JP2000169432A - Production of alpha-hydroxycarboxylic acid ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically produce an α-hydroxycarboxylic acid ester in high yield. SOLUTION: When an α-hydroxycarboxylic acid amide is reacted with an alcohol in the presence of a catalyst to produce an α-hydroxycarboxylic acid ester, (a) reactors comprising plural reactional zones arranged in series and connected so that a liquid and a gas can countercurrently be made to flow between the adjacent reactional zones are used, (b) the raw material α- hydroxycarboxylic acid amide and alcohol are fed to a first reactional zone or thereafter, (c) the respective reactional zones are kept in a boiling state and a gas containing the alcohol and ammonia formed as a by-product and fed from a specific reactional zone is fed to a previous reactional zone to feed a reactional liquid containing the raw material and the product of the reactional zone is fed to the rear reactional zone and (d) the gas is taken out of the first reactional zone and the reactional liquid is taken out of the final reactional zone. Thereby, the α-hydroxycarboxylic acid ester is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an α-hydroxycarboxylic acid ester from an α-hydroxycarboxylic acid amide and an alcohol. α-Hydroxycarboxylic acid ester is an industrially important compound, for example, lactic acid ester is used as a high boiling point solvent,
It is used as a raw material for food additives, medicinal and agricultural chemicals, and flavors. α-
Hydroxyisobutyrate is used for the production of methacrylate by dehydration and the production of amino acids by aminolysis.

[0002]

2. Description of the Related Art As a method for producing an .alpha.-hydroxycarboxylic acid ester, a method of reacting an alcohol with nitrile in the presence of an acid catalyst has been known for a long time. For example, as a method for producing lactic acid ester, Japanese Patent Publication No. 30-806
No. 1, Japanese Patent Publication No. 40-2333 discloses a method in which lactonitrile is dissolved in alcohol and water, hydrolysis and esterification are performed by adding sulfuric acid, and alcohol vapor is introduced into the resulting mixture. With respect to α-hydroxyisobutyric acid ester, a method for producing it by reacting acetone cyanohydrin with an alcohol using an acid catalyst is known. For example, U.S. Pat.
No. 0241. Since these reactions are exothermic and proceed spontaneously, the production apparatus is simpler than the other methods described below. However, since an acid catalyst is used, there is a disadvantage that a corrosion-resistant material must be used and a large amount of salt is generated as waste.

As a method for producing an α-hydroxycarboxylic acid ester, there is a method of reacting an α-hydroxycarboxylic acid amide with an ester. For example, Japanese Unexamined Patent Publication
78792 and JP-A-06-145106 disclose a method for producing α-hydroxyisobutyrate by reacting α-hydroxyisobutyrate with formate.
This reaction is an exchange reaction between an amide and an ester, and is characterized in that there is no large heat generation or heat absorption, and that there is no need to use a corrosion resistant material. However, there is a disadvantage that the reaction proceeds only up to the equilibrium composition of the amide and the ester.

Further, there is known a method for producing an α-hydroxycarboxylic acid ester by directly reacting an α-hydroxycarboxylic acid amide with an alcohol. This method has the advantage that no salt to be discarded is generated and there is in principle no upper limit on the conversion of the starting amide. For example, in Japanese Patent Application Laid-Open No. 52-3015, while purging gas intermittently,
A method for performing the reaction in the presence of a metal carboxylate is described. However, this method was not practical because of low yield and many by-products.

