Description:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

“EFFLUENT FREE PROCESS FOR PREPARATION OF POLYHALOCARBOXYLIC ACID CHLORIDES”
This patent application is a modification of the invention filed in the Indian Patent application by the same applicant and granted as patent no. IN290252.

SRF LIMITED, AN INDIAN COMPANY,
SECTOR 45, BLOCK-C, UNICREST BUILDING,
GURGAON – 122003,
HARYANA (INDIA)

The following specification particular describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to an effluent free process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl having reduced content of impurities, by the reaction of a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine, wherein R1 is a fluorinated and/or chlorinated C1-C3 alkyl.

BACKGROUND OF THE INVENTION
Acid chlorides are important intermediates and reagents that find application in various chemical industries including pharmaceutical and agriculture.
Various methods are known in the literature for the preparation of acid chlorides.
US2257868 describes a process for synthesis of trifluoroacetyl chloride by the reaction of trifluoroacetic acid and benzoyl chloride.
US4643851 discloses a process for preparation of trifluoroacetyl chloride by catalytic chlorination of trifluoroacetaldehyde with chlorine in the vapor phase in a fixed bed or a fluidized bed reactor in the presence of an activated carbon catalyst.
US5241113 discloses a process for preparation of trifluoroacetyl chloride by reacting 1,1-dichloro-2,2,2-trifluoroethane with molecular oxygen over a carbon bed.
Tetrahedron (1986), 42(2), 547-52 and J. Phys. Chem. A 2014, 118, 4, 697–707 disclose a process for preparation of trifluoroacetyl chloride by reacting trifluoroacetic acid with phosphorus pentachloride in a solvent.
US5545298 discloses a process for preparation of polyfluorochlorocarboxylic acid chlorides and perfluorocarboxylic acid chlorides by photochemical oxidation of corresponding alkanes.
EP2006274 discloses a process for preparation of 3,3,3-trifluoropropionyl chloride by chlorinating 3,3,3-trifluoropropionaldehyde using a chlorinating agent selected from the group consisting of chlorine (Cl2), sulfuryl chloride (SO2Cl2) and organic N-chloro compounds.
IN290252 filed by the same applicant discloses a process for process for preparation of trifluoroacetyl chloride comprising reacting trifluoroacetyl fluoride with a chlorinated acetyl chloride selected from a group of monochloroacetyl chloride, dichloroacetyl chloride and trichloroacetyl chloride, preferably trichloroacetyl chloride.
Most of the chlorinating agents disclosed above are less suitable at commercial scale and the use of phosphorus pentachloride results in the formation of impurities and considerable loss of yield. Additionally, being highly hygroscopic, it gives operational challenges.
It has been now found by the present applicant that using a specific ratio of phosphorus trichloride and chlorine not only improves the yield and purity but also remarkably reduces the effluents being generated in the process, thereby providing an environment friendly process for production of polyhalocarboxylic acid chlorides at commercial scale.

OBJECTIVE OF THE INVENTION
An object of the present invention is to provide an environment friendly and commercially viable process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl having a reduced content of impurities, wherein R1 is a fluorinated and/or chlorinated C1-C3 alkyl by the reaction of a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine.

