JPH0119373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing propylene glycol monoacetate starting from vinyl acetate. More specifically, the present invention relates to a method for producing propylene glycol monoacetate by hydroformylating vinyl acetate to produce α-acetoxypropionaldehyde, and then hydrogenating the α-acetoxypropionaldehyde. This method is shown by the following reaction formula. Although propylene glycol monoacetate is a compound useful as a starting material for propylene glycol and propylene oxide, no industrial production method has been established to date. Conventionally, a method has been proposed for producing acetate ester of propylene glycol by oxidizing propylene in acetic acid in the presence of a palladium salt (see British Patent No. 1124862). In this method, the product is separated from the reaction mixture by distillation, but the heating during distillation partially degrades the catalyst, making it difficult to maintain the catalyst activity stably over a long period of time. . The present inventors have conducted intensive studies to develop a method for producing propylene glycol monoacetate that is industrially more advantageous than the above-mentioned methods, and as a result, they have arrived at the present invention. That is, according to the present invention, () vinyl acetate is hydroformylated with a mixed gas of hydrogen and carbon monoxide in the presence of a substantially water-insoluble rhodium complex compound and a trisubstituted phosphine in an organic solvent; The reaction mixture obtained in step () is subjected to an extraction operation with an aqueous medium to extract and separate α-acetoxypropionaldehyde into an aqueous medium layer, and the raffinate layer is recycled to the hydroformylation reaction step of step (). , () The aqueous medium layer containing α-acetoxypropionaldehyde obtained in step () is expressed by the general formula
(A) ClH _2l+1 COOC _n H _2n+1 (A) (In the formula, l is an integer from 0 to 4, and m is an integer from 1 to
5, and the sum of l and m is 3 to 5) or the general formula (B) ROOC(CH ₂ ) _o COOR' (B) (wherein R and R' represents an alkyl group having 2 to 3 carbon atoms, and n is an integer of 0 to 2. () The α-acetoxypropionaldehyde contained in the extract layer obtained in step () is converted into α-acetoxypropionaldehyde in the reaction mixture in the liquid phase in the presence of a Raney-nickel catalyst or a modified Raney-nickel catalyst.
The concentration of acetoxypropionaldehyde is 0.1
Propylene glycol monoacetate can be produced in high yield by hydrogenating in a manner that does not exceed mol. According to the method of the present invention, α-
Since the acetoxypropionaldehydro and the dium complex compound are separated by an extraction operation using an aqueous medium, the catalytic activity of the rhodium complex compound can be stably maintained over a long period of time. Furthermore, the method of the present invention has advantages such as excellent operational stability and the ability to obtain the main raw materials vinyl acetate, carbon monoxide, and hydrogen in large quantities and at low cost. As the rhodium complex compound used in the hydroformylation reaction of vinyl acetate in the method of the present invention, any rhodium complex compound that has a hydroformylation catalytic ability under the hydroformylation reaction conditions and is substantially insoluble in an aqueous medium is used. be able to. Many such rhodium complex compounds are already known, and most of these conventionally known rhodium complex compounds can be used in the method of the present invention. Specifically, HRh(CO)(PA ₃ ) ₃ (A: aryl group), RhCl(PA ₃ ) ₃ , Rh(acac) ₃ (acac: acetylacetonato group), Rh(OAc) ₃ (OAc: acetoxyl group) ), Rh ₄ (CO) ₁₂ , Rh ₆ (CO) ₁₆ , [Rh(CO) ₂ (PA ₃ ) ₂ ] ₂ , RhCl ₃・3H ₂ O, Rh ₂ O ₃
Among these, HRh (CO)
(PA ₃ ) Type ₃ rhodium complex compounds are particularly preferred from the viewpoints of catalytic activity, solubility, ease of handling, and the like. The rhodium complex compound is usually used in a concentration range of 0.1 to 10 mmol per liter of hydroformylation reaction solution. In the method of the present invention, a substantially water-insoluble organic solvent is used in consideration of the extraction step using an aqueous medium. There are many organic solvents that can be used, but they vary depending on the solubility of the catalyst component, loss of elution of the catalyst component into the aqueous medium layer, price, physical properties considering the subsequent separation process, and chemical properties. Considering stability, hydroformylation reaction results, etc., benzene, toluene, xylene,
