Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent under solid-state and solution conditions

Article abstract of DOI:10.1016/j.molstruc.2012.05.033

A simple and efficient method for the conversion of alcohols and phenols to primary O-thiocarbamates and S-thiocarbamates in the absence of solvent (solvent-free condition) using silica sulfuric acid (SiO₂OSO ₃H) as a solid acid is described. The products are easily distinguished by IR, NMR and X-ray data. X-ray data of the compounds reveal a planar trigonal orientation of the NH₂ nitrogen atom with the partial C,N double-bond character and the CS or CO groups in synperiplanar position with C_arylO and C_alkylS moieties, respectively. Moreover, the OCSNH₂ group which is perpendicular to the plane of the benzene ring in 1c and the central thiocarbamate SCONH₂ group in 2b are essentially planar.

Full text of DOI:10.1016/j.molstruc.2012.05.033

Journal of Molecular Structure 1024 (2012) 156–162
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Journal of Molecular Structure
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Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent
under solid-state and solution conditions
a
b
Ali Reza Modarresi-Alam a, , Iman Dindarloo Inaloo , Erich Kleinpeter
⇑
a Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan, Zahedan, Iran
b Universitat Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Golm), Germany
h i g h l i g h t s
"
"
"
A green and simple method for the conversion of alcohols and phenols to primary O-thiocarbamates and S-thiocarbamates.
Using of silica sulfuric acid („SiO2AOSO3H) as a solid acid in the absence of solvent (solvent-free condition).
To report X-ray data of primary O-thiocarbamate and S-thiocarbamate for the first time.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 April 2012
Received in revised form 10 May 2012
Accepted 10 May 2012
Available online 18 May 2012
A simple and efficient method for the conversion of alcohols and phenols to primary O-thiocarbamates
and S-thiocarbamates in the absence of solvent (solvent-free condition) using silica sulfuric acid
(„SiO2AOSO3H) as a solid acid is described. The products are easily distinguished by IR, NMR and
X-ray data. X-ray data of the compounds reveal a planar trigonal orientation of the NH2 nitrogen atom
with the partial C,N double-bond character and the C@S or C@O groups in synperiplanar position with
C
arylAO and CalkylAS moieties, respectively. Moreover, the AOACSANH2 group which is perpendicular
Keywords:
Solvent-free
N-unsubstituted(primary)O-thiocarbamates
N-unsubstituted (primary) S-thiocarbamates
Isothiocyanic acid
to the plane of the benzene ring in 1c and the central thiocarbamate ASACOANH2 group in 2b are essen-
tially planar.
Ó 2012 Elsevier B.V. All rights reserved.
Solid acid
Silica sulfuric acid
1. Introduction
organic solvents. They are highly toxic reagents and hazardous to
handle, especially in large-scale preparations [1,33,34]. The used
Thiocarbamates are esters of thiocarbamic acids, the generic
name has been indiscriminately given to the tautomeric species
with the general formula R1SC(O)NR2R3 or R1OC(S)NR2R3 (R1 typi-
cally is an alkyl or an aryl group attached to the sulfur – giving S-
thiocarbamates – or to the oxygen – giving O-thiocarbamates). Thi-
ocarbamates have received much attention due to their interesting
technological, biological and synthetic applications [1–18].
Traditionally, secondary and tertiary thiocarbamates were
obtained by several-pot reaction methods [1,4–8,14–32]. The most
widely utilized method for the synthesis of them uses phosgene or
thiophosgene (and their substituted derivatives) as a reagent in
organic solvents are toxic and are not eco-friendly. From the stand-
point of ‘green chemistry’, significant efforts have been made to
find alternatives to organic solvents. A very attractive substitute
for these solvents is given in solvent–free reactions [35–37]. It is
industrially important due to reduced pollution, low costs, and
simplicity in process and handling. Therefore the conventional
method involves environmental and safety problems. Owing to
the above mentioned facts, much effort has been directed toward
alternative routes for preparation of thiocarbamates.
Furthermore, these methods cannot produce N-unsubstituted
thiocarbamates. While the secondary and tertiary thiocarbamates
are easily prepared from alcohols and phenols or thiols and
thiophenols by various methods, the synthesis of N-unsubstituted
thiocarbamates is generally quite difficult [6,14–32].
The synthesis of N-unsubstituted (primary) O-thiocarbamates 1
from alcohols and phenols has been accomplished also by the
following several-pot methods: The alkali salts of alcohols and
⇑
Corresponding author. Tel.: +98 5412431146; fax: +98 5412446767.
