Electroreductive nucleophile acceptor generation. Electrochemical synthesis of N-(4-(dimethylamino)phenyl)benzenesulfonamide

Article abstract of DOI:10.1016/j.electacta.2015.09.031

To the best of our knowledge, this is first report describing generation of Michael acceptor via electrochemical reduction. In this work, electrochemical reduction of 4-nitroso-N,N-dimethylaniline has been studied in the presence of arylsulfinic acids in

Full text of DOI:10.1016/j.electacta.2015.09.031

Accepted Manuscript
Title: Electroreductive nucleophile acceptor generation.
Electrochemical synthesis of
N-(4-(dimethylamino)phenyl)benzenesulfonamide
Author: Sadegh Khazalpour Davood Nematollahi Azizan
Ahmad Bahram Dowlati
PII:
S0013-4686(15)30443-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.electacta.2015.09.031
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24-8-2015
6-9-2015
Please cite this article as: Sadegh Khazalpour, Davood Nematollahi, Azizan Ahmad,
Bahram Dowlati, Electroreductive nucleophile acceptor generation.Electrochemical
synthesis of N-(4-(dimethylamino)phenyl)benzenesulfonamide, Electrochimica Acta
http://dx.doi.org/10.1016/j.electacta.2015.09.031
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Electroreductive nucleophile acceptor generation. Electrochemical
synthesis of N-(4-(dimethylamino)phenyl)benzenesulfonamide
Sadegh Khazalpoura, Davood Nematollahia,* nemat@basu.ac.ir, Azizan Ahmadb, Bahram Dowlatib
aFaculty of Chemistry, Bu-Ali-Sina University, Hamedan 65178-38683, I. R. Iran.
bSchool of Chemical Science and Food Technology, Faculty of Science and Technology, The
National University of Malaysia (UKM), 43600 Bangi Selangor Malaysia
*Corresponding author.
1

Graphical abstract
2

Highlights
• Electroreductive generation of Michael acceptor.
• Electrochemical synthesis of some N-(4-(dimethylamino)phenyl)-4-methylbenzenesulfonamide
derivatives.
•
Green electrochemical synthesis.
3

Abstract
To the best of our knowledge, this is first report describing generation of Michael acceptor
via electrochemical reduction. In this work, electrochemical reduction of 4-nitroso-N,N-
dimethylaniline has been studied in the presence of arylsulfinic acids in aqueous solutions.
The cathodically generated p-quinonediimine participates in Michael type addition reaction
with arylsulfinic acids and converts to the corresponding sulfonamide derivatives. This work
has led to the development of a facile and environmentally friendly reagent-less
electrochemical method for the synthesis of some sulfonamide derivatives with safe waste
under green conditions.
Keywords: Electrochemical synthesis; 4-Nitroso-N,N-dimethylaniline; Sulfonamide; Michael
type reaction; Cyclic voltammetry
4

1. Introduction
In organic synthesis, the Michael addition reaction is generally considered as the most
important C-C bond-formation [1,2]. These reactions are generally performed using strong
acids/bases [3,4], transition metals or lanthanide catalysts [5,6] and organocatalysts [7-16]
which would lead to undesirable by-products and environmentally hazardous residues.
However, due to the growing need for the organic synthesis under green conditions, great
attention has recently been focused on the using of environmentally friendly methods.
Electrochemistry on the other hand, is a powerful tool for the synthesis of complex organic
compounds [17-20]. It covers most of 12 principles of green chemistry [21-27]. In this
method, there is no need to use any kind of oxidizers or catalysts and only electrons serve as
the reagents. Therefore, in this method, the waste is nearly negligible [21-27].
Sulfonamides (sulfa drugs) are an important group of drugs. They stop the growth of
bacteria by interfering with their metabolism. They are still usually used for treatment of
urinary tract infections and acne [28,29]. These properties motivate us and others to
synthesize a number of these compounds [30-37]. Contrary to our previously published data
that are focused on electrochemical synthesis of organic compounds based on in-situ
oxidative Michael acceptor generation [24-27], in this work to increase the efficiency of the
electrochemical methods for the synthesis of organic compounds, for the first time we
introduce synthesis of organic compounds based on in-situ electroreductive Michael acceptor
generation. This idea prompted us to investigate electrochemical reduction of 4-nitroso-N,N-
dimethylaniline (NDA) in the presence of arylsulfinic acids (1a-1c) as nucleophiles. This
method represents a facile and one-pot electrochemical process for the synthesis of
sulfonamide derivatives (2a-2c) in high yields and purities under green conditions, without
5

