A mild radical method for the dimerization of dithiocarbamates

Article abstract of DOI:10.1002/ejoc.201403348

A general, practical, and efficient method for the dimerization of dithiocarbamates has been developed that can be used to prepare the corresponding bis(1-arylimino-1-alkyl/ arylthiomethyl) disulfides with dilauroyl peroxide (DLP) as mild oxidant. Notably, a lauroyl radical, rather than an undecyl radical, was established as the radical hydrogen-ab- stractor during the dimerization process. The amount of DLP impacts the dimerization yield, with 50 mol-% DLP giving the disulfides in the highest yields. The use of an excess of DLP generates the undecyl radical, which decomposes the disulfides rapidly to the corresponding isothiocyanates.

Full text of DOI:10.1002/ejoc.201403348

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FULL PAPER
DOI: 10.1002/ejoc.201403348
A Mild Radical Method for the Dimerization of Dithiocarbamates
Ning Chen,[a][‡] Xin Zhong,[a][‡] Pingfan Li,[a] and Jiaxi Xu*[a]
Keywords: Synthetic methods / Radical reactions / Coupling reactions / Sulfur / Dimerization / Peroxides
A general, practical, and efficient method for the dimeriza-
tion of dithiocarbamates has been developed that can be
used to prepare the corresponding bis(1-arylimino-1-alkyl/
arylthiomethyl) disulfides with dilauroyl peroxide (DLP) as
stractor during the dimerization process. The amount of DLP
impacts the dimerization yield, with 50 mol-% DLP giving
the disulfides in the highest yields. The use of an excess of
DLP generates the undecyl radical, which decomposes the
mild oxidant. Notably, a lauroyl radical, rather than an unde- disulfides rapidly to the corresponding isothiocyanates.
cyl radical, was established as the radical hydrogen-ab-
an efficient method with which to synthesize a series of acy-
clic disulfides from dithiocarbamates under mild condi-
Introduction
Many disulfide-containing natural products exhibit vari-
tions.
ous promising bioactivities including antibiotic, antitumor,
and anti-inflammatory activities.[1] In protein chemistry, the
disulfide bond plays an important role in stabilizing protein
structure and protein folding.[2] Recently, epidithiodioxo-
piperazine (ETP) alkaloids, possessing a key disulfide bridge
at the central bicyclo[2.2.2]octane moiety, have attracted
great attention in organic and pharmaceutical chemistry
fields because of their interesting bioactivities.[3] In ad-
dition, disulfide compounds are important intermediates in
the preparation of sulfonyl compounds, sulfinyl com-
pounds,[4] and supramolecular structures.[5]
Figure 1. Disulfide compounds containing a dithiocarbonimidate
motif.
2,2Ј-Dithiobis(benzothiazole) (Scheme 1) is prepared by
the oxidative coupling of benzothiazolidinethione with vari-
ous stoichiometrical oxidants, such as hydrogen peroxide,[11]
halogen,[12] dioxygen,[13] sodium hypochlorite,[14] or other
oxidants.[15] However, the results become much more com-
plex when these oxidants are applied to acyclic dithiocar-
bamates because of the loss of heterocyclic aromaticity.
Barrett and co-workers first mentioned that the oxidation
of dialkyl dithiocarbamates with iodine afforded an un-
stable impure oil as dimerized disulfide [Scheme 1, Equa-
tion (2)].[16] In 1988, Ishimura and Watanabe reported that
oxidation of methyl diethyldithiocarbamate produced the
corresponding (E)- and (Z)-sulfine (C=S=O) molecules.[17]
Ten years later, Metzner and Chevrie modified their method
through addition of sodium hydrogen carbonate and devel-
oped an efficient route for the preparation and separation
of (E)-sulfines.[18] However, three dimerized disulfides were
generated from the corresponding secondary dithiocarbam-
ates as byproducts in very poor yields (10–18%), and with-
out any support from spectroscopic data [Scheme 1, Equa-
tion (3)]. Our group recently prepared various substituted
taurines and homotaurines from thiazolidine-2-thione de-
rivatives[19a] (as cyclic alkyl dithiocarbamate derivatives), or
from β/γ-aminoalkyl xanthates[19b,19c] (as acyclic alkyl di-
thiocarbamate analogues), with a mixture of hydrogen per-
oxide and formic acid; even β-aminoalkanesulfonyl chlor-
N-Aryl dithiocarbonimidates have broad application in
agriculture and animal husbandry because such compounds
can be used to control infestations of acarina on mammals
and birds.[6] They have also been used in the synthesis of
azaheterocyclic compounds, such as imidazoles[7a] and
thioimidazoles.[7b] Particularly, symmetrical disulfide mo-
lecules containing the N-aryl dithiocarbonimidate scaffold
exhibit some specific activities and applications in the rub-
ber industry. For instance, 2,2Ј-dithiobis(benzothiazole)
(Figure 1) is a typical example of widely used vulcanization
accelerators in the rubber industry. It is also a significant
intermediate in organic synthesis,[8] and has been applied in
β-lactam synthesis,[9] such as in the preparation of cephalo-
sporin antibiotics.[10] In this context, we aimed to develop
[a] State Key Laboratory of Chemical Resource Engineering,
Department of Organic Chemistry, Faculty of Science, Beijing
University of Chemical Technology,
15, Beisanhuan east road, Beijing 100029, People’s Republic of
China
E-mail: jxxu@mail.buct.edu.cn
http://sci.buct.edu.cn/szll/jsml/yjhxx/9746.htm
[‡] These authors contributed equally.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403348.
