Electrochemical synthesis of p-tolylsulfonylbenzenediols

Article abstract of DOI:10.1016/S0040-4039(01)02050-0

The electrochemical synthesis of p-tolylsulfonylbenzenediols (4a-c) by anodic oxidation of catechols (1a-c) in the presence of 4-toluene sulfinic acid (3) is described. Products were obtained in an undivided cell in good yields and purity. The mechanism o

Full text of DOI:10.1016/S0040-4039(01)02050-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 147–150
Electrochemical synthesis of p-tolylsulfonylbenzenediols
Davood Nematollahi* and Ramazanali Rahchamani
Department of Chemistry, Faculty of Science, University of Bu-Ali-Sina, Hamadan, 65174, Iran
Received 6 September 2001; revised 18 October 2001; accepted 26 October 2001
Abstract—The electrochemical synthesis of p-tolylsulfonylbenzenediols (4a–c) by anodic oxidation of catechols (1a–c) in the
presence of 4-toluene sulfinic acid (3) is described. Products were obtained in an undivided cell in good yields and purity. The
mechanism of oxidation has been studied in aqueous solution using cyclic voltammetry and controlled-potential coulometry.
© 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
o-quinone produced at the surface of the electrode
under the experimental conditions. In other words, any
hydroxylation13–16 or dimerization17,18 reactions are
occurring too slowly to be observed in the time scale of
cyclic voltammetry. The oxidation of catechol (1a) in
the presence of 4-toluenesulfinic acid (3) as a nucleo-
phile was studied in some detail (Fig. 1 (curve b)).
Under these conditions, the cathodic counterpart of the
anodic peak A1 disappears. The positive shift of the A1
peak in the presence of 4-toluenesulfinic acid (Fig. 1,
curve b) that was enhanced during the repetitive recy-
Previously we have shown that catechols can be oxi-
dized electrochemically to o-quinones. The quinones
formed are quite reactive and can be attacked by a
variety of nucleophiles such as methanol,1–3 ethanol,4
4-hydroxycoumarin,5–7 b-diketones8 and 2-thiobarbi-
turic acid;9 they have been converted to the correspond-
ing alkoxyquinone, coumestan, benzofuran and
dispirothiopyrimidine derivatives, respectively. The
importance of sulfones such as arylsulfonylbenzenediols
that are known as thermally sensitive materials10,11 has
prompted many workers to synthesize a number of
these compounds by chemical routes.12 However, no
report has been published until now about the electro-
chemical synthesis of arylsulfonylbenzenediol deriva-
tives.
Therefore,
we
have
investigated
the
electrooxidation of catechol and 3-substituted catechols
in the presence of 4-toluenesulfinic acid as the nucleo-
phile and describe a facile electrochemical method for
the synthesis of some new sulfone derivatives in good
yield and purity.
Cyclic voltammetry of 1 mM catechol (1a) shows one
anodic (A1) and the corresponding cathodic peak (C1),
which correspond to the transformation of catechol
(1a) to o-benzoquinone (2a) and vice versa within a
quasi-reversible two-electron process (Fig. 1, curve a).
A peak current ratio (IPC1/IPA1) of nearly unity, particu-
larly during the repetitive recycling of the potential, can
be considered as a criterion for the stability of the
Figure 1. Cyclic voltammograms of 1 mM catechol: (a) in the
absence; (b) in the presence of 1 mM 4-toluenesulfinic acid,
and (c) 1 mM 4-toluenesulfinic acid in the absence of cate-
chol, at a glassy carbon electrode, in acetate buffer solution
(c=0.2 M, pH 4.5); scan rate: 50 mV s−1; T=25 1°C.
Keywords: electro-organic synthesis; catechol; 4-toluenesulfinic acid;
sulfone derivatives.
* Corresponding author. Tel.: 0098-811-8271541; fax: 0098-811-
8272404; e-mail: nemat@basu.ac.ir
0040-4039/02/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02050-0

148
D. Nematollahi, R. Rahchamani / Tetrahedron Letters 43 (2002) 147–150
cling of potential is probably due to the formation of a
thin film of product at the surface of the electrode,
inhibiting, to a certain extent, the performance of the
electrode process.5–9
Monitoring of the electrolysis progress was carried out
by cyclic voltammetry. It is shown that, proportional to
the advancement of coulometry, anodic peak A1
decreases and disappears when the charge consumption
becomes about 2e− per molecule of 1a.
Furthermore, it is seen that proportional to the aug-
mentation of the potential sweep rate, the height of the
C1 peak of 1a increases (Fig. 2). A similar situation is
observed when the 4-toluenesulfinic acid (3) to 1a con-
centration ratio is decreased. On the other hand, the
current function for the A1 peak, (IPA1/w1/2), changes
only slightly with increasing scan rate (Fig. 2, curve h)
and such behaviour has been adopted as being indica-
tive of the EC mechanism.5–9
These observations allow us to propose the pathway in
Scheme 1 for the electrooxidation of 1a in the presence
of 4-toluenesulfinic acid (3).
According to our results, it seems that the Michael
addition reaction of anion 3 to o-quinone (2a) (Eq. (2))
is faster than other secondary reactions, leading to the
product 4a. The oxidation of this compound (4a) is
more difficult than the oxidation of the parent starting
molecule (1a) by virtue of the presence of the electron-
withdrawing phenylsulfonyl group on the catechol ring.
The overoxidation of 4a was circumvented during the
Controlled-potential coulometry was performed in
aqueous solution containing 0.33 mmol of 1a and 0.33
mmol of 4-toluenesulfinic acid (3) at 0.45 V versus SCE.
Figure 2. Typical voltammograms of 1 mM catechol in water in the presence of 1 mM 4-toluenesulfinic acid at a glassy carbon
electrode, in acetate buffer solution (c=0.2 M, pH 4.5), at various scan rates. Scan rates from (a) to (g) are: 50, 100, 200, 500,
1000, 2000 and 5000 mV s−1, respectively; (h) variation of peak current function (IPA1/w1/2) versus scan rate. T=25 1°C.
Scheme 1.