Further, Japanese Patent Application Laid-Open Nos. 6-345692 and 7-258154
And JP-A-8-73408 propose a method of reacting in the presence of an insoluble solid acid catalyst or metal catalyst while discharging a large amount of nitrogen gas and releasing the generated ammonia. As a result of investigations by the present inventors, a large amount of nitrogen is required to produce an α-hydroxycarboxylic acid ester in a high yield by this method. Therefore, a large amount of energy is required to recover ammonia from the discharged gas. Further, the amount of the catalyst used is large, the reaction requires a long time, and there are many by-products, which is not industrially practical.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have previously published
No. 10-102880 proposed a method for carrying out the reaction while keeping the ammonia concentration in the liquid phase low. The present invention proposes a method by which this can be carried out industrially advantageously. That is, in producing an α-hydroxycarboxylic acid ester from an α-hydroxycarboxylic acid amide and an alcohol, it is an object of the present invention to provide a production method that keeps a distillate gas in an economical amount and satisfies a high yield.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for producing an α-hydroxycarboxylic acid ester by reacting an α-hydroxycarboxylic acid amide with an alcohol in the presence of a catalyst. Are arranged in series, and between adjacent zones, using a reactor connected so that liquid and gas can flow in countercurrent, (b) raw materials of α-hydroxycarboxylic acid amide and alcohol (C) keeping each reaction zone boiling,
Supplying gas from a certain reaction zone containing alcohol and by-produced ammonia to a previous reaction zone, and feeding a reaction solution containing raw materials and products of the reaction zone to a rear reaction zone;
(d) extracting a gas from the first reaction zone, and extracting a reaction solution from the last reaction zone, and a method for producing an α-hydroxycarboxylic acid ester, and (B) using a gas diffusion device as a reaction device. Characterized by taking out a gas containing alcohol and by-product ammonia
The present invention relates to a method for producing a hydroxycarboxylic acid ester.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
This reaction in which an α-hydroxycarboxylic amide and an alcohol directly react in the presence of a catalyst to produce an ester and ammonia is represented by the following formula (1). R ¹ R ² C (OH) -CONH ₂ + R ³ OH → R ¹ R ² C (OH) COOR ³ + NH ₃ (1) where R ¹ and R ² are alkyl groups having 20 or less carbon atoms. is there. For example, lactoamide and α-hydroxyisobutyric acid amide are mentioned, and lactic acid ester and α-hydroxyisobutyric acid ester are obtained, respectively. R ³ may have another substituent bonded thereto as long as the number of carbon atoms is 20 or less, for example, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, 2-ethylhexanol, 2-ethylhexanol. N, N-dimethylaminoethanol, 2-N-methylaminoethanol, and 2-aminoethanol are exemplified.

As the catalyst, either a soluble metal catalyst or a solid catalyst can be used. Desirable soluble metal catalysts include soluble compounds of Ti or Sn, more specifically, nitrates, sulfonates, chlorides, alkoxides, carboxylate salts, amide complexes of these metals. Particularly, a complex with α-hydroxycarboxylic acid amide is preferable.

[0010] Soluble compounds including soluble lanthanoids can also be used as catalysts. That is, Ce,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
1 selected from the group consisting of o, Er, Tm, Yb, and Lu
Soluble compounds containing one or more metal elements, more specifically, nitrates, sulfonates, chlorides,
Alkoxides, carboxylate and the like can be mentioned. Particularly, trifluoromethanesulfonic acid salt is desirable.

As the solid catalyst, metal oxides and hydrated oxides are desirable. For example, Sb, Sc, Y, La, C
e, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,
W, Tc, Re, Fe, Co, Ni, Cu, Al, S
An insoluble compound composed of an oxide of one or more metals selected from the group consisting of i, Sn, Pb, and Bi.
Also, Ti, Zr, Hf, V, Nb, Ta, Cr, M
o, W, Fe, Co, Ni, Cu, Ga, In, Bi,
A catalyst comprising one or more metals selected from the group consisting of Te is also used.

Since the reaction of the formula (1) is an endothermic reaction, the reaction proceeds sufficiently by applying heat energy other than the reaction heat to cause the reaction system to perform thermodynamic work. Further, the conversion of amide can be increased by promoting the vaporization of ammonia and alcohol.

As a result of the study, the present inventors have found that, in one reaction zone where the composition of the liquid phase is uniform, when the reaction solution is brought into a boiling state to distill by-product ammonia into gas and distillate with gaseous alcohol, Ratio of α-hydroxycarboxylic acid amide to alcohol in the solution (amide / alcohol)
And that the molar fraction of ammonia in the distillate gas (the molar fraction of ammonia in the gas phase) is in a proportional relationship. In addition, alcohol other than by-product ammonia is included as a component of the distillate gas, and when a gas such as nitrogen is introduced from the outside, this is also included.

In other words, the ratio of α-hydroxycarboxylic acid amide to alcohol in the liquid phase (amide /
When alcohol is small, the ratio of ammonia in the distillate gas is low, and when the ratio of α-hydroxycarboxylic acid amide to alcohol in the liquid phase (amide / alcohol) is large, the ratio of ammonia in the distillate gas is large. Means gone.