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FULL PAPER
ides were prepared from β-aminoalkyl xanthates through sponding thiazoline derivatives [Scheme 2, Equation (5)].[21]
oxidation by NaClO2 or N-chlorosuccimide under acidic Therefore, we proposed that changing the N-allyl substitu-
conditions.[20] The aforementioned methods demonstrate ent to an aryl or alkyl substituent should lead to dimeriza-
that the sulfur atom in both dithiocarbamates and xan- tion of the thiyl radical to afford the corresponding disul-
thates was easily oxidized to the corresponding sulfoxides, fide coupling products because no radical addition could
sulfonyl chlorides, or sulfonic acids and that almost no di- occur [Scheme 2, Equation (6)]. It has been reported that
merization to the corresponding disulfides occurred. To ad- thiyl radicals can easily react with olefins[23a,23b] or self-di-
dress this issue, a weak oxidant seems necessary.
merize, but they seldom attack aromatic rings and alkyl
groups.[23c] Hence, we believed that DLP would be applied
as an efficient mild oxidant for the preparation of disulfides
from dithiocarbamates (Scheme 2).
Results and Discussion
Various dithiocarbamates 1 were synthesized from the
corresponding arylamines, carbon disulfide, and alkyl hal-
ides,[24] or from isothiocyanates and mercaptans.[25]
Methyl N-(p-chlorophenyl)dithiocarbamate (1a) was se-
lected as the model compound to optimize the reaction con-
ditions. Referring to the reported methods in dithiocarb-
amate[21] and xanthate[26] radical addition processes, DLP
was first added into a solution of 1a in 1,2-dichloroethane
(DCE) at 10 mol-% per hour. After heating to reflux for
5 h, 97% yield (based on NMR analysis; 95% isolated yield
after column chromatography) of the dimerized product
bis(1-p-chlorophenylimino-1-methylthiomethyl)
disulfide
(2a) was obtained together with 3% yield of p-chlorophenyl
isothiocyanate (3a) as byproduct (Table 1, entry 1). The sig-
nal at 1575 cm–1 in the FTIR spectrum and at 162.2 ppm
in the 13C NMR spectrum support the existence of a C=N
double bond, which is the key functional group in the target
molecule structure. The results demonstrate that equimolec-
ular amounts of lauroyl radical or undecyl radical facili-
Scheme 1. Approaches to the oxidation of dithiocarbamates.
Lauroyl peroxide is well known to initiate radical reac- tated the reaction as the hydrogen abstractor. To our de-
tions through radical addition to the carbon–sulfur double light, when DLP (50 mol-%) was added in one portion, 2b
bond of N,N-disubstituted dithiocarbamates.[21] Last year, was also generated in 95% yield under heating to reflux for
our group reported that in the radical chemistry of dithio- 1 h (Table 1, entry 2). Further increasing the amount of
carbamates, the radical initiator dilauroyl peroxide (DLP) DLP resulted in a clear decrease in the yield of 2a and in-
is a good hydrogen abstractor.[22] DLP can dissociate under crease in the yield of p-chlorophenyl isocyanate 3a (Table 1,
heating to afford the lauroyl radical, which further loses a entries 3 and 4). Besides DLP, other radical initiators, such
molecule of carbon dioxide to generate the undecyl radical. as benzoyl peroxide (BPO; Table 1, entry 5), azodiiso-
Both lauroyl and undecyl radicals can abstract a hydrogen butyronitrile (AIBN; Table 1, entry 6), and di-t-butyl perox-
atom from N-allyl dithiocarbamates to yield the corre- ide (DTBPO; Table 1, entries 7 and 8), were also evaluated
sponding thiyl radicals. The thiyl radical can attack the ole- for the dimerization process. BPO reacted with 1a to give
fin moiety in an intramolecular manner to give the corre- 2a in 82% yield. The results can be attributed to the ten-
Scheme 2. Design of the dimerizaition of dithiocarbamates.
2
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A Mild Radical Method for the Dimerization of Dithiocarbamates
dency of the peroxides to decompose. Aliphatic diacyl per- Table 2. Synthesis of various bis(1-alkylthio-1-aryliminomethyl) di-
sulfides 2.
oxides are generally less stable than their aromatic counter-
parts.[27] The half-life of acetyl peroxide, a DLP analogue,
is 1 h at 85 °C, compared with 2 h at 90 °C for BPO.[27]
However, AIBN produced only 2% yield of 2a. No product
was observed when DTBPO was used in boiling DCE (b.p.
83 °C) possibly because the decomposition temperature of
DTBPO is 130 °C.[27] When the solvent was changed to o-
xylene (b.p. 139 °C), only trace amounts of dimerized prod-
uct 2a was afforded (Table 1, entry 8). Instead, 59% yield
of 3a was obtained with 41% starting material recovery.
Additionally, Wang and co-workers prepared bis[4-(tri-
fluoromethyl)benzylidene]-2-methyl-4-nitrobenzenamine-1-
disulfide, an antitumor agent, in 81% yield from the corre-
sponding thioamide with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ) as oxidant.[28] Thus, we also at-
tempted the reaction under the oxidation of DDQ, afford-
ing 2a in 93% yield (Table 1, entry 7). DDQ, however, is
much more expensive than DLP (six times more expensive
than DLP per mol according to the Alfa-Aesar website
price). Therefore, DLP was chosen as a rapid, efficient, and
inexpensive radical hydrogen-abstractor for the dimeriza-
tion of dithiocarbamates.
