Gutmann scale

As outlined in Section 1.3, the solvent acidity and basicity have a significant influence on the reactions and equilibria in solutions. In particular, differences in reactions or equilibria among the solvents of higher permittivities are often caused by differences in solvent acidity and/or basicity. Because of the importance of solvent acidity and basicity, various empirical parameters have been proposed in order to express them quantitatively [1, 2]. Examples of the solvent acidity scales are Kosower s Z-values [8], Dimroth and Reichard s Er scale [1, 9], Mayer, Gutmann and Gergefs acceptor number (AN) [10, 11], and Taft and Kalmefs a parameter [12]. On the other hand, examples of the solvent basicity scales are Gut-... 

One of them is Gutmann s donor number, DN, (Gutman and Vychera 1966) defined as the negative of the standard molar heat of reaction (expressed in kcal mol 1, 1 cal = 4.184 J) of the solvent with antimony pentachloride to give the 1 1 complex, when both are in dilute solution in the inert diluent 1,2-dichloroethane. This quantity needs to be determined calorimetrically, as was done for a considerable number of solvents at that time (Gutman and Vychera 1966). There are several problems with the DN scale. One is the fact that calorimetric equipment... 

The correlation between the Koppel and Palm, Shorter, and Kagiya B D(CH3OD)/cm-1 (circles), Eq. (4.11), and the Koppel and Paju BQ C OtTl/cm 1 (triangles), Eq. (4.12) and the Lewis basicity scales with the Gutmann ZW/kcal mob1 scale... 

The correlation between the Gutmann ZW/kcal mo"1 scale and the Taft and Kamlet (3 Lewis basicity scales, Eq. (4. 13)... 

Recently, Beckett et al. has used the Gutmann acceptor number12 (GAN) scale to assess the Lewis acidity of B(C6F5)3 in particular.13 This scale uses the perturbation in the 31P chemical shift of Et3P=0 in hexane observed when the phosphine oxide is immersed in a Lewis acidic medium. Excellent correlation is observed between the GAN and the Childs Lewis acidity for a variety of LAs, perhaps not too surprising given that they are related NMR methods. 

The electron acceptor numbers (AN) can be used as a measure solvent ability to take a share in the electron pairs from suitable donors. They are defined by means of a different experimental procedure on the basis of the NMR chemical shifts of phosphorous which are produced on transfer of EtsPO through solvents. AN values are scaled from an arbitrarily chosen value of zero for the shift produced by hexane (or 1,2-dichloroethane) to one hundred for the shift produced by the 1 1 EtsPO—SbCls adduct in 1,2-dichloroethane. An estimation of the coordinate bond energy is possible by making use of the formula after Gutmann [155]... 

Many physical chemists have embraced the concepts of donicity (donor numbers, DN) and acceptor numbers (AN) as developed by Gutmann and his co-workers [12], The DN is measured by the heat of reaction of the donor solvent and antimony pentachloride in a 1 1 ratio as a dilute solution in 1,2-dichloro-ethane. It is taken to be a measure of the strength of the Lewis base. The AN is measured as the relative shift of the 31P NMR peak in triethylphosphine oxide dissolved in the sample solvent. Hexane is given the value of zero on the scale, and antimony pentachloride is given the value of 100. The AN is taken to be a measure of the strength of the Lewis acid. The applications of the concepts have... 

Drago s EJC analysis and Gutmann s donor/acceptor approach [53, 67] have been compared [200, 217, 218], Eq. (2-12) has been extended for specific and nonspecific interactions between solutes and polar solvents [219]. Various Lewis acidity and basicity scales for polar solvents have been examined and compared by Fawcett, who concluded that the donor/acceptor scales of Gutmann seem to be the most appropriate [341],... 

A detailed discussion and comparison of all these and further solvent softness scales can be found in references [173, 238, 239]. For other Lewis acid/base parameters of EPD and EPA solvents, derived from calorimetric measurements [e.g. Gutmann s donor and acceptor numbers), see reference [65] and Section 2.2.6. 

