Carboxy late ion

The catalytic cycles for reduction of alkyl and atyl halides using Ni(o), Co(i) or Pd(o) species are interrupted by added carbon dioxide and reaction between the first formed carbon-metal bond and carbon dioxide yields an alkyl or aryl car-boxylate. These catalyses reactions have the advantage of occuriiig at lower cathode potentials than the direct processes summarised in Table 4.14. Mechanisms for the Ni(o) [240] and Pd(o) [241] catalysed processes have been established. Carbon dioxide inserts into the carbon-metal bond in an intermediate. Once the carboxy-late-metal species is formed, a further electron transfer step liberates the carboxy-late ion reforming the metallic complex catalyst. 

At the start of the peptide synthesis, the C-terminal amino acid is bonded through its carboxyl group to the resin by a nucleophilic attack of the carboxy-late ion on the chloromethyl groups. The a-amino group must be suitably protected, as with ferf-butoxycarbonyl, before carrying out this step ... 

Increasing the pH of copper alginate beads with sodium hydroxide will probably not cause the beads to dissolve. Adding beads to concentrated ammonia solution, however, will slowly dissolve the beads because the copper ions complex more strongly with NH3 (forming the deep blue Cu(NH3)42+) than they do with carboxy-late ions. 

Eq. (20)), we find that the same product, ResR—Ch(NHj)COOH, is formed. In order to substantiate this observation, the IR spectra of GLY adsorbed on the strong-acid cation-exchange resin in the H -ion form were measured [16]. It was found that IR spectra of all samples prepared from aqueous solutions of GLY at a concentration level of 0.1 mol L and at pH values corresponding to 1.42, 4.88 and 5.64 exhibit the band at 1750-1752 cm that is assigned to the unionized carboxjd and the band at 1600 cm that is assigned to the antisymmetric vibration of carboxy-late ion. In spite of the presence of different predominant species in solutions and different mechanism encountered at different pH values, the IR spectra show that the amino adds adsorbed on ion exchanger are dissociated. 

Resonance (left) and induction (right) stabilization of a carboxy-late ion. 

A classic reaction involving electron transfer and decarboxylation of acyloxy radicals is the Kolbe electrolysis, in which an electron is abstracted from a carboxy-late ion because of the oxidation potential (voltage) at the anode. The most important synthetic use of this reaction is to give products derived from coupling of... 

Aramaki, K., Shimura, T. Prevention of passive film breakdown on iron by coverage with one-dimensional polymer films of a carboxy late ion self-assembled monolayer modified with alkyltriethoxysUanes , Corrosion Science, 2004,46,2563-81. 

Dewar, M. J. S. Schmeising, H. N. Tetrahedron 1959, 5, 166. It should be noted that some species for which two equivalent resonance structures can be written do not fit this description. For example, with the carboxy late ion, there are four jr-electrons and only two a-bonds. For a recent discussion of the acidity of carbojqrlic acids, see Rablen, P. R. J. Am. Chem. Soc. 2000, 122, 357. 

The electron density of the delocalized bond is spread by means of a delocalized molecular orbital and may be regarded as a series of pi bonds extending over several atoms, for example the pi bonds in butadiene and the C-O pi bonds in the CARBOXY-LATE ION. 

Bunnett and co-workers have shown that an or Ao-carboxy-late anion decreases the rate of reaction of 4-nitrochlorobenzene with methoxide ion but rather strongly increases the reaction rate with piperidine. This effect arises from an accelerative increase in the... 

The mechanism of the C02 transfer reaction with acetyl CoA to give mal-onyl CoA is thought to involve C02 as the reactive species. One proposal is that loss of C02 is favored by hydrogen-bond formation between the A -carboxy-biotin carbonyl group and a nearby acidic site in the enzyme. Simultaneous deprotonation of acetyl CoA by a basic site in the enzyme gives a thioester eno-late ion that can react with C02 as it is formed (Figure 29.6). 

