JP2674767B2 - Method for producing polyfluoroaromatic aldehyde - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to pentafluorobenzaldehyde or 2,3, which is an important intermediate in the production of information recording materials such as medicines, agricultural chemicals and photographic agents. The present invention relates to a novel selective electrolytic reduction production method of polyfluoroaromatic aldehydes such as 5,6-tetrafluorobenzaldehyde. [Prior Art] Conventionally, as far as the present inventors know, no report has been made that the corresponding aldehyde was specifically obtained by electrolytically reducing polyfluoroaromatic carboxylic acids such as pentafluorobenzoic acid. . The electrolytic reduction of polyfluoroaromatic carboxylic acids such as polyfluorobenzoic acid is performed by FGDrakesmi.
th, J. Chem. Soc., Perkin 1, 1972, pp. 184 to 189, in which, in the process of synthesizing polyfluorobenzyl alcohol by electrolytic reduction of polyfluorobenzoic acid, polyfluorobenzaldehyde I am discussing the possibility of doing so. However, the isolation of polyfluorobenzaldehyde has not been successful. It is considered that this is because even if the aldehyde is produced, the stability is poor, and therefore the aldehyde is immediately and electrolytically reduced to polyfluorobenzyl alcohol. The present inventors have already conducted research on a method for producing polyfluorobenzyl alcohol by electrolytically reducing polyfluorobenzoic acid, and proposed the result as Japanese Patent Application No. 62-39288. In this specification, the inventors of the present invention select a reaction electrode when using polyfluorobenzoic acid as a raw material by selecting an electrode for electrolysis, a potential, an electrolytic solution, and the like. It was clarified that the reaction of can be performed effectively and selectively. As a result of continuing research on the above reaction, the present inventors further reduced the polyfluoroaromatic carboxylic acid as described below by appropriately selecting the temperature of the electrolytic solution, the current density, the conversion rate of the raw material, and the like. As a result, they have found that a polyfluoro aromatic aldehyde can be produced together with a polyfluoro aromatic alcohol, and have completed the present invention. [Problems to be Solved by the Invention] As described above, stable production of polyfluoroaromatic aldehydes by electrolytic reduction of polyfluoroaromatic carboxylic acids has not yet been successful. Therefore, the non-invention solves the problems of the prior art in the reduction of polyfluoroaromatic carboxylic acids, which have been considered difficult in the past, and electrolytically produces desired trifluoroaromatic aldehydes with industrially good yield and selectivity. It is an object of the present invention to provide a method that can be manufactured. [Means for Solving the Problems] According to the present invention, a polyfluoroaromatic carboxylic acid of the following general formula (I) is electrolytically reduced to produce a polyfluoroaromatic aldehyde of the following general formula (II). Hit [In the above formulas (I) and (II), n and m each independently represent an integer of 1 to 5, m ≦ n, X is hydrogen, a C _{1 to} C ₃ alkyl group, or a halogen other than F.] And may be the same or different when a plurality of X are present as substituents] A solid metal or solid alloy is used as the cathode, and sulfuric acid, hydrochloric acid, phosphoric acid or sulfonic acids is used as the electrolytic solution. Is characterized by carrying out electrolytic reduction with an electrolytic potential of saturated aqueous solution of -0.30 to -1.60 V using an aqueous solution of ^{3 at} a current density of 3 to 30 A / dm ² and a raw material conversion rate of 30 to 70 mol%. A method of making a polyfluoroaromatic aldehyde is provided. [Structure of the Invention and Its Effect] The present invention will be described in detail below. The number n of the substituted fluorine atoms F in the polyfluoroaromatic carboxylic acid of the general formula (I), which is the starting material of the method of the present invention, is an integer of 1 to 5, and among them, an integer of 3 to 5 is used in the present invention. Is particularly preferably used. Further, the number of the substituents X in the aromatic carboxylic acid is 5-n, and these represent hydrogen, a C ₁ -C ₃ alkyl group or a halogen other than F. When the number of X is plural, Each X may be the same or different. Examples of the C _{1 to} C ₃ alkyl group include a methyl group, an ethyl group, an n-propyl group and an iso-propyl group. Examples of halogen other than F include Cl, Br or I. Examples of the polyfluoroaromatic carboxylic acid of the general formula (I), which is the starting material of the present invention, include pentafluorobenzoic acid, 2,3,5,6-tetrafluorobenzoic acid, and 2,3,5,6-tetrafluorobenzoic acid.
