Kinetics potassium cyanide

Wiegand GH, Tremelling M. 1972. The kinetics and mechanism of the decomposition of potassium cyanide in aqueous alkaline medium. Hydrolysis of the simplest nitrile. J Org Chem 37(6) 914-916. 

The data for the reactions of potassium cyanide with benzyl halides at 85 C and 25 C are summarized in Tables I-III and graphical representations of these data are shown in Figures 1-3. The reactions carried out at 85 C were followed to 70% completion, while those at 25 C were followed to 50% completion. In general, excellent first-order kinetic plots were obtained. Each point on the graphs represents an average of at least three kinetic determinations. It is interesting to note that in the absence of added water (solid-liquid phase transfer catalysis), the rates of benzyl halide disappearance were more accurately described by zero-order kinetics. 

In addition to their thermodynamic stability, complexes of macrocyclic ligands are also kinetically stable with respect to the loss of metal ion. It is often very difficult (if not impossible) to remove a metal from a macrocyclic complex. Conversely, the principle of microscopic reversibility means that it is equally difficult to form the macrocyclic complexes from a metal ion and the free macrocycle. We saw earlier that it was possible to reduce co-ordinated imine macrocycles to amine macrocyclic complexes in order to remove the nickel from the cyclam complex that is formed, prolonged reaction with hot potassium cyanide solution is needed (Fig. 6-24). 

As ice crystals grow in the freezing system, the solutes are concentrated. In addition to increased ionic strength effects, the rates of some chemical reactions—particularly second order reactions—may be accelerated by freezing through this freeze-concentration effect. Examples include reduction of potassium ferricyanide by potassium cyanide (2), oxidation of ascorbic acid (3), and polypeptide synthesis (4). Kinetics of reactions in frozen systems has been reviewed by Pincock and Kiovsky (5). 

The mechanism for the nucleophilic displacement reaction of benzyl chloride with potassium cyanide has also been studied under multiphasic conditions, i.e., an scC02 phase and a solid salt phase with a tetraheptylammonium salt as the phase-transfer catalyst (PTC) (Scheme 3.8). The kinetic data and catalyst solubility measurements indicate that the reaction pathway involves a catalyst-rich third phase on the surface of solid salt phase. 

Recently, Agasti et al.158 studied the thermodynamic and kinetic stability of MPCs that differ in the substitution pattern on the first and second carbon next to the sulfur atom (Fig. 4.5). The rate constant of the decomposition of MPCs by potassium cyanide increases in the series iso-thiolate (a methyl group on C2) < nor-thiolate (two methylene groups next to S) < sec-thiolate (a methyl group on Cl). Moreover,... 

In addition to metabolizing some aldehydes, aldehyde oxidase also oxidizes a variety of azaheterocycles but not thia- or oxaheterocycles. Of the various purine nucleosides metabolized by aldehyde oxidase, the 2-hydroxy- and 2-amino derivatives are more efficiently metabolized, and for the N -substituents, the typical order of preference is the acyclic nucleosides is as follows 9-[(hydroxy-alkyloxy)methyl]-purines) > 2 -deoxyribofuranosyl > ribofuranosyl > arabinofuranosyl > H. The kinetic rate constants for purine analogues revealed that the pyrimidine portion of the purine ring system is more important for substrate affinity than the imidazole portion. Aldehyde oxidase is inhibited by potassium cyanide and menadione (synthetic vitamin K). 

The nucleophilic displacement of benzyl chloride with solid potassium bromide [54] or potassium cyanide [55] has been carried out with tetraheptylammonium salts as catalysts. The kinetic data together with the determination of catalyst solubility clearly indicate that the reaction proceeds through formation of a catalyst-rich third phase on the surface of the solid salt phase, where the reaction occurs. The low solubilities of traditional PTC catalysts in the CO2 phase do not hamper the process but facilitate catalyst removal and recovery. 

Kinetics of the P-700 photooxidation of potassium cyanide treated vesicles were measured as in (1) using the method described by Melis (3). 

A considerable amount of controversy appears to exist in the literature (1) regarding the mechanism of base hydrolysis of acido-pentammine-cobalt(III) complexes. Detailed investigations on the kinetics of base hydrolysis of several complexes of this type, [Co(NHj) X] , where X = Cl , Br" or N , have been reported by earlier investigators (2-4). It is known (5) that in [Co(NH ) (S20 )] the thiosulphate is so firmly bound that on treating with potassium cyanide all the ammonia are displaced leading to the formation of [Co(CN)g(S20 )l ". 

The synthesis begins with an Sn2 reaction (Chapter 10, Section 10.2) of bromide 141 with potassium cyanide to give 144. Note the use of the aprotic solvent DMF to facilitate the 8 2 reaction. A Grignard reaction of the nitrile with methylmagnesium bromide followed by hydrolysis leads to the requisite ketone (see Chapter 20, Section 20.9.3). The final step simply reacts the methyl ketone with LDA under kinetic control conditions to give the enolate anion (143), which is condensed with the ester (142) to give the diketone target, 140 (Section 22.7.2). 

The kinetics of the nucleophilic addition of potassium cyanide to a,iV-diphenyl-... 

In a subsequent study (345), this group examined the detailed mechanism of a solid salt/SCF phase transfer-catalyzed reaction. They selected a reaction similar to that depicted in Figure 11, that of the irreversible nucleophilic displacement of benzyl chloride with potassium cyanide to form phenylacetonitrile and potassium chloride. The study primarily used the catalyst THAB as in the previous study. The effects of various factors on the reaction kinetics were investigated, including the amount of catalyst, the amount of KCN, the presence of acetone cosolvent, and temperature. Measured kinetic data were consistent with irreversible pseudo-first-order kinetics in the catalyst concentration. However, the reaction rate was found to be linearly dependent on the catalyst concentra-... 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

One-electron reduction of (NH3)5Ru-4-(l 1 -dodecenyl)py + by externally added reductants followed biphasic kinetics when the complex was bound at both interfaces of PC liposomes, but only the fast step was observed when binding was limited to the external surface [111]. The slow step was first order and independent of the identity and concentrations of added reductants. The rate constant, k = 10 s", was unchanged upon adding either the potassium ionophore, valinomycin, or the proton carrier, carbonyl cyanide m-chlorophenylhydrazone, to the medium, indicating that, although electrogenic, the transmembrane reduction step was not rate-... 

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