Optically active benzene(poly)carboxamides and benzene(poly)carboxy-lates were used by Inoue and co-workers as sensitizers for the geometrical photoisomerization of (Z)-cyclooctene and (Z,Z)-cyclooctadienes in various solvents at different temperatures. Under energy-transfer conditions, enantiomeric excesses up to 64% ee in unpolar solvents like pentane were reported. The use of polar solvents diminished the product ee s due to the intervention of a free or solvent-separated radical ion pair generated through the electron transfer from the substrate to the excited chiral sensitizer (Scheme 58) [105-109]. 

Hydride donor Iminium ion Acyl halide Aldehyde Ketone Ester Amide Carboxy- late salt... 

Milk transferrin (lactoferrin51a b c also found in leukocytes), hen egg transferrin (ovotransferrin),52 52a and rabbit and human serum transferrin54 543 all have similar structures. Each Fe3+ is bonded to oxygen anions from two tyrosine side chains, an aspartate carboxy-late, an imidazole group, and the bound carbonate ion (Fig. 16-2B). 

A second method to efficientiy produce mediyl esters of carboxylic acids is to heat die acid with potassium carbonate and mediyl iodide. The mediyl ester is produced under mild conditions and is easily separated from die reaction byproducts. This method is somewhat different in tiiat die ester is formed by a nucleophilic displacement of iodide by die carboxylate ion. Normally carboxy-lates are not thought of as good nucleophiles—and tiiey are not—but mediyl iodide is a quite reactive electrophile which matches die poor nucleophilicity of die carboxylate satisfactorily. 

Lithium aluminium hydride reduction of 1,2-disubstituted cyclopropene-3-carboxy-lates occurs initially at the ester group, but with additional reagent good yields of cis-1,2-disubstituted-rranj-3-methanols are obtained 176). The reduction of the double bond is regioselective, leading to the more stable carbanion, and the attack of the hydride ion exclusively cis to the 3-substituent may be explained in terms of initial formation of an alkoxyaluminium complex followed by intramolecular hydride transfer 176). In the case of cyclopropene-1-carboxylates, direct reduction to the saturated alcohol occurs thus (253) is converted to the rranj-alcohol177) ... 

Because the reaction of the amine phosphates with metal ions yields a variety of metal phosphates with different structures [18, 39], it is conceivable that the amine carboxylates also play a similar role in the formation of metal carboxy-lates with open architectures. Reports on the synthesis and characterization of... 

We see that the alcohol and alkoxide ion are each represented satisfactorily by a single structure. However, we can draw two reasonable structures (I and II) for the carboxylic acid and two reasonable structures (III and IV) for the carboxy-late anion. Both acid and anion are resonance hybrids. But is resonance equally... 

Whilst cations such as Fe +, Co +, Mn and Pb lower the yield in the Kolbe electrolysis, alkali and alkylammonium ions have no effect and are therefore preferably used as counterions for the carboxy-late. 

The HF-SbFs system works well in the Gattermann-Koch formylatlon of arenes and the Koch carbonylation of alkanes [54]. For instance, biphenyl is diformylated in HF-SbFs-CO to afford 4,4 -diformylbiphenyl as a major isomer (Scheme 14.20). The carbonylation of alkanes with C5-C9 carbon atoms in the HF-SbFs-CO system affords mixtures of C3-C8 carboxylic acids after hydrolysis of the generated secondary carbenium ions [55]. Successive treatment of methylcyclopentane with CO in HF-SbF and with water produces cyclohexanecarboxylic acid as a major product (Scheme 14.21) [56]. It seems that a tertiary methylcyclopentyl cation readily isomerizes to the more stable cyclohexyl cation before being trapped by CO. Bicyclic a, -unsaturated ketones are functionahzed by HF-SbF or FSOsH-SbFs under a CO atmosphere to give saturated keto esters after methanolysis (Scheme 14.22) [57]. Alcohols with short carbon chains also react with CO in HF-SbFs to give the corresponding methyl esters [58]. y-Butyrolactones are carboxy-lated under the same conditions to afford 1,5-dicarboxyhc acids [59]. 

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