An expedient carbon–sulfur bond formation explored through the cellulose sulfonic acid (CSA) catalyzed dithioacetal protection of carbonyl compounds

Article abstract of DOI:10.1080/17415993.2020.1775835

A facile carbon–sulfur bond formation was observed through the cellulose sulfonic acid (CSA) catalyzed dithioacetal protection of carbonyl compounds. In a preliminary study, the synthesis and characterization of functionalized bio-polymer, cellulose sulph

Full text of DOI:10.1080/17415993.2020.1775835

Journal of Sulfur Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
An expedient carbon–sulfur bond formation
explored through the cellulose sulfonic acid (CSA)
catalyzed dithioacetal protection of carbonyl
compounds
Kailas R. Kadam
To cite this article: Kailas R. Kadam (2020): An expedient carbon–sulfur bond formation explored
through the cellulose sulfonic acid (CSA) catalyzed dithioacetal protection of carbonyl compounds,
Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2020.1775835
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2020.1775835
An expedient carbon–sulfur bond formation explored
through the cellulose sulfonic acid (CSA) catalyzed
dithioacetal protection of carbonyl compounds
Kailas R. Kadam
Research Centre and Department of Chemistry, Padmashri Vikhe Patil College Pravaranagar, Ahmednagar,
India
ABSTRACT
ARTICLE HISTORY
Received 18 April 2020
Accepted 21 May 2020
A facile carbon–sulfur bond formation was observed through the
cellulose sulfonic acid (CSA) catalyzed dithioacetal protection of car-
bonyl compounds. In a preliminary study, the synthesis and char-
acterization of functionalized bio-polymer, cellulose sulphonic acid
(CSA) was achieved and its catalytic knack for dithioacetal protection
was studied. It was discovered that CSA is an efficient, environmen-
tally benign, recyclable catalyst for the synthesis of 1,1-dithioacetals
or 1,1-dithioketals. A diverse range of aldehydes or ketones smoothly
underwent the thioacetalization either with 1,3-dithiol or 1,2-dithiol.
The 1,3-dithiol protection was found favored over 1,2-dithiol in terms
of yields and reaction times. Acetonitrile at room temperature pro-
vides the best results among the solvents studied. The biodegrad-
able nature of CSA, operationally simple protocol, good to excellent
yields, shorter reaction times and need of very small amount of
catalyst are the salient features of the present protocol.
KEYWORDS
Carbon-sulfur bond; cellulose
sulfonic acid (CSA);
dithioacetals; biodegradable;
environmentally benign;
recyclable catalyst
CONTACT Kailas R. Kadam
kailasshkadam@gmail.com
Research Centre and Department of Chemistry,
Padmashri Vikhe Patil College Pravaranagar, Loni(kd), Rahata, Ahmednagar, 413713 Maharashtra, India
This article makes reference to supplementary material available on the publisher’s website at
https://doi.org/10.1080/17415993.2020.1775835
© 2020 Informa UK Limited, trading as Taylor & Francis Group

