Title of Invention	"A PROCESS FOR THE PURIFICATION OF FLUOROMETHYL HEXAFLUOROISOPROPYL ETHER"
Abstract	The present invention 'provides a process for the purification of fluoromethyl hexafluoroisopropyl . ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsorbent having pores with a range of pore sizes whereby at least one impurity is rrmoved. from the crude romposition, and recovering the crude composition depleted in the said impurity.

Title of Invention

"A PROCESS FOR THE PURIFICATION OF FLUOROMETHYL HEXAFLUOROISOPROPYL ETHER"

Abstract

The present invention 'provides a process for the purification of fluoromethyl hexafluoroisopropyl . ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsorbent having pores with a range of pore sizes whereby at least one impurity is rrmoved. from the crude romposition, and recovering the crude composition depleted in the said impurity.

Full Text	The present invention relates to a process for the purification of fluoromethyl hexafluoroisopropyl ether. The present invention particularly provides a process for the purification of an ether of the formula CH2FOCH(CF3)2 which has anaesthetic properties and is known as 'Sevoflurane'. It is known that Sevoflurane may be produced by the reaction of formaldehyde, hydrogen fluoride and hexafluoroisopropyl alcohol (CF3) 2CHOH (HFIP). For example, US 4,250,334 describes a process in which hexafluoroisoprcpyl alcohol is added to a mixture of a stoichiometric excess of paraformaldehyde and hydrogen fluoride plus sufficient sulphuric acid to sequester most of the water formed. It is also known to produce Sevoflurane from bis(fluoromethyl)ether and hexafluoroisopropyl alcohol. WO97/25303 describes a process for the production of Sevoflurane in which essentially pure bis(fluoromethyl) ether is reacted with hexafluoroisopropyl alcohol. However, in producing Sevoflurane, by-products, unused reactants and other impurities typically are found in the reaction mixture. The type and level of any impurity depends on the process chemistry and conditions employed to produce Sevoflurane but typical impurities may include one or more of hydrogen fluoride, formaldehyde, trioxane, hexafluoroisopropanol (HFIP), bis(fluoromethyl)ether (BFME), polyethers, and fluorinated olefins, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). In addition, Sevoflurane may also undergo some decomposition either during processing or when stored for example in glass bottles prior to use. It is necessary to remove or at least reduce the level of some or all of these impurities from Sevoflurane prior to use due to the stringent requirements of purity for medical use. WO 98/32430 discloses that decomposition is thought to occur when Sevoflurane comes into contact with Lewis acids. Also, the presence of hydrogen fluoride or its formation as a decomposition product may exacerbate decomposition in glass due to the etching effect of hydrogen fluoride on glass which releases further Lewis acid and promotes further decomposition. However, US-A-5684210 discloses a process for purifying Sevoflurane in which the presence of BFME impurity has been reduced by contacting the product with' a Lewis acid, a Bronsted acid or an acidic species fixed on a resin. Especial difficulties arise in relation to impurities which have similar physical properties, for example boiling point, to the desired product as this may preclude or render difficult certain types of separation technique, for example distillation. HFIP and PFIE are both toxic and have similar boiling points to Sevoflurane and separation by distillation may present practical difficulties. Acidic species, for example hydrogen fluoride and HFIP, may be removed by washing the product with an alkaline solution. WO 99/44978 describes a process to remove HFJP from crude Sevoflurane which involves employing an aqueous alkaline wash. However, washing with alkaline solution may remove acidic impurities but may also cause the formation of olefinic impurities for example PFIE which may be difficult to separate from Sevoflurane in an efficient and economically viable manner. Removal of olefinic impurities using an amine is described in US 4328376 but this may lead to undesirable odour in the purified product. EP-A-835858 describes a purification process in which a mixture of Sevoflurane and BFME are contacted with a zeolite to remove BFME. Zeolitic materials typically contain a large number of active adsorption sites within the porous structure of the zeolite. A large proportion of the adsorption sites in the zeolite are accessed by the molecule to be adsorbed passing through pores of a certain size in the surface of the zeolite. Whether a molecule may be adsorbed accordingly depends at least in part on the size of the molecule and may lead to molecules of a comparable size being adsorbed without significant selection of one species over another. Adsorption into a zeolite may be considered, in large part, to be a physical effect