Alcoholate ion

When the added water has a molarity n, let a fraction g of positive ions be alcoholic ions, while the fraction (1 — g) is in the form of (HjO)+ ions, On extrapolating to infinite dilution, the equilibrium constant of the reaction (43) may be written... 

The first example of an oxide-anion accelerated retro Diels Alder reaction was reported by Papies and Grimme [52]. The adduct 19 (Equation 1.23) treated with tetra-w-butylammonium fluoride (TBAF) in THE at room temperature is immediately converted into 20, in contrast to the parent 21 (Equation 1.24) which undergoes cycloreversion into 22 at 100 °C. The dramatic oxide-anion acceleration (> 10 ) was ascribed to the loss of basicity of about 8pK, units in the transformation of alcoholate ion of precursor 19... 

Hubbard and Kirsch (1972) have recently proposed that histidine may act as a nucleophile in a-chymotrypsin acylation reactions of esters having a good leaving group (jO-nitrophenol). This suggestion was based on a similarity in p-value for acylation by p-substituted nitrophenyl and dinitrophenyl benzoates and nucleophilic attack on these compounds by imidazole, in contrast with less positive p-values for hydroxide ion catalysis. Hammett p-values for hydrolysis of substituted phenyl esters are given in Table 6 and show little apparent trend. The values for hydroxide ion and alcoholate ions are... 

Choline salts [ (CH3)3NCH2CH2OH] are readily acylated. Here the positive charge undoubtedly contributes to hydrolytic instability of the ester (2), but the alcohol ion is readily acylated. Apparently more than charge is involved in the reactivity of the uncoordinated hydroxyl groups in [Cr(HO-A)2]. ... 

The ratio of alcohol to acetate depends upon workup procedure, which differed in the two cases. In addition, acetates of benzylic alcohols typically break down under electron impact by a low energy process to produce ketene and the corresponding alcohol ion. The peak at the parent mass of the alcohol, throughout this work, most likely contains a contribution so derived from the acetate. A careful distinction between the alcohol and acetate was not deemed important for our purposes, so... 

Eklund et al. suggested that the side chains of Ser 48 and His 51 act as a proton relay system to remove the proton from the alcohol, in step b of Eq. 15-7, leaving the transient zinc-bound alcoholate ion, which can then transfer a hydride ion to NAD+, in step c.52 The shaded hydrogen atom leaves as H+. The role of His 51 as a base is supported by studies of the inactivation of the horse liver enzyme by diethyl pyrocarbonate57 and by directed mutation of yeast and liver enzymes. When His 51 was substituted by Gin the pKa of 7 was abolished and the activity was decreased ten-fold.58... 

In their mechanism, presented as a series of proton equilibria in Scheme 10, the reaction is controlled by three steps (a) ionization of the zinc-bound water, which destabilizes the binary complex to an extent that substrate binding cannot occur (p/ 3, Scheme 10) (b) a stabilizing effect of alcoholate ion formation in the ternary complex. The pH dependence of this step is the result of ionization of the alcohol.1449 (c) The dissociation of the alcohol from the ternary complex. This is similar in rate to the dissociation of aldehydes, which might be expected for a substitution mechanism, both neutral species forming structurally similar ternary complexes. 

Alcoholate ions are difficult to expel because they are strongly basic the pKa s of simple alcohols are about 16. The expulsion of alcohols is aided by general-acid catalysis ... 

The enantioselective esterification of 2-arylpropionic acids catalysed by a lipase was discussed earlier.26 Steady-state kinetics of the Pseudomonas cepacia lipase-catalysed hydrolysis of five analogous chiral and achiral esters (R)- and (.S )-(235 R1 = Me, R2 = H), (R)- and (reaction mixtures of water-insoluble substrates.212 The Km values were all die same and the apparent kcat values reflected the binding abilities of the alcoholate ions for the fast-reacting enantiomers. All the substrates are believed to be... 

Cleavages of the Si—Si bond mostly occur in alkaline solutions in the presence of alcoholates641. Detailed investigations were carried out by Kumada and by Atwell and Weyenburg. Kumada et cleavage rate of methylalkoxydisilanes by sodium alcoholate in alcohol. It is initially directly proportional to the concentration of the disilane and of the alcoholate ions. 

Hydrolysis of the lactone of y-hydroxystearic acid, which is a condensed or liquid-expanded film according to temperature, to the free hydroxy-acid, occurs in films on solutions of caustic soda.4 As the acid on the alkaline solution forms a gaseous film the area increases very much during the hydrolysis, and the course of the reaction may be followed by either pressure or potential measurements. The rate of reaction is proportional to the concentration of caustic soda if this and the surface pressure are kept constant the reaction appears unimolecular, with an energy of activation of 12,500 calories per gm. molecule, which is within experimental error of the energy of activation of hydrolysis by the alcoholate ion in bulk solution. 

Alcoholic potassium hydroxide and sodium alcoholates have also been used as reducing agents for aromatic nitro compounds the free alcohol or the alcoholate ion presumably acts as the reducing agent in these cases as illustrated for w,m -diiodoazoxybenzene (8 equation 6). In a few instances, where benzyl alcohol was used to prepare sodium benzylate, pure azoxy products were obtained without the formation of amino by-products. 

In anionic polymerization, B-propiolactone initiated with potassium alcoholate, gives,in initiation,both alco-holate and carboxylate anions. Alcoholate ions in every next step convert partially into carboxylate whereas carboxylate reproduce themselves quantitatively. Thus, after a few steps only carboxylate anions are left (14). Related situation was observed in the polymerization of styrene oxide (15). Here, however, it is only due to the structure of the initiator used. Thus, when in the initiation step both secondary and primary alcoholate anions are formed, due to the low steric requirements, in the next step apparently only the attack on the least substituted carbon atom takes place and already in the second step exclusively secondary alcoholate anions are present. 

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