Transesterification versus nucleophilic displacement in cyclic and open-chain organic sulphites

1968 ◽  
pp. 684
Author(s):  
P. A. Bristow ◽  
J. G. Tillett
Keyword(s):  
Open Chain ◽  
Nucleophilic Displacement

Open-chain nitrogen compounds. Part XV. A kinetic study of the hydrolysis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and related triazenes

1992 ◽  
Vol 70 (8) ◽  
pp. 2224-2233 ◽  
Author(s):  
Keith Vaughan ◽  
Donald L. Hooper ◽  
Marcus P. Merrin
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Buffer System ◽  
Open Chain ◽  
Nucleophilic Displacement ◽  
Ether Oxygen ◽  
Rate Of Hydrolysis ◽  
Electron Withdrawing Group ◽  
Ph Range ◽  
Kinetics Of

The kinetics of hydyrolysis of a series of 1-aryl-3-aryloxymethyl-3-methyltriazenes, Ar-N=N-NMe-CH2OAr′, was studied over the pH range 2–7.5. Reactions were followed by the change in UV absorbance spectra of the triazenes. The aryloxymethyltriazenes decompose more slowly at pH 7.5 than the hydroxymethyltriazenes, Ar-N=NMe-CH2OH; the hydrolysis is favoured by the presence of an electron-withdrawing group in Ar′. A mixed isopropanol/buffer system was developed in order to improve solubility of the aryloxymethyl triazenes. Lowering the pH caused an increase in the rate of hydrolysis and under strongly acidic conditions an electron-withdrawing group in Ar′ actually slows down the reaction. A Hammett plot of the pseudo-first-order rate constant, kobs, is curved, indicating that two or more mechanisms operate simultaneously and that the contribution of each mechanism is substituent-dependent. A plot of kobs vs. [buffer] is linear; the slope of the plot affords the rate constant, kb for the buffer-catalyzed reaction for each substituent. A Hammett plot of kb vs. σ is linear with ρ = +0.55, suggesting that the buffer-catalyzed reaction involves nucleophilic displacement of the phenoxy group by the buffer anion. Further analysis afforded the specific acid-catalyzed rate constants, [Formula: see text], for each substituent; this component of the reaction has a negative ρ, consistent with a mechanism involving protonation at the ether oxygen. The postulation that specific acid catalysis is a component of the reaction mechanism was confirmed by the observation of a solvent deuterium isotope effect, 2.28 > kH/kD > 1.60. Only the p-NO2 and p-CN phenyloxymethyltriazenes showed any spontaneous decomposition.

Vulcanization Accelerator and Activator Complexes. 2. Chemistry of Amine and Zinc Carboxylate Complexes of Zinc and Cadmium Benzothiazolyl Mercaptides

1966 ◽  
Vol 39 (4) ◽  
pp. 1115-1125 ◽  
Author(s):  
Brian Milligan
Keyword(s):  
Reaction Medium ◽  
Active Species ◽  
Intrinsic Activity ◽  
Insertion Reactions ◽  
Open Chain ◽  
Co Catalyst ◽  
Nucleophilic Displacement ◽  
Displacement Reactions ◽  
Vulcanization Accelerator ◽  
Interchange Reactions

Abstract The behavior of zinc benzothiazolyl mercaptide (ZMBT) and its complexes with amines and zinc carboxylates in effecting nucleophilic displacement reactions related to those which occur during accelerated sulfur vulcanization has been studied. Ligands influence the activity of ZMBT in nucleophilic displacement reactions (a) by increasing the solubility of ZMBT in the reaction medium and (b) by increasing the polarity of the Zn—S bond; this increase in polarity only enhances the intrinsic activity of the catalyst if a second zinc species (e.g., a zinc carboxylate) is present. Complexes of zinc carboxylates with ZMBT are very active catalysts for disulfide interchange reactions, but not for sulfur insertion reactions. In the latter, an amine is also necessary to act as a co-catalyst with traces of hydrogen sulfide in order to convert octa-atomic sulfur into a more reactive open-chain polysulfide species. A combination of ZMBT, an amine and a zinc carboxylate provides the best catalyst for effecting sulfur insertion reactions at high temperatures; the active species may be a ternary complex. Amine complexes of ZMBT, either in the absence or presence of a zinc carboxylate, are good accelerators for the vulcanization of cis-1,4-polyisoprene with sulfur.

