J. Chem. Thermodynamics 38 (2006) 565–571 www.elsevier.com/locate/jct

The solubilities of benzene polycarboxylic in

Alexander Apelblat a,*, Emanuel Manzurola a, Nazmia Abo Balal b

a Department of Chemical Engineering, Ben Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel b Negev Academic College of Engineering, Beer Sheva, Israel

Received 30 May 2005; received in revised form 14 July 2005; accepted 14 July 2005 Available online 26 August 2005

Abstract

The solubilities in water of all benzene polycarboxylic acids are discussed, using data determined in this work (benzoic, tere- phthalic, trimellitic, trimesic, and pyromellitic acids) and available from the literature (benzoic, phthalic, isophthalic, terephthalic, hemimellitic, trimelitic, trimesic, mellophanic, prehnitic, pyromellitic, benzene-pentacarboxylic and mellitic acids). The apparent molar enthalpies of solution at the saturation point for these benzene polycarboxylic acids were determined from the temperature dependence of the solubilities. Ó 2005 Elsevier Ltd. All rights reserved.

Keywords: Benzene polycarboxylic acids; Saturated aqueous solutions; Molar enthalpies of solution

1. Introduction cal (antifungal) aids and in the preservation of foods, fats, and fruit juices [1–5]. Ultra-pure benzoic serves There are 12 benzene carboxylic acids; one monobasic as a standard in titrimetric and calorimetric experi- acid (benzoic acid), three dibasic acids {benzene-1,2- ments. The higher benzene polycarboxylic acids are less dicarboxylic (phthalic acid), benzene-1,3-dicarboxylic important commercially. However, as they are formed (isophthalic acid), and benzene-1,4-dicarboxylic (tere- by the drastic oxidation of , coals, wood lignin phthalic acid)}, three tribasic acids {benzene-1,2,3-tri- and similar materials, they have geochemical and eco- carboxylic (hemimellitic), benzene-1,2,4-tricarboxylic logical significance. They are also of interest in the envi- (trimellitic acid), and benzene-1,3,5-tricarboxylic (trime- ronmental chemistry of natural due to the sic acid)}, three tetrabasic acids {benzene-1,2,3, formation of toxic metal-benzene polycarboxylic ligands 4-tetracarboxylic (mellophanic acid), benzene-1,2,3,5- [6]. tetracarboxylic (prehnitic acid) and benzene-1,2,4,5-tet- The solubility of benzene polycarboxylic acids in racarboxylic (pyromellitic acid)}, one pentabasic acid water as a function of temperature varies significantly. (benzene-pentacarboxylic acid), and one hexabasic acid Usually, the solubility is small and even extremely (benzene-hexacarboxylic (mellitic) acid). small for terephthalic acid. The accuracy and the agree- Lower benzene polycarboxylic acids (especially ben- ment between different solubility experiments is not zoic and phthalic acids) are produced in large quantities. very good [7–9]. It is clear from the recent tabulation Along with their various ester derivatives are used as of solubilities of organic compounds in water (prepared intermediates in the preparations of resins, plasticizers, by Yalkovsky and He [9]) that only the solubilities of dyes, inks, adhesives, alkaloidal solutions, pharmaceuti- benzoic and phthalic acids are well documented. Less attention was paid to other benzene polycarboxylic * Corresponding author. Tel.: +972 8 6461487; fax: +972 8 6472916. acids where the solubilities were determined only once E-mail address: [email protected] (A. Apelblat). at one or few temperatures in the context of separation

