This application claims priority to European application No. 12187801.1 filed 09 October 2012, the whole content of this application being incorporated herein by reference for all purposes.

The present invention concerns a method for the preparation of certain purified fluorosubstituted organic carbonates.

Fluorinated linear and cyclic carbonates, e.g. monofluoroethylene carbonate, fluoromethyl methyl carbonate, difluoroethylene carbonate and difluorinated dimethyl carbonate, but also the respective tri- and tetrafluorinated carbonates, are especially suitable as solvents or solvent additives for lithium ion batteries.

Generally, fluorosubstituted organic carbonates can be prepared by the reaction of aliphatic linear or cyclic carbonates which are not substituted by F, or which have at least one substitutable H atom with elemental fluorine.

Monofluoroethylene carbonate, for example, can be prepared from the respective unsubstituted ethylene carbonate by the reaction of 1 ,3-dioxolane-2- one (ethylene carbonate ; "EC") with elemental fluorine. This is described for example in JP-A 2000-309583 where the reaction is performed with a melt of EC or its solution in anhydrous fluoride. Optionally, perf uorohexane may be present ; in this case, a suspension of l,3-dioxolane-2-one - the starting material - is formed. According to US patent application publication 2006-0036102, ethylene carbonate is dissolved in F1EC and then is contacted with diluted fluorine. According to US patent US-A 7,268,238, the reaction is performed in a reactor with Raschig rings to provide a suitable bubble size of the diluted fluorine gas. According to the state of the art, the fluorination reactions and the isolation of the product were performed in batch processes.

WO 2011/036283 describes a process for the manufacture of

difluoroethylene carbonate, trifluoroethylene carbonate and/or

tetrafluoroethylene carbonate or a mixture of two or more thereof by reaction of an ethylene carbonate which is nonf uorinated or has a lower degree of fluorination, in the liquid phase with elemental fluorine (F ₂ ) to form

tetrafluoroethylene carbonate. WO 2009/118369 describes that mixtures with depleted hydrogen fluoride content are prepared from a mixture comprising organic carbonate, preferably fluorinated organic carbonate, and hydrogen fluoride by stripping HF from the mixture by passing inert gas through the mixture. Noble gases or their mixtures with nitrogen or carbon dioxide or its mixtures with nitrogen are also suitable as inert gas for stripping ; air also might be suitable, but it is not preferred.

Nitrogen is especially suitable as stripping gas.

WO 2009/118368 provides a process for the preparation of

fluorosubstituted organic carbonate which is depleted in HF wherein an

HF-contaminated fluorinated organic carbonate comprising at least one CH-CF group in the molecule, is contacted with an inorganic reactant comprising Si02, forming a mixture of a solid and HF-depleted fluorinated organic carbonate, and the resulting HF-depleted fluorosubstituted organic carbonate is separated from the solid. It is preferred to use solids with high surface area, especially amorphous solid silica or silica containing compounds. Silica gel is very preferred. The high surface of such gels (which can be applied in the form of shaped bodies, e.g. in the form of beads) provides for a fast HF-removing reaction.

WO 2011/020830 provides a process for the purification of a reaction mixture comprising fluoroethylene carbonate, ethylene carbonate, higher fluorinated ethylene carbonate or carbonates and hydrogen fluoride and optionally trace impurities (for example, trifluoroethylene carbonate) which is distilled in at least two distillation steps wherein the reaction mixture which is fed to the first distillation step contains not more than 5 % by weight of HF. Preferably, the reaction mixture which is fed to the first distillation column contains nor more than 1 % by weight of HF. The purified fluoroethylene carbonate obtained is so pure, especially in view of the HF content, that no recrystallization is needed.

It was observed, however, that even after treating the crude products for the removal of HF by adsorption, stripping and/or distillation, HF is set free in the treated product.

