Characterization of single chain length chlorinated paraffin mixtures with nuclear magnetic resonance spectroscopy (NMR)

Abstract

Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n-alkanes of different chain length. Despite their environmental relevance, quantification is still a challenge. Moreover, the individual structures of the molecules in technical CP mixtures are largely unknown. Here, we synthesized 21 and studied 29 single chain length CP mixtures ranging from C10- to C17-CPs with different chlorine contents between 41.8% and 62.6% Cl and analyzed them by means of nuclear magnetic resonance spectroscopy (NMR). Discrete ranges of chemical shifts were observed in one-dimensional 1H and 13C NMR spectra. Two dimensional heteronuclear single quantum coherence spectroscopy (HSQC) enabled to assign nine substructures. These measurements also verified the presence of [-CCl2-] groups and chlorine atoms on terminal carbons in highly chlorinated (>59% Cl) mixtures. 1H NMR spectra of different chain length and the same degree of chlorination looked virtually the same. However, with increasing degree of chlorination the observed patterns in the spectra were slightly shifted downfield. Based on these findings, a calculation mode was developed to estimate the chlorine content (%) of the single chain length CP mixtures. The results agreed well (<0.9% mean deviation) with parallel measurements by elemental analysis.