Densities of aqueous mixtures of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) deep eutectic solvents in temperature range 283.15–363.15 K

Accepted Manuscript Title: Densities of aqueous mixtures of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) deep eutectic solvents in temperature range 283.15 to 363.15 K Author: Anita Yadav Jyotsna Rani Kar Maya Verma Saeeda Naqvi Siddharth Pandey PII: DOI: Reference:

S0040-6031(14)00544-9 http://dx.doi.org/doi:10.1016/j.tca.2014.11.028 TCA 77085

To appear in:

Thermochimica Acta

Received date: Revised date: Accepted date:

8-10-2014 25-11-2014 27-11-2014

Please cite this article as: Anita Yadav, Jyotsna Rani Kar, Maya Verma, Saeeda Naqvi, Siddharth Pandey, Densities of aqueous mixtures of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) deep eutectic solvents in temperature range 283.15 to 363.15K, Thermochimica Acta http://dx.doi.org/10.1016/j.tca.2014.11.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Densities of aqueous mixtures of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) deep eutectic solvents in temperature range 283.15 to 363.15 K

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Anita Yadav a, Jyotsna Rani Kar a, Maya Vermab, Saeeda Naqvic, Siddharth Pandeya,*

Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi -110016, India.

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Department of Chemistry, Government Girls Post Graduate College, Banda, Uttar Pradesh - 210001, India.

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Department of Chemistry, Aligarh Muslim University, Uttar Pradesh - 202002, India.

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*To whom correspondence should be addressed.

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E-mail: [email protected], Phone: +91-11-26596503, Fax: +91-11-26581102

Highlights

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For (DES + water) mixture, density decreases with increasing T within 283.15 - 363.15 K with quadratic dependence on T.

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Excess molar volume of aqueous mixtures of DES is significant and negative at all T and compositions.

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Density dependence on DES mole fraction follows exponential-rise-to-maxima.

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The density data imply presence of strong interactions between water and DES.

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Interstitial accommodation of water within H-bonded DES network is also strongly suggested.

Abstract

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Deep eutectic solvents (DESs) are emerging as a new class of biodegradable green solvents; a cost-effective alternative to the

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conventional room temperature ionic liquids and organic solvents. Hydrophilic nature of DES finds its applications in many industrial

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and chemical processes. Aqueous mixtures of DESs have potential to afford modified properties for specific applications. A comparative study of densities of two well-known DESs named as ethaline (mixture of choline chloride and ethylene glycol in 1 : 2 molar ratio) and maline (mixture of choline chloride and malonic acid in 1 : 2 molar ratio) and their aqueous mixtures in the

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temperature range 283.15–363.15 K is presented. Decrease in density with increasing temperature is found to follow a quadratic expression. Excess molar volumes of the aqueous mixtures of both ethaline and maline are found to be negative and significant at all temperatures and compositions. Absolute excess molar volume is found to decrease as the temperature is increased from 283.15 K to 323.15 K. For temperature above 323.15 K, the excess molar volume does not change much with further increase in temperature till 363.15 K. The outcomes hint at the presence of relatively stronger interactions, preferably H-bonding type, between water and

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ethaline/maline, as compared to those among water and among ethaline/maline molecules, respectively. The excess molar volumes at higher temperatures strongly indicate facile interstitial accommodation of water within H-bonded ethaline/maline network to be also present within these aqueous DES mixtures.

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Keywords: Deep eutectic solvents; Choline chloride; Density; Excess molar volume; Aqueous mixtures.

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1. Introduction

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With the introduction of green chemistry in early 1990’s, room temperature ionic liquids (RTILs) have emerged as ‘green

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solvents’ owing to their advantageous physical and chemical properties, e.g., extremely low vapor pressure, high thermal stability, high solvation capacity, high thermal conductivity, and wide liquid range [1-4]. However, the main disadvantages to their use are their

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high cost and issues such as non-biodegradability and toxicity [5-7]. As greener alternative to RTILs, a new family of solvents, known as deep eutectic solvents (DESs) has emerged as novel media in chemistry. DES is a fluid generally composed of two or three cheap

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components that are capable of self-association, often through H-bonding interactions, to form a eutectic mixture with much lower melting point than either of the individual components [8, 9]. DESs possess similar physicochemical properties to the traditionally used RTILs, while possessing several advantages over the later. Many of the reported DESs are made from biodegradable components and are non-toxic. So, they are considered as better substitute to conventional volatile organic solvents and RTILs. DESs find major applications in the field of organic synthesis [10], electrochemistry [11-13], nanomaterial [14], biochemistry [15, 16] and other

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chemical and industrial processes. A DES can be prepared by forming a complex between a H-bond acceptor (HBA) such as an ammonium salt and a H-bond donor (HBD) such as an acid, alcohol or an amide. DESs are easier to prepare with high purity at a relatively cheaper cost. The first DES was investigated by Abbott and co-workers in 2003 containing choline chloride and urea in 1 : 2 mole ratio [17].

