Method of producing alkali metal benzenesulfinates

A method of producing alkali metal benzenesulfinates having the general formula of ##STR1## wherein M represents Na or K, which comprises: reacting nitrophenylphenyl sulfones having the general formula of ##STR2## wherein n is an integer of 1 or 2, with alkali metal thiophenolates having the general formula of ##STR3## in solvents. The reaction produces also nitrophenylphenyl sulfides as by-products in equimolar amounts to the alkali metal benzenesulfinates, and the oxidation of the sulfides provides the starting nitrophenylphenyl sulfones. A method of producing the nitrophenylphenyl sulfones is also provided wherein the sulfides are oxidized with hydrogen peroxide in the presence both of water-soluble tungstates or molybdates and of phase transfer catalysts in a two-phase heterogeneous solvent.

This invention relates to a method of producing alkali metal 
benzenesulfinates, and also to a method of producing nitrophenylphenyl 
sulfones usable as starting materials in the production of alkali metal 
benzenesulfinates. 
Alkali metal benzenesulfinates are useful intermediate raw materials for 
the production of organic sulfones and sofoxides important in organic 
synthetic industry. 
Up to date a variety of methods are already known to produce alkali metal 
benzenesulfinates. These prior methods include, for example, a method in 
which benzenesulfonyl chloride is reduced with sodium sulfite as described 
in A. D. Barnard et al., J. Chem. Soc., 1957, 4673. However, according to 
this method, sodium sulfinate is produced in solutions together with 
water-soluble compounds such as sodium sulfate, sodium chloride or sodium 
benzenesulfonate, so that it is very difficult to separate sodium 
benzenesulfinate from the by-products by crystallization on account of 
closeness of the solubilities in water of all these compounds. Therefore, 
it is generally preferred that the resultant solution is then acidified 
with a mineral acid to convert the alkali metal benzenesulfinates into the 
free acid, and then the free acid is separated by filtration or is 
extracted with organic solvents. This method is, however, at disadvantage 
from the industrial standpoint in that is requires handling of the free 
acid which is chemically rather unstable as well as it needs the aforesaid 
additional steps that incur higher production cost. 
A further method is also known in which benzene is sulfinated with sulfur 
dioxide in the presence of aluminum chloride as a catalyst, as described 
in Nippon Kagaku Zasshi, 1968, 89(8), 810. This method needs the catalyst 
in amounts equivalent to benzene used, and the catalyst cannot be 
recovered after the reaction, which makes the method uneconomical. A still 
further method is known in which 2,4-dinitrophenylphenyl sulfone is 
reacted with potassium hydroxide to provide potassium benzenesulfinate, as 
described in C. N. Kharash et al., J. Org. Chem., 19, 1704 (1954). 
However, this method has disadvantages in that the separation of potassium 
benzenesulfinate from by-products, potassium 2,4-dinitrophenolate is 
difficult. 
As described above, the methods hitherto known have disadvantages in many 
respects, and there is known no method that is advantageously applicable 
to the industrial production of alkali metal benzenesulfinates. 
The present inventors have made extensive investigations to establish an 
improved method of producing alkali metal benzenesulfinates more 
efficiently and less expensively than the prior methods, and found out 
that alkali metal benzene-sulfinates are readily obtained in high yields 
by the reaction of nitrophenylphenyl sulfones with alkali metal 
thiophenolates in solvents. 
It is, therefore, an object of the invention to provide a novel method of 
producing alkali metal benzenesulfinates. 
It is also an object of the invention to provide a novel method of 
producing nitrophenylphenyl sulfones which are usable as starting 
materials in the production of alkali metal benzenesulfinates. 
According to the invention, there is provided a method of producing alkali 
metal benzenesulfinate having the general formula of 
##STR4## 
wherein M represents Na or K, which comprises: reacting nitrophenylphenyl 
sulfones having the general formula of 
##STR5## 
wherein n is an integer of 1 or 2, with alkali metal thiophenolates having 
the general formula of 
##STR6## 
in solvents. 
The nitrophenylphenyl sulfones used in the invention include 2- and 
4-nitrophenylphenyl sulfone and 2,4-dinitro-phenylphenyl sulfone. The 
alkali metal thiophenolates used in the invention include sodium and 
potassium salts, which provide sodium and potassium benzenesulfinate, 
respectively, in almost quantitatively by the reaction with the aforesaid 
nitrophenylphenyl sulfones. In the reaction, the alkali metal 
thiophenolates are usually used in amounts of about 0.8-1.2 moles per, 
preferably in amounts equivalent to, the nitrophenylphenyl sulfones used. 
