Fluid Phase Equilibria 340 (2013) 52–62 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria j o ur nal homep age: www.elsevier.com/locate/fluid An improved simple method for prediction of entropy of fusion of energetic compounds Mohammad Hossein Keshavarz ∗ , Sajjad Zakinejad, Karim Esmailpour Department of Chemistry, Malek-ashtar University of Technology, P.O. Box 83145/115, Shahin-shahr, Islamic Republic of Iran a r t i c l e i n f o Article history: Received 26 June 2012 Received in revised form 9 November 2012 Accepted 10 December 2012 Available online 20 December 2012 Keywords: Entropy of fusion Energetic compound Correlation Safety a b s t r a c t A new general method has been introduced for prediction of entropy of fusion of important classes of ener- getic compounds including polynitro arene, acyclic and cyclic nitramine, nitrate ester and nitroaliphatic compounds. It extends earlier work, which was restricted to nitroaromatic compounds, to estimate entropy of fusions of any compound containing at least one of the groups Ar NO 2 , C NO 2 , C ONO 2 or N NO 2 through additive and correcting non-additive functions. The number of nitrogen and oxygen atoms in an energetic compound was used as additive function. For 92 compounds (corresponding to 167 measured values) belong to different types of energetic materials, the root-mean square (rms) deviation of the additive part is 13.5 J/(K mol). The reliability of the new model can be increased by considering one correcting non-additive function for which the value of rms deviation is 10.2 J/(K mol). The predicted outcomes of the new method, by using only additive part or both additive and non-additive functions, give more reliable results as compared to one of the best available methods. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Development of new energetic compounds with suitable ther- mochemical properties, performance and sensitivity is a problem of the utmost importance to chemists and chemical industries. Since synthesis and measuring of properties of energetic compounds are dangerous, expensive and time consuming or sometimes even impossible, reliable predictive methods can calculate desired prop- erties of energetic materials. Moreover, the calculated properties can help us in decision to whether it is worth the effort to attempt a new and complex synthesis [1]. Due to importance of estimating thermochemical properties related to phase transition of various classes of energetic compounds, some new methods have been recently developed to estimate these properties, e.g. enthalpy of fusion [2–7]. The entropy of fusion ( fus S), as an important property for pre- diction of melting point and solubility of organic compounds [8], is related to the enthalpy of fusion ( fus H) and fusion point tempera- ture (T fus ) because the Gibbs free energy of transition is zero at the phase transition temperature:  fus H =  fus S × T fus (1) ∗ Corresponding author. Tel.: +98 0312 522 5071; fax: +98 0312 522 5068. E-mail addresses: keshavarz7@gmail.com, mhkeshavarz@mut-es.ac.ir (M.H. Keshavarz). Some reliable simple methods have been recently developed to predict T fus for different classes of energetic compounds [9–13]. Dif- ferent approaches can be used for estimating  fus S at the melting point of some classes of organic compounds [1,14–20]. For aromatic compounds with little flexibility, the value of  fus S on the basis of Walden’s rule is constant with a value of 56.5 J/(K mol) [21]. Dan- nenfelser et al. [22] stated that the effect of molecular rotational symmetry () can be used with Walden’s rule as:  fus S = 56.5 - R ln  (2) Dannenfelser and Yalkowsky [20] have modified Eq. (2) to include the flexibility number (˚) as:  fus S = 50 - R ln  + R ln ˚ (3) For predicting  fus S of nitroaromatic compounds, a suitable cor- relation on the basis of elemental composition and non-additive function has been used [4]. For 61 nitroaromatics, it was shown [4] that the reliability of this method is higher than the method of Jain and Yalkowsky [14,15], which is based on Eq. (3). This method has been restricted to nitroaromatics because it gives large deviation for the some classes of energetic compounds. Evan and Yalkowsky [23] have reviewed further works of estimation of ˚ and improv- ing the reliability of the method of Jain and Yalkowsky [14,15] for nitroaromatics by introducing the molecular eccentricity (ε):  fus S = 50 - R ln  + R ln ˚ + R ln ε (4) The purpose of this work is to introduce a general new method for predicting entropy of fusion of various types of energetic 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2012.12.004