Measurement of the hydrogen bond acceptance of ionic liquids and green solvents by the 19F solvatomagnetic comparison method

Abstract

The ¹⁹F solvatomagnetic comparison method yields a more reliable scale (β₁) of solvent hydrogen-bond acceptance than the solvatochromic comparison method. For [C₄mim] based ionic liquids, the β₁ order MeCO₂⁻ (1.30) > Cl⁻ (0.79) > NO₃⁻ (0.67) > SCN⁻ (0.64) > I⁻ (0.44) > BF₄⁻ (0.36) > PF₆⁻ (0.27) is significantly correlated to the intrinsic hydrogen-bonding-, and even proton-, basicities of anions. For solvents of green interest, the β₁ value of water is now settled down to 0.37, and the newly determined value of limonene is 0.14, while those of α-pinene (0.14), glycerol (0.36), Cyrene™ (0.40), 2-methyltetrahydrofuran (0.66), ethyl lactate (0.58), and γ-valerolactone (0.52) are found chemically more relevant than the solvatochromic ones.