Apparent Molal Volumes and Heat Capacities of Urea and Methyl-Substituted Ureas in H₂O and D₂O at 25 °C

Abstract

The apparent molal volumes and heat capacities of urea, 1,l-and 1,3-dimethylurea, and tetramethylurea were measured in H?O and DL.O at 25 " C . From these data, ureawater interactions seem to cause an overall structure-breaking effect and the substituted ureas, an overall structure-making effect. The effect of the hydrogen-bonding interactions to the volume and heat capacity seems to be small compared with the intrinsic and hydrophobic contributions of a methylene group, as reflected by the isotope effect.

Apparent molar volumes and apparent molar heat capacities of aqueous urea, 1,1-dimethylurea, and N,N′-dimethylurea at temperatures from (278.15 to 348.15)K and at the pressure 0.35MPa

“…differences between our regression surfaces and the literature values of V / are as follows: for urea, average difference D = 0.04 cm 3 AE mol À1 , range of differences D = +0.88 cm 3 AE mol À1 [18] to D = À0.84 cm 3 AE mol À1 [5]; for 1,1-dimethylurea, average difference D = 0.40 cm 3 AE mol À1 , range of differences D = 0.75 cm 3 AE mol À1 [17] to D = 0.29 cm 3 AE mol À1 [4]; and for N,N 0 -dimethylurea, average difference D = À0.27 cm 3 AE mol À1 , range of differences D = À0.59 cm 3 AE mol À1 [19] to D = À0.10 cm 3 AE mol À1 [4]. Pandey et al [2] also reported V / values for aqueous urea and N,N 0 -dimethylurea, but their values differ from our results and from the results of others by an average D = (40 and 37) cm 3 AE mol À1 , respectively, possibly indicating that their compounds were dihydrates.…”

“…We used the reciprocals of the squares of the uncertainties reported in tables 5 to 7 as weighting factors in the regressions, and values of the resulting c i are given in table 8. The regression surfaces for equation (3), our experimental C p,/ values from tables 5 to 7, and the literature C p,/ values [4,[12][13][14]20,21] for the three aqueous urea compounds are shown in figures 4 to 6. The differences between our regression surfaces and values of C p,/ from the literature are as follows: for urea, average difference D = +0.3 J AE K À1 AE mol À1 , range of differences D = À12.7 J AE K À1 AE mol À1 [13] to D = +5.9 J AE K À1 AE mol À1 [13]; for 1,1-dimethylurea, average difference D = +1.6 J AE K À1 AE mol À1 , range of differences D = +6.0 J AE K À1 AE mol À1 [4] to D = À3.3 J AE K À1 AE mol À1 [4]; and for N,N 0 -dimethylurea, average difference D = +6.3 J AE K À1 AE mol À1 , range of differences D = +11.3 J AE K À1 AE mol À1 [4] to D = +1.9 J AE K À1 AE mol À1 [4].…”

“…It has been proposed in the literature that these interactions affect ''water structure.'' Some researchers have claimed that urea acts as a ''structure breaker'' in water, whereas others have claimed urea compounds serve to enhance the structure of water as a ''structure maker'' [1][2][3][4][5]. In an attempt to address these claims we report the apparent molar volumes V / and apparent molar heat capacities C p,/ for aqueous solutions of urea, 1,1-dimethylurea, and N,N 0 -dimethylurea.…”

Relation between van der Waals and Partial Molal Volumes of Organic Molecules in Water

“…In fact, we find that for molecules containing three or more alkyl carbon atoms for each hydrophilic group (hydroxyl, ether, amine, amide, or urea) [2] with A = 0.53 A works reasonably well. This is illustrated for eight apolar molecules in (14), tetrahydropyran (12,18,24), dioxane (18,24), npropylamine (16), n-butylamine (16), t-butylamine (12), n-pentylamine (16), n-hexylamine (16), n-heptylamine (16), diethylamine (16), di-n-propylamine (16), diethylmethylamine (16), piperidine (1 6), heptamethyleneimine (1 6), N-methylpyrrolidine (16), N-methylpiperidine (16), isopropyl urea (21), n-butylurea (21), 1,l-diethylurea (21), 1,3-diethylurea (21), and tetramethylurea (21,23).…”

Volumetric properties of binary mixtures of N, N- dimethylformamide with water or water- d2 at temperatures from 277.13 K to 318.15 K

“…(4) Thermodynamic properties of binary mixtures of H 2 O with various dipolar aprotic solvents have been extensively reported by many workers, whereas studies on the properties of corresponding systems containing D 2 O instead of H 2 O are scarce. (5)(6)(7)(8)(9)(10)(11)(12)(13) We have recently initiated in our laboratory a systematic investigation of deuterium isotope effects on thermodynamic properties in binary mixtures of water with various dipolar aprotic solvents. This is an extension of our previous research on deuterium isotope effects (14)(15)(16)(17)(18)(19)(20) and the presently ongoing study on aqueous dipolar aprotic solvents as highly basic media.…”