Field of the invention The invention relates to a commercially feasible green process for the controlled production of diphenyl sulfone compounds with high yields.

Background of the invention 4-substituted 4'-hydroxydiphenyl sulfone are useful colour developers in thermosensitive recording ' materials. Generally 4-substituted 4'-hydroxydiphenyl sulfone and 4,4'- disubstituted diphenyl sulfone are produced by reaction of 4,4'-dihydroxydiphenyl sulfone (SDP) in aqueous alkali followed by reaction with alkyl halide and like. US5284978 discloses a process for the preparation of diphenyl sulfone compounds wherein 4,4'-dihydroxydiphenyl sulfone is reacted with a compound of the formula (II) R-X, 0.3-1.5 moles weight parts of a water miscible solvent per weight part of 4,4'-dihydroxydiphenyl sulfone in the presence of 1.5-3 moles of an alkali per mole of 4,4'-dihydroxydiphenyl sulfone. The reaction proceeds at a temperature between room temperature and 150°C for 6-24 hours under normal pressure or under pressurization, preferably at a temperature between 50°C and 120°C for 6-15 hours. The product with high purity can be obtained by conventional solvent extraction, washing, recrystallization, etc. following the reaction. In an embodiment the aqueous solvent may contain metal salts. The reported process achieves conversion of 4,4'-dihydroxydiphenyl sulfone from about 75 to 85% and the monoether derivatives of bisphenol S, namely 4-substituted hydroxyl-4'- hydroxydiphenyl sulfone, in reaction mixture is 68 to 83% (Examples 1 -6).

The prior art further states:

I When the amount of the alkali is below 1.5 moles per mole of bisphenol S, the reaction selectivity is poor, and where it is beyond 3 moles, it decomposes compounds of formula (II) (Column 3, lines 20-23).

2. When the amount of water is below 0.3 weight part per weight part of bisphenol S, stirring becomes un-conductible, and when it is beyond 1.5 weight parts, the reaction efficiency becomes poor (Column 3, lines 23-27). 3. When a metal salt is added in an amount of up to 1 weight part per weight part of bisphenol S, the reaction selectivity is enhanced (Column 3, lines 47-50).

4. The reaction proceeds at a temperature between room temperature and 150°C for 6-

24 hours (Column 3, lines 62-63).

5. The product with high purity can be obtained by a conventional means such as solvent extraction, washing, recrystallization, etc. following the reaction (Column 3, lines 65- 68).

The process disclosed in the prior art produces 4-substituted 4'-hydroxydiphenyl sulfone with maximum yield of 85%. Further, it does not teach how to control the reaction to produce desired ratios of 4-substituted 4'-hydroxydiphenyl sulfone and 4,4'-disubstituted diphenyl sulfone in such a reaction system. Further the process uses high quantities of organic solvents which is makes the process undesirable on environmental considerations. The prior art process conditions are extremely narrow and sensitive to the AlkalkBisphenol S molar ratio that has to necessarily be in the range 1.5 to 3 and Water: Bisphenol S weight ratio that has to necessarily be in the range of 0.3 to 1 .5.

It is clear from the prior art that the process cannot be operated outside that operating range of the said parameters.

The present invention overcomes such shortcomings of the prior art and provides a process that can be operated at Alkali:Bisphenol S molar ratio of 0.5 to 2.2 and at Water: Bisphenol S weight ratio of 3 to 15 without reduction in percentage conversion of 4,4'-dihydroxydiphenyl sulfone (>80%) and yields of 4-substituted 4'-hydroxydiphenyl sulfone (>80%) and 4,4'- disubstituted diphenyl sulfone ( >80%).

Further the present invention provides a green and environmentally friendly process. Summary of the invention

In this document the following abbreviation are used:

SDP :- 4,4'-dihydroxydiphenyl sulfone

SDP-ME :- 4-allyloxy 4'-hydroxydiphenyl sulfone

SDP-DE :- 4,4'-diallyloxydiphenyl sulfone The main object of the invention is to provide a green process for the controlled production of 4-substituted 4'-hydroxydiphenyl sulfone and 4,4'-disubstituted diphenyl sulfone with high selectivity and yields. Another object of the invention is to provide a green process for the production of 4- substituted 4'-hydroxydiphenyl sulfone substantially free of 4,4'-disubstituted diphenyl sulfone.