In the present reaction, since ammonia and ester are produced in equal amounts, the following can be paraphrased. When the ratio of the raw material amide to the raw material alcohol (amide / alcohol) in the liquid phase is small, the amount of distillate gas is large relative to the produced ester, and when the ratio of the raw material amide to the raw material alcohol in the liquid phase is large, The amount of distillate gas is relatively small with respect to the ester produced. If the ratio of amide and alcohol of the raw materials supplied to the reaction system is constant,
When the conversion of the amide is high, the amount of the distillate gas is large with respect to the generated ester, and when the conversion of the amide is low, the distillate gas is small with respect to the generated ester. .

In order to vaporize and distill alcohol,
Since the amount of heat required to provide latent heat of vaporization is required, if the reaction is carried out in only one reaction zone where the composition of the liquid phase is uniform, the amount of heat energy supplied must be increased in order to increase the conversion of the amide. Must. By connecting a distillation column to the reactor, the molar fraction of ammonia in the gas distilled from the reactor can be increased, but heat energy is consumed by refluxing, so that the entire device is consumed. The amount of heat does not decrease. As can be seen from this, the gas for which the molar fraction of ammonia is to be defined is a gas distilled from the reaction zone, not a gas that has been subjected to a distillation operation.

Since the above-mentioned proportional relationship holds, if the reaction is carried out in only one reaction zone where the composition of the liquid phase is uniform, it is necessary to (1) increase the conversion of the amide as the raw material and ( 2)
Keeping the value of the supplied thermal energy low is incompatible. Therefore, as a method of increasing the conversion rate of the raw material amide without increasing the amount of distillate, it is conceivable that the concentration gradient of the amide, alcohol, ammonia, ester, and each component is appropriately set in the reaction zone. As a method for realizing this, (A) a method of using a plurality of reaction zones and bringing a gas containing ammonia and alcohol into contact with a liquid containing the amide in countercurrent, The inventors have invented a method for distilling off ammonia produced by reacting alcohol.

(A) The method of using a plurality of reaction zones means (a)
A plurality of reaction zones are arranged in series, and between adjacent zones, using a reactor connected so that a liquid and a gas can flow in countercurrent, (b) the raw material α-hydroxycarboxylic acid amide and alcohol (C) keeping each reaction zone boiling, feeding gas from a particular reaction zone containing alcohol and by-product ammonia to the previous reaction zone, Feeding the reaction solution containing the raw materials and products of the reaction zone to the rear reaction zone, (d) extracting gas from the first reaction zone, and extracting the reaction solution from the last reaction zone.

The reaction solution is in a boiling state in each reaction zone. Here, the boiling state is a state in which ammonia produced as a by-product is vaporized in the reaction solution together with alcohol. In each reaction zone, the starting amide is added in the presence of a catalyst.
Reacts with alcohol as raw material to convert to ester. The liquid containing the produced ester and the starting amide flows to the next reaction zone. That is, as one proceeds to the last reaction zone, the conversion of the amide increases and the ester increases.

A part of the ammonia generated in each reaction zone is vaporized together with the alcohol and supplied to the immediately preceding reaction zone. As the reaction zone progresses from the last reaction zone to the first reaction zone, the proportion of ammonia in the distilling gas increases. That is, the proportion of ammonia is higher near the first reaction zone, and the proportion of ammonia is kept lower near the last reaction zone. As a result, in each reaction zone, a proportional relationship is maintained between the molar ratio of the starting amide and the alcohol in the liquid phase and the ammonia mole fraction of the gas distilled from the reaction zone. The amide conversion can be increased without changing the distillation amount.

In order to maintain the boiling state in all the reaction zones with little heat energy, a) heating the reaction solution in the last reaction zone to vaporize a part of the alcohol or a mixture of alcohol and ammonia, Introduce successively into the previous reaction zone and withdraw from the first reaction zone, or b) Introduce alcohol vapor or a mixture of alcohol vapor and inert gas into the last reaction zone, and introduce this gas into the previous reaction zone. It may be desirable to introduce into the zone and withdraw from the first reaction zone.

The reaction zones need only be connected in series,
It is not necessary that each be a separate reactor. That is, not only a method of connecting independent reactors by piping, but also a configuration in which one reactor is partitioned and divided into a plurality of reaction zones may be used. The spatial arrangement of the reaction zones does not matter, and they may be connected side by side in any of horizontal and vertical directions. A column type reactor is a type of device in which a plurality of reaction zones are vertically connected.