2
K. R. KADAM
Introduction
The carbonyl group is one of the most studied and highly appraised functional group in
organic synthesis. Due to its’ high reactivity and wide range of transformations, it has been
contributing more than any other functional group to organic synthesis [1]. In multi-step
synthesis, its high reactivity often becomes an obstacle, especially where poly-functional
groups are involved. In such cases it needs to be temporarily protected in a suitable form.
Among the existing protecting groups, 1,1-dithioacetal protection is recognized as the
most versatile due to its ease of formation, inherent stability towards acidic or basic con-
ditions [2], and ability to revert the polarity of the carbonyl group [3]. Dithioacetals have
been used as the precursor in alkylation [4], olefination [5], fluorination [6] hydrogenoly-
sis [7], autoxidation [8] hydrodesulfurization [9] as well as in C–H or C–S bond activation
[10,11]. Sulfur-containing compounds have found an important place in the synthesis of
natural products [12], pharmaceuticals [13], structural diversifications [14] and in drug
discovery [15] as well.
Commonly the protection of the carbonyl group is achieved by treating it either with
two moles of thiol or one mole of dithiol in the presence acidic catalyst such as PTSA
[16], HCl [17], BF3.OEt2 [18], AlCl3 [19], LaCl3 [20], InCl3 [21]. Molecular I2 [22],
NBS [23], CoCl2 [24], (CH3)3SiCl [25], TiCl4 [26], TeCl4 [27], LiBr [28], H3PW12O40
[29], WCl6 [30], LiClO4 [31], Cu(BF4)2 [32], Sc(OTf)3 [33], In(OTf)3 [34] Y(OTf)3
[35], and ionic liquids [36] are also known to catalyze the thioacetalization reaction.
Though all these methods worked well for thioacetalizations, they often carry one or
more limitations such as environmental annoyance, use of toxic and hazardous chemi-
cals, side-product related issues, limited substrate scope, harsh reaction conditions, longer
reaction time and need of a stoichiometric amount of catalyst. Recently some solid-
supported reagents were also reported to catalyze thioacetalization protection, which
include SiO2-SOCl2 [37], SiO2-Cu(OTf)2 [38], SiO2-ZrCl4 [39], SiO2-FeCl3 [40] and
SiO2-HClO4 [41]. The supported reagents have their own advantages, but in all these
cases active catalytic parts are physisorbed on some suitable support (silica). Physisorp-
tion is a reversible phenomenon, which can be easily reverted even by small change
in temperature and pressure (Le Chatelier’s principle) so the use of these catalysts at
elevated temperature were restricted. Therefore a convenient, facile and environmen-
tally friendly route for the thioacetalization of carbonyl group remains to be carefully
investigated.
In recent years, the focus of chemists has shifted towards the development of renewable
and environmentally friendly protocols for organic synthesis. In this regard, the natural
polymers such as alginate, gelatin, starch, cellulose and chitosan derivatives are attractive
candidates to explore as the recyclable catalyst supports [42]. Cellulose has been stud-
ied more widely than any other natural polymer due to its anticipated properties such as
high natural abundance, renewable, biodegradable, readily available, safe to handle, and
high adsorption coefficient material [43]. These advanced properties make it a potential
alternative to the conventional inorganic supports in catalytic applications. A literature
survey reveals that cellulose sulfonic acid (CSA) has been employed as a biodegradable
catalyst for many more biologically important transformations [44], but yet its’ catalytic
potential for the synthesis of 1,1-dithioacetals from carbonyl compounds needs to be
explored.

JOURNAL OF SULFUR CHEMISTRY
3
HS
SH
2
R1
R2
S
OH
OSO3H
O
OH
O
R1
R2
S
4
O
O
O
HO
O
HO
HO
OR
OR
OH
OH
OH
n
R1
R2
S
1
Cellulose sulfonic acid (CSA), 4 mol %
Acetonitrile, RT
SH
S
HS
3
5
Scheme 1. Cellulose sulfonic acid-catalyzed dithioacetal protection of carbonyl compounds.
OH
OSO3H
O
OH
OH
OH
OH
ClSO3H
O
O
O
O
n-Hexane, 0-5 oC
Partial sulphonation
O
O
O
O
O
HO
HO
HO
HO
HO
HO
OH
OH
OSO3H
OH
n
OH
OH
n
Cellulose sulfonic acid (CSA)
Cellulose
Scheme 2. Synthesis of cellulose sulfonic acid (CSA).
With this background in mind, and in continuation of our research to develop greener
and convenient routes for important organic transformations [45–47], herewith we wish
to report our study on cellulose sulfonic acid (CSA) as an efficient, recyclable, environ-
mentally friendly catalyst for 1,1-dithioacetal protection of the carbonyl group through
the addition–elimination reaction of aldehydes or ketones with 1,2-dithiol or 1,3-dithiols
(Scheme 1). A diverse range of aldehydes or ketones smoothly underwent the protection
reaction to yield the desired products in good to excellent yields.
Materials and methods
Preparation of cellulose sulfonic acid (CSA): Cellulose sulfonic acid (CSA) was prepared
according to the literature procedure [48]. To a magnetically stirring, cold suspension of
cellulose (5 g) in n-hexane (20 ml), 1 g of chlorosulfonic acid (9 mmol) was added dropwise
(Scheme 2) and the evolved HCl gas was neutralized by a scavenger assembly. After the
completion of the addition, the suspension was further stirred for 2 h at room temperature.
The resulting suspension was filtered and washed with acetonitrile (3 × 10 ml) to remove
any trace of unreacted chlorosulfonic acid. Upon drying at room temperature cellulose
sulfonic acid (CSA, 5.25 g) was obtained as a white powder.
General procedure for synthesis of 1,1-dithioacetals: A mixture of aldehyde / ketone (2
mmol), 1,2-ethanedithiol / 1,3-propanedithiol (2 mmol) and cellulose sulfonic acid (55
mg or 4.12 mol %) was stirred together in acetonitrile at room temperature for the time
mentioned in Table 2. The progress of the reaction was monitored by TLC using n-hexane:
ethyl acetate as a mobile phase. After completion of the reaction as indicated by TLC, the

