The activity and stability of tertiary amine catalysts in the presence of hypochlorous acid

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Journal Title
Journal ISSN
Volume Title
Kemian tekniikan korkeakoulu | Master's thesis
Date
2018-08-28
Department
Major/Subject
Biomass Refining
Mcode
CHEM3021
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Language
en
Pages
63 + 13
Series
Abstract
Hypochlorous acid is an electrophilic oxidizing agent capable of reacting with a range of unsaturated organic substrates. Previously, these reactions have been shown to be catalysed by the use of a tertiary amine, and Hcat hardwood pulp bleaching stages using the tertiary amine DABCO, as well as its derivative CM-DABCO, have proved efficient. Within this work, a range of DABCO-derivative structures were synthesised, and their catalytic abilities and stabilities were tested via the use of stopped-flow UV-Vis spectroscopy. DABCO-derivatives produced in this work all involved mono-N-substitution, and generally high yields could be achieved in simple synthetic routes. Derivative structures tested included allyl (AL), carboxymethyl (CM), carboethoxymethyl (CEM), carbamoylmethyl (AA) and 2-hydroxyethyl (EA) groups. The pKa of the tertiary amine group within these were measured, and found to each be between 3.0 and 3.4, close to the second pKa of DABCO itself (2.97). Both pH and substrate structure were found to have a significant impact on the catalytic ability of all the tested structures. Due to the chlorinating action of Cl2 at pH 3, and the large difference between pH and DABCO-derivative catalyst pKa at pH 7, generally low catalytic factors were found at these pH values. At pH 5, higher catalytic factors could be found, with a catalyst pKa closer to 5 producing an increased catalytic ability. The substrate structure affects the rates of catalysis but not the order of activities between the different catalysts. CM-DABCO was the most active derivative for all substrates at pH 5, and it was concluded that further increases to the catalyst pKa could further improve the results obtained. Unlike DABCO, all the synthesised derivatives were shown to be close to fully stable for up to 10 seconds of pre-incubation with hypochlorous acid. Stability is concluded then to not be a concern in the selection and design of an optimal DABCO-derivative catalyst structure.
Description
Supervisor
Vuorinen, Tapani
Thesis advisor
Perrin, Jordan
Keywords
tertiary amine, catalysis, hypochlorous acid, DABCO, stopped-flow, UV-Vis spectroscopy
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Citation