Browsing by Author "Millan, Daniela "
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- ItemA ternary eutectic solvent for cellulose nanocrystal production: exploring the recyclability and pre-pilot scale-up(2023) Mariño, Mayra A. ; Paredes Gutierrez, Maria Gabriela; Martinez Ahumada, Natalia del Pilar; Millan, Daniela ; Tapia, Ricardo A. ; Ruiz, Domingo ; Isaacs Casanova, Mauricio Alejandro; Pavez Guerrero, Paulina IsabelDeep eutectic solvents (DES) formed using choline chloride (ChCl), p-toluenesulfonic acid (pTSA) of stoichiometry ChCl: pTSA (1:1) and (1:2), and its ternary eutectic mixtures with phosphoric acid (PA) 85% as an additive (ChCl: pTSA: PA) were evaluated for cellulose nanocrystal (CNC) isolation. Initially, the hydrolytic efficiency to produce CNC of each DES was compared before and after adding phosphoric acid by Hammett acidity parameters and the Gutmann acceptor number. Moreover, different DES molar ratios and reaction time were studied at 80°C for CNC optimization. The nanomaterial characteristics were analyzed by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The ternary eutectic mixture ChCl: pTSA: PA molar ratio (1:1:1.35) was chosen as a suitable recyclable ternary system at the laboratory scale. A CNC yield of about 80% was obtained from the hydrolysis of commercial cellulose in five cycles of recovery, but it dropped to 35% in pre-pilot scaling. However, no variation in the average size of the resulting CNC was observed (132 ± 50 nm x 23 ± 4 nm), which presented high thermal stability (Tmax 362°C) and high crystallinity of about 80% after 3 h of reaction time.
- ItemSolvatochromism and electrophilicity(ELSEVIER SCIENCE BV, 2011) Caroli Rezende, Marcos; Dominguez, Moises; Aracena, Andres; Millan, DanielaSolvatochromic dyes that exhibit a negative or a positive behaviour may be distinguished and their solvatochromism predicted with the aid of DFT-based indices, such as their electrophilicity omega, hardness eta and by the Fukui electrophilic functions f(G)(+) of the donor and acceptor moieties of the molecule, calculated in the gas-phase and in solvents treated as polarised continua. The protocol was successfully applied to 10 examples of phenolate betaines from the literature, five of them exhibiting a negative and five a positive solvatochromism. (C) 2011 Elsevier B.V. All rights reserved.
- ItemTheoretical Substituent Electrophilicities(SOC BRASILEIRA QUIMICA, 2011) Caroli Rezende, Marcos; Millan, DanielaA Hammett-like equation, relating theoretical global and substituent electrophilicities, is derived for substituted ethylenes and benzoic acids, allowing the calculation of electrophilic substituent constants a.. Correlations are given between the theoretical a, constants and kinetic or thermodynamic parameters of various chemical processes from the literature. Though electrophilic substituent constants are formally similar to the Hammett constants, they are derived from entirely different theoretical postulates. The similarities and differences between the two sets of constants are discussed and rationalized in terms of the definition of the electrophilic power of a chemical species.