4
K. R. KADAM
insoluble catalyst was recovered by simple filtration followed by acetonitrile washings. In
order to isolate the product, the solvent was removed under reduced pressure from the
soluble filtrate obtained from the isolation of catalyst, and purified by a suitable purifi-
cation technique. The purified product was screened qualitatively using a functional test
for aldehydes or ketones. The structural features of the synthesized compounds were con-
firmed from their physical and analytical data, some of the representative compounds were
characterized by 1H NMR, and 13C NMR spectroscopy and the related data is enclosed.
Reusability procedure of the catalyst: The filtered catalyst from the reaction mixture was
washed thrice with acetonitrile, and dried at 60 °C for 6 hrs. The powdered catalyst was
weighed to verify its quantitative recovery. The recovered catalyst can be employed in
further reaction cycles.
Material and experimental: All the chemicals used were purchased from the Loba or Merck
chemical companies and used without further purification.1H NMR and 13C NMR spectra
were recorded on a Bruker Avance-II FT-NMR (400 MHz). The mass spectra were run on
a Waters micromass Q-TOF micro mass spectrometer. The melting points were carried out
in open capillary tubes by gradual heating in a paraffin oil. The chemical structures were
drawn using the chem draw 0.8 version of the Cambridge software.
Result and discussion
In the preliminary study, the synthesis of cellulose sulfonic acid (CSA) as an acidic,
biodegradable, polymeric material was achieved (Scheme 2) by the reported procedure
[48]. The formation and thermal stability of the synthesized CSA were established by the
appropriate analytical techniques. Figure 1(a,b) represent the FT-IR spectra of cellulose
and cellulose sulfonic acid respectively, the significant absorptions at 1034 and 1211 cm−1
in spectrum (b) represent the symmetric and anti-symmetric stretch of O = S = O moi-
ety while the absorption at 610 cm−1 is for the sulfur-oxygen single bond stretch in CSA,
these absorptions were not found in spectrum (a). The broad absorption from 3000 to
3500 cm−1 in spectrum (a) is for the alcoholic O-H stretch of cellulose, while the extended
absorption from 2000 to 3500 cm−1 (Figure 1(b)) strongly support the O-H stretch of sul-
fonic acid. Consequently, the FT-IR technique strongly supports the formation of cellulose
sulfonic acid from cellulose. The initial weight loss around 100 °C in the TGA plot of CSA
(Figure 1(d)) is due to the evaporation of physiosorbed water molecules while the second
weight loss centered at 300 °C corresponds to the decomposition of bonded sulfonic acid
on cellulose, at higher temperatures the plot is similar to that of cellulose (Figure 1(c)). The
TGA study confirmed the thermal stability of cellulose sulfonic acid. The X-ray diffraction
studies of cellulose and CSA show five characteristic diffraction signals for 2θ at 11.07,
14.42, 23.71, 27.63 and 36.57 (Figure 1(e,f)), which are in good agreement with the liter-
ature reports [49]. The acid equivalent of the synthesized CSA was examined by a simple
acid–base volumetric analysis method and was found 1.5 milli-equivalents of acid (H+)
per gram of CSA.
In the next part of the study, the catalytic behavior of CSA was examined for the syn-
thesis of 1,1-dithioacetals from carbonyl compounds. For this study, we monitored three
separate model reactions of benzaldehyde (2 mmol), with propane-1,3-dithiol (2.1 mmol)

JOURNAL OF SULFUR CHEMISTRY
5
Figure 1. (a) and (b) FTIR spectrum of cellulose and cellulose sulfonic acid, (c) and (d) TGA-DTA plots of
cellulose and cellulose sulfonic acid, (e) and (f) XRD scan of cellulose and cellulose sulfonic acid.
and CSA (100 mg) in ethanol under stirring at room temperature along with a blank reac-
tion (without catalyst) under the same conditions. It was observed that the blank reaction
only produce a trace amount of product even after stirring for 24 h (Table 1, entry 1), while

