Reactivity effects kinetic acidity

The chemical oxidation of metal sulfides is controlled in part by the dissolution of sulfide minerals under acidic conditions and by the presence of oxidants (DO, Fe ) that lead to the disruption of sulfide chemical bonds. Bacteria can have a significant effect on the rate of oxidative dissolution of sulfide minerals by controlling mineral solubility and surface reactivity. Metal-enriched waters and solutions rich in sulfuric acid that form in association with mining can be directly linked to microbial activity. The majority of studies to date have focused on the reactivity and kinetics of sulfide minerals in the presence of A. ferrooxidans and L. ferrooxidans, and in some cases A. thiooxidans (Singer and Stumm, 1970 Tributsch and Bennett, 1981a,b Sand et al., 1992, 2001 Nordstrom and Southam, 1997 Sasaki et al., 1998 Edwards et al., 1998, 1999, 2000 Nordstrom and Alpers, 1999a Banfield and Welch, 2000 Tributsch, 2001). Additional studies have been conducted on other species of bacteria and archea (Edwards et al, 1998, 1999, 2000). 

As already mentioned, LiTMP acts usually as a stronger base than LDA or lithium diethylamide in some rare cases the reverse order of reactivity has been observed. Thus it has been found that the trimethylsilyl substituent reduces the kinetic acidity of CF3PhSeCH2SiMe3 as compared with CFaPhSeMe towards LiTMP by a factor of 2.8. With LDA as base, however, the silyl substituent has the opposite effect, since m CF3PhSeCH2SiMe3 is deprotonated at least 25 times as fast as m>CF3PhSeMe (Scheme 24, d). Presumably, steric effects cancel the normal acidifying effect of the trimethylsilyl group when a hindered base such as LiTMP is used. 

Six-membered rings are considered before five-membered ones because they have been studied in greater detail and consequently their reactions are better understood. Because rate constants for quater-nization reactions have been correlated with values pertaining to the conjugate acids of heteroaromatic nucleophiles, substituent effects on acidities will be discussed prior to kinetic results. Acidity investigations suffer from fewer complications than N-alkylation and therefore provide results that offer considerable insight into the electronic effects of substituents on reactivity. Our review mentions only incidentally such related reactions, as oxidation - and acylation at an annular nitrogen atom. 

The year 1965 featured another milestone in the development of sandstone acidizing technology. Smith and Hendrickson discussed the reactivity and kinetics of HF and the effects of common variables encountered in the field. HF reactions with rock minerals and secondary depositions were studied theoretically. In addition, core flow tests were conducted using Berea sandstone cores. 

Similarly, carboxylic acid and ester groups tend to direct chlorination to the / and v positions, because attack at the a position is electronically disfavored. The polar effect is attributed to the fact that the chlorine atom is an electrophilic species, and the relatively electron-poor carbon atom adjacent to an electron-withdrawing group is avoided. The effect of an electron-withdrawing substituent is to decrease the electron density at the potential radical site. Because the chlorine atom is highly reactive, the reaction would be expected to have a very early transition state, and this electrostatic effect predominates over the stabilizing substituent effect on the intermediate. The substituent effect dominates the kinetic selectivity of the reaction, and the relative stability of the radical intermediate has relatively little influence. 

Only within the past few years have serious attempts been made to estimate quantitatively the differences in reactivity between thiophene and benzene and between the 2- and 3-position of thiophene. Careful investigation on the acid-induced exchange of deuterium and tritium have shown that the ratios of the exchange rates in the 2- and 3-positions are 1045 61 for deuterium and 911 60 for tritium in 57% by weight aqueous sulfuric acid at 24.6°C. A kinetic isotope effect in the isotopic exchange has been found to be k-r/kr, = 0.51 0.03 in the 2-position and kr/kjy — 0.59 0.04 in the... 

When diazomethane is slowly added to excess lactam, the anions formed can interact with unreacted lactam by means of hydrogen bonds to form ion pairs similar to those formed by acetic acid-tri-ethylamine mixtures in nonpolar solvents. The methyldiazonium ion is then involved in an ion association wdth the mono-anion of a dimeric lactam which is naturally less reactive than a free lactam anion. The velocity of the Sn2 reaction, Eq. (7), is thus decreased. However, the decomposition velocity of the methyldiazonium ion, Eq. (6a), is constant and, hence, the S l character of the reaction is increased which favors 0-methylation. It is possible that this effect is also involved in kinetic dependence investigations have shown that with higher saccharin concentrations more 0-methylsaccharin is formed. 

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