Chemical synthesis and characterization of single-chain C18-chloroparaffin materials with defined degrees of chlorination

Abstract

Technical chlorinated paraffins (CPs) are produced via radical chlorination of n-alkane feedstocks with different carbon chain-lengths (∼C₁₀-C₃₀). Short-chain CPs (SCCPs, C₁₀-C₁₃) are classified as persistent organic pollutants (POPs) under the Stockholm Convention. This regulation has induced a shift to use longer-chain CPs as substitutes. Consequently, medium-chain (MCCPs, C₁₄-C₁₇) and long-chain (LCCPs, C_>17) CPs have become dominant homologues in recent environmental samples. However, no suitable LCCP-standard materials are available. Herein, we report on the chemical synthesis of single-chain C₁₈-CP-materials, starting with a pure n-alkane and sulfuryl chloride (SO₂Cl₂). Fractionation of the crude product by normal-phase liquid-chromatography and pooling of suitable fractions yielded in four C₁₈-CP-materials with different chlorination degrees (m_Cl,EA = 39-52%). In addition, polar side-products, tentatively identified as sulfite-, sulfate- and bis-sulfate-diesters, were separated from CPs. The new single-chain materials were characterized by LC-MS, ¹H-NMR and EA. LC-MS provided Relative retention times for different C₁₈-CP homologues and side-products. Mathematical deconvolution of full-scan mass spectra revealed the presence of chloroparaffins (57-93%) and chloroolefins (COs, 7-26%) in the four single-chain C₁₈-CP-materials. Homologue distributions and chlorination degrees were deduced for CPs and COs. ¹H-NMR revealed chemical shift ranges of mono-chlorinated (δ = 3.2-5.3 ppm) and non-chlorinated (δ = 1.0-3.2 ppm) hydrocarbon moieties. The synthesized C₁₈-single-chain standard materials and respective spectroscopic data are useful to identify and quantify LCCPs in various materials and environmental samples. CP- and CO-distributions resemble the ones of existing SCCP and MCCP reference materials and technical mixtures. Furthermore, these materials now allow specific studies on the environmental fate and the transformation of long-chain chloroparaffins and chloroolefins.

Keywords: Chlorinated olefins (COs); Chlorinated paraffins (CPs); Long-chain chlorinated paraffins (LCCPs); Single-chain CPs; Standard materials.