Adsorbates aniline

Formation of MH+ ions on adsorption of 2V,iV-dimethylaniline and stabilization in the adsorbed state should be accompanied by the appearance of the known 260-nm absorption band (18, 23). This band was observed in our work in the spectra of adsorbed aniline at low adsorption. In the spectra (Figure 1) this band is not visible because of the superposition of the MH+ absorption bands and the presence of the excess adsorbed N,N-... 

The effect of adsorbing aniline is shown in Fig. 19. The surface OH band at 1.365 u disappears, and the N—H band of aniline at 1.52 u shows a slight shift from the position of this band in dilute solutions of CC14 (1.50 u). Yaroslavskii and Terenin attributed the disappearance of the OH band to the formation of hydrogen bonds, 0—H N. The disappearance of the surface OH bands has also been observed in other experiments. 

Fig. 19. Effect of aniline on the OH band of porous glass (A) dried porous glass, (B to E) with increasing amounts of adsorbed aniline.

An important development, pioneered by Kuhn and coworkers,37 38 has been the deposition of conducting PAn s onto fibers and fabrics. Not only hydrophobic fibers such as polyesters and polypropylene but also hydrophilic textiles such as rayon and cotton can be coated with PAn with this in situ polymerization method. PAn/nylon-6 composite films have also been prepared by adsorbing aniline onto thin nylon-6 films and then treating with aqueous (Nn4)2S208.39 The composite films exhibited a low percolation threshold requiring just 4% PAn for electrical conductivity. 

Conclusions can be drawn concerning the nature of the specific centers on silica-alumina from the similarity of the spectrum of adsorbed aniline with that of benzene. These centers may be of two types, either Bronsted acids or Lewis acids, and may be depicted as shown in structures... 

The formation of polyaniline (PANI) between the layers of montmorillonite (Fig. 16) is an illustrative example of the in situ polymerization procedure. As already posmlated in the 1960s by several authors, montmorillonite-adsorbed aniline spontaneously oxidizes and polymerizes by the catalytic action of Cu ions (145,146) or by atmospheric oxygen (147,148). Evidence of such reactions and mechanisms were first advanced by Cloos and coworkers (149,150) 20 years... 

Therefore it is possible to determine absorption spectra directly on the TLC plate by comparison with a substance-free portion of the layer. The wavelengths usually correspond to the spectra of the same substances in solution. However, adsorbents (silanols, amino and polyamide groups) and solvent traces (pH differences) can cause either bathochromic (ketones, aldehydes [60, 61], dyestuffs [62]) or hypsochromic (phenols, aniline derivatives [63]) shifts (Fig. 23). 

Expulsion of nitrogen with formation of the A -l-methyl compound (9) occurs by heating (8) at ca. 220° or at room temperature by contact with acidic adsorbents. ° However, in this case perchloric acid or boron trifluoride etherate catalyzed fragmentation is not possible, although high yields (80 %) of (9) are obtained by heating (8) with quinoline or aniline. The la,2a-methylene compound (10) is always obtained as a by-product in 5% yield. 

Participation in the electrode reactions The electrode reactions of corrosion involve the formation of adsorbed intermediate species with surface metal atoms, e.g. adsorbed hydrogen atoms in the hydrogen evolution reaction adsorbed (FeOH) in the anodic dissolution of iron . The presence of adsorbed inhibitors will interfere with the formation of these adsorbed intermediates, but the electrode processes may then proceed by alternative paths through intermediates containing the inhibitor. In these processes the inhibitor species act in a catalytic manner and remain unchanged. Such participation by the inhibitor is generally characterised by a change in the Tafel slope observed for the process. Studies of the anodic dissolution of iron in the presence of some inhibitors, e.g. halide ions , aniline and its derivatives , the benzoate ion and the furoate ion , have indicated that the adsorbed inhibitor I participates in the reaction, probably in the form of a complex of the type (Fe-/), or (Fe-OH-/), . The dissolution reaction proceeds less readily via the adsorbed inhibitor complexes than via (Fe-OH),js, and so anodic dissolution is inhibited and an increase in Tafel slope is observed for the reaction. 

