Acetate ions

The mechanism of the reaction, which is of the aldol type, involves the car-bonyl group of tlie aldehyde and an active methylene group of the anhydride the function of the basic catalyst B (acetate ion 0H3000 or triethylamine N(0,Hb)j) is to form the anion of the active hydrogen component, i.e., by the extraction of a proton from the anhydride ... 

It was shown that in preparative experiments sulphuric acid markedly catalysed, and acetate ions markedly anticatalysed the nitration of anisole. ... 

The effect of acetate ions cannot be distinguished from that of nitrate ions, which... 

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... 

Example A common misconception is that the conjugate base of a weak acid is strong This is sometimes but not always true It is true for example for ammo nia which is a very weak acid (pK 36) Its conjugate base amide ion (H2N ) is a much stronger base than HO It is not true however for acetic acid both acetic acid and its conjugate base acetate ion are weak The conjugate base of a weak acid will be strong only when the acid is a weaker acid than water... 

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... 

Acetate ion Octadecyl tosylate Octadecyl acetate Tosylate ion y... 

FIGURE 19 3 The free energies of ionization of ethanol and acetic acid in water The electrostatic po tential maps of ethoxide and acetate ion show the concentration of negative charge in ethoxide versus dispersal of charge in ac etate The color ranges are equal in both models to al low direct comparison... 

FIGURE 19 4 Electro static potential maps of (a) acetic acid and (b) acetate ion The negative charge (red) IS equally distributed between both oxygens of acetate ion The color range IS different for (a) and (b)... 

Electron delocalization in carboxylate ions is nicely illustrated with the aid of elec trostatic potential maps As Figure 19 4 shows the electrostatic potential is different for the two different oxygens of acetic acid but is the same for the two equivalent oxygens of acetate ion... 

Likewise the experimentally measured pattern of carbon-oxygen bond lengths m acetic acid is different from that of acetate ion Acetic acid has a short C=0 and a long C—O distance In ammonium acetate though both carbon-oxygen distances are equal... 

Suppose you take two flasks one containing pure water and the other a buffer solution mam tamed at a pH of 7 0 If you add 0 1 mole of acetic acid to each one and the final volume m each flask IS 1 L how much acetic acid is present at equi librium How much acetate ion In other words what IS the extent of ionization of acetic acid m an unbuffered medium and m a buffered one ... 

Thus when acetic acid is added to pure water the ra tio of acetate ion to acetic acid is... 

The most common charge types for the acid HB and its conjugate base B are CH3COOH = H+ -f CH3C00 (acetic acid, acetate ion)... 

When an acid and a base react, the products are a new acid and base. For example, the acetate ion, C1T3COO-, in reaction 6.7 is a base that reacts with the acidic ammonium ion, N1T45", to produce acetic acid and ammonia. We call the acetate ion the conjugate base of acetic acid, and the ammonium ion is the conjugate acid of ammonia. 

Weak bases only partially accept protons from the solvent and are characterized by a base dissociation constant, kj,. For example, the base dissociation reaction and base dissociation constant for the acetate ion are... 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Silver Acetate. Silver acetate, H CCOOAg, is prepared from aqueous silver nitrate and acetate ion. Colorless silver acetate crystals and solutions made from this salt are unstable to light. 

The initiating step in these reactions is the attachment of a group to the sulfoxide oxygen to produce an activated intermediate (5). Suitable groups are proton, acyl, alkyl, or almost any of the groups that also initiate the oxidations of alcohols with DMSO (40,48). In a reaction, eg, the one between DMSO and acetic anhydride, the second step is removal of a proton from an a-carbon to give an yUde (6). Release of an acetate ion generates the sulfur-stabilized carbonium ion (7), and the addition of acetate ion to the carbonium ion (7) results in the product (eq. 15) ... 

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

Table 5.7 lists the nucleophilic constants for a number of species according to this definition. It is apparent from Table 5.7 that nucleophilicity toward methyl iodide does not correlate directly with basicity. Azide ion, phenoxide ion, and bromide are all equivalent in nucleophilicity but differ greatly in basicity. Conversely, azide ion and acetate ion are... 

Entry 4 shows that reaction of a secondary 2-octyl system with the moderately good nucleophile acetate ion occurs wifii complete inversion. The results cited in entry 5 serve to illustrate the importance of solvation of ion-pair intermediates in reactions of secondary substrates. The data show fiiat partial racemization occurs in aqueous dioxane but that an added nucleophile (azide ion) results in complete inversion, both in the product resulting from reaction with azide ion and in the alcohol resulting from reaction with water. The alcohol of retained configuration is attributed to an intermediate oxonium ion resulting from reaction of the ion pair with the dioxane solvent. This would react until water to give product of retained configuratioiL When azide ion is present, dioxane does not efiTectively conqiete for tiie ion-p intermediate, and all of the alcohol arises from tiie inversion mechanism. ... 

The behavior of compounds A and B on solvolysis in acetic acid containing acetate ion has been studied. The solvolysis of A is about 13 times faster than that of B. Kinetic studies in the case of A show that A is racemized competitively with solvolysis. A single product is formed from A, but B gives a mixture. Explain these results. 

The hydrolysis of the lactone A shows a signifieant catalysis by acetate ion in acetate buffer, with the rate expression being... 

This results in a pH-rate profile as shown in Fig. 8.P21, with the acetate catalysis being signifieant in the pH range 3-6. Discuss how this catalysis by acetate ion might oeeur. What are the most likely mechanisms for hydrolysis at pH < 2 and pH > 7, where the rates are linear in [H+] and [ OH], respectively ... 

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

An apparently related reaction involves iodination in pure methanol in the presence of calcium chloride. The main product is the 21,21-d3-iodo derivative, which on reaction with acetate ion gives, surprisingly, the 21-monoacetate ... 

While displacement of a 21-bromide by hydroxyl can be accomplished by careful control of reaction conditions,it is preferable to use acetate ion instead, and potassium acetate in refluxing acetone has been most commonly... 

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