toxic reagents and solvents at a carbon electrode in a divided cell, using an environmentally
friendly method.
Since, in this work electrochemical reduction of 4-nitroso-N,N-dimethylaniline (NDA)
has been studied, it is useful to introduce the valuable works by Moinet and co-workers on
the electrochemical generation of nitroso compounds [38-44].
2. Experimental Methods
2.1 Apparatus and reagents
Cyclic voltammetry, controlled-potential coulometry and preparative electrolysis were
performed using an Autolab model PGSTAT 302N potentiostat/galvanostat. The working
electrode used in the voltammetry experiments was a glassy carbon disc (1.8 mm2 area)
and a platinum wire was used as an auxiliary electrode. The working electrode used in
macro-scale electrolysis and controlled-potential coulometry was an assembly of four
carbon rods (31 cm2) and a large steel sheet constitute the counter electrode. The working
electrode potentials were measured versus Ag/AgCl (from AZAR electrode). NDA
,
benzenesulfinic acid, 4-chlorobenzenesulfinic acid and 4-toluenesulfinic acid were
reagent-grade materials from Aldrich. Phosphate salts were of pro-analysis grade from E.
Merck. These chemicals were used without further purification.
2.2 General electrochemical procedure
An aqueous phosphate buffer (ca. 80 ml, c
= 0.2 mol dm-3, pH = 7.0) containing NDA
(0.40 mmol) and arylsulfinic acids sodium salt (1a-1c) (0.40 mmol) was electrolyzed in a
divided cell at -0.30 V vs. Ag/AgCl. The electrolysis was terminated when the current
decreased by more than 95% (after consumption of about 85 coulombs). At the end of
6

electrolysis, the precipitated solid was collected by filtration and washed several times
with cold water.
2.3 N-(4-(dimethylamino)phenyl)-4-methylbenzenesulfonamide (C15H18N2O2S)(2a)
Isolated yield 77%. mp= 118-119 oC.1H NMR (600 MHz, CDCl3)
δ
2.40 (s, 3H), 2.92
13
(s,6H), 6.25 (s, 1H), 6.57 (s, 2H), 6.90 (s, 2H), 7.58 (s, 2H), 7.83 (s, 1H); C NMR (150
MHz, CDCl3)
δ 21.6, 40.6, 112.6, 124.6, 126.3, 127.4, 129.5, 136.3, 143.4, 149.3; IR
(KBr, cm-1): 3216, 2921, 2871, 2798, 1613, 1521, 1329, 1152, 1092, 946, 815, 679, 554,
532; MS (EI) (m/z) (relative intensity%): 290 [M] (79), 135 (100), 119 (29), 91 (31), 65
(23).
2.4 N-(4-(dimethylamino)phenyl)benzenesulfonamide (C14H16N2O2S) (2b)
o
Isolated yield 72%. mp 115-116 C.1H NMR (600 MHz, CDCl3)
δ
2.99 (s, 6H), 6.27
=6.6, 2H), 7.43 (s, 2H), 7.53 (s, 1H), 7.70 (d, =6.0,
40.5, 112.6, 124.4, 126.4, 127.3, 128.8, 132.6, 139.3,
(s,1H), 6.56 (d,
J=7.2, 2H), 6.88 (d,
J
J
2H); 13C NMR (150 MHz, CDCl3)
δ
149.4; IR (KBr, cm-1): 3216, 2923, 2853, 2801, 1614, 1521, 1447, 1334, 1156, 1092, 948,
910, 724, 577; MS (EI) (m/z) (relative intensity%): 276 [M] (32), 135 (100), 119 (12), 93
(7), 77 (15), 51 (8).
2.5 4-Chloro-N-(4-(dimethylamino)phenyl)benzenesulfonamide (C14H15ClN2O2S) (2c)
o
Isolated yield 75%. mp 106-108 C. 1H NMR (600 MHz, CDCl3)
δ
2.92 (s, 6H), 6.18
=5.4, 2H); 13C NMR (150
40.5, 112.6, 123.8, 126.6, 128.8, 129.1, 137.7, 139.1, 149.5; IR (KBr, cm-
(s,1H), 6.58 (s, 2H), 6.88 (d, J=5.4, 2H), 7.41 (s, 2H), 7.61 (d, J
MHz, CDCl3)
δ
1): 3243, 3091, 2923, 2854, 2804, 1612, 1520, 1477, 1443, 1335, 1159, 1091, 1015, 948,
7

