Aniline, acidity

The ability to adopt an extended configuration has been recognised for many years to be a desirable feature of substantive dyes. It helps to explain why J acid is such a popular choice as a central component in unsymmetrical disazo dyes. For example, it is much easier for aniline—>] acid—>H acid (3.61) with the 2,6-naphthylene substitution pattern to adopt a linear conformation than for the similar disazo dyes aniline—acid— H acid (3.62) and aniline—>H acid—>J acid (3.63) with 2,7- and 2,8-disubstitution respectively. 

Aldonic and ketoaldonic acids may be difficult to separate. Norris and Campbell separated ketogluconic acid from gluconic acid by preparing the phenylhydrazone of the keto acid, which is then easily separable from gluconic acid. A methanol-ethanol-water solvent mixture was used.64 Another useful solvent developer is 1-butanol-formic acid-water.133 Macek and Tadra separated a series of ketoaldonic acids in a number of acidic solvent developers.134 Color reagents which may be used include ammoniacal silver nitrate,94 o-phenylenediamine dihydrochloride,84 and aniline acid oxalate.138 Lactones are detectable with hydroxylamine followed by ferric chloride.128... 

Chromatographic characterization of sugar phosphates can be achieved by two different methods. First, you can usually detect the sugar portion of sugar phosphates by using sugar-specific reagents, such as the aniline-acid-oxalate spray... 

Aniline-acid-oxalate spray reagent (see Appendix) Modified Hanes-Ischerwood spray reagent [(4% (NH4)6Mo024 4 H20 1 N HC1 70% HC104 H20 (5 2 1 12)]... 

Aniline-acid-oxalate spray—Dissolve 4.5 g oxalic acid in 1 liter of distilled water, add 9 ml of aniline. Store in a brown bottle. 

Another interesting example is the aniline catalyzed formation of benzaldehyde semicarbazone [266]. Aniline and substituted anilines strongly accelerate the reaction of benzaldehyde with semicarbazide. The reaction rate and its pH dependence is equal to that of the formation of Schiff base from benzaldehyde and aniline (acid catalysis with changing rate-determining step) and does not depend on the concentration of semicarbazide. The final product is benzaldehyde semicarbazone, however. Obviously, benzaldehyde first reacts with aniline to form the Schiff base intermediate which then reacts rapidly with semicarbazide to form the semicarbazone. It has been established in separate experiments that the reaction of Schiff base with semicarbazide is fast. The detailed mechanism of the latter conversion is unknown. 

As in the case of halogenation and nitration the sulphonation of aniline takes place more easily than that of benzene itself. When aniline is heated with concentrated or fuming sulphuric acid the sulphonic acid group enters the ring in the para position. The first reaction of the sulphuric acid on the aniline is of course the formation of the salt, aniline acid sulphate, but this loses water on heating and yields the sulphonic acid.. ... 

SWNTs Chemical polymerization Aniline, acide (HCl, H2SO4), KjCraOy PANI doped with small CNT fragments, closed-shell Ceo... 

Theoretical and gas-phase experimental results for the effect of substituents on phenol acidity (10) are listed in Table 24. Similar data for aniline acidity and basicity are given in Table 25. In general, there is good agreement between the available experimental values and the theoretical results, allowing greater confidence in those theoretical values which at present remain experimentally unverified. 

Decomposition of the substituent effect into the effect on the neutral molecule and the appropriate charged species, that is, either the conjugate acid or base, is revealing. For phenol acidity, the breakdown of the substituent effect into the two components indicates quite clearly that the interaction in the substituted phenoxide ion is the dominant one (10). In other words, p-nitrophenol is a strong acid primarily because the p-nitrophenoxide ion is relatively stable. The same is true for aniline acidity. 

Fig. 1.6 A large number of PANI arrays with average diameter of 1.2 ttm and highly ordered structure are produced by change of the aniline/acid concentration ratio (Reprinted from Wu et al. [101], with permission from Elsevier)...

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