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Unlike certain PF6‒ and (CF3SO2)2N‒ RTILs, among others, the most popular class of DESs constituted of choline chloride,

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exhibit complete water miscibility. Subsequently, water, an obvious choice as environmentally-benign substance, can be used as a

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cosolvent to effectively and favorably modify properties of a choline chloride DES. In this paper, we have chosen two common and

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popular DESs, named ethaline and maline, that are composed of (choline chloride + ethylene glycol) and (choline chloride + malonic

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acid), respectively, combined in the mole ratio 1 : 2. Their melting points are significantly lower than the room temperature (ethaline: Tf = 213.15 K and maline: Tf = 283.15 K) [18]. Both the DESs are non-flammable and non-toxic and exhibit complete water

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miscibility. To assess and design the possible industrial-scale applications of DESs, it is essential to know the thermophysical properties of their aqueous mixtures. Among the key physicochemical properties, density has enormous importance as far as various

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industrial applications are concerned. Densities of aqueous mixtures of ethaline have been measured by other researchers. In a recent study, Li et al. reported the

densities of (choline chloride + ethylene glycol) and their aqueous mixtures; however, the temperature range (298.15 to 333.15 K) of this report was significantly narrower [19]. In another study, the same group reported high pressure volumetric properties of choline chloride-ethylene glycol based deep eutectic solvent and its mixtures with water covering the temperature range of 298.15 – 323.15 K

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and pressure range of 0.1 – 50 mPa [20]. The temperature range in this study again is rather restricted. In a recent contribution towards temperature-dependent density measurement of ammonium- and phosphonium-based DESs was from AlNashef et al. in which the densities were predicted using artificial intelligence and group contribution techniques [21]. In another study, AlNashef group reported predicted densities of ethaline using atomic contributions at 298.15 K [22]. The same group also reported the predicted densities of

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ionic liquids analogues by using Eotvos and Guggenheim empirical rules in the temperature range 298.15 to 328.15 K [23]. Li and

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coworkers reported the densities, viscosities, and refractive indices of (N,N-diethylethanol ammonium chloride + glycerol) and (N,N-

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diethylethanol ammonium chloride + ethylene glycol) and their aqueous mixtures from 298.15 – 343.15 K [24]. In a recent study, Li et

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al. reported the diffusivity, density and viscosity of aqueous solutions of choline chloride/ethylene glycol and choline chloride/malonic

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acid; however, the temperature range (303.15 to 323.15 K) of this report was significantly narrower [25]. Li and coworkers also reported Henry’s constant of carbon dioxide-aqueous DES (choline chloride/ethylene glycol, choline chloride/malonic acid) systems

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at the pressure 101.00 kPa in the temperatures range 303.15 to 323.15 K [26]. The temperature ranges of this report is also significantly narrower. We present densities of ethaline, maline and their aqueous mixtures (over the entire composition range) and

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covering the temperature range from 283.15 to 363.15 K.

2. Experimental 2.1 Materials

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Ethaline 197 (mol wt. 88.03 g/mol) and maline 200 (mol wt. 115.80 g/mol), a mixture of (choline chloride + ethylene glycol) and (choline chloride + malonic acid) in 1 : 2 mole ratio, respectively, were purchased from Scionix Ltd. and used as received. Alternatively, ethaline and maline were also prepared by mixing choline chloride (≥ 99%, from Sigma-Aldrich) with ethylene glycol (≥ 99.8%, from Sigma-Aldrich) and choline chloride (≥ 99%, from Sigma-Aldrich) with malonic acid (≥ 99%, from Sigma-Aldrich) in

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1 : 2 molar ratio and stirred under heating (~80⁰C) until a homogeneous, colorless liquid has been formed [18]. The density

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measurement of ethaline and maline purchased from Scionix Ltd. and that prepared by mixing (choline chloride + ethylene glycol) and

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(choline chloride + malonic acid) in our laboratory were found to be statistically similar. Doubly distilled deionised water of HPLC

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grade was obtained from Merck. Table 1 lists the chemicals used in this investigation, their sources, and purification methods used, if

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2.2 Methods

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any. In most cases, when required, drying under vacuum was carried out.

The aqueous mixtures of DESs were prepared by mass using a Denver Instrument balance having a precision of ±0.1 mg.

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Densities () of the aqueous mixtures of ethaline and maline were measured using a Mettler Toledo, DE45 delta range density meter. The density measurement with the above–mentioned density meter was based on electromagnetically-induced oscillations of a Ushaped glass tube. The density meter was calibrated by measuring the densities of distilled water which was found to be consistent with values reported in the literature and the standard deviations associated with the density measurement are ≤ 0.0001 g∙cm3. The measurements were performed at 10 degree intervals in the temperature range (293.15 to 363.15) K. Table 2 presents comparison of

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densities of pure ethaline and maline and their aqueous mixtures measured with our instrumentation with those available in literature. Although our values of water at different temperatures are in good agreement with those reported in the literature, due to the hygroscopic nature of the DES ethaline, some of our values in ethaline and (ethaline + water) mixtures appear to deviate from those reported. These apparent deviations could be comprehended based on the higher uncertainties associated with the composition (i.e.,

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the water contents) of the mixtures [19-21].

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3. Results and discussion

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3.1 Temperature dependence of densities of ethaline and maline and their aqueous mixtures

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Experimentally measured densities of ethaline and maline, respectively, and their water mixtures as a function of temperature in the range 283.15 to 363.15 K over the entire composition range are reported in Tables 3 and 4, respectively. As expected, densities

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of ethaline, maline, water, and aqueous mixtures of DESs, respectively, are found to decrease with increase in temperature. Thermal expansion usually results in decreased density of a substance as the temperature is increased. The experimentally measured densities

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are found to vary quadratically with the absolute temperature according to the equation:

   0  aT  bT 2

(1)

where,  /g·cm-3 is the density of the aqueous mixture of ethaline and maline, respectively. The values of the parameters ρo, a, and b along with the standard deviation of the fits are listed in Tables 5 and 6 for aqueous mixtures of ethaline and maline, respectively.

