1. Field of the Invention
The present invention relates to a method for preparing a 4-nitroso-substituted aromatic amine and, more particularly, to a method for selectively preparing a 4-nitroso-substituted aromatic amine by contacting an amide compound with a nitroaromatic compound in the presence of a base in a polar organic solvent.
2. Related Prior Art
In general, 4-nitroso-substituted aromatic amines partly used as an intermediate of dye or hair dyes and a light stabilizer have not been studied much with regard to their applications because of their complicated method of preparation. Among the 4-nitroso-substituted aromatic amines, 4-nitrosoaniline is used as an intermediate of dye or hair dyes and usually reduced to a raw material for preparation of p-phenylenediamine (U.S. Pat. No. 6,245,943).
Conventionally, 4-nitrosoaniline is prepared by contacting aniline with sodium nitrite (NaNO2) to produce N-nitrosoaniline and then subjecting the N-nitrosoaniline to Fischer-Hepp rearrangement in acidic condition (Tetrahedron, 1975, 31, 1343-9), or by contacting p-nitrosophenol with ammonia or ammonium chloride (NH4Cl) (U.S. Pat. No. 3,338,966; and J. Chem. Soc., 1955, 2049).
The former method involves denitrosation during the Fischer-Hepp rearrangement step to produce waste containing lots of nitroso (NO) compounds destructive to the environment. The latter one using 4-nitrosophenol has a problem in regard to an excessively low yield of 4-nitrosoaniline, which problem causes the difficulty in mass production of 4-nitrosoaniline and hence the limited uses of 4-nitrosoaniline.
Recently, there has been developed a method for selectively preparing nitroaniline by nucleophilic aromatic substitution of hydrogen (NASH). For example, benzamide or benzonitrile is contacted with nitrobenzene in the presence of an organic base, tetramethylammonium hydroxide (hereinafter, referred to as xe2x80x9cTMA(OH)xe2x80x9d) to prepare N-(4-nitrophenyl)benzamide as an intermediate, which is isolated and decomposed into 4-nitroaniline and benzoic acid (or benzamide) by addition of water (or ammonia) (J. Org. Chem., 1993, 58(24), 6883-8; U.S. Pat. Nos. 5,436,371 and 5,331,099; and International Publication No. WO 93/24447). This method is a direct amination with nitrobenzene using NASH that produces 4-nitroaniline, also called xe2x80x9cpara-nitroanilinexe2x80x9d in two steps.
Other similar methods for preparing substituted nitroaromatic compounds through direct amination using NASH reaction are also known (European Publication No. EP 695739; and Japanese Publication No. JP 8040994).
In addition, another known method involves contacting an aliphatic amide, isobutyramide with benzene to produce N-(4-nitrophenyl)butyramide as an intermediate (U.S. Pat. No. 5,331,099). In this method, N-(4-nitrophenyl)butyramide is decomposed with ammonia or subjected to hydrolysis to yield 4-nitroaniline.
As is well known, the direct amination of an amide compound with a nitroaromatic compound using NASH reaction produces an intermediate of 4-nitro-substituted aromatic amine, which is decomposed with water or ammonia into 4-nitro-substituted aromatic amine. But there is no related document on the production of 4-nitroso-substituted aromatic amine.
However, 4-nitroso- or 4-nitro-substituted aromatic amine can also be produced through direct amination that involves contacting aniline as an aromatic amine other than an amide compound with nitrobenzene for NASH reaction (J. Am. Chem. Soc., 1992, 114(23), 9237-8; and U.S. Pat. No. 5,117,063).
As stated above, the conventional method involving the reaction between an amide compound and nitrobenzene is a two-step process that first produces an intermediate of 4-nitro-substituted aromatic amide and then hydrolyzes the intermediate with ammonia or water into the final product, 4-nitro-substituted aromatic amine. In this method, the process for production of the 4-nitroso-substituted aromatic amine is unknown.
Accordingly, the inventors of the present invention have explored a one-step method for preparing a 4-nitroso-substituted aromatic amine using NASH reaction by contacting an amide compound with a nitroaromatic compound in an appropriate condition without producing 4-nitroso- or 4-nitro-substituted amide as an intermediate.
It is therefore an object of the present invention to provide a method for preparing a 4-nitroso-substituted aromatic amine and 4-nitro-substituted aromatic amine with high selectivity and high yield in one step of contacting a nitroaromatic compound with an amide compound in the presence of a base.
To achieve the object of the present invention, there is provided a method for preparing a 4-nitroso-substituted aromatic amine that includes contacting a nitroaromatic compound represented by the following formula 3 with an amide compound represented by the following formula 4 in the presence of a base to directly prepare a 4-nitroso-substituted aromatic amine represented by the following formula 1 as a main product and a 4-nitro-substituted aromatic amine as a by-product in one step: 
wherein Ar is a C4 to C16 aromatic group having one or at least one ring and containing one or two hetero atoms of N, O or S; X is a halogen atom, a cyano group, a C1 to C4alkyl group, a halongenated C1 to C4 alkyl group, a C1 to C4 alkoxy group, a C1 to C4 halogenated alkoxy group, a C1 to C4 alkylsulfonyl group, or a C1 to C4 alkylnitro group; and n is an integer of 0 to 3, wherein X is different from one another when n is greater than 1; 
wherein Ar, X and n are as defined above; 
wherein Ar, X and n are as defined above; and 
wherein R is a hydrogen atom, a C1 to C8 alkyl group, a C2 to C8 alkenyl group, or a C3 to C7 cycloalkyl group, which substituent may be replaced with 1 to 3 halogen atoms, C1 to C4 alkyl groups, amino groups or C1 to C4 alkoxy groups.
