Investigations on the Lewis-acids-catalysed electrophilic aromatic substitution reactions of thionyl chloride and selenyl chloride, the substituent effects, and the reaction mechanisms

Article abstract of DOI:10.3184/174751913X13842832780853

The previously established aluminium-chloride-(AlCl₃)-catalysed electrophilic aromatic substitution (EAS) of benzene (PhH) with thionyl chloride (SOCl₂) has been extended to toluene (PhCH₃), chlorobenzene (PhCl), and phenol (PhOH). -CH₃ was found to be mainly a para-director with a minor ortho-directing effect on the EAS reactions giving diaryl sulfoxides (Ar₂SO). -Cl was found to be exclusively a para-director for formation of Ar₂SO. All the -CH₃, -Cl, and -OH groups were shown to be exclusive para-directors for formation of diaryl sulfides (Ar₂S) from the EAS reactions. Although the reactions of PhH and PhCH₃ with SOCl₂ in the presence of AlCl ₃ gave the major Ar₂SO and minor Ar₂S at ambient temperature, the phenol (PhOH) reaction was shown to give only the reduced sulfide (p-HOC₆H₄)₂S with no sulfoxide (p-HOC₆H₄)₂SO formed. The mixed diaryl sulfoxides ArSOAr′ (Ar, Ar′=C₆H₅, p-CH ₃C₆H₄; C₆H₅, o-CH ₃C₆H₄; and C₆H₅, p-ClC₆H₄) were produced in the AlCl₃-catalysed reactions of SOCl₂ with molar 1:1 PhH-PhX mixtures (X=CH₃ and Cl). Efforts to enhance the yield of S-aryl arenesulfonothioates ArSO ₂SAr (Ar=Ph, p-CH₃C₆H₄, and p-ClC₆H₄) from the AlCl₃-catalysed EAS reactions of SOCl₂ were made, showing that decreasing the molar ratios of ArH/SOCl₂ or lowering the temperature resulted in an increase in the product yield. A detailed mechanism has been proposed to account for the formation of ArSO₂SAr. The Lewis-acid-MCl₃-(M=Al and Fe)-catalysed EAS reactions of PhH with selenyl chloride (SeOCl₂) were demonstrated to give the reduced diphenyl selenide (Ph₂Se) and diphenyl diselenide (PhSeSePh) via novel auto-redox processes in selenium of the key EAS intermediates.

Full text of DOI:10.3184/174751913X13842832780853

736 RESEARCH PAPER
DECEMBER, 736–744
JOURNAL OF CHEMICAL RESEARCH 2013
Investigations on the Lewis-acids-catalysed electrophilic aromatic
substitution reactions of thionyl chloride and selenyl chloride, the
substituent effects, and the reaction mechanisms
Xiaoping Sun*, David Haas, Samantha McWilliams, Benjamin Smith and Katrina Leaptrot
Department of Natural Sciences and Mathematics, University of Charleston, Charleston, West Virginia 25304, USA
The previously established aluminium-chloride-(AlCl3)-catalysed electrophilic aromatic substitution (EAS) of benzene (PhH)
with thionyl chloride (SOCl2) has been extended to toluene (PhCH3), chlorobenzene (PhCl), and phenol (PhOH). –CH3 was found
to be mainly a para-director with a minor ortho-directing effect on the EAS reactions giving diaryl sulfoxides (Ar2SO). –Cl was
found to be exclusively a para-director for formation of Ar2SO. All the –CH3, –Cl, and –OH groups were shown to be exclusive
para-directors for formation of diaryl sulfides (Ar2S) from the EAS reactions. Although the reactions of PhH and PhCH3 with
SOCl2 in the presence of AlCl3 gave the major Ar2SO and minor Ar2S at ambient temperature, the phenol (PhOH) reaction was
shown to give only the reduced sulfide (p-HOC6H4)2S with no sulfoxide (p-HOC6H4)2SO formed. The mixed diaryl sulfoxides
ArSOAr′ (Ar, Ar′=C6H5, p-CH3C6H4; C6H5, o-CH3C6H4; and C6H5, p-ClC6H4) were produced in the AlCl3-catalysed reactions of
SOCl2 with molar 1:1 PhH–PhX mixtures (X=CH3 and Cl). Efforts to enhance the yield of S-aryl arenesulfonothioates ArSO2SAr
(Ar=Ph, p-CH3C6H4, and p-ClC6H4) from the AlCl3-catalysed EAS reactions of SOCl2 were made, showing that decreasing the
molar ratios of ArH/SOCl2 or lowering the temperature resulted in an increase in the product yield. A detailed mechanism has
been proposed to account for the formation of ArSO2SAr. The Lewis-acid-MCl3-(M=Al and Fe)-catalysed EAS reactions of
PhH with selenyl chloride (SeOCl2) were demonstrated to give the reduced diphenyl selenide (Ph2Se) and diphenyl diselenide
(PhSeSePh) via novel auto-redox processes in selenium of the key EAS intermediates.
Keywords: organosulfur, organoselenium, auto-redox, aromatic, CH substitution, functionalisation
Diaryl sulfoxides (Ar2SO), parented by Ph2SO, are valuable
reagents in organic chemistry1 and have found substantial
utility in synthetic and biomedical applications. For example,
Ar2SO (Ar=Ph and m-CF3C6H4) have been used in carbohydrate
synthesis to facilitate the formation of glycosidic bonds.2 Ph2SO
has been used effectively in the catalytic oxidation of various
alkyl sulfides (RSR′) to sulfoxides (RSOR′).3 In medicinal
chemistry, diaryl sulfoxides [Ar=Ph, p-O2NC6H4, p-H2NC6H4,
and p-(ClCH2CH2)2NC6H4] have been used as precursors to
anti-cancer drugs.4,5 Usually, diaryl sulfoxides, including
diphenyl sulfoxide Ph2SO, are made by catalytic oxidation
of the corresponding diaryl sulfide Ar2S.6,7 The preparation
involves complicated transition-metal-complex based catalysts.
It often suffers with over-oxidation to diaryl sulfone (Ar2SO2)
side products. Particularly, preparation of the starting Ar2S is
tedious and often requires sophisticated catalysts as well.8–10
Some diaryl sulfoxides were made by reaction of aryl O-menthyl
sulfoxide with ArMgX (Grignard reagent).11 Obviously, many
efforts must be made in preparing the starting materials prior
to synthesis of the targeted Ar2SO.
Very often, functionalisation of aromatic hydrocarbons can
be readily achieved by electrophilic aromatic substitution
(EAS) reactions in which an aromatic C–H bond reacts via
a Wheland intermediate (σ–complex), and the hydrogen is
replaced by an electrophile.12,13 Following this approach, Olah
and Nishimura14 studied the AlCl3-catalysed EAS reactions of
benzene and toluene with arenesulfinyl chlorides (ArSOCl).
