JP4440006B2 - Fluorinated carbonates and process for producing the same - Google Patents

Description

  The present invention is an electrolyte used for electrochemical devices such as lithium batteries, lithium ion batteries, and electric double layer capacitors, or an additive to the electrolyte, a functional material intermediate, a pharmaceutical / agrochemical intermediate, an organic solvent, etc. The present invention relates to fluorinated carbonates which are expected to have a high temperature and a method for producing the same.

  With the development of portable devices in recent years, the development of electrochemical devices using electrochemical phenomena such as lithium batteries, lithium ion batteries, electric double layer capacitors, etc. has been actively conducted as the power source. These electrochemical devices are generally composed of a pair of electrodes and an ionic conductor filling them. As the ionic conductor of the device, a solution in which a salt called an electrolyte is dissolved in a solvent is used. When this electrolyte is dissolved, it dissociates into a cation and an anion, and conducts ions. In order to obtain the ionic conductivity required for the device, it is necessary that this electrolyte is dissolved in a sufficient amount in the solvent. In many cases, water or an organic solvent is used as the solvent. As the organic solvent, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, dimethoxyethane, diethoxyethane, tetrahydrofuran and the like are used. However, since water is vulnerable to redox, there are limits to the electrode materials that can be used. In addition, the organic solvent as described above has problems in its use temperature range, viscosity, electrochemical stability, and the like.

  In order to solve such a problem, fluorine-containing cyclic carbonates were originally proposed and studied actively (for example, Patent Documents 1 to 4). Recently, in order to further improve the performance of the electrochemical device, an electrolytic solution containing a fluorine-containing chain carbonate as a solvent has been studied (for example, Patent Documents 5 to 9).

Among these, a fluorine-containing chain carbonate (monofluoro chain carbonate) containing only one fluorine in the compound is particularly useful. For example, with respect to fluoromethyl methyl carbonate, Patent Document 10 discloses that a lithium secondary battery produced using this is more charged and discharged at a lithium electrode than a battery produced using dimethyl carbonate (DMC) that is generally used. Is high, has a long cycle life, and has a very high discharge capacity at low temperatures. Patent Document 11 discloses an electrolysis in which (C ₂ F ₅ SO ₂ ) ₂ NLi is dissolved in a solvent in which fluoromethyl methyl carbonate and ethylene carbonate (or fluoroethylene carbonate) are mixed at a volume ratio of 1: 1. It is disclosed that a high discharge capacity remaining rate is expressed in a lithium secondary battery produced using a liquid. Further, Patent Document 12 discloses that high storage characteristics can be obtained by adding ethyl (1-fluoroethyl) carbonate to a non-aqueous electrolyte secondary battery.

  However, there are very few reported examples of methods for producing these useful monofluoro chain carbonates. Patent Document 13 discloses a method for obtaining fluoromethyl methyl carbonate or ethyl (2-fluoroethyl) carbonate by introducing fluorine gas diluted with nitrogen gas into dimethyl carbonate or diethyl carbonate. . Non-Patent Document 1 discloses a method of condensing 2-fluoroethanol and methyl chlorocarbonate using pyridine to obtain (2-fluoroethyl) methyl carbonate.

Thus, in the case of a carbonate having an ethyl group, a production method of a monofluoro chain carbonate having fluorine at the terminal carbon (2-position of the ethyl group) is known, but carbon adjacent to oxygen (ethyl group) The production method of monofluoro chain carbonate having fluorine at the 1-position), for example, (1-fluoroethyl) methyl carbonate or ethyl (1-fluoroethyl) carbonate has not been known so far.
JP-A-62-290071 JP-A-62-290072 JP-A-9-251861 JP-A-7-165750 JP-A-9-147911 JP-A-9-306530 Japanese Patent Laid-Open No. 10-144346 Japanese Patent Laid-Open No. 10-247519 JP 2002-175948 A Japanese Patent Laid-Open No. 10-144346 Japanese Patent Laid-Open No. 10-247519 Japanese Patent Laid-Open No. 2004-14134 JP 2004-10491 A Electrochemistry and industrial physics, Vol. 71, No. 12, pages 1201 to 1204, 2003 (Japan)

  In general, there are two main methods for producing chain carbonates. One is a method of reacting phosgene or an equivalent thereof such as triphosgene with an alcohol in the presence of a base such as pyridine. This method has a problem in that highly toxic phosgenes are used. In addition, when monofluoro chain carbonate is produced by this method, monofluoroalcohol is required, but monofluoroalcohol also has a problem because it is highly toxic. Furthermore, since it is difficult to introduce fluorine on carbon adjacent to oxygen in the alcohol and the cost becomes high, there is a problem that there are many restrictions on the types of alcohol that can be used.

