Synthesis, structure verification and gas chromatographic determination of chlorinated catechols and guaiacols occurring in speat bleach liquors of kraft pulp mills

Abstract

Chlorination stage (C-stage) and extraction stage (Estage) spent bleach liquors (SBL) from a pine kraft pulp mill and the product from the chlorination of guaiacol (2-methoxyphenol) in aqueous solution were investigated for their content of chlorinated catechols (1,2-benzenediols) and guaiacols (2-methoxyphenols). The compounds were analysed by quartz capillary gas chromatography (GC) and GC-mass spectrometry (GC-MS) of their ethyl or acetyl derivatives. Convenient methods for the synthesis in pure form of model compounds were developed. The most useful methods for the structure verification (NMR and mass spectrometry) are indicated and the GC retention data are summarized. GC and GC-MS were used as main techniques for the identification and determination of the different structural isomers in SBLs. A brief summary is given of the most probable reactions of residual lignin producing chlorinated isomers. Finally note is made of the potential application of the results to the further synthesis of model compounds and to studies of toxicity, degradation, metabolism and off-flavour properties of chlorinated phenolic compounds. Eight chlorinated catechols were identified in a sample prepared by chlorination of an aqueous solution of guaiacol with chlorine. Only four of these compounds (3,4-dichlorocatechol, 3,4,5-trichlorocatechol, 3,4,6-trichlorocatechol and tetrachlorocatechol) were observed in C-stage SBL. Large amounts (totally ca. 4 ppm) of chlorinated guaiacols were found to be present in E-stage SBL from of a pine kraft pulp mill. 3,4,5-Trichloroguaiacol occurred in the highest concentration (ca. 1.6 ppm), with tetrachloroguaiacol, 4,5-dichloroguaiacol and 4,5,6-trichloroguaiacol as other major components Smaller amounts of 4-chloro-, 5-chloro-, 3,4-dichloro-, 4,6-dichloro- and 3,4,6-trichloroguaiacols were detected.