Selective and facile oxidative desulfurization of thioureas and thiobarbituric acids with singlet molecular oxygen generated from trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane

Article abstract of DOI:10.1080/17415993.2015.1082181

An efficient and facile procedure using trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane has been developed for oxidative desulfurization of thioureas and thiobarbituric acids. The reactions proceeded smoothly very fast under mild conditions in basic media at room temperature to afford the respective ureas in excellent yields. Simple procedure and work up, mild conditions, high yields, short reaction times, use of highly potent and non-toxic oxidant are the main merits of the present method.

Full text of DOI:10.1080/17415993.2015.1082181

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Selective and facile oxidative desulfurization of
thioureas and thiobarbituric acids with singlet
molecular oxygen generated from trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2-dioxolane
Davood Azarifar & Maryam Golbaghi
To cite this article: Davood Azarifar & Maryam Golbaghi (2015): Selective and facile oxidative
desulfurization of thioureas and thiobarbituric acids with singlet molecular oxygen generated
from trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane, Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2015.1082181
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Date: 12 October 2015, At: 10:46

Journal of Sulfur Chemistry, 2015
http://dx.doi.org/10.1080/17415993.2015.1082181
Selective and facile oxidative desulfurization of thioureas and
thiobarbituric acids with singlet molecular oxygen generated
from trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane
Davood Azarifar∗ and Maryam Golbaghi
Faculty of Chemistry, Buali Sina University, Hamedan 65178, Iran
(Received 6 July 2015; accepted 8 August 2015)
An efficient and facile procedure using trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane has been
developed for oxidative desulfurization of thioureas and thiobarbituric acids. The reactions proceeded
smoothly very fast under mild conditions in basic media at room temperature to afford the respective
ureas in excellent yields. Simple procedure and work up, mild conditions, high yields, short reaction
times, use of highly potent and non-toxic oxidant are the main merits of the present method.
Keywords: trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane; DHPODMDO; oxidation; desulfur-
ization; thioureas; thiobarbituric acid; urea
1. Introduction
Thiourea and its derivatives are known as hazardous, highly toxic and carcinoma-inducing
materials.[1] However, thioureas and many other thiocarbonyl compounds are of high indus-
trial potential,[2–4] and are employed as versatile tools in multi-step synthesis of various natural
products. Also, they are biologically active molecules, which involve transformation of thiocar-
bonyl group into the corresponding carbonyl group in final step.[5,6] On the other hand, the oxo
analogs of thioureas are non-toxic and environmentally friendly compounds which can be oxi-
dized to various nitrogen-containing heterocyclic products of pharmaceutical activities and used
as synthones in cyanine dyes.[7]
Several methods have been developed for oxidative desulfurization of thioureas and other
thiocarbonyl compounds into oxo analogs or other derivatives such as disulfides and hetero-
cyclic products.[8–10] The reagents reported in the literature for oxidative desulfurization mainly
include thionyl chloride,[11] phosgene,[12] t-butyl hypochlorite,[13] potassium superoxide,[14]
*Corresponding author. Email: azarifar@basu.ac.ir, dazarifar@gmail.com
© 2015 Taylor & Francis