based on the size and shape of the species to be adsorbed. A range of different purification processes have been developed to purify Sevoflurane but due to the number of possible impurities, some Purification measures also appear to introduce other drawbacks requiring further treatment and so leading to complexity and increased process cost. It has now been found that crude Sevoflurane containing Sevoflurane and one or more impurities may be treated to remove a range of impurities in an efficient manner by contacting the crude Sevoflurane with an adsorbent having a wide pore size distribution and, preferably, which selectively adsorbs a material by chemical rather than physical means. According to the present invention there is provided a process for the purification of fluoromethyl hexafluoroisopropyl ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsorbent having pores with a range of pore sizes whereby at least one impurity is removed from the crude compostion and recovering the crude composition depleted in the said impurity. Advantageously, the invention permits a range of impurities to be removed from Sevoflurane simultaneously. The range of pore sizes distribution of the adsorbent allows the components of the crude composition to come into contact with the adsorbent sites whereby at least one impurity in the crude composition is adsorbed. It is believed that the adsorbent may be able to preferentially adsorb one component rather than another due to selective chemisorption. Use of an adsorbent as described suitably provides the practical advantage of enabling crude Sevoflurane to be purified in a single purification step depending on the impurities in the crude composition and does not introduce further complications which require additional downstream processing. If desire, additional purification techniques known in the art may be employed in addition to that of the present invention either upstream or downstream of contacting with the adsorbent, Suitably the pores in the adsorbent have a pore size distribution of at least Inm and preferably at least 2nm. Thus the adsorbent contains pores across a range from pore size "a" to pore size "b" in which the difference between "a" and "b" is at least 1 and preferably at least 2nm. Preferably at least some of the pores in the adsorbent have a pore size across a range of 1.5 to 2.5nm and desirably across a range of 1 to 3nm. Desirably at least 50% by volume of the pores have a pore size across a range of 1 to 3nm. Further, the adsorbent suitably comprises micropores having a pore Size across the range 1 to 3nm and macropores having a pore size across the range 3 to lOOOOnm, The adsorbents suitable for use in the process of the present invention are distinguished from zeolites in that, as a bulk material, the adsorbent has pores of a size across a broad range so that a plot of distribution of pore sizes suitably provide a "bell shaped" plot whereas zeolites typically have pores of a size across a very narrow range and a plot of distribution of pore sizes on a comparable scale typically provides a "needle-shaped" plot. It is the range of pore sizes in the adsorbents suitable for use in he present process which enable components of comparable molecular sizes to be separated. The adsorbent may comprise a form of silica, alumina, carbon or mixtures thereof. It is especially preferred that the adsorbent be in activated form. Carbon, desirably in activated form as activated carbon or activated charcoal is especially preferred. The adsorbent may be acidic, basic or neutral. If desired, the adsorbent may additionally comprise a zeolite. It has further been found that a crude Sevoflurance composition may be treated to remove at least one impurity by contacting with an adsorbent comprising carbon. In a preferred embodiment of the invention, there is provided a process for the purification of fluoromethyl hexafluoroisopropyl ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsoAent having a pore size distribution of at least Inm and preferably at least 2nm and at least 50% by volume of the pores, have a pore size across a range of 1 to 3nm. It has been found that carbon in various forms is especially advantageous due to the preferential adsorption of impurities in a crude Sevoflurane composition and especially the preferential adsorption of olefinic impurities, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). In addition, Lewis acids employed as adsorbents may disadvantageously promote the degradation of Sevoflurane whereas carbon adsorbents do not • introduce such drawbacks. It is believed that the preferential adsorption takes place due to selective chemisorption arising because of the different chemical structures of the components to in the crude composition. Where a mixture of adsorbent materials is employed, they may be employed as separate adsorption materials with which the crude Sevoflura'ne composition is contacted sequentially or as a