A simple method for prediction of density of ionic liquids through their molecular structure Mohammad Hossein Keshavarz ⁎, Hamid Reza Pouretedal, Ehsan Saberi Department of Chemistry, Malek-ashtar University of Technology, Shahin-shahr, P.O. Box 83145/115, Islamic Republic of Iran abstract article info Article history: Received 16 September 2015 Received in revised form 11 January 2016 Accepted 30 January 2016 Available online xxxx This paper introduces a reliable simple method to estimate density of a wide range of different types of ionic liq- uids. This method is based on two novel correlations in which the size, structure and type of cations and anions are essential parameters. The first correlation is derived from elemental composition, which is modified on the basis of correcting functions in the second one in order to consider inter ionic interactions and obtain more reli- able results. For 249 different types of ionic liquids, where their calculated values with one of the best available methods were available, these correlations have been derived. The results of two simple correlations give good predictions as compared to the outputs of complex method. The new models have also been tested with exper- imental data of 235 new ionic liquids at atmospheric pressure and ambient temperatures that provide good predictions. © 2016 Elsevier B.V. All rights reserved. Keywords: Ionic liquid Density Correlation Structural parameter 1. Introduction Ionic liquids usually refer to room-temperature molten salts, which have been the subject of increasing attention because of their desirable physicochemical properties such as high thermal stability, large liquid range, high ionic conductivity, high solvating capacity, negligible vapor pressure, and non-flammability that make them ideal solvents for green chemistry [1,2]. Due to these appealing properties, ionic liq- uids are gaining wide recognition as potential replacements for conven- tional solvents in chemical processes [3–7]. Since they comprise at least one large and asymmetric organic cation or anion, their properties can be significantly tuned by appropriate modifications of the cation, anion, or both for a specific application [8–12]. Since density is crucial in the industrial process design involving ionic liquids, it is an important property among their physicochemical properties. It is desirable to have predictive models for calculating the ionic liquids properties as alternative to the experimental measure- ments because ionic liquids density data are either scarce and some- times absent due to the large number of ionic liquids synthesized every year [13–28]. Furthermore, most of experimental standard test methods for measuring the density are time-consuming and expensive. However, it is important to have simple and reliable predictive methods for estimation density of a desirable new ionic liquid. There are many Quantitative Structure–Activity Relationship (QSAR) or Quantitative Structure Property Relationship (QSPR) studies have been done in the past to predict the density of different classes of ionic liquids. Moreover, some studies have been done to investigate fast and reliable estimation of the molecular volume/molar volume/density of ionic liquids on the basis of group contributions. Some of these works related to the current study have been reviewed here. Rebelo et al. [29] provided an overview of phase behavior and thermodynamic properties of ionic liquids, ionic liquid mixtures, and ionic liquid solutions. Esperança and coauthors [30] studied on several phosphonium- based ionic liquids including trihexyltetradecylphosphonium chloride, trihexyltetradecylphosphonium acetate, and trihexyltetradecylphos- phonium bis [31]-amide. They employed a simple ideal-volume model for estimation of densities of phosphonium-based ionic liquids at ambi- ent conditions. Paduszynski and Domanska [32] have developed a meth- od based on generalized empirical correlation and group contributions for prediction of density of pure ionic liquids over a wide range of tem- perature and pressure. Their model parameters include the contributions to molar volume for 177 functional groups as well as universal coeffi- cients describing the P-ρ-T surface. Rebelo et al. [33] have accounted for the unique, doubly dual nature of ionic liquids through using a molec- ular perspective that emphasizes the doubly dual nature of ionic liquids underlying the existence of cations and anions forming high- and low- charge-density regions. Ye and Shreeve [34] developed volume parame- ters of some classes of ionic liquids for estimation of their densities at room-temperature. Gardas and Coutinho [35] improved group contribu- tion method of Ye and Shreeve [34] for estimation of densities of ionic liquids in wide ranges of temperature and pressure. Jacquemin et al. [36] introduce a group contribution model for prediction of molar vol- umes and densities of several classes of ionic liquids as a function of tem- perature between (273 and 423) K at atmospheric pressure. Slattery and coworkers [37] described several simple relationships for estimation of the physical properties of some categories of ionic liquids from only their molecular volumes and an anion-dependent correlation. Palomar Journal of Molecular Liquids 216 (2016) 732–737 ⁎ Corresponding author. E-mail addresses: mhkeshavarz@mut-es.ac.ir, keshavarz7@gmail.com (M.H. Keshavarz). http://dx.doi.org/10.1016/j.molliq.2016.01.095 0167-7322/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq