Isotopic exchange reactions of amines. Part 1. An 2H nuclear magnetic resonance study of the amino to methyl group deuteron exchange in methylamine

1976 ◽  
Vol 54 (23) ◽  
pp. 3775-3782 ◽  
Author(s):  
James D. Halliday ◽  
Patrick E. Bindner
Keyword(s):  
Thermal Decomposition ◽  
Isotopic Exchange ◽  
Equilibrium Mixture ◽  
Nuclear Magnetic Resonance Study ◽  
Exchange Reactions ◽  
Amino Groups ◽  
Thermal Decomposition Product ◽  
First Order ◽  
H Nmr ◽  
Exchange Kinetics

Deuteron exchange kinetics between the methyl and amino groups in methylamine, catalyzed by potassium methylamide (PMA), have been studied by 2H nmr.[Formula: see text]Typical values of kobs, the observed pseudo first-order exchange rate, are 1.0 × 10−5 s−1 at 0.21 M PMA and 323 K. Effects of added potassium methylamide and temperature are described. The rate is unaffected by the thermal decomposition product of PMA and there is little or no catalysis by an equilibrium mixture of the solvated electron species e−, (e−K+), and K−. The active catalyst in solution is shown to be monomeric PMA in equilibrium with relatively inactive dimers, …, n-mers. A mechanism that describes the exchange and relates it to the thermal decomposition of the amide is discussed.

A nuclear magnetic resonance study of the kinetics and equilibria for the oxidation of penicillamine and N-acetylpenicillamine by glutathione disulfide

1984 ◽  
Vol 62 (9) ◽  
pp. 1672-1680 ◽  
Author(s):  
Dallas L. Rabenstein ◽  
Yvon Theriault
Keyword(s):  
Equilibrium Constants ◽  
Reducing Power ◽  
Thiol Group ◽  
Nuclear Magnetic Resonance Study ◽  
Second Step ◽  
Glutathione Disulfide ◽  
Exchange Reactions ◽  
H Nmr ◽  
Mixed Disulfide ◽  
Ph Range

The kinetics and equilibria of the oxidation of penicillamine by glutathione disulfide to form, in the first step, penicillamine–glutathione mixed disulfide and glutathione and, in the second step, penicillamine disulfide and glutathione have been studied over the pH range 4–9 by 1H nmr. The reactive species are found to be penicillamine with its amino group protonated and its thiol group deprotonated and glutathione disulfide and penicillamine–glutathione mixed disulfide with their two amino groups protonated. The rate and equilibrium constants for the first step are much larger than those for the second step, indicating a small tendency for penicillamine to form its symmetrical disulfide by thiol/disulfide exchange reactions. This and the smaller reducing power of penicillamine as compared to glutathione are attributed to steric hindrance from the methyl groups adjacent to the sulfur. The kinetics and equilibria of the oxidation of N-acetylpenicillamine by glutathione disulfide were studied at neutral pH. Conditional equilibrium and rate constants for the oxidation of penicillamine by glutathione disulfide at pH 7.4 are presented and discussed in terms of the metabolism of penicillamine.

A nuclear magnetic resonance study of the equilibria and kinetics of the reaction of penicillamine with cystine and related disulfides

1985 ◽  
Vol 63 (8) ◽  
pp. 2225-2231 ◽  
Author(s):  
Yvon Theriault ◽  
Dallas L. Rabenstein
Keyword(s):  
Random Distribution ◽  
Ph Dependence ◽  
Thiol Group ◽  
Nuclear Magnetic Resonance Study ◽  
Mercaptoacetic Acid ◽  
Exchange Reactions ◽  
H Nmr ◽  
Mixed Disulfide ◽  
Ph Range ◽  
Kinetics Of

The thiol/disulfide exchange reactions of penicillamine (PSH) with cystine and several related disulfides (RSSR) have been studied by 1H nmr. The reactions take place in two steps:[Formula: see text]The equilibria and kinetics of the reactions of PSH with cystine were characterized over the pH range 5–8, while the reactions with the disulfides of cysteamine, homocysteine, 2-mercaptoethanol, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid were studied at neutral pH. From the pH dependence of the rate of the reaction of PSH with cystine, the reactive species are identified as penicillamine with its amino group protonated and its thiol group deprotonated and cystine and penicillamine–cysteine mixed disulfide with their amino groups protonated. For all the disulfides studied, the extent to which the first reaction occurs is within a factor of 2–3 of that predicted by a random distribution, while the extent to which the second reaction occurs is considerably less than for a random distribution. This is attributed to steric effects due to the two methyl groups next to the sulfur of penicillamine.