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Measured densities of (ethaline + water) and (maline + water) mixtures along with the fits to equation (1) are also presented in Figures 1 and 2, respectively. It is clear from the recovered values of r2 listed in Table 5 (for ethaline and its aqueous mixture) and Table 6 (for maline and its aqueous mixture) as well as from careful examination of Figures 1 and 2, where the fits of the measured density against the temperature according to equation (1) for (ethaline + water) and (maline + water) mixtures over the entire

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composition range are presented as solid curves, that the temperature-dependence of the densities of ethaline and maline and their

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aqueous mixtures can be conveniently expressed by a simple quadratic relation in the temperature range 283.15 to 363.15 K.

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It is important to mention that Li group has reported a linear decrease in density with temperature for ethaline and its aqueous

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mixtures [19]. It is attributed to the fact that the temperature range for density data of Li group was much narrower (298.15 K to

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333.15 K only). In another report, Li group have reported high pressure volumetric properties of choline chloride-ethylene glycol based deep eutectic solvent and its mixtures with water covering the temperature range of 298.15 – 323.15 K and pressure range of 0.1

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– 50 mPa [20]. However, the higher temperature in this report was only 323.15 K. It is clear that measurements at higher temperatures (363.15 K ≥ T > 333.15 K) reveal a more complex dependence of density on the temperature of ethaline and its aqueous mixtures.

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As DES ethaline is constituted of choline chloride and ethylene glycol, it is imperative to compare the temperature dependence of density of aqueous mixtures of ethaline with those of aqueous mixtures of ethylene glycol and aqueous mixtures of choline chloride, respectively. The difference in the temperature dependence of the density of aqueous mixtures of ethaline from that of aqueous mixtures of ethylene glycol is revealed by the measurements of Tang and coworkers [27]. They report an almost linear decrease in density with temperature for (ethylene glycol + water) system in the temperature range of 273.15 to 353.15 K. It is

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noteworthy that, for (choline chloride + water) system on the other hand, the dependence of density on temperature is quadratic in the temperature range 278.15 to 318.15 K [28]. It appears that the temperature dependence of density of (ethaline + water) resembles more that of (choline chloride + water) than that of (ethylene glycol + water) although ethaline is constituted of 2 moles of ethylene glycol and 1 mole of choline chloride. We could not find density data of (malonic acid + water) mixtures as function of temperature in

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the literature. As a result, a similar analysis of the data could not be performed. However, It can be inferred that the density variation

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with temperature of (maline + water) system is similar to that of (choline chloride + water) system.

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3.2 Composition dependence of densities of ethaline and maline and their aqueous mixtures

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In order to highlight the dependence of density on the composition of the aqueous DES mixture, we fitted the density against the mole fraction (x1) of ethaline and maline, respectively, of the aqueous mixtures. For (ethaline + water) system, the increase in the

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density with increasing x1 is found to fit best to a 3-parameter exponential-rise-to-maxima expression in the entire range of temperature investigated. However, for (maline + water) system, the increase in the density with increasing x1 is found to fit best to a

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5-parameter exponential-rise-to-maxima expression perhaps suggesting increased complexity of the (maline + water) mixture as compared to (ethaline + water) system. Densities at each temperature for (ethaline + water) and (maline + water) mixtures as a function of x1 along with the fit to 3-parameter and 5-parameter exponential-rise-to-maxima expressions, respectively, have been plotted in Figure 3 (for ethaline) and Figure 4 (for maline). It needs to be reiterated that the composition dependence of density for

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the aqueous mixtures of these DESs, however, is not very straight forward. Results of the regression analysis of density (ρ) of aqueous mixtures of ethaline and maline versus mole fraction data are tabulated in Table 7 and Table 8, respectively.

3.3 Excess molar volumes of aqueous mixtures of ethaline and maline

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In order to afford the extent of molecular-level interactions within (DES + water) mixtures, we estimated excess molar volume

m

x M x M   1 1  2 2 2  1

  

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x1 M 1  x 2 M 2 

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VE 

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(VE) from experimental density data using the relationship

(2)

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Here, x1, x2, and ρ1, ρ2 refer to the mole fractions and densities, respectively, of DES and water at a given temperature, and ρm is the density of the mixture. M1 and M2 are the molecular weights of components 1 (DES) and 2 (water), respectively. The molecular

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weights of the pure DESs were calculated from their individual components according to the equation [29]  x ChCl M

ChCl

 x HBD M

HBD

(3)

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The VE at each temperature for (ethaline + water) mixture are presented as a function of x1, the mole fraction of ethaline, in Figure 5. It is clear that VE are negative and have significant values at each temperature throughout the entire composition range for all (ethaline + water) mixtures. The temperature dependence of VE, however, is not very straight forward. Importantly, the absolute values of VE for (ethaline + water) mixtures appear to decrease with increasing temperature in the temperature ranges 283.15 to 323.15 K (Figure 5A). However, as temperature is increased for T > 323.15 K, the VE appears to change less significantly; in fact the variation

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is reversed at higher temperatures (333.15 K to 363.15 K) (Figure 5B). While, Li and coworkers also report VE of (ethaline + water) to decrease with increasing temperature in the range 298.15 K to 323.15 K; the VE at 323.15 K was reported by them to be not too different from VE at 333.15 K [19]. 333.15 K was the highest temperature in their investigation. Similarly, VE at 333.15 K was estimated to be very similar to VE at 343.15 K for a system composed of (DES + water), where the DES is constituted of N,N-

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diethylethanolammonium chloride instead of choline chloride [24]. It is important to mention that VE of (ethylene glycol + water)

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system are also estimated to be negative by several researchers [27, 30]. Further, the VE is reported to decrease with temperature in the

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range 273.15 K to 353.15 K by these researchers. Our VE clearly hints at complexity associated with aqueous mixtures of ethaline as

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far as interactions in the system are concerned.