D. Nematollahi, R. Rahchamani / Tetrahedron Letters 43 (2002) 147–150
Table 1. Electroanalytical and preparative data
149
Conversion
Applied potential V (SCE)
Product yield (%)
Melting point (°C)
Sulfur content
Calcd Found
1a“4aa
1b“4bb
1c“4cc
0.45
0.40
0.40
93
84
80
100–101 (dec.)
140–142 (dec.)
185–187 (dec.)
12.12
11.51
10.88
12.01
11.39
10.65
a (4a): 4(4-Methylphenylsulfonyl)-1,2-benzenediol (C13H12O4S), IR(KBr): 3320, 1593, 1508, 1443, 1371, 1292, 1145, 1089, 915, 810, 685, 564 cm−1
.
1H NMR, l (90 MHz, DMSO-d6): 2.38 (s, 3H methyl) [7.33 (d, J=6.1 Hz); 7.83 (d, J=7.1 Hz) 7H, aromatic]; 10.0 (broad, 2H hydroxy). MS:
m/e (relative intensity); 264(100), 157(37), 140(63), 108(78), 92(86), 65(69), 39(80).
b (4b): 3-Methyl-5-(4-methylphenylsulfonyl)-1,2-benzenediol (C14H14O4S), IR(KBr): 3400, 2900, 1620, 1589, 1512, 1419, 1299, 1138, 1093, 1029, 904,
807, 670, 590 cm−1 1H NMR, l (DMSO-d6): 2.24 (s, 3H methyl); 2.38 (s, 3H methyl); [7.28 (d, J=3 Hz); 7.38 (s); 7.78 (d, J=7.7 Hz) 6H,
.
aromatic]; 9.4 (broad, 1H hydroxy), 10.1 (broad, 1H hydroxy). MS: m/e (relative intensity); 278(100), 171(25), 139(68), 121(40), 92(60), 65(64),
39(59).
c (4c): 3-Methoxy-5-(4-methylphenylsulfonyl)-1,2-benzenediol (C14H14O5S), IR(KBr): 3520, 3240, 2920, 1605, 1500, 1456, 1295, 1202, 1141, 1081,
952, 807, 670, 581 cm−1 1H NMR, l (DMSO-d6): 2.39 (s, 3H methyl); 3.89 (s, 3H methoxy); [7.10 (s); 7.42 (d, J=8 Hz); 7.77 (d, J=7.9 Hz)
.
6H, aromatic] 9.5 (broad, 1H hydroxy), 9.8 (broad, 1H hydroxy). MS: m/e (relative intensity); 294(100), 187(31), 155(46), 139(74), 108(23),
91(47), 65(47), 39(52).
preparative reaction because of the presence of the
electron-withdrawing group as well as the insolubility
of the product in the acetate buffer solution media.
washed in acetone in order to reactivate it. At the end
of electrolysis, about 0.5 ml of acetic acid was added to
the solution and the cell was placed in a refrigerator
overnight. The precipitated solid was collected by filtra-
tion and recrystallized from a mixture of water/acetone.
After recrystallization, the products were characterized
The electrooxidation of 1b and 1c in the presence of
4-toluenesulfinic acid (3) as a nucleophile in acetate
buffer solution proceeded in a manner similar to that of
1a.
1
by IR, H NMR, MS and sulfur content.
Acknowledgements
The existence of a methyl or a methoxy group at the
C-3 position of 1b and 1c probably causes these
Michael acceptors (2b and 2c) to be attacked by the
anion (3) from the C-4 and/or the C-5 positions to yield
two types of products in each case. However, according
to thin layer chromatography (TLC) and 1H NMR
results, we suggest that o-quinones 2b and 2c are
attacked in all probability only at the C-5 position by
anion (3) leading to the formation of the products 4b
and 4c, respectively.19
This research project has been supported by grant No.
NRCI 31303 of National Research Projects and with
the support of the National Research Council of
Islamic Republic of Iran.
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2.1. Apparatus and reagents
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All chemicals (catechols and 4-toluenesulfinic acid
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