Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-07-25
2001-04-24
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S442000, C564S443000
Reexamination Certificate
active
06222074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparation of 4,6-diaminoresorcinol or salts thereof. More precisely, the invention relates to a process for preparation of 4,6-diaminoresorcinol or salts thereof by reducing 4,6-bis(substituted)phenylazoresorcinol.
4,6-Diaminoresorcinol is a monomer for polybenzoxazole, and polybenzoxazole is a polymer having high strength and high elastic modulus as well as characteristics superior in thermal resistance and chemical resistance (see the Japanese Translation of PCT International Patent Publication No. Sho 6I-501452 official gazette and the Japanese Patent Open-laid Publication No. Hei 2-229143 official gazette).
BACKGROUND ART
Reduction of 4,6-bisphenylazoresorcinol is generally carried out with hydrogen by using a noble metal catalyst (the Japanese Patent Open-laid Publication No. Hei 7-242604 official gazette). According to the Japanese Patent Open-laid Publication No. Hei 7-242604 official gazette, the reduction is carried out under a neutral condition in a solvent. As to the solvent, there is described that water, lower alcohols, aromatic hydrocarbons, halogen-substituted benzenes, halogenated aliphatic hydrocarbons, ethers, lower ketones are used alone or in combination. Furthermore, as the post-treatment after the end of the reduction reaction, two methods are described. In a first method, an acid is added and an acid salt is formed after filtration through Celite still under a nitrogen atmosphere to obtain 4,6-diaminoresorcinol, which is filtered off the catalyst and Celite, thereafter purified and isolated. In a second method, an acid is added to the reaction solution to make a salt, which is dissolved, filtered off the catalyst, thereafter purified and isolated.
The former has such effects that recovery of aniline produced in the reaction is easy and that the purification procedure is simple, but filterability is very slow. A yield is low such as 60% due to the loss of 4,6-diaminoresorcinol into the filtrate, thus the method cannot be said as an industrial method.
The latter has high stability in air and good operability since an acid is added to make a salt. Furthermore, filterability is high, which seldom cause any problem. But, it has such a disadvantage that separation and purification of a by-product, aniline, and 4,6-diaminoresorcinol become very complicated due to the presence thereof in an acidic solution.
In the reduction of 4,6-bis(substituted)phenylazoresorcinol, 2 equivalents of an aniline derivative is by-produced in addition to 4,6-diaminoresorcinol. It is the largest problem in the reduction process of 4,6-bis(substituted)phenylazoresorcinol how simply the aniline derivative can be separated with a few loss of an objective 4,6-diaminoresorcinol produced.
DISCLOSURE OF THE INVENTION
We, inventors, have studied eagerly and found an industrial process for operating freely 4,6-diaminoresorcinol to complete the present invention. That is, 4,6-diaminoresorcinol is obtained in a high yield by reducing a 4,6-bisphenylazoresorcinol derivative in a selected solvent in the presence of a noble metal catalyst with hydrogen.
However, filterability is sometimes very slow depending on the kind of the solvent. For these cases, filterability is eminently improved by adding a filter aid such as active carbon into the reaction.
An object of the invention is to provide a process by which 4,6-diaminoresorcinol having high purity can be obtained easily in a high yield from 4,6-bis(substituted)phenylazoresorcinol. Thereby, a recovery rate of the aniline derivative is improved, which is economically advantageous.
The inventors have studied eagerly and thus found a process to solve the above-mentioned subject to complete the present invention. That is, the present invention relates to a process for preparation of 4,6-diaminoresorcinol or salts thereof (herein, salts thereof mean acid salts of 4,6-diaminoresorcinol, which meaning is referred to same in the followings) by reducing 4,6-bis(substituted)phenylazoresorcinol expressed by the formula [1]
wherein, R denotes a halogen atom, an alkyl group having 1-5 carbon atoms, a hydroxycarbonyl group or an alkoxy group having 1-5 carbon atoms, n denotes 0 or any integer of 1-5, and two or more groups R may be same or different each other,
with hydrogen in the presence of a metal catalyst to obtain 4,6-diaminoresorcinol or salts thereof, characterized in that an aliphatic nitrile compound is used as a solvent.
Furthermore, the invention also relates to a process for preparation of 4,6-diaminoresorcinol or salts thereof by reducing 4,6-bis(substituted)phenylazoresorcinol expressed by the formula [1] above with hydrogen in the presence of a metal catalyst and a solvent to obtain 4,6-diaminoresorcinol or salts thereof, characterized in that at least one organic solvent selected from aliphatic nitrile compounds, aliphatic alcohols having 3-5 carbon atoms, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether and dioxane is used as the solvent and that the reduction is carried out furthermore in the presence of a filter aid.
4,6-Bis(substituted)phenylazoresorcinol which is the starting material in the invention can be obtained by diazotizing a (substituted) aniline expressed by the formula [2]
wherein, R and n are defined same as in the formula [1], to obtain a (substituted) benzene diazonium salt and subjecting the diazonium salt to the coupling reaction with resorcinol. Specifically, the (substituted) benzene diazonium salt is obtained by adding dropwise 2.5-4 equivalents, based on aniline, of an inorganic acid into a mixture of substituted aniline and 5-10 times by weight of water with cooling and then adding dropwise 1-1.5 times by mole of sodium nitrite or potassium nitrite dissolved in 2-3 times by weight, based on (substituted) aniline, of water into the mixed solution. As the inorganic acid, at least one inorganic acid selected from hydrochloric acid, hydrobromic acid, sulfuric acid and phosphoric acid is used. Hydrochloric acid is preferable industrially and economically amongst of these inorganic acids.
Specifically, there may be mentioned for example aniline, 2-chloroaniline, 4-chloroaniline, 2,6-dichloroaniline, o-toluidine, m-toluidine, p-toluidine, anthranilic acid, o-anisidine, m-anisidine and p-anisidine, and it is preferable to use any of these anilines. Aniline is the most preferable from the viewpoints of economical efficiency and stability of the compound etc.
As the coupling reaction of a (substituted) benzene diazonium salt with resorcinol, any known methods may be used, but the following methods are preferable; a method to react a (substituted) benzene diazonium salt expressed by the formula [3]
wherein, R and n are defined same as in the formula [1], and X denotes Cl, Br, OSO
3
H or OPO
3
H
2
,
in a solvent which is made alkaline which is filed as Japanese Patent Laid-open Publication No. Hei 9-124575 by the present applicant, and a method to mix a solution of the (substituted) benzene diazonium salt expressed by the formula [3] with a solution or suspension of an alkali metal or alkali earth metal hydroxide to obtain a mixed solution made alkaline and mix to react the solution with resorcinol and/or its alkali metal salt or alkali earth metal salt which is filed as Japanese Patent Laid-open Publication No. Hei 9-157239.
4,6-bis(substituted)phenylazoresorcinol which is the raw material in the invention is, therefore, one obtained by reacting resorcinol with an alkaline (substituted) benzene diazonium salt to make acidic, thereafter collecting by filtration and washing with water. It may be used as such or may be used after dried. Dried one is preferable from the viewpoint of a yield in the reduction reaction, since contamination from water causes much escape of 4,6-diaminoresorcinol into a filtrate. As the reaction mixture is used without any purification, purity of 4,6-bis(substituted)phenylazoresorcinol is about 80%, and additiona
Akimoto Kazuhiko
Hashiba Isao
Shiratori Motohito
Suzuki Hideo
Tokunaga Ken-ichi
Barts Samuel
Nissan Chemical Industries Ltd.
Oliff & Berridg,e PLC
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