Dennis N. Kevill

Bio: Dennis N. Kevill is an academic researcher from Northern Illinois University. The author has contributed to research in topics: Solvolysis & Grunwald–Winstein equation. The author has an hindex of 26, co-authored 201 publications receiving 2683 citations. Previous affiliations of Dennis N. Kevill include Wesley College & Hanyang University.

Concerning the two reaction channels for the solvolyses of ethyl chloroformate and ethyl chlorothioformate

Abstract: The extended (two-term) Grunwald−Winstein equation has been applied to the solvolyses of ethyl chloroformate and ethyl chlorothioformate. For each substrate, there is evidence for two competing rea...

Correlation of the rates of solvolysis of phenyl chloroformate

Abstract: The specific rates of solvolysis of phenyl chloroformate in 21 solvents can be very well correlated using the extended Grunwald–Winstein equation, with incorporation of the NT solvent nucleophilicity scale and the YCl solvent ionizing scale, with sensitivities towards changes in the scale having values of 1.68 ± 0.10 and 0.57 ± 0.06, respectively. This is a solvolysis which, on the basis of several other types of evidence, is believed to follow an addition–elimination pathway with addition being rate-determining (or possibly an enforced concerted variant), and these sensitivities can be considered to be representative values for chloroformate esters following such a pathway.

Rate and product studies with benzyl and p-nitrobenzyl chloroformates under solvolytic conditions

Abstract: The specific rates of solvolysis of p-nitrobenzyl chloroformate are well correlated using the extended Grunwald-Winstein equation, with a high sensitivity (l) to changes in solvent nucleophilicity (N(T)) and a moderate sensitivity (m) to changes in solvent ionizing power (Y(Cl)). The values are consistent with a rate-determining association within an association-dissociation pathway. The selectivity values (S) for the attack at the acyl carbon show a modest preference for ethanol over water and a relatively high preference for ethanol over 2,2,2-trifluoroethanol (TFE). The solvolyses of benzyl chloroformate show similar characteristics in solvents of relatively high nucleophilicity and/or low ionizing power. In solvents with considerable fluoro alcohol content, an ionization mechanism, accompanied by loss of carbon dioxide, leads to benzyl chloride, benzyl alcohol, and benzyl alkyl ether. A new correlation now applies, with a much lower l value and somewhat higher m value. The S values for this pathway are close to unity, even in TFE-ethanol mixtures, consistent with the components of the binary solvent capturing a highly reactive carbocation.

Kirk-Othmer Encyclopedia of Chemical Technology数据库介绍及实例

Abstract: 介绍了Kirk—Othmer Encyclopedia of Chemical Technology（化工技术百科全书）（第五版）电子图书网络版数据库，并对该数据库使用方法和检索途径作出了说明，且结合实例简单地介绍了该数据库的检索方法。

Boron carbide ― a comprehensive review

Abstract: Boron carbide, which has a high melting point, outstanding hardness, good mechanical properties, low specific weight, great resistance to chemical agents and high neutron absorption cross-section (10BxC, x>4) is currently used in high-technology industries—fast-breeders, lightweight armors and high-temperature thermoelectric conversion. The contents of this review are: (1) introduction; (2) preparations—industrial preparative routes, powders, sintering (additives, pressureless, hot pressing, HIP); laboratory methods of synthesis (CVD, PVD, plasma, crystal growth); (3) analytical characterization; (4) phase diagram—a peritectic, nearly pure boron, and a wide phase homogeneity range (B4C-B10·5C); (5) rhombohedral crystal structure—a comprehensive model of the whole solid solution is proposed; (6) chemical properties; (7) physical properties—density, mechanical (strength, hardness, toughness) and thermo-electrical properties; (8) main industrial applications; (9) conclusion.

Sulfur(VI) Fluoride Exchange (SuFEx): Another Good Reaction for Click Chemistry

Abstract: Aryl sulfonyl chlorides (e.g. Ts-Cl) are beloved of organic chemists as the most commonly used S(VI) electrophiles, and the parent sulfuryl chloride, O2 S(VI) Cl2 , has also been relied on to create sulfates and sulfamides. However, the desired halide substitution event is often defeated by destruction of the sulfur electrophile because the S(VI) Cl bond is exceedingly sensitive to reductive collapse yielding S(IV) species and Cl(-) . Fortunately, the use of sulfur(VI) fluorides (e.g., R-SO2 -F and SO2 F2 ) leaves only the substitution pathway open. As with most of click chemistry, many essential features of sulfur(VI) fluoride reactivity were discovered long ago in Germany.6a Surprisingly, this extraordinary work faded from view rather abruptly in the mid-20th century. Here we seek to revive it, along with John Hyatt's unnoticed 1979 full paper exposition on CH2 CH-SO2 -F, the most perfect Michael acceptor ever found.98 To this history we add several new observations, including that the otherwise very stable gas SO2 F2 has excellent reactivity under the right circumstances. We also show that proton or silicon centers can activate the exchange of SF bonds for SO bonds to make functional products, and that the sulfate connector is surprisingly stable toward hydrolysis. Applications of this controllable ligation chemistry to small molecules, polymers, and biomolecules are discussed.