Another object of the invention is to provide a green process for the preparation of 4,4'- disubstituted diphenyl sulfone substantially free of 4-substituted 4'-hydroxydiphenyl sulfone.

Thus in accordance with the invention, the process steps comprise:

- Reacting 4,4'-dihydroxydiphenyl sulfone with 0.5 to 2.2 moles of alkali in 3 to 15 weight parts of water per weight parts of 4,4'-dihydroxydiphenyl sulfone and 1 to 2.2 moles of an etherification agent such as alkyl halide and the like, at 30° to 150°C for 4 to 10 hours in autogenously generated pressure to form 4-substituted 4'-hydroxydiphenyl sulfone and 4,4'-disubstitiuted diphenyl sulfone,

- Separating the 4,4'-disubstituted diphenyl sulfone,

- Adjusting pH of the filtrate of step 2 to precipitate 4-substituted 4'-hydroxydiphenyl sulfone, - Separating the 4-substituted 4'-hydroxy diphenyl sulfone,

- Recovering the unreacted 4,4'-dihydroxydiphenyl sulfone from the mother liquor,

- Optionally treating 4,4'-disubstituted diphenyl sulfone and 4-substituted 4'-hydroxydiphenl sulfone with sequestering agent and/or activated carbon in aqueous alkali.

- Optionally treating 4,4'-disubstituted diphenyl sulfone and 4-substituted 4'-hydroxydiphenl sulfone with sequestering agent and/or activated carbon in water immiscible solvent-water mixture.

Detailed description of the invention: Suitably substituted diphenyl sulfones are prepared in high yield and enhanced selectivity by reacting 4,4'-dihydroxydiphenyl sulfone with alkyl halide and like in aqueous alkali solution. The method of the present invention comprises reaction of 4,4'-dihydroxydiphenyl sulfone with 0.5 to 2.2 moles of alkali in 3 to 15 weight parts of water per weight parts of 4,4'- dihydroxydiphenyl sulfone and 1 to 2.2 moles of an etherification agent such as alkyl halide and the like, at 30° to 150°C for 4 to 10 hours in autogenously generated pressure to form 4- substituted 4'-hydroxydiphenyl sulfone and 4,4'-disubstitiuted diphenyl sulfone. The precipitated 4,4'-disubstituted diphenyl sulfone is separated from the reaction mixture and pH of the mother liquor containing 4-substituuted 4'-hydroxydiphenyl sulfone and unreacted 4,4'-dihydroxydiphenyl sulfone is adjusted to precipitate 4, -substituted 4'-hydroxydiphenyl sulfone which is then separated leaving unreacted 4,4'-dihydroxydiphenyl sulfone in the mother liquor. The mother liquor is then precipitated by adjusting pH and recovering the unreacted 4,4'-dihydroxydiphenyl sulfone.

4,4'-dihydroxydiphenyl sulfone, alkyl halide and like and aqueous alkali solution are mixed and reacted in closed system under autogenously generated pressure. Alternatively, the reaction mixture is reacted in an open system under reflux of the alkyl halide and the like used.

The reaction is carried out at 30 to 150°C, preferably between 50 to 125°C. The molar ratio of 4,4'-dihydroxydiphenyl sulfone to alkali is 1 :0.5 - 1 :2.2. The weight ratio of 4,4'-dihydroxydiphenyl sulfone to water is 1 :3 - 1 :15. The molar ratio of 4,4'-dihydroxydiphenyl sulfone to alkyl halide and like is 1 : 1 - 1 :2.2.

The reaction time is 4 to 10 hours.

The alkali used is selected from alkali metal hydroxides and alkali metal carbonates. The alkyl halides are select from methyl halide, ethyl halide, n-propyl halide, isopropyl halide, butyl halide, pentyl halide, hexyl halide, heptyl halide, octyl halide. alkenyl halides such as allyl halide, cycloalkyl halides such as cyclohexyl halide, methylcyclohexyl halide, etc; benzyl halides or phenethyl halides which may have 1 to 3 substituents selected from halogen (e.g. chlorine, bromine, etc.), an alkyl having 1 to 4 carbon atoms, an alkoxy having 1 to 4 carbon atoms (e.g. methoxy, ethoxy, propoxy, isopropoxy, butoxy, etc.), hydroxy, a haloalkyl having 1 to 4 carbon atoms (e.g. trifluoromethyl, trifluoroethyl, etc.), nitro and amino, on the aromatic ring, and the like.