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The VE at each temperature for (maline + water) mixture are also negative and have significant values at each temperature throughout the entire composition range for all (maline + water) mixtures and follow a trend similar to that observed for (ethaline +

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water) mixtures.

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3.4 Redlich-Kister polynomials to describe VE The VE were next fitted to the Redlich-Kister type polynomial expressions [31]. According to combined nearly ideal binary

solvent/Redlich-Kister (CNIBS/R-K) model, the VE in a binary solvent mixture at a constant temperature can be expressed as: k

V E  xDES xwater  A j  xDES  xwater  j 0

j

(4)

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where, Aj and j are the equation coefficients and the degree of the polynomial expansion, respectively. The numerical values of j can be varied to find an accurate mathematical representation of the experimental data. Regression analysis was performed to fit the polynomials [i.e., equation (4)] to our experimental density data and the results of the fit are reported in Table 9. It is convenient to use a cross-validation method which is a practical and reliable method to test the predictive significance when only little data are

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available [32]. The solid lines connecting each of the VE in Figure 5 at all proportions are obtained from the CNIBS/R-K model fit

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(with j = 3) as reported in Table 9 for ethaline suggests a fair-to-good correlation between the predicted and the experimentally

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obtained values (the r2 also indicates the fits to be satisfactory).

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The negative VE generally points to contraction in volume upon mixing. The interactions within the mixture are affected by the

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temperature and the composition of the mixture. In liquid mixtures, the absolute value of VE usually decreases with increasing temperature in systems where interactions are present. The negative VE of the (DES + water) mixtures at all compositions in the

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temperature range 283.15 to 363.15 K hints at stronger interspecies interactions (between the DES and water) than intra-species interactions (i.e., among water molecules or among DES molecules) along with facile interstitial accommodation of water within H-

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bonded DES network. The interactions between water and DES could be of the H-bonding type, among others, involving ethylene glycol/malonic acid and choline chloride – the constituents of the DES. Both –OH group and chloride ion of choline chloride and –OH groups of ethylene glycol/malonic acid are capable of H-bonding with water. The interspecies interactions usually decrease more as compared to intra-species interactions with increasing temperature. As a result, we observe a decrease in absolute value of VE in the temperature range 283.15 to 323.15 K. However, a slight increase in the absolute value of VE as the temperature is increased from

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333.15 to 363.15 K could be attributed to the inherent complexity of the (DES + water) mixtures as far as interactions within the system are concerned. As mentioned earlier, the H-bonding and other interactions between the unlike components (i.e., DES and water) within the mixtures along with interstitial accommodation of water within H-bonded DES network would result in volume contraction and thus the negative VE for our system. Upon heating, further contraction in the mixture volume, albeit small, could be

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tentatively attributed to the weakening of the H-bond among ethylene glycol/malonic acid and choline chloride and/or among water

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molecules with subsequent strengthening of the H-bonding between ethaline/maline and water. The interstitial exclusion of water

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molecules from (ethylene glycol/malonic acid + choline chloride) H-bonded network in the temperature range 333.15 K to 363.15 K

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may be a more important factor in increasing absolute value of VE with increasing temperature of the mixture. It is interesting to note

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that the maximum value of VE = –0.3372 cm3mol-1 at xDES = 0.4022 at 20°C for aqueous mixtures of (choline chloride + glycerol) DES [33] is more than the maximum value of VE = –0.2971 cm3mol-1 at xDES = 0.3998 for (choline chloride + ethylene glycol) DES at the

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same temperature. This is attributed to more efficient H-bonding between water and glycerol as compared to that between water and ethylene glycol within the aqueous DES mixture as glycerol possess three alkyl –OH groups as compared to ethylene glycol that

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possesses two alkyl –OH groups. This would lead to increased contraction in volume within aqueous mixtures of (choline chloride + glycerol) DES as compared to that within aqueous mixtures of (choline chloride + ethylene glycol) DES.

4. Conclusions

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Densities of aqueous mixtures of DESs ethaline and maline and their temperature and composition dependence in the temperature range 283.15 - 363.15 K reveal interesting information on interactions present within these systems. Variation of density with temperature for these systems is found to be quadratic in nature. Negative and significant values of excess molar volume at all temperature and composition hint at the presence of stronger interactions between water and ethaline/maline as compared to those

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among water or among ethaline/maline molecules, respectively. As revealed by the trend in excess molar volume at higher

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temperatures where absolute value of excess molar volume does not decrease anymore as temperature is increased beyond 323.15 K, it

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is proposed that facile interstitial accommodation of water within H-bonded network of the DESs also contributes to the negative

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excess molar volume. Complex interplay of the two contributors results in the unusual trend in excess molar volume at higher

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temperature. Complexity of the aqueous ethaline/maline mixtures at higher temperatures are highlighted by our measurements.

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Acknowledgements. This work is generously supported by the Department of Science and Technology (DST), Government of India through a grant to SP [grant number SB/S1/PC-80/2012]. AY would like to thank CSIR, Government of India for her fellowship. MV

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and SN would like to thank Summer Faculty Research Fellow Programme 2014 at IIT Delhi.