  Another main production method is a method of condensing an alkylhalogenocarbonate and an alcohol in the presence of a base such as pyridine, as used in Non-Patent Document 1. When using this method to produce monofluoro chain carbonates, the alcohol or alkyl halogeno carbonate must have been previously introduced with fluorine. In Non-Patent Document 1, 2-fluoroethanol is used as the alcohol, but such a monofluoro alcohol has a problem because it is highly toxic as described above. In addition, monofluoroalkyl halogeno carbonates are expensive and are not industrially suitable.

  As described above, there are many problems in a method for producing a monofluoro chain carbonate using a precursor into which fluorine is introduced.

  On the other hand, a method of producing a desired monofluoro chain carbonate by fluorinating an already constructed carbonate is conceivable. In the method disclosed in Non-Patent Document 13, dimethyl carbonate and diethyl carbonate are fluorinated using fluorine gas. However, in general, fluorine gas has a problem that it is very reactive, difficult to handle, and product selectivity is difficult to control. In fact, even when referring to the examples disclosed in Patent Document 13, the conversion rate of dimethyl carbonate and diethyl carbonate as raw materials is not necessarily high, and the selectivity to the target product is not satisfactory. In addition, since a large amount of difluoro form is produced, it is difficult to separate and purify the raw material, monofluoro form, and difluoro form.

  Thus, until now, there has been no known method capable of efficiently obtaining a monofluoro chain carbonate in a high yield and industrially mass-producing it.

  The present invention provides (1-fluoroethyl) methyl carbonate, a useful new compound. The present invention also provides a novel industrial production method for efficiently obtaining a useful monofluoro chain carbonate in a high yield.

  The present inventors have intensively studied to solve the above problems. As a result, chain carbonates represented by the general formula [1], which are industrially inexpensive and easily available, and have low toxicity.

（式中、ａ，ｂ，ｃ，ｄは、それぞれ独立に、０〜２の整数を表し、（ａ＋ｂ）≦（ｃ＋ｄ）の関係が成り立つ。）
を、フッ素源としてフッ化物イオンを含む化合物の存在下、電解フッ素化することによって、これまでフッ素導入の難しかった部位にフッ素が効率よく導入され、一般式［２］で表されるモノフルオロ鎖状カーボナート

(In the formula, a, b, c and d each independently represent an integer of 0 to 2, and the relationship of (a + b) ≦ (c + d) is established.)
Is fluorinated in the presence of a compound containing a fluoride ion as a fluorine source, so that fluorine is efficiently introduced into a site where it has been difficult to introduce fluorine, and the monofluoro chain represented by the general formula [2] Carbonate

（式中のａ，ｂ，ｃ，ｄの意味は、式［１］と同じ。）
を高い選択性で得られることを見出した。

(The meanings of a, b, c and d in the formula are the same as in the formula [1].)
Has been found to be obtained with high selectivity.

  A major feature of the electrolytic fluorination of the present invention is that high product selectivity is expressed through fluorination, and a compound in which one atom of fluorine is bonded to carbon adjacent to oxygen of carbonate (the 1st carbon) can be obtained with good selectivity. In that point.

  That is, when a symmetrical carbonate (a carbonate in which the alkyl groups on both sides are the same group) is used as a raw material, a monofluoro chain carbonate in which one fluorine atom is introduced on the 1-position carbon of one alkyl group. Can be produced as the main organism. For example, when dimethyl carbonate is used as a raw material, fluoromethyl methyl carbonate can be produced, and when diethyl carbonate is used as a raw material, ethyl (1-fluoroethyl) carbonate can be produced.

