Technical note: Estimating aqueous solubilities and activity coefficients of mono- and <i>α</i>,<i>ω</i>-dicarboxylic acids using COSMO<i>therm</i>

Abstract

Abstract. We have used the COSMOtherm program to estimate activity coefficients and solubilities of mono- and α,ω-dicarboxylic acids and water in binary acid–water systems. The deviation from ideality was found to be larger in the systems containing larger acids than in the systems containing smaller acids. COnductor-like Screening MOdel for Real Solvents (COSMO-RS) underestimates experimental monocarboxylic acid activity coefficients by less than a factor of 2, but experimental water activity coefficients are underestimated more especially at high acid mole fractions. We found a better agreement between COSMOtherm-estimated and experimental activity coefficients of monocarboxylic acids when the water clustering with a carboxylic acid and itself was taken into account using the dimerization, aggregation, and reaction extension (COSMO-RS-DARE) of COSMOtherm. COSMO-RS-DARE is not fully predictive, but fit parameters found here for water–water and acid–water clustering interactions can be used to estimate thermodynamic properties of monocarboxylic acids in other aqueous solvents, such as salt solutions. For the dicarboxylic acids, COSMO-RS is sufficient for predicting aqueous solubility and activity coefficients, and no fitting to experimental values is needed. This is highly beneficial for applications to atmospheric systems, as these data are typically not available for a wide range of mixing states realized in the atmosphere, due to a lack of either feasibility of the experiments or sample availability. Based on effective equilibrium constants of different clustering reactions in the binary solutions, acid dimer formation is more dominant in systems containing larger dicarboxylic acids (C5–C8), while for monocarboxylic acids (C1–C6) and smaller dicarboxylic acids (C2–C4), hydrate formation is more favorable, especially in dilute solutions.

New Screening Protocol for Effective Green Solvents Selection of Benzamide, Salicylamide and Ethenzamide

“…Unfortunately, COSMO-RS formalism despite relying on chemical intuition, often fails in determining solubility [ 93 , 128 , 129 , 130 , 131 ] and other physicochemical properties [ 132 , 133 , 134 , 135 ]. Probably in most cases, the major explanation is the insufficient precision of available default parameterization [ 128 , 136 ], which on the other hand, in many cases provides quite an accurate match with measured values [ 56 , 90 , 91 , 137 ]. Fortunately, non-substituted benzamide is a relatively simple molecular system, which seems to be well-described by COSMO-RS.…”

“…Hence, theoretical screening enabling the rational selection of the most promising candidates seems indispensable. Unfortunately, despite great efforts [ 18 , 33 , 40 , 45 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ], there is no universal and reliable way of predicting solubility in binary aqueous solutions from the molecular structure. Methods developed for proper back-computations of measured solubility data such as Jouyban-Acree, van’t Hoff-Yaws, Wilson, Apelblat, Buchowski-Ksiazczak and Non-Random Two Liquid (NRTL) are interesting from the thermodynamic interpretation viewpoint [ 45 , 61 , 62 , 63 , 64 ], however rather of limited applicability as screening tools.…”

Predicting liquid–liquid phase separation in ternary organic–organic–water mixtures

“…COSMO-RS, implemented in the COSMO therm program, 28 has been shown to accurately estimate condensed-phase properties, such as solubilities and activity coefficients, of atmospherically relevant multifunctional compounds and water, if suitable conformer distributions are used in the calculation. [29][30][31] Here, COSMOtherm was used to calculate the phase diagrams of some of the ternary SOA-POA-water mixtures, investigated experimentally by Mahrt et al 5 Additionally, the phase separation behavior was predicted for a large set of SOA-POAwater mixtures with possible SOA constituents (p sat o 10 À5 Pa), as well as POA proxies with relatively high O : C ratios (O : C Z 0.125). The SOA constituents were selected from previous studies that have identified possible oxidation products of a-pinene, D3-carene, cyclohexene and isoprene.…”

“…COSMO-RS, implemented in the COSMO therm program, 28 has been shown to accurately estimate condensed-phase properties, such as solubilities and activity coefficients, of atmospherically relevant multifunctional compounds and water, if suitable conformer distributions are used in the calculation. 29–31…”