Proton acids, weak

We consider the case where the weak acid is initially introduced in the external aqueous medium containing the LUVs with a basic interior. Assuming that the neutral (protonated) acid is the only membrane permeable form, the rate of uptake of the weak... 

The CO insertion process also can be promoted by proton acids (20). The only compound to be studied in detail is Mn(CO)5(CH3), for which very weak acids such as acetic acid bring... 

A further measure of acidity is provided by rates of deuterium exchange between a labeled base such as DO and a proton acid. The mechanism involves exchange within weak ion-molecule encounter complexes as shown in equation 4. 

HF as the solvent the addition of BFg (ternary system) in the presence of weakly basic aromatic hydrocarbons only serves to increase the acidity of the acid. Thus the interaction of the aromatic substance always involves a proton acid. 

Electron-rich carbyne complexes can react at the carbyne carbon atom with electrophiles to yield carbene complexes. Numerous examples of such reactions, mostly protonations, have been reported [519]. Depending on the nucleophilicity of the carbyne complex, such reactions will occur more or less readily. The protonation of weakly nucleophilic carbyne complexes requires the use of strong acids, such as triflic [533], tetrafluoroboric [534] or hydrochloric acid [535,536]. More electron-rich carbyne complexes can, however, even react with phenols [537,538], water [393,539], amines [418,540,541], alkyl halides, or intramolecularly with arenes (cyclometallation, [542]) to yield the corresponding carbene complexes. A selection of illustrative examples is shown in Figure 3.25. 

Although HCo(CO)4 is a strong acid in aqueous solution and is capable of protonating even weak bases like dimethylformamide, there is no evidence that it protonates olefins in hydrocarbon solvents to form carbonium ion intermediates which might then rearrange by conventional 1,2-hydride shifts followed by proton elimination ... 

Smaller the pK j, the stronger the acid (the better it is as a proton donor). Strong acids have pK values < 1, the acids with pK values between 1 and 5 are considered to be moderately strong acids, weak acids have pKavalues between 5 and 15, and extremely weak acids have pK values >15. 

Secondly, the quaternised monomer may be replaced with a weakly basic monomer such as MEMA, which exists in its neutral, non-protonated form in alkaline media. Thus the desired zwitterionic block copolymer is prepared in its anionic/neutral form so that no isoelectric point is encountered during the copolymer synthesis. Afterwards, the solution pH can be adjusted to the isoelectric point by the addition of acid to protonate the weakly basic MEMA residues and precipitate the copolymer, which might be a useful alternative approach to column chromatography for the efficient removal of the ATRP catalyst. 

The acid has four replacable H+ ions. Its dissociation constants indicate that two H+ ions are strongly acidic while the other two protons are weakly acidic. The first dissociation constant especially is very large ... 

Perchloric acid is the strongest of the common acids in acetic acid solution and the titration medium usually used for non-aqueous titration of bases is perchloric acid in acetic acid. Addition of acetic anhydride, which hydrolyses to acetic acid, is used to remove water from aqueous perchloric acid. Weak bases compete very effectively with acetic acid for protons. Oracet blue, quinalidine red and crystal violet (very weak bases) are used as indicators in this type of titration. A typical analysis is shown in Figure 3.8 for LDOPA. 

A 1,3-dithiane is a weak proton acid (pKa = 32) which can be deprotonated by strong bases such as n-butyllithium. The resulting carbanion is stabilized by the electron withdrawing effect of the two sulphur atoms. 

W. Holl and H. Sontheimer, Ion-exchange kinetics of the protonation of weak acid ion exchange resins, Chem. Engrg. Sci., 32 (1977), p. 755. 

The acidity of a solvent that protonates the weak base, B, is defined as the Hammett acidity function ... 

When we refer to negative pH, we usually mean Hu values. For example, as measured by its ability to protonate very weak bases, 8 M HC104 has a pH close to —4. The figure shows that HC104 is a stronger acid than other mineral acids. Values of H0 for several powerfully acidic solvents are tabulated here. 

The Bronsted or proton acidity of the surface hydroxyl groups on silica and alumina is weak (51, 52, 53). Evidence for this comes from IR studies of pyridine adsorption, no surface pyridinium species (py H+)... 

Hull and Conant in 1927 showed that weak organic bases (ketones and aldehydes) will form salts with perchloric acid in nonaqueous solvents. This results from the ability of perchlonc aad in nonaqueous systems to protonate these weak bases. These early investigators called such a system a superacid. Some authorities believe that any protic acid that is stronger than sulfunc aad (100%) should be typed as a superaad. Based upon this criterion, fluorosulfuric arid and trifluoro-methanesulfonic acid, among others, are so classified. Acidic oxides (silica and silica-aluminai have been used as solid acid catalysts for many years. Within the last few years, solid acid systems of considerably greater strength have been developed and can he classified as solid superacids. 

The strength of an acid is determined by its ability to give up protons while the strength of a base is determined by its ability to take up protons. This strength is indicated by the dissociation or equilibrium constant, (pKfl), for the acid or base strong acids have a low affinity for protons, while weak acids have a higher affinity and only partially dissociate (e.g. HC1 (strong) and acetic acid (weak)). 

More recent measurements related to carbocation stabilities in strongly acidic media have involved rates of reaction rather than equilibria.52,54,72 75 Application of the X0 function to the correlation of reaction rates as well as equilibria mirrors the use of structure-based free energy relationships. Of interest is the access this gives to rate constants for (a) protonation of weakly basic alkenes and (b) acid-catalyzed ionization of alcohols to relatively unstable... 

Both the imine and the secondary amine nitrogens in polyaniline can be protonated by weak carboxylic acids of different pK values. Solid layers prepared from such doped polyanilines have different selectivity for interaction with gases. It is partially derived from the interaction of the analyte with the doping anion. 

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