JP2525868B2 - Method for producing 2-ethyl-1,3-hexanediol - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing 2-ethyl-1,3-hexanediol. 2-Ethyl-1,3-hexanediol having a high threo form ratio obtained by the method of the present invention is useful as a raw material for polymers, organic compounds, metal compounds and the like.

2. Description of the Related Art Conventionally, it is known that 2-ethyl-1,3-hexanediol can be obtained by the following method.

For example, generally, a method is used in which butyraldehyde is subjected to aldol condensation in the presence of an alkali hydroxide (eg, sodium hydroxide, potassium hydroxide, etc.), and then the aldol condensate is reduced.

Also, in hexamethylphosphoric triamide, 2,4,
It is known to be obtained by reacting butyraldehyde with 6-trimethylphenoxymagnesium bromide catalyst and then hydrolyzing it [Synthesis (Sy
nthesis), 1975 , 164]. It is also known to be obtained by butyraldehyde self-condensation in the presence of Mg-Al mixed butyrate [Chemical Abstract
acts), 53 , 6145i].

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the conventional method of using alkali hydroxide as a catalyst in the aldol condensation, an erythro-form of 2-ethyl-1,3-hexanediol is advantageously produced, and a ratio of the threo form is high. I can't get anything.

Further, it has not been reported that 2-ethyl-1,3-hexanediol having a high threo form ratio can be obtained by other methods.

A method for obtaining 2-ethyl-1,3-hexanediol having a high threo form ratio has been desired.

According to the method of the present invention, butyraldehyde is subjected to aldol condensation in the presence of an alkali metal alcoholate to reduce 2-ethyl-3-hydroxyhexanal, thereby increasing the threo ratio (ie threo / erythro). = 60/40
~ 70/30) 2-Ethyl-1,3-hexanediol can be obtained.

 Hereinafter, the present invention will be described in detail.

Butyraldehyde is subjected to aldol condensation, and then the carbonyl group of the condensation product, 2-ethyl-3-hydroxyhexanal (hereinafter sometimes abbreviated as compound I) is reduced to give 2-ethyl-1,3-hexanediol ( Less than,
Compound II may be abbreviated) is shown by the following reaction scheme.

* Indicates an asymmetric carbon atom.

Further, when the stereoscopic structures of asymmetric carbon atoms are distinguished, compound I
And II are represented as follows (both show only one enantiomer):

In the reduction step from compound I to compound II, the two asymmetric carbon atoms both retain the three-dimensional structure.
The threo / erythro ratio of is determined by the stage of formation of compound I.

Next, the method of the present invention is applied to the aldol condensation and reduction reaction
The steps will be described.

(A) Aldol Condensation As the alkali metal alcoholate of the aldol condensation catalyst used in the present invention, sodium alcoholate, potassium alcoholate and the like can be mentioned. Particularly, sodium lower alcoholate such as sodium methylate and sodium ethylate is easy to handle and priced. Is advantageous.

The catalyst amount, the reaction temperature and the reaction time range differ depending on the conditions, but generally the catalyst amount is 0.05 to 5 mol%, particularly 0.1 to 2 mol% relative to butyraldehyde, and the reaction temperature is 0 to The reaction time is preferably 1 hour or less, usually 30 minutes or less at 100 ° C, particularly 10 to 80 ° C.

It is preferable to add the catalyst after diluting it with an appropriate organic solvent rather than adding it in the form of powder, in order to prevent the catalyst from locally becoming high in concentration in the reaction solution. As the organic solvent used as the catalyst diluent, any solvent can be used as long as it dissolves the catalyst and does not react with the catalyst or butyraldehyde. For example, lower alcohols such as methanol, ethanol, propanol and butanol are preferable. Is.

The reaction can be carried out in either a batch system or a continuous system, but the continuous system is industrially more efficient. After completion of the reaction, in order to prevent a side reaction (formation of 2-ethyl-2-hexenal by dehydration of compound I) under basic conditions, the reaction solution is treated with an organic acid such as formic acid, acetic acid or hydrochloric acid, sulfuric acid,
It is preferable to neutralize with an inorganic acid such as phosphoric acid. After neutralizing the reaction solution, the compound I may be isolated and subjected to the reduction reaction in the next step. However, since the compound I is unstable, the neutralized reaction solution may be directly or simply post-treated (for example, washed with water). It is preferable that the reduction is carried out by the following method only after the removal of alkali metal salt due to excess, etc.).