The reactions gave various diaryl sulfoxides (but purity and
yields unreported) at 25 °C. Recently, we have conducted the
aluminium-chloride-(AlCl3)-catalysed Friedel–Crafts (EAS)
reactions of thionyl chloride (SOCl2) with benzene (PhH).15
Under certain conditions (such as adding SOCl2 slowly to the
PhH–AlCl3 mixture at 25 °C to keep PhH in excess during the
reaction), we were able to make pure (99.9%) Ph2SO in good
yields (~80%). Formation of Ph2SO was demonstrated to take
place by the following double consecutive EAS reactions
[Eqn (1)].15
(1)
O
S
O
S
O
S
AlCl3
AlCl3
PhH
+ HCl
2 PhH
+
+
+ 2 HCl
Ph
Ph
Ph
Cl
Cl
Cl
As the temperature and the manner of mixing starting
materials varied, Ph2S was produced from the reaction in
significant yields together with formation of PhSO2SPh (~5%)
and PhSO2Ph (trace). Formation of these aromatic organosulfur
compounds was unexpected and involved a very interesting
oxidation–reduction (redox) process in the sulfur centre. The
possible mechanisms were presented.15
In the present work, we extend our investigations on this
type of EAS reaction to substituted benzenes, including toluene
(PhCH3), chlorobenzene (PhCl), and phenol (PhOH). We now
emphasise studies of the substituent effects of –CH3, –Cl, and
–OH on the regiochemistry (directing effects) as well as the
effects on the redox chemistry occurring in the sulfur centre
during the reactions. The current studies are also extended to
formation of the mixed diaryl sulfoxides XC6H4SOPh (X=CH3
and Cl) from the AlCl3-catalysed EAS reactions of SOCl2 and
the directing effects of the substituents (–CH3 and –Cl) on the
reactions. In addition, we report our attempt on enhancing
the yields of S-aryl arenesulfonothioate ArSO2SAr (Ar=C6H5,
p-CH3C6H4, and p-ClC6H4) produced from the AlCl3-catalysed
EAS reactions of SOCl2. Directing effects of –CH3 and –Cl on
formation of ArSO2SAr are discussed. A reaction mechanism
involving more detailed molecular interactions is proposed.
Finally, we have extended our studies to the Lewis-acid-
MCl3-(M=Al and Fe)-catalysed electrophilic substitution
reactions of benzene with selenyl chloride (SeOCl2), the
selenium analogue of SOCl2. Substantially different behaviour
of SeOCl2 from that of SOCl2 has been discovered. The reaction
has been surprisingly found to give diphenyl selenide (Ph2Se)
and diphenyl diselenide (PhSeSePh). Possible mechanisms for
these novel reactions are discussed in this work. Ph2Se and
PhSeSePh have many applications in organic synthesis and
they are usually prepared by complicated approaches.16
* Correspondent. E-mail: xiaopingsun@ucwv.edu
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Table 1 Distribution of products formed in the AlCl3-catalysed reactions of PhX (X=Cl and CH3) with SOCl2 in the molar ratio of PhX:SOCl2:AlCl3 =2:1:1a
O
S
O
S
O
S
O
S
O
S
X
X
X
AlCl3
S
S
2PhX + SOCl2
+
+
+
+
+
O
X
X
X X
X
X
X
X
X
X=Cl
X=CH3
89%
55%
0
34%
0
11%
0
0
11%
0
0
0
SOCl2 added dropwise to the PhX/AlCl3 mixture at 25 °C
X=Cl
X=CH3
100%b
50%
0
26%
0
4%
0
4%
0
0
0
16%
AlCl3 added to the PhX/SOCl2 mixture piecewise at 25 °C
X=Cl
X=CH3
39%
58%
7%
27%
0
8%
51%
7%
3%
0
0
0
AlCl3 added to the PhX/SOCl2 mixture piecewise at 70 °C
aAll the percentages are relative normalised yields, estimated by comparison of areas of the GC spectra of related components, assuming that the peak area
is proportional to the number of moles of the component. The assumption is supported by the established analogous relationship for the Ph2Se–PhSeSePh
system, Eqn (8) in the experimental section.
bA sole component of (p-ClC6H4)2SO was formed based on GC–MS analysis. Its absolute (isolated) percent yield was determined to be 71% by comparison
of the actually recovered mass of the product with the theoretical yield.
only the sulfoxide Ph2SO with no reduced sulfide Ph2S formed.15
Results and discussion
Similarly, Table 1 shows that the toluene reaction under the
Substituent effects on the AlCl -catalysed electrophilic aromatic
substitution reactions of SOCl23
same conditions gave mainly diaryl sulfoxide isomers, with only
very minor sulfide (p-CH3C6H4)2S (7%) produced. However,
the PhCl reaction at 70 °C, with AlCl3 added piecewise to the
PhCl–SOCl2 mixture, resulted in formation of the major diaryl
sulfide (p-ClC6H4)2S (51%) (the only observed sulfide isomer)
together with minor sulfoxide isomers (p-ClC6H4)2SO (39%) and
p-ClC6H4SO(o-ClC6H4) (7%). This demonstrates that –Cl and –
CH3 possess substantially different effects on redox chemistry
of the sulfur centre, leading to different product distributions.
Such difference in the effects on the redox chemistry possessed
by the two substituent groups can also be seen by comparison of
the product distributions of the reactions in Table 1 under other
conditions.
The substituent effect on the redox chemistry of the sulfur
centre associated to the AlCl3-catalysed EAS reactions of SOCl2
is further demonstrated by examining the reaction of phenol
(PhOH). The experimental results (Table 2) show that quick
addition of PhOH to the SOCl2–AlCl3 mixture at 25 °C gave 91%
(p-HOC6H4)2S and 9% p-ClC6H4OH, while slow (piecewise)
addition of AlCl3 to the PhOH–SOCl2 mixture at 25 °C gave
51% ( p-HOC6H4)2S and 49% p-ClC6H4OH. Different from PhX
(X=H, CH3, and Cl) whose reactions with SOCl2 in the presence
of AlCl3 at 25 °C always gave the major Ar2SO and minor Ar2S,
the AlCl3-catalysed reactions of PhOH with SOCl2 at 25 °C only
gave the reduced bis(p-hydrophenyl) sulfide (p-HOC6H4)2S,
together with the minor p-chlorophenol (p-ClC6H4OH) side
product. The initially expected diaryl sulfoxide (p-HOC6H4)2SO
or any other sulfoxide isomers (on the basis of the reactions
of other arenes) were not found from the reaction product. No
other organosulfur compounds were formed. The –OH group
is exclusively a para-director for the AlCl3-catalysed EAS
reactions of SOCl2 giving the diaryl sulfide. Different from the
–CH3 and –Cl groups, the strongly activating –OH facilitates the
complete reduction of S(IV) in SOCl2 to S(II) in (p-HOC6H4)2S
in the course of the EAS reaction.
