JPH08119903A - Production of lactic acid ester - Google Patents

Abstract

PURPOSE: To produce a lactic acid ester under mild condition on an industrial scale at a low cost by reacting propylene glycol known as a general-purpose industrial chemical with an alcohol in the presence of a ruthenium complex compound and a hydrogen acceptor. CONSTITUTION: A lactic acid ester is produced by reacting propylene glycol with an alcohol in the presence of a ruthenium complex compound as a catalyst and a hydrogen acceptor. The ruthenium complex compound is a compound having a substituted cyclopentadienone compound as a ligand, e.g. (PR4 C4 CO)Ru(CO)3 . The presence of the hydrogen acceptor proceeds the catalyst cycle in high efficiency. Preferable hydrogen acceptors are pyruvic acid esters and hydroxyacetone. Lactic acid esters are useful as an intermediate for various organic compounds including pharmaceuticals and agrochemicals and as a cleaning solvent for the manufacture of semiconductors.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a lactate ester from propylene glycol. Lactic acid esters are useful as intermediates for various organic compounds such as pharmaceuticals and agricultural chemicals, and as a cleaning solvent during semiconductor manufacturing.

[0002]

2. Description of the Related Art As a method for producing lactic acid from propylene glycol, a method is known in which propylene glycol and molecular oxygen are brought into contact with each other in an alkaline aqueous solution using a platinum group element as a catalyst to obtain a high yield (Japanese Patent Application Laid-Open No. 2000-242242). Sho 49-30315 publication). However, in this method, lactic acid is obtained as an alkali salt, and in order to produce a lactic acid ester, a complicated step such as esterification by reaction with alcohol after further acid treatment to give free lactic acid is required. A large amount of inorganic salt is by-produced in the process, which is not desirable as an industrial production method.

Further, some reactions have been reported so far in which a ruthenium complex compound is used to produce an ester compound from an alcohol in the presence of a hydrogen acceptor such as benzalacetone and diphenylacetylene (for example, Y. Blum et a.
l., Journal of Organometallic Chemistry, 263, p. 93
(1984) / S. Murahashi et al., Journal of Organic Ch
emistry, Vol. 52, p. 4319 (1987)) is a reaction which in most cases uses one alcohol to obtain the corresponding ester. When this reaction is carried out in the coexistence of two kinds of (primary) alcohols, several kinds of esters are generally produced. However, an example of a method for producing a lactate ester by using propylene glycol by reacting with an alcohol other than propylene glycol has not been known until now.

[0004]

An object of the present invention is to provide a method for industrially advantageously producing lactic acid ester from propylene glycol, which is a general-purpose industrial product, under mild conditions.

[0005]

The present invention provides a method for producing a lactate ester, which comprises reacting propylene glycol with an alcohol in the presence of a ruthenium complex compound and a hydrogen acceptor. In the esterification reaction of propylene glycol and alcohol of the present invention, an ester consisting of two or more molecules of propylene glycol, which is an undesirable by-product, and a ester of carboxylic acid and carboxylic acid formed by the formal oxidation of alcohol and propylene glycol The generation can be almost suppressed. (Raw material) The raw material propylene glycol means 1,2-propanediol. Propylene glycol is
It is produced by hydrolysis of 1,2-dichloropropane with an aqueous sodium bicarbonate solution, hydroxylation of propylene with hydrogen peroxide, or hydrolysis reaction of propylene oxide. As the raw material used in the present invention, commercially available propylene glycol may be used as it is,
Those that have been dehydrated and degassed are more preferable.

