A PROCESS FOR THE MANUFACTURE OF TRIFLIC ACID

FIELD OF THE INVENTION

The present invention relates to synthesis of Triflic acid.

BACKGROUND

Triflic acid (Trifluoromethanesulfonic acid) is a sulfonic acid with the chemical formula CF ₃ SO ₃ H. It is one of the strongest acids and is mainly used in research as a catalyst for esterification. Triflic acid is a hygroscopic, colorless liquid at room temperature. It is soluble in polar solvents such as DMF, DMSO, acetonitrile and dimethyl sulfone. Triflic acid is a non-oxidizing thermally stable compound and is resistant to both oxidation and reduction. In the laboratory, triflic acid is useful in protonations because the conjugate base of triflic acid is non-nucleophilic. Triflic acid promotes other Friedel-Crafts-like reactions including the cracking of alkanes and alkylation of alkenes, which are very important to the petroleum industry. These triflic acid derivative catalysts are very effective in isomerizing straight chain or slightly branched hydrocarbons that can increase the octane rating of particular petroleum based fuel.

Triflic acid is also used in pharmaceutical, agrochemical and fine chemical industries. Derivatives of Triflic acid are used as a component of lithium batteries, thus finds use in various electronic items viz. calculators, laptops, digital cameras, mobiles, watches and the like.

There are various processes available for the synthesis of Triflic acid, viz. Oxidation of bis (tnfluoromethylthio) mercury with hydrogen peroxide, formation of its barium salt, followed by its reaction with sulfuric acid to evolve Triflic acid (Hazeldine & Kidd, JCS 1954, 4228). However, mercury is a poisonous metal and hence the process is not desirable.

Trifluoromethanesulfonic acid is also produced by electrochemical fluorination (ECF) of methanesulfonic acid:

CH ₃ SO ₃ H + 4 HF→ CF ₃ SO2F + H ₂ 0 + 1.5 H ₂

The resulting CF ₃ S0 ₂ F is hydrolyzed and the resulting triflate salt is preprotonated. Alternatively, trifluoromethanesulfonic acid arises by oxidation of trifluoromethylsulfenyl chloride:

CF3SCI + 2 Cl ₂ + 2 H ₂ 0→ CF ₃ S0 ₂ OH + 4 HC1

Triflic acid is then purified by distillation from triflic anhydride.

Oxidation of bis-(trifluoromethyl) disulphane to Triflic acid by various oxidizing agents is disclosed in United States Patent No. 5059711. However, Bis- (trifluoromethyl)disulphane can not be readily synthesized and is not easily available. Accordingly, it is desirable to develop a synthetic route for Triflic acid using readily available raw material and which obviates the use of poisonous chemicals.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a synthetic route for Triflic acid using easily available raw materials.

It is another object of the present invention to provide a synthetic route for Triflic acid that obviates the use of poisonous/toxic chemicals.

It is still another object of the present invention to provide a simple and commercially attractive route for the synthesis of triflic acid.

SUMMARY OF AN INVENTION

In accordance with the present invention there is provided a process for the preparation of triflic acid, said process comprising the following steps: a) treating a mixture of benzyl trifluoro methyl sulphide and water with chlorine gas in a reactor maintained at a temperature of about 5°C to about 30°C and at a pressure of about 0.1 to 1.2 kg/cm to form a reaction mixture; b) maintaining the reaction mixture at a temperature of about 5°C to about 20°C for a period of about 4 to about 8 hours at 0.1 to 1.0 kg/cm ² pressure; c) raising the temperature of the reaction mixture to about 25 °C to about 45°C followed by maintaining the reaction mixture at 25 °C to 45°C and at pressure of about 0.1 to 1.0 kg/cm to form a biphasic mixture containing an organic layer and an aqueous layer; d) separating the organic layer from the biphasic mixture followed by distilling said organic layer to obtain trifluoromethyl sulphonyl chloride; and f) hydrolyzing trifluoromethyl sulponyl chloride to form triflic acid having a purity of about 99.5 %.

Typically, benzyl trifluoro methyl sulphide is at least one selected from the group consisting of unsubstituted benzyl trifluoro methyl sulphide and substituted benzyl trifluoro methyl sulphide.

In accordance with one of the embodiments of the present invention benzyl trifluoro methyl sulphide is a substituted benzyl trifluoro methyl sulphide. Typically, the substituent is at least one selected from the group consisting of aromatic group and halogen group.