As an example of a method of connecting independent reactors by piping, a diagram of an apparatus in which three reactors are connected is shown in FIG.
Shown in In FIG. 1, an amide which is a raw material is introduced into a first reactor, and a gas is introduced into a third reactor. The reactors are connected by a gas conduit and a liquid conduit, and the liquid flows from the first reactor to the second reactor and the third reactor through the liquid conduit. The gas, on the contrary, passes through the gas conduit to 3
Flow from the first reactor to the second reactor and the first reactor. When a single reactor is partitioned into a plurality of reaction zones, each reaction zone is partitioned by a partition plate or the like, and the liquid and gas flow in countercurrent.

(B) The method of reacting the starting amide with the alcohol in the gas stripping apparatus and distilling off the produced ammonia includes feeding the starting amide and the starting alcohol into the gas stripping apparatus to distill the ammonia. While reacting, the reaction is performed in the gas diffusion device. Since the compositions of the liquid and the gas in the reactor change continuously or discontinuously, the conversion of the amide can be increased while keeping the distillation amount of the alcohol relatively low. Here, the gas diffusion device is a device that is industrially used to diffuse and separate a target component from a mixture into a gas. Since gas emission is theoretically the reverse operation of gas absorption, the equipment used is often the same as that used for gas absorption.

Although there are various types of gas dispersing devices, both liquid dispersing type and gas dispersing type are applicable. Examples of the liquid dispersion type include a packed tower, a painted wall tower, a liquid column tower, and a spray tower. Examples of the gas dispersion type include a bubble column, a gas blowing type stirrer, and a plate column. Among these, a packed tower, a bubble tower and a tray tower are preferred. As the packing used for the packed tower, any of irregular packing, structured packing and lattice packing can be used. It is also possible to mold a solid catalyst and use it as a filler. As the bubble column, any of a nozzle type and a porous plate can be used, and the bubble column may be filled with a filler.

The gas dispersion type apparatus makes it relatively easy to flow a raw material in a slurry state, and is suitable when an insoluble catalyst is used. When using a homogeneous catalyst, a liquid dispersion type,
Any type of gas dispersion type may be used. The gas used may be not only a non-condensable gas such as nitrogen but also a condensable gas such as the vapor of the alcohol. Alternatively, the lower part of the apparatus may be heated to evaporate the liquid inside, and this may be used. It is desirable that the liquid and the gas flow in countercurrent because ammonia can be more efficiently diffused than in the case where they flow in parallel. In order to make the flow countercurrent, it is desirable to introduce or generate gas from the lower part of the gas diffusion device and supply the raw material amide from the upper part.

[0027]

The method of the present invention will be described in more detail with reference to the following examples, but it should not be construed that the invention is limited thereto. Example 1 A 150 mL SUS316 reactor with an internal volume of 150 mL was equipped on the upper part of a 500 mL SUS316 reactor equipped with a forced stirring device (lower reactor).
The reactor (upper reactor) is connected so that the liquid and gas flow in countercurrent, the lower reactor is heated to evaporate the alcohol inside, the gas is extracted through the upper reactor, and the upper reactor is discharged. A device for extracting the liquid through the lower reactor was prepared (FIG. 2).

Α-Hydroxyisobutyric acid amide and methanol were supplied to the upper reactor of this reactor, and titanium isopropoxide was supplied as a catalyst at a rate of 50 g / hr, 100 g / hr and 10 g / hr, respectively, using a liquid feed pump. Methanol was supplied to the lower reactor at a rate of 100 g / hr using a liquid sending pump. The lower reactor was heated to evaporate ammonia and methanol, while keeping the upper reactor sufficiently warm to minimize condensation of methanol vapor from the lower reactor. Distillate gas from the upper reactor is liquefied in a condenser and stored in a condensate receiver. In this way, the liquid temperature in the upper reactor and the liquid in the lower reactor were kept at 170 ° C.

From the bottom of the lower reactor, 141 g / hr of the reaction solution was added.
A distillate was obtained at 110 g / hr from the upper reactor. When the reaction solution obtained from the lower reactor was analyzed by gas chromatography, the conversion of α-hydroxyisobutyric acid amide was 83 mol%, and methyl α-hydroxyisobutyrate was obtained as a product with a selectivity of 98 mol /%. . Further, the gas distilled was cooled and liquefied, and then analyzed. As a result, it was found that ammonia contained 4.1% by weight and methanol contained 95.9% by weight.

