Protonation agents for

Miscellaneous Applications. Only one attempt to use (R)-pantolactone as an enantioselective protonating agent for enolates has been reported. A series of structurally diverse chiral alcohols afforded modest ee s with (R)-pantolactone affording the largest ee noted for the series. The complexities of attempting a proto-nation of this sort in the presence of base and under exchanging conditions are discussed. Finally, the lactone has been used to resolve chiral acids by crystallization and chromatographic techniques applied to the (R)-pantolactone-derived esters. - ... 

However, the use of selected phenols such as m-cresol, 2-chlorophenol, 3-ethyl phenol etc. and sulphonic acids as protonating agents, for example camphor sulphonic acid (CSA), may produce solution spectra which are similar to those recorded for the solid firms [66]. 

Diesters of phosphoric acid are the best protonating agents for PANI and they are also good plasticizers. An oligoester of phosphoric acid was synthesized and used as plasticizer/doping agent in PANI. It was found to improve the thermostability of the plasticized polymer. ... 

Reductions of unsaturated ketones and a-acetoxy ketones usually are effected with an excess of reducing agent. For optimum yields of saturated ketones, the intermediate enolate salt obviously must not become protonated while... 

In the case of carbanion and radical intermediates the solvent is less important but the products are partially determined by the resistance of the medium to proton or hydrogen atom abstraction respectively. The increased stability of these intermediates compared with carbonium ions allows the reaction mechanism to be more readily modified by the addition of trapping agents. For example, carbanions are trapped in high yields by the presence of carbon dioxide in the electrolysis medium (Wawzonek and Wearring, 1959 Wawzonek et al., 1955). 

Hydroxyenones have also been used in catalytic amide formation, although 1,2,4-triazole is required as a co-catalyst. Assumed protonation of the Breslow intermediate and tautomerisation generates an acylazolium intermediate, which is trapped by triazole, releasing the NHC and generating the acyltriazole 60 that is the active acylating agent for the amine (Scheme 12.11) [16]. 

Oxadiazolinethiones are probably too weak bases to be protonated in, for example, acetic acid. Therefore, in their oxidation shown in Equation (2), acetic acid played the role of a solvent and not a protonating agent <1997CAR123>. 

The asymmetric synthesis achieved when the base is an optically active one is proof that the base is present in a transition state with the carbonyl and not just an agent for removal of protons from hydrogen cyanide. It has further been shown that asymmetric synthesis is still achieved even if the only optically active molecules present are quaternary ammonium compounds, i.e., positive ions without any protons to donate. This probably means that the important thing is to have some positive ion near the carbonyl oxygen, an actual covalent... 

In conclusion, the most important result is that the use of permethylated cyclodextrin as chiral solvating agent for NMR spectroscopy not only affords a simple and practical way for the determination of the stereochemical purities of trisubstituted allenes, but also allows one to simultaneously determine their absolute configuration. Indeed, TRIMEB induced only positive complexation shifts of all the allene protons, which are greater for the (S )-enantiomer than for the (R)-enantiomer, independent of the structure of the allene. This empirical correlation seems to be reliable since it has been satisfied by a large number of trisubstituted allenes. 

A significant feature of the reaction kinetics outlined is that, for each reducing agent for which the reaction rate was measured, the activated complex for the dominant path contains only the reducing agent, perchlorate ion, and no protons. In the absence of protons to stabilize the oxide ion which is released, whether the reduction is by a le or 2e change ... 

Lauffer RB (1987) Paramagnetic metal complexes as water proton relaxation agents for NMR imaging theory and design. Chem. Rev. 87 901-927. 

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