Studies on the Physicochemical Properties of Ionic Liquids Based On 1‑Octyl-3-methylimidazolium Amino Acids Ouahid Ben Ghanem,* ,† M.I. Abdul Mutalib, † Jean-Marc Le ́ ve ̂ que, ‡ Girma Gonfa, † Chong Fai Kait, ‡ and Mohanad El-Harbawi § † Faculty of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia ‡ Fundamental & Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia § Chemical Engineering Department, King Saud University, Riyadh 11421, Kingdom of Saudi Arabia * S Supporting Information ABSTRACT: A series of new synthesized ionic liquids based on 1-octyl-3- methylimidazolium with glycinate, alaninate, serinate, prolinate, and asparaginate anions were prepared. Their thermophysical properties (density, viscosity, surface tension, and heat capacity) were measured at various temperatures and atmospheric pressures. Physicochemical properties such as thermal expansion coefficient values, molecular volume, standard molar entropy, and lattice energy standard were also determined using empirical methods. The effects of anions on the studied properties were further analyzed. 1. INTRODUCTION Ionic liquids (ILs) have garnered interest as alternative solvents in green processes because of their remarkable properties, such as chemical and thermal stability, nonflammability, and negligible vapor pressure. 1,2 Moreover, considering the high number of cations and anions available, the properties of the ILs can be finely tuned. In addition, functional groups can be incorporated into the ion structure, further tuning the properties of ILs. Recently, a series of ILs containing amino acids exhibiting lower toxicity than commercially available first and second generation analogs was reported. 3-5 Given the fact that amino acid ionic liquids (AAILs) contain both amino group and carboxylic acid residue in a single molecule, they have intrinsic properties such as strong hydrogen-bonding ability, which is valuable for dissolving biomaterials like cellulose and other carbohydrates. Furthermore, AAILs can be obtained at a low cost by using naturally derived amino acids. 3-10 AAILs have high biodegradability 11 and low toxicity 12 and can be utilized in various applications, such as gas separation, 5-10 reaction medium, 13 and biomass dissolution. 14 AAILs were first prepared by Fukumoto et al. 3 in 2005 by combining 1-ethyl-3-methylimidazolium cation ([C 2 mim]) with 20 different amino acids. Tao et al. 4 then prepared AAILs with nitrate anions using amino acids as cations. Since then, various AAILs have been prepared including dual- functionalized AAILs, whose amino functional groups are used as both cation and anion. 5 However, the effective use of these AAILs is constrained by their low thermal stability and high viscosity. For instance, short-alkyl-chain imidazolium- based AAILs such as 1-ethyl-3-methylimidazolium-based AAILs have low thermal stability. 3,8,15 Phosphonium-based AAILs show good thermal 7,16 and electrochemical stabilities 17 but are relatively more viscous than 1-ethyl-3-methylimidazolium analogs. The thermophysical properties of AAILs strongly rely on both the side-chain structure of the amino acid 3-8 and the cation alkyl chain length of AAILs. 6 Although several studies have reported on certain physiochemical and thermal properties of AAILs with short to medium alkyl chains (C 2 to C 6 ), none have been provided for long-alkyl chain AAILs. In the present work, five long-alkyl-chain AAILs, namely, 1- octyl-3-methylimidazolium glycinate [C 8 mim][Gly], 1-octyl-3- methylimidazolium alaninate [C 8 mim][Ala], 1-octyl-3-methyl- imidazolium serinate [C 8 mim][Ser], 1-octyl-3-methylimidazo- lium prolinate [C 8 mim][Pro], and 1-octyl-3-methylimidazo- lium asparaginate [C 8 mim][Asn] were prepared and charac- terized. The general route to the synthesis and structure of these ILs is depicted in Figure 1. The density, viscosity, surface tension, and heat capacity of the ILs were measured at different temperatures and atmospheric pressure. Certain significant physicochemical and thermal properties were also determined from the experimental data. The thermal behavior of the AAILs Received: December 26, 2014 Accepted: May 7, 2015 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/je501162f J. Chem. Eng. Data XXXX, XXX, XXX-XXX