Acetate ions, and

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

A similar electron delocalization stabilizes acetate ion and related species... 

All these reactions of octadecyl p toluenesulfonate have been reported in the chemical literature and all proceed in synthetically useful yield You should begin by identifying the nucleophile in each of the parts to this problem The nucleophile replaces the p toluenesulfonate leaving group in an Sn2 reaction In part (a) the nucleophile is acetate ion and the product of nucleophilic substitution IS octadecyl acetate... 

Zn is determined by direct titration with EDTA with xelenol indicator after iron elimination with acetate ions and copper - with sulfide ions. 

The reductive cleavage of ketol acetates involves addition of two electrons to the system with fragmentation into an acetate ion and a ketone carbanion... 

Rule 1 Individual resonance forms are imaginary, not real. The real structure is a composite, or resonance hybrid, of the different forms. Species such as the acetate ion and benzene are no different from any other. They have single, unchanging structures, and they do not switch back and forth between resonance forms. The only difference between these and other substances is in the way they must be represented on paper. 

Look back at the resonance forms of the acetate ion and the acetone anion shown in the previous section. The pattern seen there is a common one that leads to a useful technique for drawing resonance forms. In general, any three-atom grouping with a p orbital on each atom has two resonance forms. 

Some substances, such as acetate ion and benzene, can t be represented by a single line-bond structure and must be considered as a resonance hybrid of two or more structures, neither of which is correct by itself. The only difference between two resonance forms is in the location of their tt and nonbonding electrons. The nuclei remain in the same places in both structures, and the hybridization of the atoms remains the same. 

Resolution (enantiomers), 307-309 Resonance, 43-47 acetate ion and, 43 acetone anion and. 45 acyl cations and, 558 allylic carbocations and, 488-489 allylic radical and, 341 arylamines and, 924 benzene and, 44. 521 benzylic carbocation and, 377 benzylic radical and, 578 carbonate ion and. 47 carboxylate ions and, 756-757 enolate ions and, 850 naphthalene and, 532 pentadienyl radical and. 48 phenoxide ions and, 605-606 Resonance effect, 562 Resonance forms, 43... 

Acetate ions and the other ions listed in last row of Table 10.8 act as bases in water. 

Self-Test 11.4A Calculate the ratio of the molarities of acetate ions and acetic acid needed to buffer a solution at pH = 5.25. The pKa of CH3COOH is 4.75. 

Calculate the equilibrium concentrations of acetic acid, acetate ion, and hydronium ion in a 2.5 M solution of acetic acid. 

A solution contains 0.125 mol of solid sodium acetate dissolved in 1.00 L of 0.250 M acetic acid. Determine the concentrations of hydronium ions, acetate ions, and acetic acid. 

As a result, both acetate ions and acetic acid molecules are present as major species in solution. The presence of an acid and its conjugate base means that in this region of the titration, the solution is buffered, so the pH changes slowly as hydroxide ions are added to the solution. 

The presence of ligands, either in the form of added anions such as acetate or as co-solvents or solvents, such as pyridine, markedly affect the kinetics. In pyridine or dodecylamine solvents the hydrogenation of Ag(I) acetate follows simple second-order kinetics, as does that of Cu(I) acetate. This behaviour is also shown in aqueous solutions by Ag(I) in the presence of acetate ions and by an ethylenediamine complex of Ag(I) . The rate of hydrogenation of Cu(II) acetate, on the other hand, is independent of oxidant concentration. The rate of oxidation of hydrogen by Cu(II) acetate in quinoline is also independent of oxidant concentration , but does depend on the square of the concentration of cuprous acetate which acts as a catalyst. For further details of these complicating features, reference should be made to the original papers and to Hal-pern s review ... 

The electron-withdrawing inductive effect of the carbonyl group also stabilizes the acetate ion, and therefore the acetate ion is a weaker base than the ethoxide ion. 

One could go on with examples such as the use of a shirt rather than sand reduce the silt content of drinking water or the use of a net to separate fish from their native waters. Rather than that perhaps we should rely on the definition of a chemical equilibrium and its presence or absence. Chemical equilibria are dynamic with only the illusion of static state. Acetic acid dissociates in water to acetate-ion and hydrated hydrogen ion. At any instant, however, there is an acid molecule formed by recombination of acid anion and a proton cation while another acid molecule dissociates. The equilibrium constant is based on a dynamic process. Ordinary filtration is not an equilibrium process nor is it the case of crystals plucked from under a microscope into a waiting vial. 