mixture and preferably a generally homogeneous mixture. If the purification process is operated continuously, the adsorbent suitably is arranged as an adsorbent bed through which the crude composition is passed and the bed may comprise, in the case of a mixture of adsorbent materials a homogeneous bed of the mixed adsorbents or a multi-layered bed in which different layers are made primarily from different adsorbent materials. In a batch process, the adsorbent materials may be added together to the batch process or sequentially. The process according to the invention may be operated as a part of a production process in which crude Sevoflurane is manufactured and passed to the purification step or, as desired, is also applicable to the treatment of Sevoflurane which has been stored for a period of time and contains sufficient impurities not to meet the desired specification for instance, for medical use. Sevoflurane which has been stored and contains impurities may, in the context of the present invention, be considered as crude Sevoflurane even if it has previously been subjected to a purification process. The crude Sevoflurane composition contains one or more impurities which may include one or more of hydrogen fluoride, formaldehyde, trioxane, parafo.rmaldehyde, hexafluoroisopropanol (HFIP), bis(fluoromethyl) ether (BFME), a polyether, and a fluorinated olefin, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). The invention is especially beneficial in removing olefinic impurities from the crude Sevoflurane. In a further aspect, the invention provides for use of an adsorbent having a pore size distribution of at least 1 run preferably comprising carbon in the purification of a crude composition comprising fluoromethyl hexafluoroisopropy! ether and an olefmic impurity, preferably pentafiubroisopropenyl fluoromethyl ether (PFIE), to produced purified fluoromethy) hexafluoroisopropy I ether. The quantity of adsorbent employed may be selected according to the "level of impurities in the crude Sevoflurane. The level of adsorbent is not especially criticaJ although efficacy of purification and cost are factors which may affect the specific level of adsorbent used. By way of guidance the level of adsorbent may be up to 100% w/w of Sevofiurane in the crude composition although a level of 0.1 to 50% by weight, preferably from 1 to 50% by weight or even 2 to 30% by weight of the quantity of Sevoflurane in the crude Sevofiurane mixture. The crude Sevoflurane is suitably contacted with the adsorbent for a period sufficient to remove or reduce impurities to a pre-determined level according to the manner in which the process is operated. Where the process is conducted in the gaseous phase, the contact time with the adsorbent is suitably of the order of seconds, preferably 1 to 120 seconds and more preferably 2 to 60 seconds. For a continuous liquid phase process, the contact time suitably is of the order of 1 to 45 minutes and preferably 2 to 30 minutes. In a batch liquid phase process the contact time may be up to 24 hours, preferably 1 to 10 hours and especially 2 to 6 hours. The temperature at which the.crude Sevoflurane and carbon are contacted may be elevated or below ambient but, preferably is at ambient temperature to avoid introducing complexity into that part of the process. The crude Sevoflurane may be contacted with the adsorbent in batch-wise fashion or in a continuous process as desired. In a preferred embodiment, the invention provides a process which comprises producing a crude composition comprising fluoromethyl hexafluoroisopfopyl ether and at least one impurity, contacting the crude composition with an absorbent comprising carbon so as to remove at least some of the at least one impurity from the crude composition, suitably to achieve a pre-determined specification, and recovering fluoromethyl hexafluoroisopropyl ether from the crude composition. The crude composition comprising Sevoflurane. may be produced by any known route for example by reacting formaldehyde whether as such or in another known form, for example a polymeric form of formaldehyde such as paraformaldehyde or trioxane, with hydrogen fluoride and HFIP. Preferably however, the crude Sevoflurane is produced by reacting BFME with HFIP. Optimally, the crude composition is produced in the presence of an acid, preferably a Bronsted or Lewis acid, for example sulphuric acid. The reaction between the bis(fluorometfiyl) ether and the hexafluoroisopropyl alcohol is conveniently carried out at a temperature of less than 50°C, preferably 10 to 50°C especially 10 to 35°C. Suitably the reaction is carried out at atmospheric pressure, although if desired subatmospheric or superatmospheric pressure.. The reaction is preferably carried out in the presence of an acid preferably a Lewis or Bronsted acid for example sulphuric acid. If used, BFME may be employed as is without purification and advantageously enables the operation of an integrated