The isomerization of ammonium cyanates. II. The kinetics of isomerization of ammonium and alkylammonium cyanates in dimethyl sulphoxide-water mixtures

1977 ◽  
Vol 30 (4) ◽  
pp. 903
Author(s):  
KJ Hall ◽  
DW Watts
Keyword(s):  
Side Reaction ◽  
Dimethyl Sulphoxide ◽  
Side Reactions ◽  
Solvent Mixtures ◽  
Kinetics Of ◽  
Reaction In Water

The kinetics of the isomerizations of ammonium, methylammonium and ethylammonium cyanates to urea, methylurea and ethylurea have been studied in aqueous dimethyl sulphoxide over the range 0-100% dimethyl sulphoxide. Side reactions occur at all solvent compositions and urea formation accounts for only between 65% and 90% of products. The side reaction in water produces carbonate and in dimethyl sulphoxide biuret or alkyl-substituted biurets. The proportion of each of these products in solvent mixtures has not been determined.

scholarly journals Modelling of the kinetics of transesterification reaction of rapeseed oil with different reactant dosing procedures

2019 ◽  
Vol 292 ◽  
pp. 01029
Author(s):  
Jakub Husár ◽  
Jiří Pecha ◽  
Lubomír Šánek ◽  
Karel Kolomaznik
Keyword(s):  
Main Product ◽  
Methyl Esters ◽  
Side Reaction ◽  
Raw Material ◽  
Process Equipment ◽  
Control Algorithms ◽  
Side Reactions ◽  
Initial Reaction ◽  
Industrial Manufacturing ◽  
Kinetics Of

Transesterification of triglycerides is a common method in the production of biodiesel, specifically methyl esters of fatty acids. In this work, the transesterification kinetics was studied for an unusual dosing procedure taking into account the side reaction - hydrolysis. This unwanted side reaction, called saponification, causes the deactivation of the used catalyst and decreases the purity of biodiesel, the main product of transesterification. For these reasons, a model of methanolysis has been designed and clarified considering both the main and side reactions with various dosing of raw material and catalyst. The suggested mathematical model is capable of predicting the state of the reaction mixture in time under different initial reaction mixture composition and different reaction temperature. The verified model could be useful for the estimation of optimal conditions and dosage procedure of methanolysis under which saponification is reduced, and is also important for the design of industrial manufacturing process, equipment and process control algorithms.

The isomerization of ammonium cyanates. I. The kinetics of ammonium cyanate and alkylammonium cyanate isomerization in dimethyl sulphoxide

1977 ◽  
Vol 30 (4) ◽  
pp. 781 ◽  
Author(s):  
KJ Hall ◽  
DW Watts
Keyword(s):  
Ionic Strength ◽  
Kinetic Studies ◽  
Side Reaction ◽  
Dimethyl Sulphoxide ◽  
Cyanic Acid ◽  
Subsequent Reaction ◽  
Ionic Strength Dependence ◽  
Strength Dependence ◽  
Kinetics Of

The isomerization of ammonium cyanate in dimethyl sulphoxide leads to urea with a substantial side reaction yielding biuret (c. 25 % at 60�). Biuret is formed in a process that is competitive with urea formation and not in a subsequent reaction involving urea. The production of urea, as in water, is by the reaction of ammonia and cyanic acid molecules and it is postulated that biuret is formed through an intermediate of dimerized cyanic acid. Temperature and ionic strength dependence have been studied. Kinetic studies of the isomerization of methylammonium and ethylammonium cyanates are also described.

