Preparation and Thermal Chemical Properties of Compounds of Zinc Nitrate with Valine
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Preparation and Thermal Chemical Properties of Compounds of Zinc Nitrate with Valine S. GAO*, S. CHEN, X. YANG, and Q. SHI Department of Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Xi’an, 710069, P. R. China e-mail: [email protected] Received 12 August 2002 ◦ The solubility property of the Zn(NO3)2—Val—H2Osystemat25C in the whole composition range has been investigated by the semimicrophase equilibrium method. The corresponding phase diagrams and refractive index diagrams were constructed. From the phase equilibrium results, the in- congruently soluble compounds Zn(Val)(NO3)2 · 2H2O, Zn(Val)2(NO3)2 · H2O, and Zn(Val)3(NO3)2 · H2O were synthesized and characterized by IR, XRD, TG—DTG, as well as chemical and elemen- tal analyses. The constant-volume combustion energies of the compounds, ∆cE, determined by a precision rotating bomb calorimeter at 298.15 K, were (−10064.24 ± 5.41) J g−1,(−13523.98 ± 7.54) J g−1,and(−16116.13 ± 7.58) J g−1, respectively. The standard enthalpies of combustion for −1 these compounds, ∆cH,werecalculatedtobe(−3442.21 ± 2.25) kJ mol ,(−5971.2 ± 3.32) kJ mol−1,and(−9007.26 ± 4.24) kJ mol−1 while the standard enthalpies of formation were (−1017.34 ± 2.00) kJ mol−1,(−1742.93 ± 3.61) kJ mol−1,and(−2245.70 ± 4.73) kJ mol−1. The enthalpies of solution in condition of simulating human gastric juice (37 ◦C, pH = 1, the solution of hydrochloric acid), which were also measured by a microcalorimeter, were (22.17 ± 0.05) kJ mol−1, (14.89 ± 0.04) kJ mol−1,and(6.85± 0.07) kJ mol−1, respectively. Zinc is an essential element to the life. Many dis- (purity > 99.5 %), other regents were A. R. grade. The eases aroused from the deficiency of zinc have re- temperature fluctuation of the constant-temperature ◦ ceived considerable attention worldwide. L-α-Amino water was ± 0.05 C; WZS-1 Abbe refractometer was acids are basic units of proteins. L-α-Valine is one made in the Shanghai Shiyan Apparatus Factory, the of eight species of amino acids that have to be ab- temperature of that fluctuated within ± 0.2 ◦C; ZD-2 sorbed from food due to being not synthesized by or- automatic potentiometric titrator was from the Appa- ganism. The compounds of L-α-valine and essential el- ratus Factory of Shanghai. The IR spectra of the com- ements as additives widely used in such fields as food- pounds were obtained with Bruker EQ UINOX-550 stuffs, medicine, and cosmetics [1—3] have a broader model infrared spectrophotometer (KBr pellets). TG prospect for application. Simply put, a better under- and DTG data were determined by a Perkin—Elmer standing of the research into the compounds of the thermogravimetric analyzer. All TG—DTG tests were microelements and L-α-valine is thus of considerable performed under a dynamic atmosphere of dry oxy- practical and fundamental importance. gen at a flow rate of 60 cm3 min−1, the heating rate In the previous papers, the phase chemistry of used was 10 K min−1 and sample masses were approx- the ZnSO4/ZnCl2/ZnAc—Val—H2O system and the imately 1 mg. Carbon, hydrogen, and nitrogen analy- properties of the corresponding solid compounds have ses were carried out on a 2400 type elemental analyzer been reported [4—7]. In the forthcoming work, the (PE Company, U.S.A.). 2+ phase chemistry of the Zn(NO3)2—Val—H2Osystem Zn was determined complexometrically with at 25 ◦C was investigated by the semimicrophase equi- EDTA. Valine was analyzed by the formalin method. 2+ librium method [8]. Three new solid compounds of zinc The Zn was removed by precipitating with K2C2O4 with L-α-valine were prepared under the guidance of before it was titrated. The solubility of L-α-valine was the phase equilibrium diagram, and thermal chemical 4.46 % at 25 ◦C in our experiment, and the value in properties for these compounds were determined and Ref. [9] is 8.13 % while the solubility of Zn(NO3)2 was discussed. 