SIMPOL.1: a simple group contribution method for predicting vapor pressures and enthalpies of vaporization of multifunctional organic compounds

The SIMPOL.1 group contribution method is developed for predicting the liquid vapor pressure po L (atm) and enthalpy of vaporization 1Hvap (kJ mol−1) of organic compounds as functions of temperature (T ). For each compound i, the method assumes log10 p o L,i(T )= ∑ k νk,i bk(T ) where νk,i is the number of groups of type k, and bk(T ) is the contribution to log10 p o L,i(T ) by each group of type k. A zeroeth group is included that uses b0(T ) with ν0,i=1 for all i. A total of 30 structural groups are considered: molecular carbon, alkyl hydroxyl, aromatic hydroxyl, alkyl ether, alkyl ring ether, aromatic ether, aldehyde, ketone, carboxylic acid, ester, nitrate, nitro, alkyl amine (primary, secondary, and tertiary), aromatic amine, amide (primary, secondary, and tertiary), peroxide, hydroperoxide, peroxy acid, C=C, carbonylperoxynitrate, nitro-phenol, nitro-ester, aromatic rings, non-aromatic rings, C=C–C=O in a nonaromatic ring, and carbon on the acid-side of an amide. The T dependence in each of the bk(T ) is assumed to follow b(T )=B1/T+B2+B3T+B4 ln T . Values of the B coefficients are fit using an initial basis set of 272 compounds for which experimentally based functions po L,i=fi(T ) are available. The range of vapor pressure considered spans fourteen orders of magnitude. The ability of the initially fitted B coefficients to predict po L values is examined using a test set of 184 compounds and a T range that is as wide as 273.15 to 393.15 K for some compounds. σFIT is defined as the average over all points of the absolute value of the difference between Correspondence to: J. F Pankow ([email protected]) experimental and predicted values of log10 p o L,i(T ). After consideration of σFIT for the test set, the initial basis set and test set compounds are combined, and the B coefficients reoptimized. For all compounds and temperatures, σFIT=0.34: on average, po L,i(T ) values are predicted to within a factor of 2. Because d(log10 p o L,i(T ))/d(1/T ) is related to the enthalpy of vaporization 1Hvap,i , the fitted B provide predictions of 1Hvap,i based on structure.