Energetic Control of Redox-Active Polymers Towards Safe Organic Bioelectronic Materials

2019 ◽  
Author(s):  
Alexander Giovannitti ◽  
Reem B. Rashid ◽  
Quentin Thiburce ◽  
Bryan D. Paulsen ◽  
Camila Cendra ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Organic Semiconductors ◽  
Side Reaction ◽  
Semiconducting Polymers ◽  
Side Reactions ◽  
Redox Active ◽  
Donor Acceptor ◽  
Electrochemical Devices ◽  
Biological Environment ◽  
Device Operation

<p>Avoiding faradaic side reactions during the operation of electrochemical devices is important to enhance the device stability, to achieve low power consumption, and to prevent the formation of reactive side‑products. This is particularly important for bioelectronic devices which are designed to operate in biological systems. While redox‑active materials based on conducting and semiconducting polymers represent an exciting class of materials for bioelectronic devices, they are susceptible to electrochemical side‑reactions with molecular oxygen during device operation. We show that this electrochemical side reaction yields hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), a reactive side‑product, which may be harmful to the local biological environment and may also accelerate device degradation. We report a design strategy for the development of redox-active organic semiconductors based on donor-acceptor copolymers that prevent the formation of H<sub>2</sub>O<sub>2</sub> during device operation. This study elucidates the previously overlooked side-reactions between redox-active conjugated polymers and molecular oxygen in electrochemical devices for bioelectronics, which is critical for the operation of electrolyte‑gated devices in application-relevant environments.</p>

scholarly journals Kinetics of Non-Enzymatic Synthesis of Dipeptide Cbz-Phe-Leu with AOT Reversed Micelles

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1003
Author(s):  
Michiaki Matsumoto ◽  
Tadashi Hano
Keyword(s):  
Enzymatic Synthesis ◽  
Maximum Yield ◽  
Side Reactions ◽  
Experimental Conditions ◽  
Operational Conditions ◽  
Ph Dependency ◽  
Optimum Water Content ◽  
Short Time ◽  
Kinetics Of ◽  
Aot Reversed Micelles

The non-enzymatic synthesis of N-benzyloxycarbonyl-L-phenylalanyl-L-leucine (Cbz-Phe-Leu) from lipophilic N-benzyloxycarbonyl-L-phenylalanine (Cbz-Phe) and hydrophilic L-leucine (Leu), by N, N’-dicyclohexylcarbodiimide (DCC) as a condensing agent, was carried out using a reversed micellar system composed of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) as a surfactant and isooctane. We successfully synthesized Cbz-Phe-Leu in a short time and investigated the effects of its operational conditions, the DCC concentration, w0, and the pH on the kinetic parameters and the maximum yields. For dipeptide synthesis, we had to add an excess of DCC with the substrates because of the side reactions of Cbz-Phe. From the pH dependency of the reactivity, a partially cationic form of Leu was better for a synthesis reaction because of the enrichment of Leu at the interface by anionic AOT. The optimum water content on the dipeptide synthesis was w0 = 28 due to the competition of the peptide synthesis and the side reactions. The maximum yield of Cbz-Phe-Leu was 0.565 at 80 h under optimum experimental conditions.

Stopped-flow circular dichroism

2000 ◽  
Author(s):  
Alison Rodger ◽  
Michael J. Carey
Keyword(s):  
Circular Dichroism ◽  
Detection Methods ◽  
Side Reactions ◽  
Stopped Flow ◽  
Baseline Drift ◽  
Mixing Ratios ◽  
Flow Mixing ◽  
Ideal Tool ◽  
Kinetics Of ◽  
Circular Dichroïsm