The alcohol used in the reaction may be a commercially available alcohol, but is preferably dehydrated and deaerated by a conventional method. The alcohol used is grade 1,
Corresponding lactic acid esters can be obtained with both secondary and tertiary alcohols, but primary alcohols are preferred because they have a faster reaction rate than other alcohols. Examples of the alcohol include aliphatic alcohols having 1 to 20 carbon atoms such as methanol, ethanol, propanol and butanol, and aromatic alcohols having 6 to 30 carbon atoms such as phenol and benzyl alcohol. Although an equivalent amount (equimolar amount) of alcohol is sufficient with respect to the raw material propylene glycol, in order to improve the reaction rate and to suppress by-products such as an ester composed of two or more molecules of propylene glycol. It is preferable to use 5 to 20 (molar ratio). From the viewpoint of suppressing by-products and improving kettle efficiency, it is particularly preferable to use 2 to 8 (molar ratio). (Ruthenium Catalyst) As the ruthenium complex compound used as a catalyst, a conventionally known ruthenium complex compound having an oxidizing ability to form an ester from an alcohol can be used. The ruthenium complex compound means an organometallic compound of ruthenium, and its definition is widely known at present (for example, Akio Yamamoto, Organometallic Chemistry, Yukabo, 1991).
, P6), mainly means a compound in which ruthenium and an organic group (ligand) are bonded by a direct metal-carbon bond. As such ruthenium complex compounds, some are already known as mononuclear and polynuclear complexes, and these conventionally known ruthenium complex compounds can be generally used in the method of the present invention. Specifically, H ₂ Ru (PPh ₃ ) ₄ , H ₂ Ru (CO) (P
Ph ₃ ) ₃ , Ru ₃ (CO) ₁₂ , RuCl ₂ (PPh ₃ ) _{3 and the} like. Further, ruthenium complex compounds for which alcohol esterification reaction has not been reported so far can also be used. For example, (Ph ₄ C ₄ CO) ₂ H (μ-H) (CO) ₄ R
u _{2 and the} like.

The formal oxidation number of the ruthenium atom in the ruthenium complex compound that can be used and the kind and number of the organic group as a ligand are not limited. As the ligand of the ruthenium complex compound, carbon monoxide, phosphine, hydride and substituted cyclopentadienone compounds are preferable. Particularly, a substituted cyclopentadienone compound is preferable, and a lactic acid ester can be efficiently obtained from propylene glycol and alcohol under mild conditions. Examples of such a ruthenium complex compound include (Ph ₄ C ₄ CO) Ru (CO) ₃ , [(4-ClC
₆ H ₄ ) ₄ C ₄ CO] Ru (CO) ₃ , [2,5- (C ₆ H ₄ ) _{2-
3,4- (4-MeOC 6 H 4} ) 2 C 4 CO] Ru (CO) 3,
_{[2,5- (C 6 H 4)} 2 -3,4- (4-FC 6 H 4) 2 C 4 C
O] Ru (CO) ₃ , (Ph ₄ C ₄ CO) ₂ H (μ-H) (CO) _{4
Ru 2, [(4-ClC} 6 H 4) 4 C 4 CO] 2 H (μ-H) (C
_{O) 4 Ru 2, [2,5-} (C 6 H 4) 2 -3,4- (4-Me
_{OC 6 H 4) 2 C 4} CO] 2 H (μ-H) (CO) 4 Ru 2,
_{[2,5- (C 6 H 4)} 2 -3,4- (4-FC 6 H 4) 2 C 4 C
O] ₂ H (μ-H) (CO) ₄ Ru _{2 and the} like. These are known methods (N. Menashe et al., Organometallics, V
ol.10, p.3885 (1991)).

The amount of the ruthenium complex compound used is 0.0000001 to 1 relative to the raw material propylene glycol.
(Molar ratio), preferably 0.000001 to 0.01
(Molar ratio). The catalyst is separated from the reaction product by a general method such as distillation, extraction or adsorption,
Can be used repeatedly. (Reaction Solvent etc.) The reaction of the present invention can be carried out without using a solvent, but when the ruthenium complex compound used is hardly soluble in the reaction system consisting of the raw material propylene glycol, hydrogen acceptor and alcohol, This can be carried out to dissolve it and, if necessary, in a suitable solvent. Examples of these solvents include hydrocarbons such as hexane, benzene and toluene; ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran and dioxane; esters such as ethyl acetate, butyl acetate and butyrolactone.