The reaction is carried out in solvents usually composed of a mixture of 
water and organic solvents that dissolve therein nitrophenylphenyl 
sulfones used and are inert to the reaction. The organic solvents usable 
may be either water-soluble or water-insoluble, and include, for example, 
lower aliphate alcohols of 1-5 carbons such as methanol, ethanol or 
isopropanol, aliphatic hydrocarbons such as hexane or heptane, aromatic 
hydrocarbons that may carry one or more of lower alkyls each of 1-3 
carbons such as benzene, toluene, xylene, ethylbenzene or 
isopropyl-benzene, lower alkyl esters of lower aliphatic carboxylic acids 
having in total 3-8 carbons such as methyl acetate, ethyl acetate or 
methyl propionate, nitrated aromatic hydrocarbons such as nitrobenzene or 
nitrotoluene. 
The reaction may be carried out either in homogeneous solvents or in 
two-phase heterogeneous solvents depending upon the organic solvents used. 
By way of example, a mixture of water and water-soluble organic solvents 
such as methanol or ethanol is a homogeneous sovent, whereas a mixture of 
water and water-insoluble or slightly water-soluble organic solvents such 
as ethyl acetate, toluene, nitrobenzene or nitrotoluene is a two-phase 
heterogeneous solvent. 
Water-soluble or water-miscible aliphatic alcohols such as methanol or 
ethanol may be used alone as a solvent in the reaction since such alcohols 
are capable of dissolving not only thiophenol and alkali metal hydroxides 
but also nitrophenylphenyl sulfones therein. However, thiophenol and 
alkali metal hydroxides are reacted with each other therein to produce in 
situ alkali thiophenolates, and the reaction also produces water, so that 
if the alcohols alone are used as a solvent, they inevitably include water 
therein. 
The reaction may be carried out in manners that are not specifically 
limited, but it is generally preferred that the reaction is carried out by 
adding a solution of alkali thiophenolates in water, methanol or hydrous 
methanol, to a solution of nitrophenylphenyl sulfones in organic solvents 
as hereinbefore mentioned under stirring, and then the resultant mixture 
is stirred, if desired, at elevated temperatures, for about 1-10 hours. 
The reaction temperature is usually in the range of about 
30.degree.-100.degree. C. When the reaction temperature is too low, the 
reaction proceeds too slowly to be industrially workable, whereas when the 
reaction temperature is too high, undesired side reactions take place to 
decrease the yields of the objective compounds and the selectivity of the 
reaction. The alkali metal thiophenolates may be prepared by, for example, 
reacting thiophenol with sodium or potassium hydroxide in equimolar 
amounts in water, methanol or a mixture of these. 
When a two-phase heterogeneous solvent is used, the reaction is preferably 
carried out in the presence of phase transfer catalysts, which are already 
known per se. The phase transfer catalysts usable in the invention 
include, for example, tetraalkylammoniums, such as tetramethylammonium 
chloride, tetraethylammonium chloride, tetrabutylammonium bromide or 
trioctylmethylammomium chloride, tetraalkyl-ammonium hydrogen sulfates 
such as tetrabutylammonium hydrogen sulfate, benzyltrialkylammoniums such 
as benzyl-trimethylammonium chloride, benzyltrietylammonium chloride, 
benzyldimethyllaurylammonium chloride or benzyldimethyl-tetradecylammonium 
chloride, and dibenzyldialkylammoniums such as dibenzyldimethylammonium 
chloride or dibenzyldimethylammonium chloride. The use of the phase 
transfer catalysts accelerates the reaction and increases the yields of 
the alkali metal benzenesulfinates. 
The phase transfer catalysts are used in amounts of about 0.1-5 %, 
preferably 0.2-1 % by weight, based on the weight of the alkali metal 
thiophenolates used. The use of too small amounts is ineffective to 
accelerate the reaction, while the use of too large amounts is 
uneconomical. 
When the reaction is carried out in a homogeneous solvent, the solvent is 
concentrated after the reaction, water and organic solvents such as 
toluene are added to the resultant concentrate, and the aqueous solution 
is separated and concentrated to dryness, to provide alkali metal 
benzene-sulfinates as white crystals. As by-products, nitrophenyl-phenyl 
sulfides are recovered from the organic solution. 
