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

“PROCESS FOR PREPARATION OF ALKYLBENZENES”

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 provides a process for preparation of alkylbenzenes. The alkylbenzenes are used in a wide variety of applications.

BACKGROUND OF THE INVENTION
The present invention provides a process to produce alkylbenzenes. The alkylbenzenes are important intermediates in agrochemical and pharmaceutical industries.
Organic Reactions (Hoboken, NJ, United States) (2008), 71, 1-737 broadly discloses reduction of benzyl chlorides or benzyl bromides with triethylsilane/palladium chloride to form corresponding alkylbenzenes.
EP0060617 discloses a process for preparation of 3-bromo-2,4,5,6-tetrafluorotoluene by reacting a solution of 3-bromotetrafluorobenzene magnesium bromide (obtained by the reaction of magnesium with 1,3-dibromotetrafluorobenzene) in dry tetrahydrofuran with dimethylsulphate, tetrahydrofuran and hydrochloric acid to yield 3-bromo-2,4,5,6-tetrafluorotoluene.
Despite the known methods, the research for new preparation process of halogenated alkylbenzenes is still an active field and there still persists a need in the art to develop industrially scalable and economic process for the preparation of halogenated alkylbenzenes.
Therefore, the present invention provides an alternative and an efficient process for preparation of alkylbenzenes.

