Compound formation kinetics

U. Gosele. Thin-film compound formation Kinetics and effects of volume changes / In Alloying (Eds. J.L. Walter, M.R. Jackson, Ch.T. Sims). - Metals Park (Ohio) ASM International, 1988.-P.489-519. 

This paper calls attention to the need for new ions in coordination chemistry—ions that would permit more detailed physico-chemical studies to be made, ions that would facilitate studies of less familiar metals and of less familiar coordination numbers, and ions that would help studies of chemical bonding and reaction mechanisms. Organometallic ions of the type RmM+ are such ions, and these form metal-chelate compounds of the type RmM Ch) . Three aspects of the chemistry of organometallic-chelate compounds are described (1) equilibria of compound formation ( ) kinetic and mechanistic studies of three types of reactions (a) reactions of the coordinated ligand, (b) substitution at the 4-, 5-, or 6-coordinate metal atom, and (c) reactions of the organic moiety and (3) studies of stereochemistry and chemical bonding. 

There are two possible approaches for the preparation of optically active products by chemical transformation of optically inactive starting materials kinetic resolution and asymmetric synthesis [44,87], For both types of reactions there is one principle in order to make an optically active compound we need another optically active compound. A kinetic resolution depends on the fact that two enantiomers of a racemate react at different rates with a chiral reagent or catalyst. Accordingly, an asymmetric synthesis involves the creation of an asymmetric center that occurs by chiral discrimination of equivalent groups in an achiral starting material. This can be done either by enan-tioselective (which involves the reaction of a prochiral molecule with a chiral substance) or diastereoselective (which involves the preferential formation of a single diastereomer by the creation of a new asymmetric center in a chiral molecule) synthesis. 

The kinetics of the Amadori-compound formation from D-glucose and l-lysine, as well as melanoidin formation, has been examined. The so-called Amadori compounds are formed at an exponential rate, while showing pseudo-first-order disappearance of L-lysine in the presence of... 

Baranski and Lu [209] have carried out, applying microelectrodes, voltammetric studies on ammonium amalgam in propylene carbonate solutions at room temperatures. The sweep rates up to 80 V s were appropriate for the analysis of the formation kinetics of this compound. Experimental and numerical simulation results have shown that ammonium amalgam was formed via fast charge-transfer process and its first-order decomposition was characterized by the rate constant of about 0.6 s . Diffusion coefficient of NH4 radical in mercury was estimated to be about 1.8 X 10 cm s k The formal potential of NH4+ (aq)/NH4(Hg) couple was determined as—1.723 V (SHE). 

Curing Agents for Carboxyl-Terminated Polybutadiene Prepolymers. The types of curing agents used to prepare binders for CTPB propellants are the same as those for PBAN or PBAA. The bifunctionality of CTPB, however, requires that part of the curing agents be polyfunctional to provide for the formation of the tridimensional network. Almost without exception, the polyfunctional aziridines and epoxides used with CTPB undergo side reactions in the presence of ammonium perchlorate, which affects the binder network formation. Kinetic studies conducted with model compounds have established the nature and extent of the cure interference by these side reactions. The types and properties of some of the crosslinkers and chain extenders used to prepare solid propellants are summarized in Table IV. 

Mirvish, S. S. (1975). Formation of N-nitroso compounds Chemistry, kinetics, and in i/tvo occurrence. Toxicol. Appl. Pharmacol. 31, 325-351. 

Since other possible transformations, such as, formation of dimethyl ether, higher alcohols, and hydrocarbons, are accompanied with higher negative free-energy change, methanol is thermodynamically a less probable product. Therefore, solely on a thermodynamic basis, these compounds as well as methane should be formed in preference to methanol. To avoid the formation of the former compounds, the synthesis of methanol requires selective catalysts and suitable reaction conditions. Under such conditions, methanol is the predominant product. This indicates that the transformations leading to the formation of the other compounds are kinetically controlled. In the methanol-to-hydrocarbon conversion, dimethyl ether generally is converted similarly to methanol. 

Hersey, A., Robinson, B. H., and Kelly, H. C. 1986. Mechanisms of inclusion-compound formation for binding of organic dyes, ions and surfactantsitoyclodextrin studied by kinetic methods based on competition experimentsJ. Chem. Soc. Faraday Trar 1271-1287. 

It can easily be understood that this method has practically no advantage in comparison with direct measuring the thickness of the growing ApBq layer. Its disadvantages are obvious. Firstly, the diffusional constants are calculated using the differential forms of kinetic equations. This usually produces a larger error than the calculations with the use of the integrated equations. Secondly, the amount of initial substances A and B consumed in the reaction of compound formation is in most cases much less than their... 

We have some indirect evidence on the structure of the transition complex between the reacting radical and the unsaturated compound from kinetic data. A comparison of AS with the measured value AS° (see Table 1) leads to the conclusion that the greater part of the entropy change accompanies the formation of the transition complex. This indicates that the bond between radical and substrate is more or less completed in this state, and that the transition state resembles the product. 

Models exist that describe the thermal stability Tx in terms of transformation rates (kinetic approach), where Tx is proportional to AE. In these cases AE is estimated on the basis of a weighted mean sublimation energy of the constituent elements (Davies 1976) or the heat of compound formation (Kiibler et al. 1981) or the formation enthalpy AHh of a hole of size equivalent to the smaller type of atom (Buschow 1982). Of these possibilities the latter appears to be the most promising for predicting the thermal stability of a large variety of amorphous alloys. 

As pointed out above, the desorption order markedly effects the shape of the desorption curve and the behaviour of the peak temperature with variation of initial coverage. Zero-order kinetics are shown by an increase in peak temperature with coverage and zero-order surface processes have now been observed for many systems [281—286]. Schwartz et al. [287] performed isothermal desorption measurements on the H2/Ti system and determined an order of 1.5, explaining this finding in terms of surface compound formation, with a stoichiometry of TiHl s. A very good example of the confusion which can reign in this field is exhibited by the... 

If enzymes and substrate undergo a series of reactions, the first of these will be a second-order reaction, while all subsequent steps will be first order. This argument is used throughout either to prove that a particular step studied must be the true initial enzyme-substrate combination or in other cases to demonstrate that some particular intermediate step, which follows first-order kinetics, must have been preceded by a second-order initial compound formation. 

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