Drago E and C values

TABLE 9.6 Drago E and C Values (kcal/mole) for Ceramic Powders... 

Table 9.5 is a listing of the E and C values given by Drago and others... 

A self-consistent set of E and C values is now available for 33 acids and48 bases, allowing AH prediction for over 1584 adducts. It is assumed that the conditions under which measurements are made (gas phase or poorly coordinating solvents) give rather constant entropy contribution and that most of adducts are of one-to-one stoichiometry. Table 10.2.2 gathers Drago s parameters, given in (kcaEmol) of some common solvents. 

Acid parameters E and alkaline parameters C can be used to show the acid and alkaline values of the surface of materials. To measure the E and C values of material surfaces, R. S. Drago proposed the famous Formula 2.2 ... 

A and B indicate acid and base while E and C are susceptibilities to undergoing electrostatic and covalent interactions, respectively. The other parameters in Equation 15.9 are a conversion factor (/) and is the number of acid-base interaction sites on the surface. Drago et al (1965) have provided E and C values for about 30-40 acids and bases. In the case of benzene-water, the enthalpy of interaction is -5 kJ mol which incidentally is about Vi of heat of vaporization of benzene. This enthalpy of interaction corresponds to 16.5 mN m (assuming 50 as the area per molecule for benzene) and/= 1 both assumptions have been, however, criticized, see Douillard, 1997. Using such a value the improved Fowkes equation is, as shown by Fowkes et al. (1990), in excellent agreement with the experimental interfacial tension for water-benzene (35 mN m ) ... 

Hence, is comparable to the a value of the Hammett equation, and Cg to its q value. With the aid of the appropriate mathematics, Drago [Dr 73] attempted to find a quantitative connection between the Hammett constants and his own constants E and C. However, this proved successful only in a very limited range. 

When all of these limitations are taken into account, it should be emphasized that the parameters E and C introduced by Drago, in general, faithfully reflect the sequence of acceptor and donor strengths for both acids and bases. The E and C data relating to some of the more important systems are presented in Tables 4.11 and 4.12. These data are conventionally expressed relative to elemental iodine, for which, therefore, E = 1.00 and = 1.00. This means that the absolute values of... 

Number of heats used to determine the parameters for the specified base. The solvent recommended for getting enthalpies for comparison is indicated in parenthesis H stands for cyclohexane, hexane or gas phase and C, carbon tetrachloride or gas phase. See M. S. Nozari and R. S. Drago J. Am. Chem. Soc. 94, 6877 (1972). i>) Tentative value calculated from data limited to acids with similar C/E ratios. 

Drago [Dr 73] considered how his concept could be correlated with Pearson s hard-soft acid-base theory [Pe 63b, Kl 68]. Setting out from the assumption that the terms E Eg and C Cg may serve as measures of the electrostatic and covalent interactions, respectively, and identifying the hard and soft interactions of the Pearson concept with the electrostatic and the covalent interactions, respectively, Drago wished to employ the C/E ratios for the acids or bases examined as a measure of the soft nature of the molecules. He considered that the higher the value of C/E, the softer is the given acid or base, whereas low value of C/E is indicative of a hard character. 

Similar to the perturbation theory, Drago and Wayland proposed a four-parameter equation for predicting reaction enthalpies between acid and base species (Drago and Wayland 1965). Both species are each characterized by two independent parameters an E value which measures their ability to partidpate in electrostatic bonding, and a C value which measures their ability to participate in covalent bonding, leading to ... 

However, the sequence of C/E values is not in accordance with practical experience with the solvents. Drago s parameters and his equation also could not be used to describe Pearson s hard-soft concept. 

Fowkes and coworkers extended Drago s methods to polymers and solid surfaces and have determined C and E values for them. ° Furthermore, Fowkes suggested that acid-base interactions often dominate the attraction that occurs between a liquid and a solid. He proposed, in general, that the thermodynamic work of adhesion is given by ... 

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