Analogous to the benzene reaction,15 when SOCl2 was added
slowly (dropwise) to the PhCH3–AlCl3 mixture (to keep PhCH3
in excess) at 25 °C, the reaction only gave the diaryl sulfoxide
isomers (p-CH3C6H4)2SO (55%), p-CH3C6H4SO(o-CH3C6H4)
(34%), and (o-CH3C6H4)2SO (11%) (Table 1). No other
organosulfur compounds were produced. This shows the methyl
group is mainly a para-director with a minor ortho-directing
effect on the type of EAS reactions leading to diaryl sulfoxides.
Such a directing effect has also been revealed from the toluene
reactions under different conditions in Table 1, which gave the
major diaryl sulfoxide isomers together with small percentages
of other organosulfur compounds. In many other EAS reactions
of toluene (such as halogenation, nitration, and Friedel–Crafts
alkylation), the –CH3 group is approximately an equal para-
and ortho-director.12,13,16 However, in the EAS product with
SOCl2, the sulfoxide S=O group may produce substantial
steric hindrance on its ortho-carbon, making the –CH3 group a
major para-director. Similarly, the AlCl3-catalysed reaction of
p-CH3C6H4SO2Cl with toluene has been reported to give 80%
(p-CH3C6H4)2SO2 and only 20% p-CH3C6H4SO2(o-CH3C6H4).17
When AlCl3 was added slowly (piecewise) to the PhCl–
SOCl2 mixture (to keep PhCl in excess over the reactive
SOCl2–AlCl3 adduct) at 25 °C, the reaction led to formation of
a sole sulfoxide isomer (p-ClC6H4)2SO (Table 1), showing the
–Cl group is essentially only a para-director for formation of
the diaryl sulfoxide. No other organosulfur compounds were
formed. The para-directing effect is mainly due to conjugation
of the lone-pair of electrons in –Cl.12,13,16 In addition, the lack of
the ortho-isomer of sulfoxide in most of the PhCl reactions may
be attributable to the repulsions between the –Cl electron pairs
and the electron pairs in the S=O group of the transition state
leading to the ortho-isomer (o-ClC6H4)2SO.
Our previous work showed that when AlCl3 was added
piecewise to the PhH–SOCl2 mixture at 70 °C, the reaction gave
Table 2 Product yields (normalised molar percentages) for the AlCl3-catalysed reactions of phenol (PhOH) and thionyl chloride (SOCl2) with the
molar PhOH:SOCl2:AlCl3 =2:1:1 under different conditions
t/oC
Manner of mixing
(p-HOC6H4)2S
p-HOC6H4Cl
(p-HOC6H4)2SO
25
25
PhOH/ether solution added all at once to the AlCl3–SOCl2 mixture
AlCl3 added piecewise to the PhOH–SOCl2 mixture
91%
51%
9%
49%
0
0
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738 JOURNAL OF CHEMICAL RESEARCH 2013
We believe that common to all the arenes, the first step of the
AlCl3-catalysed reaction of PhOH with SOCl2 is the aromatic
C–H bond substitution by SOCl2 giving p-HOC6H4SOCl–AlCl3
(the AlCl3 adduct of the first EAS intermediate) [Eqn (2)].
the EAS of a second C6H(CH3)5 molecule with C6(CH3)5SOCl–
AlCl3 could not happen to give [C6(CH3)5]2SO. Instead, an
intramolecular auto-redox process occurred to C6(CH3)5SOCl–
AlCl3 exclusively [see Eqn (3)] to lead to formation of the
sulfide [C6(CH3)5]2S as a sole product.
AlCl3
Cl
AlCl3
AlCl3
Cl
O
S
O
S
O
S
Formation of the mixed diaryl sulfoxides p-XC6H4SOPh (X=CH3
and Cl)
(2)
..
..
HO
HO
HO
Cl
The AlCl3-catalysed reactions of SOCl2 with the molar 1:1
mixtures of PhH–PhX (X=CH3 and Cl) were performed at
25 °C, with AlCl3 added slowly (piecewise) to the PhH–PhX–
SOCl2 mixtures. Essentially, reactions of both PhH–PhX
mixtures gave diaryl sulfoxides. Mixed diaryl sulfoxides
p-XC6H4SOPh (X=CH3 or Cl) and o-XC6H4SOPh (X=CH3) were
produced in each reaction, in addition to formation of Ph2SO
and (p-XC6H4)2SO (Table 3).
As shown in Fig. 1, SOCl2 is believed to react with both
PhH and PhX (X=CH3 or Cl) separately to give PhSOCl and
XC6H4SOCl (para- or ortho) in the first step. Then reaction
of PhSOCl with PhX or reaction of p-XC6H4SOCl with PhH
took place to lead to formation of the mixed diaryl sulfoxide
p-XC6H4SOPh and o-XC6H4SOPh, while reaction of PhSOCl
with PhH gave Ph2SO and reaction of XC6H4SOCl with PhX
gave (p-XC6H4)2SO (X=Cl or CH3), p-XC6H4SO(o-XC6H4)
(X=CH3), and (o-XC6H4)2SO (X=CH3). The observed directing
effects of –CH3 and –Cl on the reactions giving the mixed
diaryl sulfoxides p-XC6H4SOPh and o-XC6H4SOPh (Table 3)
are consistent with those on the reactions in Table 1, namely
that –CH3 is mainly a para-director with minor ortho-directing
effect on formation of diaryl sulfoxide, while –Cl is an exclusive
para-director.
Relatively, the percentage of the mixed p-ClC6H4SOPh
(43%) was higher than the total percentage (39%) of the mixed
p-CH3C6H4SOPh (33%) and p-CH3C6H4SOPh (6%) (Table 3).
This is likely because the electron-withdrawing –Cl group in
the intermediate p-ClC6H4SOCl enhances the electrophilicity
of the sulfur centre, making p-ClC6H4SOCl more reactive than
PhSOCl and p-CH3C6H4SOCl. Formation of the mixed diaryl
sulfoxides p-XC6H4SOPh (X=CH3 and Cl) provided further
evidence to support the mechanism for the AlCl3-catalysed
double consecutive EAS reactions of SOCl2 [Eqn (1)].
The electron-donating –OH on the para-carbon of
p-HOC6H4SOCl–AlCl3 canpossiblydecreasetheelectrophilicity
of the sulfur centre by delocalising the positive charge from
S=O+– to the –OH oxygen by conjugation as shown in Eqn (2).