2
D. Azarifar and M. Golbaghi
Scheme 1. Desulfurization of thioureas with DHPDMDO.
ceric ammonium nitrate,[15] m-chloroperbenzoic acid,[16] peracetic acid,[17] KBr/alkaline
solution,[18] OsO4,[19] KMnO4,[20] dimethyldioxirane,[21] mercuric oxide,[22,23] alka-
line peroxide,[24,25] N-bromosuccinimide,[26] oxone,[27] 3-carboxypyridinium and 2,2ꢀ-
bipyridinium chlorochromates,[28,29] ozone,[30] H2O2,[31] I2/Et3N,[32] n − Bu4N+IO−,[33]
4
(n-BuPPh3)2Cr2O7,[34] and cetyltrimethyl ammonium dichromate.[35] In addition, desul-
furization of 1,3-disubstituted thioureas with the hypervalent organoiodine (III) reagent,
diacetoxyiodobenzene, to form N-acylated ureas via carbodiimide intermediates has been
reported.[36] Pramod and co-workers have reported the o-iodoxybenzoic-acid-mediated desul-
furization of thioureas to carbodiimides.[37] However, many of these methods suffer from
certain drawbacks such as using noxious and toxic reagents, long reaction times, tedious
work-up, and removal of harmful by-products such as phosphorous by-products.[38] As a
result, to avoid these limitations, development of new and benign approaches for oxidative
desulfurization of sulfur-containing compounds, including thioureas, appears as an interesting
research challenge. In recent years, gem-dihydroperoxides have been extensively used as highly
potent oxidants for a variety of functional group transformations in organic synthesis.[39–46]
Herein, we report the hitherto unexplored efficient and convenient oxidative desulfurization of
mono- and disubstituted ureas and their related compounds such as thiobarbituric acids with
trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane (DHPODMDO).
In continuation of our ongoing research on the synthesis of various hydroperoxides,[47–52]
and their applications as highly potent oxidants for various organic transformations,[53–60] we
were encouraged to investigate the hitherto unexplored oxidative potential of DHPDMDO for
oxidative desulfurization of different sulfur-containing compounds such as thioureas into the
corresponding oxo analogs. As shown in Scheme 1, various substituted thioureas (1a–1s) were
reacted with DHPDMDO as an efficient oxidant. The reactions proceeded smoothly in aqueous
alkaline solution at room temperature to afford the corresponding ureas (2a–2s) in excellent
yields (Scheme 1).
2. Results and discussion
To establish the reaction conditions, we preliminarily reacted phenylthiourea 1a with
DHPDMDO in aqueous KOH solution at room temperature as the model reaction. The effects of
solvent and the oxidant loading on the reaction rate and yield were screened by using different
solvents such as EtOAc, CH2Cl2, H2O, EtOH, AcOH and CH3CN, with various amounts of the
oxidant (Table 1).
First, a separate reaction was set up for each solvent using constant 1 mmol amount of the
oxidant and 5 mL of 5% aqueous KOH solution at room temperature (Table 1, Entries 1–6).
As shown in Table 1, the best solvent appeared to be CH3CN among the other solvents exam-
ined in terms of the reaction time (20 min) and the yield (70%) (Entry 6). In the next stage, in
order to evaluate the effect of the oxidant concentration using CH3CN as the solvent of choice,
the reaction was repeated for different amounts of the oxidant with constant reaction time of 1

Journal of Sulfur Chemistry
3
Table 1. Screening the conditions for the model desulfurization reaction of phenylthiourea with
DHPDMDO/KOH at room temperaturea.
Entry
Solvent
Oxidant (mmol)
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
EtOAc
CH2Cl2
H2O
1
1
1
1
1
1
1
0.5
1.5
2
3
2
2
0
0
2
60
60
90
90
50
20
1
1
1
1
1
20
30
1
120
1
0
20
Trace
0
Trace
70
62
45
82
95
95
95
95
0
0
Trace
Trace
EtOH
CH3COOH
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
9
10
11
12
13
14
15
16c
17c
2
120
aConditions: phenyl thiourea (1 mmol), 5% aq. KOH (5 mL), solvent (5 mL), r.t.
bIsolated pure yield.
cNo base was used in the reaction.
min (Entries 7–11) and the best oxidant loading was found to be 2 mmol, as resulted in almost
complete desulfurization of phenylthiourea (Entry 10). It was noticed that, the yield of the reac-
tion was diminished when lower amounts of the oxidant are used (Entries 7–9), and no further
improvement of the yield was observed for higher amounts of the oxidant (Entry 11) with con-
stant reaction time of 1 min. More experiments were carried out (Entries 12, 13) using the best
oxidant concentration of 2 mmols at different reaction times to determine the best reaction time,
which appeared to be 1 min (Entry 10). In addition, the crucial role of the oxidant in the reac-
tion was approved by conducting the reaction in the absence of the oxidant under the optimized
conditions that ended with almost complete recovery of the starting materials even after a long
reaction time of 120 min (Entries 14, 15). Moreover, the importance of the presence of KOH
base in the reaction was evaluated when the reaction was carried out using 1,3-diphenylthiourea
as the substrate under neutral condition, which produced no detectable amount of the expected
product 2o (Entries 16, 17), but instead, diphenylcarbodiimide was obtained as the only product
which was identified on the basis of its spectral (FT-IR and NMR) data as given below. Finally,
the possible occurrence of the reaction in acidic media was examined by conducting the reaction
in acetic acid as solvent, which resulted in only trace amount of the expected product (Entry 5).
Spectral data of diphenylcarbodiimide: oily liquid. 1H-NMR (300 MHz, CDCl3): δ = 7.20 (m,
6 H), 7.31 (m, 4 H). 13C-NMR (75 MHz, CDCl3): δ = 124.3, 125.7, 129.6, 135.4, 138.4. FT-IR
(nujol): 2135, 2105, 1587, 1207, 755, 691 cm−1
.
In summary, according to the experimental results summarized in Table 1, the optimum condi-
tions found for this reaction is using CH3CN as the solvent with 2 mmols of the oxidant in basic
solution of KOH at room temperature.
To establish the generality of the reaction, a variety of mono- and 1,3-disubstituted thioureas
(1a–1q) and thiobarbituric acids (1r–1s) were subjected to the optimized conditions and the