Polyfluorobenzoic acids such as 3,4,5-tetrafluorobenzoic acid, 2,3,5-trifluorobenzoic acid, 2,4,5-trifluorobenzoic acid and 2,4,6-trifluorobenzoic acid; 3,5-dichloro-2,4,6-trifluorobenzoic acid, 4-bromo-2,
Polyfluorochlorobenzoic acid such as 3,5-trifluorobenzoic acid, 3-bromo-2,4,5-trifluorobenzoic acid, 3-chloro-2,4,5-trifluorobenzoic acid or polyfluorobromobenzoic acid Examples of the acid include polyfluorotoluic acid such as tetrafluoro-m-toluic acid; and among these aromatic carboxylic acids, pentafluorobenzoic acid is particularly preferably used in the method of the present invention. The method of the present invention comprises electrolytically reducing the polyfluoroaromatic carboxylic acid represented by the general formula (I) using a solid metal or a solid alloy as a cathode. Examples of the solid metal include zinc, lead, cadmium,
Examples of the solid alloy include copper, aluminum, tin, and the like, and examples of the solid alloy include solid metal amalgams such as zinc amalgam, lead amalgam, cadmium amalgam, copper amalgam, aluminum amalgam, and tin amalgam. The amount of mercury in the solid metal amalgam is generally 1 to 20% by weight, preferably 2 to 15% by weight. The cathode used in the present invention can be appropriately selected and used from the above-exemplified solid metals or solid alloys depending on the types of starting materials and objects, or from an economical viewpoint. For example, one obtains the corresponding polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol selectively without defluorination reduction from polyfluoroaromatic carboxylic acid, such as pentafluorobenzaldehyde and pentafluorobenzyl alcohol from pentafluorobenzoic acid. In general, as the cathode, for example,
Solid alloys such as zinc amalgam, lead amalgam, and cadmium amalgam are preferably used. Conversely, for example, from the pentafluorobenzoic acid, 2,3,5,6-tetrafluorobenzaldehyde and 2,3,5,6-tetra To obtain a fluorobenzyl alcohol, a polyfluoroaromatic carboxylic acid and a corresponding polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol having at least one less fluorine substitution are also obtained from the polyfluoroaromatic carboxylic acid with defluorination reduction. In this case, it is preferable to use a solid metal such as zinc or lead as the cathode. The electrolytic reduction of the method of the present invention requires the use of the specific aqueous electrolytic solution described above as the electrolytic solution. As described above, examples of the aqueous electrolytic solution include sulfuric acid, hydrochloric acid, phosphoric acid or sulfonic acids such as paratoluenesulfonic acid and methanesulfonic acid in water, and for the purpose of increasing the yield of a target substance, for example. Of these, for example, a lithium salt of an inorganic acid or an organic acid, a sodium salt, a potassium salt, an ammonium salt, a calcium salt, a magnesium salt, a barium salt, an aluminum salt, etc., a water-soluble one may be added. They can be used alone or as a mixture. When preparing the electrolytic solution, the electrolyte can be dissolved using water or an aqueous solution of a water-soluble organic solvent. As the aqueous electrolytic solution used in the method of the present invention, it is particularly preferable to use an aqueous sulfuric acid solution because of its nontoxicity, nonvolatility, safety, economical efficiency, and the like, because no harmful substance other than oxygen is generated from the anode. preferable. In this case, the concentration of the sulfuric acid aqueous solution is not necessarily limited, and the optimum concentration can be appropriately determined by experiment, but for example, 1 to 90% by weight, preferably about 2 to 70% by weight can be exemplified. When the electrolytic reduction without defluorination reduction as described above is desired, generally 10 to 90% by weight, preferably 15 to 70% by weight is good, and the electrolytic reduction with defluoridation reduction is desired. In this case, generally 1 to 50% by weight, preferably 2 to 40% by weight, more preferably 3 to 30% by weight.