As a result, the sulfur centre in p-HOC6H4SOCl–ACl3 was
unreactive towards an aromatic ring. Therefore, the rate of the
second EAS reaction of p-HOC6H4SOCl–AlCl3 with PhOH
was significantly reduced and the corresponding sulfoxide
(p-HOC6H4)2SO (or any other sulfoxide isomers) were not
formed. Instead, after the p-HOC6H4SOCl–AlCl3 intermediate
was produced, it underwent an exclusive intramolecular auto-
redox reaction [Eqn (3)], the mechanism of which is analogous
to that for the formation of Ph2S from the benzene reaction.15
Cl
Cl
Al
AlCl2
Ar = p-HOC6H4
O
S
O
Cl
- HOAlCl2
OH
- Cl2
HO
Ar
S
Ar
S
HO
Cl
(3)
S(II)
S(IV)
In the presence of AlCl3, a small fraction of phenol in the
reaction mixture reacted readily with Cl2, produced from the
intramolecular auto-redox and experimentally identified, to
give p-chlorophenol (p-ClC6H4OH) as a minor side product.
When AlCl3 was added slowly (piecewise) to the PhOH–SOCl2
mixture, PhOH remained in excess. Therefore, the amount of
p-ClC6H4OH formed was much greater than that produced
from the reaction by adding PhOH quickly to the SOCl2–AlCl3
mixture. Formation of p-ClC6H4OH in the reaction has provided
further support for the previously proposed intramolecular
redox process (which gives off Cl2)15 involved in the reaction
mechanism.
Our study showed that in contrast to the toluene reactions
at 25 °C which always gave the major sulfoxide and minor
sulfide products (Table 1), the AlCl3-catalysed reaction
of pentamethylbenzene [C6H(CH3)5] with SOCl2 at 25 °C
[conducted by adding C6H(CH3)5 to the SOCl2–AlCl3
mixture] gave a sole reduced di(pentamethylphenyl) sulfide
[C6(CH3)5]2S product (GC-MS), while the corresponding
di(pentamethylphenyl) sulfoxide [C6(CH3)5]2SO was not
formed. The five electron-donating methyl groups can
effectively decrease the electrophilicity of the sulfur centre in
the first EAS intermediate C6(CH3)5SOCl–AlCl3. As a result,
Enhancing yields for formation of S-aryl arenesulfonothioates
ArSO2SAr (Ar=Ph, p-CH3C H , and p-ClC6H4) and directing
effects of substituents on the r6ea4ctions
Our previous work indicated that the AlCl3-catalysed
reactions of benzene with SOCl2 very often gave a very small
amount of PhSO2SPh (only~5%)15 in addition to formation
of Ph2SO and Ph2S in more appreciable yields. Formation of
PhSO2SPh in the EAS reaction, although in a very low yield,
was still considered mechanistically interesting. Since then,
we have made substantial efforts to optimise the conditions
Table 3 The relative normalised yields of products for the AlCl3 catalysed reactions of SOCl2 with the molar 1:1 mixtures of PhH and PhX
(X=CH3 and Cl)a
O
S
O
S
O
S
O
S
O
S
O
S
X
X
X
X
AlCl3
+
+
+
+
+
PhH + PhX + SOCl2
X
X
X
X
X=Cl
X=CH3
28%
16%
43%
33%
0
6%
29%
32%
0
10%
0
2%
aAll the percentages are relative normalised yields, estimated by comparison of areas of the GC spectra of related components, assuming
that the peak area is proportional to the number of moles of the component. The assumption is supported by the established analogous
relationship for the Ph2Se–PhSeSePh system, Eqn (8) in the experimental section.
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Formation of ArSOCl
O
S
O
S
X
AlCl3
Cl
Cl
PhX + SOCl2
+
X
X = CH3
X = CH3 or Cl
O
S
AlCl3
Cl
PhH + SOCl2
Ph
Formation of ArSOAr' (mixed diaryl sulfoxide)
O
S
Cl
+ PhH
X
O
S
O
S
X
(para- or ortho-)
AlCl3
Ph
Ph
+
X
O
S
X = CH3 or Cl
X = CH3
+ PhX
Cl
Ph
Formation of ArSOAr
O
S
O
O
S
O
S
X
X
X
S
AlCl3
AlCl3
Cl
+
+
+ PhX
X
X
X
X
(para- or ortho-)
X = CH3 or Cl
X = CH3
X = CH3
O
S
O
S
+ PhH
Ph
Cl
Ph
Ph
Fig. 1 Mechanistic steps for the AlCl3-catalysed reactions of SOCl2 with the molar 1:1 mixtures of PhH and PhX (X=CH3 and Cl): Formations of the mixed
diaryl sulfoxides ArSOAr′.
for PhSO2SPh formation and to enhance its yield in order to
reinforce the proposed mechanism.15 We have found in this
work that the yield of PhSO2SPh can be greatly enhanced by
slowly (dropwise) adding PhH to the SOCl2–AlCl3 mixture
(to keep PhH in deficit). The yield can also be enhanced by
lowering the temperature. Eqn (4) shows the results for the
AlCl3-catalysed reactions of benzene and SOCl2 in the molar
ratio of PhH:SOCl2:AlCl3 =1:1:1, with benzene dropwise added
to the SOCl2–AlCl3 mixture at 0 °C and –10 °C, respectively.
CH3C6H4)]anddiarylsulfide[(p-CH3C6H4)2S],whileitfunctions
as para- and ortho-directors for formation of the diaryl sulfoxide
isomers. The ortho-isomers of arenesulfonothioate and sulfide
were not identified from the reaction. Comparison of Eqn (4)
and Eqn (5) indicates that under the same conditions (–10 °C),
the benzene reaction gave a significantly higher yield of S-aryl
arenesulfonothioate (49%) than did the toluene reaction (30%).
The reactions of chlorobenzene gave three organosulfur
compounds. Their identities and yields are shown in Eqn (6).
40% p-ClC6H4SO2S(p-ClC6H4) and 33% p-ClC6H4SO2S(p-
ClC6H4) were produced in the reactions with the
PhCl:SOCl2:AlCl3 molar ratios of 1:2:2 and 1:1:1 respectively.
This indicates that lowering the PhCl/SOCl2 ratio (from 1:1
to 1:2) facilitated formation of the S-aryl arenesulfonothioate.
For each organosulfur compound, only the para-isomer was
found. The –Cl group functions as an exclusive para-director
for formation of all the aromatic organosulfur compounds in
Eqn (6).