E-mail address: modaresi@chem.usb.ac.ir (A.R. Modarresi-Alam).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.05.033

A.R. Modarresi-Alam et al. / Journal of Molecular Structure 1024 (2012) 156–162
157
O
S
SiO2-OSO3H
ROH
+
MSCN
or
R
S
NH2
R
O
NH2
Solvent-Free, 70oC
2
1
3
4
Scheme 1. Conditions of synthesis of O-thiocarbamates 1 and S-thiocarbamates 2.
phenols react with highly toxic thiophosgene under mild conditions
and form chlorothioformates which are very suitable agents for the
thioacylation of ammonia [1,33,34]. They could be prepared also by
reaction of cyanates with hydrogen sulfide [1,38–41]. However, al-
kyl or aryl cyanates must be prepared by reaction of alcohols and
phenols with cyanogenbromide (BrCN); which is a highly toxic
and expensive reagent [1,38–41].
There are only few reports in the literature concerning the for-
mation of primary S-thiocarbamates which are carried out by
hydration of organic thiocyanates in the presence of hydrogen
chloride and concentrated sulfuric acid [18,29–32]. However, the
preparation of alkyl or aryl thiocyanates is hindered by the same
problems as mentioned for cyanates.
To the best of our knowledge, there is only one reference con-
cerning direct addition of thiocyanic acid for the synthesis of pri-
mary O-ethylthiocarbamates: The yield of the reaction of
ammonium thiocyanate with concentrated hydrochloric acid in
ethanolic suspension is very low; it has been assumed that ethanol
adds to the free thiocyanic acid [1,42].
Loev and Kormendy reported the synthesis of N-unsubstituted
carbamates from alcohols by treatment with sodium cyanate and
trifluoroacetic acid in certain organic solvents such as benzene,
methylene chloride and carbon tetrachloride [43]. However, they
reported when sodium thiocyanate and trifluoroacetic acid reacted
with alcohols and mercaptans in attempts to extend their synthetic
method to the synthesis of thiocarbamates and dithiocarbamates,
they obtained only complex mixtures of odorous products.
Thermolysis of thiocarbamates resulted in a Newman and Kar-
nes rearrangement which yields the desired S-arylthiocarbamates
from O-arylthiocarbamates [20–22]. Indeed, it is a method for
the transformation of phenols into thiophenols. However, these
rearrangements are extremely limited [1,20–22] to useful products
as are N,N-disubstituted and N-monosubstituted S-thiocarbamates.
Recently, Wynne and coworkers reported a two-step synthesis
for a variety of S-alkyl thiocarbamates (primary, secondary and ter-
tiary) from the reaction of thiols with trichloroacetyl chloride fol-
lowed by the displacement of the trichloroacetyl group upon
treatment with an amine. This procedure has the advantage of
avoiding the use of phosgene entirely [14].
yields with high selectivity. However, to the best of our knowledge
there has been no report on the use of SSA for the synthesis of O- and
S-thiocarbamates. Furthermore, the literature, so far published,
contains neither reports about the one-pot synthesis nor the X-ray
structure elucidation of primary O- and S-thiocarbamates.
In connection with the mild synthesis of primary thiocarba-
mates from phenols and alcohols, as we recently reported for the
synthesis of carbamates [37], in this work, a simple, efficient and
eco-friendly green methodology for preparation primary S- and
O-thiocarbamates 1 and 2 will be introduced (Scheme 1). The idea
was to provide a library of primary thiocarbamates by means of
commercially available reagents in a single straightforward, simple
reaction by employing non-toxic materials and preferably nongas-
eous reagents.
2. Results and discussion
SSA was obtained from silica gel and chlorosulfonic acid as des-
ribed previously [36,37]. The primary thiocarbamates 1 and 2 were
synthesized by reaction of an alcohol or phenol 3 with potassium
thiocyanate 4 (M = K) in presence of SiO2AOSO3H at 70 °C for
12 h in moderate yields. Schematic reaction is given in Scheme 1
and the results are summarized in Table 1.
The products 1a-g and 2a-b were purified by column chroma-
tography and characterized by comparing physical properties of
the products with those of authentic samples [1,3,29,32,41,44]. In
addition, they were characterized by 1H NMR (500 MHz), 13CNMR
(125 MHz), FT-IR, CHNS, HRMS and X-ray. The signals of NH2 pro-
tons in 1H NMR spectra are broad and split into a doublet at about d
6–8 ppm in 1 or a singlet in 2. The signals of the carbonyl carbon of
the O-thiocarbamates 1 appear in 13CNMR spectra at about d 191–
194 ppm (ACSAOA) and those of the S-thiocarbamates 2 at about d
169 ppm (ACOASA). Both 1 and 2 show IR vibrations at 3300 and
3400 cmÀ1 for NH2, at 1644 cmÀ1 for the carbonyl group
(ACOASA) in 2 and at 1500–1620 cmÀ1 for the thiocarbonyl group
(ACSAOA) in 1.
