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Phenols equilibrium deprotonation

As before (Chapter 5), the acid strength of alcohols is measured as a function of an ionization constant, which is defined in terms of an equilibrium between protonated (alcohol, enol, or phenol) and deprotonated (alkoxide, enolate anion, or phenoxide) species (Equations 8.1 and 8.2). [Pg.566]

Scheme 40 shows a complete set of rate and equilibrium constants for addition of water to p-H-l+ and p-l and for deprotonation of p-H-l+ and p- 1-1 -011 -the phenol product of addition of water to p-H-l+. These rate and equilibrium constants (Table 2) were determined as follows3 ... [Pg.73]

The two individual equilibria favour the carbonyl compounds over the tetrahedral intermediate but Kx < K2 so the overall equilibrium favours the amide. However, two new equilibria must be added to these if the variation of pH is considered too. In acid solution the amine will be protonated and in base the phenol will be deprotonated. [Pg.311]

Crystal structures have been reported for the octahedral phenolate [Tc(dppo)3] (307), thiolate [Tc(dppbt)3] (307, 308), and propionate [Tc(dppp)3]-2dmso (306). In each case the three P atoms occupy mer positions. For the amine ligand (25) (R = NH2) an acid-base equilibrium is established and either the triply deprotonated [Tc(dppba)3] or salts of the doubly deprotonated [Tc(dppba)2(dppbaH)]+ may be isolated depending on the pH. The crystal structure of [Tc(dppba)2(dppbaH)]-... [Pg.41]

In the care of reaction (51) it is the o-complex which is undergoing deprotonation. The pKj, values of these ketone-like o-coraplexes can be derived from the constant Kt for the tautomeric keto-enol equilibrium of the phenol and the acid dissociation constant K, for the phenol. One gets pK pteto) 1-... [Pg.40]

The Br0nsted acidity of a molecule is its capacity to give up a proton. It can be expressed either by the equilibrium constant, the pfsTa value, the change of standard free energy (AGj) or simply the energy of the deprotonation reaction AH A - - H+. The acidities of phenols were measured experimentally " , including a series of 38 meta-... [Pg.92]

The pK of HCN is 9.1, and the pK of phenol is 10.0. Thus cyanide is strong enough to pull off some of the H from the phenol, although the equilibrium would favor cyanide ion and phenol. The pK of secondary alcohols is 16-18, so there is no chance that cyanide would deprotonate an alcohol. [Pg.496]

Aha Products are favored at equilibrium, so the correct answer to the question is "Yes, triethylamine is a strong enough base to deprotonate phenol."... [Pg.695]

It is important to realise that the p Tj and pX2 values for aliphatic and aromatic amino acids, and for amino phenols are likely to be composite quantities, and that four deprotonation equilibrium constants may be involved in the acid-base behaviour. It may turn out that if the species at the first equivalence point of the pH titration is predominantly the zwitterion or the molecular species. If this is so, then the observed pKs will approximate to a single equilibrium constant. But it must not be assumed that this is always the case. [Pg.175]

Furthermore, the state of critical deprotonation involves a multistage acid-base equilibrium, comprising very fast processes that are diffusion limited, even in fluid solution. The rate of phenolate formation in the penetration zone in this case is determined by the rate of supply of the reactants. Consequently, the rate of dissolution of the resin, which is dependent on the deprotonation process, is controlled by the diffusion of the developer into the polymer matrix. ... [Pg.523]

Quinolinols and isoquinolinols in which the oxygen is at any position other than 2-and 4- for quinolines and 1- and 3- for isoquinolines are true phenols i.e. have an hydroxyl group, though they exist in equilibrium with variable concentrations of zwitterionic structures with the nitrogen protonated and the oxygen deprotonated. They show the typical reactivity of naphthols. 8-Quinolinol has long been used in... [Pg.128]

