Electrochemical oxidation of 4-substituted urazoles in the presence of arylsulfinic acids: An efficient method for the synthesis of new sulfonamide derivatives

Article abstract of DOI:10.1039/c2gc16342j

Electrochemical synthesis of some new sulfonamide derivatives was carried out via the electrooxidation of 4-substituted urazoles in the presence of arylsulfinic acids. The results show that electrogenerated 4-alkyl-4H-1,2,4- triazole-3,5-diones participated in a Michael-type reaction with arylsulfinic acids and, via an "electron transfer + chemical reaction" (EC) mechanism, were converted to the corresponding sulfonamide derivatives. In this work, some new sulfonamide derivatives with high yields in aqueous solutions, without toxic reagents and solvents at a carbon electrode using an environmentally friendly novel method, are provided.

Full text of DOI:10.1039/c2gc16342j

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PAPER
Electrochemical oxidation of 4-substituted urazoles in the presence of
arylsulfinic acids: an efficient method for the synthesis of new sulfonamide
derivatives†
Fahimeh Varmaghani,a Davood Nematollahi,*a Shadpour Mallakpourb and Roya Esmailia
Received 26th October 2011, Accepted 10th January 2012
DOI: 10.1039/c2gc16342j
Electrochemical synthesis of some new sulfonamide derivatives was carried out via the electrooxidation
of 4-substituted urazoles in the presence of arylsulfinic acids. The results show that electrogenerated
4-alkyl-4H-1,2,4-triazole-3,5-diones participated in a Michael-type reaction with arylsulfinic acids and,
via an “electron transfer + chemical reaction” (EC) mechanism, were converted to the corresponding
sulfonamide derivatives. In this work, some new sulfonamide derivatives with high yields in aqueous
solutions, without toxic reagents and solvents at a carbon electrode using an environmentally friendly
novel method, are provided.
This method represents a facile and one-pot electrochemical
process for the synthesis of new sulfonamide derivatives in high
Introduction
Sulfonamides are used to treat many kinds of infection caused
by bacteria and certain other microorganism. These compounds
competitively inhibit folic acid synthesis in microorganisms, and
formerly were bacteriostatic against a wide variety of bacteria
and some protozoa.1 Sulfonamides are still widely used for con-
ditions such as acne and urinary tract infections caused by bac-
teria resistant to other antibiotics.2–4 The importance of
sulfonamides has promoted us and other workers to synthesize a
number of these compounds.4–8 On the other hand, 4-substi-
tuted-1,2,4-triazole-3,5-diones are notable for their ability to par-
ticipate in a wide range of concerted and stepwise reactions.9–11
Some urazole derivatives were found to be potent cytotoxic
agents in murrain and human cancer cell lines and also reduce
DNA synthesis considerably with moderate reduction in RNA
synthesis.12 Other pharmaceutical properties of urazole deriva-
tives are hypolipidemic activity via lowering serum cholesterol
and triglyceride levels,13 pesticides14 and insecticides.15 With
attention to these pharmaceutical properties of urazole deriva-
tives, we anticipated that the synthesis of new sulfonamide
derivatives with the moiety of 4-alkyl-4H-1,2,4-triazole-3,5-
diones would be useful from the point of view of pharmaceutical
properties.
yields and purities via electrochemical oxidation of 4-substituted
derivatives of urazole in the presence of arylsulfinic acids under
green conditions, without toxic reagents and solvents at a carbon
electrode in a divided cell, using an environmentally friendly
method. This mild aqueous reaction expands the repertoire of
aqueous chemistries available for small molecules.
