Aromatic amines, benzene

The most important reaction of the diazonium salts is the condensation with phenols or aromatic amines to form the intensely coloured azo compounds. The phenol or amine is called the secondary component, and the process of coupling with a diazonium salt is the basis of manufacture of all the azo dyestuffs. The entering azo group goes into the p-position of the benzene ring if this is free, otherwise it takes up the o-position, e.g. diazotized aniline coupled with phenol gives benzeneazophenol. When only half a molecular proportion of nitrous acid is used in the diazotization of an aromatic amine a diazo-amino compound is formed. 

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... 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

A number of aromatic amines also function as cross-linking agents. By incorporating the rigid benzene ring structure into the cross-linked network, products are obtained with significantly higher heat distortion temperatures than are obtainable with the aliphatic amines. 

One of the most important derivatives of benzene is nitrobenzene. The nitro group is —NOi. Nitrobenzene is important chiefly because it is readily converted into an aromatic amine, aniline, by reduction. One preparative procedure uses zinc as the reducing agent ... 

Including aromatic amines (to be discussed below) the order of reactivities for substituted benzene and naphthalene coupling components is therefore O" > NR2 > NHR > NH2 > OR = OH > CH3 > unsubstituted (R = alkyl). 

Using other alkylated benzene hydrocarbons, e.g., amyl-, hexyl-, octyl-, or nonylbenzene, similar surface-active phosphinic acids are formed by reaction with PC13 in the presence of anhydrous aluminum trichloride. The resulting alkylarylphosphinic acids form stable salts with primary, secondary, or tertiary hydroxy amines or aromatic amines [166,171]. 

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). 

In a related procedure, even benzene and substituted benzenes (e.g., PhMe, PhCl, xylenes) can be converted to phenols in good yields with sodium perborate F3CS020H. " Aromatic amines, N-acyl amines, and phenols were hydroxylated with H2O2 in SbFs—HF. Pyridine and quinoline were converted to their 2-acetoxy derivatives in high yields with acetyl hypofluorite AcOF at -75°C. ... 

Both 3-amino-N-ethylcarbazole and l,4-diethoxy-2-amino-5-benzoylamino-benzene are suitable aromatic amines. Chloranil may also be replaced by 2,5-di-chloro-3,6-bisacetylamino-l,4-benzoquinone to react with appropriately substituted o-alkoxyanilines. 

The development of the intense colour of the azo-dyes provides a delicate and distinctive test for primary aromatic amines. Since the naphthalene derivatives are more deeply coloured than those of benzene, it is customary to use not phenol but j8-naphthol or the so-called R-acid ( acid for Red ), i.e. /S-naphthol-3 6-disulphonic acid ... 

As we have already seen in the case of aniline, primary aromatic amines do not couple normally a triazene derivative, diazoamino-benzene, is produced by linkage through the NH2-group just as in the case of aliphatic amines, e.g. dimethylamine ... 

The kinetics of the reaction of p-nitrobenzenesulfenyl chloride with aromatic amines in benzene as solvent follow the form (175) (Ciuffarin and Griselli, 1970 Ciuffarin and Senatore, 1970). This is indicative of a mechanism of the... 

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. 

Scheme 15 could be a reaction pathway parallel to the classical reaction (equation 1), and it was postulated to explain the third order in amine observed in the reactions of FDNB and aromatic amines in benzene and in chloroform184. The K values were calculated from the absorbances of the reaction mixture extrapolated to zero reaction time, in a wavelength range in which the starting materials do not show an appreciable absorbance value. Good agreement was observed between the values of K for the FDNB/aniline complex in chloroform by U.V. and 111-NMR spectroscopy, as well as for the K obtained kinetically (based on Scheme 15) and spectroscopically. 

Aniline is a simple aromatic compound composed of an amino group attached to a benzene ring. Other aromatic amines are aniline derivatives. Some examples of aromatic amines are shown in Figure 13-2. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

Treatment of 5-ethoxy-l,2,3,4-thiatriazolium tetrafluoroborates (161) with aromatic amines in boiling benzene affords yellow crystalline 5-arylamino-l,2,3,4-thiatriazolium salts (166) in good yields (60-70%) (Scheme 35). These are deprotonated with warm ethanolic aqueous sodium hydroxide to give the red crystalline mesoionic l,2,3,4-thiatriazolium-5-aminides (20). The mesoionic compounds show a strong IR absorption in the region 1580-1590 cm which can be assigned to the exocyclic (7=N stretching vibration. UV and visible spectra are reported e.g. (20a) 279 (e... 

Benzene and naphthalene sulfonate moieties are present in the structures of many dyes that can be found in large amounts in wastewaters from textile and food industries. Even if wastes are decolored before the final discharge, not enough attention is nowadays devoted to the identification of possible uncolored degradation products, potentially toxic, that form during the decolorization process and are discharged into the aquatic systems. Besides sulfonate derivatives, aromatic amines have also been reported as possible degradation products of dyes [109],... 

The basic components in the structure of local anesthetics are the lipophilic aromatic portion (a benzene ring), an intermediate chain, and the hydrophilic amine portion (Fig. 27.1). The intermediate chain has either an ester linkage from the combination of an aromatic acid and an amino alcohol or an amide linkage from the combination of an aromatic amine and an amino acid. The commonly used local anesthetics can be classified as esters or amides based on the structure of this intermediate chain. 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

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