Study of kinetics of TEMPO-mediated oxidation of nanocellulose by ESR

BUFFA, JUAN MANUEL; GRELA, MARÍA ALEJANDRA; ARANGUREN, MIRTA; MUCCI, VERÓNICA

Zurich

Workshop; COST Action FP1105. Final Workshop.; 2015

COST Action FP1105

TEMPO-mediated oxidation of cellulose nanocrystals (CNC) has been widely used as  a selective oxidation of the C6 carbon to obtain carboxyl groups.  By this method, high degrees of oxidation (DO) can be obtained with only a catalytic amount of TEMPO and other inexpensive reagents, such as NaClO, NaBr and NaOH. The dependence of the DO with the amount of NaClO has been already reported (Habibi, Chanzy, & Vignon, 2006) as well as some theoretical approaches on the kinetic of the reaction (Bailey, Bobbitt, & Wiberg, 2007; De Nooy, Besemer, & Van Bekkum, 1995), but with no quantitative experimental information.In this work, we measured the evolution of TEMPO concentration through the reaction by the use of electron spin resonance (ESR) spectroscopy. The correlation between this concentration, NaClO concentration (determined by iodometry) and DO (by conductimetric titration) is presented. By the use of reported procedure with optimized amounts of NaClO, we were able to obtain CNC with a DO of 26%. Additionally, we introduced a new methodology for the measurement and study of the kinetics of the reaction. Using a pH 10 buffer, we were able to eliminate the need for adding NaOH aliquots, maintaining the pH approximately constant, and making possible to determine the TEMPO concentration continuously. All three determined quantities (TEMPO and NaClO concentration and DO) were fitted using exponential functions that used the same phenomenological constant.