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Brazilian Journal of Chemical Engineering

versão impressa ISSN 0104-6632versão On-line ISSN 1678-4383

Braz. J. Chem. Eng. vol.34 no.1 São Paulo jan./mar. 2017 


Solubility of 1-Adamantanamine hydrochloride in Six Pure Solvents between 283.15 K and 333.15 K

Yu-Jiao Tu1  3  4 

Zheng-Ming Yi2  * 

Jing Liao2 

Shu-Heng Song2 

1Department of Chemical Science and Technology, Kunming University, Kunming, 650214, China.

2College of Chemical Engineering, Xiangtan University, Xiangtan, 411105, China. Fax: +86 0731 58298330. E-mail:

3Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, 650224, China.

4Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, 650224, China.


The solubility of 1-adamantanamine hydrochloride (1-AH) in ethanol, acetic acid, distilled water, N -methylpyrrolidone (NMP), N,N -dimethylformamide (DMF) and dimethylacetamide (DMAC) between 283.15 K and 333.15 K was measured using a laser monitoring observation technique. Results of these measurements were correlated with the NRTL equation and a semi-empirical equation. For six solvents studied, the data are well fitted with the two equations, which can be used as a useful model in the production process of 1-AH.

Keywords: Solubility; 1-Adamantanamine hydrochloride; Modified Apelblat equation


1-Adamantanamine hydrochloride (abbreviated 1-AH CAS Registry No. 665-66-7, structural formula listed as Figure 1) (Schild and Sutton, 1965; Oxford and Schild, 1965), is a synthetic organic compound clinically used as an antiparkinsonism agent, as well as an antiviral drug (Davies et al., 1964; Van Voris et al., 1981; Bryson, 1982; Paci et al., 2001). Since 1-AH is highly soluble, relatively non-toxic and bio logically stable (Schild and Sutton, 1965) it merited further extensive investigation.

Figure 1 Structure of 1-Adamantanamine hydrochloride. 

As we know, the solubility of a drug is not only essential information in the drug discovery process, but also an important property in the recrystallization stage of solid drugs (Shayanfar et al., 2008; Nti-Gyabaah et al., 2008).

Crystallization processes are key steps that de termine the quality of the final product. Crystal habit plays an important role in affecting the crystal prod uct physicochemical properties, such as solubility, dissolution rate, compressibility, and bulk density, that have an effect on the product biological activity and production cost. The solubility of solid com pounds in different solvents played a crucial role in the determination of proper solvents and the devel opment and operation of the crystallization process (Wu et al., 2010; Pankaj and Murthy, 2010).

Therefore, the solubility of 1-AH in different sol vents directly affects the size of crystal formation, crystal habit, yield, and cost of production. Hence, it is necessary to know the solubility of 1-AH in pure and mixed solvents. However, it was found that there were few reported experimental solubility data of 1-AH.

In recent research, the dynamic method is used as a common approach in solubility measurement (Liu et al., 2011), which incorporates laser techniques to monitor the dissolution process of the solid solute. Given the overwhelming advantages of the dynamic method (Jouyban-Guaramaleki et al., 2014; Qiao et al., 2014), it is also used in this research to measure the solubility of 1-AH in six pure organic solvents, including ethanol, acetic acid, distilled water, NMP, DMF and DMAC between 283.15 K and 333.15 K at atmospheric pressure. In addition, the experimental solubility results in pure solvents were correlated with the modified Apelblat equation and the NRTL equation, which proved good agreement with experi mental data.



ADA-NH3Cl used during the solubility measure ments had a mass purity of 0.998 and was purchased from China Langchem Inc. Its mass fraction purity was determined by HPLC and was purified through crystallization twice in distilled water before utiliza tion. The X-ray diffraction (XRD) spectra of samples are shown in Figure 2. Other reagents were analyti cal research grade reagents from Shanghai Chemical Reagent Co.

Figure 2 XRD pattern of 1-Adamantanamine hydrochloride: a, samples; b, standard XRD pattern.Apparatus and Procedure. 