OBJECT OF THE INVENTION
The object of the present invention is to provide an improved simple economical and industrially doable process for preparation of alkylbenzenes.
SUMMARY OF THE INVENTION
The present invention provides a process for preparation of an alkylbenzene, comprising the steps of:
a) reacting a halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent in another reactor to obtain the alkylbenzene.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “alkylbenzene” refers to toluene, pentafluorotoluene, ethylpentafluorobenzene, 3-bromo-2,4,5,6-tetrafluorotoluene, 3-chloro-2,4,5,6-tetrafluorotoluene, ethyl-3-bromo-2,4,5,6-tetrafluorobenzene, ethyl-3-chloro-2,4,5,6-tetrafluorobenzene, 2,3,5,6-tetrafluorotoluene, 1-ethyl-2,3,5,6-tetrafluorobenzene, 2,4,6-trifluorotoluene and 1-ethyl-2,4,6-trifluorobenzene or the like.
As used herein, “halobenzene” refers to monobromobenzene, 2,3,4,5,6-pentafluorobromobenzene, 1,3-dibromo-2,4,5,6-tetrafluorobenzene, chloro-2,3,4,5,6-pentafluorobenzene, 1-chloro-3-bromo-2,4,5,6-tetrafluorobenzene, iodo-2,3,4,5,6-pentafluorobenzene, 1-chloro-3-iodo-2,4,5,6-tetrafluorobenzene and 1-iodo-3-bromo-2,4,5,6-tetrafluorobenzene 1-iodo-2,3,5,6-tetrafluorobenzene, 1-bromo-2,3,5,6-tetrafluorobenzene, 1-chloro-2,3,5,6-tetrafluorobenzene, 1-iodo-2,4,6-trifluorobenzene, 1-bromo-2,4,6-trifluorobenzene and 1-chloro-2,4,6-trifluorobenzene or the like. Preferably, the halobenzene is a brominated benzene of concentration in the range of 30 to 50% by weight.
In an important embodiment, the reaction of halobenzene with magnesium is carried out in a separate reactor to give reaction mixture 1 which is transferred to another reactor by a cannula. This ensures that absence of excess of magnesium and curtail the side reactions leading to the impurities.
In another embodiment, the reaction of halobenzene with magnesium is carried out using finely divided magnesium in the range of 3 to 5% by weight.
In another embodiment, the molar ratio of magnesium with respect to halobenzene in the range of 1 to 1.2, preferably, in the range of 1 to 1.1.
In another embodiment, the reaction of halobenzene with magnesium is carried out in presence of an initiator such as dibromoethane, iodine and methyl iodide. The concentration of the alkylating agent is in the range of 8 to 12% by weight.
In another embodiment, the reaction of halobenzene with magnesium is carried out in a solvent is selected from diethylether, diisopropyl ether, cyclopentyl methyl ether, methyl-tert-butyl ether tetrahydrofuran, methyl tetrahydrofuran, monoglyme, diglyme and toluene or a mixture thereof.
In another embodiment, the reaction of halobenzene with magnesium is performed at a temperature of 40°C to 70°C.
As used herein, the ‘alkylating agent’ refers to methylbromide, methyliodide, methylchloride, ethyliodide, ethylchloride, dimethylsulfate, sodium methylsulfate, ethylbromide, diethylsulfate and sodium ethylsulfate or the like. Preferably, the alkylating agent is selected from dimethylsulfate, sodium methylsulfate, diethylsulfate, sodium ethylsulfate or the like.
In another embodiment, the molar ratio of an alkylating agent with respect to halobenzene is in the range of 0.5 to 0.6.
In another embodiment, the step b) of reacting the reaction mixture with an alkylating agent is performed at a temperature of 40°C to 80°C, preferably at a temperature of 40°C to 45°C.
In a preferred embodiment, the present invention provides a process for preparation of polyfluorinated alkylbenzene, comprising the steps of:
a) reacting polyfluorinated halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent in another reactor to obtain the polyfluorinated alkylbenzene from the reaction mixture 2, wherein halo group is selected from chloro, bromo and iodo.
In another embodiment, the present invention provides a process for preparation of alkylbenzene, comprising the steps of:
a) reacting a halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent to obtain a reaction mixture 2;
c) recovering the solvent from the step b) to obtain a residue;
d) adding an acid to the residue;
e) separating aqueous and organic layer; and
f) isolating the alkylbenzene from the organic layer.
In an embodiment, the acid is selected from a mineral acid such as hydrochloric acid and sulfuric acid or the like.
In another embodiment, the acid is added continuously in the reaction at a rate of 10 to 12 mL per minute. The solvent recovered in the present invention is recycled and reused.
In a preferred embodiment, the present invention provides a process for preparation of pentafluorotoluene, comprising the steps of;
a) reacting 1-bromo-2,3,4,5,6-pentafluorobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent to obtain a reaction mixture 2;
c) recovering the solvent from the reaction mixture 2 to obtain a residue;
d) adding an acid to the residue;
e) separating an organic and an aqueous layer; and
f) recovering of pentafluoro toluene from the organic layer.
The present invention provides alkylbenzene with a selectivity greater than 90%, yield greater than 75% and purity greater than 99%.
The alkylbenzenes of the present invention can be isolated by any of the method such as chemical separation, extraction, acid-base neutralization, distillation, evaporation, column chromatography and filtration or crystallization or a combination thereof.
In an embodiment of the present invention, the isolation is conducted by means of quenching, filtration followed by vacuum distillation.
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.
The reagents and intermediate used in the present invention are obtained commercially.
