Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-05-17
2001-11-20
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S763000
Reexamination Certificate
active
06320086
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a method for producing trimethylhydroquinone from isophorone. The trimethylhydroquinone is a useful substance as an intermediate compound for preparing vitamin E.
(2) Prior Art
The following methods are mainly known for preparing trimethylhydroquinone.
In one of them, 2,3,6-trimethylphenol is sulfonated with sulfuric acid and it is then oxidized with manganese dioxide (Japanese Laid-Open Patent Publication No. 62-108835). This method is not desirable because a large quantity of heavy metal waste is produced, which have a large influence on environment. In addition, the 2,3,6-trimethylphenol as a starting material is expensive, so that the cost for the production of trimethylhydroquinone is high.
Another method relates to chloro-oxidation of 2,4,6-trimethylphenol (Japanese Patent Publication No. 5-68456). Because quite toxic chlorine is used as an oxidizing agent in this method, the process is dangerous to be worked. In addition, when organic chlorine compounds are generated as by-products, the cost for the disposal of waste is expensive.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, the object of the present invention to provide an improved method for producing trimethylhydroquinone without difficulty, which method can be worked in a low cost and which is free from the problem in the disposal of waste catalyst.
That is, the primary aspect of the present invention is a method for producing trimethylhydroquinone comprising the steps of (1) to (4):
(1) Reacting isophorone in the presence of an acid catalyst and recovering &bgr;-isophorone by distillation;
(2) oxidizing the above &bgr;-isophorone in the presence of amorphous carbon such as activated carbon and a base to obtain 4-oxoisophorone;
(3) reacting the above 4-oxoisophorone with at least one member selected from the group consisting of acid anhydrides and carboxylic acids in the presence of a solid acid catalyst to obtain at least one compound represented by the following general formula [I]:
wherein each of R
1
and R
2
is a hydrogen atom or an acyl group and both of R
1
and R
2
may be the same or different; and
(4) hydrolyzing the compound having an acyl group or groups in the reaction product obtained in the step (3), thereby obtaining the trimethylhydroquinone.
In the above step (3), when an acid anhydride is used, the reaction is carried out in a liquid phase. On the other hand, when a carboxylic acid is used, the reaction is carried out in a vapor phase.
A second aspect of the present invention is that the acid anhydride in the step (3) is acetic anhydride.
A third aspect of the present invention is that the solid acid catalyst used in the step (3) is an acidic ion exchange resin.
A fourth aspect of the present invention is that the product in the step (3) is at least one member selected from the group consisting of trimethylhydroquinone, 4-acetoxy-2,3,6-trimethylphenol, 4-acetoxy-2,3,5-trimethylphenol and trimethylhydroquinone diacetate.
A fifth aspect of the present invention is that the compound having an acyl group or groups are at least one member selected from the group consisting of 4-acetoxy-2,3,6-trimethylphenol, 4-acetoxy-2,3,5-trimethylphenol and trimethylhydroquinone diacetate.
According to the method of the present invention, the trimethylhydroquinone can be produced easily in a low cost without causing the problem of the disposal of waste catalyst.
DETAILED DESCRIPTION OF THE INVENTION
In the following, each preparation step will be described in more detail.
Step (1)
[Reaction of Isophorone in the Presence of an Acid Catalyst to Obtain &bgr;-isophorone by Distillation]
In this step, isophorone is reacted by adding an acid catalyst and &bgr;-isophorone having a lower boiling point is obtained by distillation. More particularly, it is possible to produce &bgr;-isophorone by reacting isophorone in the presence of an acid catalyst, and then, the &bgr;-isophorone is recovered by distillation. In another mode of reaction, the distillation is carried out while reacting isophorone in the presence of an acid catalyst, thereby recovering the &bgr;-isophorone. Because the boiling point of &bgr;-isophorone is lower than that of isophorone, they can be separated by distillation without difficulty.
In other words, the reaction to convert the isophorone to &bgr;-isophorone is an equilibrium reaction, so that when the &bgr;-isophorone is removed from the reaction system in the progress of reaction, the equilibrium is shifted to one side, as a result, the yield of &bgr;-isophorone can be raised. Accordingly, the so-called reactive distillation is preferable in this step (1), in which the distillation is performed simultaneously with the reaction of isophorone in the presence of an acid catalyst.
More particularly, when an acid catalyst in a liquid state or in a solid state, the reaction can be done such that the mixture of an acid catalyst and isophorone is put into an appropriate distillation apparatus and distillation is carried out to take out &bgr;-isophorone from the distillation apparatus. With the mode of reaction like this, the duration of distillation is the same as the duration of reaction.
When the reactive distillation is employed, any of solid acids and high boiling point liquid acids can be used as the acid catalyst. The high boiling point liquid acids are exemplified by organic acids such as adipic acid and p-toluenesulfonic acid, inorganic acids such as phosphoric acid and sulfuric acid, which have boiling points higher than those of starting materials and reaction products. The solid acids are exemplified by synthetic solid acid catalysts, natural clay solid acid catalysts, and other solid acid catalysts which are prepared by supporting inorganic acids on porous inorganic carrier substances.
Preferable solid acid catalysts are exemplified by synthetic solid acid catalysts such as silica-alumina, alumina, silica and zeolites, and natural clay minerals such as acid clay and activated clay. When zeolite is used as a solid acid catalyst, those containing hydrogen-zeolite such as HX-type zeolite, HY-type zeolite USY-type zeolite, mordenite and ZSM-5 are preferalby employed. Furthermore, it is possible to reduce the deposition of carbon to a catalyst by causing the catalyst to support an alkali metal such as sodium or potassium.
Besides the above catalysts, it is possible to use by supporting one or a combination of inorganic acids such as phosphoric acid, and heteropoly-acids of phosphotungstic acid, silicotungstic acid and silicomolybdic acid on an appropriate porous inorganic substance. More particularly, supported acid catalysts in which an inorganic acid is supported on a porous inorganic substance such as alumina, magnesia, silica and activated carbon, can be used.
Among the above-mentioned solid acid catalyst, synthetic solid acid catalysts, especially silica-alumina, HY-type zeolite, USY-type zeolite, mordenite and ZSM-5 are preferably used in view of their durability.
The duration of reaction is selected in the range of 1 minute to 200 hours in a batch-wise process.
The pressure of distillation for recovering &bgr;-isophorone is preferably lower than 1 MPa and it is not inevitable to carry out reduced pressure distillation. If appropriate, however, it is also possible to employ the reduced pressure distillation in view of the fact that low temperature operation is desirable in order to avoid the isomerization of &bgr;-isophorone. The type of distillation is not limited. When distillation is done simultaneously with the reaction, it is possible to distill together with the acid using a packed column filled with a packing such as Dickson rings. In this case, the reflux ratio is not limited, for example, it is selected in the range of 1:1 to 100:1. For the distillation, any of continuous distillation and batch-wise distillation can be employed. The composition of isophorone and &bgr;-isophorone in the distillate varies according to the conditions of reflux ratio and the kind of packing.
The &bgr;
Kiyota Noboru
Konishi Tomohiro
Matsumura Yasuo
Suyama Kazuharu
Hollander Law Firm, P.L.C.
Nippon Petrochemicals Company Limited
Vollano Jean F.
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