Object of the present invention is to provide a method for the preparation of purified fluorosubstituted organic carbonates. This object and other objects which are apparent from the description and the claims are achieved by the process of the present invention. The present invention concerns a method for the preparation of a purified fluorinated organic carbonate comprising at least one step wherein the fluorinated organic carbonate containing impurities is contacted with a treatment agent selected from the group consisting of organic compounds having the formula (I), R-H, wherein the compound of formula (I) reacts with compounds having the group -C(0)F under formation of -C(0)R, and at least one step wherein purified fluorinated organic carbonate is isolated.

The at least one step of isolation preferably includes at least one step of distillation.

The agent of formula (I) probably forms a C-(0)-R group when reacted with a C-(0)-F group.

In the frame of the present invention, the singular form is intended to include the plural form ; and the plural form is intended to include the singular form. Thus, the term "purified fluorinated organic carbonate" is not limited to a single carbonate compound, but includes a composition comprising two or more fluorinated carbonates including isomeric forms.

The compounds of formula (I) should be essentially or completely unreactive towards fluorinated organic carbonates under the reaction, especially in view of temperature and reaction time at which the method of the invention is performed so that no undesired amounts of impurities are formed ; especially of impurities which cannot be separated or are difficult to separate during the at least one isolating step.

Water, H ₂ S or Ν¾ can be applied as treatment agent ; but they are not preferred treatment agents, and if they are applied, the treatment should be as short as possible, e.g. shorter than 5 minutes.

Preferred compounds of formula (I) are selected from the group consisting of organic compounds and include at least one OH group, NH group or SH group. Typical treatment agents are selected from the group of alkanols, alkandiols, alkane trio Is, ammonia, monoalkyl amines, dialkyl amines, and alkane thiols. These treatment agents are preferred. It is possible to apply mixtures of more than one treatment agent from this group.

Especially preferred treatment agents are selected from the group consisting of alkanols with 1 to 3 carbon atoms, alkandiols with a C2 or C3 alkylene backbone, monoakyl amines wherein the term alkyl denotes a C 1 to C3 group, and dialkyl amines wherein the alkyl groups are the same or different and denote CI to C3 alkyl. Methanol, ethanol, methylamine, dimethylamine, ethylamine, diethylamine, methane thiol and ethane thiol are especially preferred, and methanol is outstanding as treatment agent.

Preferably, the agent of formula (I) is an alcohol or amine.

Preferably, R is selected from the group consisting of R ^a O and R^R ^C N wherein R ^a is selected from linear and branched alkyl groups with 1 to 10 carbon atoms ; linear and branched alkyl groups with 1 to 10 carbon atoms, substituted by at least one halogen atom, at least one hydroxy group, at least one nitro group and/or at least one nitrile group ; linear and branched alkenyl groups with 2 to 10 carbon atoms ; linear and branched alkyl groups with 1 to 10 carbon atoms, substituted by at least one halogen atom, at least one hydroxy group, at least one nitro group and/or at least one nitrile group ; cyclic alkylene groups having 3 to 10 carbon atoms ; cyclic alkylene groups having 3 to 10 carbon atoms substituted by at least one alkyl group with 1 to 5 carbon atoms ; at least one halogen atom, at least one hydroxy group, at least one nitro group and/or at least one nitrile group ; and wherein R^ and R ^c are the same and denote CI to C6 alkyl ; a cyclic C3 to C6 alkylene group ; a saturated or unsaturated heterocyclic ring with 5 to 8 members wherein the N is incorporated in the ring. Polyols and polyamines are also useful treatment agents.

For example, alkylamines and dialkylamines are suitable purifying agents, for example, methyl amine, dimethylamine, ethyl amine, diethyl amine, or methyl ethylamine.

Alcohols are especially preferred as purifying agents. An alcohol compound can be applied in combination with an amine compound but it is preferred to apply only one or more purifying agents selected from the group of alcohols.

Alcohols having one, two or three OH groups can be applied. For example, CI to C5 alcohols with one OH group, C2 to C5 diols or C3 to C6 triols are suitable. R ^a is preferably selected from the group consisting of methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, hydroxymethoxy and hydroxy ethoxy.

