JPH08133998A - Reduction of sorbic acid - Google Patents

Abstract

PURPOSE: To obtain an aldehyde or an alcohol derivative in good yield under extremely mild conditions by reacting sorbic acid with a chloroformic acid ester, providing a mixed acid anhydride and then reducing the resultant anhydride with a metal boron hydride. CONSTITUTION: Sorbic acid is initially reacted with a chloroformic acid ester of the formula ClCOOR (R is a 1-20C alkyl, an alkenyl, etc.) (preferably methyl chloroformate or ethyl chloroformate), preferably in the presence of THF which is a reactional solvent and a base to provide a mixed acid anhydride of the formula. The resultant mixed acid anhydride is subsequently reduced with a metal boron hydride (preferably NaBH4 or LiBH4 ), preferably in THF to afford an aldehyde derivative of the formula CH3 CH=CHCH=CHCHO or an alcohol derivative of the formula CH3 CH=CHCH=CH2 OH. Furthermore, the temperature of the reducing reaction is usually -50 to +30 deg.C. When the aldehyde derivative is to be preferentially obtained, the temperature is preferably -50 to 0 deg.C. The temperature in preparing the mixed acid anhydride is preferably -20 to -l20 deg.C.

Description

TECHNICAL FIELD The present invention relates to a novel method for reducing sorbic acid, and more particularly to a method for reducing sorbic acid with metal borohydride.

(Prior Art) Conventionally, as a method for reducing a saturated carboxylic acid, lithium aluminum hydride is usually used for reduction in ether or tetrahydrofuran.

However, in the case of unsaturated carboxylic acid, it is very difficult to selectively restore only the carboxyl group because the double bond is easily hydrolyzed. For example, reduction of cinnamic acid with lithium aluminum hydride reduces dihydrocinnamyl alcohol without producing cinnamyl alcohol [R. F. Nystron et al., J. Am. Chem. Soc., 69, 2548 (1947)].

There is also a method of reacting with a reaction system of lithium aluminum hydride-anhydrous aluminum chloride in order to protect the unsaturated bond, but if this is applied to the reduction of sorbic acid having a conjugated diene bond, the yield will be significantly reduced. The rate is low.

CH ₃ CH = CH-CH = CH-CH ₂ OH Yield 20% Moreover, it is difficult to terminate unsaturated carboxylic acid with aldehyde in these reduction reactions, and lithium aluminum hydride is extremely expensive. Not an industrial method.

On the other hand, sodium borohydride, which is relatively inexpensive, has a weak reducing power and it is difficult to reduce carboxylic acid. In order to enhance its recovery, sodium borohydride-hydrous aluminum chloride may be reacted in diglyme (diethylene glycol dimethyl ether) [HC Brown et al., J. Am. Chem. Soc., 75, 6263 (1953). ], Or a method used with BF ₃ [GRPettit et al., J. Org. Chem., 27, 21 27 (1962)] has been introduced. However, since these use an inorganic Lewis acid, the process is complicated and side reactions easily occur when the reaction product is unstable, and the yield is generally low. Furthermore, there are many disadvantages such as the problem of recoverability of diglyme and the problem of wastewater treatment of aluminum chloride, and the selectivity of the reduction operation is not satisfactory either.

 Both lithium aluminum hydride and sodium borohydride are typical complex compounds that can reduce many organic compounds by giving hydrogen as hydride ions, but the former with strong reducing power is expensive in itself. However, the latter is relatively inexpensive, but has a weak reducing power, and thus requires an auxiliary agent, etc., which has the drawback of complicating the process and lowering the yield. In both cases, the carboxylic acid is suppressed by reduction to the aldehyde. That is extremely difficult.

(Means for Solving the Problems) As a result of various studies to solve these problems, the present inventors have made sorbic acid react with a chloroformate ester represented by methyl chloroformate and ethyl chloroformate. The inventors have found that by treating the mixed acid anhydride with sodium borohydride, the corresponding aldehyde or alcohol can be synthesized in high yield under extremely mild conditions, and the present invention has been completed.

Therefore, the method for reducing sorbic acid according to the present invention is a method in which sorbic acid is represented by the general formula ClCOOR (wherein R is an alkyl group, alkenyl group, alkynyl group or allyl group having 1 to 20 carbon atoms) An acid ester is reacted to form a mixed acid anhydride represented by the general formula CH ₃ CH═CHCH═CHCOOCOOR, which is then reduced with a metal borohydride to give a corresponding aldehyde CH ₃ CH═CHCH═CHCHO or an alcohol derivative. The summary is that CH ₃ CH = CHCH = CH ₂ OH.

 Hereinafter, the present invention will be described in detail.

 The method of reducing sorbic acid according to the present invention is represented by the above-mentioned general formula as follows.

As the chloroformic acid ester to be used, inexpensive methyl chloroformate or ethyl chloroformate is preferable.

 Mixed acid anhydrides include ethers such as diethyl ether, reducing ethers such as tetrahydrofuran (THF), and amines such as triethylamine and pyridine in various, preferably anhydrous solvents such as dimethoxyethane and diglyme. It is desirable to prepare at -20 ° C to 20 ° C in the presence of a base such as. In addition, at this time, a hydrochloride of a base such as triethylamine hydrochloride is simultaneously produced, but if it coexists in the reaction system, the yield of the mixed acid anhydride is slightly reduced, and therefore it is preferable to remove it by filtration.