Preferred specific examples include aromatic hydrocarbons which may be substituted with lower alkyl groups such as ethylbenzene, and substituted or unsubstituted saturated alicyclic hydrocarbons such as cyclohexane and methylcyclohexane. Trisubstituted phosphine is represented by the general formula PR′R″R (R′ and R″ represent an aromatic hydrocarbon group, and R represents an aromatic hydrocarbon group or a saturated aliphatic hydrocarbon group having 3 or more carbon atoms). . Examples of such trisubstituted phosphine include substituted or unsubstituted triarylphosphines such as trisenylphosphine, tritolylphosphine, and narinaphthylphosphine, as well as diphenylpropylphosphine, diphenylhexylphosphine, and the like. Examples include diarylalkylphosphine. Among these, substituted or unsubstituted triarylphosphines are particularly preferably used. The amount of trisubstituted phosphine used is preferably in the range of about 5 to about 50 mol per rhodium atom, and more precisely, it is practical to use it at a concentration of 10 to 150 mmol per hydroformylation reaction solution. In the method of the present invention, the hydroformylation reaction of vinyl acetate is usually carried out at a reaction temperature of 50 to 120°C and an absolute partial pressure of carbon monoxide, taking into consideration the selectivity to α-acetoxypropionaldehyde, catalyst activity life, equipment cost, etc. 4-50Kg/cm ² , reaction pressure 25-150
Kg/cm ² and a molar ratio of hydrogen to carbon monoxide of 0.5 to 5. The hydroformylation reaction can be carried out continuously or batchwise in a stirred reactor or bubble column reactor. During the reaction,
In order to suppress the accumulation of reaction heat, improve the selectivity to α-acetoxypropionaldehyde, and prevent the accumulation of high-boiling byproducts, vinyl acetate is continuously supplied to reduce the amount of vinyl in the reaction system. It is advantageous to carry out the reaction while maintaining the concentration of acetate within a certain range. Also, α in the reaction mixture
- The concentration of acetoxypropionaldehyde is determined from the viewpoints of the accumulation of high-boiling byproducts, the amount of rhodium complex compounds and trisubstituted phosphine eluted into the aqueous medium layer, and the extraction efficiency of α-acetoxypropionaldehyde into the aqueous medium layer. Approx. per reaction mixture
Advantageously, it is kept in the range from 0.5 to about 3 moles. The reaction mixture containing α-acetoxypropionaldehyde obtained in the vinyl acetate hydroformylation reaction step (step ()) is subjected to an extraction operation with an aqueous medium in step (), whereby α-acetoxypropionaldehyde is extracted from the aqueous medium layer. It is extracted and separated during In the method of the present invention, the aqueous medium used is water or an aqueous solution containing a small amount (for example, about 5 to 10%) of an organic carboxylic acid derived from vinyl acetate. As the extraction device, a stirring type extraction tower, which is known per se,
RDC-type extraction towers and perforated plate towers are applicable, but considering various points such as the extraction rate of α-acetoxypropionaldehyde and the amount of rhodium complex compounds and trisubstituted phosphine eluted into the aqueous medium layer, Most preferred is an RDC type extraction column.
According to detailed studies by the present inventors, the extraction rate of α-acetoxypropionaldehyde into the aqueous medium layer, the elution amount of rhodium complex compounds and trisubstituted phosphine into the aqueous medium layer, and the hydroformylation The aqueous medium layer depends on the contact efficiency with the reaction mixture layer, the extraction temperature, the α-acetoxypropionaldehyde concentration in the reaction mixture, the volume ratio of the aqueous medium to the reaction mixture, the atmosphere of the gas phase during extraction, etc. The higher the contact efficiency of α-acetoxypropionaldehyde with the hydroformylation reaction mixture layer, the lower the extraction temperature, and the larger the volume ratio of the aqueous medium to the hydroformylation reaction mixture, the higher the extraction rate of α-acetoxypropionaldehyde into the aqueous medium layer. It was observed that the amount of rhodium complex compound and trisubstituted phosphine eluted into the aqueous medium layer tended to decrease.
The extraction temperature is selected from a range of about 5 to 40°C. The volume ratio of the aqueous medium to the hydroformylation reaction mixture also depends on the α-acetoxypropionaldehyde concentration in the reaction mixture.
