First-order rate constant, acetylene

Butler and Heyes (1998) investigated the reductive dechlorination of hexachloroethane in water by iron sulfide. Tetrachloroethylene was the major product with pentachloroethane as a minor intermediate. Final reaction products were trichloroethylene, c/s-1,2-dichloroethylene, and acetylene. The rate of reaction increased with increasing iron sulfide concentrations and pH. At pH 7.8, first-order rate constants were 0.0726, 0.086, and 0.533/h at iron sulfide concentrations of 10, 25, and 100 g/L, respectively. At an iron sulfide concentration of 100 g/L, first-order rate... 

The electron-attractive effect of the substituents shifts the equilibrium to the side of the reactants [Eq. (1)]. The first-order rate constant decreases in the same direction. Since stability of the complexes is defined by the same factors, Pt-acetylene bond cleavage is probably the rate-determining step. The effects of phenyl ring substituents in triphenylphosphine on the reaction rate have also been studied (20). Electron-releasing substituents slow down the reaction and behave analogously to the electronegative ones in the acetylenic part of the molecule. 

The reverse reaction is determined by the nature of R. The generating [Pt(PR3)2] moiety is a rather stable intermediate. A comparison of the results obtained with the NMR data (22) of substituted phenylacetylenes led to the conclusion that there is a relation between equilibrium constant, first-order rate constants, and chemical shifts of the acetylenic proton they all depend on substituent effects on the electron density in the triple bond. 

Figure U. Apparent first-order rate constant for the reaction converting acetylene to soot. (Reproduced -with permission from Ref. 2. Copyright 1983, Gordon and Breach.)...

The first order rate constants for the irreversible inactivation by various acetylenic analogs ranged from 0.08 to 0.26 min" [81], and the affinity for the active. site was comparable to that of arachidonate (K = 5 fiM). The acetylenic analogs could still... 

The kinetic analysis is made on the basis of the following assumptions the inhibitor concentration may be considered to remain constant during the initial phase of the inactivation process ETn (the reversible enzyme-acetylene complex) is at all times in equilibrium with free enzyme (E) and free acetylene (L) and the rate of formation of the inhibitory species (Ia) far exceeds the rate of inactivation of the enzyme, i.e., k y>ka. Kitz and Wilson showed that the reciprocal of the pseudo-first-order rate constant of inactivation (l/fc pp) and the reciprocal of the inhibitor concentration ( /[ ]) obey the following linear relationship from which both the Ki and fc, values can be obtained ... 

Double reciprocal plots of the pseudo-first-order rate constants of inactivation (fcapp) with respect to inhibitor concentration are shown in Fig. 1 for two acetylenic steroids. The Ki and fe., values were obtained from the slopes and intercepts. The half-lives of the enzyme in the presence... 

The alkylation of toluene with acetylene in the presence of sulphuric acid is carried out in a batch reactor. 6000 kg of toluene is charged in each batch, together with the required amount of sulphuric acid and the acetylene is fed continuously to the reactor under pressure. Under circumstances of intense agitation, it may be assumed that the liquid is always saturated with acetylene, and that the toluene is consumed in a simple pseudo first-order reaction with a rate constant of 0.0011 s-1. 

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