Malonic acids, ionization

Thermal degradation prior to ionization can cause decarbonylation or decarboxylation of the analyte. Decarbonylation, for example, is observed from a-ketocarboxylic acids and a-ketocarboxylic acid esters, whereas decarboxylation is typical behavior of P-oxocarboxylic acids such as malonic acid and its derivatives and di-, tri-, or polycarboxylic acids. 

Figure 7. Ionization constants of acids in ethanol-water mixtures vs. the dielectric constant function at 25°C. A Malonic acid (O), lactic acid (A), succinic acid ( ). (B) Cyanoacetic acid ( ), salicyclic acid ( ), glutaric acid ( ). C Chloroacetic acid (O), glycolic acid (A), isovaleric acia(D).

Problem 18.15 Compare the acidity (first ionization) of oxalic acid with that of formic acid of malonic acid with that of acetic acid. How do you account for these differences ... 

Consider the dicarboxylic acid malonic acid, HOOC—CH2—COOH. It ionizes in two stages with pK values pK i and pK 2- How do you predict the magnitudes of these two will compare with the pXj of acetic acid, CH3COOH, which is 4.8. ... 

Malonic acid, from this point of view, is carboxyl acetic acid, and should belong to the — CO2H class. Its constant is found to be 0.164, The following substituted malonic acids, with their ionization constants, have been measured dimethylmalonic, 0.076 a, a-tetramethylenedi-... 

Consider, for example, the successive ionization of the two carboxyl groups in malonic acid,... 

Rates of ionization of monoanions of substituted malonic acids are much less than the diffusion-controlled limit, even though the equilib-... 

Ionization of dicarboxylic acids has been shown to have a profound effect on the decarboxylation rate. The disodium salt of malonic acid (NaOOCCH2COONa) was found to be relatively stable with respect to decarboxylation (Fairclough 1938) up to temperatures of 125 °C, whereas the monosodium salt decomposed by a first-order reaction. Rates for the decarboxylation of both malonic and oxalic acids were slower in polar solvents in which a high degree of ionization was expected (Richardson and O Neal 1972). Similarly, the rate of decomposition of dibromomalonic acid was found to be proportional to the concentration of the undissociated acid molecule in solution (Muus 1935). 

Giordano (1990) calculated concentrations of Ca, Mg, Na, Pb, Zn, Fe, and Al as acetate, oxalate, malonate, succinate, and catechol complexes in three reconstructed MVT ore solutions and a model oil-field brine at 100 °C. In Table 5, results are presented for revised speciation calculations for the three MVT ore fluids and calculated speciation results for a model RBRBM ore fluid. These model results are based in part on recently published data at elevated temperatures for Ca, Mg, and Al complexes and high-temperature constants for ionization reactions of oxalic and malonic acids (Table 4). In the MVT model proposed by Anderson (1975 model 1, Table 5), the ore fluid is moderately oxidized and falls well above the sulfide-sulfate boundary in logao2 - pH space at 100°C. It is slightly acid and contains 10 molal... 

Cullis PM, McClymont JD, Malone ME, Mather AN, Podmore ID, Sweeney MC, Symons MCR (1992) Effects of ionizing radiation on deoxyribonucleic acid. Part 7. Electron capture at cytosine and thymine. J Chem Soc Perkin Trans 2 1695-1702... 

Pvoblem 18.16 Arrange oxalic, malonic, succinic, and glutaric acids in order of acidity (first ionization). How do you account for this order ... 

A variation on this sequence used malonate or Meldrum s acid to form cyclopropanes and lactones, respectively. Scheme 42 [127]. An important observation in this sequence was that the second reaction was very poor in the presence of the chiral Hgand since the allylic ester that remained was mismatched to the chirality of the Hgand so ionization was very slow. The best way to overcome this problem in the cyclopropane series was to use a paUadium catalyst with an achiral ligand for the second step. The choice of base was crucial to the eventual mode of cycHzation with CS2CO3 being most effective for the cyclopropane forming reaction and K2CO3 the best base for the lactone formation. 

Amongst the acid salts of the simpler dicarboxylic acids, at any rate, we find much more frequently structures corresponding to Type A. For instance, in potassium hydrogen malonate the two carboxyl groups of the mono-ionized anion are crystallographically equivalent. Such structures we classify as Type A j. 

Activation of allylic ethers. An allylic ether y to an electron-withdrawing group is activated by forming the Fe(CO)4 complex. On acid treatment ionization occurs to generate the allyl cation (still complexed to iron), which is reactive towards nucleophiles such as silyl enol ethers, malonate ester enolates, etc. The substitution is stereoselective. ... 

The decrease in acid strength from oxalic acid to azelaic (except for succinic acid) is thus mainly an entropy effect once more. Presumably with the lower acids oxalic and malonic there is some steric restriction, due to the closeness of the negative charges, which reduces the extent of electrorestriction of water molecules. With increasing separation of the charges, as the series is ascended, the entropy losses on ionization will be increased. 

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