Bromomalonic acid

The main processes occurring in this system are the following [219] bromate oxidizes trivalent cerium to tetravalent cerium Ce4+ oxidizes bromomalonic acid, and is reduced to Ce3+. The bromide ion, which inhibits the reaction, is isolated from the oxidation products of bromomalonic acid. During the reaction, the concentration of the Ce4+ ions (and Ce3+) oscillates several times, passing through a maximum and a minimum. The shape of the peaks of concentrations and the frequency depend on the reaction conditions. The autooscillation character of the kinetics of the cerium ions disappears if Ce4+ or Br are continuously introduced with a low rate into the reaction mixture. The autooscillation regime of the reaction takes place only in a certain interval of concentrations of the reactants [malonic... 

The ether layer containing the bromomalonic acid is separated from the aqueous layer and the ether removed by distillation from a steam cone. The residual liquid is decarboxylated by refluxing for five hours in a 500-cc. round-bottomed flask on an oil bath heated to 130°. The bromo acid is then separated from the small amount of water and distilled. The material distilling at i25-i4o°/i8-2o mm. is a-bromo- -methylvaleric acid (Note 8). The yield is 150.5 g. (66.7 per cent of the theoretical amount). 

For consistency, the product HOBr must be consumed in the forward reaction of (F5) (as a precursor of bromomalonic acid), although at reasonable levels of HOBr the rate of (F5) does not depend on P explicitly. For further discussion of this point see R. M. Noyes, Proc. Faraday Soc. Symp., 9, 89 (1974). 

When it is required to prepare an a-bromo acid from a carboxylic acid which is not particularly readily available commercially, but which can be synthesised by the malonic acid route (Section 5.11.6, p. 680), advantage may be taken of the ease of bromination in the a-position of the intermediate alkylmalonic acid. The substituted bromomalonic acid undergoes ready decarboxylation on heating to yield the a-bromo acid (e.g. 2-bromo-3-methylpentanoic acid, Expt 5.166). 

Prior to our systematically designed oscillators, the inorganic oscillator most intensively studied was the BZ reaction. Examination of this reaction and the FKN mechanism reveals several features helpful to achieving an appreciation for the construction of a chemical oscillator. The driving force for the BZ reaction is the reduction of bromate and the associated oxidation of malonic acid (MA) to carbon dioxide. The stoichiometry is not that simple, however, since bromomalonic acid is also produced in the reaction, and can be oxidized to formic acid. A possible stoichiometry is... 

Then, bromine reacts with malonic acids to yield bromomalonic acid as (= Bromi-nation of malonic acid by bromine)... 

Subsequently hypobromous acid reacts with malonic acid to yield bromomalonic acid (= Bromination of malonic acid by hypobromous acid)... 

As the concentration of bromomalonic acid, BrCH(COOH)2 increases reaction (RIO) becomes important. The bromide ion, Br produced by (RIO) is destroyed by (R2) as long as the autocatalytic production of bromous acid, HBr02, by the sequence (R4) + 2(R5) is able to maintain bromous acid. The concentration of HBr02 at the value of the second-order destruction of HBr02 by (R6), which creates the steady state is given by... 

Investigating the role of bromomalonic acid during the induction period of the B-Z reaction Burger and Koros (1980-1, 2) found that bromomalonic acid concentration has to reach a certain level for oscillations to start. This crucial concentration in turn is affected by changes in the acid concentration of the medium. 

Zhabotinskii, et al. (1982), following the concentration of Ce(IV) in a CSTR with open up inflows of Br03, Ce(III) and Br by spectrophotometry, with and without added bromomalonic acid, found that production of Br- is not proportional to bromomalonic acid concentrations. A radical mechanism for bromate reduction was also proposed. 

When bromine (1 mole) is added to a suspension of malonic acid in ether, the acid dissolves whilst it is converted into bromomalonic acid 575,576 use of 2 moles of bromine in formic acid leads to dibromomalonic acid, particularly rapidly if the mixture is irradiated.578 If bromine is added to a dry ethereal solution of an alkyl- or arylalkyl-malonic acid at such a rate that the mixture... 

The clock is reset through process C. Bromomalonic acid, BrMA, is a by-product of processes A and B (possibly from HOBr) which reacts with the oxidized form of the redox catalyst. This can be represented as... 

The bromide ion should be regenerated and the catalyst is reduced back to its lower oxidation state. Bromomalonic acid produced in steps 3 and 8 by bromination of malonic acid is then oxidized by the cerium (IV), leading to bromide and cerium (III) and some other products... 

Tartronic Acid, CHOH(COOH)2, can be prepared from malonic acid, of which it is a hydroxyl derivative, by the general method used to replace a hydrogen atom by a hydroxyl group. When malonic acid is treated with bromine, bromomalonic acid is formed, which is converted into tartronic acid when boiled with silver oxide and water —... 

The bromination of malonic acid does not stop with bromomalonic acid but goes on to dibromomaIonic acid ... 

Br2 cannot be detected in solution (Zhabotinskii, 1964), because it reacts quickly with malonic acid to form bromomalonic acid (BrMA) and di-bromomalonic acid (Br MA). (See Chapter I, pp. 6-8.)... 

FN lump together all uncertainty about Ce oxidation of organic species into the stoichiometric parameter h. ZZKN separate Ce oxidation of bromomalonic acid (L3) from Ce induced decomposition of dibromomaIonic and tribromomaIonic acid (L6) - see Vavilin and Zhabotinskii (1969). For step (L3)... 

Zhabotinskii, A. M., Zaikin, A. N., Korzukhin, M. D. and Kreitser, G. P. (1971). "Mathematical model of a self-oscillating chemical reaction (oxidation of bromomalonic acid with bromate, catalyzed by cerium ions)." Kinetics and Catalysis 12, 516-521. 

See under Bromomalonic Acid. 4-Bromo-3-cyanobenzoic Acid. iSee under 4>Bromoisopbthaljc Acid. Brompcyclohestane Cyclohexyl bromideMxa-hydrobromooenzene)... 

In 1972, Field, Koros and Noyes (FKN) [21] suggested a mechanism for the B-Zh reaction involving kinetic data for individual steps and thermodynamic characteristics. The high magnitude of the Gibbs free energy for the B-Zh reaction promotes its proceeding, which results in the formation of bromomalonic acid, CO2 and other products. 

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