When the amount is about 0.5 to about 3 mol per mole, it is preferably selected from the range of 0.3 to 3. The extraction operation with aqueous media in step () is carried out using substantially oxygen-free inert gases such as nitrogen gas, helium gas and argon gas or hydrogen/monoxide having a carbon monoxide partial pressure of at least 0.1 Kg/ ^m2 . It is preferable to conduct this under an atmosphere of a carbon mixed gas or a hydrogen/carbon monoxide mixed gas diluted with the above-mentioned inert gas and having a carbon monoxide partial pressure of 0.1 Kg/cm ² or more. Elution of rhodium complex compounds can be suppressed. Although the extraction operation can be carried out in a batch manner, it is industrially advantageous to carry out the extraction operation in a continuous manner. The raffinate layer containing the catalyst component obtained in step () is recycled to the hydroformylation reaction step and reused. In this case, if necessary, a part of the raffinate layer can be separately taken out, subjected to a known catalyst activation treatment, and then recycled to the hydroformylation reaction step. By contacting the aqueous medium layer containing α-acetoxypropionaldehyde obtained in step () with a carboxylic acid ester represented by general formula (A) or a carboxylic acid ester represented by general formula (B), the aqueous medium is α-acetoxypropionaldehyde is extracted and separated from the layer (step ()). Process ()
During the operation, the extraction temperature is approximately 5℃ to approximately 90℃.
A range of from about 20°C to about 80°C is particularly preferred. Note that α-acetoxypropionaldehyde is more easily extracted at higher temperatures, but temperatures higher than 90°C are not preferred because α-acetoxypropionaldehyde and the extraction solvent are partially hydrolyzed during the extraction operation. Although the extraction operation can be carried out in a batch manner, it is more preferable to carry out the extraction operation in a continuous manner. Furthermore, all conventional extraction devices such as stirring type extraction towers and perforated plate extraction towers can be employed. Examples of the carboxylic acid ester represented by the general formula (A) used as an extraction solvent include n-butyl formate, n-amyl formate, ethyl acetate, n-propyl acetate, isopropyl acetate, t-butyl acetate, methyl propionate, ethyl propionate,
Examples include methyl acetate, methyl isoacetate, and methyl valerate. Among these carboxylic esters, ease of extraction of α-acetoxypropionaldehyde, hydrolyzability of the carboxylic ester, solubility in water, boiling point, azeotropic composition and azeotropic point with water, and the carboxylic ester Particularly preferred is isopropyl acetate in view of various points such as water solubility. m and n in general formula (A)
A carboxylic acid ester whose sum is 2 or less,
For example, when methyl acetate, ethyl formate, etc. are used as an extraction solvent, α-acetoxy or propionyloxy-propionaldehyde is easily extracted by the solvent, but water is also easily soluble in the solvent, so the interaction between water and the solvent Layer separation may be difficult, and α-acetoxypropionaldehyde cannot be effectively extracted and separated. Furthermore, when a carboxylic acid ester in which the sum of m and n in general formula (A) is 6 or more, such as n-butyl caproate, is used as an extraction solvent, α-acetoxypropionaldehyde is difficult to be extracted by the solvent. Therefore, it is industrially disadvantageous. Also in this case,
Depending on the solvent, the boiling points of the extracted α-acetoxypropionaldehyde and the solvent are close to each other, so that subsequent separation of the two requires precise distillation. Examples of the dicarboxylic acid ester represented by the general formula (B) include diethyl oxalate, diisopropyl oxalate, ethylisopropyl oxalate,
Examples include diethyl malonate and diethyl succinate. Among these dicarboxylic acid esters, physical properties such as ease of extraction of α-acetoxypropionaldehyde, hydrolyzability of the dicarboxylic acid ester, solubility in water, boiling point, and water solubility of the dicarboxylic acid ester Also, diethyl malonate and diethyl succinate are particularly preferred in view of various points such as versatility of the solvent and price. When using as an extraction solvent a dicarboxylic acid ester in which n in general formula (B) is an integer of 0 to 2 and R and R' are both methyl groups, such as dimethyl succinate, α
- Acetoxypropionaldehyde is easily extracted by the solvent, but water is also easily dissolved in the solvent, so α-acetoxypropionaldehyde cannot be effectively extracted and separated. Also, general formula (B)
When using a dicarboxylic acid ester in which n is an integer of 3 or more, such as dimethyl adipate, as an extraction solvent, α-acetoxypropionaldehyde may be difficult to extract into the solvent, or water may be easily dissolved in the solvent. Moreover, the boiling point of the solvent is too high, making it industrially disadvantageous. Among carboxylic acid esters in which n in general formula (B) is an integer of 3 or more, dicarboxylic acid esters in which R and R' are each an alkyl group having 2 to 3 carbon atoms are used as extraction solvents. When used, since the specific gravity of the solvent is very close to that of water, it takes a long time to separate the layers.