Typically, the aromatic group is at least one selected from the group consisting of aromatic hydrocarbon, heterocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon.

Typically, the aromatic hydrocarbon is at least one selected from the group consisting of Benzene, Toluene, o, p, m-Xylene, Benzophenone, substituted benzophenone, acetophenone, substituted acetophenone, tri methyl benzene, tetramethyl benzene and pentamethyl benzene.

Typically, the heterocyclic aromatic hydrocarbon is at least one selected from the group consisting of furan, pyridine, pyrazine, imidazole, Pyrazole, oxazole and thiophene.

Typically, the polycyclic aromatic hydrocarbon is at least one selected from the group consisting of naphthalene, anthracene and phenanthrene.

Typically, the halogen group is at least one selected from the group consisting of fluorine, chlorine, bromine and iodine.

In accordance with one of the embodiment the substituent is at least one selected from the group consisting of ortho chlorobenzyl chloride, 4-chloromethyl methylene dioxy benzene, 1-chloromethyl naphthalene, bis-2, 4-chloromethyl toluene and tris 2,4,6-chloromethyl toluene and bis-9,10-chloromethyl anthracene.

Typically, the ratio of benzyl trifluoro methyl sulphide to chlorine is in the range of about 1 : 6 moles.

Preferably, step (a) is carried out at a pressure of about 0.5 to 0.9 kg/cm ² .

In accordance with one of the embodiments of the present invention the hydrolyzing step comprises hydrolyzing trifluoromethylsulponyl chloride with water to form a triflic acid monohydrate and dehydrating triflic acid monohydrate with thionyl chloride at a temperature of about 40 to about 80°C to yield crude anhydrous triflic acid followed by removing the impurities from the crude triflic acid by vacuum distillation to obtain pure triflic acid.

Typically, the hydrolyzing step is carried out at a temperature of about 70 to about 120°C and at a pressure of about 3 to 6 kg/cm ² .

Preferably, the hydrolyzing step is carried out at a temperature of about 80 to about 100°C and at a pressure of about 4 to 5 kg/cm .

Typically, the amount of thionyl chloride is about 1 to about 1.5 moles per mole of triflic acid monohydrate.

Preferably, the amount of thionyl chloride is about 1.1 to about 1.2 moles per mole of triflic acid monohydrate.

Preferably, the step of dehydrating triflic acid monohydrate with thionyl chloride is carried out at a temperature of about 50 to about 60°C.

In accordance with another embodiment of the present invention the hydrolyzing step comprises hydrolyzing trifluoromethylsulponyl chloride in presence of at least one inorganic base selected from the group consisting of sodium hydroxide and potassium hydroxide and at least one aliphatic alcohol selected from the group consisting of methanol, ethanol, isopropyl alcohol and mixtures thereof to form a hydrolyzed mass followed by neutralization using at least one mineral acid selected from the group consisting of hydrochloric acid and sulphuric acid and distillation to obtain pure triflic acid. DETAILED DESCRIPTION OF THE INVENTION

In the present invention unsubstituted and substituted benzyl trifluoro methyl sulphide is converted to trifluoromethyl sulfonyl chloride by oxidation and concomitant chlorinolysis, this reaction is also referred to as chloroxidation or chlorine gas oxidation. This chlorine gas oxidation or chloroxidation process of the present invention is advantageous as it utilize low-cost chlorine gas at production scales. The obtained trifluoromethyl sulfonyl chloride is then hydrolyzed to Triflic acid.

In accordance with the present invention benzyl trifluoro methyl sulphide is chloroxidized by passing chlorine gas into a mixture of benzyl trifluoro methyl sulphide and water over a period of 1 to 5 hours at a temperature of about 5°C to 30°C. Preferably chloroxidation is carried out at a temperature of about 15 to about 20°C.

Typically, benzyl trifluoro methyl sulphide is at least one selected from the group consisting of unsubstituted benzyl trifluoro methyl sulphide and substituted benzyl trifluoro methyl sulphide.

In accordance with one of the embodiments of the present invention benzyl trifluoro methyl sulphide is a substituted benzyl trifluoro methyl sulphide. Typically, the substituent is at least one selected from the group consisting of aromatic group and halogen group.