process including the production of BFME and its direct use as a feedstock to produce Sevoflurane. Alternatively, BFME may be treated so as to purify it partly or wholly prior to use in the production of Sevoflurane. If desired, bis(fluoromethyl) ether may be separated from the reaction mixture and treated to produce essentially pure bis(fluorometh'yl) ether which may then be reacted with hexafluoroisopropyl alcohol to produce fluorqrnethylhexafluoroisopropylether. Formaldehyde and/or hydrogen fluoride may;be fed to the process of the invention in addition to BFME and HFIP as desired. The process for the production of the crude composition may be operated as a batch or continuous process or a combination thereof but is preferably operated as a batch process. The bis(fluoromethyl) ether may be produced by reaction of formaldehyde or a known form of it with hydrogen fluoride. Any of the known methods for production of the bis(fluoromethyl) ether may be employed as the ether formation step. The production of bis(fluoromethyl) ether from formaldehyde and hydrogen fluoride is described, for example, in EP-A-518506 and in WO 93/10070,'WO 93/12057 and WO 93/22265, for example. The disclosures of these publications are incorporated herein by reference. The ether production process described in WO 93/10070 is especially preferred and comprises reacting formaldehyde with hydrogen fluoride in a reaction-distillation column from which the ether is withdrawn in essentiafly pure form and in particular essentially free from water. The invention is illustrated but in now way limited by the following Examples Example Crude Sevoflurane (2.0 ml) containing PF1E at a level of about SOOppm by weight and other trace impurities was mixed with activated carbon (0.20 g) (Carbon Norit RO 1/16 inch (1.56mm) extrudates) for 2 hours at ambient temperature and pressure. The treated product was then analysed by gas chromatography and compared with the analysis of the untreated product. The carbon treatment successfully reduced the level of PFIE by at least 75% and significantly reduced the level of other impurities. We claim: 1. A process "for the purification of fluoromethyl hexafluoroisopropyl ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity such as herein described with an adsorbent having pores ' with a range of pore- sizes such as herein described whereby at least one impurity is removed from the crude composition, and recovering the crude composition depleted in the said impurity. 2. A process as claimed in claim 1 wherein the pore size distribution is at least Inm, preferably at least 2 nm. 3. A process as claimed in claim 1 or 2 wherein at least some of the pores in the adsorbent have a pore size across a range of 1.5 to 2.5nm. 4. A process as claimed in any preceding claim wherein at least 50% by volume of the pores have a pore size across a range of 1 to 3nm. 5. A process as claimed in any preceding claim wherein the adsorbent comprises micropores having a pore size across the range 1 to 3 nm and macropores having a pore size across the range 3 to lOOOOnm. 6. A process as claimed in any preceding claim •wherein the adsorbent is selected from the group consisting of silica, alumina, carbon and mixtures thereof, preferably carbon. 7. A process as claimed in claim 6 wherein the adsorbent is selected from activated carbon and activated charcoal. 8. A process as claimed in any preceding claim wherein the impurity in the crude composition comprises one or more of hydrogen fluoride, formaldehyde, paraformaldehyde, trioxane, hexafluoroisopropanol, bis (fluoromethyl) ether, a polyether, and/or a fluorinated olefins. 9. A process as claimed in any preceding claim wherein the level of adsorbent is from 0.1 to 50% by weight of the quantity of fluoromethyl hexafluoroisopropyl ether in the crude composition. 10. A process as claimed in any preceding claim wherein the crude composition is produced by contacting formaldehyde or a polymeric form thereof with hydrogen fluoride/and hexafluoroisopropyl alcohol. ' . 11. A process as claimed in any of preceding claims 1 to 9 wherein the crude composition is produced by reacting bisfluoromethyl ether and hexafluoroisopropyl alcohol together in the presence of an acid such as herein described. 12. A process as claimed in claim 13 wherein the bis (fluoromethyl) ether and the hexafluoroisopropyl alcohol are reacted together at a temperature of less than 50°C. 13. A process as claimed in any one of claims 11 and 12 wherein the bis(fluoromethyl) ether is essentially pure. 14. A process of reducing the level or removing -an olefinic impurity from a composition comprising a fluorinated' olefin impurity and fluoromethyl hexafluoroisopropyi ether' which comprises contacting the composition with an adsorbent comprising carbon and recovering the composition depleted in the impurity. 15. A process as claimed in claim 14 wherein the olefinic impurity is pentafluoroisopropenyl fluoromethyl ether.

