Journal of The Electrochemical Society, 164 (6) G65-G70 (2017)
G65
0013-4651/2017/164(6)/G65/6/$37.00 © The Electrochemical Society
Electrochemical Oxidation of Sulfinic Acids: Efficient Oxidative
Synthesis of Diaryl Disulfones
Davood Nematollahi,z Mahsa Joudaki, Sadegh Khazalpour, and Firozeh Pouladi
Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65178-38683, Iran
Electrochemical oxidation of sulfinic acids has been studied in aqueous solutions using cyclic voltammetry, controlled-potential
coulometry, chronoamperometry and chronocoulometry methods. The results indicate that the oxidation of sulfinic acids is an
irreversible one-electron transfer process. Our data also show that the electrogenerated sulfonyl radicals undergo a dimerization
reaction to form disulfone derivatives. The present work has led to the development of a facile and environmentally friendly
electrochemical method for the synthesis of diphenyl disulfone derivatives.
Manuscript submitted March 1, 2017; revised manuscript received March 21, 2017. Published April 7, 2017.
Electrochemistry is a powerful tool for the synthesis of organic
compounds. It can be used for Michael addition reaction,1–3 Diels–
utilized in several chemical reactions as reagent for selective cleavage
of methylprenyl (2,3-dimethylbut-2-en-1-yl), prenyl (3-methylbut-2-
en1-yl), and methallyl (2-methylallyl) ethers,12 and as catalyst for
isomerization of alkenes,13,14 chemoselective cleavage of methyl-
substituted allyl ethers,15 photopolymerization of vinyl monomers,16
Several methods have been reported for the synthesis of
diphenyl disulfone derivatives, including the oxidation of benzen-
sulfinic acid by KMNO4,17 and Cobalt(III),18 oxidation of 1,2-bis-
(benzenesulfonyl)hydrazine by NaOCl in CHCl3,19 thermal reaction
of benzene and sulfur dioxide in the presence of benzoyl peroxide,20
decomposition of phenylphenylsulfonyl diimide in p-xylene,21 ox-
idation of diphenyl disulfide by hydrogen peroxide,22 oxidation of
tric acid,24 reaction of sodium benzenesulfinate and benzenesulfonyl
chloride,25 and reduction of benzenesulfonyl chloride by samarium26
or lithium.27 However, these methods have the following disad-
vantages such as low yield, poor purity, lack of easy availabil-
ity/preparation of the starting materials, tedious work-up, heavy metal
pollution, strongly acidic media and safety problems. These disadvan-
tages have motivated us to develop a green protocol for the synthesis of
diphenyl disulfones by electrochemical oxidation of aryl sulfinic acids
in aqueous solution. This work leads to a straight-forward methodol-
ogy for the synthesis of diphenyl disulfones by an environmentally
friendly method in ambient conditions and in an undivided cell.
The second objective of this study is to report the electrochemical
behavior and electrochemical parameters (diffusion coefficient, D,
surface excess, ꢀ, and average area, σ) of the sulfinic acids by using
of cyclic voltammetry, chronoamperometry and chronocoulometry
methods.
under both controlled-potential and galvanostatic conditions in an un-
divided cell equipped with a magnetic stirrer. All experiments were
carried out at a temperature of 25 1◦C. Melting points of the prod-
ucts were determined in open capillary tubes and are uncorrected. IR
spectra (KBr) were recorded on Perkin–Elmer GX FT-IR spectrome-
ter. 1H and 13C NMR spectra were recorded on BRUKER Ultrashield
400 spectrometer operating at 400 and 100 MHz, respectively. Mass
spectra were recorded on a HP 5973 GC-MS instrument operating at
an ionization potential of 70 eV.
4-Toluenesulfinic acid (TS), benzenesulfinic acid (BS), 4-
chlorobenzenesulfinic acid (CS) and methansulfinic acid (MS) were
reagent-grade materials from Aldrich. Sodium hydroxide and phos-
phoric acid were of pro-analysis grade from E. Merck.
Electroorganic synthesis.—An aqueous solution of phosphate
buffer (ca. 80 mL, c = 0.2 M, pH = 2.0) containing 4-toluenesulfinic
(TS) (BS, CS or MS) (0.75 mmol) was electrolyzed in an undivided
cell at 1.1 V (1.2 V for BS, 1.1 V for CS and 1.2 V for MS) vs.
SHE, at 25
1◦C. The electrolysis was terminated when the cur-
rent decreased by more than 95% (after consumption of about 160
coulombs, during about 4 h). At the end of electrolysis, the precipi-
tated solid (white color) was collected by filtration and was washed
several times with cold water. After drying, the products were char-
acterized by FTIR, NMR (1H and 13C) and mass spectrometry. The
galvanostatic synthesis was performed under the same experimental
conditions by applying a constant current density of 0.21 mA/cm2 and
continued until the charge reached 73 C (1 F/mol). It should be noted
that, the application of these methods to the synthesis of 1,2-dimethyl
disulfone (DPD4), was not favorable.
4,4’-Dimethyldiphenyl disulfone (C14H14S2O4) (DPD1).—Iso-
lated yield: 80%. mp 199–200◦C (Lit. 211◦C28). 1H NMR (400 MHz,
CDCl3) δ: 2.54 (s, 6H, methyl), 7.45 (d, J = 8, 4 Hz, aromatic), 7.86
(d, J = 8.4 Hz, 4H, aromatic); 13C NMR (100 MHz, CDCl3) δ: 22.0
(C-3), 128.0 (C-2), 130.4 (C-1), 131.5 (C-5), 148.1 (C-4). IR (KBr) ν:
2929 (weak, C-H), 1588 (medium C=C), 1343 (strong S=O), 1135
(strong S=O), 1063, 807, 695, 633 cm−1; MS (EI, 70 eV) (m/z) (rela-
tive intensity): 310 (M+., 1), 155 (92), 91 (100), 65 (46), 139 (29), 77
(13), 51 (8).
Experimental
Apparatus and reagents.—Cyclic voltammetry, chronoamperom-
etry and chronocoulometry were performed using a Zahner pp201
potentiostat/galvanostat. Macro-scale electrolysis and controlled-
potential coulometry were carried out using a Behpajooh C 2056
potentiostat. The glassy carbon disk (1.8 mm diameter) was used as
the working electrode in the voltammetry experiments and a platinum
wire was used as the counter electrode. The working electrode used in
controlled-potential coulometry and macroscale electrolysis was an
assembly of two ordinary carbon plates (20 mm length, 10 mm width
and 40 mm height), and a large stainless steel gauze cylinder (25 cm2
area) constituted the counter electrode. The glassy carbon electrode
potentials were measured versus Ag/AgCl (from AZAR electrode) and
reported versus SHE. The electrochemical synthesis was performed
1,2-Diphenyl disulfone (C12H10S2O4) (DPD2).—Isolated yield:
68%. mp: 190–192◦C (Lit. 190–192◦C,17 193–194◦C28). 1H NMR
(400 MHz, CDCl3) δ: 7.65 (t, J = 7.6, 4H, aromatic), 7.83 (t, J =
7.6, 2H, aromatic), 7.97 (d, J = 7.6 Hz, 4H, aromatic); 13C NMR
(100 MHz, CDCl3) δ: 129.7 (C-2), 131.2 (C-1), 131.5 (C-3), 136.4
(C-4); IR (KBr) ν: 1578 (medium C=C), 1448 (strong), 1349 (strong