In a preferred embodiment the reaction is carried out at molar ratio of 4,4'-dihydroxydiphenyl sulfone to alkali is 1 : 1 to 1 : 1.1 , molar ratio of 4,4'-dihydroxydiphenyl sulfone to alkyl halide and like is 1 : 1 to 1 : 1.1 and weight ratio of 4,4'-dihydroxydiphenyl sulfone to water is 1 :4 to 1 :5, at 50°-125°C in autogenously generated pressure for atleast 6 hours. In another preferred embodiment the reaction is carried out at molar ratio of 4,4'- dihydroxydiphenyl sulfone to alkali is 1 :2 to 1 :2.2, molar ratio of 4,4'-dihydroxydiphenyl sulfone to alkyl halide and like is 1 :2 to 1 :2.2 and weight ratio of 4,4'-dihydroxydiphenyl sulfone to water is 1 :4 to 1 :5, at 50°-125°C in autogenously generated pressure for atleast 6 hours.

The 4-substitiuted 4'-hydroxydiphenyl sulfone and 4,4'-disubstituted diphenyl sulfone are further purified if required by treating with sequestering agent and/or activated carbon in aqueous alkali.

In an embodiment of the purification process, the 4-substitiuted 4'-hydroxydiphenyl sulfone and 4,4'-disubstituted diphenyl sulfone are treated with sequestering agent and/or activated carbon in water immiscible solvent-water mixture.

The optional purification of the substituted diphenyl sulfones is carried out in steps of:

1. Treating the substituted diphenyl sulfones with activated carbon and/or sequestering agent in aqueous alkali solution,

2. Separating the 4,4'-disubstituted diphenyl sulfone,

3. Adjusting pH of the mother liquor of step 2 between 8.5-9.5 to precipitate the 4- substituted 4'-hydroxydiphenyl sulfone, and

4. Separating the 4-substituted 4'-hydroxy diphenyl sulfone.

In the above purification process, the molar ratio of 4-substituted 4'-hydroxydiphenyl sulfone to alkali is 1 :2, preferably 1 : 1.2, the concentration of aqueous alkali solution is 1 to 20 % w/v, preferably 5 to 10 % w/v and the weight ratio of substituted diphenyl sulfone to the aqueous solution of sodium hydroxide is 1 : 1 to 1 :10, preferably 1 : 1.5 to 1 :5.

Alternatively, the purification process of the substituted diphenyl sulfones may be carried out in steps of:

a. Dissolving the product in water immiscible solvent-water mixture,

b. Treating with sequestering agent and/or activated carbon,

c. Washing the solvent layer with water at 85°C to 95°C,

d. Separating the solvent layer at 85°C to 95°C , and

e. Cooling the solvent layer between10°C to 40°C, preferably between 20°C to 30°C to crystallize the product for separation. The solvent is preferably selected from monochlorobenzene, toluene, trichloroethylene and tetrachloroethylene. The ratio of substituted diphenyl sulfone to the water immiscible solvent-water mixture is suitably 1 :1 to 1 :4 w/w, preferably 1 : 1.5 to 1 :2.5 w/w.

The ratio of water immiscible solvent to water is1 :0.5 to 1 :2 w/w, preferably 1 :0.8 to 1 :1.2 w/w.

The sequestering agent is selected from phosphonic acid compounds or ion-exchange resins.

The concentration of the sequestering agent range from about 0.025% to 5% w/w, preferably 0.1 to 1% w/w with respect to the substituted diphenyl sulfone.

The activated carbon is used in concentrations of 0.025% to 5% w/w, preferably 0.1 to 1% w/w with respect to the substituted diphenyl sulfone. The invention is now illustrated with reference to the following non-limiting examples.

Example 1

Preparation of 4-allyloxy-4'-hydroxydiphenyl sulfone wherein the reaction is carried out 55° to 60°C under autogenously generated pressure for 8 hours and wherein the weight ratio of Water to 4,4'-dihydroxydiphenyl sulfone (SDP) is 4.19.