The reaction of the present invention is carried out in the presence of a hydrogen acceptor in order to allow the catalytic cycle to proceed efficiently. The catalytic cycle of this reaction is considered to proceed as follows (for example, S. Murahashi et al., Journal of Organic
Chemistry, Vol.52, p.4319 (1987)). First, propylene glycol is dehydrogenated by a ruthenium complex compound at the primary hydroxyl group to become lactate aldehyde. The ruthenium hydride complex produced by dehydrogenation transfers hydrogen to the hydrogen acceptor and the original ruthenium complex compound is regenerated. Lactic acid aldehyde reacts rapidly with alcohol, and the resulting hemiacetal is dehydrogenated by the ruthenium complex compound again to form the corresponding lactate compound. The ruthenium hydride complex produced by dehydrogenation similarly transfers hydrogen to the hydrogen acceptor to produce the original ruthenium complex compound, and the catalytic cycle proceeds. Also, the hydrogen acceptor is converted to the corresponding hydride through this cycle. If necessary, this hydride can be dehydrogenated by an appropriate method and repeatedly used. Although the present invention can be carried out in the absence of a hydrogen acceptor, the elimination of molecular hydrogen from the ruthenium hydride complex requires high activation energy, and therefore the reaction rate is significantly slow and Absent.

Examples of the hydrogen acceptor include α, β-unsaturated carbonyl compounds such as mesityl oxide, methyl vinyl ketone and benzalacetone, ketones such as acetone, cyclohexanone and hydroxyacetone, and disubstituted acetylene and the like. Examples include α-keto acid esters such as acetylenes, pyruvic acid esters, and phenylglyoxylic acid esters. By using these hydrogen acceptors, lactic acid ester can be efficiently produced by the reaction of propylene glycol and alcohol in the presence of a ruthenium complex compound. Particularly, a carbonyl compound having an electron-withdrawing group at an adjacent carbon, such as hydroxyacetone and pyruvic acid ester, has a high hydrogen accepting ability and is preferable.
Pyruvate is most preferable because it has a particularly high hydrogen-accepting ability and becomes a lactate by hydrogen transfer, which simplifies the separation operation of the product. If necessary, the pyruvic acid ester can be repeatedly used by using a known dehydrogenation reaction (for example, JP-A-5-17404) in combination.

The amount of hydrogen acceptor used is in the range of 2 to 100 (molar ratio), preferably 2 to 10 (molar ratio), based on the raw material propylene glycol. (Esterification reaction) The reaction is sufficiently performed even at room temperature or lower, but is usually performed under heating in order to further improve the reaction rate. The reaction temperature is 0 to 200 ° C., preferably 50 to
It is in the range of 180 ° C. Although the reaction can be carried out in air, it is generally carried out in a deoxygenated atmosphere, and the reaction is carried out by degassing in a vacuum or substituting with an inert gas such as nitrogen or argon. Although the reaction time depends on the reaction temperature, it is usually 0.1.
~ 200 hours, preferably 0.5 to 100 hours.

The hydrogen acceptor may be allowed to coexist in a reaction solution containing a predetermined amount of propylene glycol, an alcohol and a ruthenium complex compound at the same time to carry out the reaction.
Alternatively, propylene glycol may be sequentially added to the reaction liquid containing the hydrogen acceptor. The reaction product obtained by this reaction is a lactate ester. At the same time, hydroxyacetone, which is a dehydrogenated product from the secondary hydroxyl group of the raw material propylene glycol, is also produced. Hydroxyacetone acts as a hydrogen acceptor in the system to assist the production of lactate ester. Hydroxyacetone can also be regenerated into a raw material propylene glycol by a known hydrogenation reaction. (Post-treatment) The product can be separated from the reaction mixture containing the catalyst by a known method such as distillation, extraction or adsorption.

[0013]

EXAMPLES Next, the present invention will be described in more detail with reference to experimental examples. The product was quantitatively analyzed by an internal standard method using toluene as an internal standard substance using gas chromatography, and the conversion rate and the selectivity were determined by the following formulas.

[0014]

[Equation 1]

* 1) By-product derived from raw material propylene glycol: hydroxyacetone, etc. When pyruvic acid ester is used as a hydrogen acceptor, the lactate ester (mol number) produced from propylene glycol is determined according to the following formula. Lactic acid ester formed (number of moles) = lactic acid ester (number of moles) in reaction solution-converted pyruvate ester (number of moles) The turnover number used in the examples was calculated according to the following formula.