0021-9614/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2005.07.007 566 A. Apelblat et al. / J. Chem. Thermodynamics 38 (2006) 565–571 procedures. From all the investigations mentioned TABLE 1 here, only two considered also the composition of the Solubility m of benzoic, terephtalic, mellitic, trimesic, and pyromellitic solid phase in equilibrium with the saturated solutions acids in water as a function of temperature T (Ward and Cooper [10] for benzoic acid and phthalic T/K m/m acid; Yukhno and Bikkulov [11] for all 12 benzene Benzoic acid polycarboxylic acids which were also prepared by 281.15 0.0173 them). In the temperature range T = 273.15 K to 295.65 0.0297 300.15 0.0340 T = 323.15 K, they postulated that crystals of benzoic 305.15 0.0398 acid, isomeric phthalic acids, trimellitic acid, prehnitic 309.65 0.0407 acid, and mellitic acid are anhydrous. Hemimellitic 318.15 0.0594 acid and pyromellitic acid exist as dihydrates, trimesic 333.15 0.0976 acid is monohydrate and mellophanic acid and ben- 337.15 0.1210 zene-pentacarboxylic acid form a number of hydrates in the solid state. Since the Yukhno and Bikkulov pa- Terephthalic acid per is not easily available, it is worthwhile to mention 278.15 0.000772 284.15 0.000563 their results, the mellophanic acid trihydrate changes to 288.65 0.000427 the dihydrate at about T = 274.04 K and becomes 293.15 0.000381 anhydrous above T = 315.10 K. The benzene-penta- 298.65 0.000390 carboxylic acid pentahydrate changes to the trihydrate 303.15 0.000404 at about T = 285.40 K and becomes monohydrate 307.15 0.000444 312.15 0.000455 above T = 305.85 K. Both acids easily form metastable 317.15 0.000450 supersaturated solutions. 322.15 0.000487 In this work, the solubilities of commercially avail- 326.65 0.000550 able benzene polycarboxylic acids are presented. For 331.65 0.000624 completeness of discussion, previously reported solu- bilities of polycarboxylic acids [7–12,15–24] are also Trimellitic acid included in the analysis to recommend the ‘‘best’’ sol- 280.65 0.0433 ubility curves. The molar apparent enthalpies of solu- 285.65 0.0504 tion at the saturation points are also reported. 290.15 0.0647 295.65 0.0765 300.15 0.0946 304.65 0.1144 309.15 0.1434 2. Experimental 314.15 0.1733 319.15 0.2482 Solid samples of benzoic acid (mass fraction >0.999), 323.15 0.2871 terephthalic acid (mass fraction >0.99), trimellitic acid 328.15 0.3974 331.15 0.4471 (mass fraction >0.99), trimesic acid (mass fraction >0.97) and pyromellitic acid (mass fraction 0.97) were supplied by Fluka and were used without further Trimesic acid purification. 277.15 0.00559 280.15 0.00503 The procedure of the solubility experiments was al- 282.15 0.00630 ready described in detail elsewhere [13]. After mixing 283.15 0.00598 and gravitational settling at a given temperature, 287.15 0.00794 weighed samples of saturated solutions of benzenecarb- 288.65 0.00657 oxylic acids were titrated with standardized solutions of 292.65 0.00814 293.15 0.00700 NaOH. The reported results are the average values of 297.15 0.00998 three or four determinations. 298.15 0.01077 299.15 0.01050 302.15 0.01189 304.15 0.01098 3. Results and discussion 306.65 0.01468 309.15 0.01807 The solubilities of benzoic, terephtalic, trimellitic, 311.65 0.01818 trimesic, and pyromellitic acids in water as a function of 313.65 0.01773 316.65 0.02230 temperature T are presented in table 1. The temperature 320.65 0.02648 dependence of solubility of nonelectrolytes in water, 325.65 0.03640 m/mol Æ kg1, is expressed by the Williamson equation [14] 330.15 0.03694 A. Apelblat et al. / J. Chem. Thermodynamics 38 (2006) 565–571 567