Methanol, ethanol, n-propanol and isopropanol are preferably applied as purifying agents.

The amount of the purifying agent should relate approximately to the amount of impurity or impurities to be removed. The amount may be estimated according to experience. Alternatively, the end point for the addition of the purifying agent can be determined by physical or chemical methods. For example, by gas chromatography, NIR or MIR. Often, the addition of the purifying agent such that its amount relative to the reaction mixture to be treated is 0.01 to 5 % by weight. Also water, NH ₃ or H ₂ S, if applied in an amount of from 0.01 to 5 % by weight relative to the total weight of the carbonate to be purified, are suitable purifying agents albeit less preferred than the other compounds mentioned above. Water, if applied in such a low amount, is not considered to be used as washing agent, e.g. to remove HF present, but in the context of the present invention, it is used as a purifying agent which acts by a chemical reaction. Nevertheless, alcohols as mentioned above are preferred purifying agents.

The purifying agent can be added to the crude reaction mixture or, preferably, to the pre-purified product. The agent can be contacted with the crude mixture or the pre-purified product in a batch reactor. Preferably, it is added directly to the bottom of a distillation column.

The method of the invention is especially suitable for the purification of fluorosubstituted organic carbonates which had been produced by reaction of aliphatic linear or branched organic carbonates as starting compounds with elemental fluorine.

The fluorination reaction can be performed batch wise or continuously ; it provides a crude reaction mixture. Fluorine, preferably diluted by nitrogen, is dispersed in gaseous form into the liquid carbonate. Thus, the process of the invention is a 2-phase process. Fluorine is introduced in diluted form to improve the safety of the process, and because a lot of reaction heat is generated which will be too high if pure fluorine would be applied.

Such processes are, for example, described in WO 2011/036281 which describes a continuously performed fluorination process, or in US patent application publication 2006-0036102. In one alternative, the aliphatic linear or branched organic carbonates used as starting material may not be substituted by F atoms, and after the reaction with elemental fluorine, the respective reaction product comprises fluorinated organic carbonates which are substituted by at least 1 F atom up to being perfluorinated. In another alternative, the aliphatic linear or branched organic carbonates used as starting material are substituted by at least 1 F atom and comprise at least 1 H atom, and after reaction with elemental fluorine, the respective reaction product comprises fluorinated organic carbonates which are substituted by at least 2 F atoms up to being perfluorinated. The inventors assume that a undesired impurity is present in the reaction mixture which may comprise a C(0)F group. Such a group tends to split off HF when it comes into contact with moisture. The agent of formula (I) forms a C-(0)-R group when reacted with a C-(0)-F group.

The foregoing is only a tentative explanation, and the inventors do not wish to be bound by it.

Now, fluorosubstituted organic carbonates which can be purified according to the present method are described.

According to one alternative, fluorosubstituted aliphatic linear or branched organic carbonates can be purified according to the method of the invention.

Especially, fluorosubstituted organic carbonates of formula (I), (R ¹ 0)(R ² 0)C(0) can be purified. In formula (I), R ¹ and R ² may be the same or different. R ¹ and R ² are linear alkyl or branched alkyl with the proviso that at least one of R and R ² is substituted by at least 1 F atom. The term "linear alkyl" preferably denotes a CI to C5 alkyl group or a CI to C5 alkyl group substituted by at least 1 F atom. The term "branched alkyl" preferably denotes a C3 to C5 alkyl group or a C3 to C5 alkyl group substituted by at least 1 F atom. A condition is that At least one of R ¹ and R ² , as mentioned above, must be substituted by at least 1 F atom. This condition will not be repeated below.