The crystal structure of 1c and 2b were determined by X-ray dif-
fraction methods (see Figs. 1 and 2 and Tables 2–4 for selected
structural parameters). X-ray data of compounds 1c and 2b
revealed that the nitrogen atom of NH2 is flattened to be trigonal
planar due to conjugation with the C@O or C@S groups (h = <H1A-
N1-H1B + <H1A-N1-C + <H1B-N1-C = 359°) [45,46] and coplanar
with the thiocarbamate moiety adopting hereby a considerable
double-bond character of the CAN bond.
Since the catalytic applications of solid-state supported reagents
for organic synthesis have been well established, many examples
are reported on the use of silica sulfuric acid (SiO2AOSO3H, SSA)
as solid acid [36,37]. SSA has received considerable attention as an
inexpensive, non-toxic and recyclable catalyst for various organic
transformations, affording the corresponding products in excellent
Table 1
Preparation of primary O-thiocarbamates 1a-g and primary S-alkylthiocarbamates 2a-b.
Entry
Compound containing hydroxyl group
R
%Yield (#)
Mp (°C)
Mp (°C, Ref.)
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
3g
3h
3i
C6H5
36 (1a)
39 (1b)
45 (1c)
35 (1d)
40 (1e)
41 (1f)
39 (1g)
46 (2a)
44 (2b)
130–132
132–134
147–148
166–167
35–36
18–19
38–39
106–108
89–91
134 [1]
–
153 [1,40]
–
39–41 [1]
19–21 [1]
39–39.5 [1,41]
108 [29,32]
128.5 [29,32]
2-CH3C6H4
4-CH3C6H4
2AC(CH3)3A4ACH3C6H3
CH3
CH3CH2CH2CH2
CH3CH2CHCH3
CH3CH2
(CH3)2CH

158
A.R. Modarresi-Alam et al. / Journal of Molecular Structure 1024 (2012) 156–162
Table 3
Selected bond angles (degree) as obtained from the X-ray crystallographic analysis for
O-4-methyl–phenyl thiocarbamate 1c and S-2-propyl thiocarbamate 2b.
Entry
Compound
Atom1
Atom2
Atom3
Angle
1
2
3
4
5
6
7
8
9
1c
C3
C8
N1
N1
O1
C2
C2
H1A
C1
C1
C1
C2
C2
C2
N1
N1
N1
O1
O1
O1
O1
S1
119.3(2)
118.9(2)
110.0(1)
125.4(1)
124.6(1)
120(2)
121(1)
118(2)
120.2(1)
S1
H1A
H1B
H1B
C2
10
11
12
13
14
15
16
17
18
2b
C3
C4
N1
N1
O1
C1
C1
H1A
C1
C2
C2
C1
C1
C1
N1
N1
N1
S1
S1
S1
S1
O1
S1
H1A
H1B
H1B
C2
106.7(1)
112.2(1)
113.2(1)
123.9(1)
122.9(1)
119(1)
119(1)
121(2)
101.71(7)
Fig. 1. X-ray structure for O-4-methyl–phenyl thiocarbamate 1c.
Table 4
Selected torsion angles (degree) as obtained from the X-ray crystallographic analysis
for O-4-methyl–phenyl thiocarbamate 1c and S-2-propyl thiocarbamate 2b.
Entry
Compound
Atom1
Atom2
Atom3
Atom4
Torsion
1
2
3
4
5
6
7
8
1c
C3
C8
O1
O1
S1
S1
N1
S1
C1
C1
C2
C2
C2
C2
C2
C2
O1
O1
N1
N1
N1
N1
O1
O1
C2
C2
À92.8(2)
94.3(2)
À170(2)
À4(1)
H1A
H1B
H1A
H1B
C1
Fig. 2. X-ray structure for S-2-propyl thiocarbamate 2b.
10(2)
176(1)
À179.4(1)
Table 2
C1
À0.3(2)
Selected bond distances (Angstrom, Å) as obtained from the X-ray crystallographic
analysis for O-4-methyl–phenyl thiocarbamate 1c and S-2-propyl thiocarbamate 2b.
