In an attempt to develop predictive tools for the determination of new ionic liquid solvents, QSPR models for the melting points of 126 structurally diverse pyridinium bromides in the temperature range 30-200 degrees C were developed with the CODESSA program. Six- and two-descriptor equations with squared correlation coefficients (R(2)) of 0.788 and 0.713, respectively, are reported for the melting temperatures. The models illustrate the importance of information content indices, total entropy, and the average nucleophilic reactivity index for an N atom.
The importance of melting points in characterization, in the estimation of other physical properties
and toxicity, and in practical applications such as ionic liquids is summarized, as are difficulties in the systematic
treatment of melting points in terms of QSPR. Classical correlations of melting points of congeneric and diverse
sets are discussed together with group contribution methods, combined approaches, and computer simulations.
The melting points of several imidazolium-based ionic liquids or ionic liquid analogues were correlated using the CODESSA program in order to develop predictive tools for determination of suitable ionic liquid salts. The data set consisted of melting point data (degrees C) for 104 substituted imidazolium bromides divided on the basis of the N-substituents into three subsets: A-57 compounds, B-29 compounds, and C-18 compounds. The 45 benzimidazolium bromides form set D. Five-parameter correlations were obtained for (i) set A with R2 = 0.7442, (ii) set B with R2 = 0.7517, and (iii) set D with R2 = 0.6899, while set C was correlated with a three parameter equation with R(2) = 0.9432. These descriptors for predicting the melting points of the imidazolium and benzimidazolium bromides were based on the size and electrostatic interactions in the cations.
A quantitative structure property relationship study of the flash point of a diverse set of 271 compounds provided a general three-parameter QSPR model (R(2) = 0.9020, R(2)(cv) = 0.8985, s = 16.1). Use of the experimental boiling point as a descriptor gives a three-descriptor equation with R(2) = 0.9529. Use of the boiling point predicted by a four-parameter reported relationship gives a three-parameter flash point equation with a R(2) value of 0.9247.
3,4-Dihydro-2H-1,3-benzothiazines 4, 3,4-dihydro-2H-1,3-benzoxazines 9, and 2,3,4,5-tetrahydro-1,3-benzothiazepines 6 were synthesized by directed ortho-lithiation of thiophenols and phenols and by side-chain lithiation of substituted thiophenols, respectively, in one-pot by reacting with N,N-bis[(benzotriazol-1-yl)methyl]amines 3 as 1,3-biselectrophile synthons.
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