Diphenylamine, basicity

The correlation coefficient r = 0.952 can be compared with the value r = 0.767 found in the correlation of diphenylamine basicity with the single 4-fiuorophenol basicity. 

Physical Properties, (i) Aromatic. Colourless when freshly prepared, but usually brown. MonomethylaniUne, CgHjNHCH, b.p. 193°, and monoethylaniline, CgHjNHCjHj, b.p. 206 , diphenylamine,(C6H5)2NH, m.p. 54 , are all insoluble in water, the two alkylanilines having well-marked basic properties, diphenylamine being feebly basic and insoluble in dilute mineral acids. 

Various basic substances, such as aromatic amines (naphthyl-amines dissolve with difficulty in dil. HCl, diphenylamine only in cone. HCl, triphenylamine insoluble) nitro-anilines some amino-carboxylic acids. 

Primary and secondary aliphatic and aromatic amines react readily with thiiranes to give 2-mercaptoethylamine derivatives (Scheme 76) (76RCR25, 66CRV297). The reaction fails or gives poor yields with amines which are sterically hindered e.g. N,iV-dicyclohexylamine) or whose nitrogen atom is weakly basic e.g. N,A/ -diphenylamine). Aromatic amines are less reactive and higher reaction temperatures are usually required for them. The reaction mechanism is Sn2 and substituted thiiranes are attacked preferentially at the least hindered... 

Conjugation of the amino group of an aiylfflnine with a second aiomatic ring, then a thud, reduces its basicity even further. Diphenylamine is 6300 times less basic than aniline, whereas triphenylamine is scarcely a base at all, being estimated as 10 ° times less basic than aniline and 10 " times less basic than ammonia. 

The aniline molecule is thus stabilised with respect to the anilinium cation, and it is therefore energetically unprofitable for aniline to take up a proton it thus functions as a base with the utmost reluctance (p Ka = 4 62, compared with cyclohexylamine, pKa = 10-68).Thebase-weakening effect is naturally more pronounced when further phenyl groups are introduced on the nitrogen atom thus diphenylamine, Ph2NH, is an extremely weak base (pKa = 0-8), while triphenylamine, Ph3N, is by ordinary standards not basic at all. 

Different reactivity of a-oxyalkyl and boryloxyalkyl fragments was revealed in reactions with amines of weak basicity. For example, in the reaction with diphenylamine or o-aminobenzoic acid with a reagent ratio of 1 1, substitution of the oxymethyl group by the aminomethyl one takes place [Eq. (117)]. The P,B-containing heterocycle is retained (89IZV1340). 

Several examples of typical triarylmethane dyes have already been mentioned, in particular, pararosaniline (6.161), malachite green (6.162) its o-chloro derivative (6.169), crystal violet (6.164), rosaniline (6.165) and diphenylamine blue (6.173). Cl Basic Green 1 (6.168 R = C2H5), the ethyl analogue of malachite green, is prepared by the aldehyde route and is isolated as the sulphate. The ethyl analogue of crystal violet is Cl Basic Violet 4 (6.167 R = C2H5) and is obtained by the ketone route. 

Amino groups may act not only as proton acceptor, but also as proton donor. Acidic N—H protons interact with basic solvents. In these cases an ortho-nitro group in an aniline system competes with the solvent by an internal hydrogen bond66, as depicted in 12. The stretching frequencies (by IR spectra in carbon tetrachloride) of vnh of complexes between A-methylaniline or diphenylamine (and some nitro-anilines66) and solvents depend on the proton accepting ability of the solvent (which is a moderate base)67. The frequency shifts are linearly related to the solvent s donor number (DN)3. 

Most syntheses of naturally occurring phenazines, though, are based on a two-step elaboration of the central heterocycle of the phenazine [78]. The first key step involves the generation of orf/zo-monosubstituted 88 or orf/zo, ortho -disubstituted diphenylamines 89-91 via nucleophilic aromatic substitution. Ring formation is then achieved by means of reductive or oxidative cyclization, for which a number of efficient methods are available. The main flaw of this approach is the synthesis of the substituted diphenylamines via nucleophilic aromatic substitution, as this reaction often can only be performed under strongly basic reaction conditions and at high temperatures. In addition, the diphenylamines required may only be achieved with certain substitution patterns with high yields. 