Results and discussion
Cyclic voltammograms of 1.0 mM solution of 4-propyl-1,2,4-
triazolidine-3,5-dione (1a) in aqueous solutions at various pHs
are shown in Fig. 1. In acidic pHs, cyclic voltammograms show
one anodic (A1) and a cathodic peak (C1), which corresponds to
the transformation of 4-propyl-1,2,4-triazolidine-3,5-dione (1a)
to 4-propyl-4H-1,2,4-triazole-3,5-dione (2a) and vice versa
within
a quasi-reversible two-electron process (curve a)
(Scheme 1, eqn (1)). Under these conditions, the peak current
This idea prompted us to investigate the electrochemical oxi-
dation of 4-propyl and 4-butyl derivatives of urazole in the pres-
ence of arylsulfinic acids as nucleophiles.
aFaculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran,
65178-38683. E-mail: nemat@basu.ac.ir; Fax: +98-811-8257407
bOrganic Polymer Chemistry Research Laboratory, Department of
Chemistry, Isfahan University of Technology, Isfahan 84156-83111,
I. R. Iran
Fig. 1 Cyclic voltammograms of 1.0 mM 4-propyl-1,2,4-triazolidine-
3,5-dione (1a), at a glassy carbon electrode, in buffered solutions with
various pHs and the same ionic strength. pHs from a–d are: 2.5, 6.3, 7.2
and 9.2, respectively, Scan rate: 100 mV s−1, t = 25 1 °C.
1
†Electronic supplementary information (ESI) available: FT–IR, H and
13C NMR spectra of compounds 5a–5f. See DOI: 10.1039/c2gc16342j
This journal is © The Royal Society of Chemistry 2012
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Fig. 3 (a) A cyclic voltammogram of 1.0 mM 4-propyl-1,2,4-triazoli-
dine-3,5-dione (1a) in the absence and (b) in the presence of 1.0 mM p-
chlorosulfinic acid (3a). (c) A cyclic voltammogram of 0.5 mM p-
chlorosulfinic acid (3a) in the absence of 1a. (d), A cyclic voltammo-
gram of 0.5 mM isolated product (5a), at a glassy carbon electrode, in
water–acetonitrile (30/70) solution containing phosphate buffer (c = 0.2
M, pH = 3.0). Scan rate: 100 mV s−1, t = 25 1 °C.
Scheme 1 Proposed mechanism for the electrochemical oxidation of
4-substituted urazoles in the presence of arylsulfinic acids.
This behavior can be related to the occurrence of the above men-
tioned side reaction(s) on 2a.16–21
The rates of these side reactions are pH dependent and
enhanced by increasing pH (Fig. 1). On the other hand, these
side reactions are competitive with the nucleophilic addition
reaction of arylsulfinic acids to 4-propyl-4H-1,2,4-triazole-3,5-
dione (2a). Therefore, in this investigation, in order to put off
these side reactions, the electrochemical synthesis of the sulfona-
mide derivatives has been performed in acidic media.
The oxidation of 1a in the presence of p-chlorosulfinic acid
(3a) as a nucleophile was studied in some detail. Fig. 3 (curve b)
shows the cyclic voltammogram obtained for a 1.0 mM solution
of 1a in the presence of 1.0 mM 3a. In cyclic voltammetry
experiments of 1a in the presence of 3a, acetonitrile as co-
solvent has been added. This solvent prevents the fouling of
electrode surface by the oxidation products. So, in this figure for
better appearance of the peaks, a mixture of water–acetonitrile
(30/70) has been used as a solvent (in synthesis we used water
as the solvent). As can be seen from this figure, the cathodic
peak (C1) disappeared and a new anodic peak (A2) appeared in
more positive potentials. The occurrence of a chemical reaction
is supported by the disappearance of peak C1 during the reverse
scan, which could indicate that 4-propyl-4H-1,2,4-triazole-3,5-
dione (2a) formed on the surface of the electrode is consumed
by a chemical reaction with 3a.23,24 The current of peak C1
strongly depends on the potential scan rate and appears in high
scan rates (Fig. 4)23,24 A similar situation was observed when
the 3a to 1a concentration ratio was decreased.
Controlled-potential coulometry was performed in aqueous
solution containing 0.25 mmol of 4-butyl-4H-1,2,4-triazole-3,5-
dione (1b) and 0.25 mmol of benzenesulfinic acid (3b) at 0.60 V
versus Ag–AgCl. The electrolysis progress was monitored using
cyclic voltammetry (Fig. 5). As shown, the following changes:
a) decrease in the anodic peak current A1, b) increase in the
anodic peak current A2 and c) disappearance of peak A1 after
consumption of about 2e− per molecule of 1b, are observed in
cyclic voltammograms during the advancement of coulometry.