Many of the early reports of spin-trapping experiments were focused on mechanistic investigations, and some of these feature in the early reviews (see p. 4). Unfortunately, it is in this application that inferences drawn may be most suspect. For example, the inability of the method to differentiate between radical trapping on the one hand, and a combination of nucleophile trapping with one-electron oxidation on the other, is a serious shortcoming. An early example of this was the tentative conclusion that acetoxyl radicals were spin-trapped by PBN competitively with their decarboxylation in reactions of lead tetraacetate. In view of the rapidity of the decarboxylation reaction, trapping of acetate ion and subsequent oxidation seems a likely alternative. 

Alkyl sulfides are not the only nucleophiles that can catalyze the hydrolysis of sulfinyl sulfones. The various halide ions, thiocyanate ion, acetate ion, and thiourea, are very effective catalysts (Kice and Guaraldi, 1968). The mechanism for the hydrolysis as catalyzed by these nucleophiles is shown in... 

Another mechanistically useful nucleophile is acetate ion and related carboxylates. Acetate ion is difficult to oxidize (Eberson, 1963) and reacts with radical cations in a bond-forming reaction (Eberson and Nyberg, 1976). The oxidation product, the acetoxyl radical, has properties which make trapping it very unlikely in that its decarboxylation rate constant is 1.3 X 109 s 1 (Hillborn... 

Figure 2.5. Nucleophile selectivities determined from product analysis for the reactions of ring-suhstituted 1-phenylethyl derivatives (X-l-Y) with azide ion, acetate ion and methanol in 50 50 (v/v) water/trifluoroethanol. The selectivities are plotted against the appropriate Hammett substituent constant or a. Leaving group Y ( ) ring-suhstituted benzoates ( ) chloride (T) dimethyl sulfide (A) tosylate.

Consider the parallel reactions between zinc ion and acetate ion and between zinc ion and oxalate ion. 

In the earlier kinetic study26 the rate constant for hydrolysis of lauryl-caproylimidazole PEI to caproate ion and laurylimidazole PEI was estimated to be 0.06 min-1 at pH 7.3. In the present study we have found the rate constant for hydrolysis of laurylacetylimidazole PEI to acetate ion and laurylimidazole PEI under similar conditions to be 0.1 to 0.2 min-1. In the earlier study the hydrolysis rate was inferred by an indirect method from the turnover rate in a steady-state situation. In view of the uncertainties in the indirect method and the difference in size of the acyl group in the two cases, the approximate equality of the deacylation rate constants is gratifying. 

Since acetate ion (and similar potential methyl donors) can occur in natural waters, photolysis by sunlight may well be a potential, ubiquitous route to methylmetal compounds (204-206). One such example might be the reported photolysis of some aliphatic a-amino acids to form CH3Hg+ (207) ... 

Further bromination of 3,4,6-tribromo-5-hydroxybenzo[6]thio-phene affords the 2,3,4,6-tetrabromo derivative in the absence of acetate ion, and 3,4,4,6-tetrabromo-4,5-dihydrobenzo[6]thiophen-5-one in the presence of acetate ion. 421 On treatment of 3,4-dibromo-, 4,6-dibromo-, 3,4,6-tribromo-, or 2,3,4,6-tetrabromo-5-hydroxybenzo-[6]thiophene with nitric acid in acetic acid, the corresponding unstable orange crystalline 4-bromo-4-nitro-4,5-dihydrobenzo[6]thio-phen-5-one is obtained.152,421 Hence, once both positions ortho to the hydroxyl group in 5-hydroxybenzo[6]thiophene are occupied by bromine, the properties of these compounds are analogous to the properties of l-bromo-2-naphthol which, on bromination in acetic acid in the presence of acetate ion, affords l,l-dibromo-l,2-dihydro-naphthalen-2-one whereas, in its absence, it affords l,6-dibromo-2-naphthol.616 The behavior of l-bromo-2-naphthol and its derivatives on nitration is similar to that of 4,0-dibromo-5-hydroxybenzo[6]thio-phene and its derivatives.162,616... 

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