Sulfonic Acid Functionalized Precipitated Silica as Efficient Solid Acid Catalyst for Acetylation Reactions

Introduction: Precipitated Silica has very high commercial significance in terms of ease of preparation, market volume, cost benefits and a wide range of industrial applications. The surface silanol groups of Precipitated Silica can be modified with reactive organic functional groups to achieve desired properties for specific applications, including catalysis. Objective: The objective of this study is to demonstrate sulfonic acid functionalized Precipitated Silica as a true heterogeneous catalyst in acetylation reaction, where the catalytic activity and desired product selectivity is a magnitude higher than industrial solid acid zeolite catalysts as well as similar catalysts reported in literature. Methods: A novel and cost-effective method for the functionalization of Precipitated Silica with sulfonic acid (-SO3H) is reported, where the silica nanoparticles are first functionalized in situ with a tetrasulfide organosilane, followed by oxidation of the tetrasulfide moiety to -SO3H groups, which are grafted to the surface silanol groups through covalent linkage. Results: CHNS analyses and XPS prove successful functionalization of -SO3H group onto the nano silica surface. The resultant material acts as a solid acid catalyst and shows exceptional activity in the acetylation of benzyl alcohol and >99% selectivity towards the desired product benzyl acetate. The resultant material can also be recycled and reused several times. Conclusion: The following factors make sulfonic acid functionalized Precipitated Silica a new generation of solid acid catalyst; (i) higher atom economy, (ii) recyclability and reusability, and (iii) significant cost benefits with respect to industrial catalysts.