SUMMARY OF THE INVENTION
The present invention relates to an effluent free process for preparation of polyhalocarboxylic acid chlorides by reacting polyhalocarboxylic acid with phosphorus trichloride and chlorine.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term “fluorinated and/or chlorinated C1-C3 alkyl” refers to trifluoromethyl, difluoromethyl, trifluoroethyl, trifluoropropyl, trichloromethyl, trichloroethyl and trichloropropyl or the like.
As used herein, the term “a carboxylic acid chloride of formula (I) R1-C(O)Cl” includes acid chlorides selected from a group consisting of trifluoroacetyl chloride, difluoroacetyl chloride, trifluoropropionic acid chloride, trichloroacetyl chloride and trichloropropionic acid chloride or the like.
As used herein, the term “carboxylic acid of formula (II) R1-C(O)OH” includes the acids selected from a group consisting of trifluoroacetic acid, difluoroacetic acid, trifluoropropionic acid, trichloroacetic acid and trichloropropionic acid or the like.
In an embodiment, the present invention provides a process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl having a reduced content of impurities, wherein R1 is a fluorinated and/or chlorinated C1-C3 alkyl, by the reaction of a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine.
In another embodiment, the present invention provides an effluent free process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl by reacting a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine, wherein R1 is a fluorinated and/or chlorinated C1-C3 alkyl.
In a specific embodiment, the present invention provides a process for preparation of trifluoroacetyl chloride comprising the step of reacting trifluoroacetic acid with phosphorus trichloride and chlorine.
In another embodiment, the present invention provides a process for preparation of carboxylic acid chloride of formula (I) R1-C(O)Cl comprising the step of reacting a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine in a ratio of 1:(0.8 to 2.5):(2.5 to 3.6).
In another specific embodiment, the present invention provides a process for preparation of trifluoroacetyl chloride comprising the step of reacting trifluoroacetic acid with phosphorus trichloride and chlorine, wherein the molar ratio of trifluoroacetic acid: phosphorus trichloride: chlorine is in the range 1:(1.0 to 1.5): (1.0 to 1.5).
In another embodiment, the process of the present invention is carried out at a temperature in the range of 40-90°C.
In another embodiment of the present invention, the step of reacting a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine is carried out in absence of a solvent.
In another embodiment of the present invention, the step of reacting a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine may be carried out in presence of a solvent selected from acetonitrile, ethylene dichloride, carbon tetrachloride and chloroform or the like.
In another embodiment of the present invention, the carboxylic acid chloride of formula (I) R1-C(O)Cl obtained is substantially free (0.001-0.1%) of HCl impurity, i.e., contains less than 0.1% of HCl impurity, preferably 0.001-0.1% of HCl impurity.
In another embodiment of the present invention, the product mixture obtained from the reaction of trifluoroacetic acid with phosphorus trichloride and chlorine is subjected to distillation.
In an embodiment, the present invention provides a process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl by the reaction of a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine, wherein the process results in saleable quality of phosphorus oxychloride.
In an embodiment, the present invention provides a process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl by the reaction of a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine, wherein the process results in saleable quality of phosphorus oxychloride having the content ranging from 98-99%.
In another specific embodiment, the present invention provides a process for preparation of a trifluoroacetyl chloride by the reaction of trifluoroacetic acid with phosphorus trichloride and chlorine, wherein the process results in saleable quality of phosphorus oxychloride.
In an embodiment, the present invention provides a process for preparation of trifluoroacetyl chloride by the reaction of trifluoroacetic acid with phosphorus trichloride and chlorine, wherein the process results in saleable quality of phosphorus oxychloride having the content ranging from 98-99%.
The process of the present invention can be carried out in a batch or a continuous mode.
In another embodiment, the present invention provides a process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl, wherein carboxylic acid of formula (II) R1-C(O)OH and chlorine are simultaneously added to phosphorus trichloride in a reactor.
In another specific embodiment, the present invention provides a process for preparation of a trifluoroacetyl chloride, wherein trifluoroacetic acid and chlorine are simultaneously added to phosphorus trichloride in a reactor.
In another embodiment, the present invention provides a process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl, wherein carboxylic acid of formula (II) R1-C(O)OH and chlorine are simultaneously and continuously added to phosphorus trichloride in a reactor.
In another specific embodiment, the present invention provides a process for preparation of a trifluoroacetyl chloride, wherein trifluoroacetic acid and chlorine are simultaneously and continuously added to phosphorus trichloride in a reactor.
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.
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 trifluoroacetyl chloride (comparative example)
Trifluoroacetic acid was slowly added to a reactor containing phosphorus trichloride and heated at a temperature of 70°C to obtain the titled product.
Yield: 85%; Purity: 92%;
The process involves large quantities of phosphoric acid that require extensive effluent treatment.
Example 2: Preparation of trifluoroacetyl chloride (comparative example)
Trifluoroacetic acid was slowly added to a reactor containing phosphorus pentachloride and heated at a temperature of 70°C to obtain the titled product.
Yield: 85%; Purity: 92%;
The process involves large quantities of phosphoric acid that require extensive effluent treatment.
Example 3: Preparation of trifluoroacetyl chloride
Trifluoroacetic acid (55g) and chlorine (38g) were simultaneously added to reactor containing phosphorus trichloride (73g) and heated at a temperature of 55-60°C for 3 to 4 hours. Trifluoroacetyl chloride was collected in a collection pot and hydrochloric acid was scrubbed into an aqueous solution of caustic (20%) to obtain the titled compound.
Yield: 90-95%
Purity: 99-99.8%
Phosphorus oxychloride: 98-99% (saleable quality)
Phosphorus trichloride: 0.2%.
Example 4: Preparation of difluoroacetyl chloride
Difluoroacetic acid (1 m.eq) and chlorine (2.5 m. eq) were simultaneously added to reactor containing phosphorus trichloride (1 m.eq) and heated at a temperature of 55-60°C for 3 to 4 hours. Difluoroacetyl chloride was collected in a collection pot and hydrochloric acid was scrubbed into an aqueous solution of caustic (20%) to obtain the titled compound.
Yield: 90-95%; Purity: 99-99.5%
Phosphorus oxychloride: 98-99% (saleable quality)
Phosphorus trichloride: 0.2%.

, Claims:

WE CLAIM:
1. An effluent free process for preparation of a carboxylic acid chloride of formula (I) R1-C(O)Cl by reacting a carboxylic acid of formula (II) R1-C(O)OH with phosphorus trichloride and chlorine, wherein R1 is a fluorinated and/or chlorinated C1-C3 alkyl.
2. The process as claimed in claim 1, wherein the carboxylic acid of formula (II) R1-C(O)OH is reacted with phosphorus trichloride and chlorine in a ratio of 1:(0.8 to 2.5):(2.5 to 3.6).
3. The process as claimed in claim 1, wherein the reaction is carried out at a temperature in the range of 40-90°C.
4. The process as claimed in claim 1, wherein the process is carried out in a batch or a continuous mode.
5. The process as claimed in claim 1, wherein the carboxylic acid chloride of formula (I) R1-C(O)Cl is obtained with HCl impurity in the range of 0.001-0.1%.
6. The process as claimed in claim 1, wherein the process results in saleable quality of phosphorus oxychloride having the content ranging from 98-99%.

Dated this 1st day of November 2022.