A 19F nuclear magnetic resonance study of the conjugate Brønsted–Lewis superacid HSO3F–SbF5. Part II.

2002 ◽  
Vol 80 (9) ◽  
pp. 1265-1277 ◽  
Author(s):  
Jobst Kühn-Velten ◽  
Matthias Bodenbinder ◽  
Raimund Bröchler ◽  
Gerhard Hägele ◽  
Friedhelm Aubke
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Nuclear Magnetic Resonance Study ◽  
Acid System ◽  
Exchange Reactions ◽  
Magnetic Resonance Study ◽  
Dilute Solutions ◽  
H Nmr ◽  
Anionic Species ◽  
High Concentrations ◽  
Initial Process

Solutions of SbF5 in HSO3F with xSbF5 = 0.012 to 0.405 are studied by 500 MHz 1H NMR (299 K) and 471 MHz 19F NMR (213–250 K), using NMR tubes fitted with fluoropolymer lining. The initial process during dissolution is the fast solvolysis of monomeric SbF5 in HSO3F according to SbF5 + nHSO3F [Formula: see text] SbF5 – n(SO3F)n + nHF (n = 1, 2). All HF formed during solvolysis will no longer be removed by reaction with glass, but will remain in the superacid system. Besides participation in the fast formation of various fluoro-fluorosulfato anions [SbF6 – n(SO3F)n]– (n = 0, 1, 2) and acidium ions [H2X]+(solv.) (X= F, SO3F), HF is involved in slow-exchange reactions of the type [SbF6 – n(SO3F)n]–(solv.) + HF [Formula: see text] [SbF7 – n(SO3F)n– 1]–(solv.) + HSO3F (n = 1, 2) detected because of a delay of 3 months between sample preparation and measurements and confirmed by repeating theses measurements after a further 3 months. There are three notable differences to our earlier study, affecting concentrations of the fluoro-fluorosulfato antimonate anions observed: (i) in dilute solutions [SbF6]– is formed in high concentrations (34.7–76.1%), with [Sb2F11]– now clearly detected at intermediate to high SbF5 concentrations (up to 5.8%); (ii) bis-fluorosulfato anions (cis-, trans-[SbF4(SO3F)2]–) are found in much lower concentrations only, which decrease further with time, while tris-fluorosulfato anions ([SbF3(SO3F)3]–) are now no longer observed; (iii) these reduced concentrations of poly-fluorosulfato anions in dilute solutions are responsible for the formation of fewer µ-SO3F-oligomers at lower concentrations, when more SbF5 is added. As a consequence, the HSO3F–SbF5 magic acid system is now less complex than found previously and only seven anionic species are clearly observed. Key words: superacids, antimony(V) fluoroanions, 1H NMR, 19F NMR, solvolysis.

A Proton Nuclear Magnetic Resonance Study of the Exchange Reactions of Acetonitrile – Boron Trihalide Adducts with Excess Acetonitrile

1972 ◽  
Vol 50 (8) ◽  
pp. 1262-1268 ◽  
Author(s):  
J. Fogelman ◽  
J. M. Miller
Keyword(s):  
Close Agreement ◽  
Mixed Solvents ◽  
Nuclear Magnetic Resonance Study ◽  
Proton Nuclear Magnetic Resonance ◽  
Exchange Reactions ◽  
Magnetic Resonance Study ◽  
First Order ◽  
Dissociation Energies ◽  
Donor Acceptor ◽  
Inert Solvent

Proton n.m.r. studies of the mechanism for exchange of excess acetonitrile with CH3CN•BX3 (X = F, Cl, Br) adducts show that the rates and activation energy for dissociation are influenced by solvent effects when mixed solvents such as C6H5NO2/CH2Cl2 or CD3NO2/CH2Cl2 are used. On extrapolation to inert solvent conditions, first order activation energies are obtained which are in close agreement with previously measured dissociation energies of acetonitrile adducts in solution. The relative rates of dissociation are CH3CN•BF3 > CH3CN•BCl3 > CH3CN•BBr3; in agreement with previous experimental evidence that the strength of the donor–acceptor band varies as CH3CN•BBr3 > CH3CN•BCl3 > CH3CN•BF3.