6
K. R. KADAM
Table 1. 1,3-Dithiane protection of carbonyl group of benzaldehyde under different conditions of
catalyst and solvent.
Sr. No.
Catalyst (amount)
No catalyst
Solvent
EtOH
EtOH
EtOH
Time (min)
Yields* (%)
1.
2.
3.
4.
5.
6.
7.
8.
> 24 h
10
20
> 30
30
30
30
30
30
< 30
30
30
30
30
30
< 30
< 30
< 30
26
22
30
trace
58
72
91
< 10
44
49
58
32
94
40
48
58
76
90
94
94
94
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (100 mg)
CSA (10 mg)
CSA (20 mg)
CSA (30 mg)
CSA (40 mg)
CSA (50 mg)
CSA (60 mg)
CSA (70 mg)
CSA (100 mg)
CSA (55 mg)
EtOH
Distilled water
Dioxane
THF
DMF
9.
DMSO
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
CH3CN
CH2Cl2
CH3CN
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
94
CSA (55 mg or 4.12 mol %)
NBS (5 mol %)
CoCl2 (5 mol %)
Sc(OTf)3 (5 mol %)
Y(OTf)3 (5 mol %)
94 [–]**
78 [23]**
88 [24]**
90 [33]**
89 [35]**
30
40
45
*Isolated yields, **4-chlorobenzaldehyde (2 mmol) as a model carbonyl compound.
Reaction conditions: stirring at room temperature.
the reaction with 100 mg of cellulose sulfonic acid catalyst produced 58% conversion in
the first 10 min (Table 1, entry 2), the conversion has reached to 72% in the next 10 min
(Table 1, entry 3) and it took more than 30 min to complete the reaction with a 91% yield.
With these results, we decided to explore the various dimensions of the reaction using
30 min as the model reaction time. To choose the appropriate medium for the transforma-
tion we carried out the above model reaction in different solvents for 30 min and the results
obtained are summarized in Table 1. We found that the model reaction barely produced
a 10% yield in distilled water (Table 1, entry 5), while in acetonitrile it took less time to
finish the reaction with a 94% yield (Table 1, entry 10). To optimize the amount of catalyst
the model reaction between benzaldehyde and propane-1,3-dithiol has been carried out
for 30 min in acetonitrile using different amounts of catalyst, obtained results are listed in
Table 1. The yields of the products increased with an increase in the amount of catalyst from
10 mg to 60 mg (Table 1, entries 11–16) and a further increase in the catalyst amount up
to 100 mg didn’t lead to an increase in the yields or a reduction in reaction times (Table 1,
entries 17, 18). It means that the optimum amount of catalyst lies in the range of 60–70 mg.
Again a micro examination of this range revealed that 55 mg of the catalyst produced the
best yield under the optimized set of conditions (Table 1, entry 19) and a further increase
in the amount of catalyst didn’t positively affect the yield or reaction time.
The generality of the optimized catalytic protocol was investigated by employing it for
the 1,1-dithioacetal protection of a diverse collection of aldehydes and ketones. All the
employed carbonyl compounds smoothly underwent the 1,1-dithioacetalization to offer
the products in good to excellent yields, the results summarized in Table 2. As expected,

JOURNAL OF SULFUR CHEMISTRY
7
Table 2. Cellulose sulfonic acid (CSA) catalyzed 1,3-dithiane or 1,3-dithiolane protection of carbonyl
group of various aldehydes and ketones.
R1
R2
S
S
OH
OSO3H
O
OH
HS
SH
2
R1
R2
O
O
O
O
4
O
OR
OR
HO
HO
HO
OH
OH
OH
n
R1
R2
S
SH
1
HS
Cellulose sulfonic acid (CSA), 4 mol %
Acetonitrile, RT
3
S
5
S
S
S
S
S
S
S
S
S
S
Br
Cl
Me
MeO
Cl
4a (26) 94
4b (23) 95
4c (28) 89
4d (32) 88
4e (22) 95
S
S
S
S
S
O2N
S
S
S
S
S
O2N
Cl
HO
4g (22) 94
4h (20) 96
4f (17) 94
4i (30) 82
4j (30) 88
S
S
S
S
S
S
MeO
HO
MeO
MeO
MeO
HO
S
S
S
S
OH
4k (45) 78
OMe
4l (36) 85
OMe
4o (65) 78
4n (40) 82
4m (35) 85
S
S
S
S
S
O
S
(n-Hexyl)
S
S
S
S
S
HN
4t (24) 85
4p (55) 80
4q (28) 85
4r (24) 88
4s (38) 80
S
S
S
S
S
S
S
S
S
S
S
Cl
Br
4x (35) 78
4y (45) 80
4u (46) 80
4v (40) 80
4w (40) 78
S
S
S
S
S
S
5bb (72) 78
4z (48) 82
5aa (45) 86
Compound (React. Time in minutes) Isolated Yields in %
the electronic effect of the functional group reflected well in terms of speed and ther-
modynamics of the reaction. The aldehydes reacted faster than their structural ketone
analogous (Table 2, compare 4a with 4u, 4b with 4w and 4r with 4x). The substituents
on the aromatic nucleus of aldehydes or ketones showed their electronic and steric effects
in terms of reaction times as well as yields. However, as compared to reaction times,

