15481-55-7Relevant academic research and scientific papers
A kinetic study on nucleophilic displacement reactions of aryl benzenesulfonates with potassium ethoxide: Role of K+ ion and reaction mechanism deduced from analyses of LFERs and activation parameters
Um, Ik-Hwan,Kang, Ji-Sun,Shin, Young-Hee,Buncel, Erwin
supporting information, p. 490 - 497 (2013/03/13)
Pseudofirst-order rate constants (kobsd) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k obsd into kEtO- and kEtOK (i.e., the second-order rate constants for the reactions with the dissociated EtO - and ion-paired EtOK, respectively) shows that the ion-paired EtOK is more reactive than the dissociated EtO-, indicating that K + ion catalyzes the reaction. The catalytic effect exerted by K + ion (e.g., the kEtOK/kEtO- ratio) decreases linearly as the substituent X in the benzenesulfonyl moiety changes from an electron-donating group (EDG) to an electron-withdrawing group (EWG), but it is independent of the electronic nature of the substituent Y in the leaving group. The reactions have been concluded to proceed through a concerted mechanism from analyses of the kinetic data through linear free energy relationships (e.g., the Bronsted-type, Hammett, and Yukawa-Tsuno plots). K+ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a cyclic transition state (TS) rather than by increasing the nucleofugality of the leaving group. Activation parameters (e.g., ΔH? and ΔS?) determined from the reactions performed at five different temperatures further support the proposed mechanism and TS structures.
Inscribing the perimeter of the PagP hydrocarbon ruler by site-specific chemical alkylation
Khan, M. Adil,Moktar, Joel,Mott, Patrick J.,Vu, Mary,McKie, Aaron H.,Pinter, Thomas,Hof, Fraser,Bishop, Russell E.
experimental part, p. 9046 - 9057 (2011/11/04)
The Escherichia coli outer membrane phospholipid:lipid A palmitoyltransferase PagP selects palmitate chains using its β-barrel-interior hydrocarbon ruler and interrogates phospholipid donors by gating them laterally through an aperture known as the crenel. Lipid A palmitoylation provides antimicrobial peptide resistance and modulates inflammation signaled through the host TLR4/MD2 pathway. Gly88 substitutions can raise the PagP hydrocarbon ruler floor to correspondingly shorten the selected acyl chain. To explore the limits of hydrocarbon ruler acyl chain selectivity, we have modified the single Gly88Cys sulfhydryl group with linear alkyl units and identified C10 as the shortest acyl chain to be efficiently utilized. Gly88Cys-S-ethyl, S-n-propyl, and S-n-butyl PagP were all highly specific for C12, C11, and C10 acyl chains, respectively, and longer aliphatic or aminoalkyl substitutions could not extend acyl chain selectivity any further. The donor chain length limit of C10 coincides with the phosphatidylcholine transition from displaying bilayer to micellar properties in water, but the detergent inhibitor lauryldimethylamine N-oxide also gradually became ineffective in a micellar assay as the selected acyl chains were shortened to C10. The Gly88Cys-S-ethyl and norleucine substitutions exhibited superior C12 acyl chain specificity compared to that of Gly88Met PagP, thus revealing detection by the hydrocarbon ruler of the Met side chain tolerance for terminal methyl group gauche conformers. Although norleucine substitution was benign, selenomethionine substitution at Met72 was highly destabilizing to PagP. Within the hydrophobic and van der Waals-contacted environment of the PagP hydrocarbon ruler, side chain flexibility, combined with localized thioether-aromatic dispersion attraction, likely influences the specificity of acyl chain selection.
Stoichiometric Solvation Effects. Part 2. A New Product-Rate Correlation for Solvolyses of p-Nitrobenzenesulfonyl Chloride in Alcohol-Water Mixtures
Bentley, T. William,Jones, Robert O.,Koo, In Sun
, p. 753 - 760 (2007/10/02)
For reactions involving nucleophilic attack in alcohol-water mixtures, a linear relationship between the reciprocal of product selectivities (S) and the molar ratios of alcohol and water solvents can be derived, if it is assumed that the reactions are second-order in protic solvent (e.g., with one molecule of solvent acting as a nucleophile and the other as a general base).The relationship (1/S = (slope)(/) + intercept) fits the products of solvolyses of p-nitrobenzenesulfonyl chloride in aqueous ethanol and methanol at 25 deg C (determined by refrigerated RP-HPLC) within the range from water to 80percent v/v alcohol-water.From the slopes and intercepts of these product plots and the one observed rate constant for hydrolysis in pure water, the observed first-order rate constants in alcohol-water mixtures up to 90percent (v/v) can be calculated satisfactority, further supporting the validity of the derived linear relationship; the kinetic model includes three thrid-order rate constants: kww, where water acts as both nucleophile and general base; kwa, water acts as a nucleophile and alcohol acts as a general base; kaw, alcohol acts as a nucleophile and water acts as a general base.Inclusion of a fourth rate-constant, kaa, where the alcohol acts as a nucleophile and a second molecule of alcohol acts as a general base, is necessary to account for solvolyses in 90-99percent alcohol-water; kaa can be calculated from the observed first-order rate constants in pure alcohols.Independent values of kaw and kwa can be obtained from kaa and the slopes and intercepts of linear relationships between S and the molar solvent ratio / within the range 90-99percent alcohol-water.The dominant effect of solvent stoichiometry and the absence of other substantial medium effects is confirmed by the approximately constant third-order rate constants, calculated from the observed first-order rate constants in acetonitrile-, acetone- and dioxane-water mixtures.
Photooxidation of alkyl 4-nitrophenyl sulfides and sulfoxides. Observation of oxidative C-S bond cleavage and rearrangement reactions
Pasto, Daniel J.,Cottard, Fran?ois,Jumelle, Laurent
, p. 8978 - 8984 (2007/10/02)
Alkyl 4-nitrophenyl sulfides and sulfoxides undergo a self-photoinduced, singlet oxygen oxidation to produce a variety of products, including sulfonates and carbonyl compounds formed by the oxidative cleavage of the C-S bond of the sulfides and sulfoxides. Structural rearrangements are observed in the resulting carbonyl compounds formed in the oxidative cleavage of the C-S bond in the tert-amyl and 2-phenylethyl sulfides. An overall mechanism is proposed which involves the formation of peroxysulfoxides and peroxysulfones which undergo heterolytic C-S bond cleavage to form ion pairs which recombine to form persulfenates or persulfinates which then undergo photo- and/or thermallyinduced homolytic O-O bond cleavage to form alkoxy and sulfinyl or sulfonyl radicals. The alkoxy radicals undergo β-scission, disproportionation, or recombination with the sulfonyl radical to form the observed products. These C-S oxidative cleavage reactions have only been rarely observed in the earlier studies on the singlet oxygen oxidation studies of dialkyl sulfides, and are attributed, in part, to the presence of the 4-nitro group on the aromatic ring which greatly affects the susceptibility of the sulfur atom of the sulfides and sulfoxides toward nucleophilic attack, and on the reactivity of the peroxysulfoxides and peroxysulfones toward heterolytic cleavage of the O-S bond.
Reaction of Carboxylic Acid Esters with p-Toluenesulfonic Acid
Nitta, Yoshihiro,Arakawa, Yasushi
, p. 1380 - 1386 (2007/10/02)
The reaction of carboxylic acid esters with an excess of p-toluenesulfonic acid gave the corresponding p-toluenesulfonates.The mechanism of the transesterification is discussed.