(B) Reduction Reaction In order to obtain Compound II from Compound I by a reduction reaction, catalytic reduction or reduction with a metal hydrogen complex compound such as LiAlH ₄ or NaBH ₄ may be used, but industrially catalytic reduction is preferred. As the catalytic reduction catalyst, a usual carbonyl group reduction catalyst such as Ni-based, Pt-based, Ru-based, Cu-based is used. The suitable reaction temperature and hydrogen pressure vary depending on the type and amount of the catalyst, but generally the reaction temperature is room temperature to 300 ° C, preferably 50 to 200 ° C, and the hydrogen pressure is 1 to 300 atm, preferably 5 to 200 atm. . The reaction time is 10 minutes to 10 hours, preferably 30 minutes to 5 hours.
The reaction solution is treated by a conventional method such as excess, extraction, concentration, distillation, etc., so that the threo ratio is high (ie threo / erythro = 60
/ 40-70 / 30) 2-Ethyl-1,3-hexanediol is obtained.

 Examples and reference examples are shown below.

Example 1 Three tubes with a capacity of 50 ml equipped with three tubes for introducing butyraldehyde, for introducing a catalyst solution and for withdrawing a reaction solution and a thermometer.
25 ml of butanol was added to the one-necked flask. Next, using a metering pump, butanol solution of butyraldehyde and sodium methylate (6.12 g /) was added at a rate of 2.72 ml / min, and stirred, and at the same time, the reaction solution was metered by the metering pump to 5.
It was withdrawn at a rate of 44 ml / min. This extract was neutralized with a 50% butanol solution of acetic acid. During the reaction, set the temperature in the flask to 30 ±
The neutralized solution was kept at 2 ° C. and analyzed by gas chromatography as needed.

The analytical values after the composition reached equilibrium were as follows.

2-Ethyl-3-hydroxyhexanal 45.8 area% (Hereinafter,% represents area%) 2-Ethyl-2-hexenal 4.9% Unreacted butyraldehyde 45.7% Next, 100 ml of the above neutralization liquid was used in 200 ml autoclave.
Catalytic reduction was carried out in the presence of 8.6 g of Raney Ni at a hydrogen pressure of 50 atm and 100 ° C. for 1 hour. When this reaction liquid was analyzed by gas chromatography, the threo / erythro ratio of the produced 2-ethyl-1,3-hexanediol was 64/36.

Example 2 A coil portion of a reactor in which two pipes for supplying butyraldehyde and for supplying a catalyst solution were connected to the inlet side of a SUS coil having an inner diameter of 2 mm, an outer diameter of 3 mm and a length of 8 m was immersed in a water bath. While maintaining the bath temperature at 30 ° C., butanol solution of butyraldehyde and sodium methylate (6.12 g /) was fed at a rate of 2.72 ml / min each by a metering pump. The reaction liquid discharged from the outlet was neutralized with a 50% butanol solution of acetic acid. This neutralized solution was analyzed by gas chromatography as needed. The analytical values after the composition reached equilibrium were as follows.

2-Ethyl-3-hydroxyhexanal 54.2% 2-Ethyl-2-hexenal 4.9% Unreacted butyraldehyde 35.2% Next, the neutralized solution was reduced under the same conditions as in Example 1 to produce 2-ethyl-1. The threo / erythro ratio of 3,3-hexanediol was 64/36.

Example 3 A reaction was carried out in the same manner as in Example 2 except that the concentration of the butanol solution of sodium methylate was changed to 3.06 g / and the bath temperature was changed to 40 ° C. The analytical values of the aldol condensation reaction solution and the catalytic reduction reaction solution were as follows.

2-Ethyl-3-hydroxyhexanal 52.6% 2-Ethyl-2-hexenal 8.5% Unreacted butyraldehyde 34.5% Threo / erythro ratio 68/32 Example 4 In Example 2, the concentration of sodium methylate in butanol was 12.24 g. The reaction was performed in the same manner as in Example 2 except that the bath temperature was changed to 22 ° C. in /. The analytical values of the aldol condensation reaction solution and the catalytic reduction reaction solution were as follows.

2-Ethyl-3-hydroxyhexanal 52.6% 2-Ethyl-2-hexenal 5.3% Unreacted butyraldehyde 38.8% Threo / erythro ratio 65/35 Reference Example 1 Using the same apparatus as in Example 1, butanol was charged in the flask. The reaction was carried out in the same manner as in Example 1 except that the amount was 50 ml and the sodium hydroxide aqueous solution (4.53 g /) was used in place of the sodium methylate butanol solution. The analytical values of the aldol condensation reaction solution and the catalytic reduction reaction solution were as follows.

2-Ethyl-3-hydroxyhexanal 39.7% 2-Ethyl-2-hexenal 5.0% Unreacted butyraldehyde 54.3% Threo / erythro ratio 45/55 Effect of the invention 2-Ethyl-1, which has a high threo form ratio by the method of the present invention,
3-hexanediol can be manufactured at low cost.

Claims (1)

(57) [Claims] 1. Butylaldehyde is aldol-condensed in the presence of an alkali metal alcoholate to give 2-ethyl-3-
Hydroxyhexanal is obtained, then the 2-ethyl-3
A method for producing 2-ethyl-1,3-hexanediol, which comprises reducing hydroxyhexanal.