  On the other hand, when the raw material is an asymmetric chain carbonate, the energy level of the highest occupied molecular orbital (HOMO) of the carbon-hydrogen bond on the 1st carbon of the alkyl group on both sides is compared, and the higher one A hydrogen atom (that is, a hydrogen atom having a higher ionization potential) is preferentially replaced with a fluorine atom, and a monofluoro chain carbonate is obtained.

  Specifically, when the number of carbon atoms of the alkyl groups on both sides is different, a product in which the alkyl group having the larger number of carbon atoms has been fluorinated can be obtained (see Formula [2]). Also, the number of carbons is the same, one is a straight chain alkyl group (for example, n-propyl group, n-butyl group), and the other is a branched chain alkyl group (i-propyl group, i-butyl group, t-butyl group). ), A product in which the branched alkyl group has undergone fluorination is obtained. When both alkyl groups are branched chain alkyl groups, two types of fluorinated products are obtained as isomers.

  This feature is particularly remarkable when one of the alkyl groups is a methyl group and the other is a group other than a methyl group. In this case, the selectivity is particularly high, and the “group other than the methyl group” side is subjected to fluorination. Product is obtained. In particular, when ethyl methyl carbonate is used as a raw material, fluorination occurs on the ethyl group side, and (1-fluoroethyl) methyl carbonate which has not been known at all can be obtained with high selectivity.

  In accordance with the above principle, when methylpropyl carbonate is used as a raw material, (1-fluoropropyl) methyl carbonate is (1-fluoro-1-methylethyl) when isopropylmethyl carbonate is used as a raw material. When methyl carbonate is made from isopropylethyl carbonate, the ethyl (1-fluoro-1-methylethyl) carbonate is made from propylisopropyl carbonate (1-fluoro-1- Methylethyl) propyl carbonate is obtained as the main product, respectively.

  The electrolytic fluorination method is a means of synthesizing an organic fluorine compound that can fluorinate an organic compound using clean electrical energy, and has the feature that the reaction can be controlled effectively by controlling the current and voltage. .

  Therefore, the present invention is an excellent method for efficiently producing a useful fluorine-containing compound by applying this electrolytic fluorination method to a chain carbonate.

  The present inventors have found that the above-described electrolytic fluorination proceeds particularly preferably under specific conditions, and have completed the present invention.

  That is, the present invention provides a novel monofluoro chain carbonate, monofluoro chain carbonate (1-fluoroethyl) methyl carbonate.

  The present invention also provides chain carbonates represented by the general formula [1].

（式中、ａ，ｂ，ｃ，ｄは、それぞれ独立に、０〜２の整数を表し、（ａ＋ｂ）≦（ｃ＋ｄ）の関係が成り立つ。）
をフッ化物イオンを含む化合物の存在下、電解フッ素化することを特徴とする、一般式［２］で表されるフッ素化カーボナート類

(In the formula, a, b, c and d each independently represent an integer of 0 to 2, and the relationship of (a + b) ≦ (c + d) is established.)
Fluorinated carbonates represented by the general formula [2], characterized by electrofluorination in the presence of a compound containing fluoride ions

（式中のａ，ｂ，ｃ，ｄの意味は、式［１］と同じ。）
の製造方法を提供する。

(The meanings of a, b, c and d in the formula are the same as in the formula [1].)
A manufacturing method is provided.

  The present invention also provides a method for producing a fluorinated carbonate, wherein the starting chain carbonate is a specific compound.

  The fluorinated carbonates of the present invention and the production method thereof are obtained by fluorinating chain carbonates that are easily available as industrial raw materials using an electrolytic fluorination method, such as lithium batteries, lithium ion batteries, electric double layer capacitors, etc. Fluorinated carbonates that are expected to be used as electrolytes or additives to electrolyte devices, functional material intermediates, pharmaceutical and agrochemical intermediates, and organic solvents used in electrochemical devices are much more efficient than before. There is an effect that it can be manufactured.

