The present invention provides a process for preparation of chloro substituted difluoropropanes.

BACKGROUND OF THE INVENTION
Hydrochlorodifluoropropane compounds are important precursors in synthesis of various hydrofluoroolefins, more particularly, tetrafluoropropenes. The hydrofluoroolefins possess several applications in refrigeration, air-conditioning. As the economic importance of hydrofluoroolefins has developed, so has the demand of precursor utilized in their production.
U.S. Pat. No. 9,102,579 provides a process for preparation of 1-chloro-2,2-difluoropropane by reacting 2,3-dichloropropene and hydrogen fluoride in presence of a catalyst in liquid phase. The process gives mixture of products which need purification later and selectivity of formation 1-chloro-2,2-difluoropropane is only 60%. The patent also provides an alternate two step process for preparation of 1-chloro-2,2-difluoropropane from 2,3-dichloropropane via preparing an intermediate, 1,2-dichloro-2-fluoropropane.
U.S. Pat. No. 8,907,149 gives a process for chlorination of hydrochloroalkanes and dehydrohalogenation to prepare chlorinated propenes. The chlorination gives mixture of multichlorinated compounds and 1,2,3-trichloropropane has very low selectivity.
The processes known in the art are tedious and non-economic for commercial exploitation.
The inventors of the present invention provides an improved process for preparation of chlorodifluoropropanes and intermediates thereof with high selectivity.

OBJECT OF THE INVENTION
The main object of present invention is to provide an economic and one step process for preparation of chlorosubstituted difluoropropanes from 2,3-dichloropropene. In-addition, it provides a process for preparation of chlorosubstituted difluoropropanes from allyl chloride and intermediate thereof. The present invention process is industrially doable and gives high selectivity for chlorosubstituted difluoropropanes.

SUMMARY OF THE INVENTION
In first aspect, present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating allyl chloride to obtain 1,2,3-trichloropropane;
b) dehydrochlorinating 1,2,3-trichloropropane using a base in presence of a phase transfer catalyst to obtain 2,3-dichloro-1-propene by reactive distillation; and
c) fluorinating 2,3-dichloro-1-propene 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 steps of:
a) dehydrochlorinating 1,2,3-trichloropropane using a base in presence of a phase transfer catalyst to obtain 2,3-dichloro-1-propene by reactive distillation;
b) fluorinating 2,3-dichloro-1-propene to obtain 1-chloro-2,2-difluoropropane.
In third aspect, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising fluorinating 2,3-dichloro-1-propene using hydrogen fluoride in presence of a catalyst to obtain 1-chloro-2,2-difluoropropane using hydrogen fluoride in a molar ratio of 3 to 10 w.r.to 2,3-dichloro-1-propene.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “chlorinating” refers to reaction with a chlorinating agent. The chlorinating agent for present invention is chlorine.
The reactor for present invention may be comprised of materials that are selected from 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.
As used herein, the “catalyst” for chlorination is selected from a group consisting of light, UV light, azo compounds, organic peroxides, metal halides or a mixture thereof. The azo compounds refers to azo nitriles and azo esters, may be selected from azobisisobutyronitrile, azodicarbonamide, 4,4'-azobis(4-cyanopentanoic acid), 2,2-azobis(2,4-dimethylvaleronitrile, azobis(methylisobutyrate), azobis(ethylisobutyrate rate) or like and mixture thereof. 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 halide, iron halide, chromium halide, copper halide, nickel halide, antimony halide, tantalum halide, aluminium halide or combination thereof.
The catalyst may be used in the form of liquid, powder, granules, pellets or sticks. The catalyst may be supported or unsupported. The catalyst is used in fixed bed catalyst or fluid bed catalyst. The catalyst may be supported on carbon, silica or combination thereof.
In an embodiment, chlorination of allyl chloride is carried out in presence of a catalyst.
The catalyst helps in achieving high selectivity for preparation of 1,2,3-trichloropropane from allyl chloride. The selectivity of formation of 1,2,3-trichloropropane is greater than 95%.
