Alkenyl succinic anhydride (ASA) is one of the most prominent paper sizing agents worldwide. Commercial products start from isomerized C16-18 olefins with certain distribution of the double bond along the alkyl chain. This distribution is then found again in the product ASA which renders mechanistic studies on ASA binding to the cellulose surface difficult. For studies on ASA reactivity, olefins with defined double bond location (2-, 4-, 6-octadecene and 6-icosene) were synthesized according to Wittig protocols, and further reacted with 13C-labeled maleic anhydride to give ASA model compounds with defined double bond location and 13C-labeled carbonyl group. The olefinic products of the Wittig synthesis, rich in cis-isomers, afforded exclusively trans-configured compounds upon the enereaction with maleic anhydride. The reactions afforded four products, two regioisomeric compounds with different position of the double bond, each of which as threo- and erythro-isomer in different ratios. The products were comprehensively analytically characterized including a full NMR resonance assignment in the 1H and 13C domain. The model compounds are now used in combination with gel and solid-state NMR for studies on ASA reactivity towards cellulosic surfaces with a focus on the questions whether - and to what extent - covalent binding of ASA to cellulose can occur under conditions relevant to paper production and paper sizing.
Keywords: Alkenyl succinic anhydride (ASA), attenuated total reflection infrared (ATR-IR) spectroscopy, ene reaction, isotopic labeling, nuclear magnetic resonance (NMR) spectroscopy, paper sizing, Wittig reaction.