Preparation of fluorinated organic carbonates depleted in HF using a specific absorbent

The invention concerns a process for the manufacture of fluorinated organic carbonates depleted in HF.

Fluorinated organic carbonates are useful as solvents or co-solvents, especially for the manufacture of Li ion batteries. They can for example be prepared from the respective non-fluorinated organic carbonates by direct fluorination with elemental fluorine, by reaction with high- valence metal fluorides which split off fluorine, e.g. AgF ₂ , or by electrochemical fluorination. In this kind of process, one or more C-H bonds are substituted by one or more C-F bonds. As a byproduct, hydrogen fluoride (HF) is formed. Fluorine- substituted organic carbonates comprising hydrogen fluoride may also be obtained in other types of processes. For example, HF is added as solvent in the manufacture of fluoroethylene carbonate from ethylene carbonate and elemental fluorine. Of course, HF can be detrimental especially if the product is to be used in high tech applications, e.g. in Li ion batteries, and thus must be removed. HF can be removed from the fluorinated organic carbonates by washing with water as described for example in JP 2000309583 or US-A 7,223,500. Contact with water can be disadvantageous for compounds having a CH-CF group because, according to US-A 7,268,238 (first published as US patent application publication 2006/167279), it appears to provoke the split-off of HF from the fluorinated carbonates. That US patent discloses the removal of HF from fluoroethylene carbonate by distillation.

EP-A-O 326054 discloses the removal of hydrogen fluoride and trifluoropropionyl fluoride from 2,2,3, 3-tetrafluorooxetane using silica gel or alumina. The description focuses on providing gaseous 2,2,3, 3-tetrafluorooxetane which is contacted with the inorganic reactant.

Object of the present invention is to provide a simple reliable process for the production of fluorinated organic carbonates with a depleted content of HF.

According to the process of the present invention, a process is provided for the preparation of fluoro substituted 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 SiO ₂ , forming a mixture of a solid and HF-depleted fluorinated organic carbonate, and the resulting HF-depleted fluoro substituted organic carbonate is separated from the solid. The fluoro substituted organic carbonate is kept in the liquid state during contact with the inorganic reactant when the HF depletion is under way. Of course, the process can also be applied to a mixture comprising two or more fluoro substituted carbonates, or to a mixture comprising a nonfluorinated organic carbonate or two or more non-fluorinated carbonates and one or more fluoro substituted organic carbonates. Thus, when the singular form "carbonate" is used, it shall also denote the plural form. Crystalline solids are generally suitable, e.g. SiO ₂ -containing zeolites, or glassy material, for example bodies made from glass, e.g. glass beads. Glass beads should be used in the form of small particles, e.g. with a diameter between 0.5 to 20 mm (though, of course, the diameter might be smaller than 0.5 mm, or greater than 20 mm). 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.

The term "fluorinated organic carbonates" denotes dialkyl carbonates and alkylene carbonates substituted by at least one fluorine atom and containing at least one CH-CF group.

In dialkyl carbonates, the alkyl groups (at least one of which is substituted by at least one fluorine atom) may be the same or different. Preferably, alkyl is Cl to C3 alkyl, especially methyl or ethyl. For example, fluoromethyl methyl carbonate, bis-(fluoromethyl) carbonate, difluoromethyl methyl carbonate, difluoromethyl fluoromethyl carbonate, bis-(difluoromethyl) carbonate, methyl trifluoromethyl carbonate, fluoromethyl trifluoromethyl carbonate, difluoromethyl trifluoromethyl carbonate, and bis- (trifluoromethyl) carbonate can be treated according to the process of the present invention. These compounds can be prepared by direct fluorination of dimethyl carbonate with elemental fluorine or by chlorine-fluorine exchange reactions (e.g., Halex reaction) from the respective chloro substituted carbonate. Isolation is possible by distillation or other conventional processes.