When the reaction is carried out in a heterogeneous solvent, the reaction 
mixture is separated into an aqueous solution and an organic solution 
after the reaction, the aqueous solution is water with organic solvents, 
for example, toluene, and is then concentrated to dryness, to provide 
alkali metal benzenesulfinates as white crystals. The nitrophenylphenyl 
sulfides are recovered from the organic solution. 
The reaction of nitrophenylphenyl sulfones with alkali metal thiophenolates 
according to the invention is shown below. 
##STR7## 
wherein M represents Na or K, and n is an integer of 1 or 2. 
As shown above, the reaction produces, in addition to the alkali metal 
benzenesulfinates, nitrophenylphenyl sulfides, as by-products, which can 
be oxidized with oxidizing agents to the corresponding nitrophenylphenyl 
sulfones initially used. In this regard, nitrophenylphenyl sulfones that 
have one or two nitro groups on one of the aromatic nuclei provide both 
alkali metal benzenesulfinates and nitrophenylphenyl sulfides in high 
yields, in almost equimolar amounts. 
A variety of oxidizing agents are usable for oxidizing nitrophenylphenyl 
sulfides into the corresponding nitrophenyl-phenyl sulfones. The oxidizing 
agents usable in the invention include, for example, hydrogen peroxide, 
peracids such as peracetic acid, hydroperoxides, halogens such as chlorine 
or bromine, ozone, oxygen with transition metal catalysts, potassium 
peroxysulfate, potassium permanganate, dinitrogen tetroxide, sodium 
metaperiodate, osmium (VIII) oxide, ruthenium (VIII) oxide, sodium or 
potassium dichromate and nitric acid. 
However, hydrogen peroxide is most preferred as oxidizing agents since the 
oxidation of the nitrophenylphenyl sulfides therewith provides the 
corresponding nitrophenyl-phenyl sulfones almost quantitatively. 
Therefore, as an important aspect of the invention, the recovered 
nitrophenylphenyl sulfides produced as by-products can be reused in the 
reaction after the oxidation. More specifically, the recovered 
nitrophenylphenyl sulfides are oxidized to the nitrophenylphenyl sulfones, 
and the sulfones are anew reacted with the alkali metal thiophenolates, to 
provide the alkali metal benzenesulfinates and again the nitrophenylphenyl 
sulfides. Therefore, the nitrophenylphenyl sulfones as raw materials are 
needed to initially carry out the reaction, however, if needed, only 
supplementary amounts of nitrophenylphenyl sulfones are needed in the 
succeeding reactions, and hence according to the invention, the alkali 
metal benzenesulfinates can be produced much less expensively than the 
prior known methods ever known. 
According to the invention, there is further provided a novel method of 
producing nitrophenylphenyl sulfones by the oxidation of nitrophenylphenyl 
sulfides. 
According to the invention, there is further provided a method of producing 
nitrophenylphenyl sulfones having the general formula of 
##STR8## 
wherein n is an integer of 1 or 2, which comprises: oxidizing 
nitrophenylphenyl sulfides having the general formula of 
##STR9## 
wherein n is an integer of 1 or 2, with hydrogen peroxide in the presence 
both of oxidizing catalysts selected from the group consisting of 
water-soluble tungstates and molybdates and of phase transfer catalysts in 
a two-phase heterogeneous solvent. 
The oxidation reaction is carried out in a two-phase heterogeneous solvent, 
which is composed of water and water-insoluble or slightly water-soluble 
organic solvents. Any water-insoluble or slightly water-soluble organic 
solvents are usable when they are capable of dissolving therein 
nitrophenylphenyl sulfides and are inert to the reaction. The organic 
solvents usable include, for example, aliphatic hydrocarbons such as 
hexane, heptane or octane, aromatic hydrocarbons such as benzene, toluene, 
xylene, ethylbenzene or isopropylbenzene, alicyclic hydrocarbons such as 
cyclohexane or ethylcyclohexane, and nitrated aromatic hydrocarbons such 
as nitrobenzene or nitrotoluene. Alkyl esters of acetic acid or higher 
carboxylic acids are also usable as organic solvents, such as ethyl 
acetate propyl acetate, butyl acetate, amyl acetate or ethyl propionate. 
In the oxidation reaction, hydrogen peroxide is used as oxidizing agents in 
amounts of not less than about 2 moles, preferably in the range of about 
2-2.5 moles, per mole of nitrophenylphenyl sulfides used. There is no need 
to use hydrogen peroxide in large excess amounts. 