9
10
11
12
13
14
15
16
2b
C3
C4
S1
C2
C2
C1
C1
C1
C1
C1
C1
S1
S1
N1
N1
N1
N1
S1
S1
C1
C1
160.3(1)
À76.6(1)
177(2)
1(1)
Entry
Compound
Atom1
Atom2
Length
H1A
H1B
H1A
H1B
C2
1
2
3
4
5
6
1c
C1
C2
C2
C2
N1
N1
O1
N1
O1
S1
H1A
H1B
1.411(2)
1.314(2)
1.343(2)
1.654(2)
0.81(2)
S1
O1
O1
N1
O1
À3(2)
À179(1)
À175.4(1)
4.4(1)
C2
0.88(2)
7
8
9
10
11
12
2b
C2
C1
C1
C1
N1
N1
S1
N1
S1
O1
H1A
H1B
1.824(1)
1.328(2)
1.778(1)
1.228(2)
0.86(2)
-
-
X
X
X
+
+
N
0.86(2)
R
N
R
N
R
5c
5b
5a
X = O, S
These planar conformational preference has been generally ob-
served in most N-substituted amides, thioamides, carbamates and
thiocarbamates and were rationalized in terms of negative hyper-
conjugation (anomeric effect) between the nitrogen lone-pair and
the electron-deficient C@S or C@O bond (rà or rà ) [25,46–50].
The conformation adopted by the thiocarbamate group AOC(S)NH2
or ASC(O)NH2 is syn (C@S or C@O double bond in synperiplanar orien-
tation with respect to the CarylAO and CalkylAO or CalkylAS single bond).
Furthermore, the thiocarbamate (AOACSANH2) group is oriented per-
pendicular to the plane of the benzene ring in 1c.
The CAN bond in 2b [1.329 (2) Å] in the crystaline state is long-
er than the same bond in 1c [1.314 (2) Å]. Indeed, the CAN bond in
1c seems to exhibit more double-bond character than the one in
2b: An accepted interpretation of this feature is the higher contri-
bution of the dipolar canonical structure 5c (Scheme 2), because
Scheme 2. Canonical structures of amides/thioamides.
enhanced to compensate the loss of C(2p)AS(3p) overlap in 1c. This
indicates that CAN partial double bond character increases and
CAN bond length subsequently decreases in carbamates in the or-
der (X) O < S. This implies why the chemical shift of 13C resonance
of ACSAOA group in compounds 1 (191–194 ppm) is moved to
higher frequency (downfield) than that in ACOASA group in com-
pounds 2 (169 ppm). On the other hand, the polarization of the
C@S bond will be only small because electronegativities of carbon
and sulfur are not much different. Thus, the contribution of the
canonical structure 5b will be significantly reduced (cf. Scheme
2). A similar behavior has been observed in thioamides compared
with amides [46,51]. Moreover, the CAN bond distance in O-ethyl
carbamate [1.349 (0.004) Å] is longer than the one in 2b [52]. This
again indicates that C(2p)AS(3p) overlap in the ester group of S-thio-
C@S
C@O
C
C
(2p)AS(3p) overlap in a thioamide bond is less effective than
(2p)AO(2p) overlap in an amide bond. In other words, conjugation
between the nitrogen lone pair and the thiocarbonyl group is

A.R. Modarresi-Alam et al. / Journal of Molecular Structure 1024 (2012) 156–162
159
carbamate 2b is less effective than C(2p)AO(2p) overlap in the O-eth-
ylcarbamate ester group. In other words, conjugation between the
nitrogen lone pair and the carbonyl group is much more reduced in
O-ethylcarbamate relative to that in 2b. Because one of the oxygen
lone pairs on the ester group of O-ethylcarbamate can be donated
Scheme 4. Suggested mechanism of synthesis of S-alkylthiocarbamates 2 via MNK
rearrangement of O-alkylthiocarbamates 1.
into the carbonyl
p system, and thus, it can preclude suitable p
conjugation with the nitrogen lone pair.
As shown in Table 1, several primary and secondary alcohols
and phenols have been used for the synthesis of primary thiocarba-
mates 1 and 2 employing this simple procedure.
Phenols containing electron-withdrawing substituents (CN,
COOR, CHO and Br) failed to react under these experimental condi-
tions. Most likely these functional groups decrease the nucleophi-
licity of the phenol oxygen for the effective attack to give the
intermediate 5 and/or 7, Scheme 3. It seems that steric hindrance
of tert-butyl and methyl groups in comparison to hydrogen in
ortho position could not affect the yield of reaction (compare en-
tries 1, 2 and 4 in Table 1). The product of meta-cresol, actually,
could not be characterized.
The conversions were tested using various acids such as HCl,
H2SO4, CCl3COOH, HClO4, CF3COOH, SiO2AHClO4, SiO2AOSO3H,
ClSO3H, TolSO3H in 13 different solvents such as H2O, Me2CO,
Et2O, CH2Cl2, CHCl3, THF, n-hexane, DMSO, EtOAc, MeCN,
ClCH2ACH2Cl, xylene and 1,4-dioxane. However, the formation of
thiocarbamates was observed in solvents like chloroform, dichloro-
methane, xylene and 1,2-dichloroethylene in the presence of
SiO2AOSO3H, CF3COOH and ClSO3H and the best results were ob-
tained with SiO2AOSO3H.