Preferably, R ¹ is methyl, fluoromethyl, difluoromethyl, trifluoromethyl, ethyl, fluoroethyl, difluoroethyl, trifluoroethyl, tetrafluoroethyl or

pentafluoroethyl, n-propyl, isopropyl, n-propyl, substituted by 1 to 7 F atoms, or i-propyl substituted by 1 to 7 F atoms. Preferably, R ² is methyl, fluoromethyl, difluoromethyl, trifluoromethyl, ethyl, fluoroethyl, difluoroethyl, trifluoroethyl, tetrafluoroethyl or pentafluoroethyl, n-propyl, isopropyl, n-propyl, substituted by 1 to 7 F atoms, or i-propyl substituted by 1 to 7 F atoms.

According to another alternative, fluorosubstituted aliphatic cyclic organic carbonates of formula (II), (OR ³ 0)C(0) are purified according to the method of the present invention. R ³ is preferably an aliphatic alkylene group having 2 to 10 C atoms and is substituted by at least 1 F atom. More preferably, R ³ is a C2 to C8 group substituted by at least 1 F atom. Especially preferably, R ³ is a C2 group substituted by 1, 2, 3 or 4 F atoms ; a linear or branched C3 group substituted by at least 1 F ; a methylpropylene group substituted by at least 1 F atom ; a dimethyl ethylene group substituted by at least 1 F atom ; an ethyl ethylene group substituted by at least 1 F atom ; a diethyl ethylene group substituted by at least 1 F atom ; or a methyl ethyl ethylene group substituted by at least 1 F atom. Preferably, in this alternative embodiment, R ³ is

monofluoroethylene, difluoroethylene, trifluoroethylene, tetrafluoroethylene, monofluoromethyl ethylene, difluoromethyl ethylene, methyl

monofluoroethylene, methyl difluoroethylene, monofluoromethyl

monofluoroethylene, monofluoromethyl difluoroethylene, difluoromethyl monofluoroethylene, difluoromethyl difluoroethylene, trif uoromethyl difluoroethylene, difluoromethyl trifluoroethylene, or trifluoromethyl trifluoroethylene. In this embodiment, R ³ is preferably monofluoroethylene, difluoroethylene, trifluoroethylene, tetrafluoroethylene, and most preferably, monofluoroethylene or difluoroethylene. "Difluoroethylene" may be a

CF ₂ C-CH ₂ group or a CFH-CFH group in cis or trans configuration.

The fluorinated organic carbonate can be provided as described, for example, in JP-A 2000-309583, US 2006-0036102, US-A 7,268,238 or

WO 2011036281.

The method of the invention can be applied to purify a fluorination product which was not yet subjected to a purifying treatment. Alternatively, it can be applied to purify a pre-purified fluorination product which had already been subjected to a pre-purification treatment to provide pre-purified fluorinated carbonate but which is considered as being not pure enough to be applied as solvent or additive for lithium ion batteries ; or it can be applied to a purified product which while it is considered as being pure enough for use as a solvent or an additive for lithium ion batteries, still forms some HF when stored or contacted with moisture.

It is preferred to first perform at least one preliminary step to remove HF from the crude reaction mixture containing the fluorinated organic carbonate obtained in a fluorination process with elemental fluorine. It is well known to the expert that in the fluorination step, for each consumed mol of F ₂ , one mol of HF is produced. Several processes are suitable for the preliminary purification to remove HF. The preferred methods comprise at least one step of stripping, at least one step of distillation, or steps of both. A process for stripping HF from a raw product is described in WO 2009/118369. An inert gas, e.g. N ₂ , is passed through the crude product to remove entrained HF. Distillation to remove is an alternative, e.g. by a multiple distillation as described in WO 2011/020830. Both methods can be combined with each other or with an adsorptive treatment to remove HF, e.g. by contact with silica. A combination of stripping and distillation is especially preferred as preliminary steps of purification.

The purifying agent is preferably added after the pre purification step mentioned above to remove a major part of present HF, and it is preferably added before a final purification step such as distillation.