The tungstates and molybdates used as oxidizing catalysts in the reaction 
are water-soluble, and include alkali metal salts such as lithium, sodium 
or potassium salts, alkaline earth metal salts such as magnesium salts, 
and ammoniums. Preferred catalysts are therefore lithium tungstate, sodium 
tungstate, potassium tungstate, magnesium tungstate, ammonium tungstate, 
sodium molybdate, potassium molybdate and ammonium molybdate. 
The oxidizing catalyst is used in amounts of about 0.5-5% by weight, 
preferably of about 1-2 % by weight, based on the weight of the 
nitrophenylphenyl sulfides used. The use of too small amounts is 
ineffective to accelerate the reaction, whereas the use of too large 
amounts is uneconomical. 
In the oxidizing reaction of the invention, phase transfer catalysts are 
used together with the oxidizing catalysts. The phase transfer catalysts 
hereinbefore described are also usable in the reaction. Preferred phase 
transfer catalysts used include, for example, tetraalkylammoniums such as 
tetramethylammonium chloride, tetraethylammonium chloride, 
tetrabutylammonium bromide or trioctylmethylammonium chloride, 
tetraalkylammonium hydrogen sulfates such as tetrabutylammonium hydrogen 
sulfate, benzyltrialkylammoniums such as benzyltrimethyl-ammonium 
chloride, benzyltrietylammonium chloride, benzyl-dimethyllaurylammonium 
chloride or benzyldimethyltetradecyl-ammonium chloride, and 
dibenzyldialkylammoniums such as dibenzyldiemthylammonium chloride or 
dibenzyldiethylammonium chloride. 
The phase transfer catalysts are used usually in amounts of about 0.1-3 % 
by weight, preferably of about 0.2-1 % by weight, based on the weight of 
nitrophenylphenyl sulfides used. The use of too small amounts is 
ineffective to accelerate the reaction, whereas the use of too large 
amounts is uneconomical. 
The oxidation reaction is preferably carried out in acidic or neutral 
conditions by adding a small amount of inorganic strong acids such as 
sulfuric acid or hydrochloric acid to the reaction mixture. Namely, the 
reaction is carried out preferably at a pH of not more than about 7, and 
most preferably at a pH of about 1-7. However, when ammonium hydrogen 
sulfates such as tetrabutylammonium hydrogen sulfate are used as a phase 
transfer catalyst, there is no need to add an inorganic strong aid to the 
reaction mixture to adjust the pH thereof at acidic regions since the 
ammonium hydrogen sulfates themselves are strongly acidic. 
Although the invention is not limited in theory or mechanism of the 
reaction, the oxidizing catalysts are converted into acid forms, i.e., 
tungstic acid or molybdic acid in acidic or neutral conditions, and the 
acids react with the phase transfer catalysts and transfer from the water 
phase to the organic phase in the reaction mixture, thereby to effectively 
catalyze the oxidation of the nitrophenyl-phenyl sulfides into the 
corresponding nitrophenyl-phenyl sulfones. More specifically, it is likely 
that the tungstates or molybdates are oxidized into peroxotungstic acid or 
peroxomolybdic acid, respectively, in acidic or neutral conditions, and 
the peroxoacids react with the phase transfer catalysts to transfer to the 
organic phase, thereby effectively catalyzing the oxidation of the 
sulfides to the sulfones. 
On the other hand, when the reaction is carried out in alkaline conditions, 
the oxidizing catalysts remain in the water phase in the form of the salts 
in the reaction mixture, and it is likely that the salts do not react with 
the phase transfer catalysts, thereby being prevented from transferring 
from the water phase to the organic phase where the substantial oxidation 
reaction is carried out. 
The oxidizing reaction is carried out usually at temperatures of about 
50.degree.-90.degree. C., preferably at about 60.degree.-80.degree. C. 
When the reaction temperature is too low, the reaction proceeds too 
slowly, and when the reaction temperature is too high, the selectivity of 
the reaction and the yields of the sulfones are low. 
The reaction manners are not specifically limited, however, it is preferred 
that the reaction is carried out by dissolving nitrophenylphenyl sulfides 
in the organic solvents and adding to the resultant solution the oxidizing 
catalysts, the phase transfer catalysts, and then, if necessary, an 
inorganic strong acid, and then by adding dropwise thereto aqueous 
solution of hydrogen peroxide under stirring at temperatures of about 
60.degree.-90.degree. C. After the completion of the reaction, the 
reaction mixture is separated into an organic solution and aqueous 
solution, and the organic solution is concentrated to dryness, to provide 
nitrophenylphenyl sulfones in high yields. The resultant sulfones may be 
purified by recrystallization.

