FIELD OF THE INVENTION

The present invention provides a simple and safe process for preparation of sultones.

BACKGROUND OF THE INVENTION

Sultones such as 1,3-propanesultone and 1,4-butanesultone are widely used as electroplating intermediates, pharmaceutical intermediates, photosensitive material, lithium batteries, and other household chemicals. The market for sultone is expanding owing to their applications as lithium battery electrolyte.

There are several methods are known for preparation of sultones.

Journal of the American Chemical Society, 76, 5357-60, 1954 discloses a process for preparation of 4-hydroxy- 1-butanesulphonic acid using 4-chloro-butylacetate and sodium sulphite. 4-hydroxy- 1-butanesulphonic acid was isolated by carrying out multiple distillations at high temperature of 180-200°C and under 4mm of Hg of reduced pressure.

European Journal of Organic Chemistry, Volume 586, issue 1, 1954 discloses a process for preparation of 1, 4-butane sultone by reacting tetrahydrofuran and acetyl chloride in presence of zinc chloride to form 4-chloro-butylacetate, followed by reaction with sodium sulphite, then neutralisation with acid and distillation of sultone at high temperature of 175-185°C. It also involves distillation step for isolation of 1,4-butane sultone.

CN106397392A provides a process for preparation of 1,4-butane sultone using 3- buten-l-ol and sodium sulphite. This process involves four steps for preparation of 1,4-butane sultone. It suggests vacuum dehydration in presence of a solvent at high temperature range of 150-200°C to form 1,4-butane sultone. The ethanol used in the process is highly flammable and unsafe to use at this high temperature. It involves multiple drawbacks such as high temperature range, tedious operation, excess solvent and safety hazard. Thus, there remains an urgent need to develop a simple, efficient and industrially viable process for preparation of sultones.

SUMMARY OF THE INVENTION

In first aspect, the present invention provides a process for preparation of sultones of formula I,

Formula I wherein n is 1-3 comprising the steps of: a) reacting haloalkyl acetate and alkali metal sulphite in water to obtain a mixture; b) adding an alcohol to the reaction mixture of step a); c) neutralizing the reaction mixture of step b) to obtain hydroxyalkyl sulphonic acid; d) dehydrating hydroxyalkyl sulphonic acid at a temperature of 75-115°C to obtain sultone of formula I.

In second aspect, the present invention provides a process for preparation of sultone of formula I having purity greater than 99.0% comprising, the steps of dehydrating crude hydroxyalkyl sulphonic acid at temperature of 75-115°C to obtain sultone of formula I.

OBJECT OF THE INVENTION

The main object of present invention is to provide a simple and industrially applicable process for preparation of sultones of formula I.

Formula I wherein n is 1-3 DETAILED DESCRIPTION OF THE INVENTION

Sultones have high boiling point and are usually separated from the crude mixture by distillations that leads to the decomposition and formation of sulphur dioxide. This affects the overall yield of the process and pose safety concerns during industrial scale ups. The present inventors improved the process for preparation of sultone by dehydrating crude hydroxyalkyl sulphonic acid at temperature below 100°C. Surprisingly, this step has increased the yield of present invention up to 90%.

The present invention avoids use of distillation and high temperature for preparation of sultone.

As used herein, alkali metal sulphite is selected from sodium sulphite and potassium sulphite.

As used herein, “dehydration” refers to removal of water from 4-hydroxyalkyl sulphonic acid to aid its cyclization to sultone.

In an embodiment, the step of dehydration of hydroxyalkyl sulphonic acid to isolate sultone is carried out at a temperature of 75-115°C.

In an embodiment, the step of dehydration is carried out at atmospheric or reduced pressure. The reduced pressure is in the range of 1-100 torr and preferably 10-50 torr, more preferably 10-30 torr.

In an embodiment, the step of dehydration may be carried out in presence or absence of solvent.

In another embodiment, the step of dehydration of hydroxyalkyl sulphonic acid at atmospheric pressure is carried out in presence of a solvent by azeotropically removing water with the solvent.

The solvents may be selected from a group consisting of toluene, heptane, octane, xylene, chlorobenzene, or like or a mixture thereof.

In another preferred embodiment, the step of dehydration of hydroxyalkyl sulphonic acid is carried out at a reduced pressure in absence of a solvent.

As used herein, “alkyl” refers to propyl, butyl and pentyl and “halo” refers to chloro, bromo and iodo. As used herein, haloalkyl acetate may be selected from a group consisting of 4- chlorobutylacetate, 5-chloropentylacetate, 3-chloropropylacetate, 4- bromobutylacetate, 5-bromopentylacetate, 3-bromopropylacetate.