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[23] F.S. Mjalli, G. Vakili-Nezhaad, K. Shahbaz, I.M. AlNashef, Application of the Eotvos and Guggenheim empirical rules for predicting the density and surface tension of ionic liquids analogues. Thermochim. Acta 575 (2014) 40-44. [24] K.R. Siongco, R.B. Leron, M.-H. Li, Densities, refractive indices, and viscosities of N,N-diethylethanol ammonium chloride–glycerol or – ethylene glycol deep eutectic solvents and their aqueous solutions, J. Chem. Thermodyn. 65 (2013) 65-72. [25] Y.-P. Hsieh, R.B. Leron, A.N. Soriano, A.R. Caparanga, M.-H. Li, Diffusivity, density and viscosity of aqueous solutions of choline chloride/Ethylene Glycol and choline chloride/malonic acid, J. Chem. Eng. Japan 45 (2012) 939-947. [26] C.-M. Lin, R.B. Leron, A.R. Caparanga, M.-H. Li, Henry s constant of carbon dioxide-aqueous deep eutectic solvent (choline chloride/ethylene glycol, choline chloride/glycerol, choline chloride/malonic acid) systems, J. Chem. Thermodyn. 68 (2014) 216-220.

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[27] C. Yang, P. Ma, F. Jing, D. Tang, Excess Molar Volumes, Viscosities, and Heat Capacities for the Mixtures of Ethylene Glycol + Water from 273.15 K to 353.15 K, J. Chem. Eng. Data 48 (2003) 836-840. [28] S. Shaukat, R. Buchner, Shaukat, S.; Buchner, R. Densities, Viscosities [from (278.15 to 318.15) K], and Electrical Conductivities (at 298.15 K) of Aqueous Solutions of Choline Chloride and Chloro-Choline Chloride. J. Chem. Eng. Data 56 (2011) 4944-4949. [29] A.P. Abbott, R.C. Harris, K.S. Ryder, C. D’Agostino, L.F. Gladden, M.D. Mantle, Glycerol eutectics as sustainable solvent Systems, Green Chem. 13 (2011) 82-90.

N

U

[30] N.G. Tsierkezos, I.E. Molinou, Thermodynamic Properties of Water + Ethylene Glycol at 283.15, 293.15, 303.15, and 313.15 K, J. Chem. Eng. Data 43 (1998) 989-993.

A

[31] O. Redlich, A.T. Kister, Thermodynamics of nonelectrolyte Solutions, x-y-t relations in a Binary System, Ind. Eng. Chem. 40 (1948) 341-345.

M

[32] S. Wold, M. Sjöstrom, L. Eriksson, PLS-regression: A Basic Tool of Chemometrics, Chemom. Intell. Lab Syst.: Netherlands 58 (2001) 109-130.

EP T

ED

[33] A. Yadav, S. Trivedi, R. Rai, S. Pandey, Densities and dynamic viscosities of (choline chloride + glycerol) deep eutectic solvent and its aqueous mixtures in the temperature range 293.15 K to 363.15 K, Fluid phase Equilib. 367 (2014) 135-142.

Figure and Table

A CC

Figure 1. Variation of density with temperature for ethaline (1) + water (2) mixtures at different mole fractions of ethaline (x1) (●: 0.0000; ▼ : 0.0999; ■ : 0.1999; : 0.3000; ▲ : 0.3998; : 0.4996; ●: 0.5996; ▼ : 0.6974; ■ : 0.7992; : 0.8997; ▲ : 1.0000). The 2 solid lines represents a fit to the equation    0  aT  bT . Parameters 0, a, and b along with the goodness-of-fit in terms of r2 are reported in Table 5. Figure 2. Variation of density with temperature for maline (1) + water (2) mixtures at different 0.0000; ▼ : 0.0999; ■ : 0.1998; : 0.2997; ▲ : 0.4000;

mole fractions of maline (x1) (●:

: 0.5000; ●: 0.6000; ▼ : 0.6982; ■ : 0.7988; : 0.8969; ▲ : 1.0000). The solid lines

2

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represents a fit to the equation   0  aT  bT . Parameters 0, a, and b along with of r2 are reported in Table 6.

the goodness-of-fit in terms

Figure 3. Variation of density with mole fraction of ethaline for ethaline (1) + water (2) mixtures at different temperatures as temperature is : 293.15 K; ■ : 303.15 K;: 313.15 K; ▲ : 323.15 K; : 333.15 K; ●: increased from (283.15 to 323.15) K [●: 283.15 K; ▼ : 353.15 K; ■ : 363.15 K]. The solid lines represents a fit to the 343.15 K; ▼

equation

  0  a[1  exp(bx1 )] . Parameters 0,

fit in terms of r2 are reported in Table 7.

U

a and b along with the goodness-of-

N

Figure 4. Variation of density with mole fractions of maline (x1) for maline (1) + water (2) mixtures at different temperatures as the temperature is increased from (283.15 to 323.15) K [●: 283.15 K; ▼ : 293.15 K; ■ : 303.15 K;: 313.15 K; ▲ : 323.15 K; : 333.15 K; ●: 343.15 K; ▼ : 353.15 K; ■ : 363.15 K]. The solid lines represents a fit to the equation

A

 ( g .cm 3 )   0 ( g .cm 3 )  a[1  exp(bx1 )]  c[1  exp(dx1 )] . Parameters terms of r are reported in Table 8.