In alkylene carbonates, the term "alkylene" preferably denotes C2 to C4 alkylene (substituted by at least one fluorine atom), especially ethylene, propylene (methylethylene), and 1,2-dimethylethylene. "Alkylene" preferably

denotes ethylene or propylene. For example, 4-chloro-5-fluoroethylene carbonate (described in JP-A 62-290072), 4-fluoro-5-methylethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-5-methylethylene carbonate, 4-chloro-5-fluoro-5-methylethylene carbonate (described in JP-A 62-290071), 4-fhioromethylethylene carbonate, 4-fluoromethyl-5,5-dimethylethylene carbonate, or 4-(l-fluoroethyl)ethylene carbonate (described in JP-A 09-251861). Preferably, 4-fluoroethylene carbonate ; 4,4-difluoroethylene carbonate, cis-4,5-difluoroethylene carbonate and trans-4,5-difluoroethylene carbonate ; 4,4,5-trifluoroethylene carbonate and methylethylenecarbonate (propylene carbonate) substituted by at least one fluorine atom, especially 4-fluoromethylethylene carbonate, are treated according to the process of the present invention. These fluorinated carbonates can be prepared from the respective non-fluorinated compounds by electrochemical fluorination in HF, by treatment with high- valence metal fluorides, or, preferably, by direct fluorination, e.g. with elemental fluorine diluted by inert gas, especially nitrogen. The direct fluorination of propylene carbonate, for example, is described in JP-A 07-312227. Compounds with 2 or more fluorine atoms can also be prepared by fluorination of the respective carbonates which are already substituted by fluorine in a lower degree of substitution. This is, for example, described in JP-A 2000-344763 where fluoroethylene carbonate is reacted with fluorine to provide difluorinated products.

In one embodiment of the invention, the HF-containing fluoro substituted organic carbonate which is to be treated is the reaction mixture from the fluorination reaction. It may contain unfluorinated starting material, the desired fluorinated organic carbonate, and overfluorinated organic carbonate. Preferably, the reaction mixture is pretreated to reduce the HF content below a certain level. It is preferred to reduce the HF to equal to or lower than 2.5 % by weight. More preferably, the HF content is reduced to equal to or less than 2 % by weight of the mixture to be treated as is described below in detail. This reduces the risk that side reactions might occur.

The process of the present invention is especially suitable for reducing the HF content in mono-, di- and trifluoroethylene carbonate. It will be explained in further detail in view of the HF removal from monofluoroethylene carbonate ("FlEC").

- A -

Monofluoroethylene carbonate can be prepared from ethylene carbonate by direct fluorination of ethylene carbonate. Japanese patent application JP-A 2000 309583 discloses that the reaction can be performed in the presence or absence of a solvent. US patent US-A 7223500 discloses the reaction between ethylene carbonate and fluorine to be performed in the presence of fluoroethylene carbonate as solvent. US patent US-A 7268238 discloses a process for the direct fluorination of ethylene carbonate wherein the fluorine gas is distributed in a column arranged in the reactor by means of Raschig rings. In all these processes, a mixture of fluoroethylene carbonate and, as byproduct, HF is produced. It is preferable that, before contacting the fluoroethylene carbonate/HF mixture with silica, the content of HF is reduced to equal to or less than 2.5 % by weight, more preferably to equal to or less than 2 % by weight, very preferably to equal to or less than 1 % by weight, and most preferably to equal to or less than 0.5 % by weight, of the mixture to be contacted with the HF removing reactant. For example, most of the HF can be removed by stripping the solution with inert gas, e.g. with nitrogen, or by a first distillation step. It is preferred to reduce the content of HF in such a preceding step to equal to or less than 1 % by weight, more preferably to equal to or less than 0.5 % by weight, and especially preferably, to equal to or less than 0.1 % by weight. When the content of HF is reduced to the desired level, the resulting mixture of fluoroethylene carbonate is contacted with silica gel, the preferred reactant.