Finally we mention in this section the non-catalytic selective bromination of aniline by the application of a zeolite pre-loaded with Bt2 as a slow release reagent (ref. 27). Aniline, dissolved in CCI4 was treated with Br2 adsorbed onto various zeolites and zeolite CaA was found to be most selective for monosubstitution (92%). The addition of organic bases improved the performance, probably due to scavenging of HBr. Also the toluidines could be monobrominated with this system with >95% selectivity. 

We used DFT to optimize the geometries of various Hammett bases on cluster models of zeolite Brpnsted sites. For p-fluoronitrobenzene and p-nitrotoluene, two indicators with strengths of ca. -12 for their conjugate acids, we saw no protonation in the energy minimized structures. Similar calculations using the much more strongly basic aniline andogs of these molecules demonstrated proton transfer from the zeolite cluster to the base. We carried out F and experimental NMR studies of these same Hammett indicators adsorbed into zeolites HY and HZSM-5. 

Chiral recognition of A-[Co(phen)3]3+ has been observed in a modified /3-cyclodextrin.772 Chiral discrimination has also been seen in photoinduced energy transfer from luminescent chiral lanthanoid complexes773 to [Co(phen)3]3+ and between photoexcited [Ru(bpy)3]2+ and [Co(phen)3]3+ co-adsorbed on smectite clays.774 The [Co(bpy)3]3+ ion has been incorporated into clays to generate ordered assemblies and also functional catalysts. When adsorbed onto hectorite, [Co(bpy)3]3+ catalyzes the reduction of nitrobenzene to aniline.775 The ability of [Co(phen)3]3+ to bind to DNA has been intensively studied, and discussion of this feature is deferred until Section 6.1.3.1.4. 

Figure 4. Reflection infrared spectra of aniline films (a) aniline multilayer adsorbed on Ni(111) at 165 K (b) poly(aniline) monolayer on Ni(111) at 400 K (c) electrochemically grown poly(aniline) on Pt oxidized at 0.8 V vs. Ag/AgCI(1M) (d) electrochemically grown poly(aniline) on Pt reduced at 0.35 V vs. Ag/AgCI(1M) (e) electrochemically grown poly(aniline) on Pt reduced at 0.0 V vs. Ag/AgCI(1M)...

Retention volumes of monosubstituted benzenes, benzoic acid, phenols, and anilines have been measured in RPLC [76]. Buffered acetonitrile/water and tetrahydrofuran/water eluents were used with an octadecylsilica adsorbent. From the net retention volumes, a substituent interaction effect was calculated and described with the linear free energy relationship developed by Taft. The data was interpreted in terms of hydrogen bonding between the solutes and the eluent. 

Talsky [1] illustrated the practical use of higher-order derivative spectrophotometry in estimating pollutants in soils by detailed descriptions of the simultaneous estimation of aniline in waste water, phenol in soils and the study of nickel adsorbed on to bentonite powder. 

Reductions at noble metal electrodes in acidic protic media often form adsorbed hydrogen, which is the actual reductant. For example, reduction of nitrobenzene at a Pd/C electrode in acetic acid-methanol mixtures affords aniline via adsorbed hydrogen28. This reaction is more closely related to catalytic hydrogenation of nitro groups than to the... 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

Photolytic. A carbon dioxide yield of 46.5% was achieved when aniline adsorbed on silica gel was irradiated with light (X >290 nm) for 17 h (Freitag et al., 1985). Products identified from the gas-phase reaction of ozone with aniline in synthetic air at 23 °C were nitrobenzene, formic acid, hydrogen peroxide, and a nitrated salt having the formula [CeHsNHsl NOs" (Atnagel and Himmelreich, 1976). A second-order rate constant of 6.0 x 10 " cmVmolecule-sec at 26 °C was reported for the vapor-phase reaction of aniline and OH radicals in air at room temperature (Atkinson, 1985). 

A detailed investigation of aniline N-methylation on Cui xZnxFc204 was carried out through in situ FTIR spectroscopy. The reactants (aniline and methanol) and possible products (NMA, DMA and o-toluidine) were adsorbed on the catalysts and analyzed [106,107]. Adsorption of methanol indicated a dissociative chemisorption as methoxy species on catalyst surface at 100°C. As the temperature increased, oxidation of methoxy species to formaldehyde to dioxymethylene to formate species was observed, and above 300°C complete oxidation takes place to CO, CO2 and H2. Indeed methanol alone on Cui xZnxFc204 and Cui.xCoxFc204 behaves in a similar way [79,107]. 

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