2400g water, 216g caustic soda lye of 48% strength, 600g 4,4'-dihydroxydiphenyl sulfone and 204g Allyl chloride were mixed and the reaction was carried out at 55-60°C and autogenously generated pressure of 0.8-1. Okg/cm ² for 8 hours.

204g caustic soda lye of 48% strength was added in the reaction mixture, and maintained for 1 hour at 80°C thereafter filtered at 80°C to remove 4,4'-diallyloxydiphenyl sulfone. Further, the filtrate solution was treated with 5g activated carbon and 5g sequestering agent at 85- 90°C. The pH of filtrated solution was adjusted to 8.9 with 20% sulfuric acid and cooled to 35°C. The precipitate was separated by filtration and slurred in water. The pH was adjusted to 4.94 with 20% sulfuric acid and the precipitate was separated by filtration, and washed with water and dried to obtain 615g the product 4-allyloxy 4'-hydroxydiphenyl sulfone of 96% purity. The yield was 93.5% with respect to 4,4'-dihydroxydiphenyl sulfone.

The wet cake of 4,4'-diallyloxydiphenyl sulfone was slurred in 100g of 5%w/v aqueous solution of sodium hydroxide and refluxed for 1 hour, then cooled to 80°C. The precipitate was filtered, washed with water and dried to obtain 45g of 4,4'-diallyloxy diphenyl sulfone of 91.9% purity. The yield was 6% with respect to 4,4'-dihydroxydiphenyl sulfone. pH of the mother liquor obtained after separation of 4-allyloxy 4'-hydroxydiphenyl sulfone, was adjusted to 4.5 with 20% sulfuric acid. The precipitate was separated by filtration, washed with water and dried to obtain 33g of 4,4'-dihydroxydiphenyl sulfone of 87.9% purity. The conversion of 4,4'-dihydroxydiphenyl sulfone was 94.50%.

Purification of 4-allyloxy 4'-hydroxydiphenyl sulfone:

595g of 4-allyloxy 4'-hydroxydiphenyl sulfone of 96% purity was dissolved in 230g of 48% strength caustic soda lye and 1000g water, treated with 5g activated carbon and 5g sequestering agent at 85-90°C. The slurry was filtered and pH of the filtrate was adjusted to 8.95 with 20% sulfuric acid and then cooled to 35°C. The precipitate was separated by filtration, slurried in water and the pH was adjusted to 5.0 with 20% sulfuric acid. The slurry was filtrated and the precipitate was washed with water and dried to obtain 563g of 4- allyloxy 4'-hydroxydiphenyl sulfone of 99.273% purity.

Example 2

The procedure as in Example 1 was repeated except that the molar ratio of NaOH:SDP was reduced to 0.5 moles. The comparative results of examples 1 and 2 are given in table 1.

Table 1 : SDP-ME- selection of NaOH:SDP

Example 3 and 4

The procedure as in Example 1 was repeated except that the reaction time was reduced up to 4 hours. The comparative results of examples 1 , 3 and 4 are given in table 2. Table 2: SDP-ME- selection of reaction time

Examples 5 and 6

The procedure as in Example 1 was repeated except that the weight ratio of WaterSDP increased. Table 3 gives the comparative results of examples 1 , 5, and 6.

Table 3: SDP-ME- Effect of WaterSDP weight ratio

Examples 7, 8 and 9

The procedure as in Example 1 was repeated except that the reaction temperature was varied. Table 4 gives the comparative results of examples 1 , 7, 8 and 9.

Table 4: SDP-ME- Effect of temperature

Example 10

Preparation of 4,4'-diallyloxydiphenyl sulfone wherein the reaction is carried out at 50-55°C and under autogenously generated pressure for 8 hours and wherein the weight ratio of Water to 4,4'-dihydroxydiphenyl sulfone (SDP) is 4.33.

2400g water, 400g caustic soda lye of 48% strength, 600g 4,4'-dihydroxydiphenyl sulfone and 370g. Allyl chloride were mixed and the reaction was carried out at 55-60°C under autogenously generated pressure of 0.8-1.0 kg/cm ² for 8 hours. The reaction mixture was filtered at 80°C to remove 4,4'-diallyloxydiphenyl sulfone. pH of the mother liquor solution was adjusted to 9 with 20% sulfuric acid and then cooled to 35°C. The precipitate was separated by filtration, slurried in water and pH was adjusted to 4.95 with 20% sulfuric acid. The precipitate was filtered, washed with water and dried to obtain 29g 4- allyloxy 4'-hydroxydiphenyl sulfone of 97.82% purity. The yield was 4.17% with respect to 4,4'-dihydroxydiphenyl sulfone.