  Hereinafter, the present invention will be described in more detail. The chain carbonates represented by the general formula [1] used as a starting material of the present invention are not particularly limited, but considering the availability, the value of (a + b) in the formula is 0,1. Or it is 2 and the value of (c + d) is 0, 1 or 2. Specific examples of such are dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate. And propyl isopropyl carbonate. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred from the standpoint of availability and usefulness of the product.

  As described above, the electrolytic fluorination according to the present invention is performed on the 1-position carbon of each of the two alkyl groups bonded to the —O (C═O) O— group of the chain carbonate as a raw material. Compare the energy level of the highest occupied molecular orbital (HOMO) of the carbon-hydrogen bond of the two, and the hydrogen atom with the higher energy (ie, the hydrogen atom with the higher ionization potential) is preferentially replaced with the fluorine atom. It has the characteristics. For this reason, once the structure of the raw chain carbonate is determined, the type of monofluorocarbonate to be produced is also determined.

In the electrolytic fluorination of the present invention, a compound containing fluoride ions is used as the fluorine source compound. As the fluorine source compound, hydrogen fluoride (HF), pyridine-nHF which is a pyridine polyhydrofluoride compound (n is a substance obtained by mixing n moles of hydrogen fluoride per mole of pyridine, and 1 to 20 An alkylamine polyhydrofluoride compound R ₃ N · nHF (here, an association product of a primary to tertiary alkylamine and hydrogen fluoride). R represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, n means a substance obtained by mixing n moles of hydrogen fluoride per mole of amine, and preferably 1 to 20, 1-10 are more preferable, and 3-6 are particularly preferable), or tetraalkylammonium fluoride poly which is an association of a quaternary ammonium fluoride salt and hydrogen fluoride. Tsu hydride compound R ₄ NF · nHF (wherein R represents a hydrogen atom, or .n representing a linear or branched alkyl group having 1 to 6 carbon atoms, a quaternary ammonium fluoride salt of hydrogen fluoride per mole 1 to 20 is preferable, 1 to 10 is more preferable, and 3 to 6 is particularly preferable.

Specific examples of the alkyl amine poly hydrogen fluoride salt compound R ₃ N · nHF, triethylamine _{· 3HF (Et 3 N · 3HF} ), triethylamine _{· 4HF (Et 3 N · 4HF} ), triethylamine _{· 5HF (Et 3 N · 5HF} ) , Tributylamine · 4HF (Bu ₃ N · 4HF) and the like. Specific examples of the tetraalkylammonium fluoride poly hydrogen fluoride compounds, tetraethylammonium fluoride _{· 3HF (Et 4 NF · 3HF} ), tetraethylammonium fluoride _{· 4HF (Et 4 NF · 4HF} ), tetraethylammonium fluoride · 5HF ( Et ₄ NF · 5HF), tetrabutylammonium fluoride _{· 3HF (Bu 4 NF · 3HF} ), tetrabutylammonium fluoride _{· 4HF (Bu 4 NF · 4HF} ), tetrabutylammonium fluoride · 5HF (Bu ₄ NF · 5HF ) And the like, but is not limited thereto. A plurality of fluorine source compounds may be used simultaneously.

These fluorine source compounds are used in an amount of 0.1 to 10 mol, preferably 0.2 to 5 mol, per 1 mol of the raw material compound (chain carbonate). This amount used depends on the amount of fluoride ions contained in the fluorine source compound (mainly the amount of hydrogen fluoride (n)). When focusing on the amount of the starting compound (a chain carbonate compound) 1 based on the equivalents of fluoride ions ^- Fluoride ions (F) (F ^-) required amount of 1 to 20 equivalents, preferably 1 to 5 equivalents is there. Although it is possible to add more, it is not preferable because no significant improvement in reactivity is observed and this is economically disadvantageous.

  Since these compounds also serve as a supporting electrolyte, it is not necessary to add a supporting electrolyte separately in the method of the present invention.

  The electrolytic fluorination of the present invention can also be performed using a solvent. However, when a solvent is used, impurities and by-products may be generated due to decomposition of the solvent due to the electrochemical stability of the solvent. In addition, the use of a solvent is not preferable because the yield per unit volume is reduced and it is economically disadvantageous.

