Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

1981 ◽  
Vol 59 (22) ◽  
pp. 3177-3187 ◽  
Author(s):  
Erwin Buncel ◽  
Allen W. Zabel
Keyword(s):  
Complex Formation ◽  
Rate Constants ◽  
Hydrogen Exchange ◽  
Equilibrium Constants ◽  
Medium Composition ◽  
Proton Exchange ◽  
Ion Concentrations ◽  
First Order ◽  
Order Rate ◽  
Insight Into

Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) – D2O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, kobs, show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of σ-complex formation in these systems. The profile for kobs as function of medium composition exhibits a maximum at ca. 70 mol% DMF, and εapp for σ-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for σ-complex formation, Ke, are used to calculate the free, or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k2, the second order rate constants for exchange. The k2 values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k2 and log Ke vs. H− plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the σ-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

scholarly journals Compounds of 6, 13-Diamino-6, 13-Dimethyl-1, 4, 8, 11 - Tetraazacyclotetradecane

2021 ◽  
Author(s):  
◽  
Asokamali Siriwardena
Keyword(s):  
Rate Constants ◽  
Magnetic Measurements ◽  
Order Rate Constant ◽  
Acidic Solutions ◽  
First Order ◽  
Order Rate ◽  
Pendant Arm ◽  
Nickel Copper ◽  
13C Nuclear Magnetic Resonance ◽  
Kinetics Of

<p>The reaction of bis-(diaminoethane)nickel(II) chloride, ([Ni(en)2]Cl2 in methanol with formaldehyde and nitroethane in the presence of triethylamine proceeds readily to produce (6, 13-dimethyl-6, 13-dinitro-1, 4, 8, 11-tetraazacyclotetradecane)nickel(II) chloride, [Ni(dini)] - Cl2. Reduction of the nitro groups of this compound by catalytic hydrogenation yields three isomers of the pendant arm macrocyclic complex (6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazachyclotetradecane)nickel(II) chloride, designated a-, b- and c-[Ni(diam)]Cl2. These were separated by fractional crystallization. The aisomer was observed to isomerizes slowly in solution to the b- form. A parallel dissociation reaction of the a- isomer was also observed. The demetallation of a- and b- isomers of the diam complex of nickel by reaction with cyanide or concentrated acid at 140 degrees C produces the macrocycle meso-(6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazacyclotetra-decane), diam. A variety of hexamine, pentamine and tetramine complexes of diam with nickel(II), copper(II), cobalt(II) and (III), chromium(III), palladium(II), rhodium(III), zinc(II) and cadmium(II) were prepared. Hexamine and tetramine forms of labile metal complexes could be rapidly and reversibly interconverted by altering the pH. The hexamine cobalt(III) cation, [Co(diam)]3+ was by far the most inert of the prepared cobalt(III) complexes, remaining unaffected in hot acidic solutions. In contrast, a single pendant arm of the hexamine [Cr(diam)]3+ cation could be dissociated in acid. (Two possibly triamine complexes of lead were also prepared). These compounds were characterized by elemental analysis, magnetic measurements, electronic, infrared, 1H and 13C nuclear magnetic resonance spectra. The pendant arm protonation constants (log K) of diam and selected complexes of nickel, copper and palladium were calculated from potentiometric titration measurements at 25 degrees C. The log K values for diam at 25 degrees C (I = 0.1 M NaclO4) were 11.15, 9.7, 6.2 and 5.3. Kinetics of the parallel isomerization and dissociation of a-[Ni(dimH2)]4+ in HCl/NaCl solutions were monitored spectrophotometrically at 50 degrees C. The rate of reaction in acidic solutions showed a non-linear dependency on acid concentration. The observed first order rate constant (kobs) for disappearance of a-[Ni(diamH2)]4+ (by isomerization and dissociation) in 2.0 M HCl, 0.1 M NaOH and 2.0 M NaCl were 3.05 x 10-4, 2.0(3) x 10-2 and 5.0 x 10-5 s-1 respectively. The rate of the dissociation component of the reaction of a-[Ni(diamH2)]4+ in 2.0 M HCl at 50 degrees C was 1.82 x 10-7 s-1. Acid bydrolysis kinetics of (Cu[diamH2])(ClO4)4 in hydrochloric acid and perchloric acid at 50 and 70 degrees C were studied spectrophotometrically. The reactions were slow and the observed first order rate constants were to a first approximation independent of the particular acid or its concentration. The observed first order rate constants were 1 x 10-9 and 8 x 10-9 s-1 at 50 and 70 degrees C respectively. Questions about the nature of the reaction being followed have been raised.</p>

