Method of preparing p-phenylenediamine

Details Method of preparing p-phenylenediamine Method of preparing p-phenylenediamine

2000-08-16

2001-06-12

Barts, Samuel (Department: 1621)

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

Organic compounds

Amino nitrogen containing

C564S414000, C564S420000, C564S422000

Reexamination Certificate

active

06245943

ABSTRACT:

TECHNICAL FIELD
The present invention generally relates to a method of preparing pphenylenediamine and, more particularly, to a novel method of preparing highly pure pphenylenediamine, which involves reacting urea and nitrobenzene with a base in the presence of a polar organic solvent to yield 4-nitrosoaniline and 4-nitroaniline and then performing hydrogenation using a catalyst.
BACKGROUND ART
p-phenylenediamine is a compound of various applications such as cosmetic, antioxidant, fuel additive and dyestuff and, more particularly, a useful compound as a base material of a highly resilient and heat-resistant material (e.g., aramide fiber) and a raw material of polyurethane, p-phenylenediisocyanate.
Conventionally, there have been used two commercialized methods for preparing p-phenylenediamine of such a wide use range. The first method involves reacting chlorobenzene with nitric acid and reacting the resulting product, p-nitrochlorobenzene with ammonia to yield 4-nitroaniline, followed by hydrogenation of 4-nitroaniline to produce p-phenylenediamine. The second method involves diazotation of aniline using nitrogen oxide, reaction with an excess of aniline to form 1,3-diphenyltriazene, and rearragement of 1,3-diphenyltriazene to 4-aminoazobenzene and hydrogenation of 4-aminoazobenzene to yield p-phenylenediamine and aniline.
The first method is most widely used and yields isomers of nitrochlorobenzene, i.e., ortho- and para-forms at a ratio of 65:35 through nitration of chlorobenzene in order to form an intermediate, 4-nitroaniline. At this stage, however, the final product is not isolated as pure p-phenylenediamine but stained with a small amount of isomers. Thus this method is normally used to prepare p-phenylenediamine of low purity or dyes. Another disadvantage of the method is to dispose of a large quantity of wastewater due to the chlorine-containing materials used.
The second method solves the problem related to production of an isomer such as ortho-form. Specifically, the method involves diazotating aniline with nitrogen oxide and reacting the resulting diazo-compound with an excess of aniline to yield 1,3-diphenyltriazene, which is then subjected to rearrangement and hydrogenation reaction to provide aniline such as p-phenylenediamine (See. U.S. Pat. Nos. 4,020,052 and 4,279,815). This method may produce a relatively pure p-phenylenediamine but requires complicated multi-stage reactions.
Recently, a method of preparing 4-nitroaniline in two steps has been developed (See. J. Am. Chem. Soc., 1992, 114(23); J. Org. Chem., 1993, 58, 6883-6888; U.S. Pat. Nos. 5,436,371 and 5,380,946; and WO 93/24447). The method includes the steps of performing the NASH (Nucleophilic Aromatic Substitution of Hydrogen) to synthesize an intermediate, N-(4-nitrophenyl)benzamide through the reaction of benzamide and nitrobenzene with an organic base, and adding water (or ammonia) to the intermediate to decompose the intermediate into 4-nitroaniline and benzoic acid (or benzamide). This method provides 4-nitroaniline in the para-form with a relatively high selectivity and may be used to prepare highly pure p-phenylenediamine through hydrogenation. However, the method produces 4-nitroaniline in two stages with a low yield due to the water content in the reaction mixture. Furthermore, it requires a need of using a relatively high-cost material, TMA(OH) as an organic base.
DISCLOSURE OF INVENTION
In an attempt to solve the problems of the NASH-based method, the inventors have contrived a method of selectively preparing 4-nitrosoaniline under a simple condition relative to the related arts by reacting nitrobenzene with urea instead of benzamide in the presence of an alkali base.
It is therefore an object of the present invention to provide a novel method of preparing p-phenylenediamine destitute of ortho- or meta-phenylenediamine as an isomeric byproduct through a hydrogenation using Pd/C or Pt/C as a catalyst in a single reactor (i.e., one pot) without a need of isolation or purification.