55.91 % and the value in Ref. [10] is 55.98 %. The phase diagram of the ternary system was con- EXPERIMENTAL structed by the semimicrophase equilibrium method. The constant-volume combustion energies of the com- Zn(NO3)2 · 6H2OandL-α-valinewereB.R.grade pounds have been determined by an RBC-II type ro- *The author to whom the correspondence should be addressed. Chem.Pap.58(2) 87—92 (2004) 87 S. GAO, S. CHEN, X. YANG, Q. SHI (China, Southwest Institute of Electronic Engineer- ing), which was equipped with two 15 cm3 vessels (Fig. 1) [13]. After reaching equilibrium, the spacers of the sample and reference vessels were depressed si- multaneously and the samples were mixed. The mi- crocalorimeter was calibrated by the Joule effect [13]. The experimental precision and accuracy were checked by measuring the enthalpy of crystalline KCl in deion- ized water at 298.15 K. The experimental value of H◦ ± −1 ∆sol m of (17.238 0.048) kJ mol was in good H◦ ± −1 agreement with ∆sol m of (17.241 0.018) kJ mol [14]. The measured precision of the microcalorimeter was 0.5 %. Fig. 1. Sketch of calorimetric vessels. 1. Calorimetric cell, 2. RESULTS AND DISCUSSION solid sample, 3. spacer, 4. solution. The solubility properties of the ternary system Zn(NO3)2—Val—H2O have been investigated in the tating bomb calorimeter [11]. Benzoic acid had an whole composition range by the semimicrophase equi- isothermal heat of combustion at 25 ◦Cof−26434 J librium method at 25 ◦C.Basedon28runs(Ta- g−1. The calibration for the apparatus and tempera- ble 1) of phase equilibrium data, the phase diagram ture, the determination processes of the experiment, and refractive index diagram have been constructed and the analyses of final products were identical with and are shown in Fig. 2. The solubility and re- Refs. [11, 12]. fractive index data of the system are given in Ta- The enthalpies of solution for the compounds were ble 1. obtained using a microcalorimeter, type RD496-III Clearly, it is evident for the system Zn(NO3)2— ◦ Table 1. Solubility and Refractive Index of the Zn(NO3)2—Val—H2OSystemat25 C w(Intermediate)/% w(Liquid phase)/% Wet residue/% w(Dry solid)/% Equilibrium 25 Run nD solid phase Zn(NO3)2 Val Zn(NO3)2 Val Zn(NO3)2 Val Zn(NO3)2 Val 1 – – – 4.46 – – – 100.0 1.342 5 Val 2 5.01 24.14 6.64 4.12 3.99 43.08 61.64 38.36 1.346 7 Val 3 10.11 22.83 12.88 5.01 8.32 38.04 72.00 28.00 1.354 8 Val 4 15.05 18.85 17.39 6.58 12.81 32.12 72.55 27.45 1.361 0 Val 5 19.93 15.48 21.92 8.89 16.11 32.84 71.15 28.85 1.362 4 Val 6 21.92 22.95 15.10 11.14 17.28 38.55 57.55 42.45 1.369 8 Val + E 7 25.01 21.00 15.10 11.14 24.93 32.16 57.55 42.45 1.369 8 Val + E 8 27.96 24.13 15.10 11.14 29.29 35.65 57.55 42.45 1.369 8 Val + E 9 29.82 14.47 29.31 12.29 30.55 26.58 70.46 29.54 1.410 5 E 10 33.18 20.99 33.12 14.21 33.28 31.97 69.98 30.02 1.402 0 E 11 36.23 19.76 36.75 16.56 35.81 32.10 68.94 31.06 1.428 7 E + D 12 36.98 14.06 36.75 16.56 37.11 33.99 68.94 31.06 1.428 7 E + D 13 38.20 26.01 36.75 16.56 39.85 35.22 68.94 31.06 1.428 7 E + D 14 39.99 22.95 39.31 15.14 40.89 32.04 72.19 27.81 1.430 7 D 15 42.65 20.06 42.66 13.88 42.65 28.87 75.45 24.55 1.435 5 D 16 45.58 20.00 45.92 13.29 44.54 30.05 77.55 22.45 1.452 8 D + C 17 46.99 25.85 45.92 13.29 47.39 32.99 77.55 22.45 1.458 2 D + C 18 49.66 20.97 45.92 13.29 51.98 26.13 77.55 22.45 1.452 8 D + C 19 48.81 14.10 47.96 11.81 51.11 21.00 80.24 18.76 1.456 1 C 20 53.71 14.82 52.91 8.91 54.19 21.98 85.59 14.41 1.478 5 C 21 56.78 9.93 56.82 7.93 56.24 16.96 87.75 12.25 1.483 3 C + S 22 58.62 8.74 56.82 7.93 59.99 9.86 87.75 12.25 1.483 3 C + S 23 59.98 6.78 56.82 7.93 62.13 5.97 87.75 12.25 1.483 3 C + S 24 60.10 4.02 56.82 7.93 61.49 2.31 87.75 12.25 1.483 3 C + S 25 58.18 4.38 55.97 6.21 60.84 2.28 90.01 9.99 1.469 0 S 26 57.98 2.99 55.33 4.24 59.82 2.02 92.88 7.12 1.460 2 S 27 57.86 1.02 55.41 1.78 60.20 0.66 96.89 3.11 1.451 5 S 28 57.96 – 55.91 – – – 100.00 – 1.445 0 S 88 Chem.