Electron exchange kinetics in a tetrahedrally coordinated copper(II)/(I) couple

1995 ◽  
Vol 73 (1) ◽  
pp. 61-69 ◽  
Author(s):  
Peter D. Metelski ◽  
A. Scott Hinman ◽  
Hideo D. Takagi ◽  
Thomas W. Swaddle
Keyword(s):  
Electron Transfer ◽  
Ligand Exchange ◽  
Copper Complexes ◽  
Ligand Substitution ◽  
Electron Exchange ◽  
Tetrahedral Complex ◽  
Pt Electrode ◽  
First Order ◽  
H Nmr ◽  
Exchange Kinetics

The four-coordinate anion CuI(dpym)2− (Hdpym = 3,3′,5,5′-tetramethyl-4,4′-dicarboethoxydipyrromethene) can be prepared in solution in acetone either by electrochemical reduction of the known tetrahedral complex CuII(dpym)20 (E0 = −290 mV vs. SCE) or by the quantitative reaction of 2Hdpym with Cu(CH3CN)4+ in the absence of O2. The latter reaction does not go to completion in solvents that bind relatively strongly to CuI or that are poor proton acceptors. Ligand exchange between CuI(dpym)2− excess Hdpym in acetone is "fast" in the 1H NMR timeframe, with k1 = 1.4 × 107 L mol−1 s−1at 298 K (first order in each reactant), ΔH‡1 = 3.4 ± 0.6 kJ mol−1, and ΔS‡1 = −97 ± 3 J K−1 mol−1. In the absence of excess Hdpym, dissociation of CuI(dpym)2− in acetone remains negligible. Homogeneous electron exchange between CuI(dpym)2− and CuII(dpym)20 in acetone falls in the "slow" 1H NMR timeframe, with kex = 5.9 × 103 L mol−1 s−1, ΔH‡ex = 48.5 ± 3.0 kJ mol−1, and ΔS‡ex = −10 ± 10 J K−1, at ionic strength I ≈ 0.007 mol L−1 and 298 K, while for the same self-exchange on a Pt electrode the heterogeneous rate constant kel = 0.16±0.04 cm s−1 at I ≈ 0.1 mol−1L−1 and 298 K, according to AC voltammetry. These values of Kex and Kel are of the order expected for CuII/I couples in which no significant change in coordination number or geometry accompanies electron transfer. Keywords: Electron transfer, copper complexes, ligand substitution kinetics, dynamic NMR.

scholarly journals Kinetics of ligand exchange between a uranium(IV) β-diketonate and free β-diketone

1977 ◽  
Vol 55 (20) ◽  
pp. 3559-3561 ◽  
Author(s):  
G. Folcher ◽  
N. Keller ◽  
C. Kiener ◽  
J. Paris
Keyword(s):  
Ligand Exchange ◽  
Free Ligand ◽  
Exchange Mechanism ◽  
First Order ◽  
H Nmr ◽  
Coordination Site ◽  
Exchange Kinetics ◽  
Kinetics Of

The intermolecular ligand exchange kinetics between a uranium(IV) β-diketonate and free β-diketone were studied by 1H nmr as a function of temperature and concentration. The reaction was found to be of first order in both chelate and free ligand. The results suggest that the exchange mechanism involves a ninth coordination site in the uranium(IV) chelate.

THE MANGANESE CYCLE IN SOIL: I. ISOTOPIC-EXCHANGE REACTIONS OF MN-54 IN AN ALKALINE SOIL

1962 ◽  
Vol 42 (1) ◽  
pp. 105-114 ◽  
Author(s):  
C. C. Weir ◽  
M. H. Miller
Keyword(s):  
Rate Constant ◽  
Isotopic Exchange ◽  
Specific Rate ◽  
Alkaline Soil ◽  
Exchange Reactions ◽  
First Order ◽  
Specific Rate Constant ◽  
Manganese Cycle

The manganese cycle in an alkaline soil was investigated by means of isotopic-exchange studies. Mn-54 was added to the solution in equilibrium with the soil and the rate of disappearance of the Mn-54 from solution was determined. The forms of soil manganese in equilibrium with solution manganese were studied by extracting the soil with buffered pyrophosphate and/or ZnSO4 solution after equilibration with Mn-54.The rate studies indicated that there are five or more first-order exchange reactions between soil and solution manganese. These reactions were characterized by a quantity and specific rate constant. Extraction of the soil following equilibration with Mn-54 indicated that a portion of the pyrophosphate extractable and all of the ZnSO4 extractable manganese was in equilibrium with the solution manganese. These two extractants removed all the soil manganese that had reached equilibrium with the Mn-54 in solution. It was indicated that the pyrophosphate extractable manganese existed in layered surfaces probably of a concretionary nature.

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