Aromatic amines, oxidations, benzene

Various ion-exchanged forms of zeolite Y have been investigated as catalysts for the oxidation of molecules such as y-butyrolactone (66), tetralin (67), aromatic amines (68), benzene (69), methanol (70), benzyl alcohol (71), and pyrocatechol (72). In general, transition metal ions or complexes have been incorporated into the zeolite. 

Oxidation. The reagent oxidizes primary aromatic amines in benzene solution at room temperature to azo compounds (1 -2 days), but yields are variable toluidines, 42, 56, and 6% p-nitroaniline (53%) a-naphthylamine, 3%. Oxidations in acetic... 

Reduction to aniline derivative aromatic-amine metabolism Benzene-oxide formation s ... 

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

PMMA is not affected by most inorganic solutions, mineral oils, animal oils, low concentrations of alcohols paraffins, olefins, amines, alkyl monohahdes and ahphatic hydrocarbons and higher esters, ie, >10 carbon atoms. However, PMMA is attacked by lower esters, eg, ethyl acetate, isopropyl acetate aromatic hydrocarbons, eg, benzene, toluene, xylene phenols, eg, cresol, carboHc acid aryl hahdes, eg, chlorobenzene, bromobenzene ahphatic acids, eg, butyric acid, acetic acid alkyl polyhaHdes, eg, ethylene dichloride, methylene chloride high concentrations of alcohols, eg, methanol, ethanol 2-propanol and high concentrations of alkahes and oxidizing agents. 

Secondly, the rates and modes of reaction of the intermediates are dependent on their detailed structure. For example, the stability of the cation radical formed by the oxidation of tertiary aromatic amines is markedly dependent on the type and degree of substitution in the p-position (Adams, 1969b Nelson and Adams, 1968 Seo et al., 1966), and the rate of loss of halogen from the anion radical formed during the reduction of haloalkyl-nitrobenzenes is dependent on the size and position of alkyl substituent and the increase in the rate of this reaction may be correlated with the degree to which the nitro group is twisted out of the plane of the benzene ring (Danen et al., 1969). 

Anilines are converted into nitrosoarenes ArNO by the action of hydrogen peroxide in the presence of [Mo(0)(02)2(H20) (HMPA)]224, whereas catalysis of the reaction by titanium silicate and zeolites results in the formation of azoxybenzenes ArN (0)=NAr225. Azo compounds ArN=NAr are formed in 42-99% yields by the phase-transfer assisted potassium permanganate oxidation of primary aromatic amines in aqueous benzene containing a little tetrabutylammonium bromide226. The reaction of arylamines with chromyl chloride gives solid adducts which, on hydrolysis, yield mixtures of azo compounds, p-benzoquinone and p-benzoquinone anils 234227. 

Since nitric acid, especially red fuming nitric acid RFNA which contains a small amount of nitrogen oxides, reacts vigorously with aromatic amines, during World War II the Germans employed solutions of these amines (e.g. aniline or phenylenediamine) in benzene or xylene as the combustible component. They added a small amount of ferric chloride as a reaction catalyst to the nitric acid. It was also shown that the addition of vinyl ethers to amine solutions reduces the induction period. 

Like some phenolic groups, amino groups bound to an aromatic system (e.g., benzene) may be oxidized in the environment. In some cases such transformations may lead to the formation of products that are of considerable concern (Chapter 14). Finally, some aromatic amines that form stable radicals are actually also used as antioxidants (see example given in Fig. 2.18 and Kirk-Othmer, 1992). 

Lewis acids such as A1C13, SbCl5, or PFS have been used successfully to generate a variety of radical cations. Antimony pentachloride was first used with hydrocarbons such as benzene or anthracene [22, 23]. Salts obtained from aromatic amines with this reagent were found to be paramagnetic [24] eventually, well resolved ESR spectra identified the formation of radical cations [25,26]. Although an electron transfer mechanism must be involved, the fate of the complementary radical anions and details of their decay are poorly understood. Once again, it appears doubtful that Lewis acids are suitable oxidants for the study of the sometimes delicate substrates discussed in this review. 

The oxidation of substituted aromatic amines with silver(l) carbonate on Celite has been shown to yield symmetrically substituted phenazines, albeit in poor yields. 2,7-Dimethoxy-hexafluorophenazine has been obtained upon electrolysis of solutions of 4-methoxytetrafluoro-aniline, and oxidative coupling of benzene-1,4-diamine with aniline or substituted anilines also gives phenazine derivatives. ... 

Bis(trifIuoroacetoxy)iodo]benzene (FIFA 29) also brings about the facile oxidative rearrangement of aliphatic amides to amines in mildly acidic (pH 1-3) 50% aqueous acetonitrile at room temperature within several hours, as shown in equation (22). The reagent cannot be q>plied to the formation of aromatic amines since the latter are further oxidized. The intermediates of the reaction are isocyanates, which are rapidly hydrolyzed to amines under mildly acidic conditions, llie acidic conditions protect the... 

The conversion of naphthalene to 2-naphthoic acids by irradiation with carbon dioxide and electron donors (e.g. amines or dimethoxybenzene) has been further investigated and the quantum yields of the reaction measured for different solvents and donors. Electron transfer also occurs in the photochemical phosphonation of naphthalene and phenanthrene achieved by irradiation with trialkyl-phosphites and electron acceptors such as 1,3-dicyanobenzene. The photonitration of phenol in aqueous solutions of nitrate ion has been reported and phenols have been prepared by irradiation of substituted benzenes with the aromatic N-oxide (132). ... 

Both trialkyl- and triarylstibine sulfides and selenides are known. Trimethylstibiae sulfide [15082-97-6], C3H9SSb, has been prepared from trimethylstibine oxide and hydrogen sulfide (164). It is monomeric in benzene and chloroform. Trialkylstibine sulfides and selenides have been prepared from tri-alkylstibines and sulfur or selenium, respectively (165). Unlike triphenylstibine oxide, the structure of triphenylstibine sulfide is tetrahedral, as shown by both Mu ssbauer and x-ray diffraction studies (153). A patent covering the synergistic use of triphenylstibine sulfide with aromatic amines as antioxidants in lubricating oils has been issued (166). 

By contrast, a more direct and atomically efficient route for the production of aromatic amines would be to eliminate the need for halogen mediated oxidation of benzene. This can be achieved by a class of reaction known as nucleopWlic aromatic substitution for hydrogen (NASH-Figure 7). While this type of reaction has been known for over 100 years, this chemistry generally proceeds in low yields, give mixtures of ortho and para substitution products, and requires the use of environmentally unfavorable external oxidants.23 This section will focus on two new examples of NASH chemistry applicable to the production of commercially relevant aromatic amines. The... 

Two examples of nucleophilic aromatic substitution for hydrogen reactions were described from which we have proposed two new atomically efficient processes for the manufacturing of commercially relevant aromatic amines. Our mechanistic studies have revealed that the direct oxidation of a-complex intermediates by either nitro groups or O2 can eliminate the need for chlorination of benzene as a starting point for the manufacturing of aromatic amines. Accordingly, these reactions demonstrate the key objective of alternate chemical design which is not to make the waste in the first place. 

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