In our previous work,15 we thought the formation of very
minor PhSO2SPh (~5%) in the AlCl3-catalysed EAS reactions
of PhH with SOCl2 possibly resulted from an oxygen exchange
between two molecules of the AlCl3 adduct of the initially
formed EAS intermediate (ArSOCl–AlCl3). We now propose
more detailed molecular interactions to account for the AlCl3-
catalysed oxygen exchange and subsequent transformations
involved in the formation of S-aryl arenesulfonothioates
ArSO2SAr (Ar=C6H5, p-CH3C6H4, and p-ClC6H4) in significant
yields (Fig. 2). The nucleophilic sulfur (due to a lone-pair of
electrons) in one ArSOCl–AlCl3 molecule could possibly
(4)
O
S
O
S
S
S
AlCl3
0 oC
+ SOCl2
(PhH)
+
+
O
(Ph2SO2SPh)
(Ph2S)
38%
(Ph2SO)
26%
36%
–10 oC
49%
15%
36%
At –10 °C the reaction gave the major PhSO2SPh (49%),
together with the minor Ph2SO (36%) and Ph2S (15%). The yield
of PhSO2SPh at –10 °C (49%) was significantly higher than that
at 0 °C (36%).
Wehavealsoextendedthereactionsunderthesameconditions
(dropwise adding the arene to the SOCl2–AlCl3 mixture at 0 °C
or –10 °C) to toluene and chlorobenzene. The reaction of toluene
(PhCH3) [Eqn (5)] gave 30% p-CH3C6H4SO2S(p-CH3C6H4) (the
only observed S-aryl arenesulfonothioate isomer), together with
(p-CH3C6H4)2S (25%) (the only observed diaryl sulfide isomer),
(p-CH3C6H4)2SO (35%), and p-CH3C6H4SO(o-CH3C6H4) (10%).
Eqn (5) shows that –CH3 is an exclusive para-director for
formationoftheS-arylarenesulfonothioate[p-CH3C6H4SO2S(p-
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740 JOURNAL OF CHEMICAL RESEARCH 2013
O
S
O
S
O
–10 oC
S
S
S
PhCH3 + SOCl2
+
+
+
(5)
(6)
AlCl3
O
30%
25%
35%
10%
O
S
O
S
S
S
0 oC
AlCl3
+
+
PhCl + SOCl2
O
Cl
Cl
Cl
Cl Cl
Cl
[p-ClC6H4SO2S(p-C6H4Cl)]
(p-ClC6H4)2S)
17%
(p-ClC6H4)2SO)
1
1
:
:
1
2
:
:
1
2
33%
40%
50%
40%
20%
attack the electrophilic oxygen in another in a nucleophilic
displacement reaction. This results in cleavage of an oxygen–
sulfur bond and transfer of the oxygen atom from one molecule
to another, giving ArSO2Cl–AlCl3 [S(VI)] and ArSCl [S(II)]
(Fig. 2). In the following step, the nucleophilic sulfur(II) in
ArSCl attacks the electrophilic sulfur(VI) in ArSO2Cl–AlCl3,
resulting in formation of ArSO2SAr [containing an S(VI)–S(II)
linkage] after aqueous work-up.
(PhH) with selenyl chloride (SeOCl2), the selenium analogue
of SOCl2. For each of the catalysts, the reaction was conducted
by adding MCl3 (M=Al or Fe) slowly to a PhH–SOCl2 mixture
at 25 °C, with the molar ratio of PhH:SOCl2:MCl3 =2:1:1. The
reactions catalysed by AlCl3 and FeCl3 gave 57% Ph2Se and 43%
PhSeSePh, and 40% Ph2Se and 60% PhSeSePh, respectively
(normalised yields in molar percentages) [Eqn (7)].
25 oC
Formation of diphenyl selenide (Ph2Se) and diphenyl diselenide
(PhSeSePh) from the Lewis- acid-MCl3-(M=Al and Fe)-catalysed
electrophilic substitution reactions of benzene (PhH) with selenyl
chloride (SeOCl2) and the accompanying auto-redox processes
at the selenium centres of EAS intermediates
Ph2Se + PhSeSePh
PhH + SeOCl2
(7)
AlCl3
FeCl3
57%
40%
43%
60%
No other organoselenium compounds, including the initially
expected Ph2SeO (diphenyl selenoxide) (on the basis of the
SOCl2 reaction), were identified from the products.
Following investigations of the AlCl3-catalysed EAS reactions
of SOCl2, we have conducted the Lewis-acid-MCl3-(M=Al and
Fe)-catalysed electrophilic substitution reactions of benzene
-
-
X
AlCl3
AlCl3
+
O
O
+
Cl
S
S
S
+
Cl
Cl
-
O
AlCl3
X
X
-
-
AlCl3
AlCl3
X
+
O
S
X
O
+
2+ Cl
+
Cl
S
+
Cl
S
..
S
Cl
-
-
O
O
AlCl3
AlCl3
X
X
S(VI)
S(II)
oxygen exchange
X = H, Cl, or CH3
-
AlCl3
+
O
-
AlCl3
+
O
..
..
S
Cl
Cl
S
X
..
..
+
S
:Cl:-
S
+
X
-
O
AlCl3
+
X
O Cl
X
X
+
-
S(VI)
S(II)
AlCl3
- Cl2
-
AlCl3
+
O
O
H2O
S
S
S
S
X
X
X
work-up
O
O
-
+
AlCl3
S-Aryl Arenesulfonothioate
Fig. 2 The AlCl3-catalysed oxygen exchange between the ArSOCl–AlCl3 (Ar=C6H5, p-ClC6H4, or p-CH3C6H4) adduct molecules leading to formation of S-aryl
arenesulfonothioate (ArSO2SAr): A detailed mechanism.
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JOURNAL OF CHEMICAL RESEARCH 2013 741
Our previous work showed15 that under the same conditions,
the AlCl3-catalysed reaction of benzene with SOCl2 gave the
major Ph2SO, together with the minor Ph2S, PhSO2SPh, and
Ph2SO2, while diphenyl disulfide PhSSPh (the sulfur analogue
of PhSeSePh) was not formed in the AlCl3-catalysed reactions
of benzene with SOCl2 under any conditions. Clearly, the EAS
reaction of SeOCl2 is substantially different than the reaction
of SOCl2. The selenium atom in SeOCl2 is substantially less
electrophilic than the sulfur atom in SOCl2 due to the greater
polarisability of selenium than sulfur. This is consistent with
the observation that the AlCl3-catalysed reaction of benzene
with SeOCl2 was much slower than the reaction with SOCl2
under the same conditions. We believe that the difference in the
reactivity of SeOCl2 and SOCl2 towards benzene is primarily
due to the greater polarisability of selenium than sulfur.
Fig. 3 shows the possible mechanism for the MCl3-(M=Al
and Fe)-catalysed reaction of PhH with SeOCl2. Conceivably,
SeOCl2 and MCl3 (M=Al or Fe) form an SeOCl2–MCl3 adduct,
analogous to SOCl2–AlCl3.18,19 PhH is believed to undergo
a similar EAS reaction with the SeOCl2–MCl3 adduct (much
slower than the reaction with SOCl2–AlCl3) to form PhSeOCl–
MCl3. The electron-donating –Ph group in PhSeOCl–MCl3 can
further decrease the electrophilicity of the selenium centre.
