The present invention provides a process for preparation of chlorofluoropropanes and more particularly chlorodifluoropropane.

BACKGROUND OF THE INVENTION
Chlorodifluoropropane are important precursors in synthesis of various hydrofluoroolefins, such as tetrafluoropropenes. The hydrofluoroolefins possess several applications in refrigeration, and air-conditioning. As the economic importance of hydrofluoroolefins has developed, so has the demand of precursor utilized in their production.
J. Am. Chem., Soc. 59, 1937, 2436 provides a chlorination of 2,2-difluoropropane for preparing 1-chloro-2,2-difluoropropane. It further provides preparation of 2,2-difluoropropane from 2,2-dichloropropane, which is prepared by reacting acetone and phosphorous pentachloride. The process of preparation of 1-chloro-2,2-difluoropropane involves the use of corrosive and toxic reagents such as phosphorous pentachloride. The yield obtained in the process is very low and not suitable for commercial exploitation.
J. Am. Chem., Soc., 63, 10, 1941, 2692-2693 provides a process for chlorination of 2-fluoropropane. The process gives multiple chlorinated products and no certain checkpoint is available for reaction termination. The selectivity is low for 1-chloro-2,2-difluoropropane product. The reference does not provides any economic and industrially viable process for preparation of 1-chloro-2,2-difluoropropane.
United States Patent No. 9102579B2 describes a process for preparation of 1-chloro-2,2-difluoropropane from 2,3-dichloropropene. The process gives 1,2,2-trichloropropane, as impurity.
Thus, there is an urgent need to develop an economic process for preparation of product.
The inventors of the present invention provides an improved process for preparation of chlorodifluoropropanes.

OBJECT OF THE INVENTION
The main object of present invention is to provide an economic and improved process for preparation of hydrochlorodifluoropropane from 1,2-dichloropropane.

SUMMARY OF THE INVENTION
In first aspect of present invention provides a process for preparation of 1-chloro-2,2-difluoropropane,
comprising the steps of:
a) chlorinating dichloropropane to obtain a reaction mixture 1, comprising 1,2,2-trichloropropane;
b) isolating 1,2,2-trichloropropane from reaction mixture 1; and
c) fluorinating 1,2,2-trichloropropane to obtain 1-chloro-2,2-difluoropropane.
In second aspect, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the step of fluorinating 1,2,2-trichloropropane to obtain 1-chloro-2,2-difluoropropane using hydrogen fluoride.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, the “reaction mixture 1” may comprises of trichloropropane isomers, chlorine and hydrogen chloride..
As used herein, trichloropropane isomers refers to 1,2,2-trichloropropane, 1,1,2-trichloropropane and 1,2,3-trichloropropane.
As used herein, dichloropropane refers to 1,2-dichloropropane and 2,2-dichloropropane.
As used herein, the term chlorinating refers to the reaction of dichloropropane with a chlorinating agent. The chlorinating agent for present invention is chlorine.
As used herein, the term fluorinating refers to reaction of 1,2,2-trichloropropane with fluorinating agent. The fluorinating agent for present invention is anhydrous hydrogen fluoride. The anhydrous refers to a moisture content of less than 1000ppm and more preferably between 100-500ppm.
The reactor for present invention may be comprised of materials, which are resistant to corrosion and inert to most chemicals, such as glass, Hastelloy, Inconel, Monel and/or fluoropolymers linings.
As used herein, fluoropolymer refers to fluorinated ethylene-propylene (FEP), polytetrafluoroethylene (PTFE), polychlorotrifluoro-ethylene (PCTFE) and polyvinylidene fluoride (PVDF) or like.
In an embodiment, chlorination of dichloropropane is carried out in presence of catalyst.
