Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-03-23
2001-10-30
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S212000, C560S215000, C560S096000
Reexamination Certificate
active
06310236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing an &agr;-hydroxycarboxylate. More specifically, the present invention relates to a process for efficiently preparing, from an &agr;-hydroxycarboxylic amide and an alcohol in an industrially advantageous manner, an &agr;-hydroxycarboxylate which is useful as any of raw materials for solvents, food additives, perfumes, medicines, agricultural chemicals, industrial chemicals, degradable polymers and &agr;-amino acids.
2. Description of the Prior Art
It is known that &agr;-hydroxycarboxylates are industrially extremely important compounds, and for example, lactates which are one kind of &agr;-hydroxycarboxylates are used as high-boiling solvents and as raw materials for food additives, perfumes, medicines, agricultural chemicals and degradable polymers. In addition, the &agr;-hydroxycarboxylates can be used as solvents, as raw materials for the production of methacrylates, particularly methyl methacrylate by dehydration, and as raw materials for the production of &agr;-amino acids by aminolysis.
As techniques for manufacturing the &agr;-hydroxycarboxylates, some methods are known from former days which comprise reacting an alcohol with a nitrile in the presence of an acid catalyst. For example, as preparation techniques of lactates, Japanese Patent Publication Nos. 8061/1955 and 2333/1965 disclose methods which comprise dissolving lactonitrile in an alcohol and water, adding sulfuric acid to the solution to carry out hydrolysis and esterification, and then introducing an alcohol vapor into the resultant mixture. With regard to &agr;-hydroxyisobutyrates, there are known methods for preparing them by reacting acetone cyanohydrin with an alcohol in the presence of an acid catalyst, and these methods are disclosed in, for example, U.S. Pat. No. 2,041,820 and Japanese Patent Application Laid-Open No. 230241/1992. These reactions are exothermic and can spontaneously proceed, and for the reason, a manufacturing apparatus is simpler as compared with other methods which will hereinafter be described. However, since the acid catalyst is used, an anticorrosive material is required to be used, and what is worse, a large amount of a salt is disadvantageously produced as a waste product.
As techniques for the manufacture of the &agr;-hydroxycarboxylates, there are methods which comprise reacting an &agr;-hydroxycarboxylic amide with an ester. For example, Japanese Patent Application Laid-Open Nos. 178792/1993 and 145106/1994 disclose methods which comprise reacting &agr;-hydroxyisobutyric amide with a formate to obtain an &agr;-hydroxyisobutyrate. This reaction is an exchange reaction between the amide and the ester and hence it is neither noticeably exothermic nor endothermic, so that any anticorrosive material is not necessary. However, these techniques have a drawback that the reaction proceeds merely until an equilibrium composition of the amide and the ester has been reached.
Furthermore, known is a method which comprises directly reacting an &agr;-hydroxycarboxylic amide with an alcohol to prepare the &agr;-hydroxycarboxylate. This method is characterized in that any salt to be discarded is not produced, and any upper limit of a conversion of the raw material amide is not present in principle. For example, Japanese Patent Application Laid-Open No. 3015/1977 describes a method in which the reaction is carried out in the presence of a metal carboxylate, while the reaction system is intermittently purged with a gas. In this method, however, a yield is low and a large amount of by-products is formed, and for these reasons, the disclosed method is not practical.
In addition, Japanese Patent Application Laid-Open Nos. 345692/1994, 258154/1995 and 73408/1996 suggest methods which comprise performing a reaction in the presence of an insoluble solid acid catalyst or a metallic catalyst, while a large amount of a nitrogen gas is fed and generated ammonia is discharged. According to investigation by the present inventors, it has been apparent that in order to prepare the &agr;-hydroxycarboxylate in a high yield in accordance with each of these methods, a large amount of nitrogen is necessary. Thus, for the sake of the collection of ammonia from the discharged gas, a good deal of energy is required. Furthermore, the amount of the catalyst to be used increases, a long period of time is required for the reaction, and a large amount of by-products is formed. Accordingly, the disclosed methods are not industrially practical.
SUMMARY OF THE INVENTION
The present invention has been developed under such circumstances with the intention of overcoming the above-mentioned drawbacks of conventional preparation methods of &agr;-hydroxycarboxylates, and an object of the present invention is to provide a process for efficiently preparing an &agr;-hydroxycarboxylate from an &agr;-hydroxycarboxylic amide and an alcohol in an industrially advantageous manner.
The present inventors have intensively investigated on a reaction of the following formula which is carried out in a liquid phase in order to achieve the above-mentioned object, and as a result, it has been found that when the amount of ammonia present in a reaction solution is decreased, a reaction rate can be increased and a high conversion and selectivity can be obtained, and moreover, the formation of by-products can be controlled. The reaction can be 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)
wherein R
1
and R
2
are each a hydrogen atom or an alkyl group; and R
3
is an alkyl group or an aralkyl group.
Since this reaction is an equilibrium reaction, the reaction toward a production side naturally proceeds by distilling off ammonia from a production system. As described above, it is known that a pressure rise occurs owing to the production of ammonia similarly in conventional techniques and the equilibrium moves to the production side by discharging intermittently or partially the pressure. However, ammonia dissolves in the alcohol and the &agr;-hydroxycarboxylate under the pressure, and hence an ammonia concentration in the liquid phase cannot be decreased only by this operative procedure.
The present inventors have found that when the reaction is carried out while generated ammonia is discharged as a gas into a gaseous phase by bringing the reaction solution into a boiling state or bubbling an inert gas in the reaction solution to maintain the ammonia concentration in the reaction solution at a low level, a reaction rate can be increased and a high conversion and selectivity can be obtained, and moreover, the formation of by-products can be inhibited. In particular, the present inventors have found that maintaining the ammonia concentration in the reaction solution at 0.1% by weight or less is effective to inhibit the formation of the by-products, which has not been suggested so far by anyone.
With regard to the by-products, if ammonia is present in the reaction solution, as shown by the following formula (2), a quaternary amine salt of an &agr;-hydroxycarboxylic acid is produced from the &agr;-hydroxycarboxylate which is the desired product and ammonia, and an &agr;-hydroxycarboxylic(N-alkyl)amide is then generated via the Hofmann gradation:
R
1
R
2
C
(
OH
)
COOR
3
+
NH
3
=
[
R
1
R
2
C
(
OH
)
COO
]
-
[
R
3
NH
3
]
+
=
R
1
R
2
C
(
OH
)
CONR
3
H
+
H
2
O
(
2
)
wherein R
1
, R
2
and R
3
are as defined above.
If the ammonia concentration in the reaction solution is more than 0.1% by weight, the production of this &agr;-hydroxycarboxylic(N-alkyl)amide increases, so that the selectivity noticeably decreases.
In addition, the present inventors have found that if the ammonia concentration in the reaction solution is high, not only the equilibrium reaction scarcely proceeds toward the production system, but also ammonia is coordinated with or adsorbed on a catalyst. Consequently, the co
Kawataka Futoshi
Nakamura Ken'ichi
Ueno Wataru
Yamada Kazuhiro
Antonelli Terry Stout & Kraus LLP
Killos Paul J.
Mitsubishi Gas Chemical Company
Oh Taylor V.
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