The invention will be understood more readily with reference to the 
following examples; however these examples are intended to illustrate the 
invention only and are not to be construed as limitation to the invention. 
EXAMPLE 1 
(i) Production of Sodium Benzenesulfinate and Recovery of 2- 
Nitrophenylphenyl Sulfide 
An amount of 26.3 g (0.1 mole) of 2-nitrophenylphenyl sulfone was dissolved 
in 100 g of methanol in a 300 ml capacity four-necked flask provided with 
a stirrer, a thermometer, a dropping funnel and a reflux condensor. An 
amount of 11.0 g (0.1 mole) of thiophenol and 4.0 g (0.1 mole) of sodium 
hydroxide were dissolved in 30 g of methanol. The resultant methanol 
solution of sodium thiophenolate was added to the aforesaid solution of 
2-nitrophenylphenyl sulfone, and the reaction was carried out at 
60.degree. C. for 4 hours. 
After the reaction, methanol was concentrated, toluene and water were added 
to the concentrate, and the aqueous solution was separated from the 
organic solvent. The aqueous solution was concentrated to dryness, to 
provide 16.1 g (97.1 % yield) of sodium benzenesulfinate as white 
crystals. The purity was found 99.0 % by liquid chromatography. 
The removal of toluene from the organic solution by distillation provided 
22.6 g (96.7 % yield) of 2-nitrophenyl-phenyl sulfide as yellow crystals. 
The purity was found 98.8 % by liquid chromatography. 
(ii) Oxidation of 2-Nitrophenylphenyl Sulfide and Reuse 
An amount of 21.1 g (0.09 mole) of the recovered 2-nitrophenylphenyl 
sulfide was plaed in a 200 ml capacity flask together with 83.3 g of 
acetic acid and heated to 50.degree. C. to provide a uniform solution. The 
solution was further heated to 85.degree. C., and 26.2 g of a 35% aqueous 
solution of hydrogen peroxide (0.27 mole) were dropwise added to the 
solution of the sulfide over 30 minutes while the solution was maintained 
at 85.degree. C. 
After stirring the 5 hours at 85.degree. C., the resultant reaction mixture 
was left standing at room temperature, the resultant precipitates were 
filtered and dried, to provide 23.0 g (95.4 % yield) of 
2-nitrophenylphenyl sulfone, mp. 146.9.degree.-148.6.degree. C., which was 
found 98.2 % in purity by liquid chromatography. 
An amount of 21.4 g (0.08 mole) of the thus obtained 2-nitrophenylphenyl 
sulfone was dissolved in 80 g of methanol, and was reacted with sodium 
thiophenolate in the same manner as above-mentioned. 
After the reaction, methanol was concentrated, toluene and water were added 
to the concentrate, and the aqueous solution was separated from the 
organic solution. The aqueous solution was then concentrated to dryness, 
to provide 12.7 g (95.8 % yield) of sodium benzenesulfinate as white 
crystals. The purity was found 99.1 % by liquid chromatography. 
2- Nitrophenylphenyl sulfide was recovered from the toluene solution. 
EXAMPLE 2 
(i) Production of Sodium Benzenesulfinate and Recovery of 2- 
Nitrophenylphenyl Sulfide 
A mixtue of 100 g of ethyl acetate and 100 g of water was used as a 
solvent, and the reaction was carried out in the same manner as in Example 
1 in the presence of 0.1 g of benzyltriethylammonium chloride as a phase 
transfer catalyst. 
After the reaction, the reaction mixture was left standing at room 
temperature, the resulting aqueous solution was separated from the ethyl 
acetate solution containing 2-nitrophenylphenyl sulfide, and concentrated 
to dryness, to provide 13.7 g (82.7 % yield) of sodium benzenesulfinate as 
white crystals, which was found 99.1 % in purity by liquid chromatography. 
The removal of ethyl acetate by distillation from the ethyl acetate 
solution provided 22.4 g (95.8 % yield) of 2-nitrophenylphenyl sulfide as 
yellow crystals. The sulfide was found 98.9 % in purity by liquid 
chromatography. 