The amount of the carboxylic acid ester represented by the general formula (A) or the dicarboxylic acid ester represented by the general formula (B) to be used in the aqueous solution containing α-acetoxypropionaldehyde ranges from about 0.5 to about 5 in terms of volume ratio. It is practical to choose. The raffinate layer can be recycled as is to the process () and reused as an aqueous medium. α-acetoxypropionaldehyde is directly hydrogenated in step () without being separated from the extract layer obtained in step (). α―
The catalysts used for the hydrogenation of acetoxypropionaldehyde are Raney-nickel catalysts and Raney-nickel catalysts modified with one or more of the following metals: chromium, rhenium, molybdenum, tungsten, titanium, iron, lead, manganese, and the like. In addition, other commonly used catalysts for hydrogenation reactions include stabilized nickel catalysts such as nickel diatomaceous earth and ruthenium/carbon catalysts, but Raney nickel catalysts and modified nickel catalysts are used for the hydrogenation of α-acetoxypropionaldehyde. It was found that the Raney-nickel catalyst has excellent catalytic activity. These Raney-nickel catalysts and modified Raney-nickel catalysts are used in a proportion of 0.1 to 10% by weight based on the reaction mixture, as in the case of general hydrogenation reactions.
In particular, concentrations of 0.5 to 5 percent by weight are used. In the hydrogenation reaction of α-acetoxypropionaldehyde according to the method of the present invention, the concentration of α-acetoxypropionaldehyde in the reaction mixture is
It is necessary to conduct the reaction under conditions where the concentration does not exceed 0.1 mol/mole, thereby stably maintaining the catalyst activity over a long period of time. If the concentration of α-acetoxypropionaldehyde in the reaction mixture exceeds 0.1 mol/liter, it is presumed that this is due to side reactions such as polymerization of α-acetoxypropionaldehyde, but this is desirable because the catalytic activity tends to be shortened. do not have. The concentration of α-acetoxypropionaldehyde in the reaction mixture can be easily adjusted by adding the extraction layer containing α-acetoxypropionaldehyde obtained in step () into the reaction system continuously or intermittently depending on the reaction rate. Can be adjusted.
In addition, the rate at which α-acetoxypropionaldehyde is consumed in the reaction can be increased by keeping the concentration of Raney-Nickel catalyst or modified Raney-Nickel catalyst relatively high in the reaction mixture. This is an effective method for keeping the concentration within the above range. Water is present in the extract layer (monocarboxylic acid ester or dicarboxylic acid ester layer) obtained in step (), but considering the catalyst life of the hydrogenation catalyst, hydrolysis of α-acetoxypropionaldehyde, etc. The amount present is desirably 10% by weight or less based on the extract.
The hydrogenation reaction is carried out under a hydrogen partial pressure of 1 to 150 absolute atmospheres, particularly preferably 5 to 100 absolute atmospheres.
The reaction temperature is selected from the range of 70-140°C, preferably 90-130°C. The reaction can be carried out in a stirred reactor or in a bubble column reactor, which are known per se. Although the reaction can be carried out either batchwise or continuously, it is industrially advantageous to carry out the reaction continuously. It is also a desirable embodiment of the present invention to provide a finishing hydrogenation tank to increase the conversion rate of α-acetoxypropionaldehyde. Propylene glycol monoacetate can be obtained by removing the Raney-nickel catalyst or modified Raney-nickel catalyst from the hydrogenation reaction mixture by filtration, sedimentation, centrifugation, etc., and then subjecting it to a conventional distillation operation. In addition, when the purpose is to finally obtain propylene glycol by hydrolyzing propylene glycol monoacetate, the reaction mixture after removing the nickel catalyst may be subjected to an extraction operation with water. It can also be extracted and separated into a propylene glycol monoacetate aqueous layer. The present invention will be specifically explained below using Examples. Example 1 () Synthesis of α-acetoxypropionaldehyde and separation of α-acetoxypropionaldehyde from the reaction mixture The synthesis reaction of α-acetoxypropionaldehyde and the water extraction operation were repeated using the following reaction apparatus. In addition, throughout each experimental operation, the mixing of air into the system was avoided as much as possible, and distilled water and toluene were used after displacing and removing dissolved oxygen with nitrogen gas. Reactor: A stainless steel autoclave with contents 1 equipped with a thermometer, a stirring device, a liquid feed pump, a liquid extraction port, and a gas inlet and outlet was used. Extraction device: Contents 1 with thermometer, stirring device, liquid inlet, liquid extraction port and gas inlet/outlet
A four-necked flask was used as an extraction device. The extractor is directly connected to the autoclave by a pipe. HRh(CO) [P(C ₆ H ₅ ) ₃ ] ₃ 918 mg (1.0 mmol) and triphenylphosphine 2620 mg (10
After washing 420 ml of toluene solution with 420 ml of toluene solution dissolved in hydrogen and carbon monoxide (H ₂ /CO molar ratio 2/1) at room temperature with 420 ml of distilled water while stirring twice, A mixed gas of hydrogen and carbon monoxide (H ₂ /CO molar ratio 2/
After replacing the gas sufficiently with 1), use the same mixed gas.