The wet cake of 4,4'-diallyloxydiphenyl sulfone was slurried with 1500g of 5%w/v aqueous solution of sodium hydroxide, refluxed for 1 hour and cooled to 80°C. The precipitate was filtered, washed with water and dried to obtain 755g of 4,4'-diallyloxy diphenyl sulfone of 94.688% purity. The yield was 95.19% with respect to 4,4'-dihydroxydiphenyl sulfone. pH of the mother liquor obtained after separation of 4-allyloxy 4'-hydroxydiphenyl sulfone, was adjust to 4.5 with 20% sulfuric acid. Purification of 4,4'-diallyloxydiphenyl sulfone:

720g of 4,4'-diallyloxydiphenyl sulfone of 94.688% purity was slurried with 1000g of 5%w/v aqueous solution of sodium hydroxide and 5g sequestering agent then heated to 90-95°C for 1 hour under stirring and cooled to 80°C and the precipitate was filtered, washed with water and dried to obtain 612g of 4,4 -diallyloxy diphenyl sulfone of 98.992% purity.

Example 1 1

The procedure as in Example 10 was repeated except that the reaction time was reduced to 4 hours. Table 5 gives the comparative results of examples 10 and 1 1. Table 5: SDP-DE- Effect of reduced reaction time

Example 12 and 13

The procedure as in Example 10 was repeated except that the weight ratio of WaterSDP was increased. Table 6 gives the comparative results of examples 10, 12 and 13.

Table 6: SDP-DE- Effect of increased WaterSDP ratio

Example 14, 15 and 16

The procedure as in Example 10 was repeated except that the reaction temperature increased.- Table 7 gives the comparative results of examples 10, 14, 15 and 16.

Table 7: SDP-DE- Effect of increase in reaction temperature

Ex. NaOH: Water: Conversion

No. SDP SDP Temp. Time of SDP SDP-ME SDP-DE

Molar

Ratio w/w °C Hrs % % %

10 2 4.33 55-60 8 100 4.17 95.19

14 2 4.33 80-85 8 100 6.61 92.67

15 2 4.33 120-125 8 100 5.89 93.30

16 2 4.33 30-35 8 100 17.82 81.32 Example 17

Purification of 4-allyloxy 4'-hydroxydiphenyl sulfone by using halogenated solvent:

480g of 4-allyloxy 4'-hydroxydiphenyl sulfone of 95.08% pure, was dissolved in 500g chlorobenzene and 1000g water at 85°C to 95°C. The solution was treated with 1.5g of sequestering agent followed by separation of the aqueous layer. This step was repeated. The filtrate was cooled to 30°C to precipitate pure 4,4'-diallyloxydiphenyl sulfone which was separated, and washed with water and dried to obtain 414g of the product of 99.237% purity.

Example 18

Purification of 4,4'-diallyloxydiphenyl sulfone by using halogenated solvent:

500g of 4,4'-diallyloxydiphenyl sulfone of 94.80% pure, was dissolved in 500g chlorobenzene and 1000g water at 85°C to 95°C. The solution was treated with 1.5g of sequestering agent followed by separation of the aqueous layer. This step was repeated. The filtrate was cooled to 30°C to precipitate pure 4,4'-diallyloxydiphenyl sulfone which was separated, washed with water and dried to obtain 409g the product of 99.258% purity.

The present invention provides an economical and environmentally friendly green process for the preparation of substituted diphenyl sulfones overcoming all the shortcomings of the prior art and achieves the set objectives:

> Final products substantially free of the corresponding by-products

> Yield of 4-substitute 4'-dihydroxydiphenyl sulfone and 4,4'-disubstitute diphenyl sulfone >80%

> Conversion of 4,4'-dihydroxydiphenyl sulfone >80%

> Single step reaction of 4,4'-dihydroxydiphenyl sulfone, alkyl halide and like and aqueous alkali solution with substantially reduced reaction times

> Final products with significantly reduced colour to meet stringent product colour specification.