% By weight is good. Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, and propyl alcohol (n.-,
aliphatic monohydric alcohols having 1 to 3 carbon atoms such as i.-); other monohydric alcohols such as allyl alcohol and furfuryl alcohol; ethylene glycol and propylene glycol (1,2-, 1,3-) , Glycerin, etc. with 1 carbon atom
Aliphatic polyhydric alcohols of 1 to 3; polyethylene glycol liquid at room temperature; ethylene glycol such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethylene glycol dimethyl ether;
To mono- or di-etherified products with aliphatic monohydric alcohols; diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc., and monohydric aliphatic monovalent alcohols having 1 to 4 carbon atoms Mono- or di-ether compound with alcohol; glycerin such as 1-glyceryl monomethyl ether and C 1
~ 3 mono-etherified products with aliphatic monohydric alcohols; tetrahydrofuran, dioxane (1,3-, 1,4-); and acene, acetonitrile, lactonitrile, N, N-dimethylformamide, dimethyl sulfoxide, diethyl sulfo Other examples include water-soluble organic solvents such as oxides, and methyl alcohol can be particularly preferably used from the viewpoint of easy availability and economical aspects. The onium salt can be added to the aqueous electrolytic solution used in the method of the present invention by contacting with it in addition to the various electrolytes and the water-soluble organic solvent. As the above-mentioned onium salt, general formula R ₄ NX, R ₃ SX, R ₄ PX
(However, R is an alkyl group having 1/8 carbon atoms, X is HSO ₄ , BF ₄ , ClO ₄ or halogen) can be used, eg Et ₄ NHS
O ₄ , Et ₄ NBF ₄ , Et ₄ ClO ₄ , Bu ₄ NBF ₄ , Bu ₄ ClO ₄ , Bu ₃ SBF ₄ , Bu ₃ SClO ₄ , Bu ₄ PBr and the like. These onium salts, in particular,
It is effective when electrolytic reduction accompanied by the defluorination reduction reaction is desired, and the addition amount of the onium salt is generally 0.0001 to 0.1 mol /, preferably about 0.001 to 0.
It is about 05 mol / degree. In the electrolytic reduction according to the method of the present invention, further, aqueous electrolyte temperature, electrolytic potential or current density, conversion rate of cost,
That is, the amount ratio (molar ratio) of the produced polyfluoroaromatic aldehyde to the polyfluoroaromatic alcohol can be increased by appropriately adjusting the ratio of the starting material consumed by the electrolytic reduction to the total amount of the starting materials. In order to increase the amount ratio, in the present invention, the electrolytic potential is set to -0.30V to -0.60V (low potential electrolysis) with respect to the saturated sweet koh electrode.
And the current density is 3 to 30 A / dm ² , preferably 5 to 10 A / dm ^2.
(Constant current electrolysis, cell voltage 3 to 6 V), more preferably the temperature of the aqueous electrolyte is -20 ° C or higher, and further preferably 0.
The reaction can be carried out at a temperature of 25 to 25 ° C. and a raw material conversion of 30 to 70 mol%, preferably 40 to 60 mol%. The raw material conversion rate can be appropriately adjusted by those skilled in the art by adjusting the amount of electricity passed. After the completion of electrolysis, the target product such as polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol can be obtained as a unit by a generally known separation operation. For example,
After completion of electrolysis with a solvent that does not mix with water, extract the reaction product in the aqueous electrolytic solution, wash the extract with an aqueous solution of sodium hydrogen carbonate, then remove the solvent, concentrate and distill to obtain the desired product. be able to. Further, the extract after washing is back-extracted with an aqueous solution of sodium sulfite, and further acid-decomposed to obtain a solution containing only the target substance, similarly, through extraction, concentration, and distillation operation,
You can also obtain the object. Further, a reagent such as hydrazine or semicarbazide may be added to the extract after washing to form a hardly soluble compound, which may be isolated by an operation such as filtration and then acid-decomposed to obtain the desired product. Which method is used to obtain the target product may be appropriately selected in consideration of the apparatus, operation, and economy. As a solvent that does not mix with water that can act on the above separation operation (hereinafter, also referred to as a water-insoluble solvent), there is no particular limitation as long as it is a solvent showing a solubility of less than 10 g in 100 g of water. , For example, n-pentane, iso-pentane, neopentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, methylcyclopentane, n-heptane, iso-heptane, methylcyclohexane, n-octane, iso-octane, Aliphatic hydrocarbons such as 2,2,4-trimethylpentane, ethylcyclohexane, nonane, decane, decalin, dodecane, bicyclohexyl, petroleum ether, ligroin, gasoline, mineral spirits, light oils; aromatics such as benzene, toluene, xylene Group hydrocarbons such as ethyl ether
Ethers such as isopropyl ether; ketones such as methyl isobutyl ketone; esters such as ethyl acetate; carbon tetrachloride, chloroform, 1,1,2,2