In preferred embodiment, chlorination of allyl chloride is carried out in presence of metal chloride 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, aluminium chloride or a combination thereof.
The metal catalyst is added in allyl chloride at a temperature between 10-20°C.
In an embodiment, metal catalyst is added in allyl chloride under inert atmosphere. The inert gas for present invention is nitrogen, helium, xenon or argon.
The chlorine is added in the reaction mass at a flow rate of 10-100 g/hour or for a period of 20-30 hours.
In an embodiment, chlorination of allyl chloride to obtain 1,2,3-trichloropropane is carried out without using any organic solvent.
In an embodiment, the chlorination is carried out at a temperature selected in the range from 10-100°C and more preferably between 10-70°C.
In a preferred embodiment, chlorination of allyl chloride to obtain 1,2,3-trichloropropane is carried out in a glass reactor.
In specific embodiment, chlorination of allyl chloride to obtain 1,2,3-trichloropropane is carried out in presence of aluminium chloride without using any organic solvent.
In an embodiment, reacting allyl chloride and chlorine in presence of aluminium chloride gives 1,2,3-trichloropropane with a selectivity of greater than 95%.
In an embodiment, chlorination of allyl chloride gives a reaction mixture. The reaction mixture may comprise of 1,2,3-trichloropropane, unreacted allyl chloride, chlorine, hydrogen chloride or like. The reaction mixture contains 1,2,3-trichloropropane greater than 95%.
In an embodiment, inert gas is purged in the reaction mixture to remove unreacted chlorine and hydrogen chloride.
In an embodiment, reaction mixture is distilled at a temperature selected in the range from 80-150°C and vacuum range of 300-5mmHg to isolate 1,2,3-trichloropropane.
The 1,2,3-trichloropropane is having purity greater than 95% and more preferably greater than 97%.
In an embodiment, the yield of formation of 1,2,3-trichloropropane is greater than 95% and more preferably greater than 97%.
In an embodiment, 1,2,3-trichloropropane is dehydrochlorinated with a base in presence of a phase transfer catalyst to obtain 2,3-dichloro-1-propene.
The base used for present invention is an aqueous solution. The base is selected from a group consisting of metal hydroxides, metal carbonates and metal bicarbonates. The metal hydroxides is selected from a group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide or like and metal carbonate is selected from a group consisting of sodium carbonate, potassium carbonate, magnesium carbonate, lithium carbonate or like and metal bicarbonate is selected from a group consisting of sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate or like.
The phase transfer catalyst refers to quaternary ammonium salts and may be selected from a group consisting of methyltrioctylammonium chloride, tetraethylammonium chloride, tetramethylammonium chloride, methyltriethylammonium chloride or like. The molar ratio of phase transfer catalyst w.r.t 1,2,3-trichloropropane is selected in the range of 0.01-0.1%.
The concentration of base in aqueous solution is between 20-50% and more preferably 30-50%. The molar ratio of the base w.r.t 1,2,3-trichloropropane is between 1-1.5.
In an embodiment, dehydrochlorination of 1,2,3-trichloropropane with base is carried out at a temperature selected in a range of 70-120°C and more preferably 80-110°C.
In particular embodiment, dehydrochlorination of 1,2,3-trichloropropane is carried out using an aqueous sodium hydroxide solution in presence of N-methyl-N,N,N-trioctylammonium chloride.
In an embodiment, present invention provides a process for preparation of dehydrochlorinating 1,2,3-trichloropropene using base and collecting 2,3-dichloro-1-propene by reactive distillation.
As used herein, reactive distillation refers to a process where addition of reactant or reaction and isolation of product happens simultaneously. The reactive distillation prevents formation of polymerised product and saves multiple step purification.
In an embodiment, selectivity of formation of 2,3-dichloro-1-propene is greater than 95% and more preferably greater than 98%.
In an embodiment, optionally, re-distillation of 2,3-dichloropropane is carried out at a temperature selected in the range of 70-130°C.
In an embodiment, 2,3-dichloropropene is having purity greater than 96% and more preferably between 96-99%.
In an embodiment, dehydrochlorination of 1,2,3-trichloropropane is carried in a glass reactor.