4
D. Azarifar and M. Golbaghi
results are summarized in Table 2. In general, the reactions proceeded very fast and smoothly to
furnish the products in excellent and comparable yields (80–98%) irrespective of the nature of
the substituent groups on the aromatic rings.
All the products obtained were characterized on the basis of their physical and spectral (IR,
NMR) analysis as presented in experimental section.
3. Conclusion
In summary, an efficient and environmentally friendly method based on oxidative desulfurization
of mono- and 1,3-disubstituted thiourea derivatives and barbituric acids to the corresponding
oxo analogs employing DHPDMDO in aqueous KOH solution at room temperature has been
developed. Use of highly potent and non-toxic oxidant, avoiding any expensive and/or toxic
catalyst, mild reaction conditions, improved reaction rates and yields make this approach superior
over many other reported methods.
4. Experimental
1
FT-IR spectra were taken on a Perkin Elmer GX FT IR spectrometer in KBr pellets. H- and
13C-NMR spectra were recorded on a 300 MHz and 400 MHz BRUKER instrument in DMSO-d6
solutions using TMS as internal standard. Melting points were measured on an SMPI apparatus.
Caution: Although we did not encounter any problem with DHPDMDO, it is potentially explo-
sive and should be handled with precautions; all reactions should be carried out behind a safety
shield inside a fume hood and transition metal salts or heating should be avoided.
4.1. Preparation of DHPDMDO
Following our previously reported procedure,[55] this compound was prepared from acetyl
acetone upon treatment with 30% aqueous H2O2 under the catalytic effect of SnCl2·2H2O as
described below.
To a stirred solution of acetylacetone (100 mg, 1 mmol) in CH3CN (5 mL) was added
SnCl2.2H2O (45 mg, 0.2 mmol) and the resulting mixture was stirred for 5 min at room tem-
perature. Then, aqueous 30% H2O2 (5 mmol) was added to the reaction mixture and let to stir
for 12 h at room temperature. After completion of the reaction as monitored by TLC, water (15
mL) was added and the product was extracted with ethyl acetate (2 × 10 mL). The combined
organic layer was dried over anhydrous MgSO4 and evaporated under reduced pressure to leave
an almost pure white crystalline product in 85% yield (140 mg); mp 98–100°C; 1H-NMR (300
MHz, CDCl3) δ (ppm): 8.43 (bs, 2H, OOH), 2.67 (s, 2H, CH2-4), 1.59 (s, 6H, CH3). 13C-NMR
(75 MHz, D2O) δ: 16.5 (CH3), 50.7 (CH2-4), 112.7 (C-3, C-5); IR (KBr pellet) ν(cm−1): 3389
(w), 1433, 1380, 1333, 1173, 848, 790, 470.
4.2. Typical procedure for desulfurization of thiourea derivatives 1a–1s to oxo analogs
2a–2s
To a stirred solution of phenylthiourea 1 (1 mmol) and 5% aq. KOH (5 mL) in acetonitrile (5 mL)
was added DHPDMDO (0.332 g, 2 mmol). The resulting mixture was allowed to stir at room
temperature for an appropriate time (Table 2). After completion of the reaction as monitored

