Equilibria alcohol decomposition

The differenee in reaction rates of the amino alcohols to isobutyraldehyde and the secondary amine in strong acidic solutions is determined by the reactivity as well as the concentration of the intermediate zwitterions [Fig. 2, Eq. (10)]. Since several of the equilibrium constants of the foregoing reactions are unknown, an estimate of the relative concentrations of these dipolar species is difficult. As far as the reactivity is concerned, the rate of decomposition is expected to be higher, according as the basicity of the secondary amines is lower, since the necessary driving force to expel the amine will increase with increasing basicity of the secondary amine. The kinetics and mechanism of the hydrolysis of enamines demonstrate that not only resonance in the starting material is an important factor [e.g., if... 

Ketones play an important role in the decomposition of peroxides to form radicals in alcohols undergoing oxidation. The formed hydroxyhydroperoxide decomposes to form radicals more rapidly than hydrogen peroxide. With an increase in the ketone concentration, there is an increase in the proportion of peroxide in the form of hydroxyhydroperoxide, with the corresponding increase in the rate of formation of radicals. This was proved by the acceptor radical method in the cyclohexanol-cyclohexanone-hydrogen peroxide system [59], The equilibrium constant was found to be K — 0.10 L mol 1 (373 K), 0.11 L mol 1 (383 K), and 0.12 L mol 1 (393 K). The rate constant of free radical generation results in the formation of cyclohexylhydroxy hydroperoxide decomposition and was found to be ki = 2.2 x 104 exp(—67.8/7 7) s 1 [59]. 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

FIGURE 7.6 Decomposition of a mixed anhydride (A) to the 2-alkoxy-5(4//)-oxazolone and the alkyl carbonate.9 The latter is in equilibrium with the anion whose reaction (B) with a second molecule of anhydride produces pyrocarbonate and the acid anion whose reaction (C) with a third molecule produces the symmetrical anhydride. The oxazolone eventually reacts with the alcohol to give the ester. (D) Acyloxonium ions formed by reaction of the anhydride with dimethylformamide and tetrahydrofuran. 

Prior to 1967 acetal hydrolysis had been found to be a specific-acid catalysed reaction with the accepted mechanism [equation (46)] involving fast pre-equilibrium protonation of the acetal by hydronium ion, followed by unimolecular rate-determining decomposition of the protonated intermediate to an alcohol and a resonance stabilized carbonium ion (Cordes, 1967). An A-1 mechanism was supported by an extremely large body of evidence, but it appeared unlikely that such a mechanism could expledn the... 

The reactions are reversible and the equilibrium is less favourable for the decomposition of a thiol to an alkene and H2S than of the corresponding alcohol to an alkene and H20 under the same conditions data on equilibria in the reactions of propene with water [245] and with hydrogen sulphide [246] indicate that the equilibrium constant of propene hydration is smaller than that for propene sulphidation by approximately two orders of magnitude. 

An alternative and more generally used oxidation method employs chromic acid. This process is an exception to our general theme, because here the alcohol is transformed to a carbonyl group by removal of electron density from oxygen rather than from carbon. The first step has been shown to be a rapid equilibrium between the alcohol and its chromate ester, followed by rate-determining decomposition of the ester in the manner shown in Scheme 7.42 It will be noted that the species eliminated from the carbon that becomes the carbonyl carbon is a Lewis acid, not a Lewis base. 

All Bi(OAlk)3 derivatives of n- and z -alcohols are volatile, which permits their purification by distillation, but the yields of the sublimates are low as the processes are accompanied by partial decomposition. A much higher thermal stability is demonstrated by Bi(OBu )3. According to the mass-spectrometry data the first members of the homologous series are dimeric in the gas phase, while Bi(OR% and Bi(0C2H40Me)3 are monomeric [967], However the solid state structure of the latter contains the polymer chains and its solutions in benzene — the dimeric molecules. The NMR spectra indicate the equilibrium in solution of aggregates with different number of chelated ligands [1069]. This obstacle hinders the crystallization of 2-methoxyethoxide from solutions (Table 12.15). 

A study of the decomposition of /f-hydroxy-/V-chloroamines in aqueous medium has established that pre-equilibrium formation of the conjugate alcoholate is a prerequisite feature of the competing fragmentation and intramolecular elimination paths (Scheme 13).98 A very high effective molarity (EM = 2 x 105 M) has been estimated for the intramolecular process, which cannot occur in the case of (/V-chloro)butylethanolaminc. For reaction of (A-c h I o ro )ct hy I cth an o I am i nc kmln/k g = 6.1 and the solvent isotope effect ( oh- /koo- )obs = 0.68 is consistent with pre-equilibrium deprotonation followed by a unimolecular reaction in which there is no participation by solvent. 

You can see why hemiacetals are unstable they are essentially tetrahedral intermediates containing a leaving group and, just as acid or base catalyses the formation of hemiacetals, acid or base also catalyses their decomposition back to starting aldehyde or ketone and alcohol. That s why the title of this section indicated that acid or base catalysts increase the rate of equilibration of hemiacetals with their aldehyde and alcohol components—the catalysts do not change the position of that equilibrium ... 

A high CO pressure would shift equilibrium (4.3) to the left and the catalytic reaction would become slower. In this complex CO is a far better ligand than an alkene. On the other hand the reaction uses CO as a substrate, so it cannot be omitted. Furthermore, low pressures of CO may lead to decomposition of the cobalt carbonyl complexes to metallic cobalt and CO, which is also undesirable. Finally, the product alcohol may stabilize divalent cobalt species which are not active as a catalyst ... 

The rate of decomposition of the tetroxide, as determined by oxygen evolution at low temperatures, is given in Table 116. Equilibriiun between peroxy radicals and the tetroxide has been studied and the pertinent data are reported in Table 117. The y4-factors reported in Table 116 are lower than expected from a unimolecular decomposition of the tetroxide. This is probably due to the equilibrium between the peroxy radicals and the tetroxide . Secondary tetroxides appear to be considerably less stable than tertiary tetroxides in agreement with the suggested non-radical decomposition of secondary tetroxides to ketone, alcohol and oxygen (ref. 488). 

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