Table 1. Optimization of dimerization conditions.
(1q), afforded the corresponding dimerized disulfides 2 in
Entry H-abstractor
[mol-%]
Solvent
Yield [%][a]
2a
good to excellent isolated yields. It seems that substituents,
including a strong electron-donating group (methoxy),
weak electron-donating group (CH3), weak electron-with-
drawing group (Cl), and strong electron-withdrawing group
(CF3), on the aryl ring do not affect the dimerization yields
significantly. All the N-aryl S-alkyl dimerized products 2a–
o were easily crystallized, and their melting points are listed
in Table 2. A relatively low dimerization yield (48%) was
obtained from diphenyl dithiocarbamate (1p). We then dis-
covered that 1p easily decomposed to phenyl isothiocyanate
(3p) and thiophenol in its pure liquid state or in a solution,
on the basis of FTIR analysis. When pure 1p was dissolved
in DCE for 1 h at 82 °C, an absorption peak at 2093 cm–1
was detected, indicating the existence of the isothiocyanate
3a
1
2
3
4
5
6
7
8
9
DLP (50)[b]
DLP (50)[e]
DLP (75)[e]
DLP (100)[e]
BPO (50)[e]
DCE[c]
DCE
DCE
DCE
DCE
97 (95[d]
)
3
3
95
7
trace
82
2
75
93 (86[d]
)
2
–
–
53
0
AIBN (50)[e]
DTBPO (50)[e]
DTBPO (50)[e]
DDQ (50)[e]
DCE
DCE
–
o-xylene[f]
DCE
trace
93
[a] Reactions were conducted on 0.5 mmol scale of 1a. NMR yield
with dimethyl maleate as an internal standard. [b] DLP was added
at 10 mol-% per hour, and the reaction time was 5 h in total. [c]
Boiling point of DCE is 83 °C. [d] Isolated yield after column
chromatography. [e] DLP (50 mol-%) was added, and the reaction
time was 1 h. [f] Boiling point of o-xylene is 139 °C.
1
group. Further H NMR analysis of the mixture demon-
strated that half the amount of 1p decomposed to phenyl
With the optimized conditions, we synthesized a series of isothiocyanate and thiophenol in DCE at reflux after 1 h.
substituted disulfide derivatives 2 (Table 2). A range of N- We were delighted to find that high dimerization yield
aryldithiocarbamates (1a–q), containing p-chlorophenyl (91%) was obtained from 1q with N-(m-methylphenyl) sub-
(1a–d), phenyl (1e–h, and 1p), p-methylphenyl (1i–k), p- stitution (Table 2, 2q). Additionally, a cyclic analogue 2,2Ј-
methoxyphenyl (1l), p-(trifluoromethyl)phenyl (1m), o- dithiobis(benzothiazole) (2r) was obtained from benzothi-
chlorophenyl (1n), 1-naphthyl (1o), and m-methylphenyl azolidinethione (1r) in 90% yield (Table 2, 2r).
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Interestingly, S-allyl N-(p-chlorophenyl)dithiocarbamate demonstrate that it is the lauroyl radical, rather than unde-
(1d) also gave rise to the corresponding dimerized disulfide cyl radical, that abstracts the hydrogen from dithiocarb-
2d in 91% isolated yield. During this process, none of the amates 1. Similarly, equimolar amounts of benzoic acid
intramolecular addition product between thiyl radical and with 2a were observed from the reaction mixture of 1a and
olefin was detected. The result was remarkably different BPO (Table 1, entry 5; for details, see the Supporting Infor-
from that obtained with N-allyldithiocarbamates, which af- mation, page S13).
ford thiazolines through an intramolecular addition from
thiyl radical and olefin according to our previously re-
ported results (Scheme 3).[21]
Figure 3. 1H NMR spectrum of the reaction system of 1a and DLP.
Based on the experimental results, a detailed reaction
mechanism is proposed, which is shown in Scheme 4. DLP
Scheme 3. Differences in the reactions of and S-allyl N-allyldithio-
first dissociates into two lauroyl radicals upon heating. The
carbamates.
lauroyl radical abstracts a hydrogen from the dithiocarb-
To further confirm the structure of products 2, single- amate 1, forming the corresponding N-radical inter-
crystals of 2n were obtained by crystallization from di- mediates A, which further convert into the more stable thiyl
chloromethane and were submitted to X-ray diffraction radicals B. The latter radicals dimerize at the reaction tem-
analysis.[29] The XRD results verified the structure (Fig- perature to give disulfides 2. They can decompose to iso-
ure 2).
thiocyanates 3 and alkylthio radicals at high temperature
It is well-known that DLP can act as a radical initiator (Table 1, entry 8). The alkylthio radicals can also dimerize
after it dissociates to two lauroyl radicals under heating. to dialkyl disulfides 4 (Scheme 4).
The lauroyl radical can further lose a molecule of carbon
We noted that the use of an excess amount of DLP de-
dioxide to generate an active and nucleophilic undecyl radi- creased the yield of dimerized products 2 and increased the
cal. Both lauroyl and undecyl radicals are also efficient yield of isothiocyanates 3 rapidly (Table 1, entries 3 and 4).
hydrogen abstractors. To distinguish which is the hydrogen There are two possibilities to rationalize the phenomenon.
abstractor in our reaction system, we analyzed the process One is that the disulfides 2 generate first and then decom-
by 1H NMR spectroscopy and found that equimolar pose to isothiocyanates 3 in the presence of excess DLP.
amounts of lauric acid, rather than undecane, with 2a were The second is that the isothiocyanates 3 generate directly
observed in the reaction mixture (Figure 3). The results from dithocarbamates 1 in the presence of excess DLP.
Figure 2. Single X-ray crystal structure of disulfide 2n.
4
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A Mild Radical Method for the Dimerization of Dithiocarbamates
Furthermore, 2a was heated to reflux in DCE for 1 h in the
presence of 25, 50, 75, and 100 mol-% DLP, affording 3a in
17, 51, 81, and 93% yield, respectively, with 70, 40, 10, and
0% yield of raw material (2a) recovered [Scheme 5, Equa-
tion (8)]. In addition, many complex low-polarity byprod-
ucts were formed in large amounts.
The reaction mixture was submitted to GC–MS analysis,
which indicated that several sulfur compounds, including
dimethyl disulfide (4a), methyl undecyl thioether (5a), and
methyl undecyl p-chlorophenylcarbonimidodithioate (6a),
were generated during the decomposition procedure
[Scheme 5, Equation (9)]. Moreover, some DLP decom-
posed products, including n-docosane, n-undecane, 1-unde-
cene, dodecanoic acid, and undecyl dodecaoate, were also
detected, as previously reported.[21] The results demonstrate
that disulfides 2 decomposed easily upon heating to reflux
in DCE in the presence of DLP. In the current case, it is
impossible to determine whether isothiocyanate 3a is gener-
ated from dithiocarbamate 1a directly or from disulfide 2a
experimentally.
Scheme 4. Proposed reaction mechanism of dithicarbamates and
DLP.
Hence, the mechanism for the decomposition of disulf-
ides 2 was proposed as shown in Scheme 6. First, both lau-
royl and undecyl radical may be generated by heating of
DLP. Herein, the GC–MS results demonstrate it is the un-
decyl radical, rather than lauroyl radical, which participates
in the decomposition of the disulfide 2a. An n-undecyl radi-
cal attacks the sulfur atom in one of the methylthio groups
To investigate the reaction mechanism in the presence of
excess DLP, disulfide 2a was dissolved in DCE and then
heated to reflux; none of the decomposed compounds were
observed even after 12 h, indicating that disulfide 2a is
stable under reflux in DCE [Scheme 5, Equation (7)].
Scheme 6. Proposed decomposition mechanism of disulfides under
DLP initiation.
Scheme 5. Decomposition of disulfides in the presence of DLP.
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pliers and used without purification. Column chromatography was
carried out with silica gel (200·300 mesh) with petroleum ether (PE,
60–90 °C) and ethyl acetate (EtOAc) as the eluent. All reactions
were followed by thin-layer chromatography (TLC) where practical,
using silica gel 60 F254 fluorescent-dye treated silica gel plates,
which were visualized under UV light (254 nm).
to generate one molecule of the N-(4-chlorophenyl)isothio-
cyanate (3a), one molecule of methyl undecyl thioether (5a),
and thiyl radical Ba. The thiyl radical Ba may be captured
by the undecyl radical to afford S-methyl S-undecyl (p-
chlorophenyl)carbonimidodithioate (6a). It can also further
decompose to 3a and a methylthio radical. The simple
methylthio radical, which is a highly reactive and unstable
radical, dimerizes to form dimethyl disulfide (4a).
Volatile dimethyl disulfide (4a) was recovered in small
amounts and quantified. To further verify the decomposi-
tion mechanism, S-butyl disulfide 2g was submitted to the
decomposition reaction with 100 mol-% DLP. The results
demonstrated that two compounds with similar polarity
were formed and could not be separated on both TLC and
column chromatography (Scheme 7). 1H NMR analysis
showed that the ratio of phenyl isothiocyanate (3g) to di-
butyl disulfide (4g) was approximate 2:1, revealing that de-
composition of thiyl radicals B to aryl isothiocyanates 3
and alkylthio radicals, rather than capture by the undecyl
radical, is a dominant process (see the Supporting Infor-
mation, page S52).
General Procedure for the Preparation of Bis(1-alkyl/arylimino-1-
alkyl/arylthiomethyl) Disulfides 2: To a solution of dithiocarbamate
1 (0.5 mmol) in 1,2-dichloroethane (2.5 mL) heated to reflux, was
added DLP (100 mg, 0.25 mmol) in one portion. The reaction mix-
ture was heated to reflux for 1 h and then cooled to room tempera-
ture. After removal of the solvent under reduced pressure, the resi-
due was purified by flash chromatography on silica gel (PE/EtOAc,
200:1 to 100:1 v/v) to afford the desired disulfide 2.