The ‘catalyst’ is selected from a group consisting of light, UV light, azo compounds, organic peroxides, metal halides or combination thereof. The azo compounds are esters and nitriles selected from azobisisobutyronitrile, azodicarbonamide, 4,4'-azobis(4-cyanopentanoic acid), 2,2-azobis(2,4-dimethylvaleronitrile), azobis(methylisobutyrate), azobis(ethylisobutyrate) or like. The organic peroxides may be selected from a group consisting of di-tert-butylperoxides, benzoyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane or like. The metal halides may be selected from a group consisting of stannic dichloride, stannic tetrachloride, iron chloride, chromium chloride, copper chloride, nickel chloride, antimony chloride, antimony fluoride, tantalum pentachloride, aluminium chloride or combination thereof.
The molar ratio of catalyst w.r.t dichloropropane is selected from 0.001-0.1 %.
In preferred embodiment, the chlorination of dichloropropane is carried out in presence of UV light, as catalyst.
In another preferred embodiment, chlorination of dichloropropane is carried out using an azo compound, as catalyst.
In an embodiment, the chlorination is carried out in the temperature range selected between 0-100°C and preferably between 10-50°C.
In an embodiment, chlorine is purged at a flow rate of 10-100g/hour for 20-30 hours. The chlorine is suitably provided to a reaction mixture at a constant flow.
In an embodiment, material of construction of reactor for chlorination reaction is glass.
In specific embodiment, the chlorination of 1,2-dichloropropane is carried out in a glass reactor.
In an embodiment, chlorination of 1,2-dichloropropane is carried out in presence of UV light at 0-30°C to obtain a reaction mixture 1 containing 1,2,2-trichloropropane.
In another embodiment, chlorination of dichloropropane is carried out in presence of azobis(isobutyronitrile) at 50-80°C to obtain a reaction mixture 1 containing 1,2,2-trichloropropane.
In an embodiment, the chlorination is terminated at a conversion of dichloropropane between 40-70 % and more preferably 50-70 %. It prevents formation of unwanted chlorinated impurities and gives high yield of product.
As used herein, prevent refers to formation of unwanted impurities in less than 10 % and preferably between 1-5%. The unwanted chlorinated impurities may refer to tetra chlorinated, pentachlorinated or like.
In another embodiment, after the chlorination is terminated, an inert gas is purged in the reaction mixture to remove hydrogen chloride and excess chlorine. The inert gas is selected from nitrogen, helium, argon or mixture thereof.
In an embodiment, chlorination of dichloropropane in presence of catalyst gives a reaction mixture 1 containing 1,2,2-trichloropropane. The reaction mixture 1 containing 1,2,2-trichloropropane have greater than 50 % of 1,2,2-trichloropropane, preferably 50-60% and more preferably 50-70%.
In another embodiment, reaction mixture 1 containing 1,2,2-trichloropropane may be used in situ for preparation of hydrochlorodifluoropropane.
In a preferred embodiment, 1,2,2-trichloropropane is isolated from a reaction mixture 1 by distillation.
In another embodiment, reaction mixture 1 may comprise of 1,2,2-trichloropropane in the range between 50-70%, 1,1,2-trichloropropane in the range between 20-30% and 1,2,3-trichloropropane in the range between 10-30% or like, are separated by distillation and preferably distillation using a column.
In another embodiment, distillation is carried out at a temperature of 60-150°C and vacuum may be applied in the range of 350 to 1mmHg.
In another embodiment, 1,2,2-trichloropropane is isolated, having purity greater than 95 %.
In another embodiment, 1,2,3-trichloropropane is recycled and used for preparation of 2,3-dichloropropene.
In another embodiment, 1,2,3-trichloropropane is used for preparation of 1-chloro-2,2-difluoropropane.
As used herein, the “fluorination” refers to reacting 1,2,2-trichloropropane with fluorinating agent. The fluorinating agent is hydrogen fluoride and preferably anhydrous hydrogen fluoride. The molar ratio of hydrogen fluoride w.r.t 1,2,2-trichloropropane is selected in the range 2-30.
In preferred embodiment, fluorination is carried out in a Hastelloy reactor.
In another embodiment, reaction mixture 1 is used in-situ for preparation of 1-chloro-2,2-difluoropropane.