The pressure was increased to 30 Kg/cm ² (G), and the mixture was heated in an oil bath until the internal temperature became constant at 70°C. Stirring was started at a speed of 600 rpm and 71 g (830 mmol) of vinyl acetate was continuously introduced over 1.5 hours. Off gas flow rate is 20/hour, 70℃, 30Kgcm ² /(G)
The reaction was carried out under stirring under the following conditions. Low-boiling compounds (vinyl acetate,
propionaldehyde, toluene, etc.) were collected on top in dry ice-acetone. After the vinyl acetate feed was completed, the reaction was further accelerated by continuing stirring for an additional 2 hours under the same conditions. Analysis of the reaction mixture by gas chromatography revealed that the conversion rate of vinyl acetate 3.5 hours after the start of the reaction was 90%, and the selectivity of α-acetoxypropionaldehyde based on the converted vinyl acetate was 95%. After the reaction mixture was cooled to room temperature, it was pumped using the internal pressure into the above-mentioned extractor, which was purged with a mixed gas of hydrogen and carbon monoxide (H ₂ /CO molar ratio 2/1). α-acetoxypropionaldehyde in the toluene solution (reaction mixture) was extracted with water by charging 90 ml of nitrogen-substituted distilled water and stirring at 20° C. and 500 rpm for 20 minutes. After the aqueous layer obtained by standing was taken out of the system, 90 ml of distilled water was added again to the toluene solution, water extraction was performed under the same conditions, and the aqueous layer was taken out of the system. Through these two extraction operations, 92% of α-acetoxypropionaldehyde was extracted into the aqueous layer side.
The rhodium concentration (measured by atomic absorption spectrometry) in the extracted aqueous layer is 0.05 ppm, and the concentration of phosphorus compounds (measured by colorimetric analysis) is 5 ppm as phosphorus atoms.
It was hot. The raffinate layer, a triene solution containing catalyst components, was pumped into the reaction autoclave using the pressure of a mixed gas of hydrogen and carbon monoxide. Under the conditions of 70℃, 30Kg/cm ² (G), 600rpm,
After continuously adding vinyl acetate at a rate of 48 g/hour for 80 minutes while stirring, the reaction was driven by continuing stirring for 2 hours. After the reaction, the reaction mixture was extracted with water in the same manner as above under the same conditions. The raffinate was again pumped into the reaction autoclave to carry out a hydroformylation reaction of vinyl acetate. In this way, the hydroformylation reaction of vinyl acetate and water extraction were repeated 10 times in total. This results in a total of approximately
An extracted aqueous layer of 2.3 was obtained. The conversion rates of vinyl acetate in the 3rd, 6th and 10th runs are 91%, 90% and 91%, respectively;
Furthermore, the rhodium concentrations in the extracted aqueous layer were 0.05 ppm, 0.06 ppm, and 0.06 ppm, respectively, in atomic terms, and these values did not change at all depending on the number of repetitions. The extracted aqueous layer in each round was stored at 5°C under a nitrogen gas atmosphere. () Separation of α-acetoxypropionaldehyde from the extracted aqueous layer The inside of a glass extraction device with an internal volume of 1, equipped with a stirring device, a reflux condenser, and a thermometer, is replaced with nitrogen gas in advance, and the inside of the extraction device is filled with nitrogen gas. In an atmosphere, 240 ml of the extracted aqueous layer and 480 ml of isopropyl acetate purged with nitrogen gas were charged,
α-acetoxypropionaldehyde was extracted by stirring at 60°C and 500 rpm for 30 minutes. Through this extraction procedure, 78% of α-acetoxypropionaldehyde in the aqueous solution was extracted.
was extracted into the isopropyl acetate layer. By repeating the extraction a total of five times in this manner, approximately 2.5 volumes of an isopropyl acetate solution containing α-acetoxypropionaldehyde was obtained. () Content capacity 500ml equipped with α-acetoxypropionaldehyde hydrogenation thermometer, pressure regulator, off-gas flow control valve and raw material supply port.