[0016]

[Equation 2]

<Embodiment 1> A glass ampoule having an internal volume of 20 ml was charged with a stirrer and (Ph ₄ C ₄ CO) ₂ H (μ) under a nitrogen stream.
_{-H) (CO) 4 Ru 26.3} mg (0.006 mmol), propylene glycol 482.8 mg (6.34mmol),
Ethanol 937.2 mg (20.3 mmol), ethyl pyruvate 1404 mg (12.1 mmol) and toluene 180 mg as an internal standard substance for analysis were charged, the ampoule was sealed, and the reaction was carried out at 90 ° C. for 12 hours. It was After completion of the reaction, the ampoule was opened and the contents were analyzed by gas chromatography.

As a result, 290 mg of propylene glycol
(3.81 mmol), ethyl pyruvate 2.6 mg (0.0
2mmol) was recovered and ethyl lactate 1574.3mg (1
3.3 mmol) was produced. In addition, hydroxyacetone (32%) was produced. The conversion of the raw material propylene glycol was 39.8%, the selectivity of ethyl lactate from propylene glycol was 49.3%, and the turnover number was 204 (mol / mol). Glass ampule <Example 2> internal volume 20 ml, under nitrogen stream, stirring _{bar, (Ph 4 C 4 CO)} 2 H (μ-H) (CO) 4
Ru ₂ 2.7 mg (0.003 mmol), propylene glycol 554.2 mg (7.28 mmol), ethanol
1251 mg (27.2 mmol), ethyl pyruvate 29
After charging 54 mg (25.4 mmol) and 273 mg of toluene as an internal standard substance for analysis, the ampoule was sealed and the reaction was carried out at 115 ° C. for 3 hours. After completion of the reaction, the ampoule was opened and the contents were analyzed by gas chromatography.

As a result, propylene glycol 288 mg
(3.78 mmol), 2049 mg of ethyl pyruvate (1
7.6 mmol) was recovered and 1162 mg of ethyl lactate
(9.8 mmol) was produced. In addition, hydroxyacetone (42%) was produced. The conversion of the raw material propylene glycol was 48.1%, the selectivity of ethyl lactate from propylene glycol was 57.8%, and the turnover number was 772 (mol / mol). Glass ampule <Example 3> internal volume 20 ml, under nitrogen stream, stirring _{bar, (Ph 4 C 4 CO)} 2 H (μ-H) (CO) 4
Ru ₂ 2.0 mg (0.002 mmol), propylene glycol 307.0 mg (4.03 mmol), ethanol 8
85.7 mg (19.2 mmol), ethyl pyruvate 22
After charging 16 mg (19.1 mmol) and 206 mg of toluene as an internal standard substance for analysis, the ampoule was sealed and the reaction was carried out at 145 ° C. for 3 hours. After the reaction,
The ampoule was opened and the contents were analyzed by gas chromatography.

As a result, propylene glycol 37.1
mg (0.49 mmol), ethyl pyruvate 379 mg (3.
3 mmol) was recovered and 1708 mg of ethyl lactate (14.
5 mmol) was produced. In addition, hydroxyacetone (4
3%) was produced. The conversion of the raw material propylene glycol was 87.9%, the selectivity of ethyl lactate from propylene glycol was 52.3%, and the turnover number was 955 (mol / mol).

[0021]

Industrial Applicability According to the method of the present invention, lactic acid ester can be industrially advantageously produced from propylene glycol under mild conditions.

Claims (3)

[Claims] 1. A method for producing a lactate ester, which comprises reacting propylene glycol with an alcohol in the presence of a ruthenium complex compound and a hydrogen acceptor. 2. The method for producing a lactic acid ester according to claim 1, wherein the ruthenium complex compound is a ruthenium complex compound having a substituted cyclopentadienone compound as a ligand. 3. The method for producing a lactate ester according to claim 1, wherein the hydrogen acceptor is a pyruvate ester.