Mechanism alcohols

The metal-alcoholate mechanism is well established for allylic alcohol epoxidation in the presence of Ti and V catalysts. [41, 51, 52, 111-113], In principle, it can provide a viable pathway also for catalysis by a Re complex. In fact, allylic alcohols may add, at least formally, to either an oxo-Re or peroxo-Re moiety (e.g. of 5a or 5b) in a process which is referred to as metal-alcoholate binding this mechanism gives rise to metal-alcoholate intermediates. We identified four intermediates of alcohol addition to di(peroxo) complexes two resulting transition states, S-8 and S-9b, are shown in Figure 11. All metal-alcoholate intermediates he significantly higher in energy (by 10-22 kcal/mol) than 5b + propenol, except the... 

In the homogeneous mechanism, the reaction is assumed to start by protonation of one of the reactants, either ester (mechanisms denoted as Aac1 and Aac2 [397,398]) or, less frequently, alcohol (mechanism Aal1). It seems likely that protonation of reactants is an important step in esterification catalysed by ion exchangers, too. This follows from all that has been said above about the effect of the acidic properties of ion exchangers on their catalytic activity and is further supported by the effect of the dielectric constant of solvents (Fig. 18), which indicates that the reaction mechanism involves a positive ion and a dipolar molecule [454]. 

As shown in Figure 3, a positive p-value (+0.92) was observed in the hydrogenation of substituted benzaldehydes, giving strong support to the postulation by Heil and Marko that the rate determining step in the formation of alcohol (Mechanism 2) is the hydride addition step. It is therefore suggested that coordination of amine to rhodium increases the hydridic character of the Rh-H bond, much the same as is postulated in cobalt-tributylphosphine complexation (20). The differing effect of amine on rhodium (promoter) and on cobalt (inhibitor) is attributed to the more hydridic nature of a Rh-H bond as compared with the very protonic HCo(CO)4. Addition of amines to HCo(CO)4 results in formation of inactive species similar to I. 

The reaction of CH3CH2OH with HBr illu.strates the Sfj2 mechanism of a I ° alcohol (Mechanism 9.5). Nucleophilic attack on the protonated alcohol occurs in one step the bond to the nucleophile X is formed as the bond to the leaving group (H2O) is broken. 

The mechanism by which xenobiotic alcohols or esters are converted to fatty acid esters has not been studied. They could be formed by the action of lyase enzymes in the presence of fatty acid glyceryl esters, as in the conversion of farnesol to farnesol fatty acid esters (150). Some lipolytic acyl hydrolase enzymes from plants readily catalyze the transfer of lipid-bound fatty acids to low MW alcohol acceptors (150.151) and enzymes of this class could be responsible for the occasional formation of fatty acid conjugates of xenobiotic alcohols. Mechanisms involving fatty acid acyl CoA, phospholipids, or direct esterification with fatty acids might also be involved (1 ). 

However, this proposed mechanism has not found experimental substantiation and has in fact been quite largely disproved.80 Hence, it is somewhat difficult to establish the industrial utility of the proposed organic acid synthesis on the basis of the higher alcohol mechanism. 

Kitamura. M. Okada, S. Suga, S. Noyori, R. Enantiose-lective addition of dialkylzinks to aldehydes promoted by chiral amino alcohols. Mechanism and nonlinear effect. J. 

Deninno, M. P. "Anomalous ozonolysis of cyclic allylic alcohols Mechanism and synthetic utility. Journal of the American Chemical Society 1995,117(39), 9927-9928. Razumovskii, S. D. Rakovski, S. K. Zaikov, G. E. Influence of the Paraffine Hydrocarbon Structure on its Reaction Rate with Ozone. Izv. Akad. Nauk, ser. khim. 1975, 9,... 

Silicic esters, (RO)4Si, form in the reaction of alcohols with SiCl4. They react with water to form silica and an alcohol. Mechanisms for the hydrolysis can be written that involve Sj 2 attack of water on silicon or at the carbon atom of the R group. Suggest an experiment using isotopes that would distinguish between these two possible mechanisms. 

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