As is apparent from previous chapters (Chapters 6, 8 and 9), understanding the kinetics of chemical and biological processes is extremely important. Questions we often consider, explicitly or implicitly, include: Has something happened ‘instantaneously’ or will it take 20 years? Does changing the conditions or available reagents affect either the end product or the rate of a process? What intermediates are produced during a reaction? Can we characterize any intermediates? Do we need to remove them to prevent side reactions? If some or all of the reactants or products are chiral, then circular dichroism (CD) detection may be the ideal tool for following the kinetics of a reaction, and if the half-life of the reaction is of the order of milliseconds to seconds or even minutes then stopped-flow mixing of the reagents will almost certainly be the appropriate choice of sample handling method. For reactions with half-lives of a few minutes to tens of minutes the reagents can be mixed by hand in a normal cuvette and the signal monitored at an appropriate wavelength. CD is not well suited to kinetics on timescales of hours due to the baseline drift that does occur (see Chapter 4, Section 2.5). Some CD spectropolarimeters have the useful facility of being able to perform a wavelength scan at pre-set intervals as well as monitoring continuously (except during the wavelength scan) at a chosen wavelength, thus facilitating the characterization of any intermediates. In this chapter we shall highlight some of the considerations of the stopped-flow technique that are particularly relevant to CD experiments. Particular problems may be encountered when performing CD (as opposed to other detection methods) stopped-flow experiments. The measured signals are very small (typical CD intensities are 0.1% or less of the absorbance signal), and the noise level observed is particularly sensitive to any inhomogeneities or turbulence in the samples. Also, as one of the main applications of stopped-flow CD is in the study of protein folding and unfolding, samples are often very viscous and/or corrosive, have significant absorbances due to buffers etc., and the experiments often require wide and variable mixing ratios.

Kinetics and Mechanism of Oxidation of Dimethyl Sulphoxide by Mono- and Di-Substituted N,N-Dichlorobenzenesulphonamides in Aqueous Acetic Acid

2003 ◽  
Vol 58 (8) ◽  
pp. 787-794 ◽  
Author(s):  
B.Thimme Gowda ◽  
K. L. Jayalakshmi ◽  
K. Jyothi
Keyword(s):  
Acetic Acid ◽  
Benzene Ring ◽  
Dimethyl Sulphoxide ◽  
Aqueous Acetic Acid ◽  
Isokinetic Temperature ◽  
Free Energies ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
First Order Kinetics ◽  
Kinetics Of

In an effort to introduce N,N-dichloroarylsulphonamides of different oxidising strengths, four mono- and five di-substituted N,N-dichlorobenzenesulphonamides are prepared, characterised and employed as oxidants for studying the kinetics of oxidation of dimethyl sulphoxide (DMSO) in 50% aqueous acetic acid. The reactions show first order kinetics in [oxidant], fractional to first order in [DMSO] and nearly zero order in [H+]. Increase in ionic strength of the medium slightly increases the rates, while decrease in dielectric constant of the medium decreases the rates. The results along with those of the oxidation of DMSO by N,N-dichlorobenzenesulphonamide and N,N-dichloro-4- methylbenzenesulphonamide have been analysed. Effective oxidising species of the oxidants employed in the present oxidations is Cl+ in different forms, released from the oxidants. Therefore the introduction of different substituent groups into the benzene ring of the oxidant is expected to affect the ability of the reagent to release Cl+ and hence its capacity to oxidise the substrate. Significant changes in the kinetic and thermodynamic data are observed in the present investigations with change of substituent in the benzene ring. The electron releasing groups such as CH3 inhibit the ease with which Cl+ is released from the oxidant, while electron-withdrawing groups such as Cl enhance this ability. The Hammett equation, log kobs = −3.19 + 1.05 σ , is found to be valid for oxidations by all the p-substituted N,N-dichlorobenzenesulphonamides. The substituent effect on the energy of activation, Ea and log A for the oxidations is also analysed. The enthalpies and free energies of activation correlate with an isokinetic temperature of 320 K.

Manipulating the ion-transfer kinetics and interface stability for high-performance zinc metal anodes

2020 ◽  
Vol 13 (2) ◽  
pp. 503-510 ◽  
Author(s):  
Xuesong Xie ◽  
Shuquan Liang ◽  
Jiawei Gao ◽  
Shan Guo ◽  
Jiabao Guo ◽  
...  
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Dendrite Growth ◽  
Side Reactions ◽  
Ion Transfer ◽  
Interface Stability ◽  
Zinc Metal ◽  
New Class ◽  
Kinetics Of ◽  
Metal Anodes

We report a new class of Zn anodes modified by a three-dimensional nanoporous ZnO architecture (Zn@ZnO-3D), which can accelerate the kinetics of Zn2+ transfer and deposition, inhibit dendrite growth, and reduce the side-reactions.

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