The reactions were also tested at various temperatures, times
and stoichiometry ratios. The best results were obtained at the
1:1:1 stoichiometry ratio (acid, starting material and thiocyanate
salt, respectively) under reflux temperature of the solvent for
24 h. Furthermore, using ammonium thiocyanate instead of potas-
sium thiocyanate led to higher yield because of the better solubil-
ity of ammonium thiocyanate (4, M = NH4).
In solid-state, similar to solution, various conditions were
tested; the best results were obtained for similar stoichiometric ra-
tios 1:1:1 when reacting alcohols or phenols 3 with potassium
thiocyanate 4 in the presence of SiO2AOSO3H at 70 °C for 12 h;
moderate yields were obtained (cf. Table 1 and Scheme 1). How-
ever, in contrast to the results obtained in solution, higher yields
were obtained when using potassium thiocyanate.
The most probable reaction mechanism is given in Scheme 3
and proves to be in agreement with the reaction mechanism of car-
bamates, published recently [37]. The reaction of potassium thio-
cyanate 4 (M = K) with an acid (SSA) to produce isothiocyanic
acid 5 should be the first step [53]. Next, for the generation of
the intermediate 7 (N-protonation is favored [53]), the proton of
SSA is added to isothiocyanic acid 5 where it should be added to
nitrogen rather than sulfur. Finally, the thiocarbamate 1 is ex-
pected to be formed when either the alcohol or phenol 2 attacks
the carbon atom of intermediate 7, Scheme 3.
Scheme 5. Suggested mechanism of synthesis of S-alkylthiocarbamates
thiocyanation of alcohols.
2 via
purification yielded primary S-alkylthiocarbamates 2a and 2b,
respectively. This was, in sharp contrast to the results obtained with
3a-g. The mechanism for this transformation is not completely
understood. However, based on the forgoing results, the following
two mechanisms is proposed for the reaction as depicted in
Schemes 4 and 5. According to the proposed mechanism, the tauto-
meric Miyazaki–Newman–Kwart (MNK) rearrangement can occur
through a four-membered ring transition state for the formation
of primary S-alkylthiocarbamates 2a and 2b, Scheme 4 [20–22].
There have been earlier reports of similar conversion of O-thiocar-
bamates to the corresponding S-thiocarbamates brought about by
boron trifluoride-etherate or p-toluenesulfonic acid [54,55]; but
the yields have not been mentioned. A better yield was achieved
when a catalytic amount of concentrated sulfuric acid was used
in chloroform solution [55].
The sulfuric acid catalyzed isomerisation was found to be quite
general. The reason for the high efficiency of the sulfuric acid cat-
alyzed process is not completely clear [55]. Therefore, similar reac-
tions can occur with ethanol and isopropyl alcohol in the present of
SSA.
Alternatively, a proton-transfer process leads to the formation
of a protonated alcohol or carbocation intermediate (ion-pair inter-
mediate), Scheme 5. Subsequent nucleophilic attack of the thiocy-
anate ion to one of these intermediates via SN1 or SN2 should lead
to alkylthiocyanate 8 and its hydrolysis to the formation of primary
S-alkylthiocarbamates 2a and 2b, Scheme 5 [18,29–32]. The solid
state reaction supports the stabilization of relatively unsolvated
carbonium ions and can be also of value for proceeding SN1 thiocy-
anations [56].
Surprisingly, we did not find products of primary O-thiocarba-
mates 1 in the case of ethanol and isopropanol. Isolation and
3. Conclusions
A new method to synthesize primary O-aryl (alkyl) thiocarba-
mates 1 and primary S-alkyl thiocarbamates 2 under mild condi-
tions (1 atm, 70 °C without using additional base) is reported.
These primary O- and S-thiocarbamates 1 and 2 could be readily
prepared from cheap alcohols or phenols in a single step. Further-
more, this simple solvent-free method affords various primary thi-
ocarbamates, with moderate yields, without involvement of toxic
Scheme 3. Suggested mechanism of synthesis of O-thiocarbamates 1.

160
A.R. Modarresi-Alam et al. / Journal of Molecular Structure 1024 (2012) 156–162
solvents and expensive starting materials. Solvent-free condition,
mildness of the conversion, a simple experimental procedure, clear
reaction profiles and short reaction times are the noteworthy
advantages of the protocol.
(d, J = 7.5, 2H), 8.23 (s, br, 1H, NH), 8.32 (s, br, 1H, NH). 13CNMR
(125 MHz, 300 K, CDCl3), dppm; 16.01, 122.61, 126.58, 126.85,
130.96, 131.16, 151.95, 191.39.