Comparative Example 1 α-Hydroxyisobutyric acid amide and methanol were placed in a 500 mL SUS316 reactor equipped with a forced stirring device.
50 g / hr each of titanium isopropoxide as a catalyst,
200 g / hr and 10 g / hr were introduced. The reactor was heated to distill off ammonia and methanol. Reaction temperature was 17
While maintaining the temperature at 0 ° C., 141 g / hr of the reaction solution and 110 g / hr of the distillate were obtained.

When the reaction mixture obtained from the lower part of the reaction mixture was analyzed by gas chromatography, the conversion of α-hydroxyisobutyric amide was 63 mol%, and methyl α-hydroxyisobutyrate was obtained as a product with a selectivity of 98 mol%. Was done. Also,
After cooling and liquefaction of the distilled gas, the analysis showed that
It contained 3.4% by weight of ammonia and 96.6% by weight of methanol.

Example 2 The same operation as in Example 1 was performed, except that lactoamide was used instead of α-hydroxyisobutyric acid amide. The conversion of lactoamide was 80 mol%, and the selectivity for methyl lactate was 98 mol%.

Example 3 The same operation as in Example 1 was carried out except that tributyltin oxide was used instead of titanium isopropoxide. α-
The conversion of hydroxyisobutyric acid amide was 70 mol%, and the selectivity for α-methyl hydroxyhydroxybutyrate was 98 mol%.

Example 4 The same operation as in Example 1 was carried out except that lanthanum triflate was used instead of titanium isopropoxide. The conversion of α-hydroxyisobutyric acid amide was 83 mol%, and the selectivity for methyl α-hydroxyisobutyrate was 98 mol%.

Example 5 The same operation as in Example 1 was performed, except that bismuth oxide was used in the form of slurry instead of titanium isopropoxide. The conversion of α-hydroxyisobutyramide is 50 mol%,
The selectivity for methyl α-hydroxyisobutyrate was 98 mol%.

Example 6 An apparatus having a liquid-dispersion packed column with an inner diameter of 2 cm and a length of 2 m packed with Dickson packing having a diameter of 3 mm was connected to the upper part of a pressure-resistant container having an inner volume of 100 mL, and at a position 50 cm from the top of the tower, α-Hydroxyisobutyric acid amide 30wt%, methanol
57 g / hr of a mixed solution of 64 wt% and titanium isopropoxide 6 wt%
And methanol at 85 cm from the bottom of the column.
g / hr, and heat the pressure vessel to gasify methanol.
Stripped at g / hr. At this time, the reaction solution temperature was 170
The pressure was maintained at 2 MPa so that the temperature became 0 ° C., and the reaction solution was withdrawn from the bottom of the pressure-resistant container so that the liquid volume in the pressure-resistant container was 50 mL.

When the reaction solution obtained from the bottom was analyzed by gas chromatography, the conversion of α-hydroxyisobutyric acid amide was 86 mol%, and methyl α-hydroxyisobutyrate was obtained as a product with a selectivity of 97 mol /%. Was. After cooling and liquefaction of the stripped gas, analysis showed that ammonia was 2.7% by weight and methanol was 97.2% by weight.
Included.

Example 7 Using a bubble column having an inner diameter of 2 cm and a tower length of 1 m, 25 cm from the top of the tower
A mixture of 30% by weight of α-hydroxyisobutyric amide, 64% by weight of methanol and 6% by weight of titanium isopropoxide.
Feed at 57 g / hr, and add methanol to a position 25 cm from the bottom of the tower.
The reactor was supplied at 85 g / hr, and the bottom of the column was heated to gasify methanol.
Stripped at g / hr. At this time, the reaction solution temperature was 170
C., the pressure was maintained at 2 MPa, and the reaction liquid was withdrawn from the bottom of the column such that the liquid level was constant at a height of 10 cm from the top of the column.

When the reaction solution obtained from the bottom of the column was analyzed by gas chromatography, the conversion of α-hydroxyisobutyric acid amide was 82 mol%, and methyl α-hydroxyisobutyrate was obtained as a product with a selectivity of 97 mol /%. Was done. After the stripped gas was cooled and liquefied, it was analyzed and found to be 2.6% by weight of ammonia and 97.3% by weight of methanol.
% Included.

Example 8 The same operation as in Example 6 was performed, except that lactoamide was used instead of α-hydroxyisobutyric acid amide. Lactamide conversion is 81 mol%, methyl lactate selectivity is 97 mol%,
Met.

