Synthesis of phthalazine compounds using heterogeneous base catalyst based on silica nanoparticles obtained from rice husk

Abstract

In this study, the nanoparticles of amorphous silica were easily extracted from low-cost rice husk ash. They were functionalized with 3-(chloropropyl) trimethoxysilane by incorporating chloropropyl groups directly through the condensation of nanosilica and 3-chloropropyl trimethoxysilane. The target composite was synthesized by nucleophilic substitution of 1,4-diazabicyclo[2.2.2]octane (DABCO) onto the propyl groups. The effective required extent of this nanocomposite for the preparation of phthalazine-trione and phthalazine-dione derivatives is surprising under reflux conditions via the one-pot three-component condensation reaction of phthalhydrazide, aromatic aldehydes, and diketones. This green catalyst is easily recovered and re-utilized for the next reaction at least four runs without having any considerable influence on the yields. This simple green methodology not only improves the purity of the product, but also provides environmental and economic advantages. Furthermore, ¹H and ¹³C chemical shift values, X-ray spectra, and the structural characteristics of phthalazine-dione compounds have been investigated in detail. The obtained values from DFT calculations including chemical shifts and structural parameters were compared with the corresponding experimental data. The calculated ¹H and ¹³C chemical shifts and X-ray spectra are in good agreement with experimental ones.