4.5. O-4-Methyl–phenyl thiocarbamate
4. Experimental section
Reaction afforded white crystals 1c (45% yield), mp = 147–
148 °C ([1,40] 153 °C). IR (KBr); 3412 (s), 3270 (m), 3158 (m),
1601 (s), 1503 (s), 1419 (s), 1291 (m), 1219 (m), 1190 (s), 1162
(m), 1104 (w), 1016 (s), 864 (m), 817 (w), 782 (vw), 713 (vw),
541 (w), 496 (w), 450 (vw) cmÀ1. 1HNMR (500 MHz, 293 K, CDCl3),
dppm; 2.39 (s, 3H), 6.46 (s, br, 1H, NH), 6.73 (s, br, 1H, NH), 7.02 (d,
J = 8.4 Hz, 2H), 7.23 (d, J = 8.4 Hz, 2H). 1HNMR (500 MHz, 293 K,
acetone-d6), dppm; 2.32 (s, 3H), 6.94 (d, J = 8.4 Hz, 2H), 7.18 (d,
J = 8.4 Hz, 2H), 8.21 (s, br, 1H, NH), 8.31 (s, br, 1H, NH). 1HNMR
(500 MHz, 293 K, CD3CN), dppm; 2.35 (s, 3H), 6.96 (d, J = 8.3 Hz,
2H), 7.21 (d, J = 8.3 Hz, 2H), 7.31 (s, br, 1H, NH), 7.44 (s, br, 1H,
NH). 1HNMR (300 MHz, 298 K, DMSO), dppm; 2.30 (s, 3H), 6.92
(d, J = 9.0 Hz, 2H), 7.17 (d, J = 9.0 Hz, 2H), 8.97 (s, br, 1H, NH),
9.17 (s, br, 1H, NH).13CNMR (125 MHz, 300 K, CDCl3), dppm;
20.95, 122.05, 129.87, 136.17, 151.30, 192.23. 13CNMR (125 MHz,
300 K, acetone-d6), dppm; 20.75, 123.15, 130.14, 135.88, 152.45,
192.77. HRMS Calcd. m/z 168.0483 [(M + 1)]+, Found 168.0485
[(M + 1)]+. Anal. Calcd. for C8H9NOS: C, 57.46; H, 5.42; N, 8.38; S,
19.70, Found: C, 57.63; H, 5.26; N, 8.28, S, 19.70.
4.1. General
1HNMR and 13CNMR spectra were recorded by BRUKER AVA-
NACE DRX500 (500 MHz). The FT-IR spectra were obtained on a
JASCO FT-IR-460 plus. HRMS spectra were obtained on Q-TOF
Micromass (Wakes Inc. UK). Elemental analysis was performed
using Heraeus CHN-O-Rapid analyser. Melting points were re-
corded by Electro thermal 9100 and are uncorrected. Thin layer
chromatography (TLC) was carried out using plastic sheets pre-
coated with silica gel 60 F. Crystallographic data (excluding struc-
ture factors) for the structures in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplemen-
tary publication nos. CCDC 833793 for 1c and CCDC 833794 for
2b. Copies of the data can be obtained, free of charge, on applica-
tion to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44
(0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
Silica sulfuric acid (SSA) was prepared from silica gel and chlo-
rosulfonic acid according to the literature [36,37].
4.2. General procedure
In a typical procedure, SiO2AOSO3H (2 g, 1.0 mmol) was added
to a mixture of potassium thiocyanate (1.0 mmol) and alcohol or
phenol (1.0 mmol). Then, the mixture was heated and stirred at
70 °C in oil bath under solid-state conditions for 12 h. The reaction
was monitored in TLC. After completion of reaction, ethyl acetate
(3 Ã 10 ml) was added and the mixture was filtered. The solvent
(EtOAc) was removed under reduced pressure and the product
was purified by column chromatography (petroleum ether and
ethyl acetate) and characterized correctly. Pure products were ob-
tained in moderate yields, as summarized in Table 1.