Other conditions for carrying out the electrolytic fluorination of the present invention may be in accordance with known methods and are not particularly limited. Usually, the temperature is preferably in the range of −50 to + 100 ° C., more preferably −10 to + 40 ° C. The current density is preferably in the range of 10~500mA / cm ^2, more preferably in the range of 50 to 200 mA / cm ^2.

The electrolytic cell is not particularly limited, and known ones can be used. The material can be iron, stainless steel, nickel, nickel alloy, or the like. When the above-mentioned R ₃ N · nHF or R ₄ NF · nHF is used as the fluorine source compound, when the number of n is smaller than 3, a glass material can also be used. When free HF is used as the fluorine source compound, and when R ₃ N · nHF or R ₄ NF · nHF is used, the glass is corroded when the number of n is larger than 4, so the glass material is not suitable. It is. In such a case, an electrolytic cell made of fluororesin or lined with fluororesin can be used, and in a small amount, an electrolytic cell made of plastic can be used.

  In the electrolytic reaction of the present invention, either a diaphragm type or a diaphragm type electrolytic cell can be used. Both constant current electrolysis and constant potential electrolysis are effective. When performing constant current electrolysis, the current value may be set so as to achieve the above-described current density. In the case of constant potential electrolysis, within a potential range of 3 to 5 V with respect to the silver / silver chloride type reference electrode, What is necessary is just to set to the electric potential which becomes the above-mentioned current density. As an electrode, a platinum electrode, a carbon electrode, a lead dioxide electrode, a silver electrode, a copper electrode, a nickel electrode, an iron electrode, or an alloy electrode thereof can be used. In particular, when a platinum electrode is used for the positive and negative electrodes, the target product can be obtained with good yield. If stirring is performed during the reaction, the reaction can be carried out particularly smoothly.

  In the electrolytic reaction, first, 2 F / mol which is the theoretical energization amount of this reaction is energized. After that, it is desirable to continue while measuring the composition of the electrolytic solution by means of analysis such as thin phase chromatography, gas chromatography, NMR, etc., and select the desired product for the conversion rate of the raw chain carbonates The reaction is preferably terminated at the point where the rate begins to decrease. If electrolysis is continued for an excessively long time, higher order fluorinated products and decomposition products may be by-produced, which is not preferable.

  A method for isolating the target product from the reaction mixture after completion of the reaction may be in accordance with a known technique, and is not particularly limited. For example, after the electrolytic reaction is completed, the electrolytic solution is distilled at atmospheric pressure as it is, or extracted with an organic solvent such as ether to separate the fluorine source compound from the target product, followed by column chromatography, distillation, etc. Thus, the target product can be isolated.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these embodiments.

[Example 1] Production of ethyl (1-fluoroethyl) carbonate 2.36 g (20 mmol) of diethyl carbonate and 2.5 g (10.0 mmol) of Et ₄ NF · 5HF were added to a cylindrical cylindrical electrolytic cell. An electrolyte was used. A constant current electrolysis was performed using a platinum plate (2 × 2 cm ² ) as the positive and negative electrodes at a current density of 100 mA / cm ² . The reaction temperature was controlled at 5-15 ° C. The composition of the electrolytic solution at the time of energizing 2 F / mol, which is the theoretical energization amount, is 39% of diethyl carbonate, which is a raw material, and 59% of ethyl (1-fluoroethyl) carbonate, which is a target product, and the selectivity is 97%. The composition of the electrolytic solution at the time when 2.5 F / mol was energized was 69% of ethyl (1-fluoroethyl) carbonate, which is the target product, with respect to 19% of diethyl carbonate, and the selectivity was 85%. The composition of the electrolyte when 3 F / mol was energized was 73% ethyl (1-fluoroethyl) carbonate, the target, compared to 11% diethyl carbonate, the raw material, and the selectivity was 82%. It was. The electrolyte was distilled at atmospheric pressure to separate ethyl (1-fluoroethyl) carbonate and Et ₄ NF · 5HF, and then ethyl (1-fluoroethyl) carbonate was isolated by column chromatography.