It is preferred to pre-purify the crude reaction mixture of the fluorination reaction by stripping, distillation or both such that the content of HF is reduced to equal or less than 1 % by weight in the pre-purified raw product. Often, the content of HF is reduced to less than 100 ppm by weight. A range of from 100 to 1000 ppm by weight of HF is preferred after pre-purification, especially after stripping.

Consequently, a preferred embodiment of the method is performed in several steps to provide purified carbonate.

This embodiment comprises a step of providing a crude reaction mixture comprising a fluorinated organic carbonate obtained in a reaction of an organic carbonate with elemental fluorine to provide a crude reaction mixture comprising a fluorinated organic carbonate having a higher degree of fluorination than the starting material ; at least one subsequent step comprising the removal of a major part of entrained HF from the crude reaction mixture to provide a pre-purified product ; at least one subsequent step comprising the addition of the purifying agent ; and at least one step of isolating the purified fluorinated organic carbonate.

In another embodiment the process comprises a further purification step of treating a mixture comprising the fluorinated organic carbonate with an organosilicon compound having at least one -Si-N- bond, preferably the organosilicon compounds is selected from organosilazane compounds, organodisilazane compounds and organotrisilazane compounds. More preferably, the organosilicon compound having at least one -Si-N- bond is selected from the group consisting of (N,N-diethylamino)trimethylsilane, Ν,Ο- bis(trimethylsillyl)acetamide, N,N ' -bis(trimethylsillyl)- 1 ,4-butanediamine,

1,1,1 ,3 ,3 ,3-hexamethyldisilazane, 1 , 1 ,3 ,3 ,5 ,5-hexamethylcyclotrisilazane, and any combination thereof. 1,1,1 ,3 ,3 ,3-hexamethyldisilazane is especially preferred. This embodiment allows to further reduce the contamination with e.g. HF and/or water.

The crude reaction mixture comprising a fluorosubstituted carbonate and

HF can be provided as described in the documents cited above by the reaction of a carbonate starting material which is not substituted by a fluorine atom, or which has a lower degree of fluorination, and elemental fluorine, optionally in a solvent, e.g. in HF as a solvent, in an inert solvent, e.g. in a perfluorocarbon solvent, or in the presence of a fluorinated organic carbonate as diluent.

The removal of entrained HF in the subsequent step can be performed in a known manner, for example, by stripping with inert gas like nitrogen as described in WO 2009/118369. The HF removal can also be performed by distillation as described in WO 2011/020830. Combinations of stripping and distillation provide a suitably pre-purified product.

Mixtures which contain HF in a broad range can be treated according to the present invention. In the most preferred embodiments where the reaction mixture to be treated originates from the preparation of fluorosubstituted ethylene carbonates or fluorosubstituted dialkyl carbonates, one molecule of HF is formed per hydrogen atom which is substituted by fluorine. Usually, in such reaction mixtures, the content of HF is equal to or lower than 10 % by weight. But mixtures which comprise higher amounts of HF can be treated, too.

The content of HF in the mixtures after treatment is preferably equal to or lower than 5 % by weight, more preferably equal to or lower than 2 % by weight of the reaction mixture. Especially preferably, it is equal to or lower than 1 % by weight. Still more preferably, it is equal to or lower than 0.5 % by weight.

Especially preferably, it is equal to or lower than 0.1 % by weight.

In a most simple manner, stripping could be performed in a vessel containing reaction mixture by blowing inert gas through the reaction mixture. This can be done batch wise or continuously.

It is preferred to perform stripping in a way which provides for a sufficient contact area between reaction mixture and gas. For example, reaction mixture could be sprayed into a stream of inert gas, or stripping gas and liquid to be treated can be contacted in a bubble tray column. A very preferred method is performed in a stripping column. In a stripping column, internals or packings are installed with a high specific area per m ³ of the equipment to provide a high contact surface between gas and liquid. Suitable packings are, for example, Raschig rings. The stripping column is usually a cylindrical tube positioned vertically. The inert gas is introduced at the bottom of the stripping column below the packings ; the reaction mixture is fed at the top. Inert gas comprising HF leaves the column via a separate line at the top. The efficiency of the removal of HF from the HF-containing carbonate is higher at higher temperatures. If the contact is performed in a vessel, heat can be supplied in a known manner, for example, by heating the walls of the vessel. Optionally, the inert gas and/or the liquid to be treated can be heated.