Full Text

The present invention relates to a process for the purification of fluoromethyl hexafluoroisopropyl ether. The present invention particularly provides a process for the purification of an ether of the formula CH2FOCH(CF3)2 which has anaesthetic properties and is known as 'Sevoflurane'.
It is known that Sevoflurane may be produced by the reaction of formaldehyde, hydrogen fluoride and hexafluoroisopropyl alcohol (CF3) 2CHOH (HFIP). For example, US 4,250,334 describes a process in which hexafluoroisoprcpyl alcohol is added to a mixture of a stoichiometric excess of paraformaldehyde and hydrogen fluoride plus sufficient sulphuric acid to sequester most of the water formed. It is also known to produce Sevoflurane from bis(fluoromethyl)ether and hexafluoroisopropyl alcohol. WO97/25303 describes a process for the production of Sevoflurane in which essentially pure bis(fluoromethyl) ether is reacted with hexafluoroisopropyl alcohol.
However, in producing Sevoflurane, by-products, unused reactants and other impurities typically are found in the reaction mixture. The type and level of any impurity depends on the process chemistry and conditions employed to produce Sevoflurane but typical impurities may include one or more of hydrogen fluoride, formaldehyde, trioxane, hexafluoroisopropanol (HFIP), bis(fluoromethyl)ether (BFME), polyethers, and fluorinated olefins, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). In addition, Sevoflurane may also undergo some decomposition either during processing or when stored for example in glass bottles prior to use.
It is necessary to remove or at least reduce the level of some or all of these impurities from Sevoflurane prior to use due to the stringent requirements of purity for medical use.
WO 98/32430 discloses that decomposition is thought to occur when Sevoflurane comes into contact with Lewis acids. Also, the presence of hydrogen fluoride or its formation as a decomposition product may exacerbate decomposition in glass due to the etching effect of hydrogen fluoride on glass

which releases further Lewis acid and promotes further decomposition. However, US-A-5684210 discloses a process for purifying Sevoflurane in which the presence of BFME impurity has been reduced by contacting the product with' a Lewis acid, a Bronsted acid or an acidic species fixed on a resin.
Especial difficulties arise in relation to impurities which have similar physical properties, for example boiling point, to the desired product as this may preclude or render difficult certain types of separation technique, for example distillation. HFIP and PFIE are both toxic and have similar boiling points to Sevoflurane and separation by distillation may present practical difficulties. Acidic species, for example hydrogen fluoride and HFIP, may be removed by washing the product with an alkaline solution. WO 99/44978 describes a process to remove HFJP from crude Sevoflurane which involves employing an aqueous alkaline wash. However, washing with alkaline solution may remove acidic impurities but may also cause the formation of olefinic impurities for example PFIE which may be difficult to separate from Sevoflurane in an efficient and economically viable manner. Removal of olefinic impurities using an amine is described in US 4328376 but this may lead to undesirable odour in the purified product.
EP-A-835858 describes a purification process in which a mixture of Sevoflurane and BFME are contacted with a zeolite to remove BFME. Zeolitic materials typically contain a large number of active adsorption sites within the porous structure of the zeolite. A large proportion of the adsorption sites in the zeolite are accessed by the molecule to be adsorbed passing through pores of a certain size in the surface of the zeolite. Whether a molecule may

be adsorbed accordingly depends at least in part on the size of the molecule and may lead to molecules of a comparable size being adsorbed without significant selection of one species over another. Adsorption into a zeolite may be considered, in large part, to be a physical effect based on the size and shape of the species to be adsorbed.
A range of different purification processes have been developed to purify Sevoflurane but due to the number of possible impurities, some

Purification measures also appear to introduce other drawbacks requiring further treatment and so leading to complexity and increased process cost.
It has now been found that crude Sevoflurane containing Sevoflurane and one or more impurities may be treated to remove a range of impurities in an efficient manner by contacting the crude Sevoflurane with an adsorbent having a wide pore size distribution and, preferably, which selectively adsorbs a material by chemical rather than physical means.
According to the present invention there is provided a process for the purification of fluoromethyl hexafluoroisopropyl ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsorbent having pores with a range of pore sizes whereby at least one impurity is removed from the crude compostion and recovering the crude composition depleted in the said impurity.
Advantageously, the invention permits a range of impurities to be removed from Sevoflurane simultaneously. The range of pore sizes distribution of the adsorbent allows the components of the crude composition to come into contact with the adsorbent sites whereby at least one impurity in the crude composition is adsorbed. It is believed that the adsorbent may be able to preferentially adsorb one component rather than another due to selective chemisorption. Use of an adsorbent as described suitably provides the practical advantage of enabling crude Sevoflurane to be purified in a single purification step depending on the impurities in the crude composition and does not introduce further complications which require additional downstream processing. If desire, additional purification techniques known in the art may be employed in addition to that of the present
invention either upstream or downstream of contacting with the adsorbent,

