JPH01119686A - Production of polyfluoro-aromatic aldehyde - Google Patents

Abstract

PURPOSE:To produce the title aldehyde at a good yield by using a specific metal or alloy as a cathode and specifying the conversion rate of raw material arom. polyfluorocarboxylic acid to its aldehyde at the time of electrolytically reducing an aq. acidic soln. of the carboxylic acid. CONSTITUTION:The metal such as Zn, Pb, Cd, Cu, Al or Sn or the amalgam of said metals contg. 1-20% Hg as the cathode is electrolytically reduced by using, as an electrolyte,the liquid which is the aq. sulfuric acid soln. of the polyfluoro-arom. carboxylic acid such as pentarfluoro-benzoic acid expressed by the formula I, has 30-70mol.% conversion rate of the carboxylic acid and contains an onium salt as a catalyst. The polyfluoro-arom. aldehyde expressed by the formula II, such as pentafluorobenzaldehyde and 2,3,5,6- tetrafluorobenzaldehyde is obtd. at the high raw material yield.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to pentafluorobenzaldehyde or 2,3, The present invention relates to a novel selective electrolytic reduction production method for polyfluoroaromatic aldehydes such as 5゜6-titrafluorobenzaldehyde.

[Conventional technology]

As far as the present inventors are aware, there has not yet been a report that a corresponding aldehyde has been specifically obtained by electrolytically reducing polyfluoroaromatic carboxylic acids such as pentafluorobenzoic acid. Electrolytic reduction of polyfluoroaromatic carboxylic acids such as polyfluorobenzoic acid can be performed using F, G, Dra
kesmi th, J, Chem, Soc, +Pe
rkin 1.1972+, pages 184 to 189, in which the possibility of using polyfluorobenzaldehyde in the synthesis process of polyfluorobenzyl alcohol by electrolytic reduction of polyfluorobenzoic acid is discussed. However, isolation of polyfluorobenzaldehyde has not been successful. this is,
Even if the aldehyde were to be produced, it would have poor stability;
It is thought that this is due to subsequent electrolytic reduction to polyfluorobenzyl alcohol.

The present inventors have already conducted research on a method for producing polyfluorobenzyl alcohol by electrolytically reducing polyfluorobenzoic acid, and published the results in patent application No. 62-3928.
I proposed it as No. 8. In this specification, the present inventors effectively and selectively carry out reactions when polyfluorobenzoic acid is used as a raw material, for example, by selecting electrolytic electrodes, potentials, electrolytic solutions, etc. It became clear that it is possible.

As a result of continuing research on the above reaction, the present inventors further reduced polyfluoroaromatic carboxylic acid as described below by appropriately selecting the temperature of the electrolytic solution, current density, conversion rate of raw materials, etc. They discovered that polyfluoroaromatic aldehyde can be produced together with polyfluoroaromatic alcohol, and completed the present invention.

[Problem that the invention seeks to solve]

As mentioned above, stable production of polyfluoroaromatic aldebide by electrolytic reduction of polyfluoroaromatic carboxylic acid has not yet been successful.

Therefore, the present invention solves the problems of the conventional techniques in reducing polyfluoroaromatic carboxylic acids, which were considered difficult in the past, and electrolyzes desired polyfluoroaromatic aldehydes with industrially good yield and selectivity. The purpose of the present invention is to provide a method that can be manufactured in a straightforward manner.

[Means for solving problems]

According to the present invention, the above problem can be solved by electrolytically reducing polyfluoroaromatic carvone of the following general formula (1) to produce a polyfluoroaromatic aldehyde of the following general formula (II) [the above formula ( In 1) and (II), n and m each represent an integer of 1 to 5, and m≦n, and each X is independently hydrogen, an alkyl group of 01 to C3, or a halogen other than F] Cathode This problem can be solved by using a solid metal or a solid alloy as the electrolyte and using an aqueous solution of sulfuric acid, hydrochloric acid, phosphoric acid, or sulfonic acids as the electrolyte.

[Structure of the invention and its effects]

The present invention will be explained in detail below.

The number n of substituted fluorine atoms F in the polyfluoroaromatic carboxylic acid of the -catalytic formula (I) which is the starting material for the method of the present invention is an integer of 1 to 5, and among them, those with an integer of 3 to 5 are used in the present invention. It is particularly suitable for use in Further, the number of substituents X in the aromatic carboxylic acid is 5-n, and these represent hydrogen, an alkyl group of 01 to C1, or a halogen other than F, and when the number of X is plural, each X may be the same or different.

Examples of the alkyl group for C, -C, above include a methyl group, an ethyl group, an n-propyl group, and a 1so-propyl group. In addition, halogens other than F include C1
, Br or ■.

