Rate-limiting steps in bromide-free TEMPO-mediated oxidation of cellulose-Quantification of the N-Oxoammonium cation by iodometric titration and UV-vis spectroscopy

Timo Pääkkönen*, Carlo Bertinetto, Raili Pönni, Gopi Krishna Tummala, Markus Nuopponen, Tapani Vuorinen

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)
286 Downloads (Pure)

Abstract

A iodometric titration method was introduced to study the conversion of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) to the corresponding N-oxoammonium cation (TEMPO+) by hypochlorite in the absence and presence of bromide ion. The validity of the titration was verified with UV-vis spectroscopy combined with a multivariate curve resolution (MCR) algorithm to calculate the concentrations and spectral signatures of the pure components (i.e., TEMPO, Cl(+1) and TEMPO+). The formation of the oxoammonium cation was successfully followed during the activation of TEMPO by HOCl and HOBr. It was found that HOBr is a more effective activator for TEMPO than HOCl is. Moreover, the importance of a separate activation step for TEMPO with bromide-free TEMPO oxidations could be identified with this titration method. The content of TEMPO+ was also monitored during the TEMPO-mediated oxidation of a cellulosic pulp by hypochlorite in the absence and presence of bromide. It was found that the oxidation of the alcoholic groups by TEMPO+ was generally the rate-determining step and much slower than the regeneration of TEMPO+ through oxidation of the hydroxylamine by HOCl and HOBr. However, at high pH the latter reaction became rate-limiting.

Original languageEnglish
Pages (from-to)532-538
Number of pages7
JournalAPPLIED CATALYSIS A-GENERAL
Volume505
Issue numberSeptember 25
DOIs
Publication statusPublished - 2015
MoE publication typeA1 Journal article-refereed

Keywords

  • Birch pulp
  • Iodometric titration
  • Multivariate curve resolution
  • Oxoammonium cation
  • TEMPO-mediated oxidation
  • UV-vis spectrometry

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