Anilines fluorescence reaction

Figure 3. Relative fluorescence intensities of n-butylamine and aniline after reaction with o-phthalaldehyde, a-naphthylamine, and 7-hydroxycoumarin (O) aniline (O) n-butylaminej(A) a-naphthylamine (9) 7-hydroxycoumarin...

The same authors studied the CL of 4,4,-[oxalylbis(trifluoromethylsulfo-nyl)imino]to[4-methylmorphilinium trifluoromethane sulfonate] (METQ) with hydrogen peroxide and a fluorophor in the presence of a, p, y, and heptakis 2,6-di-O-methyl P-cyclodextrin [66], The fluorophors studied were rhodamine B (RH B), 8-aniline-l-naphthalene sulfonic acid (ANS), potassium 2-p-toluidinylnaph-thalene-6-sulfonate (TNS), and fluorescein. It was found that TNS, ANS, and fluorescein show CL intensity enhancement in all cyclodextrins, while the CL of rhodamine B is enhanced in a- and y-cyclodextrin and reduced in P-cyclodextrin medium. The enhancement factors were found in the range of 1.4 for rhodamine B in a-cyclodextrin and 300 for TNS in heptakis 2,6-di-O-methyl P-cyclodextrin. The authors conclude that this enhancement could be attributed to increases in reaction rate, excitation efficiency, and fluorescence efficiency of the emitting species. Inclusion of a reaction intermediate and fluorophore in the cyclodextrin cavity is proposed as one possible mechanism for the observed enhancement. 

The above properties (a and b) are interpreted by Cohen and Schmidt (21) on the basis of a detailed crystallographic study of photochromic and thermochromic anils. They conclude that photochromic crystals involve structures in which the central portion of adjacent molecules are essentially isolated from one another, so that, to a first approximation the energetics are that of an isolated molecule. On the other hand, when the alignment of the molecular dipoles is such as to give strong intermolecular interactions then the transition to the quinoid form requires much less energy and can occur thermally. For crystals in which thermochromism occurs, the photochemical isomerization is still possible but the reverse reaction is so rapid that no buildup of color is observed. In fact, fluorescence measurements on the thermochromic 5 -chlorosalicylidene-aniline (Fig. 5) indicate that photochemical isomerization precedes the luminescence process via the photochromic route ... 

Chloro-7-nitrobenz-2,l,3-oxadiazole (NBD-C1) reacts with primary and secondary aliphatic amines to produce intensely fluorescent derivatives. Although anilines, phenols and thiols react with NBD-C1, they produce derivatives which do not fluoresce or which are only weakly fluorescent. This limits the types of compounds which can be analyzed with this reagent and thus makes the technique more selective. This selectivity is desirable in trace analysis because of a lower degree of interference from co-extractives. The general reaction scheme for formation of the fluorescent amine derivatives is shown in Fig.4.50. 

Many fluorescent brighteners are derivatives of 4,4 diamino-stilbene-2,2 -disulfonic acid (59), an example of which is C.I. Fluorescent Brightener 32 (Fig. 13.138). In this case, successive reactions involving diamine 59 with two molecules of cyanuric chloride and two molecules of aniline followed by hydrolysis of the final chloro groups give the target compound. 

The photolysis of aniline at high temperatures results in N-H and C-N clea-vage, but at room temperature the major reaction is fluorescence. Below 2800 A some photodecomposition takes place the lifetime and dissociation probability of excited aniline molecules have been calculated Flash photolysis of aniline followed by kinetic mass spectroscopy failed to reveal the presence of dissociation products. Irradiation of halogen derivatives of aniline between 2480 and 2562 A produces halide ions in measurable yields . Positive mesomeric effects increase, and negative mesomeric effects decrease... 

Mauveine was the first aniline dyestuff prepared on a large scale (Perkinj 1856), and is certainly closely related to the saffranine dyestuffs. Like these, it has strong basic properties, and gives similar reactions with sulphuric acid. Finally, a saffranine (para-saffranine, CjoHigNi [28]) is formed by oxidation of mauveine in acetic acid solution. The fluorescence characteristic of alcoholic saffranine solution is, however, absent with mauveine. 

The proton-dissociation reaction of alkylated ANIs in the excited 5) state tends to decrease significantly in A-monoalkylanilines but to increase in the A-dialkylated derivatives, with much larger activation energies111. The differences in the observed kiiss rate coefficient between protonated aniline and protonated alkylated derivatives has been explained on the basis of the charge density on the N-atom in the excited S state, the water structure in the vicinity of the amino group which acts as a proton acceptor and steric hindrance of the alkyl groups. As a consequence, the acidity (pKa values) and fluorescence lifetime of protonated anilines in aqueous solution are remarkably dependent on the substituent position in the ring. 

Wetzler and coworkers123 employed 4-aminophthalimide (63) and 4-amino-lV-methyl-phthalimide (64) as solvatochromic (and thermochromic) fluorescent probes in solvent mixtures. A bathochromic shift of the emission spectra was found in mixtures of toluene with ethanol and with acetonitrile123 when the more polar solvent was added to toluene, but raising the temperature causes a relative hypsochromic effect. Mixtures of benzene and acetonitrile were studied by Nevecna and coworkers124 for their polarity by means of the probes 46 and 47 and with respect to the correlation of this with the rate constants of the reaction of triethylamine with ethyl iodide. The fluorescence of the ammonium salt of 4-(l-naphthylsulfonate)aniline (84) in dioxane and water mixtures was studied by Hiittenhain and Balzer125. 

Analytical Procedure. Method for Determination of AA. Residual AA was determined immediately after irradiation by spectrophoto-fluorometry. In general the solutions were acidified to pH = 2.8 and analyzed using AeXit = 342 and Aemit = 428 m/x. To avoid quenching of the fluorescence because of AA, the irradiated solutions were diluted to an initial concentration of 2 X 10"5M AA. In experiments with nitrate, residual AA was determined by two different spectrophotofluorometric procedures. In the first method, carried out as described above, it was necessary to correct for a decrease in fluorescence caused by radiation induced nitrite which slowly diazotized AA. This reaction was followed with time and AA at the time of acidification was determined by extrapolation. In the second method, AA was determined by fluorescence assay of the diluted neutral solution (AeXit = 290 m/x and Aemit = 340 m/x). The radiation products (aniline 3-hydroxy- and 5-hydroxyanthranilic acid) did not interfere in either method, and both gave the same value for residual AA in the irradiated solutions (33). 

Reaction Conditions. After stirring the reaction mixture at room temperature for 15 min, begin monitoring the system byTLC (plates with fluorescent indicator). Using as a solvent system ethyl acetate hexane (3 2) and a UV lamp for visualization, the Revalue for maleardlic add is 0.2.The Revalues for aniline and maleic anydride are 0.73 and 0.67, respectively. Once complete as judged by TLC, cool the reaction mixture in an ice bath for 5-10 min. 

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