Since the mixed acid anhydride thus obtained is relatively unstable, it is preferable to keep the temperature as low as possible and proceed to the next reduction step promptly.

 In the reduction step, sodium borohydride may be suspended in the same various solvents as described above, and the mixed acid anhydrous solution may be added dropwise thereto. The reaction temperature is −50 to 30 ° C., but −50 to 0 ° C. is preferable when it is desired to obtain the aldehyde derivative in a dominant manner. The solvent in this case need not be anhydrous and may be an aqueous solution. It is preferable to use THF for both the steps of mixed acid anhydride and reduction.

 Sodium borohydride is added in an amount of 1.0 to 1.5 equivalents relative to sorbic acid when the aldehyde form is to be obtained predominantly, and the reaction time is 2 to 6 hours. When the alcohol form is to be obtained, 1.5 to 2.5 equivalent is required. The reaction may be carried out for 1 to 5 hours as an equivalent. Normally, if 3.0 equivalents to sorbic acid are used, all alcohols will be formed. When the aldehyde form is obtained predominantly, the yield is slightly lower than when the alcohol form is obtained. After completion of the reaction, 20% hydrochloric acid water is added to easily isolate the product from the organic layer.

As an example of this reaction, using ethyl chloroformate as the chloroformate ester le, the yield in the case of performing at 10 to 15 ° C. in THF was added to 2 moles of sodium borohydride, the alcohol compound (CH ₃ CH = CHCH = CHCHO) 9%, aldehyde form _{(CH 3 CH = CHCH = CH} 2 - OH) was 58%.

 Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to the description of the Examples.

Example 1 28 g (0.25 mol) of sorbic acid was dissolved in 100 ml of THF, 25 g of triethylamine was added, and ethyl chloroformate was added dropwise at 0 to 10 ° C over 30 minutes. After the dropwise addition was completed, the mixture was stirred at 10 ° C for 30 minutes and quickly filtered to remove triethylamine. Then, 19 g (0.5 mol) of sodium borohydride is suspended in 100 ml of THF, and a THF solution of the above mixed acid anhydride is added dropwise at 10 to 15 ° C. under N ₂ atmosphere. After completion of dropping, the mixture was stirred at 20 ° C for 30 minutes, 100 ml of 10% HCl water was added for liquid separation, and THF in the organic layer was removed by a rotary evaporator and then distilled to yield 16.4 g of product (bp 80 to 86 ° C). / 10 mmHg) was obtained (yield: 67%). The ratio of the aldehyde form (2,4-hexadiene-1-al) and the alcohol form (2,4-hexadiene-1-ol) was confirmed by gas chromatography to be 14:86.

Example 2 The procedure of Example 1 was repeated except that the amount of sodium borohydride was 28.5 g (0.75 mol), and the product was 16.7 g (bp 85 to 86 ° C./10 mmHg). Was obtained (yield: 68%). When this was confirmed by gas chromatography, it was 2,4-hexadiene-1-ol which was an alcohol compound.

Comparative Example 1 12 g (0.31 mol) of lithium aluminum hydride was dissolved in 100 ml of anhydrous THF, 13 g (0.1 mol) of anhydrous aluminum chloride at 0 to 10 ° C was gradually added, and the mixture was stirred at 10 ° C for 30 minutes. Next, 28 g (0.25 mol) of sorbic acid dissolved in 100 ml of anhydrous THF was added dropwise at 0 to 20 ° C for 1 hour. After the completion, 100 ml of 10% HCl was added for liquid separation, and THF of the organic layer was removed by a rotary evaporator and then distilled to obtain 4.9 g (yield: 20%) of 2,4-hexadien-1-ol. It was

Comparative Example 2 12 g (0.31 mol) of sodium borohydride was dissolved in 100 ml of anhydrous diglyme, 13 g (0.1 mol) of anhydrous aluminum chloride at 0 to 10 ° C was gradually added, and the mixture was stirred at 10 ° C for 30 minutes. Then, 28 g (0.25 mol) of sorbic acid dissolved in 100 ml of anhydrous diglyme was added dropwise at 0 to 20 ° C for 1 hour. After completion of the dropping, 100 ml of 10% HCl was added for liquid separation, and the organic layer was distilled to obtain 4.0 g (b.p. 79-81 ° C / 15 mmHg) of the product. When this was identified by gas chromatography, it was 5.1% for 2,4-hexadiene-1-ol (1.0% yield to sorbic acid) and 94.9% for n-hexanol (19%).

(Effects of the Invention) According to the method of the present invention, reduction of sorbic acid can be performed in a high yield under extremely mild conditions, and the molar ratio of metal borohydride and the reaction temperature can be changed. It is also possible to change the ratio of the corresponding alcohol form and aldehyde form.

Claims (2)

[Claims] 1. A chloric acid ester represented by the general formula ClCOOR (wherein R is an alkyl group, an alkenyl group, an alkynyl group or an allyl group having 1 to 20 carbon atoms) is reacted with sorbic acid to give a general formula CH ₃ CH═CHCH═CHCOOCOOR is used as a mixed acid anhydride, which is then reduced with a metal borohydride to give the corresponding aldehyde CH ₃ CH═CHCH═CHCHO or alcohol CH ₃ CH═CHCH═CH ₂ A method for reducing sorbic acid, which comprises using OH. 2. The method for reducing a carboxylic acid according to claim 1, wherein the metal borohydride is sodium borohydride or lithium borohydride.