8
K. R. KADAM
OH
S
OSO3H
O
OH
HS
SH
2
S
7
S
S
S
S
S
S
S
S
O
O
O
O
HO
HO
OR
HO
OR
OH
OH
OSO3H
n
6
8
SH
3
HS
Cellulose sulfonic acid (CSA), 4 mol %
Acetonitrile, RT
Not observed
Scheme 3. Catalytic dimerization or cyclization of dithiol moieties.
Figure 2. Catalytic activity in five runs of reuse.
yields were less affected (Table 2, compare 4d with 4f, 4i with 4k, and 4u with 4v).
Carbonyl compounds bearing electron-withdrawing groups (Table 2, compounds 4e-4i)
took shorter times to react than those bearing electron-donating groups (Table 2, com-
pounds 4j-4n), while increased steric hindrances at the reaction site caused to increase
the reaction times (Table 2, compounds 4i, 4k). When ethane-1,2-dithiol is used instead
propane-1,3-dithiol as the masking agent, the reaction took longer to complete and the
yields of products were also affected negatively (Table 2, compare 4a with 5aa and 4z
with 5bb). The beauty of our new protocol is that side reactions such as dimerization
or cyclization of dithiols (Scheme 3) were not observed as previously reported in the
literature [50].
To examine the catalytic potency of CSA, a comparative study has made between the
important catalysts from the literature and CSA for the synthesis of 1,1-dithioacetal of
4-chlorobenzaldehyde (Table 1, entries 20–24). From this study, it was concluded that a
small amount, 4.12 mol % of CSA is sufficient to bring out the transformation with better
results of reaction time and yield (Table 1, entry 20) than those of the reported cata-
lysts. This establishes the superiority of the catalyst and present protocol over the reported
methods.
The reusability of the catalyst was examined for the model reaction under optimized
conditions. It demonstrated, CSA is capable of catalyzing up to 5 reactions without a
decrease in yield and only a minor loss of reactivity. These results are summarized in
Figure 2. The catalyst from the reaction mixture was recovered nearly quantitatively with
only a trace amount of catalyst lost in the isolation process. The quality check of the
recovered catalyst was conducted by titrating against standardized alkali solution using
phenolphthalein as an indicator. The result obtained showed 1.5 milli-equivalents of H+