The solubility of 1-AH was determined by a laser monitoring dynamic method. The experimental in strument and procedure were similar to those de scribed in the previous literature 14-18 . A predeter mined excess mass of solvent (about 30 g) and a known mass of solute were added to a jacketed glass vessel (about 200 mL) with the laser light adjusted accordingly. The solution in the vessel was main tained at a constant temperature by water circulating through the outer jacket from a thermostatic water bath (type MPG-10C, China). The temperature of the solution was determined by a mercury glass ther mometer with an uncertainty of ± 0.05 K. The pro cess of dissolution was facilitated by continuously stirring at a desired temperature. At the beginning of the experiment, the intensity of the laser beam dropped due to a large number of undissolved 1-AH particles suspended in the solution. As the solid par ticles dissolved, the intensity of the laser beam in creased. When the solid particles dissolved com pletely, the laser beam intensity reached a maximum level, and the solution in the vessel was clear. Then additional solid solute of known mass (about 1 mg to 3 mg) was added to the solution in the vessel.

This process was repeated several times until the maximum intensity of the laser beam started to de cline after the last addition of solute. The time inter val depended on the dissolution speed of 1-AH, usu ally more than 60 min. When the intensity of the laser beam could no longer reach 90% of the maxi mum, the mixture was considered to be in phase equilibrium. The total amount of the solute added to the vessel was recorded. Then the undissolved solute was separated and identified to be 1-AH by X-ray diffraction (XRD). Through all of the experiments in this work, polymorphic transformation was not found.

The weight of all the chemicals was measured by an electronic analytical balance (Sartorius CP124S, Germany) with the precision of ± 0.0001 g. In order to ensure the accuracy of the experimental data, all of the above processes were repeated more than three times, and the average value was taken as the final experimental value. The standard uncertainty of the measured solubility values was estimated to be less than 2%. The uncertainty in the solubility values can be due to uncertainties in the weighing procedure, temperature measurements, excess addition of solute, and instabilities of the water bath.


Modified Apelblat Equation

The Apelblat equation is the commonly used (Hefter and Tomkins, 2003; Wang et al., 2005; Li et al., 2010; Apelblat and Manzurola, 1997; Kondepudi and Prigogine, 2002) semi-empirical expression which is used to correlate experimental solubilities with calculated ones and to evaluate the influence of tem perature on the mole fraction solubility of the solute.

According to the solid-liquid phase equilibrium theory, the relationship between solubility and tem perature is generally modeled by (Apelblat and Man zurola, 1997):

lnx1=ΔHf,1RTf,1Tf,1T1ΔCpf,1RTf,1T1+ΔCpf,1RlnTf,1Tlnγ1 (1)

where x1, y1, ∆Hf,1, ∆Cpf,1, Tf,1, R and T stand for the mole fraction of the solute, activity coefficient, en thalpy of fusion, difference in the solute heat capaci ty between the solid and liquid at the melting tem perature, melting temperature of the solute, gas con stant, and equilibrium temperature in the saturated solution, respectively. The values of ∆Hf, ∆C pf, Tf were estimated by ASPEN PLUS software version 8.4 (∆Hf =-1.3673×108 J/kmol, ∆C pf=23.0446 kJ/(kmol∙K), T f = 300 ℃).

Equation (2) can be written as

lnχ1=A+BT+lnT 2

where x1 is the mole fraction solubility of 1-AH, T stands for the absolute temperature (K), A, B and C are the dimensionless parameters.

NRTL Model

In the binary system, the activity coefficient can be calculated by the following formula (Domanska and Marciniak, 2003):

lnγ1=χ22[τ21G212(χ1+G21χ2)2+τ12G122(χ2+G12χ1)2] 3


G12=exp(α12τ12)G21=exp(α21τ21) 4

τ12=g12g12RTτ21=g21g21RT 5

where ∆g12 (= g12 - g22) and ∆g21 (=g21 - g11) are cross in teraction energy parameters, independent of tempera ture and composition. In addition, α12 is a constant that reflects the non-randomness of the mixture and its value generally varies between 0.20 and 0.47 (Wei and Pei, 2008). Different values of α12 were chosen to correlate the solubility data of 1-AH. It turns out that α12 = 0.30 is the most suitable value because of the smallest relative deviation for the measurement system.