Suitably the pores in the adsorbent have a pore size distribution of at least Inm and preferably at least 2nm. Thus the adsorbent contains pores across a range from pore size "a" to pore size "b" in which the difference between "a" and "b" is at least 1 and preferably at least 2nm.
Preferably at least some of the pores in the adsorbent have a pore size across a range of 1.5 to 2.5nm and desirably across a range of 1 to 3nm. Desirably at least 50% by volume of the pores have a pore size across a range of 1 to 3nm.
Further, the adsorbent suitably comprises micropores having a pore Size across the range 1 to 3nm and macropores having a pore size across the range 3 to lOOOOnm,
The adsorbents suitable for use in the process of the present invention are distinguished from zeolites in that, as a bulk material, the adsorbent has pores of a size across a broad range so that a plot of distribution of pore sizes suitably provide a "bell shaped" plot whereas zeolites typically have pores of a size across a very narrow range and a plot of distribution of pore sizes on a comparable scale typically provides a "needle-shaped" plot. It is the range of pore sizes in the adsorbents suitable for use in he present process which enable components of comparable molecular sizes to be separated.
The adsorbent may comprise a form of silica, alumina, carbon or mixtures thereof. It is especially preferred that the adsorbent be in activated form. Carbon, desirably in activated form as activated carbon or activated charcoal is especially preferred. The adsorbent may be acidic, basic or neutral. If desired, the adsorbent may additionally comprise a zeolite.
It has further been found that a crude Sevoflurance composition may be treated to remove at least one impurity by contacting with an adsorbent comprising carbon.
In a preferred embodiment of the invention, there is provided a process for the purification of fluoromethyl hexafluoroisopropyl ether which comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity with an adsoAent having a pore size distribution of at least Inm and preferably at least 2nm and at least 50% by volume of the pores, have a pore size across a range of 1 to 3nm.
It has been found that carbon in various forms is especially advantageous due to the preferential adsorption of impurities in a crude Sevoflurane composition and especially the preferential adsorption of olefinic
impurities, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). In addition, Lewis acids employed as adsorbents may disadvantageously promote the degradation of Sevoflurane whereas carbon adsorbents do not • introduce such drawbacks.
It is believed that the preferential adsorption takes place due to selective chemisorption arising because of the different chemical structures of the components to in the crude composition.
Where a mixture of adsorbent materials is employed, they may be employed as separate adsorption materials with which the crude Sevoflura'ne composition is contacted sequentially or as a mixture and preferably a generally homogeneous mixture. If the purification process is operated continuously, the adsorbent suitably is arranged as an adsorbent bed through which the crude composition is passed and the bed may comprise, in the case of a mixture of adsorbent materials a homogeneous bed of the mixed adsorbents or a multi-layered bed in which different layers are made primarily from different adsorbent materials. In a batch process, the adsorbent materials may be added together to the batch process or sequentially.
The process according to the invention may be operated as a part of a production process in which crude Sevoflurane is manufactured and passed to the purification step or, as desired, is also applicable to the treatment of Sevoflurane which has been stored for a period of time and contains sufficient impurities not to meet the desired specification for instance, for medical use. Sevoflurane which has been stored and contains impurities may, in the context of the present invention, be considered as crude Sevoflurane even if it
has previously been subjected to a purification process.

The crude Sevoflurane composition contains one or more impurities
which may include one or more of hydrogen fluoride, formaldehyde, trioxane, parafo.rmaldehyde, hexafluoroisopropanol (HFIP), bis(fluoromethyl) ether (BFME), a polyether, and a fluorinated olefin, for example pentafluoroisopropenyl fluoromethyl ether (PFIE). The invention is especially beneficial in removing olefinic impurities from the crude Sevoflurane.