In an embodiment, the present invention provides a process for preparation of 2,3-dichloro-1-propene, comprising:
a) chlorinating allyl chloride to obtain 1,2,3-trichloropropane; and
b) dehydrochlorinating 1,2,3-trichloropropane using a base in presence of phase transfer catalyst to obtain 2,3-dichloro-1-propene by reactive distillation.
In a specific embodiment, the present invention provides a process for preparation of 2,3-dichloro-1-propene, comprising:
a) chlorinating allyl chloride to obtain 1,2,3-trichloropropane; and
b) dehydrochlorinating 1,2,3-trichloropropane using aqueous sodium hydroxide solution in presence of methyltrioctylammonium chloride to obtain 2,3-dichloro-1-propene by reactive distillation.
As used herein, “fluorinating” refers to reaction of 2,3-dichloro-1-propene with fluorinating agent. The fluorinating agent for present invention is hydrogen fluoride and more preferably anhydrous hydrogen fluoride. The anhydrous refers to a moisture content of less than 1000ppm and more preferably between 1-1000ppm.
In an embodiment, fluorination of 2,3-dichloro-1-propene is carried out in absence of catalyst, wherein molar ratio of hydrogen fluoride w.r.t 2,3-dichloro-1-propene is greater than 20 and preferably between 20-30.
In another embodiment, fluorination of 2,3-dichloro-1-propene is carried out in presence of catalyst. The catalyst is metal halides and is selected from a group consisting of stannic dichloride, aluminium chloride, stannic tetrachloride, iron chloride, chromium chloride, copper chloride, nickel chloride, antimony chloride, antimony fluoride, tantalum pentachloride or like.
Most of the prior art available is using a large quantity of hydrogen fluoride and suggest that catalyst does not help in any way. However, it is observed in the present invention that by using a catalyst, a significant amount of hydrogen fluoride can be reduced. The catalyst is advantageous in increasing product selectivity and reducing hydrogen fluoride quantity. The less quantity of hydrogen fluoride is helpful in reducing process cost, recycling operations and hazardous waste and makes process industrially more satisfactory. The reduction in hydrogen fluoride quantity will save recycling operations.
The anhydrous hydrogen fluoride is added in the fluorination reactor at temperature below 0°C and more preferably less than -10°C.
When the fluorination of 2,3-dichloro-1-propene is carried out in presence of a catalyst using hydrogen fluoride in a molar ratio less than 10 moles and more preferably 2-5 w.r.t 2,3-dichloro-1-propene.
The molar ratio of catalyst w.r.t to 2,3-dichloro-1-propene is selected from 0.001 to 0.1.
In an embodiment, fluorination of 2,3-dichloro-1-propene is carried out at a temperature selected in the range of 30 to 150°C and more preferably 80-130°C.
The fluorination of 2,3-dichloro-1-propene gives a reaction mixture containing 1-chloro-2,2-difluoropropane 1,2-dichloro-2-fluoropropane, hydrogen fluoride and 1,2,2-trichloropropane, unreacted 2,3-dichloro-1-propene.
In an embodiment, 1-chloro-2,2-difluoropropane is isolated from reaction mixture by quenching with base, extraction and distillation. The quenching refers to neutralising acidic content.
In another embodiment, 1-chloro-2,2-difluoropropane is isolated from reaction mixture by distillation without quenching, to prevent any product loss at plant scale.
In an embodiment, the present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, having purity greater than 90% and more preferably greater than 95% and most preferably greater than 98%.
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.
In specific embodiment, fluorination of 2,3-dichloro-1-propene is carried out using hydrogen fluoride in presence of stannic chloride and molar ratio of hydrogen fluoride w.r.t to 2,3-dichloro-1-propene is 3 to 8, preferably 3 to 4.
In a specific embodiment, fluorination of 2,3-dichloro-1-propene is carried out using hydrogen fluoride in presence of stannic chloride and isolated 1-chloro-2,2-difluoropropane by distillation.
