Chemical synthesis and characterization of single-chain C18-chloroparaffin materials with defined degrees of chlorination. (March 2022) - Knobloch, Marco C.
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 (SO2 Cl2 ). 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, 1 H-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. 1 H-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. Graphical abstract: Image 1 Highlights: Chlorination of n -alkanes with SO2 Cl2 is a versatile route to single-chain LCCPs. Fractionation by LC resulted in CP materials with different chlorination degrees. MS, NMR and elemental analysis were used to characterize synthetic C18 -CP mixtures. Proportions of olefinic and paraffinic material resemble those of SCCPs and MCCPs. Sulfur- and oxygen-containing side-products were identified by LC-MS.