In a further aspect, the invention provides for use of an adsorbent having a pore size distribution of at least 1 run preferably comprising carbon in the purification of a crude composition comprising fluoromethyl hexafluoroisopropy! ether and an olefmic impurity, preferably pentafiubroisopropenyl fluoromethyl ether (PFIE), to produced purified fluoromethy) hexafluoroisopropy I ether.
The quantity of adsorbent employed may be selected according to the "level of impurities in the crude Sevoflurane. The level of adsorbent is not especially criticaJ although efficacy of purification and cost are factors which may affect the specific level of adsorbent used. By way of guidance the level of adsorbent may be up to 100% w/w of Sevofiurane in the crude composition although a level of 0.1 to 50% by weight, preferably from 1 to 50% by weight or even 2 to 30% by weight of the quantity of Sevoflurane in the crude Sevofiurane mixture.
The crude Sevoflurane is suitably contacted with the adsorbent for a period sufficient to remove or reduce impurities to a pre-determined level according to the manner in which the process is operated. Where the process is conducted in the gaseous phase, the contact time with the adsorbent is suitably of the order of seconds, preferably 1 to 120 seconds and more preferably 2 to 60 seconds. For a continuous liquid phase process, the contact time suitably is of the order of 1 to 45 minutes and preferably 2 to 30 minutes. In a batch liquid phase process the contact time may be up to 24 hours, preferably 1 to 10 hours and especially 2 to 6 hours. The temperature at which the.crude Sevoflurane and carbon are contacted may be elevated or below ambient but, preferably is at ambient temperature to avoid introducing complexity into that part of the process.
The crude Sevoflurane may be contacted with the adsorbent in batch-wise fashion or in a continuous process as desired.
In a preferred embodiment, the invention provides a process which comprises producing a crude composition comprising fluoromethyl hexafluoroisopfopyl ether and at least one impurity, contacting the crude composition with an absorbent comprising carbon so as to remove at least

some of the at least one impurity from the crude composition, suitably to achieve a pre-determined specification, and recovering fluoromethyl hexafluoroisopropyl ether from the crude composition.
The crude composition comprising Sevoflurane. may be produced by any known route for example by reacting formaldehyde whether as such or in another known form, for example a polymeric form of formaldehyde such as paraformaldehyde or trioxane, with hydrogen fluoride and HFIP. Preferably however, the crude Sevoflurane is produced by reacting BFME with HFIP. Optimally, the crude composition is produced in the presence of an acid, preferably a Bronsted or Lewis acid, for example sulphuric acid. The reaction between the bis(fluorometfiyl) ether and the hexafluoroisopropyl alcohol is conveniently carried out at a temperature of less than 50°C, preferably 10 to 50°C especially 10 to 35°C. Suitably the reaction is carried out at atmospheric pressure, although if desired subatmospheric or superatmospheric pressure.. The reaction is preferably carried out in the presence of an acid preferably a Lewis or Bronsted acid for example sulphuric acid.
If used, BFME may be employed as is without purification and advantageously enables the operation of an integrated process including the production of BFME and its direct use as a feedstock to produce Sevoflurane. Alternatively, BFME may be treated so as to purify it partly or wholly prior to use in the production of Sevoflurane. If desired, bis(fluoromethyl) ether may be separated from the reaction mixture and treated to produce essentially pure bis(fluorometh'yl) ether which may then be reacted with hexafluoroisopropyl alcohol to produce fluorqrnethylhexafluoroisopropylether. Formaldehyde and/or hydrogen fluoride may;be fed to the process of the invention in addition to BFME and HFIP as desired.
The process for the production of the crude composition may be operated as a batch or continuous process or a combination thereof but is preferably operated as a batch process.
The bis(fluoromethyl) ether may be produced by reaction of formaldehyde or a known form of it with hydrogen fluoride. Any of the known

methods for production of the bis(fluoromethyl) ether may be employed as the ether formation step. The production of bis(fluoromethyl) ether from formaldehyde and hydrogen fluoride is described, for example, in EP-A-518506 and in WO 93/10070,'WO 93/12057 and WO 93/22265, for example. The disclosures of these publications are incorporated herein by reference. The ether production process described in WO 93/10070 is especially preferred and comprises reacting formaldehyde with hydrogen fluoride in a reaction-distillation column from which the ether is withdrawn in essentiafly pure form and in particular essentially free from water.
The invention is illustrated but in now way limited by the following Examples
Example
Crude Sevoflurane (2.0 ml) containing PF1E at a level of about SOOppm by weight and other trace impurities was mixed with activated carbon (0.20 g) (Carbon Norit RO 1/16 inch (1.56mm) extrudates) for 2 hours at ambient temperature and pressure. The treated product was then analysed by gas chromatography and compared with the analysis of the untreated product. The carbon treatment successfully reduced the level of PFIE by at least 75% and significantly reduced the level of other impurities.

