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The low oxidation potential of 1-phenyl-2-(4-methylphenyl)diazene 4′-substituted with a dimethylamino or methoxy group ( 10 and 11 ) allows the easy single electron transfer with radical cation generation in the presence of FeCl 3 . At the same time, the stabilizing effect of the positive charge exerted by 4-dimethylaminophenyl > 4-methoxy groups on the intermediate carbocation favors the hydrogen atom elimination in comparison with proton loss. Whereas benzylic substitution towards di- and triarylmethane derivatives takes place starting from diazene 11 , the oxidation of diazene 10 leads mainly to products of C–azo breaking. This difference is well-supported by the idea that the electron, in the first step of oxidation, is extracted from the azo and (or) from the amino nitrogen atom.Key words: diazenes, oxidation, single electron transfer, benzylic substitution, C–azo bond breaking.

In this paper the adsorption of pyridine, a toxic pollutant, on naturally occurring clay, namely bentonite? was studied at a basic pH and room temperature. Sodium saturated bentonite as well as modified with a cationic surfactant were used and the results compared. The influence of contact time and of the initial pollutant concentration on the pyridine uptake was determined by GC-MS. The adsorbents were characterized before and after being in contact with the pyridine solution by BET specific surface area and porosity, XRD and FTIR analysis. The hydroxyl groups of bentonite in contact with pyridine solution led to protonated pyridine forms which can be responsible for hydrogen bonds formation and electrostatic interactions with the clay and for surfactant removal. Chemical adsorption prevailed over the partition/physical adsorption in both cases and the process followed the pseudo-second-order kinetics with the Freundlich isotherm model representing well the equilibrium adsorption data. The equilibrium adsorptive efficiency was 82.88% for the surfactant modified bentonite and 97.82%o for sodium bentonite, the latter being a better alternative for sequestering pyridine from solution.

Sol-gel obtained silica and organo silica particles, doped with rhodamine B (Rh B), with potential applications as sensing platforms for fluorescent pH probes were obtained. The silica matrices were generated by sol-gel method from different SiO2 sources and using different routes: the aqueous one with colloidal silica as precursor and the alkoxide one starting with tetraethoxysilane (TEOS) as such and with different organic functionalities. The product was characterized from structural and compositional point of view (FTIR, UV-VIS, SEM, BET surface area and porosity). The leaching of the dye from the matrices was detected by GC-MS. The fluorescence properties and variation with pH were determined. Structural interconversions of the dye take place as a function of the matrices and pH which influence the maximum absorption and emission wavelength of RhB. The presence of organic substituents in TEOS generates a quenching of the RhB fluorescence.