Examples of the polyfluoroaromatic carboxylic acid of general formula (I) which is a starting material of the present invention include pentafluorobenzoic acid, 2,3,5.6-tetrafluorobenzoic acid, 2.3,4. 5-tetrafluorobenzoic acid, 2,3.
Polyfluorobenzoic acids such as 5-trifluorobenzoic acid, 2.4.5-1-lifluorobenzoic acid, 2°4.6-)lifluorobenzoic acid; 3,5-dichloro-2,4,6-
) polyfluorobenzoic acid, 4-bromo2.3.5-trifluorobenzoic acid, 3-bromo2.4.5-trifluorobenzoic acid, 3-chloro-2,4,5-trifluorobenzoic acid, etc. Examples include fluorochlorobenzoic acid or polyfluorobromobenzoic acid; polyfluorotoluic acid such as tetrafluoro-m-)ruylic acid; and among these aromatic carboxylic acids, pentafluorobenzoic acid is used in the present invention. It is particularly suitable for use in the method.

The method of the present invention involves electrolytically reducing the polyfluoroaromatic carboxylic acid of general formula (I) using a solid metal or solid alloy as a cathode.

Examples of the solid metals include zinc, lead, cadmium, copper, aluminum, tin, etc. Examples of the solid alloys include zinc amalgam, lead amalgam, cadmium amalgam, copper amalgam, aluminum amalgam, and tin. Mention may be made of solid metal amalgams such as amalgams. The amount of mercury in the solid metal amalgam is generally 1 to 20% by weight, preferably 2 to 15% by weight.
It is.

The cathode used in the present invention can be appropriately selected from among the solid metals and solid alloys exemplified above depending on the starting material, the type of target object, or from an economic standpoint. For example, the corresponding polyfluoroaromatic aldehydes and polyfluoroaromatic alcohols can be selectively obtained from polyfluoroaromatic carboxylic acids without defluorination reduction, such as pentafluorobenzaldehyde and hypotafluorobenzyl alcohol from pentafluorobenzoic acid. When it is desired to obtain a .6-Titrafluorobenzaldehyde and 2,3,5,6-titrafluorobenzyl alcohol are obtained from polyfluoroaromatic carboxylic acids by defluorination reduction to obtain corresponding polyfluoride having at least one less fluorine substitution. When attempting to selectively obtain fluoroaromatic aldehydes and polyfluoroaromatic alcohols, for example, zinc,
Preferably, a solid metal such as lead is used.

The electrolytic reduction of the method of the present invention requires the use of the specific aqueous electrolyte described above as the electrolyte.

As mentioned above, the aqueous electrolyte includes water with sulfuric acid, hydrochloric acid,
For example, phosphoric acid or sulfonic acids such as para-toluenesulfonic acid and methanesulfonic acid can be mentioned, and for example, for the purpose of increasing the yield of the target substance, for example, lithium salts, sodium salts, potassium salt, ammonium salt, calcium salt, magnesium salt,
Among barium salts, aluminum salts, etc., water-soluble salts may be added, and these salts can be used alone or in combination. In addition, in preparing the electrolytic solution, the electrolyte can be dissolved using water or an aqueous solution of a water-soluble organic solvent.

As the aqueous electrolyte used in the method of the present invention, Mengyan water-based electrolyte is selected because it is non-toxic, nonvolatile, safe, economical, and because no harmful substances other than oxygen are emitted from the anode. It is particularly preferred to use Enoki. The concentration of the sulfuric acid aqueous solution in this case is not necessarily limited, and the optimum concentration can be appropriately determined by experiment, but for example, 1 to 90% by weight, preferably 2 to 70% by weight.
The degree can be exemplified, but if electrolytic reduction without the above-mentioned defluorination reduction is desired, it is generally 10 to 90% by weight, preferably 15 to 70% by weight; When electrolytic reduction accompanied by is desired, the amount is generally 1 to 50% by weight, preferably 2 to 40% by weight, and more preferably 3 to 30% by weight.

Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, and propyl alcohol (II, -
C1-C3 aliphatic alcohols such as , i, -); other monohydric alcohols such as allyl alcohol and furfuryl alcohol; ethylene glycol, propylene glycol (l.