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 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (450 g, 1.82 mole) was added to a mixture of tetrahydrofuran (1260 ml), magnesium (48.7 g, 2.0 mole) and 1,2-dibromoethane (3.4 g, 0.02 mole) at 60°C in 2 hours. A solution of dimethylsulfate (138.5 g, 1.1 mole) in tetrahydrofuran (270 ml) was added into the reaction mixture at 45°C and the mixture was stirred for 15 minutes. After completion of the reaction, hydrochloric acid (5%, 750 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get 2,3,4,5,6-pentafluorotoluene.
Yield: 85%; Purity: 99%; Selectivity: 90%
Example 2: Preparation of 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (450 g, 1.82 mole) was added to a mixture of diethylether (900 ml), magnesium (48.7 g, 2.0 mole) and 1,2-dibromoethane (3.4 g, 0.02 mole) at 30°C in 3 hours. A solution of dimethylsulfate (138.5 g, 1.1 mole) in tetrahydrofuran (270 ml) was added into the reaction mixture at 45°C and stirred the mixture for 2 hours. After completion of the reaction, hydrochloric acid (5%, 750 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get pure 2,3,4,5,6-pentafluorotoluene.
Yield: 86.5%; Purity: 99; Selectivity: 94%
Example 3: Preparation of 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (40 g, 162 mmol) was added to a mixture of tetrahydrofuran (112 ml), magnesium (4.33 g, 178 mmol) and 1,2-dibromoethane (0.3 g, 1.6 mmol) at 60°C in 2 hours. Methyl bromide (18 g, 189.6 mmol) was added into the reaction mixture at 45°C and the reaction mixture was stirred for 6-8 hours. After completion of the reaction, hydrochloric acid (5%, 65 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get 2,3,4,5,6-pentafluorotoluene.
Yield: 65%; Purity: 99%; Selectivity: 85%
Example 4: Preparation of 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (40 g, 162 mmol) was added to a mixture of diethylether (80 ml), magnesium (4.3 g, 176.9 mmol) and 1,2-dibromoethane (0.3 g, 1.6 mmol) at 30°C in 2 hours. Methyl bromide (20 g, 210.7 mmol) was added into the reaction mixture at 40°C and stirred the reaction mixture for 8-10 hours. After completion of the reaction, hydrochloric acid (5%, 60 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get 2,3,4,5,6-pentafluorotoluene.
Yield: 66%; Purity: 99%; Selectivity: 85%
Example 5: Preparation of 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (450 g) was added to a mixture of tetrahydrofuran (1260 ml), magnesium (48.7 g) and 1,2-dibromoethane (3.4 g) at 60°C in 2 hours. A solution of sodium methylsulfate (138.5 g) in tetrahydrofuran (270 ml) was added into the reaction mixture at 45°C and the mixture was stirred for 15 minutes. After completion of the reaction, hydrochloric acid (5%, 750 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get 2,3,4,5,6-pentafluorotoluene.
Yield: 85%; Purity: 99.4%; Selectivity: 95%
Example 6: Preparation of 2,3,4,5,6-pentafluorotoluene.
Pentafluorobromobenzene (450 g) was added to a mixture of diethylether (900 ml), magnesium (48.7 g) and 1,2-dibromoethane (3.4 g) at 30°C in 3 hours. A solution of sodium methylsulfate (138.5 g) in tetrahydrofuran (270 ml) was added into the reaction mixture at 45°C and stirred the mixture for 2 hours. After completion of the reaction, hydrochloric acid (5%, 750 g) was added into reaction mass in an hour at 40°C. The layers were separated, and the organic layer was distilled to get pure 2,3,4,5,6-pentafluorotoluene.
Yield: 85.9%; Purity: 99.5; Selectivity: 96%
,CLAIMS:WE CLAIM
1. A process for preparation of an alkylbenzene, comprising the steps of:
a) reacting a halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture 1 with an alkylating agent in another reactor to obtain the alkylbenzene.
2. The process as claimed in claim 1, wherein 3 to 5% by weight of finely divided magnesium is used for reaction with halobenzene.
3. The process as claimed in claim 1, wherein the conversion of halobenzene to alkylbenzene is carried out in presence of an initiator selected from a group consisting of dibromoethane, iodine and methyl iodide.
4. The process as claimed in claim 1, wherein the conversion of halobenzene to alkylbenzene is carried out in presence of a solvent selected from a group consisting of diethylether, diisopropyl ether, cyclopentyl methyl ether, methyl-tert-butyl ether tetrahydrofuran, methyl tetrahydrofuran, monoglyme, diglyme and toluene or a mixture thereof.
5. The process as claimed in claim 1, wherein the conversion of halobenzene to alkylbenzene is carried out at a temperature of 40°C to 80°C.
6. The process as claimed in claim 1, wherein the alkylating agent is selected from a group consisting of methyl bromide, methyl iodide, methyl chloride, ethyl iodide, ethyl chloride, dimethylsulfate, sodium methylsulfate, ethyl bromide, diethylsulfate and sodium ethylsulfate.
7. The process as claimed in claim 1, wherein the molar ratio of alkylating agent with respect to halobenzene is in the range of 0.5 to 0.6.
8. The process as claimed in claim 1, wherein the process involves preparation of polyfluorinated alkylbenzene, comprising the steps of:
a) reacting polyfluorinated halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent in another reactor to obtain the polyfluorinated alkylbenzene from the reaction mixture 2, wherein halo group is selected from chloro, bromo and iodo.
9. The process for preparation of alkylbenzene as claimed in claim 1, comprising the steps of:
a) reacting a halobenzene with magnesium in a solvent to obtain a reaction mixture 1;
b) reacting the reaction mixture with an alkylating agent to obtain a reaction mixture 2;
c) recovering the solvent from the step b) to obtain a residue;
d) adding an acid to the residue;
e) separating aqueous and organic layer; and
f) isolating the alkylbenzene from the organic layer.
10. The process as claimed in claim 9, wherein the acid is a mineral acid selected from a group consisting of hydrochloric acid and sulfuric acid.

Dated this 21st day of February, 2022.