As we move to A-methylaniline, we see only a modest change in pK ,. This is undoubtedly due to the electron-donating effect of the methyl group, and this would be expected to stabilized the conjugate acid, increasing observed basicity. There is a modest increase in basicity, but it is apparent that the resonance effect, as in aniline, is also paramount here, and this compound is also a weak base. However, diphenylamine (A-phenylaniline) is an extremely weak base this can be ascribed to the resonance effect allowing electron delocalization into two rings. 

Treatment of diphenylamine with base and traces of oxygen in DMSO solution yielded a significant ESR signal that we have identified as I. The same radical is formed spontaneously from the mono-anil of p-benzoquinone in basic DMSO and by the oxidation of 4-hydroxydi-... 

Reppe has shown that secondary amines of low basicity, such as carbazole, diphenylamine, indole, imidazole, and benzimidazole, and amides such as pyrrolidone react with acetylene in the presence of strong alkali to give vinyl derivatives [81, 83, 84a, b] (Eq. 30). As described by Reppe, these reactions are... 

Investigations have shown that the basic properties of diphenylamine are so weak that it cannot hydrolyse nitrocellulose, but they are sufficiently strong to neutralize any acid product arising either from the decomposition of impurities in the nitrocellulose, from the oxidation of residual solvent or even from decomposition of the nitrocellulose itself. It was also demonstrated that the basic properties of diphenylamine may have a deleterious effect on the powder if the diphenylamine content exceeds 5%. The best stabilizing results are achieved by using 1.0-2.5% diphenylamine. 

Apart from diphenylamine a number of other organic bases were tested for use as stabilizers. Some of them, e.g. aniline, were used only temporarily, chiefly during World War I when diphenylamine was in short supply. The basic properties of aniline are too marked and this is detrimental to stability. On the other hand, relatively good results have been obtained with carbazole which resembles diphenylamine in its structure ... 

Ballistites initially consisted of equal amounts by weight of nitroglycerine and soluble nitrocellulose CP2 with the addition of aniline or diphenylamine as stabilizers. It was found, however, that the presence of aniline and diphenylamine is detrimental to the stability of the powder, and they were therefore omitted. The valuable properties of centralite as a solvent of low basicity were then recognized and it was used both for its ability to dissolve the nitrocellulose and for its stabilizing action. 

Only fews solids have been used as catalysts for deamination and disproportionation reactions. Among them, alumina has been studied most frequently, and some attention has also been paid to silica—alumina and to molecular sieves [149]. The activity of alumina for the disproportionation of weakly basic aniline to diphenylamine can be enhanced by impregnation with HC1 [149] or H3B03 [150]. 

The influence of the rigid structure on the basicity of quinuclidine derivatives30 is demonstrated by comparison of the pKa values of benzo- and dibenzoquinuclidines with the structurally allied diethyl-aniline and diphenylamine (see Table II). 

Unsubstituted polysaccharides do not appreciably absorb ultraviolet and visible radiation, but they can be made to do so intensely by combining them with chromophores and chromogens (e.g., a-naphthol, dihydroxynaph-thalein, anthrone, carbazole, phenol-sulfuric acid, 2-thiobarbituric acid, tolu-idine blue, diphenylamine, Congo red, aniline blue, and methyl orange), usually in acidic or basic media. Coloration is normally preceded by depoly-... 

Although a variety of amines, particularly trimethylamine and n-butylamine have widely been used as poisons in catalytic reactions and for surface acidity determinations (20), comparably few spectroscopic data of adsorbed amines are available. As with ammonia, coordinatively adsorbed amines held by co-ordinatively unsaturated cations have preferentially been found on pure oxides (176, 193-196), whereas the protonated species were additionally observed on the surfaces of silica-aluminas and zeolites (196-199). However, protonated species have also been detected on n-butylamine adsorption on alumina (196) and trimethylamine adsorption on anatase (176) due to the high basicity of these aliphatic amines. In addition, there is some evidence for dissociative adsorption of n-butylamine (196) and trimethylamine (221) on silica-alumina. Some amines undergo chemical transformations at higher temperatures (195, 200) and aromatic amines, such as diphenylamine, have been shown to produce cation radicals on silica-alumina (201, 201a). 

In diphenylamine and finally triphenylamine the basicity is still lower, so that this last amine only forms salts with the strongest acids of all, such as HC104. A condition for maximum resonance is a completely plane structure, which can, however, not be satisfied in the last-mentioned substance. This is also the case with dimethyl 0-toluidine, which is a weaker base than dimethylaniline, while 0-toluidine has practically the same strength as aniline. 

---