Bis[(Z)-1-p-chlorophenylimino-1-methylthiomethyl] Disulfide (2a):
Yield 103 mg (95%); colorless crystals; m.p. 158–160 °C (CH2Cl2/
n-hexane). IR (CH Cl ): ν = 2923, 1594, 1575 (νC=N), 1479, 1203,
˜
2
2
1012, 939, 911, 825, 603 cm–1. 1H NMR (400 MHz, CDCl3): δ =
7.31 (d, J = 8.4 Hz, 4 H, ArH), 6.87 (d, J = 8.4 Hz, 4 H, ArH),
2.48 (s, 6 H, SCH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ =
162.2, 146.9, 130.1, 129.3, 121.6, 16.2 ppm. HRMS (ESI): m/z
+
calcd. for C16H15Cl2N2S4 [M + H]+ 432.9490; found 432.9486.
Bis[(Z)-1-p-chlorophenylimino-1-propylthiomethyl] Disulfide (2b):
Yield 114 mg (93%); colorless crystals; m.p. 74–75 °C (CH2Cl2/n-
hexane). IR (CH Cl ): ν = 2962, 2929, 1576 (νC=N), 1480, 1205,
˜
2
2
1088, 1011, 942, 912, 825 cm–1. H NMR (400 MHz, CDCl3): δ =
7.30 (d, J = 8.6 Hz, 4 H, ArH), 6.85 (d, J = 8.6 Hz, 4 H, ArH),
3.04 (t, J = 7.2 Hz, 4 H, CH2S), 1.74 (sextet, J = 7.2 Hz, 4 H,
CH2CH2S), 1.03 (t, J = 7.2 Hz, 6 H, CH3) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 161.6, 147.0, 129.9, 129.3, 121.6, 35.0,
1
Scheme 7. Decomposition of disulfide 2g under DLP initiation.
+
22.1, 13.5 ppm. HRMS (ESI): m/z calcd. for C20H23Cl2N2S4 [M
+ H]+ 489.0116; found 489.0116.
Conclusions
Bis[(Z)-1-p-chlorophenylimino-1-butylthiomethyl] Disulfide (2c):
Yield 119 mg (92%); colorless crystals; m.p. 84–85 °C (CH2Cl2/PE).
Various disulfide compounds containing the dithiocar-
bonimidate motif were synthesized from the corresponding
dithiocarbamates and dilauroyl peroxide under mild condi-
tions. DLP is an efficient hydrogen abstractor for the dimer-
ization and its amount is a key factor for the dimerization
process. Half equimolecular DLP to dithiocarbamates pro-
duces disulfides in the highest yields, whereas an excess
amount of DLP can decompose the disulfides rapidly to
the corresponding isothiocyanates. Interestingly, it is the
IR (CH Cl ): ν = 2957, 2928, 1578 (νC=N), 1481, 1205, 1087, 1011,
˜
2
2
941, 914, 825 cm–1. H NMR (400 MHz, CDCl3): δ = 7.30 (d, J =
8.6 Hz, 4 H, ArH), 6.85 (d, J = 8.6 Hz, 4 H, ArH), 3.06 (t, J =
7.4 Hz, 4 H, CH2S), 1.69 (quintet, J = 7.4 Hz, 4 H, CH2CH2S),
1.45 (sextet, J = 7.4 Hz, 4 H, CH2CH3), 0.95 (t, J = 7.2 Hz, 6 H,
CH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 161.6, 147.0, 129.9,
129.2, 121.6, 32.9, 30.7, 22.0, 13.7 ppm. HRMS (ESI): m/z calcd.
1
+
for C22H27Cl2N2S4 [M + H]+ 517.0429; found 517.0432.
Bis[(Z)-1-p-chlorophenylimino-1-allylthiomethyl] Disulfide (2d):
undecyl radical, rather than lauroyl radical, that partici- Yield 111 mg (91%); colorless crystals; m.p. 79–81 °C (CH2Cl2/n-
hexane). IR (CH Cl ): ν = 2923, 1635, 1579 (νC=N), 1480, 1231,
˜
pates in the decomposition of the disulfides. In addition,
the stability of the thiyl radical intermediates is a crucial
factor for realization of the dimerization because the less
stable aliphatic thiyl radicals undergo decomposition to iso-
thiocyanates and alkyl disulfides.
2
2
1205, 1088, 1011, 943, 913, 825 cm–1. 1H NMR (400 MHz, CDCl3):
δ = 7.30 (d, J = 8.6 Hz, 4 H, ArH), 6.85 (d, J = 8.6 Hz, 4 H, ArH),
5.90 (ddt, J = 16.8, 10.0, 6.8 Hz, 2 H, CHCH2S), 5.31 (dt, Jtrans
=
16.8, 1.2 Hz, 2 H, HtransCH=), 5.18 (d, Jcis = 10.0 Hz, 2 H,
HcisCH=), 3.71 (dd, J = 6.8, 1.2 Hz, 4 H, CH2S) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 160.7, 146.7, 132.1, 129.3, 126.3, 121.6,
+
118.9, 36.0 ppm. HRMS (ESI): m/z calcd. for C20H19Cl2N2S4 [M
+ H]+ 484.9803; found 484.9800.
Experimental Section
General: Melting points were determined with a Yanaco MP-500 Bis[(Z)-1-methylthio-1-phenyliminomethyl] Disulfide (2e): Yield
melting point apparatus and are uncorrected. 1H and 13C NMR
spectra were recorded with a Bruker 400 NMR spectrometer at
400 and 100.6 MHz, respectively, in CDCl3 with TMS as an in-
ternal standard and chemical shifts are reported in ppm. IR spectra
were recorded with a Nicolet AVATAR 330 FTIR spectrometer.