The 4-nitroso- and 4-nitro-substituted aromatic amines thus obtained are susceptible to normal hydrogenation to yield a diamine-substituted aromatic compound.
The present invention is directed to a method for preparing a 4-nitroso-substituted aromatic amine with a very high selectivity from an amide compound and a nitroaromatic compound in the presence of an inorganic or organic base in a polar organic solvent.
In the preparation method of the present invention, the nitroso-substituted aromatic amine prepared from the nitroaromatic compound of the formula 3 and the amide compound of the formula 4 is represented by the formula 1 and produced together with a small amount of a nitro-substituted aromatic amine (formula 2). The oxygen and air atmosphere may suppress production of azoxybenzene as a by-product and therefore enable selective production of the nitroso-substituted aromatic amine.
More specifically, examples of the nitroaromatic compound of the formula 3 suitable as a starting material may include nitrobenzene, 3-nitroanisole, 3-nitrotoluene, 2-nitroanisole, 2-nitrotoluene, m-chloronitrobenzene, 2,3,4-nitropyridine, and 5,6,7-nitroquinoline.
Specific examples of the amide compound of the formula 4 being contacted with the nitroaromatic compound may include urea, acetamide, formamide, biuret, phenylurea, and isobutyramide.
The base available in the present invention includes both inorganic and organic bases. Specific examples of the inorganic base may include alkali metal hydroxides, alkali metal amides, alkali metal alkoxides, and alkali metal hydrides. Among these inorganic bases, the preferred alkali metal hydroxides are sodium hydroxide (NaOH), potassium hydroxide (KOH), and potassium tert-butoxide (t-BuOK), which are preferably in the form of powder or fine particles.
Specific examples of the organic base may include tetraalkylammonium hydroxides, and TMA(OH) is particularly preferred.
The use of a phase transfer catalyst with the inorganic base may increase the reactivity Specific examples of the phase transfer catalyst may include crown ethers and tetraalkylammonium salts. Among these catalysts, 18-crown-6 and tetramethylammonium chloride (hereinafter, referred to as xe2x80x9cTMA(Cl)xe2x80x9d) are particularly preferred.
The mole ratio of the base to the amide compound of the formula 4 is 1:0.5 to 1:10, preferably 1:1 to 1:6.
Specific examples of the solvent may include polar organic solvents, such as dimethylsulfoxide (hereinafter, referred to as xe2x80x9cDMSOxe2x80x9d), dimethylformamide (hereinafter, referred to as xe2x80x9cDMFxe2x80x9d), N-methylpyrrolidinone (hereinafter, referred to as xe2x80x9cNMPxe2x80x9d), pyridine, dioxane, and tetrahydrofurane (hereinafter, referred to as xe2x80x9cTHFxe2x80x9d). These solvents may be used alone or in combination. Among these solvents, DMSO is most preferred. Alternatively, the amide compound or the nitroaromatic compound itself can be used as a solvent.
The weight ratio of the solvent to the amide compound of the formula 4 is 1:0.5 to 1:50, preferably 1:1 to 1:20.
To enhance the selectivity for the product of the present invention, 4-nitroso-substituted aromatic amine, the nitroaromatic compound is slowly added to the amide compound used as a starting material for a predetermined time.
The mole ratio of the amide compound of the formula 4 to the nitroaromatic compound of the formula 3 is 1:1 to 1:30, preferably 1:1.5 to 1:6. The higher proportion of the amide compound increases the selectivity for 4-nitroso-substituted aromatic amine, while the higher proportion of the nitroaromatic compound not only increases the proportion of 4-nitro-substituted aromatic amine but also results in the product of the secondary reaction, 4,4xe2x80x2-dinitrodiphenylamine as a by-product. So the amount of the amide compound of the formula 4 is preferably in the above range.
Vacuum distillation or the use of a drying agent may be employed to eliminate water produced from the reaction solution in the early stage of the reaction or during the reaction. Specific examples of the drying agent available in the present invention may include anhydrous potassium carbonate, anhydrous sodium sulfate, anhydrous magnesium sulfate, sodium hydroxide, potassium hydroxide, sodium hydride, and molecular sieve. But the use of the drying agent or continuous distillation to remove water from the solution makes little difference in the yield of the product, because the amount of water hardly affects the reaction in the preparation method of the present invention.
The reaction temperature is properly in the range of 20 to 150xc2x0 C., preferably 70 to 100xc2x0 C. Temperature lower than 20xc2x0 C. retards the rate of the reaction and deteriorates the selectivity for 4-nitroso-substituted aromatic amine, while temperature higher than 150xc2x0 C. increases production of the by-product to deteriorate the yield of the product.
Nitrogen, oxygen or air is available as the reaction atmosphere in the present invention. The nitrogen atmosphere results in production of azoxybenzenes as a by-product, while the oxygen or air atmosphere suppresses production of azoxybenzenes and increases the yield of the product.
In the present invention, the products are analyzed and identified using NMR and GC-MSD measurements, and the reactants and the products are subjected to quantitative analysis using high performance liquid chromatography (hereinafter, referred to as xe2x80x9cHPLCxe2x80x9d) under the following conditions. For HPLC, a Hitachi product composed of a L-6200 intelligent pump and a L-4200 UV-VIS detector is used with Cosmosil 5C18 (4.6xc3x97150 mm, packed column) for measurements at 254 nm, the development rate of the chromatographic eluant being 1 ml/min. The conditions of solvent gradient elution are presented in Table 1.
Pyrene is used as an internal standard material for determination of the product, and the area ratio for the concentration of each material based on the pyrene area is determined for standard calibration to calculate the molar concentration of the product from the calibration curve.