SULFONES TO CHLOROBENZENE

The invention relates to an economical and environmentally friendly process for the single step conversion of isomeric mixture of dichlorodiphenyi sulfones to chlorobenzene.

Isomeric mixture of dichlorodiphenyi sulfone is a obtained as a by product in production of 4,4'-dichlorodiphenyl sulfone which is commercially produced by various known process such as:

^■ Reaction of monochlorobenzene with dimethyl pyrosulfate and sulfur trioxide in presence or absence of catalyst,

^■ Reaction of 4-chlorobenznesulfonic acid and monochlorobenzene in sulfuric acid in presence or absence of catalyst,

^■ Friedel-crafts reaction of 4-chlorobenzenesulfonyl chloride and monochlorobenzene in the presence of ferric chloride as a catalyst

The isomeric mixture produced in these processes contain 4,4'-dichlorodiphenyl sulfone; 3,4'- and 2,4'-isomers of which 4,4'-dichlorodiphenyl sulfone is the commercially useful product. The residue, after isolation of 4,4'-dichlorodiphenyl sulfone comprising of a mixture of 3,4'- and/or 2;4'-and/or 4,4'-dichlorodiphenyl sulfone is generally converted to isomeric mixture of Dihydroxydiphenyl sulfones or isomeric mixture of Diaminodiphenyl sulfones. This is - both cost and time intensive and provides no added value. This also reduces the yield of the process of manufacture of 4,4'-dichlorodiphenyl sulfone based on chlorobenzene consumed.

It is desirable to decisively reduce and/or eliminate these intermediates.

UK Patent Application GB 2476147A describes a process for conversion of isomeric mixture of dichlorodiphenyi sulfones to commercially viable products such as diphenyl sulfone, 2- aminodiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone and 4,4'-dihydroxydiphenyl sulfone.

US Patent Applications 2011/0218357 A1 describes a process for conversion of isomeric mixture of dichlorodiphenyi sulfones to mixture of 2-, 3- and 4-chlorobenzenesulfonic acid and their subsequent conversion 2- and/or 3-chlorobezenesulfonic acid to 4- chlorobenzenesulfonic acid. The present invention addresses some of the shortcomings in the prior art by converting these · intermediates to chlorobenzene for reuse in the process of 4,4'-dichlorodiphenyl sulfone.

Objects of the invention:

It was an object of the present invention to provide a process of converting isomeric mixture of dichlorodiphenyl sulfones to chlorobenzene.

It is another object of the invention is to re-circulate the chlorobenzene in the production process of 4,4'-dichlorodiphenyl sulfone.

It is another object of the invention to re-circulate the spent (residual) sulfuric acid in the process of conversion of isomeric mixture of dichlorodiphenyl sulfone to chlorobenzene.

It is yet another object of the invention to provide a "green process" by substantially reducing effluent production and treatment.

The process of the invention may be carried out in the manner described below:

The process of the invention can be carried out batch wise in a stirred vessel or semi- continuously or continuously in continuous flow reactors packed with packing elements.

Thus in accordance with the invention the isomeric mixture of dichlorodiphenyl sulfone is converted to chlorobenzene in a single step reaction and reused in the process of 4,4'- dichlorodiphenyl sulfone comprising:

1. Treating the isomeric mixture of dichlorodiphenyl sulfone with dilute sulfuric acid,

2. Azeotropically distilling of the reaction product to obtain chlorobenzene,

3. Neutralizing the chlorobenzene with aqueous alkali solution and distilling the same obtain significantly moisture free chlorobenzene,

4. Reusing the residual acid of step 2 and re-circulating chlorobenzene in the process for production of ^'-dichlorodiphenyl sulfone.

Sulfuric acid used in the process is 30 to 85%w/w The molar ratio of isomeric mixture of dichlorodiphenyl sulfone with sulfuric acid is 1 :0.25 to 1 :7, Preferably 1 :0.50 to 1 :7

The reaction temperature is 170 to 260°C, preferably 200 to 240°C. In one of the embodiments the reaction is carried out under reduced pressure at <170°C. The invention is now illustrated with reference to the following non-limiting examples. Example 1

Conversion of isomeric mixture of dichlorodiphenyl sulfone to chlorobenzene by reacting with 60% w/w sulfuric acid at 210-230°C with molar ratio of 1:1.4.