HRMS spectra were recorded with a Bruker LC/MSD TOF mass
spectrometer. Reagents used were obtained from commercial sup-
85 mg (93%); colorless crystals; m.p. 133–134 °C (CH2Cl2/n-hex-
ane). IR (CH Cl ): ν = 3053, 2923, 1576 (νC=N), 1482, 1203, 928,
˜
2
2
911, 891 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.34 (t, J =
7.6 Hz, 4 H, m-ArH), 7.14 (t, J = 7.6 Hz, 2 H, p-ArH), 6.94 (d, J
= 7.6 Hz, 4 H, o-ArH), 2.49 (s, 6 H, CH3) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 161.5, 148.5, 129.2, 124.7, 120.3,
16.2 ppm. IR (CH Cl ): ν = 3052, 2922, 1575, 1481, 1448, 1384,
˜
2
2
6
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O43348
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Pages: 9
A Mild Radical Method for the Dimerization of Dithiocarbamates
1202, 1070, 927 cm–1. HRMS (ESI): m/z calcd. for C16H17N2S4
Bis[(Z)-1-methylthio-1-p-methoxyphenyliminomethyl] Disulfide (2l):
Yield 100 mg (94%); colorless crystals; m.p. 165–167 °C (CH2Cl2/
+
[M + H]+ 365.0269; found 365.0276.
n-hexane). IR (CHCl ): ν = 2946, 2922, 2835, 1583 (νC=N), 1501,
˜
3
Bis[(Z)-1-phenylimino-1-propylthiomethyl] Disulfide (2f): Yield
95 mg (90%); colorless crystals; m.p. 68–69 °C (CH2Cl2/n-hexane).
1289, 1245, 1204, 1103, 1031, 934, 911, 827 cm–1. 1H NMR
(400 MHz, CDCl3): δ = 6.91–6.87 (m, 8 H, ArH), 3.80 (s, 6 H,
CH3O), 2.48 (s, 6 H, SCH3) ppm. 13C NMR (100.6 MHz, CDCl3):
δ = 161.2, 156.9, 141.7, 121.4, 114.4, 55.4, 16.2 ppm. HRMS (ESI):
m/z calcd. for C18H21N2O2S4+ [M + H]+ 425.0480; found 425.0493.
IR (CH Cl ): ν = 3060, 2961, 2923, 1575 (νC=N), 1483, 1455, 1205,
˜
2
2
923, 911, 886, 757, 693 cm–1. 1H NMR (400 MHz, CDCl3): δ =
7.33 (t, J = 7.6 Hz, 4 H, m-ArH), 7.14 (t, J = 7.6 Hz, 2 H, p-ArH),
6.94 (d, J = 7.6 Hz, 4 H, o-ArH), 3.05 (t, J = 7.2 Hz, 4 H, CH2S),
1.75 (sextet, J = 7.2 Hz, 4 H, CH2), 1.03 (t, J = 7.2 Hz, 6 H,
CH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 160.8, 148.6, 129.1,
124.5, 120.2, 35.0, 22.1, 13.5 ppm. HRMS (ESI): m/z calcd. for
Bis[(Z)-1-butylthio-1-p-trifluorophenyliminomethyl] Disulfide (2m):
Yield 110 mg (88%); colorless crystals; m.p. 193–195 °C (CH2Cl2/
n-hexane). IR (CHCl ): ν = 2921, 1595 (νC=N), 1328, 1214, 1171,
˜
3
C20H25N2S4 [M + H]+ 421.0895; found 421.0894.
+
1121, 1104, 1068, 922, 840 cm–1. 1H NMR (400 MHz, CDCl3): δ =
7.60 (d, J = 8.3 Hz, 4 H, ArH), 7.02 (d, J = 8.3 Hz, 4 H, ArH),
2.50 (s, 6 H, SCH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ =
162.6, 151.4, 126.8 (q, J = 32.6 Hz), 126.5 (q, J = 3.7 Hz), 124.2
(q, J = 271.7 Hz), 120.3, 16.2 ppm. HRMS (ESI): m/z calcd. for
Bis[(Z)-1-butylthio-1-phenyliminomethyl] Disulfide (2g): Yield
101 mg (90%); colorless crystals; m.p. 55.5–56.5 °C (CH2Cl2/n-hex-
ane). IR (CH Cl ): ν = 2957, 2928, 1578 (νC=N), 1483, 1206, 924,
˜
2
2
1
886, 757, 693 cm–1. H NMR (400 MHz, CDCl3): δ = 7.33 (dd, J
= 8.0, 7.2 Hz, 4 H, m-ArH), 7.13 (t, J = 7.2 Hz, 2 H, p-ArH), 6.92
(d, J = 8.0 Hz, 4 H, o-ArH), 3.07 (t, J = 7.4 Hz, 4 H, CH2S), 1.70
(quintet, J = 7.4 Hz, 4 H, CH2CH2S), 1.46 (sextet, J = 7.4 Hz,
4 H, CH2CH3), 0.95 (t, J = 7.2 Hz, 6 H, CH3) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 160.9, 148.6, 129.1, 124.5, 120.2, 32.8,
30.7, 22.1, 13.7 ppm. HRMS (ESI): m/z calcd. for C22H29N2S4+ [M
+ H]+ 449.1208; found 449.1212.
+
C18H15F6N2S4 [M + H]+ 501.0017; found 501.0016.
