Potassium trichloroacetate, decomposition

Table 59 presents activation parameters for the decarboxylation of trichloroacetic acid in various basic solvents. Presumably the acid is in the form of its anion in these solvents. The activation parameters fall into a fairly narrow range and the differences presumably represent specific solvation effects. In an acidic solvent, decanoic acid, the activation parameters for the decomposition of potassium trichloroacetate are increased considerably. The values are A/f = 41.4 kcal.mole" and A5 = 27.7 eu . The activation parameters presumably reflect a composite of a prior equilibrium between decanoic acid and the trichloroacetate anion along with decarboxylation of the latter anion. The rate of decarboxylation of sodium nitroacetate is about five times faster in methanol than in water . This effect was attributed to dispersion of the negative charge at the transition state , a process which is more favorable in the less polar methanol solvent. Similarly, the decar-... 

For general or typical procedures for 1,1-dichlorocyclopropanes (from chloroform and base under phase-transfer catalysis conditions), see Houben-Weyl, Vol. E19b, p 1527 1,1-di-chloro-2-methylcyclopropane (from propene, chloroform, oxirane and tetraethylammonium bromide as a catalyst), see Houben-Weyl, Vol. 4/3, p 376 7,7-dichlorobicyclo[4.1.0]heptane (from chloroform and potassium /er -butoxide), see Houben-Weyl, Vol. 4/3, p 162 and Vol. 5/3, pp 977-978 (from thermal decomposition of sodium trichloroacetate and from ethyl trichloroacetate and sodium methoxide)," see Houben-Weyl, Vol. 4/3, pi62. 

The reactivity of dichlorocarbene towards carbon-carbon triple bonds was systematically investigated by Dehmlov in the sixties, and this work has been reviewed". Dehmlov generated the carbene e.g. by decomposition of sodium trichloroacetate in 1,2-dime thoxy ethane. In additions to ene-yne substrates, sometimes the triple bond, whereas in other cases the double bond accepted the carbene. He observed, for instance, that reaction of the carbene with (E)-l,4-diphenylbutene-l-yne-3 gave the triple-bond addition product 20 exclusively. In reaction with 2-methylpentene-l-yne-3, however, the carbene preferred the double bond, leading to 21. Dichlorocarbene generated from potassium f-butylate and chloroform does not add to electron-poor alkynes, indicating electrophilic behavour of the carbene. 

If organic compounds containing halogen are heated with a mixture of potassium permanganate and concentrated sulfuric acid, oxidative decomposition occurs with production of free halogen. The latter. Like other strong oxidants, converts diphenylamine dissolved in concentrated sulfuric acid into a blue quinoidal compound. If, however, a saturated solution of diphenylamine in ethyl acetate that contains some trichloroacetic acid is used, only chlorine yields a blue coloration. Bromine and iodine produce a yellow color that can be discharged by means of sodium thiosulfate. 

The convenience and potential of this method was immediately apparent and its disclosure was followed by numerous examples and extensions. The method was of particular interest because previous methods used to generate dichlorocarbene all required rigorous exclusion of moisture. Among these methods are treatment of chloroform with potassium -butoxide in pentane, pyrolysis of anhydrous sodium trichloroacetate, and the thermal decomposition of phenyl(bromodichloromethyl)-mercury. 

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