Elisa Leyva

Photocatalytic degradation of paracetamol: intermediates and total reaction mechanism.

The advanced oxidation of paracetamol (PAM) promoted by TiO(2)/UV system in aqueous medium was investigated. Monitoring this reaction by HPLC and TOC, it was demonstrated that while oxidation of paracetamol is quite efficient under these conditions, its mineralization is not complete. HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol in the reaction mixtures. Further evidence of p-nitrophenol formation was obtained following the reaction by UV-vis spectroscopy. Continuous monitoring by IR spectroscopy demonstrated the breaking of the aromatic amide present in PAM and subsequent formation of several aromatic intermediate compounds such as p-aminophenol and p-nitrophenol. These aromatic compounds were eventually converted into trans-unsaturated carboxylic acids. Based on these experimental results, an alternative deacylation mechanism for the photocatalytic oxidation of paracetamol is proposed. Our studies also demonstrated IR spectroscopy to be a useful technique to investigate oxidative mechanisms of pharmaceutical compounds.

Photocatalytic degradation of the herbicide “Paraquat”

Abstract The photocatalytic degradation of pure paraquat ( 1,1′-dimethyl-4,4′-bipyridinium dichloride ) aqueous solutions with UV light over titanium oxide was investigated. Experimental results have confirmed that paraquat is slowly degraded by direct photolysis in the presence of dissolved oxygen. Addition of TiO2 to the reaction system substantially increases the initial rate of reaction and the overall conversion of paraquat. Complete photocatalytic degradation of paraquat at high pH values was found to occur in less than three hours of reaction.

Spectrometric and 2D NMR Studies on the Complexation of Chlorophenols with Cyclodextrins

The formation and structure of inclusion complexes of α- andβ-cyclodextrins with 2-chlorophenol (2CP), 3-chlorophenol (3CP),4-chlorophenol (4CP), 2,4-dichlorophenol (24DCP), 2,6-dichlorophenol(26DCP) and 3,4-dichlorophenol (34DCP) have been studied by UV-VIS and1H NMR spectroscopy. Both cyclodextrins were found to form 1:1inclusion complexes. Bindingconstants estimated from titration studies revealed that the stability of the complexes was highly dependent on the structure and polarity of the chlorophenol and on the cyclodextrin used. In general, weaker binding constants were observed for a given chlorophenol with α-cyclodextrin than withβ-cyclodextrin. The weakest binding constants (Kb < 200 M-1) were obtained for the ortho-substituted chlorophenols (2CP and 26DCP) and the largest binding constants were obtained between para-chlorophenols (4CP, 24DCP and 34DCP) andβ-cyclodextrin. 2D-TROESY studies of chlorophenol-cyclodextrincomplexes in D2O provided insight into the structure of the complexes.

Photochemistry of fluorophenyl azides in diethylamine. Nitrene reaction versus ring expansion

Abstract Several fluorophenyl azides were photolyzed with diethyl amine at room temperature. Pentafluoro and 2,6-difluorophenyl azides gave hydrazines as the major products. On the other hand, several mono- and difluorophenyl azides gave azepines under similar conditions. Ortho-fluoro singlet phenyl nitrene produces the azirine by ring closure away from the substituent.

Synthesis of novel fluorobenzofuroxans by oxidation of anilines and thermal cyclization of arylazides

The synthesis of several fluorobenzofuroxans by oxidation of fluoroanilines and thermal cyclization of fluoroarylazides is presented. The fluorobenzofuroxans prepared in this study presented tautomerism as evidenced by their NMR data. Benzofuroxans in general have biological activity and are synthetic intermediates for the preparation of several compounds with important pharmaceutical applications.

Synthesis and studies of the antifungal activity of 2-anilino-/2,3-dianilino-/2-phenoxy- and 2,3-diphenoxy-1,4-naphthoquinones

Several synthetic and natural naphthoquinone derivatives have been associated with antifungal activity. Candida albicans is a fungus that is known to exist in the normal human flora, but under certain conditions it can cause mild to fatal infections. Its pathogenicity has been associated with fungus conversion from cellular yeast to filamentous form Y–M. Inhibition of this process by several anilino-, dianilino-, phenoxy-, and diphenoxy-1,4-naphthoquinones was investigated in order to find some correlation between structure, redox properties and biological activity.

Ultrasound-assisted reaction of 1,4-naphthoquinone with anilines through an EDA complex

Naphthoquinone amino derivatives exhibit interesting physicochemical properties and a wide range of biological activities with potential medicinal applications. A clean, fast and simple method for the preparation of phenylamino-1,4-naphthoquinones is presented by the reaction of naphthoquinone (NQ) and anilines under ultrasound irradiation (US). Anilino derivatives were synthesized in good yields and shorter reaction times in comparison with the conventional method. This ultrasound procedure can be applied to the preparation of naphthoquinone derivatives with anilines containing electron-donor substituents (2-OMe, 4-OMe, 4-Me and 4-OEt) or halogen or electron-withdrawing substituents (4-F, 4-Cl, 4-Br, 3-F, 3-Cl, 3-Br, 4-Ac). This procedure was also applied to the reaction of anilines with 2,3-dichloro-1,4-naphthoquinone (DCNQ). A reaction mechanism involving an EDA complex is proposed based on NMR experiments and previous studies about solid/solid reactions.Graphical Abstract

One-pot methodology for conversion of o-halogen nitrobenzenes to benzofuroxans

ABSTRACT Reaction of o-halonitrobenzenes with sodium azide under reflux of DMF/H2O gives benzofuroxans in one step in moderate to good yields. This is a faster methodology compared to the conventional procedure involving the preparation and subsequent pyrolysis of o-nitrophenyl azides. For comparison, the reaction was also performed under phase-transfer catalysis. GRAPHICAL ABSTRACT