In a preferred embodiment, 1,2,2-trichloropropane is isolated from the reaction mixture 1 by distillation.
In a preferred embodiment, 1,2,2-trichloropropane used for fluorination process have purity greater than 95%.
In an embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the step of fluorinating 1,2,2-trichloropropane to obtain 1-chloro-2,2-difluoropropane using hydrogen fluoride in absence of catalyst. The hydrogen fluoride is also used as solvent. The molar ratio of hydrogen fluoride w.r.t 1,2,2-trichloropropane is selected in the range of 10-30.
In another embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the step of fluorinating 1,2,2-trichloropropane to obtain 1-chloro-2,2-difluoropropane using hydrogen fluoride in presence of catalyst. The molar ratio of hydrogen fluoride w.r.t 1,2,2-trichloropropane is from 2-10.
The fluorination of 1,2,2-trichloropropane to prepare 1-chloro-2,2-difluoropropane, involves reaction of hydrogen fluoride vapours with 1,2,2-trichloropropane.
The catalyst for fluorination is selected from metal catalyst, particularly metal halides and mixed halides. The metal halides is selected from a group consisting of stannic dichloride, stannic tetrachloride, iron chloride, chromium chloride, copper chloride, nickel chloride, antimony chloride, antimony fluoride, tantalum pentachloride or like and mixture thereof. The catalyst for the fluorination can also be selected from chromium oxide, chromium oxyfluoride or the like. The chromium catalyst can be supported on the carbon, nickel or aluminium.
In one embodiment, the mass percentage of catalyst in fluorination may vary from 0.1 % to 10 % and more preferably between 0.1 to 5 %.
In a specific embodiment, the fluorination of 1,2,2-trichloropropane is carried out using a stannic chloride as catalyst.
In an embodiment, the anhydrous hydrogen fluoride is added in the reactor at temperature below 0°C and preferably less than -10°C.
The fluorination is carried out at a temperature selected in the range of 50 to 150°C and more preferably 80-120°C.
In an embodiment, organic layer is washed with a base to neutralise hydrogen fluoride content. The base is selected from a group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate or like and aqueous solution thereof.
In an embodiment, fluorination of 1,2,2-trichloropropane gives a mixture of 1-chloro-2,2-difluoropropane, 1,2,2-trichloropropane and 1,2-dichloro-2-fluoropropane or like.
In an embodiment, 1-chloro-2,2-difluoropropane is isolated from a mixture of 1-chloro-2,2-difluoropropane, 1,2,2-trichloropropane and 1,2-dichloro-2-fluoropropane by distillation. The 1,2-dichloro-2-fluoropropane may be recycled in fluorination step.
In an embodiment, the selectivity of formation of 1-chloro-2,2-difluoropropane in fluorination is greater than 85 % and more preferably greater than 90 %.
In an embodiment, the yield of formation of 1-chloro-2,2-difluoropropane in fluorination is greater than 70 % and more preferably greater than 80 %.
In one embodiment, 1-chloro-2,2-difluoropropane is having purity greater than 90 % and more preferably greater than 95 %.
In an embodiment, fluorination catalyst and excess hydrogen fluoride are recycled for next batches.
In a specific embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane from 1,2,2-trichloropropane using hydrogen fluoride in presence of antimony chloride.
In another specific embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane from 1,2,2-trichloropropane using hydrogen fluoride in presence of aluminium chloride.
In another specific embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane from 1,2,2-trichloropropane using hydrogen fluoride in presence of chromium chloride.
In another specific embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane from 1,2,2-trichloropropane using hydrogen fluoride in absence of catalyst.
In an embodiment, present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating dichloropropane using chlorine in presence of UV light to obtain a reaction mixture 1 comprising 1,2,2-trichloropropane;
b) isolating 1,2,2-trichloropropane from reaction mixture 1; and
c) fluorinating 1,2,2-trichloropropane using hydrogen fluoride in presence of stannic chloride to obtain 1-chloro-2,2-difluoropropane.