(ii) Oxidation of 2-Nitrophenylphenyl Sulfide and Reuse 
An amount of 21.0 g (0.09 mole) of the recovered 2-nitrophenylphenyl 
sulfide was oxidized with 26.2 g (0.27 mole) of a 35 % aqueous solution of 
hydrogen peroxide in the same manner as in Example 1. After the reaction, 
the reaction mixture was cooled, and resulting precipitates were filtered 
and dried, to provide 23.1 g (95.9 % yield) of 2-nitrophenylphenyl sulfone 
as white crystals, mp. 147.0.degree.-148.7 .degree. C. The purity was 
found 98.4 % by liquid chromatography. 
An amount of 21.4 g (0.08 mole) of the thus obtained 2-nitrophenylphenyl 
sulfone was dissolved in a mixture of 80 g of ethyl acetate and 80 g of 
water, and was reacted with sodium thiophenolate in the same manner as in 
Example 1. 
After the reaction, ethyl acetate was concentrated, toluene and water were 
added to the concentrate, and the aqueous solution was separated from the 
organic solution. The aqueous solution was concentrated to dryness, to 
provide 12.5 g (94.2 % yield) of sodium benzenesulfinate as white 
crystals. The purity was found 99.0 % by liquid chromatography. 
2- Nitrophenylphenyl sulfide was recovered from the toluene solution. 
EXAMPLE 3 
4-Nitrophenylphenyl sulfone was used in place of 2-nitrophenylphenyl 
sulfone and otherwise the reaction was carried out in the same manner as 
in Example 1. 
After the reaction, methanol was concentrated, toluene and water were added 
to the concentrate, and the aqueous solution was separated from the 
organic solution containing 4-nitrophenylphenyl sulfide as by-products. 
The aqueous solution was concentrated to dryness, to provide 14.8 g (88.5 
% yield) of sodium benzenesulfinate as while crystals. The purity was 
found 98.2% by liquid chromatography. 
EXAMPLE 4 
4- Nitrophenylphenyl sulfone and a solvent as a mixture of 100 g of toluene 
and 100 g of water were used in place of 2-nitrophenylphenyl sulfone and 
methanol, respectively, and the reaction was carried out in the presence 
of 0.1 g of tetrabutylammonium hydrogen sulfate as a phase transfer 
catalyst otherwise in the same manner as in Example 1. 
After the reaction, the reaction mixture was left standing at room 
temperature, the aqueous solution was separated from the toluene solution 
containing 4-nitrophenylphenyl sulfide as by-products. The aqueous layer 
was concentrated to dryness, to provide 14.6 g (88.4 % yield) of sodium 
benzenesulfinate as white crystals. The purity was found 99.4 % by liquid 
chromatography. 
EXAMPLE 5 
(i) Production of Sodium Benzenesulfinate and Recovery of 2- 
Nitrophenylpheny Sulfide 4-Nitrophenylphenyl sulfone and a solvent 
composed of a mixture of 100 g of nitrobenzene and 100 g of water were 
used in place of 2-nitrophenylphenyl sulfone and methanol, respectively, 
and the reaction was carried out in the presence of 0.1 g of 
tetrabutylammonium hydrogen sulfate as a phase transfer catalyst otherwise 
in the same manner as in Example 1. 
After the reaction, the reaction mixture was left standing at room 
temperatures, the aqueous solution was separated from the nitrobenzene 
solution containing 4-nitrophenylphenyl sulfide. The aqueous layer was 
concentrated to dryness, to provide 15.3 g (92.5 % yield) of sodium 
benzene sulfinate as white crystals. The purity was found 99.3 % by liquid 
chromatography. 
The nitrobenzene solution was concentrated by distillation to dryness, to 
provide 22.6 g (96.5 % yield) of 4-nitro-phenylphenyl sulfide, which was 
found 98.7 % in purity by liquid chromatography. 
(ii) Oxidation of 4-Nitrophenylphenyl Sulfide and Reuse 
An amount of 21.1 g (0.09 mole) of the recovered 4-nitrophenylphenyl 
sulfide was oxidized with hydrogen peroxide in the same manner as in 
Example 1. After the reaction, the reaction mixture was cooled, and 
resulting precipitates were filtered and dried, to provide 23.1 g (96.0 % 
yield) of 4-nitrophenylphenyl sulfone as white crystals, mp. 
141.4.degree.-142.9.degree. C. The purity was found 98.5 % by liquid 
chromatography. 
An amount of 21.4 g (0.08 mole) of the thus obtained 4-nitrophenylphenyl 
sulfone was dissolved in a two phase solvent composed of a mixture of 80 g 
of nitrobenzene and 80 g of water, and was reacted with sodium 
thiophenolate in the same manner as in Example 1. 