The mean values were used to calculate the mole fraction solubility x1 based on

x1=m1/M1m1/M1+m2/M2 (6)

where m1 and m2 are the mass of the solute and sol vent respectively, M1 and M2 the molecular weight of the solute and solvent respectively. The solubility data of 1-AH in distilled water, acetic acid, ethanol, DMF, NMP and DMAC between 283.15 K and 333.15 K are listed in Table 1.

Table 1 Mole fraction solubility (x1) of 1-adamantanamine hydrochloride in selected solvents with the temperature range from 278.15 to 333.15 K and pressure p = 0.1 MPaa

T (K) 100x1exp 100x1calc T (K) 100x1exp 100x1calc
Apelblat NRTL Apelblat NRTL
278.35 1.863 1.873 1.815 307.95 2.700 2.730 2.678
282.75 2.007 2.029 2.033 313.15 2.803 2.818 2.805
288.05 2.213 2.207 2.292 318.15 2.857 2.881 2.888
292.45 2.405 2.345 2.406 322.85 2.898 2.922 2.934
298.65 2.536 2.519 2.499 328.95 2.961 2.949 2.985
302.65 2.620 2.618 2.575 333.15 2.979 2.950 2.932
278.35 1.414 1.436 1.430 307.95 1.829 1.835 1.859
282.75 1.503 1.502 1.501 313.15 1.873 1.892 1.887
288.25 1.602 1.582 1.577 318.15 1.905 1.943 1.859
292.45 1.662 1.641 1.641 322.85 1.975 1.986 1.973
298.65 1.731 1.723 1.737 328.95 2.047 2.037 2.050
302.65 1.784 1.773 1.806 333.15 2.094 2.068 2.099
283.45 1.849 1.854 1.928 312.85 4.178 4.118 4.250
288.15 2.226 2.225 2.310 318.15 4.399 4.403 4.467
293.25 2.643 2.644 2.728 323.15 4.525 4.606 4.590
298.45 3.075 3.073 3.158 328.15 4.690 4.738 4.752
303.25 3.467 3.453 3.546 333.35 4.874 4.800 4.932
308.25 3.809 3.820 3.885
Acetic acid
293.35 1.132 1.125 1.138 318.15 2.999 2.943 3.003
298.05 1.377 1.353 1.386 323.25 3.601 3.573 3.596
303.35 1.606 1.664 1.617 328.15 4.339 4.299 4.327
308.15 1.978 2.005 1.990 333.15 5.097 5.184 5.081
313.25 2.456 2.440 2.465
278.05 2.660 2.660 2.771 308.15 6.399 6.331 6.414
282.95 3.193 3.193 3.284 313.25 6.928 6.953 6.937
288.45 3.833 3.838 3.902 318.65 7.481 7.572 7.485
293.05 4.356 4.407 4.410 323.35 7.986 8.064 7.987
298.35 5.128 5.082 5.165 328.05 8.485 8.504 8.484
303.35 5.777 5.723 5.801 333.12 9.013 8.914 9.014
283.55 4.126 4.201 4.040 313.25 6.452 6.461 6.390
287.85 4.651 4.590 4.759 318.15 6.700 6.692 6.661
293.35 5.162 5.069 5.219 323.25 6.884 6.878 6.889
298.05 5.466 5.453 5.478 328.15 7.012 7.004 7.047
303.35 5.822 5.850 5.792 333.15 7.094 7.079 7.126
308.15 6.081 6.169 6.047

aThe standard uncertainties u are u(T) = 0.1 K, ur(p) = 0.05, ur(x) =0.03

To evaluate the correlation results and select the most suitable model for 1-AH solubility in pure sol vents, the relative deviation (RD %) and the average relative deviation (ARD %) were calculated. The relative deviation and the average relative deviation are defined as

RD%=x1,iexpx1,icalx1,iexp (7)

ARD%=100Ni=1N|x1,iexpx1,icalx1,iexp| (8)

The parameters of the mentioned equations and the root mean square deviations ( RMSD) are listed in Table 2. The RMSD is defined as (Douglas, 1997):

RMSD=i=1N(x1,iexpx1,ical)2N11/2 (9)

Table 2 Parameters of Equation (2) for 1-adamantanamine hydrochloride in Different Solvents. 