287g (1 mole) of isomeric mixture of dichlorodiphenyl sulfone containing 33.41% 4,4'-; 11.75% 3,3'-; and 52.40% 2,4'-isomer, was added to 230g sulfuric acid, 60%w/w (1.4mole) under stirring and heated to 220°C, and azeotropic mixture of water and chlorobenzene is collected in Dean and Stark water trap. Reaction is continued at the end of the chlorobenzene; 207g crude chlorobenzene is collected. The obtained chlorobenzene is acidic in nature hence was neutralized with aqueous alkali solution and washed with water and distilled to obtain 188g chlorobenzene with 0.79% moisture. The yield of chlorobenzene recovery is 83.55% based on isomeric mixture of dichlorodiphenyl sulfone. 285g residual spent acid collected containing 59.67%w/w sulfuric acid.

Example 2

Conversion of isomeric mixture of dichlorodiphenyl sulfone to chlorobenzene by reacting with 60% w/w sulfuric acid at 210-230°C with molar ratio of 1 :4.0

287g (1mole) of isomeric mixture of dichlorodiphenyl sulfone containing 33.41% 4,4'-; 11.75% 3,3'-; and 52.40% 2,4'-isomer, was added to 650g sulfuric acid, 60%w/w (4.0mole) under stirring and heated to 220°C, and Azeotropic mixture of water and chlorobenzene is collected in Dean and Stark water trap. Reaction is continued at the end of the chlorobenzene; 226g crude chlorobenzene is collected. The obtained chlorobenzene is acidic in nature hence was neutralized with aqueous alkali solution and washed with water and redistilled to obtain 205g chlorobenzene with 0.63% moisture. The yield of chlorobenzene recovery is 91.11% based on isomeric mixture of dichlorodiphenyl sulfone. 570g residual spent acid collected containing 60.57%w/w sulfuric acid. Example 3

Conversion of isomeric mixture of dichlorodiphenyl sulfone to chlorobenzene by reacting with 30% w/w sulfuric acid at 210-230°C with molar ratio of 1 :4.0

287g (1mole) of isomeric mixture of dichlorodiphenyl sulfone containing 33.41% 4,4'-; 11.75% 3,3'-; and 52.40% 2,4'-isomer, was added to 1306g sulfuric acid, 30%w/w (4.0mole) under stirring and heated to 220°C, and Azeotropic mixture of water and chlorobenzene is collected in Dean and Stark water trap. Reaction is continued at the end of the chlorobenzene; 221 g crude chlorobenzene is collected. The obtained chlorobenzene is acidic in nature hence was neutralized with aqueous alkali solution and washed with water and redistilled to obtain 203g chlorobenzene with 0.89% moisture. The yield of chlorobenzene recovery is 90.22% based on isomeric mixture of dichlorodiphenyl sulfone. 553g residual spent acid collected containing 70.64%w/w sulfuric acid.

Examples 4 to 30

Several experiments were carried out as per Example 1 except that the mole ratio of isomeric mixture of dichlorodiphenyl sulfone: sulfuric acid was varied from 1 :0.5 to 1 :7.0 and concentration of sulfuric acid was varied from 30 to 80%.

The results are presented in table 1 :

15 60 1:5.74 87.11 78.49

16 60 1:7.0 84.00 78.95

17 80 1:0.50 88.88 76.02

18 80 1:0.75 85.77 59.35

19 80 1:1.0 88.88 80.75

20 80 1.1.4 87.11 80.56

21 80 1:1.8 87.11 76.27

22 80 1:4.0 91.55 80.97

23 80 1:5.74 88.44 81.67

24 80 1:7.0 91.11 80.30

25 70 1:1.40 89.77 75.17

26 70 1:1.8 87.11 61.06

27 70 1:4.0 92.00 73.52

28 70 1:1.0 ^' 88.44 70.61

29 · 50 1:4.0 93.33 69.02

30 40 1:4.0 86.22 78.68

The present invention provides an economic and environmentally friendly method for the conversion of isomeric mixture of dichlorodiphenyl sulfone to chlorobenzene and reuse in production process of 4,4'-dichlorodiphenyl sulfone overcoming all the shortcomings of the nrinr art