The amount of silica is very variable ; the minimum amount depends on the admissible residual quantity of HF. Silica should be applied in an amount which provides the desired level of purity in reasonable time. Often, depending on the HF level, equal to or less than 4 g of silica are applied per 100 g of fluoroethylene carbonate/HF mixture. Higher amounts can be applied, but possibly, some of the silica and/or the desired product may be wasted. The expert can perform simple trials to find out optimum amounts of silica. The temperature during contact of the HF containing mixture and the silica is not very critical, especially in view of the small amounts usually applied. The temperature should be higher than the melting point of the respective carbonate and not as high that undesired side reactions occur. In principle, the contact can be performed between the solidification temperature of the carbonate or carbonate mixture, and rather high temperatures, e.g. up to HO ⁰ C or even more.

Preferably, the temperature is equal to or higher than 1O ⁰ C. For example, the contact can be performed at ambient temperature.

According to one embodiment, contact between the reaction mixture to be treated and silica is performed at a temperature of lower than 5O ⁰ C. Treatment at such low temperature, especially in a range from 10 to 5O ⁰ C, allows a smooth treatment.

According to another embodiment, , the contact temperature is equal to or higher than 5O ⁰ C, more preferably, equal to or higher than 8O ⁰ C. Preferably, it is equal or lower than 100 ⁰ C. A temperature range of 8O ⁰ C to 100 ⁰ C is very advantageous is especially when the fluoro compound to be treated with the inorganic reactant leaves another treatment process at such a high temperature, e.g. a stripping process wherein HF is removed by stripping with inert gas in such a temperature range.

The contact time should be as long as necessary, but not unduly extended. Preferably, it is equal to or lower than 60 minutes, more preferably equal to or lower than 30 minutes. Preferably, it is equal to or longer than 1 minute, more preferably equal to or longer than 5 minutes.

Especially if the treatment is performed at a temperature in the upper range, e.g. in a range of 50 to 100 ⁰ C, and especially, 80 to 100 ⁰ C, it can be advantageous to apply a slight vacuum. It is assumed that this helps to remove any water and thus prevents side reactions caused by water.

It is possible to apply the silica material in any desired form, e.g. as beads or extrudates.

In one embodiment, the silica is contacted with the fluorinated compound in the form of bulk material. After contact, solids are removed from the reaction mixture by known methods, e.g. by filtration, decantation, centrifugation or distillation.

In another, preferred embodiment, silica, especially silica gel beads, is contained in a filter through which the fluorinated compound to be contacted is passed. The advantage of a filter is that the silica is enclosed therein and remains in this filter during contact. Thus, it must not be removed from the organic compound in a separate step after the treatment.

The content of HF can be reduced to equal to or less than 300 ppm by weight by applying silica, especially silica gel. It is often preferred to purify the liquid further, notably by distillation.

This is especially the case if a raw product comprising e.g. fluoroethylene

carbonate, HF, starting material (in this case, ethylene carbonate) and/or higher fluorinated products (in this case, difhioroethylene carbonates) is purified according to the process of the present invention. The HF content can thus be further reduced, to equal to or less than 30 ppm, and even to equal to or less than 10 ppm by weight.

In one preferred embodiment of the present invention, the silica treatment is performed in the bottom of a distillation column ; this alternative is especially feasible when the distillation is performed batch wise. This embodiment has the additional advantage, too, that a separation step is obviated. Considering that water (which is formed during the treatment) causes side reactions in the fluoroethylene carbonate, it is very surprising in view of the thermal strain on the fluoroethylene carbonate during the distillation that this embodiment works very satisfactorily at all.

The treatment with silica is preferably performed with a preceding stripping step wherein HF is removed by introducing inert gas into the raw material at an elevated temperature, and/or with a subsequent distillation step. Such a combination has the advantage that the energy needed for heating the fluorinated organic compound can be utilized for several treatment steps.