2-. 1.3-), aliphatic polyhydric alcohols having 1 to 3 carbon atoms such as glycerin; polyethylene glycol that is liquid at room temperature; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, etc. Mono- or dietherized products of ethylene glycol and aliphatic alcohols having 1 to 4 carbon atoms; diethylene glycol and carbon atoms such as diethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc. Mono- or dietherized product with aliphatic-hydric alcohol having numbers 1 to 4; glycerin and carbon number 1 such as 1-glycerin 7-methyl ether
~ Monoetherified product with aliphatic-hydric alcohol of 3; tetrahydrofuran, dioxane (1,3-, 1°4-)
; and acene, acetonitrile, lactonitrile, N
, N-dimethylformamide, dimethyl sulfoxide, diethyl sulfoxide, and other water-soluble organic solvents, and methyl alcohol is particularly preferably used from the viewpoint of easy availability and economics.

In addition to the various electrolytes and water-soluble organic solvents described above, an onium salt can be added as a catalyst to the aqueous electrolyte used in the method of the present invention.

The above onium salts include general formulas R, NX, R35
X.

R4PX (L and R are alkyl groups having 1 to 8 carbon atoms,
can be used as H5Oa, BFa, rs<huge) (represents: R3, ClO4 or AO gene), for example, Et4NISO
<, EtJBF4+Et403S+CH3+ Et4C
I04+ Bu4NBF4+ Bu4C104+Buz
Examples include SBFa, BusSCI04+Bu4PBr, etc. These onium salts are particularly effective when electrolytic reduction accompanied by the above-mentioned defluorination reduction reaction is desired, and the amount of the onium salt added is generally 0.0001 to 0.1 mol per electrolytic solution. 2, preferably about 0.00
It is about 1 to 0.05 mol/l.

In the electrolytic reduction according to the method of the present invention, the temperature of the aqueous electrolyte, the electrolytic potential or current density, the conversion rate of the raw material,
That is, by appropriately adjusting the ratio of the starting materials consumed by electrolytic reduction to the total amount of starting materials, the quantitative ratio (molar ratio) of the polyfluoroaromatic aldehyde to the polyfluoroaromatic alcohol to be produced can be increased.

In order to increase the quantitative ratio, for example, the temperature of the aqueous electrolyte should be lowered by -2
0°C to -50°C 1 Preferably 0°C to 20°C or -0.30°C to saturate the electrolytic potential to the electrode.
V ~ -1,60 V (low potential electrolysis), or the current density is 3 to 30 A/dm, preferably 5 to 10 A/dm.
dm2 (constant current electrolysis, cell voltage 3 to 6 V) or the raw material conversion rate to 30 to 70 mol%, preferably 40 to 60
Reaction conditions such as mol % can be adopted.

': After S decomposition, the target products such as polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol can be isolated and obtained by generally known separation operations. For example, after electrolysis is complete, the reaction products in the aqueous electrolyte are extracted with a solvent that is not mutually miscible with water, the extract is washed with an aqueous sodium bicarbonate solution, the solvent is distilled off, the concentration is concentrated, and the desired product is obtained by distillation. can be obtained. Alternatively, the extracted solution after washing can be back-extracted with an aqueous sodium sulfite solution, followed by acid decomposition to obtain a solution containing only the target product, and the target product can also be obtained by performing similar extraction, concentration, and distillation operations. . Furthermore, it is also possible to add a reagent such as hydrazine or semicarbazide to the washed extract to form a poorly soluble compound, isolate it by filtration or the like, and then perform acid decomposition to obtain the desired product. Which method is used to obtain the desired product may be selected as appropriate, taking into consideration the equipment, operation, and economic efficiency.

The solvent that is immiscible with water (hereinafter also referred to as water-insoluble solvent) that can be used in the above separation operation is less than 10 g per 100 g of water.

There is no particular restriction as long as the solvent exhibits solubility; examples include n-pentane, 1so-pentane, neopentane, cyclopentane, n-hexane, iso-hexane, cyclohexane, methylcyclopentane, n-hebutane,
1so-hebutane, methylcyclohexane, n-octane, 1so-octane, 2.2.4-trimethylpentane, ethylcyclohexane, nonane, decane, decalin, dodecane, bicyclohexyl, petroleum ether, ligroin, gasoline, mineral spirit, light oil Aromatic hydrocarbons such as benzene, toluene, and xylene; Ethers such as ethyl ether and isopropyl ether; Ketones such as methyl isobutyl ketone; Esters such as ethyl acetate; Examples include halogenated hydrocarbons such as carbon tetrachloride, chloroform, and 1,1,2,2-tetrachloro-1°2-difluoroethane.

Among the above water-insoluble solvents, halogenated hydrocarbons, aliphatic hydrocarbons, and aromatic hydrocarbons are preferred for reasons such as ease of separation operation and economic efficiency. Also, n-hexane, 1
Performing the separation operation using a solvent such as so-octane or ligroin that hardly dissolves the starting material polyfluoroaromatic carboxylic acid but well dissolves the target polyfluoroaromatic aldehyde and polyfluoroaromatic alcohol. This not only makes it easier to isolate the target product, but also allows the extraction residue to be reused as it is as an electrolytic solution.