After the reaction, the resultant aqueous solution was separated from the 
organic solvent. The aqueous solution was concentrated to dryness, to 
provide 12.6 g (95.2 % yield) of sodium benzenesulfinate as white 
crystals. The purity was found 99.2 % by liquid chromatography. 
EXAMPLE 6 
An amount of 5.6 g (0.1 mole) of potassium hydroxide was used in place of 
sodium hydroxide, and the reaction was carried out otherwise in the same 
manner as in Example 1. 
After the reaction, methanol was concentrated, toluene and water were added 
to the concentrate, and the aqueous solution was separated from the 
organic solution containing 2-nitrophenylphenyl sulfide. The aqueous 
solution was concentrated to dryness, to provide 15.0 g (82.4 % yield) of 
sodium benzenesulfinate as white crystals. The purity was found 99.0 % by 
liquid chromatography. 
EXAMPLE 7 
An amount of 30.8 g (0.1 mole) of 2,4-dinitrophenylphenyl sulfone was used 
in place of 2-nitrophenylphenyl sulfone, and the reaction was carried out 
otherwise in the same manner as in Example 1. 
After the reaction, methanol was concentrated, toluene and water were added 
to the concentrate, and the aqueous solution was separated from the 
toluene solution containing 2,4-dinitrophenylphenyl sulfide. The aqueous 
solution was then concentrated to dryness, to provide 13.8 g (83.4 % 
yield) of sodium benzenesulfinate as white crystals. The purity was found 
99.2 % by liquid chromatography. 
EXAMPLE 8 
Ethanol was used as a solvent in place of methanol, and the reaction was 
carried out otherwise in the same manner as in Example 1. 
After the reaction, ethanol and methanol were concentrated, toluene and 
water were added to the concentrate, and the aqueous solution was 
separated from the toluene solution. The aqueous solution was then 
concentrated to dryness, to provide 16.0 g (96.7 % yield) of sodium 
benzenesulfinate as white crystals. The purity was found 99.2 % by liquid 
chromatography. 
The removal of toluene from the toluene solution provided 22.5 g (96.1 % 
yield) of 2-nitrophenylphenyl sulfide. The purity was found 99.1 % by 
liquid chromatography. 
EXAMPLE 9 
An amount of 46.2 g (0.2 mole) of 2-nitrophenylphenyl sulfide was dissolved 
under heating in 200 g of toluene in a 500 ml capacity four-necked flask 
provided with a stirrer, a thermometer, a dropping funnel and a reflux 
condensor, and there were added thereto 1 g of sodium tungstate dihydrate 
and 2 g of tetrabutylammonium hydrogen sulfate. To the resultant mixture 
were then dropwise added 40.9 g (0.42 mole) of 30 % of weight aqueous 
solution of hydrogen peroxide at temperatures of about 80.degree. C. under 
stirring, and the reaction was carried at the temperature for 3 hours. The 
pH of the reaction mixture was found about 1. 
After the completion of the reaction, the reaction mixture was separated 
into a toluene solution and an aqueous solution, and the toluene solution 
was concentrated to dryness, to provide 51.8 g (97.8 % yield) of 
2-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.5% by liquid chromatography. 
EXAMPLE 10 
An amount of 46.2 g (0.2 mole) of 2-nitrophenylphenyl sulfide was dissolved 
under heating in 200 g of toluene in a 500 ml capacity four-necked flask 
provided with a stirrer, a thermometer, a dropping funnel and a reflux 
condensor, and there were added thereto 1 g of sodium tungstate dihydrate, 
2 g of benzyltrimethylammonium chloride, and 1.5 g of sulfuric acid in 
this order. To the resultant mixture were then added dropwise 40.9 g (0.42 
mole) of aqueous hydrogen peroxide at temperatures of about 80.degree. C. 
under stirring, and the reaction was carried at the temperature for 3 
hours. the pH of the reaction mixture was found about 1. 
After the completion of the reaction, the reaction mixture was separated 
into a toluene solution and an aqueous solution, and the toluene solution 
was concentrated to dryness, to provide 51.6 g (97.6 % yield) of 
2-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.5 % by liquid chromatography. 
EXAMPLE 11 
Trioctylmethylammonium chloride was used in amounts of 2 g as phase 
transfer catalysts in place of tatrabutyl-ammonium hydrogen sulfate, and 
1.5 g of sulfuric acid were added to a toluene solution of the sulfide 
together with hydrogen peroxide, and the reaction was carried out 
otherwise in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 51.8 g (97.4 % yield) of 
2-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.0 % by liquid chromatography. 