Journal of Sulfur Chemistry
5
Table 2. Desulfurization of thioureas and barbituric acids with DHPDMDO/aq. KOH in CH3CN at room temperaturea.
Mp (°C)
Entry
Substrate 1
Product 2
Time (min)
1
Yield (%)b
95
Found
Reported [34,61]
142
A
141–144
S
O
HN
NH2
HN
NH2
B
C
D
E
F
10
93
89
84
91
81
180–183
205–208
165–168
226–228
192–194
180
204
168
228
S
O
O
O
HN
NH2
HN
NH2
NH2
NH2
Me
Me
2
S
HN
NH2
HN
Cl
Cl
10
S
HN
NH2
HN
OMe
S
OMe
O
1
HN
NH2
HN
NH2
NO2
HN
NO2
HN
15
190–195
S
O
NH2
NH2
Me
Me
(Continued).

6
D. Azarifar and M. Golbaghi
Table 2. Continued.
Mp (°C)
Reported [34,61]
Entry
Substrate 1
Product 2
Time (min)
10
Yield (%)b
83
Found
186
G
186–188
O
S
HN
NH2
HN
NH2
F
F
H
20
89
358
–
O
S
HN
NH2
NH2
HN
H2N
NH
H2N
NH
S
O
I
10
87
95
100–102
218–221
101–103
O
S
HN
NH2
NH2
NH2
HN
NH2
F3C
F3C
J
5
222
S
O
HN
HN
NH2
K
L
5
96
87
182
179–181
204–205
S
O
HN
HN
NH2
O
O
O
O
15
202–204
O
S
HN
NH2
HN
NH2
H3C
H3C
CH3
CH3
(Continued).

Journal of Sulfur Chemistry
7
Table 2. Continued.
Mp (°C)
Entry
Substrate 1
S
Product 2
Time (min) Yield (%)b Found Reported [34,61]
10 89 220–221 220–223
M
O
HN
NH2
HN
NH2
Cl
Cl
Cl
Cl
N
10
94
248–251
248
S
O
HN
NH2
HN
NH2
Cl
Cl
NO2
NO2
O
O
P
1
2
98
93
238–240
235–236
242
236
S
S
S
N
H
N
H
N
H
N
H
Me
Cl
Me
Me
Me
Cl
O
O
N
H
N
H
N
H
N
H
Q
R
1
92
85
234
235–236
252
Cl Cl
N
H
N
H
N
H
N
H
10
248–251
H
N
H
N
O
O
O
S
NH
NH
O
O
S
15
80
121–123
123
Me
N
Me
N
O
S
O
O
N
N
Me
Me
O
O
aCondition: substrate (1 mmol), oxidant (2 mmol), 5% aq. KOH (5 mL), CH3CN (5 mL), r.t.
bIsolated pure yield.

