Quantification of activated (2,2,6,6-tetramethylpiperIdin-1-yl) oxyl radical

Abstract

Cellulose oxidation is a known chemical pretreatment for nanocellulose production. The use of (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl radical (TEMPO) as a catalyst in oxidation of cellulose is well-known. TEMPO is commercially available as a radical and it needs to be activated by some other chemical or method for it to catalyze cel-lulose oxidation. The cost of TEMPO catalyst is very high and any unnecessary use is a direct loss. Hence the chemistry of activation of TEMPO is of very high importance to understand the process and optimize the process variables and chemicals.

So far there is no easy method to quantify activated TEMPO. This work aims to find a method to determine the quantity of activated TEMPO and apply the method to other TEMPO based chemical compounds and compare the results. Further this work explores the stoichiometric conversion of radical TEMPO to activated TEMPO. The theoretical section of this thesis will describe the catalysis in brief, provide in-formation on chemistry of nitroxyl radicals in general, describe reactions and appli-cations of TEMPO and provide a brief note on TEMPO derivatives.

In the experimental section the three point titration method used for analysis of chlorine compounds was applied here to measure the activated TEMPO. TEMPO solution was activated by chlorine dioxide or hypochlorous acid and titrated imme-diately. ClO2/TEMPO and HOCl/TEMPO ratio was varied to reach the optimum degree of activation in each case. UV-Vis spectrometry was used to verify whether TEMPO was activated completely or not. The effect of chloride ion and 1-propanol on the systems was studied. The method was later applied on TEMPO derivatives to observe the response.

It was found that TEMPO reacts with chlorine dioxide and hypochlorous acid very fast. The titration method estimated approximately 50% conversion of TEMPO to nitrosonium ion. The data from UV-Vis spectroscopy indicates the absence of radical TEMPO after activation. It was found that chloride ion has no effect on the titration results. Although the three point titration method was able to quantify TEMPO par-tially using the conditions shown in this thesis, the results attained show that it could however be possible to refine the method for better estimation.