The preferred haloalkyl acetate for present invention are chloroalkyl acetate selected from the group consisting of 4-chlorobutylacetate, 5-chloropentylacetate, 3-chloropropylacetate .

In an embodiment, the present invention provides a process for preparation of sultone of formula I having purity greater than 99.0%, comprising the steps of: a) dehydrating hydroxy alkyl sulphonic acid at a temperature of 75-115°C under reduced pressure in absence of solvent to obtain sultone of formula I; and b) isolating sultone of formula I.

In an embodiment, the present invention provides a process for preparation of sultone of formula I having purity greater than 99.0% comprising, the step of dehydrating hydroxy alkyl sulphonic acid at a temperature of 75-115°C at an atmospheric pressure in presence of a solvent, by azeotropically removing water to obtain sultone of formula I.

In a specific embodiment, the present invention provides a process for preparation of 1,4-butane sultone comprising dehydrating 4-hydroxybutane sulphonic acid under reduced pressure in absence of a solvent.

In another specific embodiment, the present invention provides a process for preparation of 1,4-butane sultone comprising dehydrating 4-hydroxybutane sulphonic acid at an atmospheric pressure in toluene, by azetropically removing water from the mixture.

In an embodiment, the present invention provides a process for preparation of sultones of formula I, comprising the steps of: a) reacting haloalkyl acetate and alkali metal sulphite in water to obtain a mixture; b) adding an alcohol to the reaction mixture of step a); c) neutralizing the reaction mixture of step b) to obtain hydroxyalkyl sulphonic acid; d) dehydrating hydroxyalkyl sulphonic acid at a temperature of 75-115°C to obtain sultone of formula I. The molar ratio of alkali metal sulphite to haloalkyl acetate is in the range of 1-1.5. The alcohol is selected from a group consisting of methanol, ethanol, and propanol or like.

In another embodiment, the step of dehydration is carried out without purifying hydroxyalkyl sulphonic acid.

The step of neutralization is carried out in presence of an acid selected from a group consisting of sulphuric acid, hydrochloric acid or phosphoric acid or like. The acid may be used in anhydrous or aqueous form. The preferred acid is anhydrous hydrochloric acid.

In a preferred embodiment, haloalkyl acetate and alkali metal sulphite were reacted in presence of water to obtain a mixture containing hydroxyalkyl sulphonic acid. The mixture obtained was diluted with an alcohol and neutralized using anhydrous hydrochloric acid. The neutralised mixture was filtered and filtrate was concentrated to obtain crude hydroxyalkyl sulphonic acid. The crude hydroxyalkyl sulphonic acid was dehydrated at a temperature of 75- 115°C under reduced pressure of 10-30 torr.

In another preferred embodiment, haloalkyl acetate and alkali metal sulphite were reacted in presence of water to obtain a mixture containing hydroxyalkyl sulphonic acid. The mixture obtained was diluted with an alcohol and neutralized using anhydrous hydrochloric acid. The neutralised mixture was filtered and filtrate was concentrated to obtain crude hydroxyalkyl sulphonic acid. The crude hydroxyalkyl sulphonic acid was dehydrated at a temperature of 75-115°C in a solvent such as toluene by azeotropically removing water at atmospheric pressure.

In an embodiment, sultone is isolated by solvent extraction. The solvent for extraction is selected from a group consisting of dichloromethane, methanol, ethyl acetate, pentane, hexane, heptane, xylene, chlorobenzene, ethylbenzene, chloroform, toluene or like.

The yield of sultone of formula I is in the range of 75%-95%. The sultone for present invention is obtained with a purity of 99.0% to 99.9%.

In a specific embodiment, the present invention provides a process for preparation of 1,4-butane sultone, comprising the steps of: a) reacting 4-chlorobutyl acetate and alkali metal sulphite in water to obtain a reaction mixture; b) adding methanol to the reaction mixture of step a); c) neutralizing the reaction mixture of step b) using anhydrous hydrochloric acid to obtaining crude 4-hydroxybutane sulphonic acid; d) dehydrating crude 4-hydroxybutane sulphonic acid at 75-115°C at a reduced pressure of 10-30 torr to obtain 1,4-butane sultone to isolate 1,4-butane sultone of purity more than 99.0%.