If the reaction is performed in a stripping column with internals or packings, it is preferred to heat inert gas, liquid to be treated or both to improve the efficiency of the stripping process.

Thus, the inert gas, especially nitrogen, advantageously is heated before introducing it into the reaction mixture. The temperature to which it is heated is preferably equal to or higher than 60°C ; more preferably, it is equal to or higher than 75°C. Very preferably, it is equal to or higher than 100°C. The temperature can still be higher, for example, equal to or higher than 120°C. Preferably, it is equal to or lower than 150°C. Depending on the heat resistance and the resistance of corrosion of the vessel, column, pipes, fittings etc used, the temperature can be higher than 150°C.

The reaction mixture preferably is also heated before a continuous stripping process is performed. If a vessel is used to perform a batch wise process, the reaction mixture can be heated before and/or during the stripping process. Preferably, it is heated to a temperature equal to or greater than 60°C. Preferably, it is heated to a temperature equal to or lower than 120°C.

It is very advantageous to perform the stripping step at ambient pressure. If desired, a slight vacuum can be applied. For example, the pressure can be reduced to 0.5 bar or even 0.2 bar. The temperature should not be so high that organic compounds would be carried out of it with the flow of inert gas.

In a batch wise process, stripping is performed until the desired maximal amount of HF is present.

In a continuous process in a stripping column, the height of the column is selected such that, for a given HF concentration, flow rate of inert gas and reaction mixture, the desired residual HF concentration is reached.

The pre-purification can also be performed by several distillations as described in WO 2011/020830. In this method, a crude reaction mixture is distilled in at least two distillation steps wherein the reaction mixture which is fed to the first distillation step contains not more than 5 % by weight of HF. Preferably, the reaction mixture which is fed to the first distillation column contains nor more than 1 % by weight of HF. Excess HF can be removed for example by stripping before the distillation steps. The wording "at least two distillation steps" denotes passing the mixture at least twice through a distillation column. According to one embodiment, this is one distillation column through which the mixture to be separated is passed at least twice. This embodiment can be performed in a batch wise distillation.

According to another embodiment, the at least two distillation steps are performed in at least two distillation columns. This embodiment is especially suitable for performing a continuous distillation process.

In the first distillation step, a mixture of substances with a lower boiling point (for example, HF and carbonates with higher degree of fluorination)) is drawn off from the top ; the higher boiling constituents are drawn off from the bottom and are fed into the second distillation step. Often, the pressure at the top of the column of the first distillation step is equal to or lower than

100 mbar (abs). Preferably, the pressure at the top of the column of the first distillation step is equal to or lower than 75 mbar (abs.). Preferably, it is equal to or higher than 10 mbar (abs.). A pressure at the top of the column of the first distillation step in the range between 10 and 50 mbar (abs.) is especially preferred.

The mixture of substances with a lower boiling point drawn off from the top of the column of the first distillation step can be separated from each other if desired. For example, HF can be removed by washing the mixture with water or, which is highly preferred, by stripping the mixture with an inert gas. The remaining fluorinated carbonates can be separated by distillation. Alternatively, the mixture from the top of the column of the first distillation step can be separated into the different compounds simply by distillation without any other treatment like washing or stripping. Carbonates with higher degree of fluorination are valuable side products because they can be applied as additive for lithium ion battery solvents. If desired, they may be dumped or burned. Any recovered hydrogen fluoride also is a valuable product per se.

