In-situ Nitrous Acid Generation over Silica Imidazole Catalyst for Dyes Production

Abstract

The objective of this research is to prepare a new type of heterogeneous catalyst and to study its usage for in-situ nitrous acid generation to form a diazonium salt. The high pure silica (> 95%) was produced by burning the clean rice husk at 800 °C. After that, the silica was transferred to sodium silicate using 1.0 M of NaOH, followed by immobilizing with 3-(chloropropyl)triethoxysilane in a simple one-pot synthesis. Finally, the material was refluxed with (0.015 mol) of p-xylyl di-imidazolium chloride. The silicon solid-state nuclear magnetic resonance shows the Q4, Q3, T3, and T2 chemical shifts at expected position. Carbon solid-state nuclear magnetic resonance spectrum shows different peaks at different chemical shifts related to the carbon structures of the organic moieties. The catalyst is stable up to 277 ºC according to the thermal analysis. TEM images show smooth and porous regularly shaped particles with an estimation size of ca. 5 nm. Coupling reaction of aromatic compounds was carried out with a diazonium salt of aniline to yield a monoazo dye. All dyes were showed matching the elemental analysis with the theoretical calculation. Besides this, the spectrum of FT-IR and UV-Visible were recorded. The catalyst was stable, easy separation from the reaction mixture, and reusable by a simple experimental procedure. The catalyst could be used successfully for the nitrous acid generation.

Keywords

• surface modification
• rice husk ash
• diazotization
• imidazole
• azo dyes
• coupling reaction