TABLE 1 (continued) TABLE 2 Coefficients A, B and C of the solubility equation (2) for benzene T/K m/m polycarboxylic acids Pyromellitic acid Acid ABCR2 278.15 0.0150 279.15 0.0168 Benzoic 223.33 7178.8 34.345 0.9946 282.15 0.0205 Phthalic 330.13 12114 50.261 0.9970 283.15 0.0226 Isophthalic 89.595 209.5 14.340 0.9925 286.15 0.0235 Terephthalic 623.75 27945 91.648 0.8743 288.15 0.0266 Hemimellitic 491.94 17917 75.543 0.9990 290.15 0.0296 Trimellitic 177.08 4529.7 27.997 0.9952 293.15 0.0329 Trimesic 169.94 4147.2 26.575 0.9579 297.15 0.0352 Mellophanic 282.34 15956 40.155 0.9964 298.15 0.0432 Prehnitic 42.677 261.2 7.193 0.9993 302.15 0.0516 Pyromellitic 287.12 8811 44.651 0.9943 306.65 0.0697 Pentacarboxylic 321.29 17257 46.251 0.9988 307.15 0.0693 Mellitic 20.529 771.5 3.332 0.9974 311.15 0.0896 319.15 0.1444 326.15 0.1947 In order to illustrate the agreement between the solu- 330.65 0.2176 bilities coming from different investigations they are plotted in figures 1 to 8. Benzoic acid was studied many times in the literature [8] and therefore only results of systematic determina- o lnðm=mÞ D HðT Þ ¼ sol ; tions in the (273.15 to 373.15) K are considered here o 1=T R 1 0.001hM m f ð Þ ½ 1 [2,7,10,11,15]. The solubility of benzoic acid is relatively o ln c f ¼ 1 þ 2 ; ð1Þ high, compared with other benzene polycarboxylic o lnðm=m Þ T acids, and therefore a reasonable agreement between where h denotes a number of water molecules in the hy- various investigations should be expected. This expecta- drate, D H(T) is the molar enthalpy of solution, c is tion is confirmed as can be seen in figure 1. sol 2 Similar to benzoic acid, the solubility of phthalic acid the activity coefficient of the solute, M1 is the of water, R is the gas constant and m =1 in water is well known [9–12,16–19,24] and concordant mol Æ kg1. In equation (1), it is assumed that the disso- (figure 2). Phthalic acid dissolves more in water than ciation of the benzene polycarboxylic acids at the satu- benzoic acid and considerably more than other isomeric ration point is small [6] and they can be treated as acids, isophthalic and terephthalic acids. nonelectrolytes or hydrated nonelectrolytes. As the In the case of isophthalic acid (figure 3) it is clear that change of activity coefficients with m near the saturation the results of Freidlin and Davidov [20] differ consider- point is unknown, the factor f is replaced by unity and ably from the measurements of other investigations the enthalpy of solution becomes the apparent molar en- [9,11,17–19,21,24]. The assumption that their solubilities thalpy of solution. If it is assumed that the enthalpy of solution depends linearly on the temperature, the inte- 0.35 gral form of equation (1) is B 0.30 lnðm=mÞ¼A þ þ C lnðT =KÞ; ð2Þ T = ð KÞ 0.25 where A, B, and C are adjustable coefficients which were determined by an unweighted multivariable least-square -1 0.20 method and R2 is the squared correction coefficient of 0.15 the regression. These coefficients are reported in table 2 /mol·kg m for benzene polycarboxylic acids. They were calculated 0.10 combining the solubilities from this work and from the literature and can be treated as the ‘‘best’’ solubility 0.05 curves. It follows from equations (1) and (2) that the appar- 0.00 270 280 290 300 310 320 330 340 350 360 370 ent molar enthalpy of solution at the saturation point is T/K DsolHðT Þ¼Rð1 0.001hM 1mÞðCT BÞ; ð3Þ FIGURE 1. Plot of solubility m of benzoic acid in water as a function where h values were taken from the Yukhno and Bikku- of temperature T. , Reference [2]; n, reference [10]; d, reference [11]; lov work [11]. m, reference [15]; and h, this work. 568 A. Apelblat et al. / J. Chem. Thermodynamics 38 (2006) 565–571

1.2 0.0025

1.0 0.0020

0.8 -1 -1 0.0015

0.6 /mol·kg /mol·kg 0.0010 m m 0.4 0.0005 0.2 0.0000 0.0 260 280 300 320 340 360 380 260 280 300 320 340 360 380 T/K

T/K FIGURE 4. Plot of solubility m of terephthalic acid in water as a d m FIGURE 2. Plot of solubility m of phthalic acid in water as a function function of temperature T. , Reference [11]; , reference [17]; n, n h of temperature T. , Reference [10]; d, reference [11]; h, reference reference [18]; , reference [20]; , reference [24]; , this work; and [12]; n, reference [16]; n, reference [18]; and m, reference [24]. ——, equation (2).

0.036 2.4 0.032 2.0 0.028

0.024 1.6 -1 -1 0.020 1.2 /mol·kg /mol·kg 0.016 m m 0.012 0.8 0.008 0.4 0.004

0.000 280 300 320 340 360 380 0.0 280 300 320 340 360 380 T/K T/K FIGURE 3. Plot of solubility m of isophthalic acid in water as a function of temperature T. d, Reference [11]; n, reference [17]; n, FIGURE 5. Plot of solubility m of trimellitic acid in water as a d reference [18]; , reference [20]; h, reference [21]; and m, reference [24]. function of temperature T. , Reference [11]; , reference [17]; n, reference [22]; and h, this work. are in the constant numerical error and therefore should be shifted (probably divided by the factor two) is in con- of the solid dispersed in the liquid phase is difficult. The tradiction with the high-temperature part of the solubil- solubility of terephthalic acid always increases with ity curve where their points would be lying considerably increasing temperature T in the determinations of Yukh- below the ‘‘expected’’ solubilities (figure 3). In the eval- no and Bikkulov [11] and Rathousky´ et al. [18], but uation of coefficients from equation (3) the Freidlin and unfortunately, these two sets of solubilities differ consid- Davidov results are excluded. erably (figure 4). In our experiments, the solubility de- Terephthalic acid has the extremely small solubility in creases up to about T = 298.15 K and above this water (table 1) and as can be seen from figure 4, the dis- temperature increases with T. The solubilities of Avi- agreement between different works is considerable dova and Khodzhaev [17] and of Freidlin and Davidov [11,17,18,20,24]. All solubilities have the same order of [20] support our results. Recently, the solubility of tere- magnitude but the temperature dependence of the solu- phthalic acid was determined by Han et al. [24], but only bility is inconsistent. The large scattering of results can above T = 301.45 K where it is clear that the solubility be perhaps attributed to the fact that in the cases of increases with T. At present, the ‘‘best’’ solubility curve low solubilities the analysis and especially the separation for terephthalic acid is considerably less accurate then A. Apelblat et al. / J. Chem. Thermodynamics 38 (2006) 565–571 569

