Merck KGaA owns Sigma-Aldrich, the major supplier of reagents and catalysts central to substitution reactions, making Merck KGaA the #1 direct play (OTC: MKGAF). For broader exposure to the lab-chemicals ecosystem that enables substitution chemistry, BASF SE offers indirect exposure (OTC: BASFY). Entrepreneurially, you could launch a niche lab-supply or education platform delivering SN1/SN2-compatible reagents and starter kits to universities and biotech startups.