Theoretical investigation of the chemoselectivity and synchronously pyrazole ring formation mechanism from ethoxymethylenemalononitrile and hydrazine hydrate in the gas and solvent phases: DFT, meta-GGA studies and NBO analysis

Abstract

In this work, structural and kinetic aspects of pyrazole (P) ring formation by the reaction of<br><br>ethoxymethylenemalononitrile (R1) and hydrazine hydrate (R2) were theoretically studied in the gas and<br><br>solvent phases. Two major possible mechanisms were considered. One of them was initiated by<br><br>nucleophilic attack of nitrogen atom of R2 on carbon atom of C]C double bond of R1 (Route 1) and the<br><br>other was started by nucleophilic attack of nitrogen atom of R2 on carbon atom of cyanide group in R1<br><br>(Route 2). In order to investigate the solvent effect on the reaction mechanism, all the possible paths<br><br>were reconsidered in methanol as the solvent. Obtained results showed that the most probable path is<br><br>route 2 in the gas and solvent phases. Theoretical studies showed that the chemoselectivity of the<br><br>nucleophilic attack of nitrogen atom in the gas phase is similar to the solvent. Solvent was able to<br><br>decrease the barrier energy of the rate determining step and enforce the reaction to proceed through<br><br>subroute 5 of route 2.