Typically, the aromatic group is at least one selected from the group consisting of aromatic hydrocarbon, heterocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon. Typically, the aromatic hydrocarbon is at least one selected from the group consisting of Benzene, Toluene, o, p, m-Xylene, Benzophenone, substituted benzophenone, acetophenone, substituted acetophenone, tri methyl benzene, tetramethyl benzene and pentamethyl benzene.

Typically, the heterocyclic aromatic hydrocarbon is at least one selected from the group consisting of furan, pyridine, pyrazine, imidazole, Pyrazole, oxazole and thiophene.

Typically, the polycyclic aromatic hydrocarbon is at least one selected from the group consisting of naphthalene, anthracene and phenanthrene.

Typically, the halogen group is at least one selected from the group consisting of fluorine, chlorine, bromine and iodine.

In accordance with one of the embodiment the substituent is at least one selected from the group consisting of ortho chlorobenzyl chloride, 4-chloromethyl methylene dioxy benzene, 1-chloromethyl naphthalene, bis-2, 4-chloromethyl toluene and tris 2,4,6-chloromethyl toluene and bis-9,10-chloromethyl anthracene.

Typically, the ratio of benzyl trifluoro methyl sulphide to chlorine is in the range of about 1 : 6 moles.

In accordance with the preferred embodiment of the present invention the substituted benzyl trifluoro methyl sulphide is ortho chlorobenzyl trifluoromethyl sulphide. The reaction mixture is then further maintained at the same temperature for a period of about 4 to about 8 hours at 0.1 to 1.0 kg/cm ² pressure. The temperature is then increased to about 25°C to about 45 °C and the reaction is further continued by maintaining the reaction mixture at the same temperature and pressure for a time effective to form a biphasic product mixture containing an organic layer and an aqueous layer. The product (trifluoromethyl sulphonyl chloride) is formed in the organic layer. The organic layer is then separated and distilled to give pure trifluoromethyl sulphonyl chloride.

In the preferred embodiment of the present invention water is used as a solvent during chloroxidation step and thus avoids the use of double solvent system.

The obtained trifluoromethyl sulphonyl chloride is further hydrolyzed using water at liquid temperature of about 70 to about 120°C and at a pressure of about 3 to about 6 kg/cm without using any solvent to get Triflic acid monohydrate. Preferably, the hydrolysis is carried out at 80 to 100°C and at a pressure of about 4 to about 5 kg/cm .

The quantity of water used for hydrolysis is about 400 to about 1000 ml per mole of trifluoromethyl sulphonyl chloride. Preferably, the quantity of water used for hydrolysis is about 600 to about 750 ml per mole of trifluoromethyl sulphonyl chloride. Monohydrate form of Triflic acid is then converted to anhydrous form using a dehydrating agent such as thionyl chloride without using any solvent. Typically, Triflic acid monohydrate is treated with thionyl chloride at a temperature of about 40°C to about 80°C, preferably at 50 to 60°C to get crude anhydrous Triflic acid. Typically, the amount of thionyl chloride is about 1 to about 1.5 moles per mole of Triflic acid monohydrate. The obtained crude Triflic acid is then further purified by vacuum distillation to get Triflic acid having a purity more than 99.5%.

In accordance with another embodiment of the present invention the hydrolyzing step comprises hydrolyzing trifluoromethylsulponyl chloride in presence of at least one inorganic base selected from the group consisting of sodium hydroxide and potassium hydroxide and at least one aliphatic alcohol selected from the group consisting of methanol, ethanol, isopropyl alcohol and mixtures thereof to form a hydrolyzed mass followed by neutralization using at least one mineral acid selected from the group consisting of hydrochloric acid and sulphuric acid and distillation to obtain pure triflic acid.

Typically, trifluoromethyl sulfonyl chloride on treatment with aqueous sodium hydroxide gives sodium triflate having a melting point of about 300°C.

Alternatively, trifluoromethyl sulphonyl chloride on treatment with aqueous potassium hydroxide gives potassium triflate having a melting point of about 230°C.

The above synthesis of triflic acid represents the only synthesis, which does not use the rather aggressive reaction condition in which electrochemical fluorination of methanesulfonyl chloride is carried out using HF as well as other synthesis where ozone depleting substances are used. The present invention will now be explained below in further detail with examples of specific embodiments. However, it should be understood that the present invention is by no means restricted to the specific examples given below.

