Anion derived from acids

Pajerski, A.D., Squiller, E.P., Parvez, M., Whittle, R.R. and Richey, H.G., Preparation and properties of RMg(macrocycle) cations with acconpanying anions derived from acidic hydrocarbons or a hindered phenol, Organometallics 24 (5), 809-814 (2005). 

This reaction is useful in the preparation of anionic derivatives from the chlorides when the nucleophilic displacement route is unsatisfactory. Even weak acids, eg, phenols, mercaptans, and cycHc nitrogen compounds, can be made to undergo reaction with triorganotin hydroxides or bisoxides if the water of reaction is removed a2eotropicaHy as it forms. 

The reactions of ketenes or ketene equivalents with imines, discussed above, all involve the imine acting as nucleophile. Azetidin-2-ones can also be produced by nucleophilic attack of enolate anions derived from the acetic acid derivative on the electrophilic carbon of the imine followed by cyclization. The reaction of Reformatsky reagents, for example... 

The relative stability of the anions derived from cyclopropene and cyclopentadiene by deprotonation is just the reverse of the situation for the cations. Cyclopentadiene is one of the most acidic hydrocarbons known, with a of 16.0. The plCs of triphenylcyclo-propene and trimethylcyclopropene have been estimated as 50 and 62, respectively, from electrochemical cycles. The unsubstituted compound would be expected to fall somewhere in between and thus must be about 40 powers of 10 less acidic than cyclopentadiene. MP2/6-31(d,p) and B3LYP calculations indicate a small destabilization, relative to the cyclopropyl anion. Thus, the six-7c-electron cyclopentadienide ion is enormously stabilized relative to the four-7c-electron cyclopropenide ion, in agreement with the Hixckel rule. 

Pyroglntamic acid is a useful starting material for the synthesis of several naniral products, such as pyrtolidme alkaloids, kainoids, and other unnaniral amino acids. Interesting chemose-lecdve Michael additions of anions derived from pyroglntamates have been reported fsee Eqs. 4.54 and4.55. ... 

Anions. An anion derived from a weak add is itself a weak base. A typical example is the fluoride ion, F-, which is the conjugate base of the weak acid HF. The reaction of the F- ion with water is... 

Intermediate 10 must now be molded into a form suitable for coupling with the anion derived from dithiane 9. To this end, a che-moselective reduction of the benzyl ester grouping in 10 with excess sodium borohydride in methanol takes place smoothly and provides primary alcohol 14. Treatment of 14 with methanesulfonyl chloride and triethylamine affords a primary mesylate which is subsequently converted into iodide 15 with sodium iodide in acetone. Exposure of 15 to tert-butyldimethylsilyl chloride and triethylamine accomplishes protection of the /Mactam nitrogen and leads to the formation of 8. Starting from L-aspartic acid (12), the overall yield of 8 is approximately 50%, and it is noteworthy that this reaction sequence can be performed on a molar scale. 

Nucleophiles such as alkyllithium, or the anion derived from 2-nitropropane, readily add to y-hydroxy-a,/1-unsaturated sulfones (equations 69 and 70)59. Oxidation followed by elimination of f-butylsulfinic acid leads to the formation of dienones (equation 70). 

The parent acids of common polyprotic acids other than sulfuric are weak and the acidity constants of successive deprotonation steps are normally widely different. As a result, except for sulfuric acid, we can treat a polyprotic acid or the salt of any anion derived from it as the only significant species in solution. This approximation leads to a major simplification to calculate the pH of a polyprotic acid, we just use Kal and take only the first deprotonation into account that is, we treat the acid as a monoprotic weak acid (see Toolbox 10.1). Subsequent deprotonations do take place, but provided Kal is less than about fCal/1000, they do not affect the pH significantly and can be ignored. 

Table Some stable all-hydrocarbon anions derived from hydrocarbon acids with pA a values 7.

Carboxylate anions derived from somewhat stronger acids, such as p-nilrobcnzoic acid and chloroacetic acid, seem to be particularly useful in this Mitsunobu inversion reaction.53 Inversion can also be carried out on sulfonate esters using cesium carboxy-lates and DMAP as a catalyst in toluene.54 The effect of the DMAP seems to involve complexation and solubilization of the cesium salts. 