In a specific embodiment, 1-chloro-2,2-difluoropropane is isolated from a mixture of 1-chloro-2,2-difluoropropane 1,2-dichloro-2-fluoropropane, hydrogen fluoride and 1,2,2-trichloropropane by distillation.
In a preferred embodiment, fluorination of 2,3-dichloro-1-propene is carried out using hydrogen fluoride in presence of stannic chloride and isolated 1-chloro-2,2-difluoropropane by quenching with sodium bicarbonate solution and distillation.
In an embodiment, present invention provides a process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of:
a) chlorinating allyl chloride using chlorine to obtain 1,2,3-trichloropropane;
b) dehydrochlorinating 1,2,3-trichloropropane using aqueous sodium hydroxide solution in presence of N-methyl-N,N,N-trioctylammonium chloride to obtain 2,3-dichloro-1-propene by reactive distillation; and
c) fluorinating 2,3-dichloro-1-propene using hydrogen fluoride in presence of stannic chloride to obtain 1-chloro-2,2-difluoropropane.
In an embodiment, 1-chloro-2,2-difluoropropane may also be prepared from 1,2-dichloropropane.
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.
The completion of the reaction may be monitored by any one of chromatographic techniques such as thin layer chromatography (TLC), high pressure liquid chromatography (HPLC), ultra-pressure liquid chromatography (UPLC), Gas chromatography (GC), liquid chromatography (LC) and alike.
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 1,2,3-trichloropropane
Allyl chloride (921g) was charged in a reactor equipped with condenser and mechanical stirrer. The reaction mass was cooled to 10°C and aluminium chloride (1g) was added under nitrogen atmosphere. Then, chlorine gas (854g) was purged in the reaction mass at the rate of 40-50g/hour at 20-30°C. After chlorine purging, the nitrogen was purged in the reaction mass to remove excess chlorine. The reaction mass was boiled off to isolate pure 1,2,3-trichloropropane (1737g).
Purity: 97%; Yield: 96%.
Example 2: Preparation of 1,2,3-trichloropropane
Allyl chloride (500g) was charged in a reactor equipped with condenser and mechanical stirrer. The reaction mass was cooled to 10°C and iron chloride (0.65g) was added under nitrogen atmosphere. Then, chlorine gas (474g) was purged in the reaction mass at the rate of 40-50g/hour at 20-30°C. After chlorine purging, the nitrogen was purged in the reaction mass to remove excess chlorine. The reaction mass was boiled off to isolate the pure 1,2,3-trichloropropane
Purity: 97%; Yield: 95%.
Example 3: Preparation of 1,2,3-trichloropropane
Allyl chloride (500g) was charged in a reactor equipped with condenser and mechanical stirrer. Then, chlorine gas (474g) was purged in the reaction mass at the rate of 40-50g/hour at 10-20°C. After chlorine purging, the nitrogen was purged in the reaction mass to remove excess chlorine. The reaction mass was used as such for further reactions.
Purity: 97%; Yield: 95%.
Example 4: Preparation of 2,3-dichloro-1-propene
1,2,3-trichloropropane (15 moles) was charged into a reactor equipped with reflux divider and mechanical stirrer. N-methyl-N,N,N-trioctylammonium chloride (0.019 mole) was added to the reaction mass and heated to 110°C. Aqueous sodium hydroxide solution (45%, 16.5 moles) was added dropwise to the reactor and simultaneously product was collected by reactive distillation. The distilled product was fractionated to get pure 2,3-dichloro propene.
Purity: 95%; Yield: 91%.
Example 5: Preparation of 2,3-dichloro-1-propene
1,2,3-trichloropropane (15 moles) was charged in a reactor equipped with reflux divider and mechanical stirrer. N-methyl-N,N,N-trioctylammonium chloride (0.019 mole) was added in the reaction mass and heated to 110°C. Aqueous sodium hydroxide solution (45%, 15.75 moles) was added dropwise in the reactor and simultaneously product was collected by reactive distillation. The distilled product was fractionated to get pure 2,3-dichloro-1-propene.
Purity: 98%; Yield: 90%.