8
D. Azarifar and M. Golbaghi
HO
S
O
S
H
Ar
N
NH2
Me
O
Ar
N
NH2
O
O
H
1
N
H
NH2
Ar
1O2
S
O
I
O
O
HOO
HO
Me
OOH
OOH
O
e
M
O
Me
OH
Me
O
OOH
O
Me
HOO-
SO3H
N
O
Me
Me
H2O
Ar
N
C
NH
HSO3
HN
H
Ar
+
Ar
N
NH2
II
O
O
H
2
HO
Scheme 2. Proposed mechanism for desulfurization of thioureas with the oxidant DHPDMDO in aqueous KOH
solution.
by TLC, the reaction mixture was diluted with water (10 mL) and the product was extracted in
dichloromethan (3 × 5 mL). The combined organic layer was washed with water (2 × 5 mL)
and dried over anhydrous Na2SO4. Evaporation of the solvent under reduced pressure gave
almost pure products. Structures of the known products were established on the basis of their
physical and spectroscopic (IR, 1H-NMR and 13C-NMR) data, which were consistent with those
reported.[34,61]
Based on the formation of carbodiimide II as the intermediate, which was detected in the
course of the reaction, and also according to the 1O2-based mechanisms proposed for the
oxidative desulfurization of thioureas in the literature,[61–66] a plausible reaction mechanism
proposed to explain the desulfurization of thioureas 1a–1s to the respective oxo analogs 2a–2s
with DHPDMDO in aqueous KOH solution is depicted in Scheme 2. Based on our previously
reported evidence,[57] it is likely that the reaction initially involves the generation of singlet
oxygen molecule via ring-opening decomposition of the oxidant, which acts as the main source
of oxidant to produce a four-membered 1,2,3-dioxathietane intermediate I. To provide evidence
for the involvement of 1O2 in the reaction, and in virtue of prolonged liftime of 1O2 in deuterated
solvents, we repeated the reaction for 1,1ꢀ-(1,4-phenylene)bis(thiourea) 1h in CD3CN solvent
under the same optimized conditions and noticed substantial improvements of the reaction time
and the yield as well.
4.3. Characterization data for the products 2 [34,61]lit:
4.3.1. 1-Phenyl urea (2a)
White solid; m.p. 141–144 °C. IR (KBr).3429, 3314, 3268, 1656, 1614, 1597, 1553, 1497, 1357,
1
751, 697 cm−1. H-NMR (DMSO-d6): δ(ppm) 8.55 (s, 1H), 7.38 (d, 2H), 7.20 (t, 2H), 6.87
(t, 1H), 5.84 (s, 2H). 13C-NMR (DMSO-d6): δ(ppm) 156.5, 141.0, 129.0, 121.5, 118.2.
4.3.2. p-Tolylurea (2b)
White solid; m.p. 180–183°C.IR (KBr).3430, 3311, 3216, 1654, 1620, 1591, 1549, 1407, 1256,
1109, 1024, 824, 811, 779 cm−1. 1H-NMR (DMSO-d6): δ(ppm) 8.35 (s, 1H), 7.24 (d, 2H), 7.00

