species in the present study.

2346
R. V. JAGADEESH ET AL.
Scheme 2. Detailed mechanism for the synthesis of 2-aminobenzenesulfonic acids.
The synthesis of 2-aminobenzenesulfonic acid from benzothiazole proceeds
with the formation of 2-aminothiophenol as the intermediate. Benzothiazole
first utilizes 2 mol of chloramine-B to form 2-aminothiophenol. The formed
isatin consumes another 3 mol of chloramine-B to yield the ultimate and
desired compound, 2-aminobenzenesulfonic acid. The reaction is shown in
Scheme 2.
Ultraviolet–visible (UV-vis) spectroscopic studies indicate that the intermedi-
ate complex forms between Pd catalyst and chloramine-B. Absorption maxima in
alkaline medium appear at 350 nm for PdCl2, 236 nm for chloramine-B, and
340 nm for a mixture of both. A hypsochromic shift of 10 nm from 350 nm to
340 nm of PdCl2 suggests that the complexation occurs between PdCl2 and
chloramine-B. The detailed reactions for the synthesis of 2-aminobenzenesulfonic
acids from benzothiazoles are depicted in Scheme 2.
The synthetic reactions were also performed with other N-haloamines,
namely chloramine-T and bromamine-B. Reactions with bromamine-B are faster
when compared to both chloramine-T and chloramine-B. This is attributable to
the difference in electrophilicities of the halo cations Brþ and Clþ involved in
the oxidation process and is also related to the ease with which these species are
generated in reactions. In these reactions, the electronegativity values of Brþ and
Clþ play a vital role. Bromine has an electronegativity of 2.7, while chlorine has
a higher value of 3.0. As the electronegativity increases, the electropositive nature
decreases, because the halo cations are the reactive species in these oxidation reac-
tions and the electropositive nature is Br > Cl. Hence, it can be generalized that
bromamines are stronger oxidants compared to chloramines. Oxidizing power of
chloramine-B is more than chloramine-T. This is due the participation of –CH3
group in chloramine-T, which exerts a strong inductive effect in enriching the elec-
=
tron density at the polar N-X (X Cl or Br) bond, thereby reducing the electrophi-
licity of the X atom. A similar behavior has been reported[5] in the N-haloamine
reactions.

AMINOBENZENESULFONIC ACIDS
2347
CONCLUSION
Palladium-catalyzed synthesis of 2-aminobenzenesulfonic acids was achieved
efficiently using chloramine-B in the presence of alkali. Chloramine-B=palladium
chloride system was efficient for the facile conversion of benzothiazoles into
2-aminobenzenesulfonic acids in an alkaline medium in good to excellent yields.
The present method developed for the synthesis of 2-aminobenzenesulfonic acids
from benzothiazoles offers many advantages including good conversion, short
reaction times, and the involvement of nontoxic reagents.
EXPERIMENTAL
Melting points were determined on an X-4 apparatus and are uncorrected.
Infrared (IR) spectra were obtained using Shimadzu Fourier transform (FT)–
IR-8900 spectrometer. Mass spectral (MS) data were obtained on a 17A Shimadzu
gas chromatograph with a QP-5050A Shimadzu mass spectrometer. The mass spec-
trum was obtained using the electron-impact ionization technique.
Preparation of Chloramine-B
It is prepared by the action of chlorine on benzenesulfonamide in the presence
of NaOH. Benzenesulfonamide (1 mol) was added gradually to 4–5 N NaOH sol-
ution (2–3 mol) at 298 K with stirring. When the solution became homogeneous, it
was filtered, and the filtrate was heated to 338–343 K. Chlorine was bubbled slowly
over a period of 1 h. The mass was stirred for 1 h at the same temperature, then
heated to 358 K and filtered through a Schott’s funnel. A yield of 99% was obtained.
The purity of chloramine-B was assayed iodometrically to determine the active halo-
gen content. Chloramine-B was confirmed by IR and MS analysis.
Synthesis of 2-Aminobenzenesulfonic Acids
Catalyst (2 mmol) was added to a stirred solution of benzothiazole (1 mmol)
and chloramine-B (5 mmol) in alkaline acetonitrile=water (1:1) mixture (20 mL),
and the mixture was stirred at 80 ꢀC for 24–26 h. After completion of the reaction,
the reduction product of bromamine-B, benzenesulfonamide (PhSO2NH2), was
extracted with ethyl acetate, identified by thin-layer chromatography (TLC), and
confirmed by MS analysis. The aqueous part of the reaction mixture was neutralized
with acid, followed by solvent evaporation under reduced pressure. The residue was
dissolved in dichloromethane, and the dichloromethane layer was washed twice with
water and then dried over sodium sulfate. The solvent was evaporated under reduced
pressure, and the residue thus obtained was purified by passing through a short
silica-gel column using dichloromethane as eluent. Evaporation of the solvent yields
2-aminobenzenesulfonic acids around 85% yield. The products were identified by
TLC and mp by comparison with authentic samples. Further, the compounds were
confirmed by IR and MS analysis. The reaction times and yields are given in Table 1.
Alternatively, after extracting out benzenesulfonamide, the aqueous layer was neu-
tralized with acid and the 2-aminobenzenesulfonic acids are estimated as their zinc

2348
R. V. JAGADEESH ET AL.
orthanilates. The procedure for the estimation is as follows:[21] To the reaction
mixture, a calculated volume of 1 mol dmꢂ3 HCl was added, followed by 10 mL of
pH 5.0 buffer and 10 mL of 1% zinc chloride. The precipitate was filtered, dried at
105–110 ꢀC, and weighed, and the recovery of (C6H7SO3N)2 Zn was found be
around 85%.
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