M

2

0, a, b, c and d along with the goodness-of-fit in

A CC

EP T

ED

Figure 5. Variation of excess molar volume (VE/cm3.mol-1) with mole fraction of ethaline (x1) for (ethaline + water) mixtures as the : 293.15 K; ■ : 303.15 K; : 313.15 K; ▲ : 323.15 K]. (B) temperature is increased from (A) (283.15 to 323.15) K [●: 283.15 K; ▼ : 343.15 K; ■ : 353.15 K; : 363.15 K]. Solid (333.15 to 363.15) K [●: 333.15 K; ▼ curves show fits according to the Redlich-Kister equation [eq 4] with parameters (Aj) reported in Table 9.

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Table 1. Description of the chemicals used in this work.

______________________________________________________________________________ Chemicals used Purity (% mass) Source Purification done ______________________________________________________________________________ ≥99

Ethaline 197

Scionix Ltd.

(1 mole choline chloride

≥99

A

Maline 200

Scionix Ltd.

Further dried

ED

M

(1 mole choline chloride + 2 moles malonic acid)

N

U

+ 2 moles ethylene glycol)

Further dried

Doubly distilled deionized water

≥99

Merck

None

≥99

Sigma-Aldrich

None

Ethylene glycol

≥99.8

Sigma-Aldrich

None

Malonic acid

≥99

Sigma-Aldrich

None

EP T

(HPLC grade)

A CC

Choline chloride

______________________________________________________________________________

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Table 2. Comparison of experimental densities (ρ e) of ethaline (1) + water (2) mixtures with the literature values at pressure (p)f = 0.101 MPa for different temperatures (x1g is the mole fraction of ethaline).

___________________________________________________________________________________________

____________________________

A CC

EP T

ED

M

A

N

U

ρ/g·cm-3 h T (K) x1 0.0000 0.0999 0.1999 0.3998 0.6974 0.7992 1.0000 ________________________________________________________________________________________________________ 303.15 Exp. 0.9957 1.0378 1.0628 1.0889 1.1046 1.1074 1.1114 a b b b a a Lit. 0.9957 1.0403 1.0658 1.0923 1.1077 1.110 1.1142a, 1.1146 c, 1.116 d 313.15 Exp. 0.9922 1.0332 1.0576 1.0833 1.0989 1.1017 1.1057 a b b b a a Lit. 0.9923 1.0357 1.0606 1.0867 1.1019 1.1047 1.1084a, 1.1088 c, 1.110 d 323.15 Exp. 0.9980 1.0283 1.0523 1.0777 1.0932 1.0961 1.1001 a b b b a a Lit. 0.9981 1.0307 1.0552 1.0809 1.0962 1.0990 1.1027a, 1.1036 c, 1.104 d 333.15 Exp. 0.9932 1.0879 1.0908 1.0947 a a a Lit. 0.9932 1.0905 1.0932 1.0970a, 1.0974 c 343.15 Exp. 1.0887 Lit. 1.0916c 353.15 Exp. 1.0819 Lit. 1.0854c 363.15 Exp. 1.0744 Lit. 1.0791c ____________________________________________________________________________________________________________ a Ref 19, bRef 20, cRef 21, dRef 23 Uncertainties (standard deviations): eu(ρ) = ± 0.0001 g/cm3, fu(p) = ± 0.005 MPa, gu(x1) = ± 10 3, hu(T) = ± 0.05 K. The reported values are average of the 3-4 densities acquired with both commerical and home-made samples.

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Table 3. Densities (ρa/g·cm-3) of ethaline (1) + water (2) mixtures at pressure (p)b = 0.101 MPa and T = 283.15 to 363.15 K as a function of mole fraction of ethaline (x1). ________________________________________________________________________________ T/Kd c

x1

283.15

293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15

0.9997

0.9982

0.9957 0.9922 0.9880 0.9832 0.9778 0.9717 0.9650

0.0999

1.0457

1.0420

1.0378 1.0332 1.0283 1.0233 1.0176 1.0112 1.0042

0.1999

1.0724

1.0677

1.0628 1.0576 1.0523 1.0472 1.0414 1.0349 1.0277

0.3000

1.0889

1.0837

1.0785 1.0731 1.0675 1.0623 1.0564 1.0499 1.0426

0.3998

1.0998

1.0944

1.0889 1.0833 1.0777 1.0724 1.0665 1.0599 1.0525

0.4996

1.1070

1.1015

1.0958 1.0902 1.0846 1.0793 1.0733 1.0666 1.0593

0.5996

1.1122

1.1066

1.1009 1.0953

1.1160

1.1103

1.1046 1.0989 1.0932 1.0879 1.0819 1.0752 1.0677

1.1188

1.1131

1.1074 1.1017 1.0961 1.0908 1.0847 1.0780 1.0705

0.8997

1.1213

1.1155

1.1097 1.1040 1.0983 1.0930 1.0869 1.0802 1.0727

1.0000 (Ethaline)

1.1229

1.1171

1.1114 1.1057 1.1001 1.0947 1.0887 1.0819 1.0744

0.6974

A

M

ED

A CC

0.7992

N

0.0000 (Water)

EP T

U

________________________________________________________________________________

1.0896 1.0843 1.0783 1.0716 1.0642

Uncertainties (standard deviations): au(ρ) = ± 0.0001 g/cm3, bu(p) = ± 0.005 MPa, cu(x1) = ± 103, du(T) = ± 0.05 K. The reported values are average of the 3-4 densities acquired with both commerical and home-made samples.

