Acid-base function

In this monograph, the concept of acid-base function is based on the inevitable change in intramolecular electron density pattern as molecules approach each other, a change giving rise to intermolecular forces. It is appreciated that there is a wide range of intensities, but I contend that any attempt to draw a line of demarcation between what certain persons call physical as distinct from chemical interactions is not merely arbitrary but unnecessary and undesirable. Descriptions involving such a distinction carry ad hoc reservations and excuses which tend to cancel out on passing from one specialist to another. 

The charge-transfer theory of Mulliken (1952) is a quantum-mechanical explanation of electron donor-electron acceptor function. In a conference on the properties of liquids (Paris, 1964), I contributed to the discussion on Mulliken s paper by expressing my opinion that it is helpful to look upon electron acceptor or electron donor function as a property of a particular part of a molecule. At one part of a molecule there may be acceptor function, and at another part of the same molecule there may be donor function. A donor part can donate to the acceptor part of another molecule, or to the acceptor part of the same molecule. In his reply, Mulliken emphasized that one should speak rather of electron donor or acceptor functioning than of donors and acceptors. I can find no unequivocal argument in the literature against my expression acid-base function in place of electron acceptor (acid)-electron donor (base) function. In a comment on Mulliken s exposition, H. C. Brown referred to the utmost importance of the widespread phenomena relating to acid-base function and pressed for simplicity of expression in order to ensure ready and clear communication of such ideas among all chemists. 

There does not appear to be any universally valid quantitative order of intensity of acid-base function. 

When it all comes down to details, we are confronted with the same fundamental problem which overshadows the investigation of intermolecular forces. The mass of publications on so-called acids and bases defies any generalization less general than the one I have adopted. Reviews of reviews tend to get further and further away from the reality of the original experimental data and do no more than add to the confusion in terminology. The outstanding causes of confusion result from the emphasis on aqueous systems, and extremely dilute ones at that, and, above all, the tendency to look upon the formation of ions as an essential and predominant feature of acid-base function. 

The so-called proton acids involve a hydrogen atom at the acid site, whereas the so-called Lewis acids are deemed to have acid function because of a tendency to 

---

Impurities must contain acid—base functional groups or other reactive groups. 

Various solvents sorted in accord with their acid-base functionality... 

One intra-annular acid-base function Intra-annular acids and bases only... 

An /n-geometry can be ensured by appropriate substitution of the building block which carries the acid-base functionality, for instance by using 2,6-disubstituted aromatic compounds like pyridines, 2,6-disubstituted benzoic acids or other 2,6-disubstituted phenyl derivatives (see Scheme 1). The use of 2,6-disubstituted arenes is sometimes called the 1,3-xylyl trick and assures an intra-annular orientation. 

This quick glance at the acid-base properties of some (poly)azamacro-cycles already suggests which parameters will determine the p a of macrocyclic and related acids and bases. Hydrogen bonds will probably be very important and in polyions Coulomb interactions have to be taken into consideration. But the geometry of the acid-base function has to be defined. In Sections 2, 3 and 4 we shall therefore focus on compounds with intra-annular acid-base functionalities (the 1,3-xylyl trick). 

It is worth mentioning that both the carboxylation of epoxides and anilines are acid-base reactions, which do not entail redox processes. Therefore a catalyst active in these reactions must provide acid-base functionality. In this perspective, positively charged gold could be the real player, although a co-catalytic or promotion effect of ze-rovalent gold could also be important. Therefore the catalysts for the oxidative carbonylation of aniline, supported on Merck Ion-exchanger IV, could be actually bifunctional. On one side, Au could catalyze the oxidation of CO with O2 to CO2, a reaction for which it is... 

Fig. 9 Three haptens, [15]—[17], containing a 1,2-aminoalcohol functionality were investigated as alternatives for esterase and amidase induction. Of antibodies raised against hapten [15], 50% were shown to catalyse the hydrolysis of ester [18], thereby establishing the necessity for a compact haptenic structure. Hapten [19] along with [16] was employed in a heterologous immunization programme to elicit both a general and acid/base function in the antibody binding site.

Baddeleyite has a monocHnic structure with space group Plljc. The Zr + ion has seven-fold coordination, while the idealized ZrOz polyhedron is close to tetrahedral orientation, where one angle in the structure is different significantly from the tetrahedral value. Natural baddeleyite is a raw material for zirconium. In industry ZrOz, named usually zirconia, is important in areas such as surface chemistry, where its activity as a red ox material and its acid-based functions are important. As a ceramic material, zirconia can resist very high temperatures and its stabihzed form, yttrium-stabihzed zirconiiun, shows remarkable mechanical properties. 

Note that for compound classes such as phenols, anilines, and pyridines where the acid (base) function is in resonance with the aromatic ring, the p values obtained are significantly greater than 1 (Table 8.6) that is, the electronic effect of the substituents is greater than in the case of benzoic acid. 

S)-3-(A-Isopropyl-A-3-pyridinylaminomethyl)BINOL (4) has been established as an efficient asymmetric bifunctional organocatalyst for the aza-MBH reaction.23 The acid-base functionalities cooperate in substrate activation and fixing of the organocatalyst conformation to promote the reaction with high enantiocontrol. 

A. Introduction of Acid-Base Function into the Distal Site of Mb / 457... 

Scheme 8. Active site structure and acid—base function of glutamic acid (Glul83) in CPO.

Another class of bifunctional organocatalysts for the enantioselective aza-Morita-Baylis-Hillman reaction of imines (112) with enones (113) (Scheme 6) is based on BINOL (115). The efficiency of the catalysts proved to be mainly influenced by the position of the Lewis basic moiety attached to the BINOL scaffold. The activation of the substrate by acid-base functionalities and the fixing of conformation of the catalyst (115) are apparently harmonized to maximize the enantiocontrol (<95% ee) 52... 

R X = Alkylating agent Fig. 1. Dual acid-base function of zeolite. 

Zeidan RK, Davis ME (2007) The effect of acid-base pairing on catalysis An efficient acid-base functionalized catalyst for aldol condensation. J Catal 247 379... 

In conclusion, even if the CH3OH oxidation occurs for supported electrocatalysts in a similar way as on smooth Pt electrodes, the surface characteristics of the catalysts, besides Pt dispersion, may play a significant role in the reduction of the overpotential for this process. The acid-base functional groups influence the oxidation mechanism as they establish the level of metal-support interaction and the surface adsorption behavior. Thus, the optimization of such parameters can significantly improve the activity of Pt electrocatalysts for CH3OH oxidation. 

---