In another specific embodiment, the present invention provides a process for preparation of 1,4-butane sultone, comprising the steps of: a) reacting 4-chlorobutyl acetate and alkali metal sulphite in water to obtain a reaction mixture; b) adding methanol to the reaction mixture of step a); c) neutralizing the reaction mixture of step b) using anhydrous hydrochloric acid to obtain crude 4-hydroxybutane sulphonic acid; d) azeotropically removing water from a solution of 4-hydroxybutane sulphonic acid and toluene at 75-90°C to obtain 1,4-butane sultone;

In an embodiment, the side product acetic acid may be recovered from the reaction mixture.

The solvents used in the present invention may be recycled and acetic acid formed can be recovered.

In present invention, inventors have taken care of economical aspect of process and used minimal quantities of solvents to carry out the reaction.

In one embodiment, the haloalkyl acetate used as raw material has purity greater than 95%.

The haloalkyl acetate used in present invention may be prepared by any method known in the literature or can be obtained commercially. 4-chlorobutylacetate may be prepared using tetrahydrofuran and acetyl chloride.

The alkali metal sulphite, solvents and acid used for present invention are obtained commercially. The product may be 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 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 1,4-butanesultone.

A mixture of 4-chlorobutyl acetate (20g), sodium sulphite (25.5g) and water (86g) were refluxed for 4-6 hours. Water was removed using vacuum and subsequently methanol (64g) was added to the reaction mass. Anhydrous hydrochloric acid was passed for 4 hours at reflux temperature and stirred. The reaction mass was filtered and filtrate was concentrated using rotary evaporator to remove methanol to obtain crude mass. The crude mass was dehydrated under vacuum (30 torr) at 90°C in absence of solvent until complete conversion to 1,4-butane sultone takes place. Reaction mass was cooled to room temperature and dichloromethane and water were added. Organic and aqueous layers were separated and aqueous layer was washed with dichloromethane and separated. The combined organic layer was concentrated using rotary evaporator to give pure 1,4-butane sultone.

Yield: 90 % Purity: 99.55%

Example 2: Preparation of 1,4-butanesultone.

A mixture of 4-chlorobutyl acetate (20g), sodium sulphite (25.5g) and water (86g) were refluxed for 4-6 hours. Water was removed using vacuum and subsequently methanol (64g) was added to the reaction mass. Anhydrous hydrochloric acid was passed for 4 hours at reflux temperature and stirred. The reaction mass was filtered and filtrate was concentrated using rotary evaporator to remove methanol to obtain crude mass. The crude mass was dehydrated under vacuum (20 torr) at 110°C in absence of solvent until complete conversion to 1,4-butane sultone takes place. Reaction mass was cooled to room temperature and dichloromethane and water were added. Organic and aqueous layers were separated and aqueous layer was washed with dichloromethane and separated. The combined organic layer was concentrated using rotary evaporator to give pure 1,4-butane sultone.

Yield: 92 %

Purity: 99.8%

Example 3: Preparation of 1,4-butanesultone.

A mixture of 4-chlorobutyl acetate (20g), sodium sulphite (17.5g) and water (90g) was refluxed for 4-6 hours. Water was removed using vacuum and subsequently methanol (64g) was added to the reaction mass. Anhydrous hydrochloric acid was passed for 4 hours at reflux temperature and stirred. The reaction mass was filtered and filtrate was concentrated using rotary evaporator to obtain crude mass. The crude mass was dehydrated under vacuum (20 torr) at 90°C until complete conversion to 1,4-butane sultone takes place. Reaction mass was cooled to room temperature and dichloromethane and water were added. Organic and aqueous layers were separated and the aqueous layer was washed with dichloromethane. The combined organic layer was concentrated using rotary evaporator to give pure 1,4- butane sultone.

Yield: 90 %

Purity: 99.75% Example 4: Preparation of 1,4-butanesultone

A mixture of 4-chlorobutyl acetate (50g), sodium sulphite (63g) and water (210g) was refluxed for 5 hours. Water was removed using vacuum and subsequently methanol (160g) was added to the reaction mass. Anhydrous hydrochloric acid was passed for 4 hours at reflux temperature and stirred. The reaction mass was filtered and filtrate was concentrated using rotary evaporator to obtain crude mass. Toluene was added in crude mass and dehydrated at atmospheric pressure at 98°C. Water was continuously removed azeotropic ally until complete conversion to 1,4-butane sultone takes place. Reaction mass was cooled to room temperature and dichloromethane and water were added. Organic and aqueous layers were separated and the aqueous layer was washed with dichloromethane. The combined organic layer was concentrated using rotary evaporator to give pure 1,4-butane sultone. Yield: 80%

Purity: 99.55%