Solvent Apelblat NRTL
A B C RMSD% Δg12 (J·mol−1) Δg21 (J·mol−1) RMSD%
DMAC 187.88 -9324.5 -28.133 0.027 2725.3 14731.3 0.039
DMF 52.886 -3102.2 -8.1694 0.02 -3524.8 22243.5 0.02
NMP 437.00 -21630 -64.578 0.043 1626.3 11973.3 0.20
acetic acid -118.93 2139.7 18.859 0.048 -1061.8 3247.6 0.47
water 261.07 -13673 -38.297 0.058 1377.1 7453.6 1.61
ethanol 217.28 -10890 -32.235 0.05 9692.3 9193.3 0.05

Table 3 lists the ARD % of different correlation models. The average relative deviations of the two models are 0.86% (Apelblat) and 1.13% (NRTL). Therefore, the Apelblat model fits well with the experimental solubility data of 1-AH in pure solvents.

Table 3 ARD% of different models in pure solvents. 

Solvent Water DMF DMAC NMP Acetic acid Ethanol
Apelblat 0.6750 0.8992 0.7742 0.6316 1.4729 0.7050
NRTL 0.9688 0.9081 1.3524 2.3161 0.4149 0.8532

We can conclude from Figure 3 that: (1) Solubili ty of 1-AH is the lowest in DMF and the highest in water when the temperature is higher than 310 K; this may be because of the intermolecular interaction between solvent and solute molecules. 1-AH is a salt and most salts can be dissolvent in water, especially in hot water. In addition, the structure of 1-AH is much more complicated and is harder to disperse in organic solvents. Hence, solvents which have com plicated structures such as DMF show a lower solu bility value than in water. (2) Solubility increases with temperature in all the selected solvents; (3) the solubility curves of 1-AH in NMP and ethanol show almost the same curvature, which may mean that both solubilities have the same sensitivity to temper ature though their solubility values are different. The reason for this phenomenon needs to be studied further.

Figure 3 Mole fraction solubility of 1-Adamantanamine hydrochloride (x1) in different solvents between 278 K and 333 K: ◄, NMP; ▷ acetic acid; ▼, DMAC; ▲, water; △, DMF; ▽, ethanol. 

The solid line solubility curve was calculated by the modified Apelblat equation.


The solubility of 1-adamantanamine hydrochlo ride (1-AH) in ethanol, acetic acid, distilled water, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF) and dimethylacetamide (DMAC) between 283.15 K and 333.15 K were measured using a laser monitoring observation technique. The solubilities in all selected solvents are functions of temperature and increase with the rise of temperature.

The modified Apelblat equation based on solid-liquid phase equilibrium principles and the NRTL equation were used to correlate the solubility data of 1-AH in these solvent systems. The RDs of the mod ified Apelblat Equation among all of these values does not exceed 1.82%. The average relative devia tion of the two models are 0.86% (Apelblat) and 1.13% (NRTL). Therefore, the modified Apelblat equation fits well with the experimental solubility data of 1-AH in pure solvents.

The solubility values calculated by the modified Apelblat equation and NRTL equation show good agreement with experimental values. Both the exper imental solubility and correlation equation can be used as essential data in the purification process of 1-AH, as well as good support for further development of solubility models for 1-AH.


We are grateful for the financial support of the National Natural Science Foundation of China (No. NNSFC 21306158), and General project of Hunan Provincial Education Department (grant no. 13C911).


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Received: December 21, 2014; Revised: November 02, 2015; Accepted: December 08, 2015

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