Bis[(Z)-1-o-chlorophenylimino-1-methylthiomethyl] Disulfide (2n):
Yield 103 mg (95%); colorless crystals; m.p. 118–119 °C (CH2Cl2/
n-hexane). IR (CH Cl ): ν = 2924, 2853, 1708, 1591, 1579 (νC=N),
˜
2
2
1465, 1437, 1310, 1240, 1214, 1057, 941, 915, 752 cm–1. H NMR
(400 MHz, CDCl3): δ = 7.41 (dd, J = 8.0, 1.2 Hz, 2 H, ArH), 7.23
(ddd, J = 7.9, 7.8, 1.2 Hz, 2 H, ArH), 7.07 (ddd, J = 8.0, 7.8,
1.4 Hz, 2 H, ArH), 6.94 (dd, J = 7.9, 1.4 Hz, 2 H, ArH), 2.54 (s, 6
H, CH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 163.8, 145.4,
130.1, 127.4, 125.6, 125.2, 121.3, 16.3 ppm. HRMS (ESI): m/z
1
Bis[(Z)-1-benzylthio-1-phenyliminomethyl] Disulfide (2h): Yield
115 mg (89%) colorless crystals; m.p. 126.5–129 °C (CH2Cl2/n-hex-
ane). IR (CH Cl ): ν = 2922, 1576 (νC=N), 1494, 1482, 1474, 1452,
˜
2
2
1
1385, 1028, 922, 694 cm–1. H NMR (400 MHz, CDCl3): δ = 7.38
(d, J = 6.8 Hz, 4 H, ArH), 7.33–7.28 (m, 10 H, ArH), 7.11 (t, J =
7.4 Hz, 2 H, ArH), 6.87 (d, J = 7.4 Hz, 4 H, ArH), 4.27 (s, 4 H,
CH2) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 160.1, 148.3, 136.5,
129.3, 129.1, 128.4, 127.4, 124.6, 120.2, 37.6 ppm. HRMS (ESI):
+
calcd. for C16H15Cl2N2S4 [M + H]+ 432.9490; found 432.9498.
Bis[(Z)-1-(1-naphthylimino)-1-methylthiomethyl] Disulfide (2o):
Yield 104 mg (90%); colorless crystals; m.p. 148–150 °C (CH2Cl2/
n-hexane). IR (CHCl ): ν = 3056, 2923, 1569 (νC=N), 1504, 1482,
˜
3
1426, 1388, 1311, 1262, 1225, 1077, 914, 800, 772 cm–1. H NMR
1
+
m/z calcd. for C28H25N2S4 [M + H]+ 517.0895; found 517.0901.
(400 MHz, CDCl3): δ = 7.92 (d, J = 8.8 Hz, 2 H, ArH), 7.89 (d, J
= 8.8 Hz, 1 H, ArH), 7.63 (d, J = 8.0 Hz,2 H, ArH), 7.49–7.45 (m,
2 H, ArH), 7.43–7.37 (m, 4 H, ArH), 6.98–6.97 (m, 2 H, ArH),
2.59 (s, 6 H, SCH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ =
162.5, 144.8, 134.3, 127.9, 126.3, 125.7, 125.6, 124.8, 123.5,
Bis[(Z)-1-methylthio-1-p-tolyliminomethyl] Disulfide (2i): Yield
93 mg (95%); colorless crystals; m.p. 185–186 °C (CH2Cl2/n-hex-
ane). IR (CH Cl ): ν = 2920, 1579 (νC=N), 1499, 1211, 1204, 1088,
˜
2
2
1011, 940, 914, 814, 709 cm–1. 1H NMR (400 MHz, CDCl3): δ =
7.14 (d, J = 8.2 Hz, 4 H, ArH), 6.83 (d, J = 8.2 Hz, 4 H, ArH), 2.48
(s, 6 H, SCH3), 2.33 (s, 6 H, ArCH3) ppm. 13C NMR (100.6 MHz,
CDCl3): δ = 161.2, 146.0, 134.2, 129.8, 120.1, 20.9, 16.2 ppm.
+
16.3 ppm. HRMS (ESI): m/z calcd. for C24H21N2S4 [M + H]+
465.0582; found 465.0584.
Bis[(Z)-1-phenylimino-1-phenylthiomethyl] Disulfide (2p): Yield
HRMS (ESI): m/z calcd. for C18H21N2S4 [M + H]+ 393.0582;
+
59 mg (48%); colorless oil. IR (CHCl ): ν = 3058, 2924, 1587
˜
3
found 393.0580.
(νC=N), 1483, 1440, 1206, 1168, 1069, 1024, 921, 883, 758, 744,
689 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.59–7.57 (m, 4 H,
ArH), 7.40–7.30 (m, 10 H, ArH), 7.12–7.09 (dd, J = 7.2, 7.6 Hz, 2
H, ArH), 6.92–6.90 (d, J = 7.6 Hz, 2 H, ArH) ppm. 13C NMR
(100.6 MHz, CDCl3): δ = 157.9, 148.9, 135.9, 129.9, 129.2, 128.9,
Bis[(Z)-1-propylthio-1-p-tolyliminomethyl] Disulfide (2j): Yield
92 mg (82%); colorless crystals; m.p. 60–62 °C (CH2Cl2/n-hexane).