We claim:
1. A process "for the purification of fluoromethyl hexafluoroisopropyl ether which
comprises contacting a crude composition comprising fluoromethyl hexafluoroisopropyl ether and at least one impurity such as herein described with an adsorbent having pores ' with a range of pore- sizes such as herein described whereby at least one impurity is removed from the crude composition, and recovering the crude composition depleted in the said impurity.
2. A process as claimed in claim 1 wherein the pore size distribution is at least Inm,
preferably at least 2 nm.
3. A process as claimed in claim 1 or 2 wherein at least some of the pores in the adsorbent
have a pore size across a range of 1.5 to 2.5nm.
4. A process as claimed in any preceding claim wherein at least 50% by volume of the pores
have a pore size across a range of 1 to 3nm.
5. A process as claimed in any preceding claim wherein the adsorbent comprises
micropores having a pore size across the range 1 to 3 nm and macropores having a pore
size across the range 3 to lOOOOnm.
6. A process as claimed in any preceding claim •wherein the adsorbent is selected from the
group consisting of silica, alumina, carbon and mixtures thereof, preferably carbon.
7. A process as claimed in claim 6 wherein the adsorbent is selected from activated carbon
and activated charcoal.
8. A process as claimed in any preceding claim wherein the impurity in the crude
composition comprises one or more of hydrogen fluoride, formaldehyde,
paraformaldehyde, trioxane, hexafluoroisopropanol, bis (fluoromethyl) ether, a
polyether, and/or a fluorinated olefins.
9. A process as claimed in any preceding claim wherein the level of adsorbent is from 0.1 to
50% by weight of the quantity of fluoromethyl hexafluoroisopropyl ether in the crude
composition.

10. A process as claimed in any preceding claim wherein the crude composition is produced
by contacting formaldehyde or a polymeric form thereof with hydrogen fluoride/and
hexafluoroisopropyl alcohol. ' .
11. A process as claimed in any of preceding claims 1 to 9 wherein the crude composition is
produced by reacting bisfluoromethyl ether and hexafluoroisopropyl alcohol together in
the presence of an acid such as herein described.
12. A process as claimed in claim 13 wherein the bis (fluoromethyl) ether and the
hexafluoroisopropyl alcohol are reacted together at a temperature of less than 50°C.
13. A process as claimed in any one of claims 11 and 12 wherein the bis(fluoromethyl) ether
is essentially pure.
14. A process of reducing the level or removing -an olefinic impurity from a composition
comprising a fluorinated' olefin impurity and fluoromethyl hexafluoroisopropyi ether'
which comprises contacting the composition with an adsorbent comprising carbon and
recovering the composition depleted in the impurity.
15. A process as claimed in claim 14 wherein the olefinic impurity is pentafluoroisopropenyl
fluoromethyl ether.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=0LkIExrWGwu9ay65crT/bg==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

279850

Indian Patent Application Number

7699/DELNP/2007

PG Journal Number

05/2017

Publication Date

03-Feb-2017

Grant Date

31-Jan-2017

Date of Filing

08-Oct-2007

Name of Patentee

INEOS FLUOR HOLDINGS LIMITED

Applicant Address

P.O.BOX 13, THE HEATH RUNCORN CHESHIRE, WA7 4QF, UK

Inventors:

#	Inventor's Name	Inventor's Address
1	SHARRATT, ANDREW, PAUL	11 WHITEHALL DRIVE HARTFORD, NORTH-WICH, CHESHIRE CW8 1SJ, GREAT BRITAIN
2	CORR, STUART	31 FOXHILLS, CLOSE, APPLETON, WARRINGTON, CHESHIRE WA4 5DH, UK

PCT International Classification Number

C07C 41/36

PCT International Application Number

PCTGB01/05727

PCT International Filing date

2001-12-21

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0031303.1	2000-12-21	U.K.