Example 6: Preparation of 2,3-dichloro-1-propene
1,2,3-trichloropropane (15 moles) and tetrabutyl ammonium chloride (0.020 mole) were charged in a reactor equipped with reflux divider and mechanical stirrer. The reaction mass was heated to 110°C and aqueous sodium hydroxide solution (16.5 moles) was added dropwise in the reactor. The product was collected simultaneously by reactive distillation. The distilled product was fractionated to get pure 2,3-dichloro-1-propene.
Purity: 98%; Yield: 91%.
Example 7: Preparation of 1-chloro-2,2-difluoropropane
2,3-dichloro-1-propene (11 moles) was charged into an Inconel reactor and was cooled to 0°C. Anhydrous hydrogen fluoride (165 moles) was slowly added at 0°C and temperature was maintained below 0°C during addition. The reaction mass was heated to 110°C and stirred for 15 hours. The reaction mass was distilled to isolate pure product.
Purity: 95%; Yield: 75%.
Example 8: Preparation of 1-chloro-2,2-difluoropropane
2,3-dichloro-1-propene (11 moles) and stannic chloride (0.05 mole) were charged in a Hastelloy reactor and reaction mass was cooled to 0°C. Anhydrous hydrogen fluoride (88 moles) was added slowly in the reactor at 0°C and temperature was maintained below 0°C during addition. The reaction mass was heated to 100°C and stirred. The reaction mass was cooled to room temperature and hydrogen chloride and excess hydrogen fluoride were vented out from the reactor. The reaction mass was poured into distilled water and separated aqueous and organic layers. The organic layer was washed with sodium bicarbonate solution and distilled to isolate product.
Purity: 98%; Yield: 70%.
Example 9: Preparation of 1-chloro-2,2-difluoropropane
2,3-dichloro-1-propene (11 moles) and stannic chloride (0.03 mole) were charged in an Inconel reactor and reactor was cooled to -30°C. Anhydrous hydrogen fluoride (77 moles) was slowly added at 0°C and temperature was maintained below 0°C during addition. The reaction mass was heated to 110°C and stirred for 15 hours. The reaction mass was distilled to isolate pure product.
Purity: 98%; Yield: 72%.

WE CLAIM:

1. A process for preparation of 1-chloro-2,2-difluoropropane, comprising the steps of :
a) dehydrochlorinating 1,2,3-trichloropropane using a base in presence of a phase transfer catalyst to obtain 2,3-dichloro-1-propene by reactive distillation; and
b) fluorinating 2,3-dichloro-1-propene to obtain 1-chloro-2,2-difluoropropane.
2. The process as claimed in claim 1, wherein the phase transfer catalyst is a quaternary ammonium salt selected from a group consisting of methyltrioctylammonium chloride, tetraethylammonium chloride, tetramethylammonium chloride and methyltriethylammonium chloride.
3. The process as claimed in claim 1, wherein the base is selected from a group consisting of metal hydroxides, metal carbonates and metal bicarbonates.
4. The process as claimed in claim 1, wherein the base is an aqueous sodium hydroxide solution.
5. The process as claimed in claim 1, wherein fluorination is carried out using hydrogen fluoride in a molar ratio of 3 to 5 with respect to 2,3-dichloro-1-propene in presence of a catalyst.
6. The process as claimed in claim 1, wherein 1,2,3-trichloropropane is obtained by chlorinating allyl chloride in presence of a metal halide catalyst.
7. The process as claimed in claim 6, wherein an inert gas selected from nitrogen, helium, xenon or argon is purged in the reaction mixture after chlorination.
8. The process as claimed in claim 6, wherein the chlorination is carried out in presence of a catalyst selected from a group consisting of light, UV light, azo compounds, organic peroxides and metal halides or a mixture thereof.
9. The process as claimed in claims 5 and 6, wherein the catalyst is a metal chloride, selected from a group consisting of stannic dichloride, stannic tetrachloride, iron chloride, chromium chloride, copper chloride, nickel chloride, antimony chloride, antimony fluoride, tantalum pentachloride and aluminium chloride or a combination thereof.
10. The process as claimed in claim 1, wherein 1,2,3-trichloropropane is obtained with a selectivity of greater than 95%.