The thermal decompositions of carbamates. I. Ethyl N-Methyl-N-phenylcarbamate

1971 ◽  
Vol 24 (12) ◽  
pp. 2541 ◽  
Author(s):  
NJ Daly ◽  
F Ziolkowski
Keyword(s):  
Carbon Dioxide ◽  
Gas Phase ◽  
Rate Constants ◽  
Volume Ratio ◽  
Reaction Vessel ◽  
First Order ◽  
Order Rate

Ethyl N-methyl-N-phenylcarbamate decomposes in the gas phase over the range 329-380� to give N-methylaniline, carbon dioxide, and ethylene. The reaction is quantitative, and is first order in the carbamate. First-order rate constants are described by the equation ������������������� k1 = 1012.44 exp(-45,380/RT) (s-1) and are unaffected by the addition of cyclohexene or by increase in the surface to volume ratio of the reaction vessel. The reaction is considered to be unimolecular and likely to proceed by means of a mechanism of the type represented by the pyrolyses of acetates, xanthates, and carbonates.

HUMAN MEIZOTHROMBIN 1, ITS ISOLATION AND PROPERTIES

1987 ◽  
Author(s):  
Zbigniew S Latallo ◽  
Craig M Jackson
Keyword(s):  
Rate Constants ◽  
Antithrombin Iii ◽  
Order Rate Constant ◽  
Red Cross ◽  
Apparent Lack ◽  
First Order ◽  
Order Rate ◽  
Matching Grant ◽  
Echis Carinatus

Meizothrombin (MT) and meizothrombin des Fragment 1 (MT1) are intermediates in the conversion of prothrombin to α-thrombin (αTH). Due to their transient character, properties of these enzymes are difficult to establish. Isolation of MT1 was achieved by affinity chromatography on D-Phe-Pro-Arginal (FPRal)immobilized on Affi-Gel 10 as originally employed for thrombin purification (Patel et al. Biochim.Biophys. Acta 748,321 (1983)). Human prethrombin 1 was activated with the purified activator from Echis carinatus venom in the presence of Ca++;, benzamidine and FPRal gel at pH 7.8. After exhaustive washing the MT1 was eluted with 0.1 M hydroxylamine in 0.15 M Na acetate buffer, pH 5.5. Under these conditions the MT1 is stable and can bestored at -70°C. Upon changing the pH of the preparation to 8.0, complete conversion into aTH occurred atroom temperature within 48 hours. Homogeneity of both preparations wasdemonstrated by PAGE. The Km and ke, values for MT1 measured on Tos-Gly-Pro-Arg pNA(0.1 M NaCl, 0.01 M TRIS, 0.01 M HEPES, 0.1% PEG, pH 7.8, 25°C) were 15.7 /iM and 126 s-1. The kinetic con stants for the aTH resulting from autocatalytic degradation of MT1 were indistinguishable from those previously established forαTH obtained by Xa activation i.e. 4.77 /μM and 126 s-1. Clotting activity of MT1 was found to be only one fifth as high as that of the resulting μTH(746 u/mg vs. 3900 u/mg as tested using the NIH standard) .Inhibitionof MTl by antithrombin III was alsomuch less rapid than αTH andmost importantly, it was not affected by high affinity heparin( Mr20,300). Under conditions of the experiment (0.3 M NaCl, 0.0rl M TRIS, 0.01 M HEPES, 2.5 mM EDTA, 0.1% PEG, pH 7.8, 25°C; [ATIII] 100 nM, [E] 10 nM), the pseudo first order rate constants in the absence of heparin were 4.04 × 10-3V1 (MTl) and 1.13 × 10-3V1 (αTH), giving apparent second order rate constants of 4.04 × 103 and 1.13 × 10-4M-1s-1. In the presence of 4.5 nM of heparin the observed first order rate constant for MTl remained unchanged whereas it increased to 6.241 × 10-3s-1 (5.5 fold) for αTH. This apparent lack of an effect of heparin may be of significance in vivo.Supported by a Matching Grant from the American National Red Cross and by the Southeastern Michigan Blood Service.

The mercury(II)-induced aquation of trans-Chloroamminebis(dimethylglyoximato)cobalt(III) complex

1975 ◽  
Vol 28 (5) ◽  
pp. 1133 ◽  
Author(s):  
S Chan ◽  
S Tan
Keyword(s):  
Rate Constants ◽  
Aqueous Ethanol ◽  
Association Constants ◽  
First Order ◽  
Order Rate ◽  
Leaving Group ◽  
Pseudo First Order ◽  
Activated Complex

The pseudo first-order rate constants for the mercury(II)-induced aquation of trans-[Co(Hdmg)2(NH3)Cl] (Hdmg = dimethylglyoximate ion) have been measured in aqueous and aqueous ethanol solutions (ethanol- water mole ratio 1 : 5.1) containing various excess amounts of mercury(II)ion at 273.2 K. Association constants of the complex formed with mercury(II) ion and rate constants for dissociation of the activated complex in both solutions have been calculated. The kinetic results are discussed in terms of formation of an activated complex Co-C1-Hg, followed by a simple rate-determining aquation in which HgCl+ acts as the leaving group.

Kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions assessed by voltammetry

2009 ◽  
Vol 74 (10) ◽  
pp. 1531-1542 ◽  
Author(s):  
Vlado Cuculić ◽  
Ivanka Pižeta
Keyword(s):  
Ionic Strength ◽  
Complex Formation ◽  
Rate Constants ◽  
Glycine Concentration ◽  
First Order ◽  
Mercury Drop Electrode ◽  
Calculated Rate ◽  
Cathodic Voltammetry ◽  
Kinetics Of ◽  
Voltammetric Measurements

The kinetics of iron(III) hydrolysis and precipitation in aqueous glycine solutions were studied by cathodic voltammetry with a mercury drop electrode. The kinetics was controlled by changing ionic strength (I), pH and glycine concentration. Voltammetric measurements clearly showed formation and dissociation of a soluble Fe(III)–glycine complex, formation of iron(III) hydroxide and its precipitation. The rate constants of iron(III) hydroxide precipitation were assessed. The precipitation is first-order with respect to dissolved inorganic iron(III). The calculated rate constants of iron(III) precipitation varied from 0.18 × 10–5 s–1 (at 0.2 M total glycine, pH 7.30, I = 0.6 mol dm–3) to 2.22 × 10–3 s–1 (at 0.1 M total glycine, pH 7.30, I = 0.2 mol dm–3). At 0.5 M total glycine and I = 0.6 mol dm–3, the iron(III) precipitation was not observed.

scholarly journals Biotransformation of trace organic chemicals during groundwater recharge: How useful are first-order rate constants?

2015 ◽  
Vol 179 ◽  
pp. 65-75 ◽  
Author(s):  
J. Regnery ◽  
A.D. Wing ◽  
M. Alidina ◽  
J.E. Drewes
Keyword(s):  
Groundwater Recharge ◽  
Rate Constants ◽  
Organic Chemicals ◽  
First Order ◽  
Order Rate ◽  
Trace Organic Chemicals ◽  
Trace Organic

Hydrothermal Transformation of Inorganic and Biogenic Silica as Studied Using in Situ Hydrothermal Infrared Microspectroscopy

2018 ◽  
Vol 72 (10) ◽  
pp. 1487-1497
Author(s):  
Naoto Morifuji ◽  
Satoru Nakashima
Keyword(s):  
Activation Energy ◽  
Rate Constants ◽  
Biogenic Silica ◽  
Zero Order ◽  
Silica Gels ◽  
Dissolution Rates ◽  
First Order ◽  
Order Rate ◽  
Hydrothermal Transformation

Infrared (IR) spectral changes with time of biogenic and inorganic silica have been examined using in situ IR micro-spectroscopy by using an original hydrothermal diamond cell. Centric diatoms (diameters = 100–350 µm) and silica gels (C-300, Wako Chemicals) were heated at 125–185 ℃ range with a pressure of 3 MPa. Decreases of 950 cm−1 (Si–OH) peak heights could be fitted by a combination of exponential and linear decreases (y = A1 exp (−k1t) − k0 t + A0). The first-order rate constants k1 [s−1] for Si–OH decreases of diatoms and silica gels are similar but the activation energy was lower for diatoms (61 kJċmol−1 < 106 kJċmol−1). The first-order rate constants k1 [s−1] for Si–OH decreases of diatoms and silica gels are much faster than reported hydrothermal transformation rates of silica (Opal A to Opal CT and Opal CT to quartz). These results indicate that the exponential Si–OH decreases observed in biogenic and inorganic silica during hydrothermal reactions are considered to correspond to dehydration–condensation reactions in the amorphous states (Si–OH + HO–Si → Si–O–Si). In fact, band area ratios 1220 cm−1/1120 cm−1 increased exponentially indicating more bridging of Si–O–Si. On the other hand, the linear decreases of Si–OH of silica gels (k0 [s−1]) were considered to be due to dissolution of silica. By using the grain size and density of silica gels, the zero-order dissolution rate constants k0* [molċm−2ċs−1] were calculated from k0 [s−1]. The obtained dissolution rates k0* are larger than reported values for silica glass and quartz. The zero-order dissolution rates k0 [s−1] for diatoms are similar to those for silica gels but with a lower activation energy (32 kJċmol−1 < 60 kJċmol−1). The smaller activation energy values for diatoms than silica gels both for the first and zero-order decrease rates of Si–OH might indicate catalytic effects of organic components bound to biogenic silica for the dehydration–condensation reaction and dissolution. The present in situ hydrothermal IR micro-spectroscopy is useful for characterizing transformation of amorphous materials including inorganic–organic composites.

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