Fig. 2 Cyclic voltammograms of 1.0 mM 4-propyl-1,2,4-triazolidine-
3,5-dione (1a) in phosphate buffer (c = 0.2 M, pH = 3.0) solution at
different scan rates. Scan rates from a–d are 10, 25, 50 and 100 mV s−1
Inset: Variation of anodic peak current function versus scan rate. t = 25
1 °C.
.
ratio (IpC1/IpA1) of nearly unity can be considered a criterion for
the stability of 2a produced at the surface of the electrode under
the experimental conditions. In other words, any side reactions,
such as hydroxylation,16,17 dimerization18–20 or oxidative ring
cleavage21,22 on electrochemically generated 2a are too slow to
be observed at the time scale of cyclic voltammetry.16–21 With
increasing pH, the peak current ratio (IpC1/IpA1) is less than unity
and decreases with increasing pH (Fig. 1) and also with decreas-
ing potential sweep rate (Fig. 2). In addition, the current function
for the peak A1, (IpA1/v1/2), decreases with increasing the scan
rate and such behavior is adopted as indicative of occurrence a
following chemical reaction after electron transfer reaction.23
964 | Green Chem., 2012, 14, 963–967
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Fig. 4 A cyclic voltammogram of 1.0 mM 4-propyl-1,2,4-triazolidine-
3,5-dione (1a) in the presence of 0.5 mM p-chlorosulfinic acid (3a) in
various scan rates at a glassy carbon electrode, in water–acetonitrile (30/
70) solution containing phosphate buffer (c = 0.2 M, pH = 3.0). Scan
rates from a to d are: 10, 25, 50 and 100 mV s−1. t = 25 1 °C.
Fig. 6 Cyclic voltammograms of 1.0 mM 4-propyl-1,2,4-triazolidine-
3,5-dione (1a) in the presence of 0.13 mM: (a) toluenesulfinic acid (3c),
(b) benzenesulfinic acid (3b) and (c) p-chlorosulfinic acid (3a) at a
glassy carbon electrode, in water–acetonitrile (30/70) solution containing
phosphate buffer (c = 0.2 M, pH = 3.0). Scan rate: 100 mV s−1, t = 25
1 °C.
sulfonamides 5a–5f as the final products. The oxidation of 5a–5f
is more difficult than the oxidation of the starting molecules 1a
and 1b by virtue of the presence of the electron-withdrawing
phenylsulfonyl group on 5a–5f. Therefore, in this work, the oxi-
dation of sulfonamides 5a–5f was circumvented during the reac-
tion because of the presence of the electron-withdrawing group
as well as by the insolubility of the final products 5a–5f in the
aqueous phosphate buffer solution (pH = 3.0). According to
these results, the anodic and cathodic peaks A1/C1 pertain to the
oxidation of 4-propyl-1,2,4-triazolidine-3,5-dione (1a) to 4-
propyl-4H-1,2,4-triazole-3,5-dione (2a) and vice versa
(Scheme 1). Also, comparison of the cyclic voltammogram of 4-
propyl-1,2,4-triazolidine-3,5-dione (1a) in the presence of p-
chlorosulfinic acid (3a) (Fig. 3, curve b) with the cyclic voltam-
mogram of isolated product (5a) (Fig. 3, curve d) shows that the
anodic peak A2 corresponds to the oxidation of sulfonamide 5a
(see EpA2 in the curves b and d).4 It should be noted that, 1a and
1b in the presence of 3a, 3b or 3c show basically the same elec-
trochemical behavior.
Fig. 5 Cyclic voltammograms of 0.25 mmol 4-butyl-1,2,4-triazolidine-
3,5-dione (1b) in the presence of 0.25 mmol benzenesulfinic acid (3b),
at a glassy carbon electrode during controlled-potential coulometry at
0.60 V versus Ag–AgCl. After consumption of: 0, 20, 32 and
41 C. Inset: Variation of peak current (IpA1) versus charge consumed.
Other conditions are the same as Fig. 3.
Since in the ECi mechanism, the peak current ratio (IpC1/IpA1
)
is a criterion for the homogeneous reaction that is coupled to the
electron-transfer step, k (Scheme 1, eqn (3)),23 here we studied
the nucleophilicity of 4-chlorobenzenesulfinic acid (3a), benze-
nesulfinic acid (3b) and toluenesulfinic acid (3c), toward 2a.
