Process for producing aromatic hydroxy compound

Details Process for producing aromatic hydroxy compound Process for producing aromatic hydroxy compound

2000-04-28

2002-11-12

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S741000, C568S753000, C568S629000, C568S803000

Reexamination Certificate

active

06479711

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a catalyst for hydroxylating an aromatic compound and to a process for producing an aromatic hydroxy compound using such catalyst, in particular, by hydroxylating a phenol by hydrogen peroxide to obtain the contemplated aromatic hydroxy compound. The aromatic hydroxy compound, such as hydroquinone or catechol, to be produced by the production process according to the present invention is useful as an intermediate or a starting material for synthesizing various organic compounds and has found its application to fields of, such as reducing agent, rubber additives, dyestuffs, medicaments, agricultural chemicals, polymerization inhibitor and antioxidants.
BACKGROUND OF THE INVENTION
There had, from of old, been known for hydroxylating a phenol using hydrogen peroxide a method in which the reaction is performed in the presence of divalent iron ion {Nature, 165, 401 (1950)}, a method in which hydrofluoric acid is employed {J. Org. Chem., 35, 4028 (1970)} and so on. It was also reported that a technique using pyrophosphoric acid in combination with perchloric acid or an alkaline earth metal salt thereof is industrially useful {Japanese Patent Kokai Hei 3-240743 A (corresponding to U.S. Pat. No. 5,245,086)}.
However, these prior art methods reveal problems in that laborious and bothersome works are required for isolation of the contemplated compound by removing the catalyst from the reaction product, since the catalyst is dissolved in the reaction liquor homogeneously; that a precious material is required for the apparatus for the reaction due to the use of a highly corrosive acid; and that neutralization with a base is required for disposal of the spent catalyst acid.
Afterwards, techniques were proposed, in which a catalyst of heterogeneous system for easy removal from the reaction mixture, for example, crystalline titanosilicate or the like, is used {Japanese Patent Kokai Hei 1-149744 A (corresponding to EP No. 314582 A and to U.S. Pat. No. 5,254,746), Japanese Patent Kokai Hei 2-298350 A and Japanese Patent Kokai hei 4-66546 A}. Among these prior art techniques, a method using a crystalline titanosilicate of MFI structure is industrially advantageous, since the removal of the catalyst from the reaction product can be effected simply by a physical means. However, there remains a problem in that all these prior art techniques can attain a lower selectivity, since hydroquinone and catechol are formed by the hydroxylation reaction in nearly equal proportion.
In order to obviate these problems, there was proposed a technique in which a phenol is subjected to a hydroxylation with hydrogen peroxide in the presence of a cyclic ether, such as dioxane or the like, and of a crystalline titanosilicate catalyst {Japanese Patent Kokai Hei 5-170684 A (corresponding to U.S. Pat. No. 5,426,244) and Japanese Patent Kokai Hei 6-263670 A (corresponding to U.S. Pat. No. 5,426,244) and Japanese Patent Kokai Hei 7-2714 A}. In these Patent Gazettes, it is noted that the selectivity of hydroquinone becomes increased by the addition of a cyclic ether. In this prior technique, however, the hydroquinone/catechol ratio amounts to only about 7/1 and, therefore, a more pronounced suppression of by-production of catechol is desirable.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a novel and useful catalyst for hydroxylation of an aromatic compound having a hydroxy or an alkoxy substitutent group, which catalyst can afford to introduce a hydroxyl group directly into the aromatic ring at the para-position with respect to the hydroxy or the alkoxy substituent group at a high selectivity.
The second object of the present invention is to propose a process for producing an aromatic hydroxy compound, in which a hydroxyl group is introduced in the aromatic ring at the para-position with respect to a hydroxy or an alkoxy substitutent group on the aromatic ring, which process can afford to produce the aromatic hydroxy compound in a simple manner at a high yield and at a high selectivity.
Thus, the present invention consists in the catalyst for hydroxylation and the process for producing an aromatic hydroxy compound as given below:
(1) A catalyst for hydroxylation of an aromatic compound comprising an oleophilized crystalline titanosilicate.
(2) The catalyst as defined in the above (1), wherein the oleophilization is effected with an organosiloxane.
(3) The catalyst as defined in the above (2), wherein the organosiloxane is a dialkylsiloxane oligomer.
(4) The catalyst as defined in at least one of the above (1) to (3), wherein the crystalline titanosilicate has a structure of MFI.
(5) A process for producing an aromatic hydroxy compound, comprising reacting at least one compound selected from the group consisting of phenols, alkoxybenzenes and derivatives of them with hydrogen peroxide in the presence of a catalyst as defined in any one of the above (1) to (4).
(6) A process for producing an aromatic hydroxy compound, comprising reacting at least one compound selected from the group consisting of phenols, alkoxybenzenes and derivatives thereof with hydrogen peroxide in the presence of a compound having ether linkage and of a catalyst as defined in any one of the above (1) to (4).
DETAILED DESCRIPTION OF THE INVENTION
For the crystalline titanosilicate to be oleophilized, those represented by the structural formula (SiO
2
)
x
·(TiO
2
)
1−X
may be employed without any restriction. For the ratio x/(
1
−x), namely, the Si/Ti atomic ratio, of the crystalline titanosilicate, there is no special restriction, while usually preference is given to those in the range from 1 to 10,000, preferably from 5 to 1,000, especially preferably from 10 to 500. For the crystalline titanosilicate, those of MFI type having MFI structure are preferred.
The crystalline titanosilicate can be prepared by known techniques. It may be produced, for example, by formulating first a reaction mixture composed of a silicon source, a titanium source, nitrogen source and water and subjecting the mixture then to a hydrothermal synthesis. As the silicon source, there may be employed, for example, alkoxides of silicon and colloidal silica. As the titanium source, there may be exemplified alkoxides of titanium, titanium halides, titanic acid and titanium sulfide. As the nitrogen source, there may be enumerated nitrogen-containing compounds, for example, quaternary ammonium salts, such as salts of tetrapropyl ammonium and tetrabutyl ammonium.
As a concrete technique for producing the crystalline titanosilicate, the following method may be exemplified. The mixture of the silicon source, the titanium source, the nitrogen source and water as given above is agitated while adjusting the pH thereof at an adequate value, whereby a gel-formed precipitate is formed. This precipitate is then subjected to a hydrothermal reaction while heating at a temperature of 100-250° C. for 1-100 hours to obtain a solid product. This solid product is washed with deionized water and dried, whereupon it is calcined at a temperature of 400-600° C. in air, whereby the crystalline titanosilicate is obtained. In such a production method, a crystalline titanosilicate of MFI structure can easily be obtained, when a tetrapropyl ammonium salt is employed as the nitrogen source.
Processes were disclosed for producing crystalline titanosilicates in, for example, Japanese Patent Kokai Sho 56-96720 A (corresponding to U.S. Pat. No. 4,410,501) and Japanese Patent Kokai Hei 4-66546 A and the crystalline titanosilicates produced by these processes can also be employed. As the crystalline titanosilicate, commercial products may also be used. Also, for the MFI type crystalline titanosilicate, commercial products can be used.
For oleophilizing the crystalline titanosilicate, there may be employed, for example, a method in which the crystalline titanosilicate is treated with a compound having oleophilic group(s) to cause the crystalline titanosilicate to ca

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