Example 1:

In a reactor, 226.5 gm (1.0 M) of ortho-c oroberizyltrifluoromethylsulphide was mixed with 1000 ml of water to obtain a mixture. The mixture was then cooled to 10°C followed by passing the chlorine gas (142 gm, 4 moles) into the mixture over a period of 3 to 4 hours, at 0.1 to 1.0 kg/cm pressure. After passing the chlorine gas the reaction mixture was further maintained at the same temperature and pressure for 6 hours.

The temperature was then raised to 25 to 30°C and the reaction was further continued at raised temperature for 10 hours. After completion of the reaction, a two phase product mixture containing an organic layer and an aqueous layer was obtained. As the organic layer contains trifluoromethyl sulphonyl chloride, it was separated from two phase mixture and trifluoromethyl sulphonyl chloride was obtained by distilling the organic layer. Weight of distilled trifluoromethyl sulphonyl chloride was found to be 152 gm with 99.5% purity.

168.5 gm of the trifluoromethyl sulphonyl chloride thus isolated was reacted with 750 ml of water and heated to 80°C in a glass pressure reactor. Typically, the initial pressure inside the reactor is about 4.5 to 5 kg/cm . The reaction mixture was further heated at 80-85°C for 16 hrs in order to drop the pressure inside the reactor. Typically, the pressure drop is about 0.5 kg./cm ² . The pressure drop indicates complete conversion of Trifluoromethyl sulphonyl chloride to Triflic acid. Then water was removed from the reaction mass and the obtained Triflic acid monohydrate was vacuum distilled to get 165 gm of Triflic acid monohydrate with 88% purity.

170 gm (88% pure) hydrated Triflic acid was treated with 148 gm of thionyl chloride at 50 to 55°C and maintained at same temperature till no evolution of off gases. Crude anhydrous Triflic acid was then vacuum distilled to get anhydrous 149 gm of Triflic acid having purity more than 99.5%.

Example 2:

In a reactor, 226.5 gm (1.0 M) of ortho-chlorobenzyltrifluoromethylsulphide was mixed with 1000 ml of water to obtain a mixture. The mixture was then cooled to 10°C followed by passing the chlorine gas (177 gm, 5 moles) into the mixture over a period of 3 to 4 hours, at 0.1 to 1.0 kg/cm ² pressure. After passing the chlorine gas, the reaction mixture was further maintained at the same temperature and pressure for 6 hours.

The temperature was then raised to 25 to 30°C and the reaction was further continued at raised temperature for 10 hours. After completion of the reaction, two phase product mixture containing an organic layer and an aqueous layer was obtained. As the organic layer contains trifluoromethyl sulphonyl chloride, it was separated from two phase mixture and trifluoromethyl sulphonyl chloride was obtained by distilling the organic layer. Weight of distilled trifluoromethyl sulphonyl chloride was found to be 155 gm with 99.5% purity.

168.5 gm of the trifluoromethyl sulphonyl chloride thus isolated was reacted with 1000 ml of water and heated to 80°C in a glass pressure reactor. Typically, the initial pressure inside the reactor is about 4.5 to 5 kg/cm . The reaction mixture was further heated at 80-85°C for 16 hrs in order to drop the pressure inside the reactor. Typically, the pressure drop is about 0.5 kgJcm . The pressure drop indicates complete conversion of Trifluoromethyl sulphonyl chloride to Triflic acid.

Then water was removed from the reaction mass and the obtained Triflic acid monohydrate was vacuum distilled to get 167 gm of Triflic acid monohydrate with 88% purity.

170 gm (88% pure) hydrated Triflic acid was treated with 143 gm of thionyl chloride at 50 to 55°C and maintained at same temperature till no evolution of off gases. Crude anhydrous Triflic acid was then vacuum distilled to get anhydrous 149 gm of Triflic acid having purity more than 99.5%.

TECHNICAL ADVANCEMENT

■ The present invention provides a simple and feasible route of synthesis of triflic acid using easily available raw materials.

■ The present invention obviates the use of poisonous/toxic chemicals.

■ The present invention obviates the use of strong oxidizing agents.

While considerable emphasis has been placed herein on the specific steps of the preferred process, it will be appreciated that additional steps can be made and that many changes can be made in the preferred steps without departing from the principles of the invention. These and other changes in the preferred steps of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.