Solvent similarity analysis−from qualitative to quantitative

We put forward a new expression of similarity between solute and solvent in terms of the cohesive energy for unlike molecules, which provides a quantitative measure of the principle that 'like dissolves like'. The investigation results indicate that as Vr (volume ratio) and SHSPR (the Square of Hansen Solubility Parameter Ratio) are far larger than unity (Vr ≫ 1, SHSPR ≫ 1), the similarity degree between solute and solvent is dominate by difference in molecular structure (size and interaction energy); as SHSPR approaches unity (SHSPR → 1), the similarity degree is irrelative with molecular size, and it depends only on its deviation from ideal solution (positive or negative deviation). Its applications in water−solvent miscibility analysis, appropriate solvent selection for polymers and chemical products purification (liquid-liquid extraction and re-crystallization) have been verified with successful results.