899, 828, 815, 757, 613, 577; MS (EI) (m/z) (relative intensity %): 310 [M] (24), 284
(15), 135 (100), 119 (18), 93 (8), 75 (9), 42 (5).
3. Results and discussion
Cyclic voltammogram of 4-nitroso-N,N-dimethylaniline (NDA) (1.0 mmol dm-3) in
aqueous solution at pH = 7.0 is shown in Fig. 1,curve a. During the cathodic scan (starting
potential, 0.00 V), NDA shows a well-defined cathodic peak (C1) at −0.18 V versus
Ag/AgCl, which is assigned to the reduction of NDA to N,N-dimethyl-p-
phenylenediamine (DMP) within an irreversible four-electron process (Scheme 1) [27,45-
47].
Under these conditions, during the anodic scan, the voltammogram shows three anodic
peaks, A2, A3 and A4 at 0.24, 0.33 and 0.82 V versus Ag/AgCl, and in the reverse scan
from 0.90 V to starting potential, it shows three cathodic peaks C2, C3 and C4 at 0.19, 0.29
and 0.75 V versus Ag/AgCl, respectively, which are counterparts of anodic peaks, A2, A3
and A4, respectively. The anodic peaks A2 and A3 correspond to the transformation of
DMP to the radical cation (DMP.+), and DMP.+ to QDI, respectively, within two
successive one-electron processes (Scheme 2). Obviously, cathodic peaks C2 and C3 are
related to the reduction of QDI to DMP.+ and DMP.+ to DMP, respectively (Scheme 2)
[48].
Moreover, the anodic and cathodic peaks A4 and C4 are attributed to the oxidation of
NDA to the nitroso-
p-quinonediimine (NQD) and vice versa within a reversible two-
electron process (Scheme 3).
8

The reduction of NDA in the presence of 4-toluenesulfinic acid (1a) as a nucleophile
was studied in some detail. Figure 1 curve b, shows the cyclic voltammogram obtained
for NDA (1.0 mmol dm-3) in the presence of 1a (10.0 mM). Comparison of this
voltammogram with curve a shows that: (a) IpC1 is decreased. (b) The cathodic peaks C2,
C3 and C4 are disappeared and (c) a new anodic peak (A5) is appeared at 0.46 V versus
Ag/AgCl.
More studies were conducted by increasing the potential scan rate and decreasing 1a
concentration. The results show that the cathodic peaks C2, C3 and C4 appear again with
increasing potential scan rate and/or decreasing 1a concentration. In addition, under these
conditions, IpC1 is comparable to the unperturbed IpC1
.
Controlled potential coulometry (CPC) and monitoring of electrolysis progress by
cyclic voltammetry were used to obtain information about the reaction process and the
number of electrons involved in reaction (Fig. 2). CPC was performed in aqueous solution
containing NDA and 1a at -0.30 V versus Ag/AgCl, at pH = 7.0. It shows that
proportional to the progress of coulometry, the cathodic peak C1 decreased and disappears
when the charge consumption becomes about 2e− per molecule of NDA. The
voltammetric and coulometric data as well as the spectroscopic data of final products
allow us to propose an ECC mechanism for the electrochemical reduction of NDA in the
presence of arylsulfinic acids (1a-1c) (Scheme 4).
According to the proposed mechanism, the electrogenerated
p-quinonediimine QDI
,
involved in a Michael type addition reaction with 1a, before further reduction to DMP
,
producing the sulphonamide 2a as the final product. In order to the study of the
electrochemical properties of one of the isolated products, the cyclic voltammetric
9