As a result, PhSeOCl–MCl3 does not react with a second
benzene molecule to give Ph2SeO. Instead, it undergoes an
exclusive intramolecular auto-redox process, analogous to that
for p-HOC6H4SOCl–AlCl3 [Eqn (3)], and Se(IV) in PhSeOCl–
MCl3 was reduced to Se(II) in PhSeO–MCl2 (Fig. 3). The
proposed auto-redox process is supported by identification
of Cl2 from the reaction mixture (using wet KI-starch paper,
see the Experimental section). Similar to HOC6H4SO–AlCl2
[Eqn (3)], the selenium atom in PhSeO–MCl2 could be attacked
by a second benzene molecule to lead to formation of Ph2Se
(Fig. 3). On the other hand, the selenium centre in PhSeO–
MCl2, with a lone-pair of electrons, is fairly nucleophilic
due to its relatively large polarisability. Therefore, it could
effectively attack the selenium atom in a second PhSeO–MCl2
molecule concurrently, leading to formation of a Se–Se bond
and cleavage of a Se–O bond. The subsequent cleavage of the
second Se+–O bond was facilitated by the positive charge on
selenium. This eventually resulted in formation of PhSeSePh
(Fig. 3). In the FeCl3-catalysed reaction, the dπ orbital in Fe(III)
in the PhSeO–FeCl2 adduct might donate electron density to
selenium by a dπ–pπ back bonding, making the selenium centre
more nucleophilic than that of PhSeO–AlCl2. This may account
for the fact that the FeCl3-catalysed reaction of benzene with
SeOCl2 produced a significantly greater percentage (60%) of
PhSeSePh than did the AlCl3-catalysed reaction (43%).
-
-
MCl3
MCl3
+
O
+
O
EAS
- HCl
Ph
H
Se
Se
M = Al or Fe
+
Cl
Ph
Cl
Cl
Se(IV)
Cl
Cl
Cl
-
Cl
Cl
M
M
+
O
O
Auto-redox
Se
Se
+ Cl2
Ph
Cl
Ph
Se(IV)
Se(II)
Formation of diphenyl selenide (Ph2Se):
Cl
H
M
- M(OH)Cl
EAS
Se
Se
O
Ph
Cl
+
-OMCl2
Ph
Ph
H
+
Se
Ph
Se(II)
Formation of diphenyl diselenide (PhSeSePh):
Cl
Cl
Cl
Cl
Cl
M
M
M
O
O
O
Cl
..
..
+
+ :
Se
:Cl:-
Se
Se Se
+
+ MOCl
..
Ph
Ph
Ph
Ph
Ph
Se(II)
Se(II)
Se Se
+ Cl2 + 2 MOCl
Ph
Se(I) Se(I)
Fig. 3 Mechanism for the Lewis-acid-MCl -(M=Al and Fe)-catalysed electrophilic substitution of benzene (PhH) with selenyl chloride (SeOCl2) giving
diphenyl selenide (Ph2Se) and diphenyl disel3enide (PhSeSePh).
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742 JOURNAL OF CHEMICAL RESEARCH 2013
diphenyl diselenide (PhSeSePh). To our surprise, the initially
expected diphenyl selenoxide (Ph2SeO) was not produced at
all in the reaction. A mechanism involving novel auto-redox
processes in selenium has been proposed to account for the
reactivity of SeOCl2 towards aromatic hydrocarbons. This work
has furnished the classical chemistry of aromatic compounds
with novel aspects.
Conclusions
In this work, the previously established AlCl3-catalysed
EAS reaction of benzene with SOCl2 possibly giving Ph2SO,
Ph2S, and PhSO2SPh in various yields15 has been extended
to other substituted benzenes, including PhCH3, PhCl, and
PhOH. The substituent effects of –CH3, –Cl, and –OH on
the regiochemistry of the reactions (directing effects) and
the effects on the redox chemistry of the sulfur centre in the
reactions have been studied. –CH3 was found to be mainly a
para-director with minor ortho-directing effect on formation
of diaryl sulfoxide (Ar2SO) from the EAS reaction. However,
it is an exclusive para-director for formation of diaryl sulfide
(Ar2S). On the other hand, –Cl and –OH are exclusively
para-directors for formation of all the aromatic organosulfur
compounds. The –CH3, –Cl, and –OH groups were found to
possess different effects on the redox chemistry of the sulfur
centre in SOCl2 during the EAS reactions, leading to different
product distributions (percentages) under comparable reaction
conditions. The difference in the effects on the redox chemistry
is particularly remarkable on comparing the PhOH reaction
with the reactions of PhX (X=H and CH3). Although the
AlCl3-catalysed EAS reactions of benzene and toluene with
SOCl2 give the major diaryl sulfoxides with minor reduced
diaryl sulfides,15 the reaction of PhOH at ambient temperature
has been shown in this work to give only the reduced sulfide
(p-HOC6H4)2S (together with the minor p-chlorophenol side
product). The corresponding sulfoxide (p-HOC6H4)2SO or any
other sulfoxide isomers are not formed. This special reactivity
of phenol is attributable to the conjugation of –OH, which
lowers the electrophilicity of the sulfur centre in the first EAS
intermediate p-HOC6H4SOCl–AlCl3 to make it unreactive
towards an aromatic ring. Instead, an exclusive intramolecular
auto-redox occurs to lead to the formation of a diaryl sulfide
[Eqn (3)].
It has been shown in this work that in the presence of AlCl3,
SOCl2 can undergo double consecutive EAS reactions with
two different arene molecules to give a mixed diaryl sulfoxide
XC6H4SOPh (X=CH3 or Cl). The directing effects of –CH3 and
–Cl on formation of XC6H4SOPh are consistent with those on
the EAS reactions leading to diaryl sulfoxides Ar2SO, namely,
that –CH3 is mainly a para-director with minor ortho-directing
effect, and –Cl is exclusively a para-director for formations of
XC6H4SOPh.
Our previous work indicated that the AlCl3-catalysed
reactions of benzene with SOCl2 under many conditions
gave a very small amount of PhSO2SPh (only~5%).15 In this
work, optimisation in reaction conditions has been attempted
so that the yields of ArSO2SAr (Ar=Ph, p-CH3C6H4, and
p-ClC6H4) have been enhanced up to (40–50)% (e.g. dropwise
addition of PhH to the SOCl2–AlCl3 mixture at –10 °C gave
PhSO2SPh in 49% yield). Our studies have shown that in
general decreasing the molar ratio of ArH/SOCl2 or lowering
the reaction temperature results in enhancement of the yield for
formation of S-aryl arenesulfonothioate (ArSO2SAr) from the
AlCl3-catalysed EAS reaction of SOCl2. Both –CH3 and –Cl
were shown to be exclusive para-directors for formations of
ArSO2SAr. A mechanism with detailed molecular interactions
has been proposed in this work to account for formations of
ArSO2SAr (Ar=Ph, p-CH3C6H4, and p-ClC6H4) in significant
yields via an AlCl3-catalysed oxygen exchange between two
EAS intermediate ArSOCl–AlCl3 molecules.