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Table 4 Densities (ρa/g·cm-3) of maline (1) + water (2) mixtures at pressure (p)b = 0.101 MPa and T = 283.15 to 363.15 K as a function of mole fraction of maline (x1). ________________________________________________________________________________ c

T/K b

x1

283.15 293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15

U

_________________________________________________________________________________________ 0.9997 0.9982 0.9956 0.9922 0.9881 0.9832 0.9778 0.9717 0.9650

0.0999

1.0796 1.0750 1.0700 1.0648 1.0593 1.0541 1.0483 1.0417 1.0345

0.1998

1.1185 1.1130 1.1073 1.1016 1.0957 1.0904 1.0843 1.0776 1.0701

0.2997

1.1410 1.1352 1.1293 1.1234 1.1175 1.1120 1.1059 1.0990 1.0914

0.4000

1.1560 1.1500 1.1439 1.1379 1.1319 1.1264 1.1202 1.1132 1.1055

0.5000

1.1667 1.1606 1.1545 1.1485 1.1425 1.1369 1.1306 1.1236 1.1158

0.6000

1.1747 1.1684 1.1621 1.1560 1.1497 1.1441 1.1377 1.1306 1.1228

A

M

ED

A CC

0.7988

EP T

0.6982

N

0.0000 (water)

1.1805 1.1741 1.1678 1.1616 1.1555 1.1498 1.1435 1.1363 1.1284 1.1852 1.1788 1.1724 1.1662 1.1600 1.1544 1.1480 1.1408 1.1329

0.8969

1.1887 1.1824 1.1760 1.1696 1.1634 1.1577 1.1513 1.1441 1.1361

1.0000 (maline)

1.1915 1.1851 1.1786 1.1723 1.1660 1.1603 1.1540 1.1466 1.1388

(Predicted)e

________________________________________________________________________________ Uncertainties (standard deviations): au(ρ) = ± 0.0001 g/cm3, bu(p) = ± 0.005 MPa, cu(x1) = ± 103, du(T) = ± 0.05 K.

e

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Could not acquire due to bubble formation within the sample at these temperatures.

M

A

N

U

The reported values are average of the 3-4 densities acquired with both commerical and home-made samples.

ED

Table 5. Result of the regression analysis of density (/g.cm-3) versus temperature (T/K) data according to equation: /(g.cm-3) = o/(g.cm-3) + a(T/K) + b(T/K)2 for ethaline (1) + water (2) mixtures over the temperature range (283.15 to 363.15) K. Standard deviations are given as ± in parentheses. _____________________________________________________________________________________________________

0 (g.cm3)

EP T

x1

a × 103

b × 106

r2

___________________________________________________________________________ 0.755 (± 0.010) 1.879 (± 0.064) 3.585 (± 0.099)

0.9998

0.0999

0.970 (± 0.012) 0.877 (± 0.074) 2.152 (± 0.114)

0.9998

0.1999

1.072 (± 0.020) 0.428 (± 0.125) 1.515 (± 0.193)

0.9996

0.3000

1.120 (± 0.024) 0.244 (± 0.148) 1.259 (± 0.228)

0.9995

0.3998

1.152 (± 0.027) 0.122 (± 0.166) 1.088 (± 0.257)

0.9994

A CC

0.0000

1.165 (± 0.028) 0.090 (± 0.173) 1.045 (± 0.027)

0.9994

0.5996

1.175 (± 0.029) 0.064 (± 0.180) 1.011 (± 0.028)

0.9993

0.6974

1.182 (± 0.030) 0.041 (± 0.185) 0.980 (± 0.287)

0.9993

0.7992

1.183 (± 0.030) 0.054 (± 0.189) 0.999 (± 0.292)

0.9993

0.8997

1.191 (± 0.031) 0.022 (± 0.194) 0.954 (± 0.299)

0.9992

1.0000

1.187 (± 0.031) 0.055 (± 0.193) 1.004 (± 0.298)

U

0.9992

N

SC RI PT

0.4996

A CC

EP T

ED

M

A

______________________________________________________________________________

SC RI PT

Table 6. Result of the regression analysis of density (/g.cm-3) versus temperature (T/K) data according to equation: /(g.cm-3) = o/(g.cm-3) + a(T/K) + b(T/K)2 for maline (1) + water (2) mixtures over the temperature range (283.15 to 363.15) K. Standard deviations are given as ± in parentheses. ________________________________________________________________________ x1

0 (g.cm3)

a × 103

b × 106

r2

U

_____________________________________________________________________________________________________________

0.756 (±0.010)

1.874 (±0.061) 3.579 (±0.095) 0.9999

0.0999

1.082 (±0.019)

0.421 (±0.121) 1.514 (±0.187) 0.9997

0.1998

1.179 (±0.026)

0.080 (±0.163) 1.044 (±0.252) 0.9994

0.2997

1.216 (±0.029)

0.4000

1.238 (±0.031)

0.037 (±0.190) 0.899 (±0.294) 0.9993

0.5000

1.249 (±0.032)

0.032 (±0.197) 0.915 (±0.305) 0.9993

A

M

ED

EP T

0.6000

N

0.0000

0.001 (±0.177) 0.943 (±0.274) 0.9994

1.275 (±0.032)

0.135 (±0.196) 0.775 (±0.304) 0.9993

1.283 (±0.034)

0.150 (±0.211) 0.753 (±0.327) 0.9992

1.288 (±0.035)

0.153 (±0.217) 0.752 (±0.336) 0.9991

0.8969

1.293 (±0.033)

0.157 (±0.204) 0.755 (±0.315) 0.9993

1.0000

1.303 (±0.035)

0.200 (±0.215) 0.690 (±0.333) 0.9992

0.6982

A CC

0.7988

__________________________________________________________________________

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Table 7. Result of the regression analysis of density (/g.cm-3) of ethaline versus mole fraction data according to equation:

 ( g .cm 3 )   0 ( g .cm 3 )  a[1  exp(bx1 )] for ethaline (1) + water (2) mixtures over the temperature range (283.15 to 363.15) K. Standard deviations are given as ± in parentheses.