Bifluoride Ion Mediated SuFEx Trifluoromethylation of Sulfonyl Fluorides and Iminosulfur Oxydifluorides

2018 ◽  
Author(s):  
Christopher J. Smedley ◽  
Bing Gao ◽  
Suhua Li ◽  
Qinheng Zheng ◽  
Andrew Molino ◽  
...  
Keyword(s):  
Breast Cancer Cells ◽  
Catalytic Mechanism ◽  
Bioactive Molecules ◽  
Chromatographic Purification ◽  
Rapid Exchange ◽  
Nucleophilic Displacement ◽  
Sulfur Fluoride ◽  
Reactions With Nucleophiles ◽  
New Generation ◽  
Selection Of

Sulfur-Fluoride Exchange (SuFEx) is the new generation click chemistry transformation exploiting the unique properties of S-F bonds and their ability to undergo near-perfect reactions with nucleophiles. We report here the first SuFEx based protocol for the efficient synthesis of pharmaceutically important triflones and bis(trifluoromethyl)sulfur oxyimines from the corresponding sulfonyl fluorides and iminosulfur oxydifluorides, respectively. The new protocol involves the rapid exchange of the S-F bond with trifluoromethyltrimethylsilane (TMSCF<sub>3</sub>) upon activation with potassium bifluoride in anhydrous DMSO. The reaction tolerates a wide selection of substrates and proceeds under mild conditions without need for chromatographic purification. A tentative catalytic mechanism is proposed supported by DFT calculations, involving formation of the free trifluoromethyl anion followed by nucleophilic displacement of the S-F through a five-coordinate intermediate. The preparation of a benzothiazole derived bis(trifluoromethyl)sulfur oxyimine with cytotoxic selectivity for MCF7 breast cancer cells demonstrates the utility of this methodology for the late-stage functionalization of bioactive molecules.<br>

Reactions of Bis(phenyldiazenido)rhenium Complex [ReBr2(NNPh)2(PPh3)2]Br with Carbon Monoxide and Alk-1-ynes

2007 ◽  
Vol 72 (5-6) ◽  
pp. 599-608 ◽  
Author(s):  
Maria Teresa A. R. S. da Costa ◽  
Maria Fátima C. Guedes da Silva ◽  
João J. R. Fraústo Da Silva ◽  
Armando J. L. Pombeiro
Keyword(s):  
Carbon Monoxide ◽  
Rhenium Complex ◽  
Nucleophilic Displacement

The conversion of the bis(diazenido) complex [ReBr2(NNPh)2(PPh3)2]Br (1) to the mono(diazenido) complex [ReBr3(NNPh)(PPh3)2] (2) is promoted by alk-1-ynes, whereas the reaction with CO leads to the mixed dicarbonylmono(diazenido) Re(III) species [ReBr(CO)2- (NNPh)(PPh3)2]Br (3). Both reactions are suggested to occur via related pathways involving a nucleophilic displacement of one of the diazenide ligands by Br-. Reduction of the phenyldiazenide ligand in 2 occurs in the attempted reaction with HC≡CPh to give the nitrido complex [ReBr2(N)(PPh3)2] (4) and the bis(diazenido) species [ReBr2(NNPh)2(PPh3)2] (5) and [ReBr(NNPh)2(PPh3)2] (6).

