Acid/base functionality

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. 

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