0 ×102(g.cm3)

a

b

r2

N

T (K)

U

______________________________________________________________________________

1.001 (±0.001)

0.122 (±0.002)

4.304 (±0.135)

0.9988

293.15

0.999 (±0.001)

0.118 (±0.001)

4.232 (±0.127)

0.9989

303.15

0.997 (±0.001)

0.115 (±0.001)

4.178 (±0.126)

0.9989

313.15

0.993 (±0.001)

0.112 (±0.001)

4.129 (±0.124)

0.9989

EP T

ED

M

283.15

323.15

0.989 (±0.001)

0.111 (±0.001)

4.088 (±0.123)

0.9989

333.15

0.984 (±0.001)

0.111 (±0.001)

4.088 (±0.123)

0.9989

343.15

0.979 (±0.001)

0.110 (±0.001)

4.088 (±0.123)

0.9989

353.15

0.973 (±0.001)

0.109 (±0.001)

4.088 (±0.123)

0.9989

A CC 363.15

A

_____________________________________________________________________________

0.966 (±0.001)

0.109 (±0.001)

4.088 (±0.123)

0.9989

____________________________________________________________________________

SC RI PT

Table 8. Result of the regression analysis of density (ρ/g.cm−3) of maline versus mole fraction (x1) data according to equation:

 ( g .cm 3 )   0 ( g .cm 3 )  a[1  exp(bx1 )]  c[1  exp(dx1 )] for maline (1) + water (2) mixtures over the temperature range (283.15 to 363.15) K. Standard deviations are given as ± in parentheses.

__________________________________________________________________________________________

0 ×10 2(g.cm3)

a

b

c

d

r2

U

T/K

99.970 (±0.000)

0.076 (±0.001)

293.15

99.820 (±0.000)

0.074 (±0.001)

303.15

99.560 (±0.000)

313.15

2.637 (±0.011)

1.0000

10.808 (±0.118) 0.122 (±0.001)

2.586 (±0.025)

0.9999

0.071 (±0.002)

10.653 (±0.183)

0.120 (±0.001)

2.601 (±0.039)

0.9999

99.220 (±0.000)

0.069 (±0.002)

10.604 (±0.189)

0.120 (±0.001)

2.634 (±0.039)

0.9999

323.15

93.810 (±0.000)

0.067 (±0.003)

10.433 (±0.304)

0.119 (±0.002)

2.632 (±0.064)

0.9999

333.15

98.320 (±0.000)

0.067 (±0.003)

10.433 (±0.309)

0.119 (±0.002)

2.628 (±0.065)

0.9999

99.780 (±0.000)

0.068 (±0.003)

10.339 (±0.308)

0.117 (±0.002)

2.603 (±0.067)

0.9999

97.170 (±0.000)

0.066 (±0.003)

10.446 (±0.320) 0.117 (±0.002)

2.636 (±0.067)

0.9999

0.067 (±0.003)

10.351 (±0.318)

2.610 (±0.068)

0.9999

363.15

M

ED

A CC

353.15

EP T

343.15

96.500 (±0.000)

11.214 (±0.056)

0.125 (±0.000)

A

283.15

N

__________________________________________________________________________________________

0.116 (±0.002)

_____________________________________________________________________________________________

T/K

A0

283.15

− 1.2444

− 1.0161

A CC

EP T

313.15

−0.2745

r2

−0.0160

0.0697

0.3719

0.1398

0.3127

0.1840

0.2739

0.2001

0.2783

0.2044

0.2808

0.2050

0.9951

− 0.9732

0.9953

− 0.9764

−0.2728

343.15

A3

0.9945

ED

−0.3217

A

− 1.0731

M

0.9892

303.15

333.15

0.4218

N

− 1.1534

−0.3585

−0.2708

0.5046 0.9918

293.15

323.15

A2

U

−0.3300

−0.2802

A1

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Table 9. Fit parameters (Ajs) and correlation coefficient (r2) in the Redlich-Kister equation [Eq. (4)] for excess molar volume (VE) of ethaline (1) + water (2) mixtures.

0.9952 − 0.9821 0.9948

− 0.9875

−0.2775

0.2832 0.9953

363.15

− 0.9946

−0.2758

0.2831 0.9950

0.2071

SC RI PT

353.15

0.2102

A CC

EP T

ED

M

A

N

U

_____________________________________________________________________________________

ED

EP T

A CC Figure 1

A

M

N

U

SC RI PT

Figure 2

ED

EP T

A CC

A

M

N

U

SC RI PT

ED

EP T

A CC Figure 3

A

M

N

U

SC RI PT

Figure 4

ED

EP T

A CC

A

M

N

U

SC RI PT

Ffigure 5

ED

EP T

A CC

A

M

N

U

SC RI PT