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.