Malonic acid stability

The final decarboxylation of mevalonate 5-diphosphate appears unusual because decarboxylations of acids do not typically occur except in /3-keto acids and malonic acids, in which the carboxylate group is two atoms away from an additional carbonyl group (Section 22.7). The function of this second carbonyl group is to act as an electron acceptor and stabilize the charge resulting from loss of CC>2- In fact, though, the decarboxylation of a /3-kelo acid and the decarboxylation of mevalonate 5-diphosphate are closely related. 

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Although the reaction mechanism of this type of reactions is not fully elucidated, it is easily anticipated that no intramolecular special stabilization effect for the carbanion generated from decarboxylation is expected, different from the case of malonic acid-type compounds. Moreover, cinnamic acid derivatives that have both the electron-donating and withdrawing substituents have been reported to undergo this reaction. This fact suggests that the enzyme itself stabilizes the transition state without the aid of mesomeric and inductive effects of the other part of the substrate molecule itself. If such unknown mechanism also works for other... 

The decarboxylation reaction usually proceeds from the dissociated form of a carboxyl group. As a result, the primary reaction intermediate is more or less a carbanion-like species. In one case, the carbanion is stabilized by the adjacent carbonyl group to form an enolate intermediate as seen in the case of decarboxylation of malonic acid and tropic acid derivatives. In the other case, the anion is stabilized by the aid of the thiazolium ring of TPP. This is the case of transketolases. The formation of carbanion equivalents is essentially important in the synthetic chemistry no matter what methods one takes, i.e., enzymatic or ordinary chemical. They undergo C—C bond-forming reactions with carbonyl compounds as well as a number of reactions with electrophiles, such as protonation, Michael-type addition, substitution with pyrophosphate and halides and so on. In this context,... 

Dicarbonyl donors bearing a thioester has been applied in the Mannich reaction to A -tosyl imines. Ricci presented an enantioselective decarboxylative addition of malonic half thioester 37 to imine 38. In the Mannich-type addition, catalyst 36 deprotonates the malonic acid thioester followed by decarboxylation to generate a stabilized thioacetate enolate. This stabilized anion reacts with facial selectivity to the imine due to steric-tuning from 36 [47] (Scheme 8). 

Many formation constants involve polycarboxylates Table 28 summarizes the data. Nagyp l and Fabian s report on the oxalic and malonic systems seems the most complete as hydrolysis of both metal ion and complexes has been included.584 A concentration distribution of the complexes in the malonic system is shown in Figure 25. The order of basicities is succinic > citraconic > itaconic > maleic > malonic acid and log /3U0 should follow the same order. However, from Table 28, the order of stabilities is citraconic > malonic > maleic > itaconic > succinic acid.608... 

Eutectics formed between quaternary ammonium salts and hydrogen bond donors (HBD) have potential windows that tend to be controlled by the stability of the carboxylic acid, amide or alcohol. In general the potential windows depend upon the pfCa of the HBD. Figure 4.13 shows the potential windows of eutectics formed between ChCl with ethylene glycol, urea and malonic acid. 

On the other heuid,if this were the correct forr..ula the con.pound should readily add bromine and reduce potassium penuangante the first reaction it gave only in the sunlight,the other not at all. These facts,its stability towards reduction with sodium aiualgam, the value of its magnetic rotation and the fact that it behaved like a disubstituted malonic acid settled the dispute in favor of Perkin. 

Some crystals have a frustrating property as grown they are quite stable and mechanically strong, but when shaped into a sphere they have a strong tendency to cleave almost spontaneously and to fall apart into thin sheets. Gypsum, malonic acid, and oxalic acid dihydrate examplify this type of behavior, which highlights the role of surface tension in the stability of crystals. 

The carboxylation of boron-stabilized carbanions followed by acidification has been reported to give malonic acids in yields of 65-70% (equation 39). The carboxylation of (39), however, did not yield any of the correspon ng malonic acids. ... 

Stability constants for the complexation of Cd by edta (H L) to yield [Cd(HL)] and [CdL] have been determined, as well as data on the complexation of zinc with propylenediaminetetra-acetic acid, zinc and cadmium with trans-1,2-cyclohexanediaminetetra-acetic acid, ° and mercury with diamino derivatives of succinic and malonic acids. Substituted hydroxamic acids have also been used as chelates in the complexation of zinc and cadmium. ... 