EXAMPLE 12 
Benzyldimethyllaurylammonium chloride was used in amounts of 2 g as phase 
transfer catalysts in place of tetra-butylammonium hydrogen sulfate, and 
1.5 g of sulfuric acid were added to a toluene solution of the sulfide 
together with hydrogen peroxide, and the reaction was carried out 
otherwise in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 51.7 g (97.4 % yield) of 
2-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.2 % by liquid chromatography. 
EXAMPLE 13 
An amount of 46.2 g (0.2 mole) of 4-nitrophenylphenyl sulfide was used in 
place of 2-nitrophenylphenyl sulfide, and the reaction was carried out 
otherwise in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 51.9 g (97.7 % yield) of 
4-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.1 % by liquid chromatography. 
EXAMPLE 14 
An amount of 46.2 g (0.2 mole) of 4-nitrophenylphenyl sulfide was used in 
place of 2-nitrophenylphenyl sulfide, and nitrobenzene was used as organic 
solvents in place of toluene, and the reaction was carried out otherwise 
in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a nitrobenzene 
solution and an aqueous solution, and the nitrobenzene solution was heated 
and concentrated, and then cooled. The resultant solids were separated by 
filtration, washed with methanol, and then dried, to provide 50.3 g (95.2 
% yield) of 4-nitrophenylphenyl sulfone as pale yellow crystals. The 
purity was found 99.7 % by liquid chromatography. 
EXAMPLE 15 
An amount of 46.2 g (0.2 mole) of 4-nitrophenylphenyl sulfide was used in 
place of 2-nitrophenylphenyl sulfide, and 1 g of ammonium molybdate was 
used in place of sodium tungstate, and the reaction was carried out 
otherwise in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 51.5 g (97.5 % yield) of 
4-nitrophenylphenyl sulfone as pale yellow crystals. The purity was found 
99.7% by liquid chromatography. 
EXAMPLE 16 
Amount of 55.2 g (0.2 mole) of 2,4-dinitrophenyl-phenyl sulfide was used in 
place of 2-nitrophenylphenyl sulfide, and the reaction was carried out 
otherwise in the same manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 60.4 g (97.3 % yield) of 
2,4-dinitrophenylphenyl sulfone as yellow crystals. The purity was found 
99.3 % by liquid chromatography. 
EXAMPLE 17 
An amount of 55.2 g (0.2 mole) of 2,4-dinitrophenyl-phenyl sulfide was used 
in place of 2-nitrophenylphenyl sulfide, and 2 g of 
benzyldimethyltetradecylammonium chloride in place of tetrabutylammonium 
hydrogen sulfate, and the reaction was carried out otherwise in the same 
manner as in Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was 
concentrated to dryness, to provide 60.5 g (97.2 % yield) of 
2,4-dinitrophenylphenyl sulfone as yellow crystals. The purity was found 
99.1 % by liquid chromatography. 
EXAMPLE 18 
Benzyltrimethylammonium chloride was used in amounts of 2 g as phase 
transfer catalysts in place of tatrabutyl-ammonium hydrogen sulfate, and 
the reaction was carried to otherwise in the same manner as in Example 9. 
Since there was added no sulfuric acid to the reaction mixture, the pH of 
the reaction mixture was found about 7. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was analyzed by 
liquid chromatography. The toluene solution was found to contain 
2-nitrophenylphenyl sulfone in amounts of 85.6 % and 2-nitrophenylphenyl 
sulfoxide (by-products) in amounts of 14.4 %. 
EXAMPLE 19 
Benzyltrimethylammonium chloride was used in amounts of 2 g as phase 
transfer catalysts in place of tatrabutyl-ammonium hydrogen sulfate, and 
1.5 g of sodium hydroxide were added to a toluene solution of the sulfide 
together with hydrogen peroxide, and the reaction was carried out in an 
alkaline condition at a pH of about 14 otherwise in the same manner as in 
Example 9. 
After the reaction, the reaction mixture was separated into a toluene 
solution and an aqueous solution, and the toluene solution was analyzed by 
liquid chromatography. The toluene solution was found to contain 
2-nitrophenylphenyl sulfide (unreacted) in amounts of 73.2 %, 
2-nitrophenylphenyl sulfoxide (by-products) in amounts of 15.5 %, and 
2-nitro-phenylphenyl sulfone in amounts of 11.3 %.