〔Example〕

The present invention will be described in more detail below with reference to Examples, but it goes without saying that the technical scope of the present invention is not limited to these Examples.

(Polyfluorobenzaldehyde Experimental Example) Implementation ■Electric Ce1l divided into negative and positive polarity chambers through an Enafion membrane (DuPont's Nafion 423, fluorine-based ion exchange membrane).
A filter press type microcell (cathode chamber capacity: 10 d) manufactured by AB) was used, and a lead plate (effective electrode area: 10 d) was used as the cathode.
c+fl), and a platinum-titanium plate (effective electrode area 1
An electrolyzer equipped with 0afl) was used. 120ml of 1% by weight sulfuric acid for both Yin and Yang electrolytes! was used. 1.27 g of pentafluorobenzoic acid (6
,00 mmol) and as onium salts tetraethylammonium, valatoluenesulfone) 0. 72g
(2.40 mmol) was added.

Next, add the electrolyte to 0.74! The temperature of the catholyte was maintained at 20 to 22°C while circulating it through each electrode chamber at a flow rate of 15 mF at a current density of 4^/dm''.
Electrolytic reduction was performed by passing an amount of electricity.

After the electrolysis, the catholyte was extracted with ether, and the extracted liquid was analyzed by gas chromatography. The results were as follows.

Conversion rate of pentafluorobenzoic acid (starting material) 41.6
Mol% 1.38 mmol of 2,3.5.6-titrafluorobenzaldehyde produced (selectivity 55 mol%, current efficiency 37%)
) Produced 0.65 mmol of 2.3,5.6-titrafluorobenzyl alcohol (selectivity 26 mol%, current efficiency 26
%) Tsubasayo I The same equipment as in Example 1 was used, except that 1.16,5 gr (6 mmol) of 2,3,5,6-tetrafluorobenzoic acid was used instead of pentafluorobenzoic acid as the raw material. Electrolytic reduction was performed under exactly the same conditions as in Example 1.

Ether extraction was performed in the same manner as in Example 1, and gas chromatography analysis gave the following results.

Conversion rate of 2.3,5.6-tetrafluorobenzoic acid (raw material) 44 mol% 1.48 mmol of 2.3,5.6-titrafluorobenzaldehyde produced (selectivity 56 mol%, current efficiency 20%)
) Produced 0.84 mmol of 2.3,5.6-titrafluorobenzyl alcohol (selectivity 32 mol%, current efficiency 22
%) The same equipment as in Example 1 was used, and 1% by weight of sulfuric acid (120-) was used for both the anode and negative electrodes as the electrolyte, and 2,3.5-) lifluorobenzoic acid (0) was used for the cathode electrolyte. .88
1 gr (5 mmol) was added.

Next, add each electrolyte to 0.71. The electrolysis temperature was maintained at 25℃ while circulating at a flow rate of 6 A/dm.
Electrolytic reduction was carried out through a current density of 20 mF.

After the electrolysis was completed, the catholyte was extracted with ether.

The results of gas chromatography analysis of the obtained extract were as follows.

2.3.5-Conversion rate of 1-lifluorobenzoic acid (raw material) 32.1 mol% Production 2,3.5) Lifluorobenzaldehyde 0.
512 mmol (selectivity 32.5 mol%, current efficiency 5.
2%) Production 2.3.5-1-Lifluorobenzyl alcohol 1
．． 00 mmol (selectivity 62.3 mol%, current efficiency 20
．． 0%)

Claims (1)

[Claims] 1. In producing a polyfluoroaromatic aldehyde of the following general formula (II) by electrolytically reducing a polyfluoroaromatic carboxylic acid of the following general formula (I), ▲mathematical formula, chemical formula,
There are tables, etc. ▼・・・・・・・・・(I) [In the above formulas (I) and (II), n and m each independently represent an integer from 1 to 5, m≦n, X represents hydrogen, an alkyl group of C_1 to C_3, or a halogen other than F, and when multiple Xs exist as substituents, they may be the same or different.] Solid metal or solid as the cathode 1. A method for producing polyfluoroaromatic aldehyde, which comprises using an alloy and using an aqueous solution of sulfuric acid, hydrochloric acid, phosphoric acid, or sulfonic acids as an electrolyte. 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.
The manufacturing method according to item 1 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. 6. The conversion rate of the polyfluoroaromatic carboxylic acid is 30
Claim 1, which adjusts to a range of ~70 mol%~
The manufacturing method according to any one of Item 5.