Experimental
Chemical reagents
Thionyl chloride (SOCl2) (purified) from J. T. Baker Chemical
Company was used. Benzene (PhH) (99.9%), toluene (PhCH3) (99.9%),
chlorobenzene (PhCl) (99%), pentamethylbenzene [C6H(CH3)5]
(99%), and phenol (PhOH) (99%) were obtained from Sigma Aldrich.
Granular anhydrous aluminium chloride (AlCl3) (99%, extra pure) was
obtained from Acros Organics. Anhydrous sodium sulfate (99.5%,
drying agent), dichloromethane (99.9%, the solvent for GC-MS
samples), diethyl ether (solvent), selenyl chloride (SeOCl2) (99%), and
iron (III) chloride (FeCl3) (98%) were purchased from Fisher Scientific
Company.
The GC-MS measurements
Reaction products were identified using a Varian CP-3800 gas
chromatograph-Varian Saturn 2200 mass spectrometer. The
sample of each product was prepared by dissolving the product in
dichloromethane to make the mass percentage of the product in
the solution approximately 1%. One-microlitre of the solution was
injected onto a Chrompack CP-SIL 8-CB 30m×0.25mm capillary
column using a He carrier gas of 1.0 mL min–1, a 1/100 injection
split ratio, and a temperature ramp of 150 to 240°C (10 °C min–1).
All chemical compounds were eluted in 10 minutes. The individual
compounds (components) contained in each product, including Ar2SO
(Ar=p-CH3C6H4, o-CH3C6H4, p-ClC6H4), Ar2S [Ar=p-CH3C6H4,
p-ClC6H4, p-HOC6H4, C6(CH3)5], ArSO2SAr (Ar=C6H5, p-CH3C6H4,
p-ClC6H4), Ar2SO2 (Ar=p-CH3C6H4, p-ClC6H4), ArSOAr′ (Ar,
Ar′=C6H5, p-CH3C6H4; C6H5, o-CH3C6H4; C6H5, p-ClC6H4; p-CH3C6H4,
o-CH3C6H4), Ph2Se, and PhSeSePh, were identified by comparison
of their mass spectra with those on the available National Institute
of Standards and Technology database. Their molar percentages
(normalised) in the product were estimated by comparing the related
GC peak areas on the basis of the assumption that the peak area is
proportional to the number of moles of the related compound.
In order to support the above assumption, a standard sample
containing Ph2Se and PhSeSePh with the molar ratio of Ph2Se(mol)/
PhSeSePh(mol)=2.0 was made by dissolving known quantities of the
diphenyl selenide (Ph2Se) and diphenyl diselenide (PhSeSePh) reagents
in CH2Cl2. It was then measured by GC-MS, showing that ratio of the GC
peak areas Ph2Se(peak)/PhSeSePh(peak)=2.2. Thus, the relationship
between the molar ratio and the ratio of peak areas is [Eqn (8)].
Ph2Se(mol)/Ph2SeSePh(mol)=0.91×[Ph2Se(peak)/PhSeSePh(peak)]
(8)
The molar ratio is approximately equal to the ratio of the corresponding
GC peak areas with only about 10% difference.
CAUTION: Reactions should be conducted in a fume hood.
Protective gloves should be worn because harmful gases such as
hydrogen chloride and/or chlorine may be produced in various
reactions detailed below.
Aluminium-chloride-(AlCl3)-catalysed reactions of thionyl chloride
(SOCl2) with arenes PhX (X=CH3 and Cl)
Approach 1: The reactions were conducted in the fume hood at 25 °C
and 70 °C, respectively, with the molar ratio of PhX:SOCl2:AlCl3
being 2:1:1 and usage of SOCl2 approximately 10 mmol. For each
reaction, granular AlCl3 was added piecewise to the PhX–SOCl2
mixture (X=CH3 or Cl) in a large test tube (~80 mL) as follows: First,
The Lewis-acid-MCl3-(M=Al and Fe)-catalysed Friedel–
Crafts (EAS) reactions of benzene (PhH) with selenyl chloride
(SeOCl2), the selenium analogue of SOCl2, have been shown
in this work to give the reduced diphenyl selenide (Ph2Se) and
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JOURNAL OF CHEMICAL RESEARCH 2013 743
one piece of AlCl3 was added and gas (HCl) bubbles started to form
immediately. The piece of AlCl3 was crushed using a stirring rod.
When most of the piece of AlCl3 had dissolved and bubbling occurred
very slowly, another piece of AlCl3 was added. All the AlCl3 granules
were eventually added into the PhX–SOCl2 mixture piece-by-piece.
The solution was initially light green and it turned dark green as the
reaction went to completion, indicated by ceasing of bubbling after all
the AlCl3 had been added. Then iced water (40 mL) was poured into the
reaction mixture and the green colour disappeared. This was followed
by addition of diethyl ether (20 mL). All the contents were transferred
into a separating funnel and shaken well to assure the organic product
being fully extracted into the ether phase. The ether and water phases
were separated. The water phase was extracted by diethyl ether
(20 mL) again. Then all the ether solutions were combined and dried
by anhydrous sodium sulfate. The dried ether solution was filtered
off and left in the fume hood. Eventually, all the diethyl ether solvent
evaporated, giving the final reaction product. The product was then
characterised by GC-MS, and the results are shown in Table 1.
Approach 2: The reactions were conducted in the fume hood at 25 °C,
with the molar ratio of PhX:SOCl2:AlCl3 being 2:1:1 and usage of
SOCl2 approximately 10 mmol. For each reaction, SOCl2 was added
dropwise to the PhX–AlCl3 mixture (X=CH3 or Cl) with constant
stirring. The reaction took place quickly, indicated by bubbling as
above. After all the SOCl2 was added, the reaction went to completion,
indicated by cessation of bubbling. Then aqueous work-up was
performed as above. The final product was characterised by GC-MS,
and the results are shown in Table 1.
to a SOCl2–AlCl3 mixture in a large test tube. The solution turned
green and gas bubbles were produced. After all the benzene had been
added, the reaction mixture was kept at the same temperature (0 °C
or –10 °C) for one hour. Then aqueous work-up was done, followed by
extraction of the organic product using ether as above. The GC–MS
analysis showed that the product made at each temperature contained
three components, PhSO2SPh, Ph2S, and Ph2SO, in different molar
percentages (normalised) [Eqn (4)].
p-CH3C6H4SO2S(p-C6H4CH3): The yield enhancement was conducted
by the AlCl3-catalysed reaction of toluene (PhCH3) and SOCl2 in the
fumehood at –10 °C, with the molar ratio of PhCH3:SOCl2:AlCl3 being
1:1:1 and usage of SOCl2 approximately 25 mmol. With constant
stirring PhCH3 was added dropwise to a SOCl2–AlCl3 mixture.