Fig. 6 shows the cyclic voltammograms of 1.0 mM 4-propyl-
1,2,4-triazolidine-3,5-dione (1a) in the presence of 0.13 mM
arylsulfinic acids (3a–3c). As can be seen, the peak current ratio,
(IpC1/IpA1), was found to vary in the order 4-chlorobenzenesulfi-
nic acid (3a) > benzenesulfinic acid (3b) > toluenesulfinic acid
(3c). This is related to the higher nucleophilicity of 3c because
of the existence of a methyl group with electron-donating charac-
ter in the structure of 3c. Also, as can be seen, the anodic peak
current ratio, (IpA1/IpA2), was found to vary in the order 3a > 3b
> 3c. Since the anodic peak A2 corresponds to the oxidation of
sulfonamide 5a–5c, these data confirm that the observed homo-
geneous rate constants (kobs) of the reaction of arylsulfinic acids
(3a–3c) with 2a varies in the order 3a > 3b > 3c.
Diagnostic criteria of cyclic voltammetry, including disappear-
ance of peak C1 during the reverse scan in cyclic voltammetry of
1a in the presence of 3a (Fig. 3) and reappearance of it with
increasing scan rate (Fig. 4),23,24 on the one hand and controlled
potential coulometry (consumption of about 2e−, disappearance
of peak A1 and increasing of anodic peak current A2, Fig. 5), on
the other hand, accompanied by the IR and NMR (1H and 13C)
data (see section and ESI†) and molecular mass of 317 of final
product, indicates that the reaction mechanism of electrochemical
oxidation of urazoles 1a and 1b in the presence of arylsulfinic
acids 3a–3c, is EC (electron transfer and then chemical reaction)
(Scheme 1).23,24
According to this scheme, the generation of 4-alkyl-4H-1,2,4-
triazole-3,5-diones 2a (or 2b) is followed by a Michael type
addition reaction of 3a–3c on 2a (or 2b) producing the
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calcd for C11H12ClN3O4S: C, 41.58; H, 3.81; N, 13.22; S,
10.09%. found: C, 41.03; H, 3.79; N, 13.37; S, 9.78.
Conclusions
The importance of sulfonamides as valuable drugs prompted us
to synthesis a number of these compounds. The prominent fea-
tures of this paper, the synthesis of valuable compounds in
aqueous solution25,26 instead of toxic solvents, room temperature
conditions, high energy efficiency and using the electrode as an
electron source instead of toxic reagents, are in accord with the
principle of green chemistry. The results of this work show that
1-[(Phenylsulfonyl)]-4-propyl-1,2,4-triazolidine-3,5-dione (5b).
IR (KBr, cm−1): 3463, 3231, 3098, 2967, 1805, 1734, 1448,
1418, 1396, 1384, 1348, 1316, 1194, 1178, 1131, 1083, 1047,
1
1024, 899, 876, 835, 771, 688, 578, 563. H NMR (90 MHz,
CDCl3): δ 0.49 (t, J = 7.4 Hz, 3H), 1.29 (m, 2H), 3.28 (t, J = 6.9
Hz, 2H), 7.59 (m, 3H), 7.75 (NH, 1H), 7.89(d, J = 7.3 Hz, 2H).
13C NMR (CDCl3, 100 MHz): δ 10.4, 20.5, 41.5, 129.2, 129.5,
133.0, 135.5, 151.3, 153.5. MS (EI) m/z (relative intensity): 284
[M + H]˙+ (1.5), 283 [M]˙+ (1.3), 219 (0.5), 141 (95), 77 (100).
Anal. calcd for C11H13N3O4S: C, 46.63; H, 4.63; N, 14.83; S,
11.32%. Found: C, 46.11; H, 4.18; N, 14.16; S, 10.97.
electrogenerated
4-alkyl-4H-1,2,4-triazole-3,5-diones
are
attacked by arylsulfinic acids. Final products are obtained via an
EC mechanism, after consumption of 2e− per molecule of 1a
and 1b. Finally, although one-pot reactions are performed poten-
tiostatically on a mmol scale in divided cells, there is little diffi-
culty in producing larger quantities by using larger cells.