JOURNAL OF SULFUR CHEMISTRY
9
present per gram of recovered CSA. In short, there is no loss of acidic strength of the recov-
ered CSA. The optimized amount, 55 mg of the catalyst holds 0.0825 milli-equivalents of
H+ (acid). The amount 0.0825 milli-equivalent of H+ (acid) in comparison with substrate
amount (2 milli-mol) in model reaction becomes equal to 4.125 mol %.
Conclusion
In summary, the synthesis and characterization of cellulose sulfonic acid (CSA) as a
bio-polymer supported acid has been achieved and its utility as a recyclable catalyst
for the 1,1-dithioacetal protection of carbonyl groups was studied. Under the optimized
conditions of the protocol, cellulose sulfonic acid (CSA) has proved as an efficient, envi-
ronmentally benign, operationally simple, non-toxic, solid acid catalyst for the synthesis
of 1,1-dithioacetals from carbonyl compounds and 1,3-dithiol or 1,2-dithiol. 1,3-Dithian
protection was found preferred over 1,2-dithiol in terms of reaction times and yields. The
protocol is free from the side reactions such as dimerization or cyclization of dithiols, which
is an additional advantage of the protocol. The protocol worked smoothly for a collection
of structurally diverse aldehydes as well as ketones.
Spectroscopic data of the representative compounds
2-Phenyl-1,3-dithiane (4a): mp 71-73°C (lit. 72–74°C); 1H NMR (400 MHz, CDCl3) δ:
7.37 (m, 2H), 7.29 (m, 3H), 4.81 (d, 1H), 2.91 (m, 4H), 2.11 (m, 1H), 1.89 (m, 1H);13C
NMR (100 MHz, CDCl3) δ: 136.33, 128.83, 128.34, 126.91, 47.94, 30.47, 25.46.; MS (EI, 70
ev) m/z: 196, 153, 135, 121, 105, 91.
1
2-(4-chlorophenyl)-1,3-dithiane (4e): mp 91-93°C (lit. 89-91°C); H NMR (400 MHz,
CDCl3) δ: 7.41 (d, 2H), 7.30 (d, 2H), 5.13 (s, 1H), 3.05 (m, 2H), 2.91 (m, 2H), 2.18 (m,
1H), 1.94 (m, 1H); 13C NMR (100 MHz, CDCl3) δ: 141.35, 134.66, 130.26, 128.84, 128.30,
126.32, 50.90, 32.16, 25.23.; MS (EI, 70 ev) m/z: 230, 195, 152, 134, 120, 104, 91.
1
4-(1,3-dithian-2-yl)-2-methoxyphenol (4l): mp 136–139°C, (lit.131-133 °C); H NMR
(400 MHz, CDCl3) δ: 7.26 (m, 1H), 6.96 (m,1H), 6.85 (br s, 1H), 5.11 (s, 1H), 3.87 (s,
3H), 3.03(m, 2H), 2.90 (m, 2H), 2.12 (m, 1H), 1.91 (m, 1H); 13C NMR (100 MHz, CDCl3)
δ: 164.84, 145.98, 131.34, 121.05, 114.70, 110.52, 56.23, 51.53, 32.45, 25.30; MS (EI, 70 ev)
m/z: 242, 199, 168, 167, 152, 137, 109.
1
2-(Thiophen-2-yl)-1,3-dithiane (4r): mp 36–38°C (lit. 39–41 °C); H NMR (400 MHz,
CDCl3) δ: 7.54 (dd,1H), 7.30 (t,1H), 7.14 (t, 1H), 5.60 (s, 1H), 3.12 (t, 2H), 2.92 (d, 2H),
2.18(m, 1H), 1.95 (m, 1H); 13C NMR (100 MHz, CDCl3) δ: 130.01, 129.98, 128.34, 123.34,
50.97, 32.53, 25.37; MS (EI, 70 ev) m/z: 188, 155, 145, 114, 81.
2-(Naphthalen-1-yl)-1,3-dithiane (4s): liquid at room temp.; 1H NMR (400 MHz, CDCl3)
δ: 8.30, (d, 1H), 7.84 (d, 1H), 7.79 (d, 2H), 7.55 (m, 1H), 7.43 (m, 2H), 5.91 (s,1H), 3.91
(m, 2H), 2.97 (m, 2H), 2.24 (m, 2H), 1.98 (m, 1H); 13C NMR (100 MHz, CDCl3) δ: 135.26,
134.14, 130.46, 129.26, 129.20, 126.55, 126.46, 126.10, 125.82, 123.57, 48.63, 33.01, 25.75;
MS (EI, 70 eV) m/z 246.0, 181.1, 172.0, 171.0, 127.0, 105.
2-Phenyl-1,3-dithiolane (5(aa)): 1H NMR (400 MHz, CDCl3) δ: 7.38 (m, 2H), 7.32 (m,
2H), 7.25(m, 1H), 5.24 (d,1H), 3.37 (m, 2H), 3.28 (m, 2H); 13C NMR (100 MHz, CDCl3)δ:

10
K. R. KADAM
136.40, 129.42, 128.86, 128.14, 54.82, 39.93; MS (EI, 70 eV) m/z 232.0, 203.0, 185.0, 171.0,
127.0.
Acknowledgement
The author is thankful to the Head and Professor, Department of chemistry, Institute of Science,
Nagpur (India) for the fruitful discussions during the work. The athors acknowledge the charac-
terization facility provided by BCUD, Savitribai Phule Pune University, Pune (India). The authors
also acknowledge the Director, School of Chemical Sciences, Swami Ramanand Teerth Marathwada
University, Nanded for their affiliation support.
Disclosure statement
No potential conflict of interest was reported by the author.
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