Para-substituted anilines

Amino-5-methylthiazole does not react with diazotized p-nitroaniline in solutions acidified with acetic or hydrochloric acid (391). 2-Amino-4,5-dimethylthiazole with the diazonium salts of para-substituted anilines, however, gives product 193, involving reactivity of the exocyclic nitrogen (Scheme 122) (399). 

The Gassman indole synthesis provides a single regioisomer when ortho/para substituted anilines are employed, the yields of which are quite good generally. This provides some advantage in the preparation of 7-substituted indoles compared to other methods which normally give low yields, that is, the Fischer indole process. ... 

Good yields of 10-aryl-3,6-dinitroacridones were obtained merely by heating 2,2, 4,4 -tetranitrobenzophenone (419) with an excess of the corresponding aryl amines at 125°C. For example, aniline provided 420 in 80% yield (Eq. 38). The reaction is fairly general for meta- and para-substituted anilines, though it proceeds less readily with orf/io-substituted compounds (79JCS(P1)1364). A method of isolation of the intermediate diarylamine in the synthesis of certain 10-aryl-3,6-dinitroacridones from 2,2, 4,4 -tetranitrobenzophenone has also been described (93JCR(M)2779). 

The hydrogenation of para-substituted anilines over rhodium catalysts has been investigated. An antipathetic metal crystallite size effect was observed for the hydrogenation of /Moluidinc suggesting that terrace sites favour the reaction. Limited evidence was found for catalyst deactivation by the product amines. Catalysts with pore diameters less than 13.2 nm showed evidence of diffusion control on the rate of reaction but not the cis trans ratio of the product. 

N chemical shifts for para-substituted anilines (I) and para-substituted jV/Z-dimethyl-... 

The 15N chemical shifts of 1 and 2 together with the data for the relevant para-substituted anilines (3) are summarized in Table 8. At first glance it is clear that the... 

When (5(15N) values for the previously used series of 13 para-substituted anilines were measured in acetone42, a significantly weaker hydrogen-bond acceptor solvent than DMSO, a smaller shift dependence on para TT-electron-acceptor substituent solvation (SSAR) effects in acetone was observed (Table 10). This reduction42 was expressed by the (rather unsatisfactory) forms, 4 and 5. 

Some para-substituted anilines in strongly hydrogen bonding solvents show two non-equivalently hydrogen bonded species with differently hybridized aniline nitrogens72 rehybridization of aromatic amino nitrogens depends on the OH acidity of the solvent molecule and the basicity of the substituted anilines. 14 shows three possible modes of interaction of p-aminoacetophenone and acohol, where the amino group is simultaneously both a proton donor and an acceptor. 

TABLE 10. The secondary alpha deuterium and secondary incoming nucleophile deuterium kinetic isotope effects found for the S 2 reactions between para-substituted anilines and benzylamines with benzyl, methyl and ethyl para-substituted benzensulfonates in ace- ... 

The kinetics of oxidation of several para-substituted anilines and aliphatic acetals by peroxomonosulfate in aqueous acetic acid have been investigated. In the oxidation of sulfides to sulfoxides by peroxymonosulfate (Oxone), the observed increase in second-order rate constants with increasing concentration of H2SO4 has been shown to be due to the increasing polarity of the medium, rather than to acid catalysis. Similar conclusions were arrived at for the oxidation of aryl thiobenzoates and thiol-phosphorus(V) esters. 

In general, it appears that para-substituted anilines react more rapidly than other position isomers and that the order of reactivity is F > Cl > Br > I. 

The rate of reaction of 2-bromo-3,5-dinitrothiophene (470) with meta and para substituted anilines has been determined (76JOC968). The kinetic data are accommodated by the Ingold-Yukawa-Tsuno equation (1). 

Correlation with Hammett substituent constants alone was not satisfactory. The reaction has been extended to ortho substituted anilines also the results have been treated by the Fujita-Nishioka method. Combining these with the previous data for meta and para substituted anilines, a multiparameter regression equation (2) has been developed (79JCS(P2)219>. 

The oxidation of meta- and para-substituted anilines with imidazolium fluorochro-mate (IFC)18 and nicotinium dichromate (NDC),19 in several organic solvents, in the presence of p-toluenesulfonic acid (TsOH) is first order in the oxidant and TsOH and is zero order with respect to substrate. A correlation of rate data in different solvents with Kamlet-Taft solvatochromic parameters suggests that the specific solute-solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute-solvent complexation. The oxidation rates with NDC exhibited negative reaction constants, while the oxidation with IFC did not correlate well with any linear free energy relationships. 

Scheme 9.19 Formation of ortho- and para-substituted anilines in the hydrogenation of nitrobenzene in an acidic medium.

Anhydrobases 179 have been condensed with a number of para-substituted anilines (ArNH2) to give thiopyrylium salts 187 (84ZC183). The same anhydrobases have been converted, at room temperature in... 

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