4.6. O-2-tert-butyl-4-methylphenyl thiocarbamate
Reaction afforded white crystals 1d (35% yield), mp = 166–
167 °C. IR (KBr); 3396 (m), 3282 (m), 3177 (s), 2958 (m), 2924
(m), 2857 (w), 1613 (vs), 1508 (vw), 1475 (w), 1422 (s), 1366
(w), 1288 (w), 1204 (s), 1092 (m), 1022 (m), 966 (vw), 913 (vw),
877 (vw), 847 (m), 814 (vw), 757 (w), 682 (w), 576 (w), 526 (w),
457 (vw), 418 (vw) cmÀ1. 1H NMR (500 MHz, 293 K, CDCl3), dppm;
1.39 (s, 9H), 2.38 (s, 3H), 6.48 (s, br, 1H, NH), 6.93 (s, br, 1H, NH),
7.00 (d, J = 8.7 Hz, 1H), 7.08 (d, J = 8.7 Hz, 1H), 7.23 (s, 1H). 1H
NMR (500 MHz, 293 K, acetone-d6), dppm; 1.34 (s, 9H), 2.30 (s,
3H), 6.92 (d, J = 7.9 Hz, 1H), 7.01 (d, J = 7.9 Hz, 1H), 7.19 (s, 1H),
8.29 (s, br, 2H, NH). 1H NMR (500 MHz, 293 K, CD3CN), dppm;
1.33 (s, 9H), 2.33 (s, 3H), 6.92 (d, J = 8.2 Hz, 1H), 7.03 (dd,
J = 8.2 Hz, J = 2.2 Hz, 1H), 7.23 (d, J = 2.2 Hz, 1H), 7.43 (s, br, 2H,
NH2)). 13C NMR (125 MHz, 300 K, CDCl3), dppm; 21.31, 30.49,
34.50, 124.73, 127.18, 128.07, 135.81, 140.92, 149.67, 191.93. 13C
NMR (125 MHz, 300 K, acetone-d6), dppm; 21.12, 30.80, 34.96,
126.13, 127.51, 128.18, 135.49, 141.65, 150.91, 192.72. HRMS
Calcd. m/z 224.1109 [(M + 1)]+, Found 224.1107 [(M + 1)]+. Anal.
Calcd. for C12H17NOS: C, 64.53; H, 7.67; N, 6.27; S, 14.36, Found:
C, 63.98; H, 7.62; N, 6.10; S, 13.70.
4.3. O-Phenyl thiocarbamate
Reaction afforded white crystals 1a (36% yield), mp = 130–
132 °C ([1] 134 °C). IR (KBr); 3410 (s), 3269 (s), 3159 (s), 3016
(vw), 2957 (vw), 2925 (m), 2854 (w), 1590 (s), 1587 (vs), 1487
(s), 1421 (s), 1287 (m), 1223 (vw), 1199 (s), 1163 (vw), 1095 (w),
1025 (m), 999 (m), 910 (w), 851 (s), 772 (m), 710 (m), 690 (m),
561 (m), 507 (vw) cmÀ1 1HNMR (500 MHz, 293 K, CDCl3), dppm;
.
6.47 (s, br, 1H, NH), 6.69 (s, br, 1H, NH), 7.12 (d, J = 7.7 Hz, 2H),
7.29 (t, J = 7.4 Hz, 1H), 7.42 (t, J = 7.7 Hz, 2H). 1HNMR (500 MHz,
293 K, acetone-d6), dppm 7.08 (d, J = 7.5 Hz, 2H), 7.24 (t,
J = 7.5 Hz, 1H), 7.39 (t, J = 7.5 Hz, 2H), 8.28 (s, br, 1H, NH), 8.37 (s,
br, 1H, NH). 13CNMR (125 MHz, 300 K, CDCl3), dppm; 122.46,
126.44, 129.31, 153.52, 191.97.
4.7. O-Methyl thiocarbamate
4.4. O-2-Methyl–phenyl thiocarbamate
Reaction afforded white crystals 1e (40% yield), mp = 35–36 °C
([1] 39–41 °C). IR (KBr); 3385 (w), 3300 (m), 3250 (m), 2952 (w),
2853 (w), 1621 (vs), 1509 (w), 1438 (s), 1304 (s), 1179 (vw),
Reaction afforded white crystals 1b (39% yield), mp = 132–
134 °C. IR (KBr); 3406 (s), 3267 (m), 3162 (m), 1597 (vs), 1489
(m), 1424 (s), 1287 (m), 1227 (m), 1177 (vs), 1113 (s), 1040 (m),
1016 (s), 856 (m), 786 (w), 774 (m), 719 (m), 569 (w), 472 (w),
1106 (s), 943 (m), 713 (w), 419 (w) cmÀ1 1H NMR (500 MHz,
.
293 K, CDCl3), dppm; 3.97 (s, 3H), 6.26 (s, br, 1H, NH), 7.00 (s, br,
1H, NH). 1H NMR (500 MHz, 293 K, acetone-d6), dppm; 3.88 (s,
3H), 7.65 (s, br, 1H, NH), 7.90 (s, br, 1H, NH). 13C NMR (125 MHz,
300 K, CDCl3), dppm; 58.15, 193.45. HRMS Calcd. m/z 92.0170
[(M + 1)]+, Found 92.0172 [(M + 1)]+. Anal. Calcd. for C2H5NOS: C,
26.36; H, 5.53; N, 15.37; S, 35.19, Found: C, 26.51; H, 5.60; N,
15.12; S, 33.80.