Since the equilibrium (71a) is shifted to the left, the concentration of OH anions in the organic phase is thus low, and PTC is only a moderately efficient methodology for fi-elimination. Nevertheless, there are many examples of successful applications of PTC for practical realization of this process. The effectiveness of PTC for p-elimination reactions becomes much higher when cocatalysts are used. The cocatalysts, mostly alcohols or phenols such as benzyl alcohol, 2,2,2-trifluoroethanol, or mesitol, are deprotonated at the interface and the alkoxide anions produced, introduced into the organic phase by the lipophilic cation of the catalyst, act there as basic agents [80] ... [Pg.187]

In contrast with arylations of other heterocycles, the palladium-catalyzed arylation of benzoxazoles at C-2 proceeds readily at ambient temperature (Scheme 11.21) [67]. Although, as in other cases no kinetic isotope effect was found for 59a, a Hammett plot revealed a correlation with ct with a positive p, which indicates that a phenolate intermediate is formed in this reaction. Therefore, this reaction has been shown to proceed by a totally different mechanism. According to experimental results and DFT calculations, the reactions proceed by the deprotonation of benzoxazoles 59 to form 61, which is in equilibrium with o-phenoxyisocyanide 62. Coordination of the oxidative addition product PdI(Ph)L2 to the isocyanide then forms 63 which cyclizes to form palladate 64, from which the 2-phenylbenzoxazoles 60 are formed by reductive ehmination. [Pg.375]

Ni extraction proceeds according to Eqn. 8, via deprotonation of the phenol and chelation of the phenolate oxygen and the oxime nitrogen. Since the extraction is in ammoniacal medium, ammonium ions are formed rather than protons, in a 2 1 L M stoichiometry [10]. Ni stripping can be effected by reversing the equilibrium with strong NH3 solution, or with dilute H2SO4. [Pg.397]

Figure 17 Acid-base switch process in second-generation Zn + calix complexes (a). The five-coordinate complex (1) yields the five-coordinate complex (2) upon deprotonation of its capping phenol ligand. (2) is in equilibrium with the guest-free four-coordinate complex (3). Excess base generates a four-coordinate complex (4) devoid of host-guest properties. Proposed mechanism for the peptidase activity of astacin and serralysin, in view of the acid-base switch process of the model (b)." ... Figure 17 Acid-base switch process in second-generation Zn + calix complexes (a). The five-coordinate complex (1) yields the five-coordinate complex (2) upon deprotonation of its capping phenol ligand. (2) is in equilibrium with the guest-free four-coordinate complex (3). Excess base generates a four-coordinate complex (4) devoid of host-guest properties. Proposed mechanism for the peptidase activity of astacin and serralysin, in view of the acid-base switch process of the model (b)." ...
Two reports have appeared of kinetic studies of the base hydrolysis of complex ions of the type [Co(NH3)5(OCOR)] +. Activation parameters are reported from rate constants extrapolated to zero ionic strength for R = CM3 CI (/i = 1,2, or 3). When RCO2" = salicylate ion a simple second-order rate law is not observed owing to the importance of the deprotonation of the phenolic group. " If K is the equilibrium constant for this deprotonation reaction, the pseudo-first-order rate constant (k) in the presence of an excess of OH" ion is given by k=(A iis [OH-] k2K[OH-] )IH J5 [OH"])... [Pg.215]


See other pages where Phenols equilibrium deprotonation is mentioned: [Pg.215]    [Pg.146]    [Pg.79]    [Pg.3307]    [Pg.241]    [Pg.383]    [Pg.44]    [Pg.200]    [Pg.145]    [Pg.335]    [Pg.107]    [Pg.690]    [Pg.183]    [Pg.297]    [Pg.690]    [Pg.211]    [Pg.522]    [Pg.41]    [Pg.90]    [Pg.547]    [Pg.547]    [Pg.8401]    [Pg.208]    [Pg.211]    [Pg.413]    [Pg.690]    [Pg.243]   
See also in sourсe #XX -- [ Pg.79 ]




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