In a stainless steel electromagnetic stirring autoclave, 0.68 g of developed Raney nickel catalyst (manufactured by Kawaken Fine Chemical Co., Ltd.) was washed with water, ethanol, and isopropyl acetate in this order (in terms of nickel metal), and 50 ml of isopropyl acetate was added as a solvent. After charging and sufficiently replacing the inside of the system with hydrogen gas, hydrogen gas was introduced until the pressure reached 20 Kg/cm ² (absolute pressure). Thereafter, the autoclave was immersed in an oil bath and heated until the internal temperature was constant at 100°C. Stirring was started at a rotational speed of 600 rpm, and the isopropyl acetate solution of α-acetoxypropionaldehyde obtained by the operation in () above was continuously supplied from the raw material supply port at a rate of 60 ml/hr for 3 hours. During the raw material supply period, the internal pressure was maintained constant at 20 Kg/cm ² through a pressure regulator, and the off-gas flow rate was adjusted to 15/hr using an off-gas flow rate control valve. After the raw material supply was completed, the reaction was continued by continuing stirring for an additional 15 minutes at the same temperature and pressure. The α-acetoxypropionaldehyde concentration in the reaction mixture at the end of raw material supply was 0.005 mol/. As a result of analyzing the reaction solution by gas chromatography, the hydrogenation rate of α-acetoxypropionaldehyde at the end of the reaction was 100%, and the selectivity of propylene glycol monoacetate was 99.5% (based on converted α-acetoxypropionaldehyde). It was hot. After separating the catalyst from the reaction mixture, the isopropyl acetate-water azeotrope and isopropyl acetate were removed from the solution under normal pressure, and a small amount of acetic acid was distilled off under reduced pressure. Propylene glycol mono was obtained as a fraction at 95°C/200mmHg. Approximately 17 g of acetate was obtained. Examples 2 to 6 The hydroformylation reaction of vinyl acetate and the water extraction operation were repeated 10 times in total under the same conditions as in Example 1 () except that 100 ml of distilled water was used for each extraction operation. , about 2.5 moles of an aqueous solution containing about 2.5 moles of α-acetoxypropionaldehyde and small amounts of acetic acid and propionaldehyde.
I got it. Example 1 except that various monocarboxylic acid esters and dicarboxylic acid esters were used in place of isopropyl acetate, the extraction temperature was variously changed, and various modified Raney-nickel catalysts were used in place of the Raney-nickel catalyst, and the reaction conditions were variously changed.
α-acetoxypropionaldehyde was extracted, separated, and hydrogenated by the same method and operation as in () and (). The results are summarized in Table 1. 【table】

Claims (1)

[Claims] 1 () Hydroformylating vinyl acetate with a mixed gas of hydrogen and carbon monoxide in the presence of a substantially water-insoluble rhodium complex compound and a trisubstituted phosphine in an organic solvent; () The reaction mixture obtained in step () is subjected to an extraction operation with an aqueous medium to extract and separate α-acetoxypropionaldehyde into an aqueous medium layer, and the raffinate layer is recycled to the hydroformylation reaction step of step (). , () The aqueous medium layer containing α-acetoxypropionaldehyde obtained in step () is expressed by the general formula
(A) ClH _2l+1 COOC _n H _2n+1 (A) (In the formula, l is an integer from 0 to 4, and m is from 1 to
5, and the sum of l and m is 3 to 5) or the general formula (B) ROOC(CH ₂ ) _o COOR' (B) (wherein R and R' represents an alkyl group having 2 to 3 carbon atoms, and n is an integer of 0 to 2. () The α-acetoxypropionaldehyde contained in the extract layer obtained in step () is converted into α-acetoxypropionaldehyde in the reaction mixture in the liquid phase in the presence of a Raney-nickel catalyst or a modified Raney-nickel catalyst.
The concentration of acetoxypropionaldehyde is 0.1
A method for producing propylene glycol monoacetate, which comprises hydrogenating in a manner not to exceed mol.