The use of silica for removal of HF from organic compounds is principally known from US patent US-A 6252105. It is assumed that SiO ₂ and HF react to form SiF ₄ (a gaseous product) which then forms H ₂ SiFo, and water. Fluoroethylene carbonate appears sensitive towards dehydrofluorination. Water, as was indicated in US-A 7268238, is considered to cause a split-off of HF from fluoroethylene carbonate ; thus, the expert would have expected that SiO ₂ -containing compounds should not be suitable as agents for HF removal for those compounds : reaction of HF with silica forms water, formed water causes the formation of HF from fluoroethylene carbonate, the thus formed HF causes the formation of water from silica and so on ; consequently, one would have expected a detrimental effect on both yield and purity. It is very surprising that silica (or silica containing compounds) can be applied as purifying reagent to remove HF at all, especially for fluoroethylene carbonate, but also for the other fluorinated carbonates mentioned above.

The invention will now be described by examples which explain the invention further, but without intention to limit it. General remarks : All % are area-% except for HF (expressed in weight-%).

The mixtures to be treated were synthesized by following the procedure described in WO 2004/076439 : into a solution of ethylene carbonate in fluoroethylene carbonate, fluorine diluted with nitrogen was introduced while the reaction. Example 1 :

1000 g of a mixture of 4-fluoro-l,3-dioxolane-2-one (monofluoroethylene carbonate, FlEC ; 50 %, 4.7 mol), (4R,5R)-4,5-difluoro-l,3-dioxolan-2-one (trans-F2EC, 24 %, 1.9 mol), (4S,5R)-4,5-difluoro-l,3-dioxolan-2-one (cis-F2EC, 18 %, 1.5 mol), 4,4-difluoro-l,3-dioxolan-2-one (4,4-F2EC ; 6 %, 0.5 mol), ethylene carbonate (EC ; 1.2 %, 0.1 mol), and anhydrous hydrogen fluoride (HF ; 0.8 %, 0.4 mol) was stirred at room temperature in a PE-coated reactor.

15 g (0.25 mol) of SiO ₂ (Silica gel, 60, Sigma- Aldrich, CAS No. 112926-00-8) was added stepwise. The temperature was kept between 25-3O ⁰ C during silica gel addition.

After gas formation (SiF ₄ ) was finished, a sample of the mixture was analyzed by gas chromatography. No significant decomposition of the fluorinated compounds could be detected. The mixture was separated by distillation under reduced pressure. The formed water from reaction of HF with SiO ₂ was removed by distillation. Example 2 :

1000 g of a mixture of 4-fluoro-l,3-dioxolane-2-one (monofluoroethylene carbonate, FlEC, 55 %, 5.2 mol), (4R,5R)-4,5-difluoro-l,3-dioxolan-2-one (trans-F2EC, 5 %, 0.4 mol), (4S,5R)-4,5-difluoro-l,3-dioxolan-2-one (cis-F2EC, 4 %, 0.3 mol), 4,4-difluoro-l,3-dioxolan-2-one (4,4-F2EC, 1 %,

0.1 mol), ethylene carbonate (35 %, 4.0 mol), and anhydrous hydrogen fluoride (HF, 2.5 %, 1.3 mol) was stirred at room temperature in a PE-coated reactor.

50 g (0.8 mol) of SiO ₂ (Silica gel, 60, Sigma- Aldrich, CAS No. 112926-00-8) was added stepwise. The temperature was kept between 25-3O ⁰ C during silica gel addition by external cooling of the reactor.

After gas formation (SiF ₄ ) was finished, a sample of the mixture was analyzed by gas chromatography. No significant decomposition of the fluorinated compounds could be detected. The HF content of the mixture after SiO ₂ neutralization was < 300 ppm HF. The mixture was separated by distillation under reduced pressure. The formed water from reaction of HF with SiO ₂ was removed by distillation.

Example 3 :

Another mixture analogous to example 2 was used with the difference that HF concentration was 5.4 % (2.7 mol).

For HF removal 100 g SiO ₂ were added stepwise. The temperature was kept between 25-3O ⁰ C. After gas formation (SiF ₄ ) was finished, a sample of the mixture was analysed by gas chromatography. The result indicates decomposition of the higher fluorinated ethylene carbonate derivatives and the formation of new unidentified peaks on the GC trace.