Example 9 The same operation as in Example 6 was performed, except that tributyltin oxide was used instead of titanium isopropoxide. α-
The conversion of hydroxyisobutyric acid amide was 69 mol%, and the selectivity of α-methyl hydroxyhydroxybutyrate was 97 mol%.

Example 10 The same operation as in Example 6 was performed except that lanthanum triflate was used instead of titanium isopropoxide. The conversion of α-hydroxyisobutyric acid amide was 84%, and the selectivity for methyl α-hydroxyisobutyrate was 97 mol%.

Example 11 The same operation as in Example 7 was performed, except that bismuth oxide was used in the form of slurry instead of titanium isopropoxide. The conversion of α-hydroxyisobutyramide is 50 mol%,
The selectivity for methyl α-hydroxyisobutyrate was 97 mol%.

Example 12 The same operation as in Example 6 was carried out except that titanium isopropoxide was not used, and instead of Dickson packing, CeO ₂ molded to a diameter of 3 mm and a length of 5 mm was used as a solid catalyst filler. Was done. The conversion of α-hydroxyisobutyric acid amide is
50 mol%, selectivity of methyl α-hydroxyisobutyrate is 97 mol
l%.

[0045]

According to the present invention, it is possible to minimize the amount of distillate gas, and it is economical to obtain α-
It has become possible to produce hydroxycarboxylic acid esters.

[0046]

[Brief description of the drawings]

FIG. 1 shows a reactor connected to an independent reactor.

FIG. 2 shows a reaction apparatus of Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st reactor 2 2nd reactor 3 3rd reactor 4 Liquid conduit 5 Liquid conduit 6 Liquid conduit 7 Gas conduit 8 Gas conduit 9 Gas conduit 10 Methanol 11 Liquid sending pump 12 Lower reactor 13 Gas conduit 14 Liquid conduit 15 Valve for keeping the liquid level of the lower reactor constant 16 Cooler 17 Boiler receiver 18 Gas conduit 19 Condenser 20 Condensate receiver 21 Valve 22 Liquid feed pump 23 Raw material liquid (α-hydroxyiso) Butyric acid amide, titanium isopropoxide, methanol mixture) 24 Upper reactor

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Kenichi Nakamura 22nd Wadai, Tsukuba-shi, Ibaraki F-term in Mitsubishi Gas Chemical Company, Ltd. BA36 BD20 BD34 BD84 BN10 BT12

Claims (8)

[Claims] (1) In producing α-hydroxycarboxylic acid ester by reacting α-hydroxycarboxylic acid amide and alcohol in the presence of a catalyst, (a) a plurality of reaction zones are arranged in series, and Using a reactor connected so that liquid and gas can flow in countercurrent, (b) supplying the raw material α-hydroxycarboxylic amide and alcohol to the first and subsequent reaction zones, (c) The reaction zone is kept boiling, gas from a certain reaction zone containing alcohol and by-product ammonia is supplied to the previous reaction zone, and the reaction solution containing the raw materials and products of the reaction zone is fed to the rear. (D) removing a gas from the first reaction zone and removing a reaction solution from the last reaction zone; 2. A method for producing an α-hydroxycarboxylic acid ester by reacting an α-hydroxycarboxylic acid amide with an alcohol in the presence of a catalyst, using a gas-dissipating apparatus as a reaction apparatus and containing alcohol and by-product ammonia. A method for producing an α-hydroxycarboxylic acid ester, comprising extracting a gas. 3. The method according to claim 2, wherein the gas diffusion device is a packed tower, a bubble tower or a plate tower. 4. The method according to claim 1, wherein the α-hydroxycarboxylic acid amide is lactamide or α-hydroxyisobutyric acid amide. 5. The production method according to claim 1, wherein the catalyst is soluble titanium or soluble tin. 6. The catalyst according to claim 1, wherein the catalyst comprises a compound of at least one metal selected from soluble lanthanoids.
Or the production method according to 2. 7. The catalyst comprises Sb, Sc, Y, La, Ce, T.
i, Zr, Hf, V, Nb, Ta, Cr, Mo, W, T
c, Re, Fe, Co, Ni, Cu, Al, Si, S
3. An insoluble compound comprising an oxide of one or more metals selected from the group consisting of n, Pb, and Bi.
The manufacturing method as described. 8. A catalyst comprising Ti, Zr, Hf, V, Nb, T
a, Cr, Mo, W, Fe, Co, Ni, Cu, Ga,
The method according to claim 1, wherein the method comprises one or more metals selected from the group consisting of In, Bi, and Te.