[Example 2] Production of fluoromethyl methyl carbonate An electrolytic reaction was carried out in the same manner as in Example 1 except that 2.70 g (30 mmol) of dimethyl carbonate was used instead of diethyl carbonate. The composition of the electrolytic solution at the time of energizing 2 F / mol which is the theoretical energization amount is 47% of the target product, fluoromethyl methyl carbonate, with respect to 27% of dimethyl carbonate as a raw material, and the selectivity is 64%. Met. This electrolytic solution was distilled at atmospheric pressure to separate fluoromethylmethyl carbonate and Et ₄ NF · 5HF, and then fluoromethylmethyl carbonate was isolated by column chromatography.

[Example 3] Production of (1-fluoroethyl) methyl carbonate An electrolytic reaction was carried out in the same manner as in Example 1 except that 2.60 g (25 mmol) of ethylmethyl carbonate was used instead of diethyl carbonate. The composition of the electrolytic solution at the time of energizing 2 F / mol which is the theoretical energization amount is 47% of the target product (1-fluoroethyl) methyl carbonate with respect to 34% of ethyl methyl carbonate as a raw material, The by-product ethyl fluoromethyl carbonate was 2%. The selectivity of (1-fluoroethyl) methyl carbonate with respect to the conversion rate of the raw material was 71%. The electrolyte was subjected to atmospheric distillation to separate (1-fluoroethyl) methyl carbonate and Et ₄ NF · 5HF, and then (1-fluoroethyl) methyl carbonate was isolated by column chromatography.
[Physical properties of (1-fluoroethyl) methyl carbonate]
A colorless transparent liquid at room temperature. ¹ H-NMR (reference material: TMS, solvent: CDCl ₃ ) σ (ppm): 6.35 (dq, J = 56 Hz, 4.9 Hz, 1H), 3.85 (s, 3H), 1.57 ( dd, J = 21 Hz, 4.6 Hz, 3H). ¹³ C-NMR (reference substance: TMS, solvent: CDCl ₃ ) σ (ppm): 155.6, 104.18 (d, J = 222 Hz), 54.57, 19.65 (d, J = 23.4 Hz) ). ¹⁹ F-NMR (reference substance: CCl ₃ F, solvent: CDCl ₃ ) σ (ppm): −44.57 (dq, J = 55 Hz, 20 Hz, 1F). MS (m / z): 122 (M ^<+> ), 121, 103, 77. HRMS m / z calcd _{C 4 H 7 FO 3: 122.0379} , Found: 122.0365.

Claims (8)

(1-Fluoroethyl) methyl carbonate. Chain carbonates represented by the general formula [1]

(In the formula, a, b, c and d each independently represent an integer of 0 to 2, and the relationship of (a + b) ≦ (c + d) is established.)
Is fluorinated carbonate represented by the general formula [2], characterized in that it is electrolytically fluorinated in the presence of a compound containing fluoride ions

(The meanings of a, b, c and d in the formula are the same as in the formula [1].)
Manufacturing method. A method for producing ethyl (1-fluoroethyl) carbonate, comprising subjecting diethyl carbonate to electrolytic fluorination in the presence of a compound containing fluoride ions. A process for producing fluoromethyl methyl carbonate, which comprises electrolytically fluorinating dimethyl carbonate in the presence of a compound containing fluoride ions. A method for producing (1-fluoroethyl) methyl carbonate, which comprises electrolytically fluorinating ethylmethyl carbonate in the presence of a compound containing a fluoride ion. In any one of claims 2 to 5, a compound containing a fluoride ion, tetraethylammonium fluoride _{· 4HF (Et 4 NF · 4HF} ), chosen from tetraethylammonium fluoride _{· 5HF (Et 4 NF · 5HF} ) The method for producing a fluorinated carbonate according to any one of claims 2 to 5, wherein the method is a product. The fluorinated carbonate according to any one of claims 2 to 6, wherein the electrolytic fluorination is performed in a current density range of 10 to 500 mA / cm ² in any one of claims 2 to 6. Manufacturing method. The method for producing a fluorinated carbonate according to any one of claims 2 to 7, wherein the electrolytic fluorination is performed at -50 to + 100 ° C in any one of claims 2 to 7.