Daniel S. Rampon

Novel selenoesters fluorescent liquid crystalline exhibiting a rich phase polymorphism

A simple and efficient procedure for the synthesis of a new class of selenoesters 4a and 4b was developed. Polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction showed that the selenoester 4a with a shorter alkyl chain displayed a wide nematic range (ΔT = 110.7 °C), while 4b with a longer alkyl chain possesses a rich phase polymorphism: Cr → SmI → SmC → N → I mesophase sequence during heating cycle and I → N → SmC → SmI → SmX → Cr transition on cooling. For 4b, a large temperature range (135.7 °C) from crystal to isotropic phase can be observed. In addition, UV-Vis, steady-state fluorescence emission and excitation spectra in solution were also applied in order to characterize their photophysical behaviour. Compounds 4a and 4b are fluorescent in the blue region and present a Stokes shift at around 80 nm and 39 nm in dichloromethane and dioxane, respectively.

Selenides and diselenides containing oxadiazoles: a new class of functionalised materials

A simple and efficient procedure for the synthesis of a new class of organoselenium liquid crystal compounds was developed. The coupling of aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent. This is the first report of the synthesis and characterisation of liquid crystal-based diselenides. Their mesophases were characterised by polarising optical microscopy and differential scanning calorimetry. Compounds 1, 2 and 4b exhibited the smectic A phase. In addition, these compounds showed weak blue fluorescence in solution (λmax. em. 350–405 nm) and a Stokes shift of around 90 nm.

Palladium-catalyzed direct arylation of selenophene.

An efficient and convenient method was developed for the regioselective formation of 2-aryl- or 2,5-diarylselenophenes via a palladium-catalyzed direct arylation. This protocol is suitable for a wide range of aryl halides containing different functional groups. The 2-arylated substrates can undergo an additional regioselective direct arylation event furnishing symmetrical or unsymmetrical 2,5-diaryl selenophenes in good yield. Competition experiments and the role of the acid additive are in agreement with a concerted metalation deprotonation (CMD) pathway.

Production of Furan Compounds from Sugarcane Bagasse Using a Catalytic System Containing ZnCl2/HCl or AlCl3/HCl in a Biphasic System

In this work, two catalytic systems combining Lewis and Brønsted acids (ZnCl2/HCl and AlCl3/HCl) were applied in a tetrahydrofuran (THF)/NaClaq biphasic system to produce furan compounds from plant polysaccharides. The following cellulosic matrices were applied for this purpose: α-cellulose, microcrystalline cellulose and both native and steam-exploded sugarcane bagasse. The AlCl3/HCl catalytic system afforded the best yields for α-cellulose conversion to furan compounds (hydrolysis followed by dehydration). The highest yields of 5-(hydroxymethyl)-furfural (HMF) and furfural were 44.0 and 92.2% for AlCl3/HCl and 36.5 and 81.4% for ZnCl2/HCl, respectively. Cellulosic materials with lower crystallinity indexes afforded the best performance in hydrolysis followed by dehydration, giving relatively high yields of HMF and furfural. The HMF yields were similar for both native and steam-exploded sugarcane bagasse and the presence of lignin had a negative effect on HMF production. The highest furfural yield from native sugarcane bagasse was 60.6% with AlCl3/HCl catalytic system.