0.040 those for other benzene carboxylic acids (table 2 and fig- ure 4). 0.035 The solubility of hemimellitic acid in water was inves- 0.030 tigated by Yukhno and Bikkulov [11] and only at two temperatures by Avidova and Khodzhaev [17] and they -1 0.025 are consistent. 0.020 There is a nice agreement between our and the Yukhno

/mol·kg and Bikkulov [11] and the Tudorovskaya et al. [22] sol- m 0.015 ubilities of trimellitic acid. However, two solubilities of Avidova and Khodzhaev [17] are considerably lower 0.010 than all others (figure 5) and they were omitted in the 0.005 calculation of the solubility curve (table 2). The solubilities of trimesic acid in water are similar to 0.000 270 280 290 300 310 320 330 those of trimellitic acid (table 1) and were determined by T/K Yukhno and Bikkulov [11], Avidova and Khodzhaev [17] and by us. As can be seen in figure 6, these three sets FIGURE 6. Plot of solubility m of trimesic acid in water as a function of of data concur in general, but our solubilities are sys- temperature T. d, Reference [11]; ; and h, this work. , reference [17] tematically higher than those of Yukhno and Bikkulov. From the two solubilities of Avidova and Khodzhaev, 0.25 one point supports the Yukhno and Bikkulov results while the other point supports ours (figure 6). Since all solubilities of trimesic acid were used in the calculation 0.20 of the coefficients of equation (2), R2 is evidently much lower than for previously considered benzene polycarb- 0.15 oxylic acids. -1 The solubilities of mellophanic acid, prehnitic acid and benzene-pentacarboxylic acid in water in the

/mol·kg 0.10 (273.15 to 323.15) K temperature range are known only m from the Yukhno and Bikkulov investigation [11]. According to them, mellophanic acid in the solid phase 0.05 exists in the forms of trihydrate and dihydrate. The pen- tahydrate, trihydrate and monohydrate are formed in 0.00 the case of benzene-pentacarboxylic acid. Both acids 270 280 290 300 310 320 330 340 easily form the supersaturated solutions. Formally, the T/K solubilities are expressed here by one equation (table FIGURE 7. Plot of solubility m of pyromellitic acid in water as a 2), that covers the solubility regions with different function of temperature T. d, Reference [11]; and h, this work. hydrates. In addition to the Yukhno and Bikkulov results [11], 3.3 the solubilities of pyromellitic acid in water were deter- mined by us (table 1) and both sets of solubilities are 3.2 in reasonably good agreement (figure 7). 3.1 Finally, benzene-hexacarboxylic (mellitic) acid is con- sidered. Its solubilities in water were determined by 3.0 Yukhno and Bikkulov [11] below T = 323.15 K and -1 2.9 by Chaigneau [23] at T = 293.15 K and T = 369.15 K. These two points are important because they confirm 2.8 /mol·kg the Yukhno and Bikkulov results and considerably ex- m 2.7 tend the temperature range of solubilities (figure 8). Mel- litic acid is very soluble in water and its solubility only 2.6 slightly increases with increasing temperature. 2.5 The solubilities of benzene polycarboxylic acids in 2.4 water, as compared at T = 298.15 K, can be arranged 280 300 320 340 360 380 in the following series: terephthalic acid (m = 0.00028 T/K mol Æ kg1) < isophthalic acid (m = 0.00074 mol Æ 1 1 FIGURE 8. Plot of solubility m of mellitic acid in water as a function kg ) < trimesic acid (m = 0.0099 mol Æ kg ) < benzoic 1 of temperature T. d, Reference [11]; and , reference [23]. acid (m = 0.0283 mol Æ kg ) < pyromellitic acid 570 A. Apelblat et al. / J. Chem. Thermodynamics 38 (2006) 565–571