418 (w) cmÀ1 1HNMR (500 MHz, 293 K, CDCl3), dppm; 2.25, (s,
.
3H), 6.49 (s, br, 1H, NH), 6.87 (s, br, 1H, NH), 7.04 (d, J = 7.7 Hz,
1H), 7.21–7.27 (m, 3H). 1HNMR (500 MHz, 298 K, acetone-d6),
dppm; 2.18, (s, 3H), 6.98 (dd, J = 7.8 Hz, J = 1.1 Hz, 1H), 7.14 (dt,
J = 7.5 Hz, J = 1.3 Hz, 1H), 7.18 (dt, J = 7.8 Hz, J = 1.6 Hz, 1H), 7.23

A.R. Modarresi-Alam et al. / Journal of Molecular Structure 1024 (2012) 156–162
161
4.8. O-1-Buthyl thiocarbamate
Appendix A. Supplementary material
Reaction afforded white crystals 1f (41% yield), mp = 18–19 °C
([1] 19–21 °C). IR (KBr); 3400 (m), 3289 (vs), 3171 (s), 2960 (vs),
2933 (m), 2872 (m), 1604 (vs), 1508 (vw), 1458 (m), 1409 (s),
1378 (s), 1308 (vs), 1092 (vs), 1011 (vw), 944 (w), 901 (vw), 856
Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.molstruc.2012.05.033.
Supplementary data [FT-IR, 1H and 13C NMR spectra (500 and
125 MHz) of thiocarbamates in different solvents and X-ray and
HRMS data] associated with this article can be found in the online
version.
(w), 738 (vw), 705 (vw), 472 (vw), 419 (vw) cmÀ1 1H NMR
.
(500 MHz, 293 K, CDCl3), dppm; 0.93 (t, J = 7.4 Hz, 3H), 1.39 (m,
2H), 1.68 (m, 2H), 4.39 (t, J = 6.7 Hz, 2H), 6.11 (s, br, 1H, NH),
6.78 (s, br, 1H, NH). 1H NMR (500 MHz, 293 K, acetone-d6), dppm;
0.91 (t, J = 7.4 Hz, 3H), 1.38 (m, 2H), 1.64 (m, 2H), 4.34 (t, J = 6.6 Hz,
2H), 7.62 (s, br, 1H, NH), 7.84 (s, br, 1H, NH). 13C NMR (125 MHz,
300 K, acetone-d6), dppm; 13.92, 19.62, 31.42, 70.92, 193.74.
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4.9. O-2-Buthyl thiocarbamate
Reaction afforded white crystals 1g (39% yield), mp = 38–39 °C
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(s), 2877 (w), 1664 (s), 1601 (s), 1456 (w), 1379 (m), 1310 (s),
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4.10. S-Ethyl thiocarbamate
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Reaction afforded white crystals 2a (46% yield), mp = 106–
108 °C ([29,32] 108 °C). IR (KBr); 3381 (s), 3219 (m), 3182 (m),
2970 (w), 2929 (w), 1644 (vs), 1617 (m), 1313 (m), 1255 (m),
1115 (w), 978 (vw), 823 (vw), 715 (m), 578 (w) cmÀ1 1H NMR
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(500 MHz, 293 K, CDCl3), dppm; 1.29, (t, J = 7.4 Hz, 3H), 2.89 (q,
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J = 7.4 Hz, 3H), 2.80 (q, J = 7.4 Hz, 2H), 6.03 (s, br, 2H, NH). 13C
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C, 34.35; H, 6.81; N, 13.37; S, 30.24.
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4.11. S-2-Propyl thiocarbamate
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(s), 2985 (m), 2965 (s), 2926 (m), 2862 (w), 2757 (w), 1644 (vs),
1614 (vs), 1462 (vw), 1441 (m), 1367 (m), 1301 (s), 1238 (s),
1156 (m), 1117 (m), 1057 (m), 931 (vw), 883 (vw), 758 (vw), 711
(s), 654 (w), 570 (m), 472 (vw), 426 (m) cmÀ1
.
1H NMR
(500 MHz, 273 K, CDCl3), dppm; 1.31 (d, J = 6.9 Hz, 6H), 3.56 (h,
J = 6.9 Hz, 1H), 5.54 (s, br, 2H, NH). 1H NMR (500 MHz, 293 K, ace-
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Acknowledgement
The Sistan & Baluchestan University Graduate Council sup-
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