4-Propyl-1-tosyl-1,2,4-triazolidine-3,5-dione (5c). IR (KBr,
cm−1): 3440, 3257, 3091, 3038, 2966, 2884, 1803, 1733, 1720,
1594, 1453, 1421, 1394, 1348, 1194, 1180, 1132, 1080, 1044,
1012, 896, 872, 826, 770, 707, 665. 1H NMR (CDCl3,
90 MHz): δ 0.53 (t, J = 7.3 Hz, 3H), 1.38 (m, 2H), 2.41 (s, 3H),
3.32 (t, J = 6.9 Hz, 2H), 7.33 (d, J = 8.3 Hz, 2H), 7.84 (d, J =
8.3 Hz, 2H), 8.42 (NH, 1H). 13C NMR (CDCl3, 100 MHz): δ
10.3, 20.5, 21.8, 41.4, 129.2, 130.1, 147.0, 151.4, 153.5. MS
(EI) m/z (relative intensity): 298 [M + H]˙+ (0.7), 297 [M]˙+
(0.3), 155 (97), 139 (19), 91 (100). Anal. calcd for
C12H15N3O4S: C, 48.47; H, 5.08; N, 14.13; S, 10.78%. Found:
C, 47.48; H, 4.93; N, 13.95; S, 10.33.
Experimental section
General remarks
Reaction equipment is described in an earlier paper.27 Urazole
derivatives were synthesis according to previously reported pro-
ducers.28,29 Toluene, benzene and chlorobenzene derivatives of
sulfinic acid were obtained from commercial sources. These
chemicals were used without further purification. The purity of
1
products has been checked by TLC, melting points, H NMR,
13C NMR and elemental analysis. The peak current ratios
(IpC1/IpA1) were determined using the following equation given
in ref. 23, page 240.
4-Butyl-1-(4-chlorophenylsulfonyl)-1,2,4-triazolidine-3,5-dione
(5d). IR (KBr, cm−1): 3453, 3159, 3098, 2945, 2937, 1731,
1716, 1454, 1400, 1180, 1176, 1111, 1085, 769, 653, 620, 568.
1H NMR (CDCl3, 400 MHz): δ 0. 82 (t, J = 7.6 Hz, 3H), 0.94
(m, 2H), 1.40 (m, 2H), 3.43 (t, J = 7.0 Hz, 2H), 7.60 (d, J = 8.8
Hz, 2H), 7.63(broad, NH, 1H), 7.97 (d, J = 8.8 Hz, 2H). 13C
NMR (CDCl3, 100 MHz): δ 13.4, 19.2, 29.1, 39.9, 129.8, 130.7,
131.3, 142.7, 151.1, 152.9. MS (EI) m/z (relative intensity) =
333 [M + 2H]˙+ (12), 332 [M + H]˙+ (23), 331 [M]˙+ (28), 175
(100), 111 (95). Anal. calcd for C12H14ClN3O4S: C, 43.44; H,
4.25; N, 12.67; S, 9.66%. Found: C, 43.07; H, 4.07; N, 12.29; S,
9.40.
Ipc=Ipa ¼ ðIpcÞ0=Ipa þ 0:485ðIspÞ0=Ipa þ 0:086
where (Ipc)0 and (Isp)0 are cathodic peak current and “switching
potential” current with respect to the zero current, respectively.
I
pc and Ipa have their usual meanings.
