Activity coefficients carbon number

Once established, the H scale is used to find pKa values for weak acids. A number of measurements have been made by various groups.53-57 The results obtained at first appeared to disagree with Streitwieser s, but revision of values for some compounds on the basis of further measurements brought the results of the two methods into fairly good agreement. At the same time, however, it became clear that the problems discussed in the previous sections relating to the different behavior of substances of different structural type also apply to the // scale work.58 The activity coefficient ratio evidently is not the same for carbon acids as for the nitrogen acids used to establish the scale.59 Thus the pAa values found by these methods, while probably internally consistent for similar compounds, are not on a firm basis with respect to their absolute relationship to the water scale. 

Pierotti-Deal-Derr Method (4). Infinite dilution activity coefficients (y°) of structurally related systems are correlated in this method to the number of carbon atoms of the solute and solvent (nx and n ). For the members of the homologous series H(CH2)mXi (solute) in the members of the homologous series H(CH2)n2Y2 ... 

A number of other proton transfer reactions from carbon which have been studied using this approach are shown in Table 8. The results should be treated with reserve as it has not yet been established fully that the derived Bronsted exponents correspond exactly with those determined in the conventional way. One problem concerns the assumption that the activity coefficient ratios cancel, but doubts have also been raised by one of the originators of the method that, unless solvent effects on the transition state are intermediate between those on the reactants and products, anomalous Bronsted exponents will be obtained [172(c)]. The Bronsted exponents determined for menthone and the other ketones in Table 8 are roughly those expected by comparison with the values obtained for ketones using the conventional procedure (Table 2). For nitroethane the two values j3 = 0.72 and 0.65 which are shown in Table 8 result from the use of different H functions determined with amine and carbon acid indicators, respectively. Both values are roughly similar to the values (0.50 [103], 0.65 [104]), obtained by varying the base catalyst in aqueous solution. The result for 2-methyl-3-phenylpropionitrile fits in well with the exponents determined for malononitriles by general base catalysis but differs from the value j3 0.71 shown for l,4-dicyano-2-butene in Table 8. This latter result is also different from the values j3 = 0.94 and 0.98 determined for l,4-dicyano-2-butene in aqueous solution with phenolate ions and amines, respectively. However, the different results for l,4-dicyano-2-butene are to be expected, since hydroxide ion is the base catalyst used in the acidity function procedure and this does not fit the Bronsted plot observed for phenolate ions and amines. The primary kinetic isotope effects [114] also show that there are differences between the hydroxide ion catalysed reaction (feH/feD = 3.5) and the reaction catalysed by phenolate ions (kH /kP = 1.4). The result for chloroform, (3 = 0.98 shown in Table 8, fits in satisfactorily with the most recent results for amine catalysed detritiation [171(a)] from which a value 3 = 1.15 0.07 was obtained. 

FIGURE 2-5 Infinite-dilution activity coefficients yi as a function of carbon, number for n-alkanes. A, n-heptane at 90°C B, 2-butanone at 90°C C, phenol at 90°C D, triethylene glycol at 90°C E, water at 25°C. Fi om Pierotti, Deal, Derr, and Porter ")... 

If.. separately, we knew the activity coefficients for bromine in carbon tetrachloride, we could u.se the data in the table to evaluate the activity coefficient of bromine in water (Problem 11.4-3). Since the regular solution model can be used to represent the Bri-CC mixture, we can then surmise that will be on the order of magnitude of unity. This suggests that y will be a large number, on the order of 100 or more. Such behavior for the activity coefficient o f the minor component is not unusual in mixtures of species with such different molecular characteristics as strongly quadrupolar liquid bromine and strongly polar and hydrogen-bonded water. H... 

The most reliable and comprehensive g.l.c. activity coefficient measurements for n-alkane systems have been done by the Bristol group > " using medium-high-pressure g.l.c. and taking all carrier-gas and solute imperfections into account. They have looked at the Q to Cg n-alkane solutes in Cig to Cga n-alkane solvents. Generally, the results indicate that the smaller the disparity in carbon number between solute and solvent, the closer is the activity coefficient to unity. The measured activity coefficients range from 0.930 for heptane + hexadecane at 303 K to 0.695 for heptane + dotriacontane at 348 K. Activity coefficients for many alk-l-ene + alkane systems have also been measured by this group. ... 

Pierotti et al. 88), Tsonopoulos and Prausnitz (99), and Mackay and Shiu (70) studied the activity coefficients of aromatic compounds in water (y ) and showed that y could be correlated with the number of carbon atoms and the types of groups present in the aromatic compound. The substituent contribution to y was found to be reasonably additive for relatively simple molecules. Tsonopoulos and Prausnitz (99) defined a constant A, similar to II, to account for the effect of substituent X on y for compounds in dilute aqueous solutions ... 

Codogan et al. [14] have studied the systems (Cg—C,) alcohols-squalane at 323,333 and 343 K the activity coefficients decrease with the increasing number of carbon atoms of the alcohol, for example from 8.19 for 2-propanol to 2.94 for 1,1-dimethyl-l-propanol at 323 K. 

Scott and Simpson studied the adsorption of ahphatic alcohols, aldehydes and carboxylic acids in binary mixtures with water by ODS-2 sUica [9]. They found that the distribution coefficient increases exponentially with the carbon number of the moderator. When using an aliphatic moderator having a chain length of four or five carbon atoms, the surface of a bonded phase could be completely covered with a monolayer. They stated further that the chromatographic characteristics of the surface could be changed by choosing appropriately active groups. 

Experiments under the restrictions of classical thermoelectrochemistry in open cells with moderate temperature variation addressed, to some extent, also the conditions in the bulk electrolyte solution and the properties of ions. Potentiometric measurements in aqueous solutions of hydrogen and potassium bromides yielded the temperature dependence of activity coefficients of important ions [58]. As mentioned in Chap. 2, all electrolyte solutions tend to approach the ideal state with increasing temperature. The conductance of various electrolytes has been studied in dependence on temperature [59-66]. Solvents studied were propanol [59], propylene carbonate [60, 64], dimethoxyethane [65], primary alcohols and acetonitrile [62]. Conductance values were used to determine transference numbers of ions in non-aqueous solution [62]. Salt melts of sodium and caesium halides also have been studied [66]. Theoretical considerations were subject of [63]. 

The large dataset of partition coefficients (or activity coefficients at infinite dilution) published in the literature may be used to present a general behaviour of solutes in ionic liquids. The values of activity coefficients at infinite dilution () for the -alkanes increase with an increase in carbon number. In most ionic liquids, the high y" values observed with n-alkanes indicate their low solubility in ionic liquids. The values of n-alkanes are higher than the values obtained with cyclohexane, alkenes, alkynes and aromatics. Introduction of a double or triple bond in the n-alkanes decreases the values. 

Consider, for example, the binary systems of aliphatic ketones with n-heptane. The polar character of ketones - originating from the presence of the CO group - decreases with increasing values of N, the number of carbon atoms in the ketone they become progressively more hydrocarbon-like, which explains the observed decrease in the infinite dilution activity coefficient values of ketones in heptane as Nj increases. 

Note added in proof Large differences in activity coefficient behavior have recently been observed between phloroglucinol and its methyl ethers. Although these compounds protonate on carbon the acidity function that each follows is mainly determined by the number of hydroxyl groups that are free for hydrogen bond donation to the solvent. [W. M. Schubert and R. H. Quacchia, J. Am. Chem. Soc., 84, 3778 (1962) and A. J. Kresge, G. W. Barry, K. R. Charles, and Y. Chiang, ibid., 4343.]... 

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