In an embodiment, present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating dichloropropane using chlorine in presence of azobis(isobutyronitrile) to obtain a reaction mixture 1 comprising 1,2,2-trichloropropane; and
b) fluorinating reaction mixture comprising 1,2,2-trichloropropane using hydrogen fluoride in presence of stannic chloride to obtain 1-chloro-2,2-difluoropropane.
In an embodiment, present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating dichloropropane using chlorine in presence of UV light to obtain a reaction mixture 1 containing 1,2,2-trichloropropane;
b) isolating 1,2,2-trichloropropane from reaction mixture 1; and
c) fluorinating 1,2,2-trichloropropane using hydrogen fluoride in absence of catalyst to obtain 1-chloro-2,2-difluoropropane.
In one embodiment, 1-chloro-2,2-difluoropropane is used for preparation of 1,1,1-trichloro-2,2-difluoropropane.
In one embodiment, 1-chloro-2,2-difluoropropane is used for preparation of 2,3,3,3-tetrafluoropropene.
1-chloro-2,2-difluoropropane is isolated by any method known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, evaporation, column chromatography and filtration or a mixture thereof.
The chlorosubstituted difluoropropanes as prepared by process of the present invention can be isolated or can be used as such without isolation for the preparation of hydrofluoro olefins.
In preferred embodiment, 1-chloro-2,2-difluoropropane is monitored and analysed on gas chromatography.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example 1: Preparation of 1,2,2-trichloropropane
1,2-dichloropropane (2274 g) was charged in a glass reactor, fitted with condenser and 300W light source. The chlorine (1153g) was purged for 15-20 hours. The reaction mixture was analysed on gas chromatography and chlorine purging was terminated after 50 % conversion of 1,2-dichloropropane. Nitrogen was purged in the reaction mixture to remove hydrogen chloride and excess chlorine. The reaction mixture was distilled to isolate 1,2,2-dichloropropane.
Purity: 95.6 %; Yield: 45 %.
Example 2: Preparation of 1,2,2-trichloropropane
1,2-dichloropropane (1000 g) and azobisisobutyronitrile (4.21 g) was charged in a glass reactor fitted with condenser. The reaction mass was heated to 90°C and chlorine (633g) was purged. The chlorine flow was terminated at conversion of 1,2-dichloropropane between 50-60%. Nitrogen was purged in the reaction mass to remove hydrogen chloride and chlorine. The reaction mass was distilled and isolated 1,2,2-dichloropropane.
Purity: 96 %; Yield: 47 %.
Example 3: Preparation of 1-chloro-2,2-difluoropropane
In Hastelloy reactor, 1,2,2-trichloropropane (100 g, Purity: 95.6%) and stannic chloride (5 g) were charged and cooled to -30°C. Anhydrous hydrogen fluoride (55 g) was charged in reaction mass and temperature was maintained below 0°C during addition. After hydrogen fluoride addition, the reaction mass was heated to 100°C and stirred for 15 hours. The reaction mass was cooled to room temperature and vented off by-product hydrogen chloride and excess hydrogen fluoride. Distilled water was poured in the reaction mass and separated aqueous and organic layers. The organic layer was washed with sodium bicarbonate solution. The crude product was distilled to obtain 1-chloro-2,2-difluoropropane.
Purity: 95.3 %; Yield: 73 %
Example 4: Preparation of 1-chloro-2,2-difluoropropane
In Hastelloy reactor, 1,2,2-trichloropropane (100 g, Purity: 95.6%) and anhydrous hydrogen fluoride (70 g) was charged in reaction mass and maintained temperature below 0°C during addition. After hydrogen fluoride addition, the reaction mass was heated to 100°C and stirred for 15 hours. The reaction mass was cooled to room temperature and vented off by-product hydrogen chloride and excess hydrogen fluoride. Distilled water was poured in the reaction mass and separated aqueous and organic layers. The organic layer was washed with sodium bicarbonate solution. The crude product was distilled to obtain 1-chloro-2,2-difluoropropane.
