Electroacoustic activation of natural quartz nanoparticles for the Guareschi-Thorpe synthesis of novel pyridine derivatives.

Natural quartz, the most abundant piezoelectric mineral in the Earth's crust, offers a promising platform for catalysis owing to its intrinsic piezoelectric response, chemical stability, and natural abundance. In this study, natural quartz nanoparticles (NQNs) were prepared from quartz type of (rock crystal) and evaluated as a recyclable catalyst with a proposed piezocatalytic contribution for the Guareschi-Thorpe synthesis of pyridine derivatives. Mechanical stress was applied via a newly designed granite resonance chamber that amplified low-frequency acoustic waves (400-500 Hz, function generator) to a sound intensity of 115-117 dB, which is proposed to induce piezoelectric polarization in the NQNs and generate transient surface charges that promote catalytic activation without external heating. Under these electroacoustic conditions, hydroxynicotinonitrile and aminonicotinonitrile derivatives were obtained in excellent isolated yields (92-99%) within markedly short reaction times (10-25 min) at ambient temperature. Comparative experiments performed under three conditions (i) NQNs combined with acoustic stimulation, (ii) acoustic stimulation alone, and (iii) conventional stirring without either NQNs or acoustic activation showed that NQNs markedly accelerate the acoustically driven reaction: acoustic irradiation alone required four- to twelve-fold longer reaction times with lower yields, while conventional stirring afforded no detectable product even after prolonged standing. Compared with a previously reported thermal protocol requiring 80 °C for up to 300 min, the present method reduced reaction time by more than 90% while maintaining comparable or superior yields. The catalyst retained its activity over six consecutive cycles with only a marginal yield decrease (98% to 95%), confirming its robustness and recyclability. These findings identify natural quartz nanoparticles as an effective, recyclable catalyst for acoustically driven multicomponent heterocyclic synthesis, with a lower estimated energy input than the thermal benchmark; the piezoelectric contribution is proposed and remains to be proven mechanistically.