Journal of Sulfur Chemistry
9
(d, 2H), 5.73 (s, 2H), 2.20 (s, 3H). 13C-NMR (DMSO-d6): δ(ppm) 156.7, 138.0, 130.4, 129.9,
118.2, 25.4.
4.3.3. 2-Fluorophenylurea (2 g)
White solid; m.p. 186°C. IR (KBr). 3424, 3322, 3217,1657, 1624, 1600, 1552, 1492, 1456, 1359,
1257, 754 cm−1 13C-NMR (DMSO-d6): δ(ppm) 156.1, 154.0, 150.2, 128.8, 128.6, 124.7, 122.0,
.
121.9, 120.8, 120.8, 115.3, 115.0.
4.3.4. 1,1ꢀ-(p-Phenylene)bis(thiourea) (2 h):new
Purple solid; m.p. > 345°C. IR (KBr). 3464, 3430, 3336, 1645, 1604, 1552, 1409, 1340, 813,
1
644 cm−1. H-NMR (DMSO-d6): δ(ppm) 8.46 (s, 2H), 7.18 (s, 4H), 5.76 (s, 4H); 13C-NMR
(DMSO-d6): δ(ppm) 156.6, 134.8, 118.9. m/z (EI): 52, 81, 108, 157, 194 (M+).
4.3.5. 2-Trifluoromethylphenylurea (2i)
White solid; m.p. 100–102°C. IR (KBr). 3479, 3440, 3339, 3186, 1742, 1708, 1689, 1657,
1617, 1590, 1543, 1461, 1363, 1322, 1285, 1108, 760 cm−1. 1H-NMR (DMSO-d6): δ(ppm) 8.94
(s, 1H), 7.99–8.00 (d, 1H), 7.67–7.69 (d, 1H), 7.41–7.44 (t, 1H), 7.31–7.34 (t, 1H), 5.97 (s, 2H).
13C-NMR (DMSO-d6): δ(ppm) 156.4, 156.2, 152.4, 137.6, 135.7, 133.6, 133.1, 126.4, 126.3,
126.2, 125.7, 125.5, 125.0, 124.5, 123.3, 123.2, 122.3, 119.3.
4.3.6. 1-Naphthylurea (2j)
Purple solid; m.p. 218–221°C. IR (KBr). 3443, 3304, 3208, 1651, 1608, 1555, 1530, 1505, 1359,
1
784, 760 cm−1. H-NMR (DMSO-d6): δ(ppm) 8.65 (s, 1H), 8.15 (s, 1H), 7.96 (d, 1H), 7.84
(s, 1H), 7.75–7.35 (m, 4H), 6.19 (s, 2H). 13C-NMR (DMSO-d6): δ(ppm) 156.2, 135.7, 133.5,
128.6, 126.3, 16.1, 125.7, 123.3, 123.2, 117.0, 109.2
4.3.7. 1,3-benzodioxol-4-yl urea (2k):new
Black solid; m.p. 182–183°C. IR (KBr). 3416, 3360, 3214, 2909, 2797, 1647, 1608, 1547, 1500,
1486, 1447, 1366, 1280, 1247, 1197, 1042, 857, 790 cm−1. 1H-NMR (DMSO-d6): δ(ppm) 8.33
(s, 1H), 7.66–7.68 (d, 1H), 6.98–7.02 (t, 1H), 6.33–6.35 (d, 1H), 5.95 (s, 1H), 5.85 (s, 1H), 5.17
(s, 2H). 13C-NMR (DMSO-d6): δ(ppm) 156.5, 147.7, 141.8, 135.4, 110.7, 108.4, 101.0, 100.9.
m/z (EI): 79, 108, 109, 136, 137, 180 (M+).
4.3.8. 2-Chloro-4-nitrophenylurea (2n)
1
Yellow solid; m.p. 248–251°C. IR (KBr). 3500, 3392, 3324, 1676 cm−1. H-NMR (DMSO-
d6): δ(ppm) 6.88 (s, 2H), 7.43–8.66 (d, 1H).13C-NMR (DMSO-d6): δ(ppm) 155.6, 147.8, 132.0,
122.9, 119.0, 114.0.

10 D. Azarifar and M. Golbaghi
4.3.9. 1,3-Diphenylurea (2o)
White solid; m.p. 238–240 °C. IR (KBr). 3299, 1649, 1558, 1544, 1474, 1385, 1292, 1098, 818
1
cm−1. H-NMR (DMSO-d6): δ(ppm) 8.63 (br, 2H), 7.46 (d, 4H), 7.29 (d, 4H), 6.98 (t, 2H).
13C-NMR (DMSO-d6): δ(ppm) 152.4, 134.9, 129.1, 127.9, 123.7.
4.3.10. 1,3-Bis(4-chlorophenyl)urea (2q)
White solid; m.p. 234 °C [28, 43]lit. IR (KBr). 3296, 1633, 1591, 1492, 1290, 1086, 823, 639
cm−1. 1H-NMR (CDCl3): δ(ppm) 8.05 (br, 2H), 7.55 (d, 4H), 7.48 (d, 4H). 13C-NMR (CDCl3):
δ(ppm) 152.2, 134.0, 129.9, 129.1, 123.0.
4.3.11. N,Nꢀ-Dimethylbarbituric acid (2s)
White solid; m.p. 121–123 °C. IR (KBr). 3168, 3082, 1766, 1718, 1679 cm−1. 1H-NMR (DMSO-
d6): δ(ppm) 3.06 (s, 6H), 3.63 (s, 2H). 13C-NMR (DMSO-d6): δ(ppm) 173.4, 150.2, 31.5, 9.5.
Funding
The authors wish to thank the Research Council of Bu-Ali Sina University for financial support.
Supplemental data
Supplemental data for this article can be accessed at doi:10.1080/17415993.2015.1082181 description of location.
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