(m = 0.0421 mol Æ kg1) < phthalic acid (m = 0.0440 At T = 298.15 K, the apparent molar enthalpies of solu- 1 1 1 mol Æ kg ) < trimellitic acid (m = 0.0938 mol Æ kg )< tion are: DsolH(benzoic acid) = 25.5 kJ Æ mol ; DsolH 1 1 hemimellitic acid (m = 0.2389 mol Æ kg ) < prehnitic (phthalic acid) = 23.9 kJ Æ mol ; DsolH(isophthalic 1 1 acid (m = 0.4406 mol Æ kg ) < benzene-pentacarboxylic acid) = 33.8 kJ Æ mol ; DsolH(terephthalic acid) = 4.8 1 1 1 acid (m = 0.8972 mol Æ kg ) < mellophanic acid (m = kJ Æ mol ; DsolH(hemimellitic acid) = 38.0 kJ Æ mol ; 1 1 1 1.035 mol Æ kg ) < mellitic acid (m = 2.617 mol Æ kg ). DsolH(trimellitic acid) = 31.7 kJ Æ mol ; DsolH(trimesic 1 At least qualitatively, this series can be related to the acid) = 31.4 kJ Æ mol ; DsolH(mellophanic acid) = 31.9 1 1 positions of the carboxylic groups in the benzene ring kJ Æ mol ; DsolH(prehnitic acid) = 15.7 kJ Æ mol ; 1 and their possibility to form hydrogen bonds with polar DsolH(pyromellitic acid) = 37.4 kJ Æ mol ; DsolH(ben- molecules of water and to form hydrogen-bonded di- zene-pentacarboxylic acid) = 27.5 kJ Æ mol1 and 1 meric units between carboxylic groups of the same acid DsolH(mellitic acid) = 1.8 kJ Æ mol , which represents or coming from two different molecules of the acid. The a very weak change in the solubility of mellitic acid. lowest solubility is associated with the acids with the carboxylic groups which are far apart and are probably unable to form the internal dimers (1,4-, 1,3- and 1,3,5- References positions, terephtalic, isophthalic and trimesic acids). The solubility of benzoic acid which is partially dimer- [1] S. Budavari (Ed.), The Merck Index: An Encyclopedia of ized and capable to form hydrogen bonds with water Chemicals, Drugs and Biologicals, 12th ed., Merck Co. Inc., Whitehouse Station, NJ, 1996. molecules, is only slightly higher than that of benzene [2] A.E. Williams, 3rd ed., in: H.F. Mark, D.F. Othmer, C.G. 1 in water (m = 0.022mol Æ kg , [25]). When few adjacent Overberger, G.T. Seaborg (Eds.), Kirk-Othmer Encyclopedia of COOH groups exist in the ring to form mostly the inter- Chemical Technology, vol. 3, Wiley, New York, 1978, pp. 778– nal dimers, the acid molecules bear a resemblance to 792. substituted benzene compounds and the solubility is [3] J.L. Opgrande, C.J. Dobratz, E.E. Brown, J.C. Liang, G.S. Conn, J. Wirth, J. Shelton, 4th ed., in: J.I. Kroschwitz, M. Howe-Grant higher yet continue to be of the same order of magnitude (Eds.), Kirk-Othmer Encyclopedia of Chemical Technology, vol. as benzene in water (1,2,3,5-, 1,2-, and 1,2,4-positions, 4, Wiley, New York, 1992, pp. 103–115. pyromellitic, phthalic, and trimellitic acids). Evidently, [4] C.M. Park, R.J. Shechan, in: B. Elvers, S. Hawkins, G. Schultz with increasing number of carboxylic groups, the possi- (Eds.), Ullmanns Encyclopedia of Industrial Chemistry, fifth rev. bility to form the hydrogen-bonded associates between ed., vol. 18, Basel, 1991, pp. 991–1043. [5] D.E. Read, C.B. Purves, J. Am. Chem. Soc. 74 (1952) acid-acid and acid-water molecules increases which is 116–119. manifested by a significant increase in the solubility. Tri- [6] D.E. Giammar, D.A. Dzombak, J. Solution Chem. 27 (1998) 89– mellitic acid (benzene-1,2,4-carboxylic) has one COOH 105. group in the ring far from the adjacent carboxylic group, [7] A. Seidell, 3rd ed.Solubilities of Organic Compounds, vol. 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