Another approach to a new solvent scale was introduced by Gutmann in 1966 [26, 27]. Based on the fact that many chemical reactions are influenced primarily by coordi-... 

This 5phOH scale was further extended by Makitra et al. [242]. It has been shown that the spectroscopically determined 5phOH values correlate well with Gutmann s calori-metrically measured donor numbers DN [243] cf. Eq. (7-10). 

Interesting solvent scales based on NMR measurements have been proposed by Taft et al. [90] and by Gutmann, Mayer et al [91]. A solvent polarity parameter, designated as P, has been defined by Taft et al [90] as the F chemical shift (in ppm) of 4-fluoro-nitrosobenzene in a given solvent, relative to the same quantity in the reference solvent cyclohexane cf. Table 6-6 and the discussion in Section 6.5.1). These parameters define a scale ranging from P = 0.0 in cyclohexane to P = 2.7 in sulfolane, and can easily be measured in a wide variety of solvents. The P values appear to be related to the ability of the solvents to form specific 1 1 complexes with the nitroso group of the standard compound. A compilation of P values can be found in reference [92], In addition, chemical shifts of (trifiuoromethyl)benzene and phenylsulfur pentafiuoride have been used by Taft et al. to study nonspecific dipolar interactions with HBD solvents and utilized to define n values of solvent dipolarity/polarizability for protic solvents [249]. 

Saxena R, Thakurta DG, Gutmann RJ, Gill WN. A feature scale model for chemical mechanical planarization of damascene structures. Thin Solid Films 2004 449 192-206. 

Thakurta DG, Schwendeman DW, Gutmann RJ, Shankar S, Jiang L, Gill WN. Three-dimensional wafer-scale copper chemical-mechanical planarization model. Thin Solid Films 2002 414(l) 78-90. 

Various criteria have been followed in an attempt to establi quantitative scales of acidity and basicity. In order to account for solvation and ionic dissociation phenomena Gutmarm introduced a parameter called donor number, DN, which correlates the behaviour of a donor sdvent towards a given solute with respect to the coordinating ability of a reference solvent towards the same sdute. The basicity of a solvent can be related to the enthalpy of its reaction with a reference acid. Gutmann s DN scale is built on the equation... 

Acidity and basicity scales in polar solvents have been discussed [260] and it has been concluded that the most appropriate scales are the acceptor number AN or donor number DN introduced by Gutmann [261-263], although it does not directly allow one to estimate the basicity of a protic solvent. 

The Gutmann s Donor Number (DN) was proposed [Gutmann, 1978] as a quantitative empirical parameter for solvent nueleophilicity. For most solvents it was found to correlate well with the p scale. 

The donor number, DN, of a solvent, proposed by Gutmann, is a measure of the Lewis base donor power of the solvent.3 The DN is determined by measuring the negative enthalpy for the reaction of the standard Lewis acid, SbCl5, with solvent (Scheme 1), and reflects the ability of the solvent to solvate Lewis acids. The scale commences at zero for solvents with no Lewis basicity (1,2-dichloroethane is used as a reference), and extends to 38.8 kcalmol-1 for hexa-methylphosphoramide (HMPA). Certain solvents like alcohols and water solvolyse SbCl5 and the DN must be estimated by indirect methods. Sometimes values of DN are quoted as DNn, which corresponds to the DN/38.8 thereby giving a scale between 0 and l.4... 

The organic molecules or "probes used to investigate the dispersive surface energies of the fiber surfaces were a series of n-alkanes. The probes used to study the non dispersive forces were chosen based on their acidic or basic character as determined by Gutmann (8). Gutmann has practically defined basicity as the donor number, DN, or electron-donor capability in the Lewis sense. The donor scale is based on the value of the molar enthalpy for the reaction of the electron donor with a reference acceptor, SbCl. ... 

Schreiber et al. [57] proposed also another definition of acceptor and donor numbers (assigned here as ANsch and DNsch, respectively) not related to Gutmann s scale and defined as follows ... 

