Ghorbani-Choghamarani & Zamani
+
OH NO3-
O
CH Cl (20 ml). Anhydrous Na SO (1.5 g) was added to the
2
2
2
4
filtrate and filtered off after 20 min. Finally CH
2
Cl was
2
Neat
rt
H N
2
NH2 + HNO (65%)
H N
NH2
evaporated and allyl methyl sulfoxide 2h obtained as colorless
3
2
1
oil (0.066 g, 64%). H NMR (200 MHz, CD
3
SOCD ): δ =
3
5
(
.75-5.97 (m, 1H), 5.31-5.39 (m, 2H), 3.34-3.62 (m, 2H), 2.50
Scheme 1
s, 3H) ppm; 13C NMR (50 MHz, CD SOCD ): δ = 127.5,
3
3
1
23.3, 56.5, 37.4 ppm; (Ref. [20]).
OH NO3-
+
Selected Representative Spectral Data
-
H O
2
H NCONHNO .XH O
-(Phenylsulfinyl)ethanol (2e). 1H NMR (200 MHz,
H N
NH2
2
2
2
2
2
X=1-2.5
CD
3
SOCD
3
): δ = 7.51-7.94 (m, 5H), 5.89 (s, 1H), 3.63-3.88
1
3
(
m, 2H), 2.83-3.01 (m, 2H) ppm; C NMR (50 MHz,
Scheme 2
CD
3
SOCD
3
): δ = 144.9, 132.1, 131.1, 123.6 ppm.
1
4
-Thianthrene mono sulfoxide (2g). H NMR (400 MHz,
CD SOCD ): δ = 7.80-7.84 (m, 2H), 7.65-7.68 (m, 1H), 7.55-
3
3
oxidizing property in the presence of an acid. Therefore, we
decided to apply nitro urea in the presence of silica sulfuric
1
3
7
1
.58 (m, 1H) ppm; C NMR (100 MHz, CD SOCD ): δ =
3 3
41.2, 130.9, 129.8, 129.3,128.2, 124.7 ppm.
acid (SiO
2
-OSO H) and catalytic amounts of ammonium
3
Benzyl methyl sulfoxide (2k). 1H NMR (200 MHz,
bromide for the chemoselective oxidation of sulfides to the
sulfoxides.
Initially, to find an appropriate solvent for this
transformation, we screened different solvents for the
oxidation of dibenzyl sulfide, as a standard model the results
of which are summarized in Table 1. As is evident from Table
CD SOCD ): δ = 7.34 (s, 5H), 5.07 (s, 2H), 3.91-4.16 (dd, J =
3
3
1
3
2
1
4.1, 12.7 Hz, 2H) ppm; C NMR (50 MHz, CD
3
SOCD ): δ =
3
31.7, 130.7, 128.9, 128.2, 59.0, 37.6 ppm.
4
1
-Chlorophenyl methyl sulfoxide (2o). H NMR (200
MHz, CDCl ): δ = 7.47-7.63 (dd, J = 14.0, 8.6 Hz, 4H) 2.75
3
(
s, 3H), ppm; 13C NMR (50 MHz, CDCl ): δ = 143.8, 137.1,
3
1
, oxidation reaction proceeds more rapidly and selectively in
1
29.5,125.0, 43.7 ppm.
dichloromethane and acetonitrile compared to other solvents.
However, dichloromethane has been selected as the reaction
solvent in all reactions because dichloromethane has lower
toxicity than acetonitrile.
RESULTS AND DISCUSSION
Recently, we have introduced different approaches for the
chemoselective oxidation of sulfides to the sulfoxides via in
situ generation of bromonium ion [21-28]. In continuation of
this investigation, we decided to explore catalytic and metal-
free media for the in situ generation of Br . To this end, we
synthesized urea nitrate by reaction of urea with nitric acid
With the optimal conditions at hand, herein we report
chemoselective oxidation of a wide range of aliphatic and
aromatic sulfides 1 to the corresponding sulfoxides 2 via
treatment of nitro urea (NH CONHNO .xH O) I, silica
2
2
2
+
sulfuric acid (SiO -OSO H) II in the presence of catalytic
2
3
amounts of NH Br III in dichloromethane at room
4
(
Scheme 1). Urea nitrate has been reported previously by
Shead [29].
Urea nitrate can be readily dehydrated to nitro urea
NH CONHNO .xH O) (Scheme 2). This structure might be
temperature with good to excellent yields (Scheme 3 and
Table 2).
As is evident from Table 2, a good range of turn over
number (TON) and turn over frequency (TOF) of the catalyst
(
2
2
2
easily approved by its mass spectrum (Fig. 1), whose
is observed. To prove the catalytic role of NH Br, dibenzyl
4
+
molecular ion peak appears at m/e = 105 and base peak (NO
appears at m/e = 46.
2
)
sulfide (as typical example) was selected for the oxidation
reaction in the absence of this catalyst. Surprisingly, no
sulfoxide was observed for 24 h (Table 2, entry 4). We found
that the sulfoxidation reaction for dibenzyl sulfid did not
In continuation of our studies on the properties of nitro
urea (NH CONHNO .xH O), we found that this reagent has
2
2
2
1
43