(Solid + liquid) phase equilibria and solid-compound formation in (N-methyl-2-pyrrolidinone + phenol, or 3,5-dimethylphenol)

(Solid + liquid) equilibria for the binary systems (N-methyl-2-pyrrolidinone + phenol, or 3,5-dimethylphenol) have been determined using a cryometric dynamic method. Congruently melting compounds form with the formulae: C5H9NO·C6H5OH, or C5H9NO·(C6H5OH)2, and C5H9NO·C8H9OH, or C5H9NO·(C8H9OH)2. Compound formation is attributed to a charge-transfer interaction of N-methyl-2-pyrrolidinone with phenol or 3,5-dimethylphenol, or is attributed to a strong OH⋯O hydrogen bond between the oxygen atom of N-methyl-2-pyrrolidinone and hydroxyl group of phenol. The larger intermolecular interaction is observed for the (N-methyl-2-pyrrolidinone + phenol) binary mixture, where the melting temperature of the 1:1 congruently melting compound is higher. mental solubility results are compared with values calculated by means of the Ott equation using parameters derived from the SLE results. The correlation of the solubility data is obtained with a average root-mean-square deviation in temperature σT = 0.25 K and σT = 0.19 K for the systems with phenol or 3,5-dimethylphenol, respectively.