Photoredox Reactions of Iodo Iron(III) Complexes Containing Tetradentate Ligands

2001 ◽  
Vol 66 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jozef Šima ◽  
Dáša Lauková ◽  
Vlasta Brezová
Keyword(s):  
Schiff Bases ◽  
Spin Trapping ◽  
Molar Ratio ◽  
Oh Radicals ◽  
Solvated Electrons ◽  
Open Chain ◽  
Tetradentate Ligands ◽  
Visible Irradiation ◽  
Epr Spin Trapping ◽  
Spin Trapping Technique

Photoredox reactions occurring in irradiated methanolic solutions of trans-[FeIII(R,R'-salen)(CH3OH)I], where R,R'-salen2- are N,N'-ethylenebis(R,R'-salicylideneiminato), tetradentate open-chain N2O2-Schiff bases with R,R' = H, 5-Cl, 5-Br, 3,5-di-Br, 3,5-di-(CH3), 3-OCH3, 5-OCH3, have been investigated and their mechanism proposed. The complexes are redox-stable in the dark. Ultraviolet and/or visible irradiation of methanolic solution of the complexes induces photoreduction of Fe(III) to Fe(II). Depending on the composition of the irradiated solutions, •CH2OH radicals or solvated electrons were identified by the EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde and the molar ratio of Fe(II) and CH2O is close to 2 : 1. The efficiency of the photoredox process is strongly wavelength-dependent and influenced by the peripheral groups R,R' of the tetradentate ligands.

Additions and Corrections - Photoelectron Spectra of Open Chain C6H6Isomers

1976 ◽  
Vol 98 (8) ◽  
pp. 2371-2371
Author(s):  
Peter Bischof ◽  
Rolf Gleiter ◽  
Hennig Hopf ◽  
Frank Lenich
Keyword(s):  
Photoelectron Spectra ◽  
Open Chain

Aiding Factors in the Formation of Azaplatinacyclobutane Rings – X-ray and Crystal Structure of [Pt{CH(Ph)CH2NEt2-κC,κN}(N,N,N′,N′-tetramethylethylenediamine)]+ and of Its Open-Chain Precursor

2007 ◽  
Vol 2007 (15) ◽  
pp. 2144-2150 ◽  
Author(s):  
Giuseppe Lorusso ◽  
Carmen R. Barone ◽  
Nicola G. Di Masi ◽  
Concetta Pacifico ◽  
Luciana Maresca ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Open Chain ◽  
X Ray

Synthesis of sandwich type acyclic tetra-nuclear silver(I)-N-heterocyclic carbene complexes for wound healing applications

2020 ◽  
Vol 75 (9-10) ◽  
pp. 369-376
Author(s):  
Ayesha Riaz ◽  
Muhammad Adnan Iqbal ◽  
Haq Nawaz Bhatti ◽  
Muhammad Shahid
Keyword(s):  
Alkyl Halides ◽  
Wound Contraction ◽  
Spectroscopic Techniques ◽  
Open Chain ◽  
Standard Drug ◽  
Sandwich Type ◽  
Benzimidazolium Salts ◽  
Multistep Reaction

AbstractTwo meta-xylyl linked tetrakis-benzimidazolium salts (L1-L2) as multidentate ligands and two respective silver complexes (C1 and C2) were synthesized. A multistep reaction was done at room temperature, starting with simple benzimidazole and alkyl halides, going through precursors and salt formation by reflux and finally in situ deprotonation of tetrabenzimidazolium salts with Ag2O to yield respective tetra-nuclear Ag(I)-N-heterocyclic Carbene (NHC) complexes. Propyl and butyl groups were bonded at the terminal positions of tetra-azolium open chain salts. Characterization of compounds was done by analytical and spectroscopic techniques. On the basis of spectroscopic data, a chemical structure with open chains having four Ag(I) ions sandwiched between NHC layers was established. Potential of synthesized complexes (C1 & C2) for wound contraction was evaluated and compared with standard wound contraction gel. Percentage wound contraction of both complexes was found very close to that of standard drug used in parallel.

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