IR (CH Cl ): ν = 3023, 2963, 2927, 1579 (νC=N), 1501, 1455, 1240,
˜
2
2
1
1212, 1106, 941, 912, 814, 710 cm–1. H NMR (400 MHz, CDCl3):
δ = 7.13 (d, J = 8.2 Hz, 4 H, ArH), 6.82 (d, J = 8.2 Hz, 4 H, ArH),
3.04 (t, J = 7.2 Hz, 4 H, CH2S), 2.33 (s, 6 H, ArCH3), 1.74 (sextet,
J = 7.2 Hz, 4 H, CH2CH2S), 1.03 (t, J = 7.2 Hz, 6 H, CH3) ppm.
13C NMR (100.6 MHz, CDCl3): δ = 160.4, 146.1, 134.1, 129.7,
120.1, 35.0, 22.1, 20.9, 13.5 ppm. HRMS (ESI): m/z calcd. for
+
124.5, 120.1 ppm. HRMS (ESI): m/z calcd. for C26H21N2S4 [M +
H]+ 489.0582; found 489.0587.
Bis[(Z)-1-phenylthio-1-m-tolyliminomethyl] Disulfide (2q): Yield
117 mg (91%); colorless oil. IR (CHCl ): ν = 2919, 2851, 1592,
˜
3
1577, 1508, 1144, 925, 906, 878, 779, 687 cm–1. 1H NMR
(400 MHz, CDCl3): δ = 7.59–6.72 (m, 18 H, ArH), 2.33 (s, 6 H,
CH3) ppm. 13C NMR (100.6 MHz, CDCl3): δ = 157.4, 148.9, 138.9,
135.9, 129.8, 129.1, 129.0, 125.2, 120.7, 117.0, 21.4 ppm. HRMS
C22H29N2S4 [M + H]+ 449.1208; found 449.1204.
+
Bis[(Z)-1-butylthio-1-p-tolyliminomethyl] Disulfide (2k): Yield
100 mg (84%); colorless crystals; m.p. 73–74 °C (CH2Cl2/n-hex-
ane). IR (CH Cl ): ν = 2957, 2925, 1578 (νC=N), 1501, 1461, 1384,
˜
2
2
+
(ESI): m/z calcd. for C28H25N2S4 [M + H]+ 517.0895; found
1240, 1203, 1141, 1074, 938, 815, 758, 694 cm–1. 1H NMR
517.0903.
(400 MHz, CDCl3): δ = 7.13 (d, J = 8.2 Hz, 4 H, ArH), 6.82 (d, J
= 8.2 Hz, 4 H, ArH), 3.06 (t, J = 7.4 Hz, 4 H, CH2S), 1.69 (quintet, 2,2Ј-Dithiobis(benzothiazole) (2r): Yield 75 mg (90%); silver gray
J = 7.4 Hz, 4 H, CH2CH2S), 1.45 (sextet, J = 7.4 Hz, 4 H,
crystals; m.p. 187–189 °C (CHCl3) (ref.[15g] 185 °C). IR (CH2Cl2):
˜
1
CH2CH3), 0.94 (t, J = 7.4 Hz, 6 H, CH3) ppm. 13C NMR ν = 3064, 2929, 1468, 1454, 1429, 1006, 757, 724 cm–1. H NMR
(100.6 MHz, CDCl3): δ = 160.6, 146.1, 134.1, 129.7, 120.1, 32.8,
(400 MHz, CDCl3): δ = 7.94 (d, J = 8.2 Hz, 2 H, ArH), 7.77 (d, J
30.7, 22.1, 20.9, 13.7 ppm. HRMS (ESI): m/z calcd. for = 7.8 Hz, 2 H, ArH), 7.47 (ddd, J = 8.2, 7.3, 1.1 Hz, 2 H, ArH),
C24H33N2S4 [M + H]+ 477.1521; found 477.1523.
7.36 (ddd, J = 7.8, 7.3, 1.1 Hz, 2 H, ArH) ppm. 13C NMR
+
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Pages: 9
N. Chen, X. Zhong, P. Li, J. Xu
FULL PAPER
Chim. Acta 2006, 359, 3996–4000; c) H. Golchoubian, F. Hos-
seinpoor, Catal. Commun. 2007, 8, 697–700.
[14] a) J. M. Khurana, S. Singh, A. Sehgal, Indian J. Chem. Sect.
B: Org. Chem. Incl. Med. Chem. 1997, 36, 819–821; b) A.
Tanaka, M. Fukuoka, T. Adachi, T. Yamaha, J. Labelled
Compd. Radiopharm. 1986, 23, 405–413.
(100.6 MHz, CDCl3): δ = 167.8, 154.5, 136.1, 126.6, 125.3, 122.7,
121.3 ppm.
Acknowledgments
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21372025 and 21172017).
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Received: October 15, 2014
Published Online: ᭿
8
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

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Date: 17-12-14 14:37:21
Pages: 9
A Mild Radical Method for the Dimerization of Dithiocarbamates
Radical Reactions
N. Chen, X. Zhong, P. Li, J. Xu* ..... 1–9
A Mild Radical Method for the Dimeri-
zation of Dithiocarbamates
Keywords: Synthetic methods / Radical re-
actions / Coupling reactions / Sulfur / Di-
merization / Peroxides
A general, practical, and efficient method
for the dimerization of dithiocarbamates
has been developed that can be used to pre-
pare the corresponding bis(1-arylimino-1-
alkyl/arylthiomethyl) disulfides with di-
lauroyl peroxide as oxidant.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9