behaviour of 2c was examined (Fig. 3). As can be seen, voltammogram exhibits a quasi-
reversible system with E1/2= 0.56 V vs. Ag/AgCl (at pH 3.0). In addition, according to
these data, the anodic peak A5 is pertain to the oxidation of sulphonamide 2a, to its
oxidized form (2aox) (Scheme 5) [35-37].
The control experiment was conducted with no applied potential, by stirring a solution
of 4-nitroso-N,N-dimethylaniline and 4-toluenesulfinic (1a) in phosphate buffer solution
(
c
= 0.2 mol dm-3, pH = 7.0). The monitoring of the reaction was carried out by cyclic
voltammetry. It shows that, there was no change over time (48 h) in the height of peak C1
IpC1). The results confirm that, under these conditions, no reaction happens between
NDA and 1a
(
.
4. Conclusions
To our knowledge, this is first report describing generation of Michael acceptor via
electrochemical reduction. The present method for the synthesis of
N-(4-
(dimethylamino)phenyl)benzenesulfonamide derivatives has several advantages over
conventional methods and led to the development of a new strategy in accordance with
the principles of green chemistry for the synthesis of some sulfonamide
derivatives.Although the experiments were conducted on a relatively small scale, there is
little difficulty in producing larger quantities either by using larger cells or by running
several cells in series.
Acknowledgements
10

We acknowledge the Bu-Ali Sina University Research Council and the Center of
Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis
(CEDEFMCS) for their support of this work.
11

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Figure Captions
Fig. 1. Cyclic voltammograms of NDA (1.0 mmol dm-3) (a) in the absence, (b) in the
presence of 4-toluenesulfinic acid (1a) (10.0 mmol dm-3). Sweeping direction: reduction
of NDA in the first stage. (c) as (a), but oxidation of NDA in the first stage. At a glassy
carbon electrode, in aqueous phosphate buffer (pH = 7.0,
c
= 0.2 mol dm-3). Scan rate:
100 mV s-1. Temperature = 25±1 °C.The arrows 1-4, show sweeping direction.
Fig. 2. a) Cyclic voltammograms of NDA (0.4 mmol) in the presence of 1a (1.20 mmol)
at a glassy carbon electrode in aqueous phosphate buffer solution (pH = 7.0,
c = 0.2 mol
dm-3) during controlled-potential coulometry at -0.30 V versus Ag/AgCl after
consumption of 0, 25, 50, 75 and 85 C. Scan rate: 100 mV s-1. b) Plot of IpC1 versus
charge passed. Temperature = 25 ± 1 oC.
Fig. 3. Cyclic voltammogram of 2c (1.0 mmol dm-3) at glassy carbon electrode in water
(phosphate buffer, pH = 3.0,
rate: 100 mV s-1. Temperature = 25±1 °C.
c
= 0.2 mol dm-3)/acetonitrile (70/30, v/v) mixture. Scan
18

Fig. 1
19

Fig. 2
20

Fig. 3
21

Scheme 1. Electrochemical reduction of NDA to DMP
.
Scheme 2. Two steps electrochemical oxidation of DMP.
Scheme 3. Two-electron oxidation of NDA.
22

Scheme 4. Proposed mechanism for the electrochemical reduction of NDA in the
presence of 1a-1c
.
Scheme 5. Redox behaviour of 2a/2aox.
23