The procedure and observations were the same as those of the above
benzene reactions. The GC-MS analysis showed that the product
contained several components whose identities and molar percentages
(normalised) are indicated in Eqn (5).
p-ClC6H4SO2S(p-C6H4Cl): The yield enhancement was conducted
by the AlCl3-catalysed reactions of chlorobenzene (PhCl) and SOCl2
in the fumehood at 0 °C, with the molar ratios of PhCl:SOCl2:AlCl3
being 1:1:1 and 1:2:2, respectively, and the usage of PhCl approximately
20 mmol. For both reactions, with constant stirring PhCl was
added dropwise to the SOCl2–AlCl3 mixtures. The procedure and
observations were the same as those of the above benzene and
toluene reactions. The products were characterised by GC-MS.
Three components, p-ClC6H4SO2S(p-C6H4Cl), (p-ClC6H4)2S, and
(p-ClC6H4)2SO, were found in each of the products in different molar
percentages (normalised) [Eqn (6)].
The AlCl3-catalysed reaction of phenol (PhOH) with SOCl2
The reaction was conducted in the fume hood at 25 °C, with the
molar ratio of PhOH:SOCl2:AlCl3 being 2:1:1 and the usage of SOCl2
approximately 10 mmol. A solution of PhOH in diethyl ether (10 mL)
was poured all at once quickly into a SOCl2–AlCl3 mixture in a large
test tube. The resulting solution turned light brown immediately
with a large amount of gas bubbles evolved. The gas produced from
the reaction was tested by using wet KI-starch paper over the mouth
of the test tube, and the paper turned dark blue [Cl2 + K I-st a rch → I 2-
starch (blue)+KCl], consistent with formation of Cl2 in the reaction.
After bubbling ceased (completion of the reaction), aqueous work-
up was performed as above. The GC-MS characterisation showed
that the product contained 91% (p-HOC6H4)2S [bis(p-hydrophenyl)
sulfide] and 9% p-ClC6H4OH (p-chlorophenol) (normalised yields in
molar percentages). Another reaction was performed by adding AlCl3
piecewise to a PhOH–SOCl2 mixture, followed by aqueous work-up.
The GC-MS characterisation showed that the product contained 51%
(p-HOC6H4)2S and 49% p-ClC6H4OH (normalised yields in molar
percentages). (p-HOC6H4)2SO [bis(p-hydrophenyl) sulfoxide] was not
identified from either of the reaction products. The results are included
in Table 2.
Aluminium-chloride-(AlCl3)- and iron(III)-chloride-(FeCl3)-catalysed
reactions of selenyl chloride (SeOCl2) with benzene
The Lewis-acid-MCl3-(M=Al and Fe)-catalysed reactions of benzene
(PhH) with SeOCl2 were performed in the fumehood at 25 °C, with
the molar ratio of PhH:SeOCl2:MCl3 being 2:1:1 and usage of SeOCl2
approximately 6 mmol. For the AlCl3-catalysed reaction, granular
AlCl3 was added piecewise to the PhH–SeOCl2 mixture (slightly
yellow) in a large test tube and then crushed. Initially, the mixture
turned cloudy. Then it became brown with gas evolved. The gas was
tested by using wet KI-starch paper over the mouth of the tube, and
the paper turned dark blue [Cl2 +KI-starch  I2-starch (blue)+KCl],
consistent with formation of Cl2 in the reaction. When all the AlCl3
was added and crushed, the liquid mixture became dark brown. The
reaction mixture was maintained in the fumehood at 25 °C for 1 hour.
Then aqueous work-up was conducted in the same manner as that
adopted for the above SOCl2 reactions as described in the Approach 1.
Eventually, an orange liquid product was recovered from the ether
extraction after the ether solvent evaporated. For the FeCl3-catalysed
reaction, powdery FeCl3 was added in 10 aliquots to the PhH–SeOCl2
mixture. The detailed procedure and observation were essentially
the same as those for the AlCl3-catalysed reaction. The MCl3-(M=Cl
and Fe)-catalysed reactions of SeOCl2 with benzene were apparently
much slower than the AlCl3-catalysed reaction of SOCl2 with benzene
at the same temperature, which was indicated by much slower rate of
bubbling in the SeOCl2 reactions. The products from MCl3-(M=Al and
Fe)-catalysed reactions of benzene with SeOCl2 were characterised
by GC-MS, showing that two compounds, diphenyl selenide (Ph2Se)
and diphenyl diselenide (PhSeSePh), were produced in each reaction
in different molar percentages [Eqn (7)], which were established
by examining the GC peak areas according to Eqn (8). The initially
expected diphenyl selenoxide (Ph2SeO) was not identified by GC-MS
in either of the reaction products.
Aluminium-chloride-(AlCl3)-catalysed reactions of thionyl chloride
(SOCl2) with 1:1 mixtures of benzene (PhH) and substituted benzenes
PhX (X=CH3 and Cl)
The reactions were conducted in the fumehood at 25 °C, with the
molar ratio of PhH:PhX:SOCl2:AlCl3 being 1:1:1:1 and usage of SOCl2
approximately 10 mmol. For each reaction, granular AlCl3 was added
piecewise to the PhH–PhX–SOCl2 mixture (X=CH3 or Cl). The
reaction was followed by aqueous work-up. The detailed procedure
was the same as that for the above reactions in Approach 1. The product
was characterised by GC-MS, and the results are shown in Table 3.
Producing S-aryl arenesulfonothioates ArSO2SAr (Ar=Ph, p-CH3C6H4,
and, p-ClC6H4) in significant yields
PhSO2SPh: The yield enhancement was conducted by the AlCl3-
catalysed reactions of benzene (PhH) and SOCl2 in the fumehood at
0 °C and –10 °C, respectively, with the molar ratio of PhH:SOCl2:AlCl3
being 1:1:1 and usage of SOCl2 approximately 25 mmol. For each
of the reactions, with constant stirring PhH was added dropwise
Received 13 July 2013; accepted 27 September 2013
Paper 1302099 doi: 10.3184/174751913X13842832780853
Published online: 6 December 2013
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744 JOURNAL OF CHEMICAL RESEARCH 2013
11 K.K. Andersen, W. Gaffield, N.E. Papanikolaou, J.W. Foley and R.I.
Perkins, J. Am. Chem. Soc., 1964, 86, 5637.
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P. Page, Organosulfur chemistry: synthetic aspects, Academic Press, New
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12 G.A. Olah, R. Malhotra and S.C. Narang, Nitration, methods and
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