Bronsted LFERs also apply to reactions of metal ions (Lewis acids). Dissociation rates of Ni(II) complexes are correlated with corresponding dissociation equilibrium constants. This suggests that the reactions occur by dissociative interchange, in which breakage of the Ni(II)-ligand bond predominates over formation of the Ni(II)-water bond in the rate-determining step (Hoffmann, 1981). In addition, rates of metal-catalyzed decarboxylation of malonic acid are correlated with the stability constants for the metal-malonate complexes (Prue, 1952). 

Few data are available on the concentration of dicarboxylic acid anions in subsurface waters. C2 through C q saturated acid anions have been reported in addition to maleic acid (cz5-butenedioic acid) (5. 15-16L Oxalic acid (ethanedioic) and malonic acid (propanedioic) appear to be the most abundant. Reported concentrations range widely from 0 to 2540 mg/1 but mostly are less than a few 100 mg/1. Concentrations of these species in formation waters are probably limited by several factors, including the very low solubility of calcium oxalate and calcium malonate (5), and the susceptibility of these dicarboxylic acid anions to thermal decomposition (16). This paper will focus on the monocarboxylic acids because they are much more abundant and widespread, and stability constants for their complexes with metals are better known. We do recognize that dicarboxylic acid anions may be locally important, especially for complexing metals. 

The pyrimido[2,1 -b][ 1,3]thiazine-diones (369)-(372) can be described only by a series of mesomeric forms. For (370) <77ZN(B)1204> and (369) <74ZN(B)258> the IR spectrum supports the mesoionic enolate/enol forms. Compounds (371) have poor stability, (371 R = H) decomposes above its melting point with the expulsion of C3O2 in water or alcohols it undergoes ring fission to malonic acid/esters (72S312). 

The pigmentation of red cabbage is caused by cyanidin derivatives which are acylated with various phenolic acids. Cyanidin 3-sophoroside-5-glucoside and its derivatives acylated with malonic acid and one or two residues of /7-coumaric, ferulic or sinapic acids have also been detected [59 60]. The relative stability of these pigments seems to be related to their degree of acylation. 

Triazole blocked isocyanates are stable up to 130-140°C. The blocking reaction can be performed at a temperature of about 15-25 C below the unblocking temperature. The storage stability is distinctly improved in comparison to those formulations that are exclusively blocked with CH-acidic esters, such as malonic acid diethyl ester. ... 

It should be noted that chaos control can only be obtained if deterministic chaos is involved. In case of (i) chaotic laser (ii) diode (iii) hydrodynamic and magneto-elastic systems and (iv) more recently myocardial tissue, feedback algorithm has been successfully applied to stabilize periodic oscillations. Quite recently, in order to stabilize periodic behaviour in the chaotic regime of oscillatory B-Z reaction, Showalter [14] and co-workers (1998) applied proportional feedback mechanism. Feedback was applied to the system by perturbing the flow rate of cesium-bromate solutions in the reactor keeping the flow rate of malonic acid fixed in these experiments. This experimental arrangement helped the stabilization of periodic behaviour within the chaotic regime. 

Formation of stabilized free radicals as reactive intermediates (e.g. malonic acid, malononitriles and R-CH-R - containing compounds, with / , / being activating substituents (e.g. esters)). 

Theophylline has also been co-crystallized with urea [87] A-(2-ammonioethyl)carba-mate [88], chlorosalicylic acid [89], sulfathiazole, 5-fluorouracil [90], p-nitroaniline [91], succinic acid, malonic acid, maleic acid and oxalic acid [92]. There is evidence that at least one of these co-crystals, between theophylline and oxalic acid, can improve the physical stability of theophylline by protecting it from converting to the less soluble hydrate at high humidities. In this case, oxalic acid and water both hydrogen bond with theophylline at the same site. It is unclear whether or not the occupancy of the hydrogen bonding site by another molecule, in this case oxalic acid prevents the conversion to the hydrate or, if a general decrease in solubility of the oxalic acid co-crystal versus the hydrate is responsible for the protective effects. 

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