A novel synthesis of branched high-molecular-weight (C⁺₄₀) long-chain alkanes

Many biological and geochemical questions remain concerning the structures, functions, and properties of naturally occurring high-molecular-weight (C₄₀⁺) alkanes with various mid-chain alkylation patterns. Above C40, these alkanes are exceedingly difficult to separate and purify, and syntheses can be blocked by the low solubility of intermediates. To overcome these problems, a facile three-step synthesis employing the alkylation of 1,3-dithiane with a suitable a, v-dibromoalkane was developed. Bisalkylation of the bis(dithianyl)alkane intermediate with the appropriate 1-bromoalkane and subsequent desulfurization with Raney nickel furnished the desired long-chain alkane. Long-chain alkanes modified at mid-chain and/or symmetrically near the chain termini (or unmodified, i.e., long-chain α, ω-paraffins) are accessible by the selection of appropriate bromoalkanes. Nine mid-chain methylated (C₃₈H₇₈ to C₅₃H₁₀₈), one symmetrical terminal-chain dimethylated (C₄₀H₈₂), and fourlinear (C₄₄H₉₀ to C₅₈H₁₁₈) long-chain alkanes were synthesized by using this approach. High-temperature gas chromatography (HTGC) was found to have important advantages for evaluating the purity of the synthetic high-molecular-weight alkanes.