The anion derived from ethyl 2-nitropropionate reacts with various reductive alkylating agents (S l substrates) to give new unsymmetrically disubstitutednitro esters (Eq. 5.35), which are interesting precursors for unusual amino acids.53... 

As ligands in metal complexes, the anions derived from these acids display a broad variety of coordination patterns (Scheme 2). Usually, the ligands are described as monodentate, bidentate chelating or bridging, and polydentate. We use here a description based upon the number of connections between the... 

The mixed carbonic anhydride procedure8-7 has been useful in the preparation of amide linkages and thiol esters. Mixed carbonic anhydrides have successfully acylated, under very mild conditions, the carb-anions derived from diethyl ethylmalonate and diethylcadmium.8 The latter gives as a product the corresponding ketone. Mixed anhydrides derived from acetic and acetylsalicylic acids give results similar to those described here.8... 

Alternatively, Ballini devised a new strategy to synthesize tri-alkylated pyrroles from 2,5-dialkylfurans and nitroalkanes <00SL391>. This method involves initial oxidation of 2,5-dimethylfuran with magnesium monoperoxyphthalate to cA-3-hexen-2,5-dione (6). Conjugate addition of the nitronate anion derived from the nitro compound 7 to 6 followed by chemoselective hydrogenation of the C-C double bond of the resulting enones 8 (obtained by elimination of nitrous acid from the Michael adduct) completes the conversion to the alkylated y-diketones 9. Final cyclization to pyrroles 10 featured improved Paal-Knorr reaction conditions involving reaction of the diketones with primary amines in a bed of basic alumina in the absence of solvent. 

Published equilibrium constants for monocarboxylato complexes are summarized in Table VII. All that can be deduced with certainty from these data is that the anions derived from monocarboxylic acids form rather weak complexes with beryllium. In all probability they act as monodentate ligands. The possibility of bidentate chelation using both carboxylate oxygen atoms can be ruled out on the grounds... 

See the chart on page 158. Any anion derived from a weak acid acts as a base in a water solution. The carbonate polyatomic anion, C032 laq), is derived from the weak acid carbonic acid, H2C03. There are no common basic cations. 

The second reason is that Satchell [78] has shown that in the protonation of m-xylene by catalysts composed of stannic chloride and acetic acid or the three chloroacetic acids as co-catalysts, the rate of reaction is inversely related to the aqueous acidity of these acids. Satchell rightly points out that, since the polymerisations are complicated reactions the rates of which are also affected by the terminating efficiency of the anion derived from the co-catalyst, no valid conclusions can be drawn from such studies about catalytic efficiency in any fundamental sense. He interprets the order of effectiveness of the cocatalysts in terms of the stability of the complexes which they form with the metal halide. 

A new synthesis (Scheme 4) of 2-aminoethylphosphonic acid (24) has been described in which bis(dimethylamino) phosphorochloridate is condensed with an a-anion derived from an aliphatic nitrile.71 An advantage of this synthesis is that the intermediate (25) can be alkylated, which constitutes the simplest synthesis so far published for substituted aminoethylphosphonic acids. Both C-3 and the phosphorus atom of PEP are incorporated into (24) in Tetrahymena pyriformis,72 which confirms... 

Anion derived from a strong acid Anion derived from a weak acid... 

Resonance stabilization is also responsible for the increased acidity of a C-H group situated adjacent to a carbonyl group. The anion is stabilized through delocalization of charge, similar to that seen with the allyl anion derived from propene but this system is even more favourable, in that delocalization allows... 

Vitamin C, also known as L-ascorbic acid, clearly appears to be of carbohydrate nature. Its most obvious functional group is the lactone ring system, and, although termed ascorbic acid, it is certainly not a carboxylic acid. Nevertheless, it shows acidic properties, since it is an enol, in fact an enediol. It is easy to predict which enol hydroxyl group is going to ionize more readily. It must be the one P to the carbonyl, ionization of which produces a conjugate base that is nicely resonance stabilized (see Section 4.3.5). Indeed, note that these resonance forms correspond to those of an enolate anion derived from a 1,3-dicarbonyl compound (see Section 10.1). Ionization of the a-hydroxyl provides less favourable resonance, and the remaining hydroxyls are typical non-acidic alcohols (see Section 4.3.3). Thus, the of vitamin C is 4.0, and is comparable to that of a carboxylic acid. 

---