%Greenness, a new metric to assess solvents

Abstract

Seven solvents (green and non-green) were used in the nitration and α-halogenation reactions. The parameters "% Greenness" (%G) and “% Price-Affected Greenness” (%PAfG) are proposed for solvent analysis. Partial conversion of benzothiophene to the expected nitro compounds was observed when the reaction was carried out at reflux in dimethylcabonate (60.5%G) or acetic acid (36.8%G). However, in dichloromethane (39.5%G) where there was higher substrate conversion, the reaction was not chemoselective. In the case of cinammic acid, β-nitrostyrene was observed when the nitration reaction was carried out at reflux in dimethylcarbonate or acetonitrile (42.1%G). In ethyl acetate (65.8%G) and dichloromethane, cinnamic acid did not react and, in cyclopentyl methyl ether (31.6%G), by-products of the solvent were observed. Finally, in the halogenation reaction, the best solvent to obtain α-bromopropiophenone was ethyl acetate. All reactions were analysed with different green metrics such as AE, EcoScale, RME, and GWP, among others. For example, the best %GSAI values, in the three reactions studied, were obtained at dimethylcarbonate (45.0, 52.5, and 62.5, respectively). While the best EcoScale values were 50 in acetic acid in the aromatic nitration, 55 in dimethylcarbonate in the alkene nitration, and 68 in ethyl acetate in the halogenation reaction.