In the second column, the bottom product of the first column is distilled. Preferably, the pressure at the top of the column of the second distillation step is equal to or lower than 50 mbar (abs.). More preferably, the pressure at the top of the second column is equal to or lower than 30 mbar (abs.). Preferably, the pressure at the top of the column of the second distillation step is equal to or higher than 5 mbar (abs). At the top of the column of the second distillation step, highly pure fluorinated carbonate, for example, monofluoroethylene carbonate, is obtained. The content of HF in the purified carbonate is equal to or lower than 30 ppm by weight, preferably equal to or lower than 20 ppm by weight. Even lower HF content can be achieved, e.g. equal to or lower than 10 ppm.

In a preferred embodiment, the content of HF in the crude reaction mixture is brought to equal to or less than 0.1 % by weight (i.e., equal to or less than 1000 ppm by weight), to provide a pre-purified reaction product ; then the purifying agent, preferably an alcohol, e.g. isopropanol, more preferably, ethanol, and especially, methanol is added. Preferably, the amount of the purifying agent is from 0.01 to 2 parts by weight, per 100 parts by weight of pre- purified reaction product. Surprisingly, the amount of methanol may be lower than the amounts of ethanol or isopropanol. For example, ethanol may be applied in amounts equal to or lower than 1 part by weight, while methanol may even be added in an amount of equal to or lower than 0.6 % by weight.

During the addition of the purifying agent, the temperature of the reaction mixture is preferably kept in a range from 0°C to 100°C, preferably, 60 to 100°C, and the pressure corresponds to the ambient pressure.

If desired, the reaction mixture can be kept in a post reaction phase, for example, for equal to or more than 1 minute to equal to or less than 5 hours. For reactive purifying agents, e.g. methanol, the residence time may be lower than for less reactive agents, e.g. isopropanol.

The reaction mixture is then distilled to provide purified fluorinated organic carbonate.

The distillation is preferably performed in a column having a sufficient number of theoretical plates, e.g. 10 to 50, to provide a sufficiently pure product.

The advantage of the purified product is that any impurity which could form HF upon storage or when brought into contact with moisture, is removed by the method of the invention. This is also advantageous during the

determination of residual HF content because this determination is performed under addition of water. The impurities react with water under HF formation ; this results in the determination of a higher content of free HF than was originally present.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The invention will now be explained in examples which are not intended to limit the invention. Abbreviations :

EC : Ethylene carbonate

F1EC : Fluoroethylene carbonate

F2EC : Difluoroethylene carbonate

GC : Gas Chromatography

Example 1 : Preparation and pre-purification of mono fluoroethylene carbonate

1.1. Preparation of a crude reaction mixture comprising mono fluoroethylene carbonate ("F1EC")

The manufacture of F1EC was performed by the reaction of ethylene carbonate ("EC") with F ₂ /N ₂ in a volume ratio of 13:87 which was passed continuously into the EC in the reactor. The crude reaction mixture contained as organics, as determined by GC, 50 area % of EC, 45 area % of F1EC and

5 area % of difluoroethylene carbonate ("F2EC") as measured by GC ; it also contained 10 % by weight of HF.

1.2. Pre-purification of the crude reaction mixture

The crude reaction mixture of example 1.1 was subjected to stripping by contacting the crude mixture with N ₂ in a stripping column at a temperature of about 110°C to reduce the content of HF to about 0.2 % by weight.

1.3. Addition of methanol

To the pre-purified reaction mixture of example 1.2, methanol was added in an amount of 0.5 g methanol per lOOg of the mixture. The reaction was performed at 80°C.

1.4. Isolation step

After the addition of methanol, the resulting reaction mixture was distilled under vacuum to provide highly purified F 1 EC .

Example 2 : Purification with ethanol

Example 1 is repeated, but the amount of ethanol is set to 0.85 % by weight.

Example 3 : Manufacture of fluoromethyl methyl carbonate

Highly purified mono fluoromethyl methyl carbonate is manufactured in a process comprising the steps of reaction of dimethyl carbonate with a fluorine/inert gas mixture, subsequent stripping of HF, followed by the addition of methanol and distillation analogously as described in example 1.