A popular method of estimating solvent basicity is based on the donor number scale, DN, introduced by Gutmann [44, 45]. The donor number is defined as the value of the heat of reaction of the polar solvent with the strong Lewis acid SbCls when these reactants are dissolved in 1,2-dichloromethane (fig. 4.14). The scale suffers from the problem that DN cannot be measured directly for protic solvents because of the instability of SbCls in these systems. However, values of DN for these solvents have been estimated by a variety of other techniques [46]. 

FIGURE 7.3 Plots of (a) rNO, IR stretching frequency, and (b) i mlct. lowest energy visible band, for (TBA)2[Fe(CN)5NO], against solvent acceptor number in the Gutmann s scale. A = acetone B = acetonitrile C = methanol D = water. Ref. 24... 

The Lewis acid-base reaction leading to complex formation has been recently considered in relation to the role of solvation effects. Many scales of thermodynamic parameters have been suggested. The concept of donor numba- (DN) was proposed by Gutmann, and defined as the AH (kcalmoD ) for the intoaction of a basic solvent with SbCls in 1,2-dichloromethane at room temperature ... 

The importanee of aeid-base interactions in various fields of ehemistry led to extensive research in the 1960s to obtain acid-base scales. This resulted in the Hard and Soft Aeids and Bases (HSAB) seales of Pearson [30], Drago s E and C eonstants [31], and Gutmann s donor and aeeeptor numbers [32]. Bolger and Miehaels [33] have used Bronsted acid base ehemistry to predict the adhesion of organie and inorganic species. 

Conversely, the AN seale ean be viewed as a scale of hardness for adds since EtsPO is a hard reference base. Nevertheless, the merit of Gutmann s approach Kes in the fact that his scales provide both addic and basic parameters for amphoteric species, which is not the case with Drago s E and C classifications. 

Criticism (ii) is also unfair because it is well known that acid-base scales strongly depend on the choice of the test probes. For example, Gutmann s DN scale is based on the... 

Correlation of with Gutmann s DN. The relationship between the scale and Gutmann s Solvent Donicity (DN) numbers provides a context for several additional interesting correlations. Gutmann has defined donicity as the negative A -value in kcal mole for the interaction of the nucleophilic solvent (Lewis base) with SbCIs in a highly diluted solution in dichloroethane. DN values have been reported for 17 HBA solvents whose /5 values are known (3,7,9,11,13,14,18,23,24,25,26,28,29,37,50,52,61) (175). 

This raises a very fundamental question regarding the scope and applicability of the DN scale. If A(7ys of 4-fluorophenol complexes with a series of HBA bases are not linear with A///s of the self-same complexes when bases with different type H BA sites are considered together, why should they, or any free energy-proportional, solvent-dependent properties be linear with A//ys of complexes of the solvents with the particular electrophile chosen by Gutmann It is of particular interest in this regard to compare correlations between /3 and properties which, like DN, depend upon interactions between nonprotonic Lewis acid indicators and bases. Preferably the comparisons should involve sets that include triethylamine (3) and/or pyridine (24), the out-of-line solvents in Fig. 28. 

Solvatation, solvolysis and ionic dissociation phenomena, in both aqueous and nonaqueous solutions are subsumed by the Lewis definitions. In addition to the previous discussion of the dual polarity character of Lewis acids and bases, it should be noted that many of them are amphoteric, by definition. Donor number, DN, was developed in order to correlate the behavior of a solute in a variety of donor solvents with a given basicity or donicity. A relative measurement of the basicity of a solvent D is given by the enthalpy of its reaction with an arbitrarily chosen reference acid (SbCls in the Gutmann s scale). Latter Mayer introduced an acceptor number, AN, as the relative P NMR shift induced by triethylphosphine, and relative to acidic strength (AN=0 for hexane and 100 for SbCls). In 1989, Riddle and Fowkes modify these AN numbers, to express them, AN ", in correct enthalpic unit (kcaLmol). Table 10.2.3 gathers electron acceptor number AN and AN " and electron donor number DN for amphoteric solvents. 

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