Purity: 93 %; Yield: 60 %
Example 5: Preparation of 1-chloro-2,2-difluoropropane
1,2,2-trichloropropane (50 g) and antimony pentachloride (2.5 g) were charged in a Hastelloy reactor and cooled to -30°C. Anhydrous hydrogen fluoride (26 g) was slowly charged in the reaction mass and temperature was maintained below 0°C during addition. Then, reaction mass was heated to 100°C and stirred for 12 hours. The reaction mass was cooled to room temperature and vented off by-product hydrogen chloride and excess hydrogen fluoride. Distilled water was poured in reaction mass and separated aqueous and organic layers. The organic layer was washed with sodium bicarbonate solution and purified with distillation to obtain 1-chloro-2,2-difluoropropane.
Purity: 95 %; Yield: 74%.
Example 6: Preparation of 1-chloro-2,2-difluoropropane
1,2,2-trichloropropane (70 g) was charged in a Hastelloy reactor and cooled to -10°C. Anhydrous hydrogen fluoride (75 g) was added in the reactor and temperature was maintained below 0°C during addition. The reaction mass was heated to 100°C and stirred for 15 hours. The reaction mass was cooled to room temperature and vented off by-product hydrogen chloride and excess hydrogen fluoride. Distilled water was poured in reaction mass and separated aqueous and organic layers. The organic layer was washed with sodium bicarbonate solution and distilled to obtain product.
Purity: 94 %; Yield: 70 %.
Example 7: Preparation of 1-chloro-2,2-difluoropropane
1,2,2-trichloropropane (0.68 moles) and chromium chloride (0.019 mole) were charged in a Hastelloy reactor, and cooled to -30°C. Anhydrous hydrogen fluoride (3 moles) was added in reaction mass and temperature was maintained below 0°C during addition. The reaction mass was heated to 100°C and stirred. Then, distilled water was poured in the reaction mass and separated layers. The organic layer was washed with sodium carbonate solution and purified by distillation.
Purity: 95.8 %; Yield: 75 %.

WE CLAIM

1. A process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating dichloropropane to obtain a “reaction mixture 1”, comprising 1,2,2-trichloropropane;
b) fluorinating 1,2,2-trichloropropane to obtain 1-chloro-2,2-difluoropropane.
2. The process as claimed in claim 1, wherein 1,2,2-trichloropropane is isolated from “reaction mixture 1” prior to the step of fluorination.
3. The process as claimed in claim 1, wherein the “reaction mixture 1” comprises of chlorine, hydrogen chloride, and trichloropropane isomers selected from 1,2,2-trichloropropane, 1,1,2-trichloropropane and 1,2,3-trichloropropane.
4. The process as claimed in claim 1, wherein the chlorination is followed by a step of purging inert gas selected from nitrogen, helium or argon to remove hydrogen chloride and chlorine.
5. The process as claimed in claim 1, wherein the dichloropropane is selected from 1,2-dichloropropane and 2,2-dichloropropane.
6. The process as claimed in claim 1, wherein the chlorination reaction is terminated at a conversion of dichloropropane between 40-70 %.
7. The process as claimed in claim 1, wherein the chlorination of dichloropropane is carried out in presence of a catalyst selected from a group consisting of UV light, azo compounds, organic peroxides and metal halides or a mixture thereof.
8. The process as claimed in claim 1, wherein the chlorination is carried out at a temperature selected in the range of 10 to 50°C.
9. The process as claimed in claim 1, wherein the fluorination is carried out in presence of metal halides and mixed halide catalyst selected from a group consisting of stannic dichloride, stannic tetrachloride, iron chloride, chromium chloride, copper chloride, nickel chloride, antimony chloride, antimony fluoride, tantalum pentachloride or like and mixture thereof.
10. The process as claimed in claim 1, wherein the fluorination is carried out at a temperature selected in the range of 50 to 150°C.

Dated this 07th day of February, 2020.