Examples thereof include halogenated hydrocarbons such as tetrachloro-1,2-difluoroethane and the like. Among the above water-insoluble solvents, halogenated hydrocarbons, aliphatic hydrocarbons and aromatic hydrocarbons are preferable for reasons such as ease of separation operation and economy. In addition, n-hexane,
A separation operation should be performed using a solvent that does not dissolve polyfluoroaromatic carboxylic acid, which is a starting material, such as iso-octane and ligroin, and that dissolves polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol target products well. This makes it possible to further facilitate isolation of the target product, and to reuse the extraction residual liquid as it is as an electrolytic solution. [Examples] Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples. (Experimental example of polyfluorobenzaldehyde) Example 1 A filter press type microcell manufactured by Electro Cell AB Co., Ltd., which is divided into positive and negative electrode chambers via a Nafion membrane (Dafon's Nafion423, fluorine ion exchange membrane). using about 10ml) cathode chamber volume, the lead plate (effective electrode area 10 cm ²⁾ to the cathode, a platinum anode - using the electrolytic apparatus mounted titanium plate (effective electrode area 10 cm ^2). 120 m of 1% by weight sulfuric acid was used for both the positive and negative electrolytes. Pentafluorobenzoic acid 1.27 g (6.00
Milmol) and onium salt tetraethylammonium, paratoluenesulfonate 0.72 g (2.40 milmol)
Was added. Next, while circulating the electrolyte solution by flowing it into each electrode chamber at a flow rate of 0.7 / min, keep the temperature of the cathode electrolyte solution at 20 to 22 ° C, pass an electric quantity of 15 mF at a current density of 4 A / dm ² , and perform electrolysis. The reduction was performed. After the electrolysis was completed, the catholyte was extracted with ether, and the results of gas chromatographic analysis of the extract were as follows. Conversion of pentafluorobenzoic acid (starting material) 41.6 mol% Produced 2,3,5,6-tetrafluorobenzaldehyde 1.38 mmol (selectivity 55 mol%, current efficiency 37%) Produced 2,3,5,6-tetra Fluorobenzyl alcohol 0.65
Milmol (selectivity 26 mol%, current efficiency 26%) Example 2 Using the same apparatus as in Example 1, 2,3,5,6-tetrafluorobenzoic acid 1.165 gr (instead of pentafluorobenzoic acid as a raw material) (6 mmol) was used, and electrolytic reduction was carried out under the same conditions as in Example 1. Ether extraction was carried out in the same manner as in Example 1 and gas chromatographic analysis was carried out. The following results were obtained. Conversion rate of 2,3,5,6-tetrafluorobenzoic acid (raw material) 44
Mol% 2,3,5,6-Tetrafluorobenzaldehyde 1.48 mmol (selectivity 56 mol%, current efficiency 20%) Product 2,3,5,6-tetrafluorobenzyl alcohol 0.84
Milmol (selectivity 32 mol%, current efficiency 22%) Example 3 Using the same apparatus as in Example 1, using 120 ml of 1% by weight sulfuric acid for both the positive and negative electrodes as the electrolytic solution, and further 2 for the cathode electrolytic solution. 0.881 gr (5 mmol) of 3,3,5-trifluorobenzoic acid was added. Next, while maintaining the electrolysis temperature at 25 ° C while circulating each electrolyte at a flow rate of 0.7 / min, at a current density of 6 A / dm ² , 20 mF
The electrolytic reduction was performed through the amount of electricity. After completion of electrolysis, the catholyte was extracted with ether. The results of gas chromatographic analysis of the obtained extract were as follows. Conversion of 2,3,5-trifluorobenzoic acid (raw material) 32.1 mol% Produced 2,3,5-trifluorobenzaldehyde 0.512 milmol (selectivity 32.5 mol%, current efficiency 5.2%) Produced 2,3,5- Trifluorobenzyl alcohol 1.00 mmol (selectivity 62.3 mol%, current efficiency 20.0%)

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Katsumasa Soejima               1-8-11 Fujigaoka, Midori-ku, Yokohama-shi, Kanagawa               Issue 308

Claims (1)

(57) [Claims] In producing the polyfluoroaromatic aldehyde of the following general formula (II) by electrolytically reducing the polyfluoroaromatic carboxylic acid of the following general formula (I), [In the above formulas (I) and (II), n and m each independently represent an integer of 1 to 5, m ≦ n, X is hydrogen, a C _{1 to} C ₃ alkyl group, or a halogen other than F.] And may be the same or different when a plurality of X are present as substituents] A solid metal or solid alloy is used as the cathode, and sulfuric acid, hydrochloric acid, phosphoric acid or sulfonic acids is used as the electrolytic solution. Is characterized by carrying out electrolytic reduction with an electrolytic potential of saturated aqueous solution of -0.30 to -1.60 V using an aqueous solution of ^{3 at} a current density of 3 to 30 A / dm ² and a raw material conversion rate of 30 to 70 mol%. Method for producing polyfluoroaromatic aldehyde. 2. The manufacturing method according to claim 1, wherein the cathode is a solid metal amalgam. 3. Claim 1 wherein the electrolytic solution is an aqueous sulfuric acid solution.
Item 3. The production method according to item 2 or 2. 4. The manufacturing method according to any one of claims 1 to 3, wherein the electrolytic solution contains an onium salt. 5. The manufacturing method according to any one of claims 1 to 4, wherein the polyfluoroaromatic carboxylic acid is pentafluorobenzoic acid.