It is another object of the present invention to provide a novel method of preparing p-phenylenediamine, in which inexpensive urea and an alkali base are used to reduce the production cost and 4-nitrosoaniline is formed as an intermediate to yield p-phenylenediamine with a high selectivity, thereby requiring no purification process after isolation of the product.
To achieve the above object, there is provided a method of preparing p-phenylenediamine including the steps of: reacting urea and nitrobenzene with a base in the presence of a polar solvent to yield 4-nitrosoaniline and 4-nitroaniline; and subsequently, diluting the resulting mixed solution in an alcohol and performing hydrogenation using a catalyst.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will now be described in detail as follows.
The present invention is directed to a novel method of preparing highly pure p-phenylenediamine by reacting urea and nitrobenzene with a base in the presence of a polar organic solvent such as dimethyl sulfoxide to yield 4-nitrosoaniline and 4-nitroaniline and performing hydrogenation using a Pd/C or Pt/C catalyst.
In the preparation of p-phenylenediamine according to the present invention, urea and nitrobenzene are first reacted with a base in the presence of a polar organic solvent such as dimethyl sulfoxide to yield 4-nitrosoaniline and 4-nitroaniline.
Examples of the base as used herein may include a relatively inexpensive organic base such as alkali metals and alkali earth metals. And, examples of the solvent as used herein may include a polar solvent such as dimethyl sulfoxide, dimethyl formamide, N-methyl pyrrolidinone, etc., which is chosen in consideration of the solubility of the organic base.
The proportion of 4-nitrosoaniline or 4-nitroaniline to be yielded is controllable by regulating the ratio of urea to nitrobenzene. That is, an increase in the ratio of urea to nitrobenzene raises the yield proportion of 4-nitrosoaniline. A high proportion of nitrobenzene to urea leads to a large yield of 4-nitroaniline so as to make the secondary product of 4-nitroaniline, 4,4′-dinitrodiphenylamine detectable. Preferably, the ratio of urea to nitrobenzene is in the range of 1 to 10 equivalents.
Subsequently, the primary products of urea and nitrobenzene, i.e., 4-nitrosoaniline and 4-nitroaniline are hydrogenated with a Pd/C or Pt/C catalyst to yield highly pure p-phenylenediamine.
It is desirable that an alcohol such as ethanol or isopropanol is added to dilute the mixed solution of 4-nitrosoaniline and 4-nitroaniline prior to hydrogenation and that the added amount of the alcohol is 50 to 500 parts by weight based on 100 parts by weight of the polar solvent. The reaction will not occur unless the solvent is diluted with alcohol prior to hydrogenation.
The amount of the hydrogenation catalyst such as Pd/C or Pt/C is preferably in the range of 0.1 to 10 parts by weight based on 100 parts by weight of 4-nitrosoaniline and 4-nitroaniline in total.
Preferably, the reaction temperature is in the range from the room temperature to 200° C. The reaction temperature below the range inactivates the reaction and the lower reaction temperature retards the reaction. Contrarily, the higher reaction temperature causes an increase in the reaction velocity.
Preferably, the hydrogen pressure is in the range of 50 to 500 psi. An increase in the hydrogen pressure also raises the reaction velocity.
The present invention is preferable in preparing highly pure p-phenylenediamnine without an isomeric byproduct by hydrogenation, because it yields 4-nitrosoaniline and 4-nitroaniline as intermediates without an ortho-compound as a byproduct, such as 2-nitrosoaniline or 2-nitroaniline from inexpensive urea and nitrobenzene.
Advantageously, the present invention also provides a preparation of highly pure p-phenylenediamine through hydrogenation in a single reactor (i.e., on e pot) neither requiring a separate reactor for providing an anhydrous condition nor an isolation process after production of 4-nitrosoaniline, because the

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