Electroorganic synthesis of 5a–5f
Aqueous phosphate buffer solution (70 ml, c = 0.2 M, pH = 3.0)
containing 0.25 mmol of 4-propyl-1,2,4-triazolidine-3,5-dione
(or 4-butyl-1,2,4-triazolidine-3,5-dione) and 0.25 mmol of 4-
chlorobenzenesulfinic acid (benzenesulfinic acid or toluenesulfi-
nic acid) were subjected to electrolysis at 0.60 V versus Ag–
AgCl, in a divided cell. The electrolysis was terminated when
the decay of current became more than 95%. The process was
interrupted during the electrolysis and the graphite anode was
washed by acetone in order to reactivate it. The precipitated solid
was collected by filtration and was washed several times with
4-Butyl-1-(phenylsulfonyl)-1,2,4-triazolidine-3,5-dione (5e). IR
(KBr, cm−1): 3429, 3158, 3087, 2958, 2941, 1801, 1722, 1584,
1452, 1421, 1384, 1188, 1138, 1100, 1056, 942, 847, 773, 755,
1
711, 683, 595, 564. HNMR (400 MHz, CDCl3): δ 0.77 (t, J =
7.2 Hz, 3H), 0.91 (m, 2H), 1.33 (m, 2H), 3.41 (t, J = 7.0 Hz,
2H), 7.62 (t, J = 7.8 Hz, 2H), 7.77 (t, J = 7.6 Hz, 1H), 8.03 (d, J
= 7.6 Hz, 2H), 8.24 (broad, NH, 1H). 13C NMR (CDCl3,
100 MHz): δ 13.4, 19.1, 29.1, 39.7, 129.2, 129.4, 133.1, 135.5,
151.3, 153.4. MS (EI) m/z (relative intensity) = 298 [M + H]˙+
(90), 297 [M]˙+ (90), 219 (29), 141 (100), 125 (96), 77 (96).
Anal. calcd for C12H15N3O4S: C, 48.47; H, 5.08; N, 14.13; S,
10.78%. Found: C, 48.30; H, 4.99; N, 14.04; S, 10.28.
1
water. After drying, the products were characterized by IR, H
NMR, 13C NMR, MS and elemental analysis.
1-[(4-Chlorophenylsulfonyl)]-4-propyl-1,2,4-triazolidine-3,5-
dione (5a). IR (KBr, cm−1): 3445, 3331, 3100, 2967, 1810,
1748, 1724, 1452, 1422, 1394, 1190, 1085, 1053, 833, 764, 624,
4-Butyl-1-tosyl-1,2,4-triazolidine-3,5-dione (5f). IR (KBr,
cm−1): 3333, 3095, 2950, 2931, 1794, 1729, 1726, 1453, 1395,
1194, 1178, 1110, 761, 666, 581, 543. 1HNMR (400 MHz,
CDCl3): δ 0.78 (t, J = 7.2 Hz, 3H), 0.91 (m, 2H), 1.36 (m, 2H),
2.49 (s, 3H), 3.41 (t, J = 6.8 Hz, 2H), 7.40 (d, J = 8.0 Hz, 2H),
7.68 (broad, NH, 1H), 7.90 (d, J = 8.4 Hz, 2H). 13C NMR
(CDCl3, 100 MHz): δ 13.4, 19.2, 21.8, 29.1, 39.7, 129.3, 130.0,
1
571 H NMR (400 MHz, CDCl3): δ 0.64 (t, J = 7.4 Hz, 3H),
1.48 (m, 2H), 3.40 (t, J = 7.0 Hz, 2H), 7.60 (d, J = 8.8 Hz, 2H),
7.96 (d, J = 8.4 Hz, 2H), 8.05 (Broad, NH, 1H). 13C NMR
(100 MHz, CDCl3): δ 10.4, 20.6, 41.6, 129.9, 130.6, 131.4,
142.7, 151.1, 153.2. MS (EI) m/z (relative intensity): 319 [M +
2H]˙+ (10), 317 [M]˙+ (28), 245 (12), 177 (100), 113 (50). Anal.
966 | Green Chem., 2012, 14, 963–967
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147.0, 151.2, 153.1. MS (EI) m/z (relative intensity) = 312
[M + H]˙+ (23), 311 [M]˙+ (25), 175 (15), 155 (100), 139 (37),
91 (100). Anal. calcd for C13H17N3O4S: C, 50.15; H, 5.50; N,
13.50; S, 10.30%. Found: C, 50.10; H, 5.46; N, 13.40; S, 10.23.
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Acknowledgements
We acknowledge the Bu-Ali Sina University Research Council
and Center of Excellence in Development of Chemical Methods
(CEDCM) for their support of this work. Further partial financial
support from National Elite Foundation (NEF) and Center of
Excellency in Sensors and Green Chemistry Research Isfahan
University of Technology is also gratefully acknowledged.
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3 http://medical-dictionary.thefreedictionary.com/sulfonamide
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