(109b) Solid Acid Catalyzed Acetalization of Glycerol Derived Ether-Ones

Continued US federal incentives for biodiesel production and consumption provide a stable excess of inexpensive glycerol. Published works have previously reported both glycerol etherification with primary alcohols over solid acid catalysts and production of symmetric glycerol-derived diether alcohols (e.g., 1,3-dimethoxy-propan-2-ol) through epichlorohydrin ring opening and etherification at high pH. Previous work in our group has established that these glycerol-derived secondary alcohols can be oxidized to symmetric glycerol-derived diether ketones (e.g., 1,3-dimethoxy-propan-2-one) via oxidative dehydrogenation with O₂ over platinum catalysts at ~333 K and ambient pressure. From these ketones we can perform acetalizations with bioderived C₃ and C₄ polyols (i.e., glycerol, 1,2-propanediol, 1,4-butanediol) to produce acetals, which are useful as green solvents and fuel additives. Metallosilicate catalysts (M = Zr, Hf, Ga) were synthesized via simple one-pot method such that metal atoms were incorporated into a silicon xerogel matrix (M-xerogels), resulting in formation of dispersed Lewis acid sites. These materials were characterized by N₂ physisorption, inductively coupled plasma optical emission spectroscopy, pyridine chemisorption followed by transmission FTIR spectroscopy, X-ray absorption spectroscopy, and ex situ diffuse reflectance UV-Visible spectroscopy. Acetalization of 1,3-dimethoxy-propan-2-one—and similar glycerol-derived diether-ketones—with various diols was observed over all M-xerogels (tert-butanol solvent, T=313-343 K, autogenous pressure). The formation of 2,2-bis(methoxymethyl)-4-methyl-1,3-dioxolane and similar dioxolanes, reported here, are previously unreported. Per-Lewis-acid site-time yields (STYs) were highest for Ga-xerogel (~1.8*10^-2 s^-1) and lowest for Hf-xerogel (~4.7*10^-5 s^-1). Product yields, selectivities, apparent activation energies, and apparent reaction orders will be discussed as a function of the identity of the Lewis acid center. Additionally, the impact of solvent identity, equilibrium limitations (both calculated by DFT and measured experimentally), and water concentration on STY and catalyst reusability will be reported. These findings provide a roadmap towards formation of functionalized (and tunable) glycerol-derived acetals over simple amorphous solid Lewis acid catalysts.