Acetone, bromination decomposition

Its solutions in dilute hydrobromic acid are a carmine-red (0.025 M PoBr4) and in more dilute solution (10 3 M), orange red. The tetrabromide is soluble in ethanol, acetone and some other ketones, and is sparingly soluble in liquid bromine. It is hygroscopic and is easily hydrolyzed to a white, basic bromide of variable composition. It forms a yellow ammine in ammonia gas and this yields polonium dibromide and polonium metal on standing, presumably because of radiation decomposition of the ammonia and subsequent hydrogen reduction of the tetrabromide (7). 

Decomposition of Coa(CO)e(RC2R ) 48, 64) and Co4(CO)io(RC2R ) 48) complexes with bromine gives fra i-a,)3-dibromoolefins. With iodine, free alkynes have been liberated from Co2(CO)e(RC2R ) complexes 19, 64). The anion Co(CO)4 has been detected in the iodine decomposition of Co2(CO)e(n-PrC2H). Several other reagents have been used to obtain the free alkyne from Co2(CO)e(RC2R ) complexes. These include ceric ammonium nitrate in acetone 49, 66), ferric nitrate in ethanol 49), sodium hydroxide in methanol 64), and triphenylphosphine in petroleum ether 80),... 

Very reactive substances are treated with NBS alone, but in other cases a radical-former is added. The favored radical activator for bromination of olefins by NBS is 2,2/-azoisobutyronitrile, 1 part per 100-1000 parts of NBS. This nitrile is obtained by reaction of bromine water with 2,2 -hydrazoiso-butyrodinitrile, which is prepared from acetone, KCN, and hydrazine sulfate in warm water365 (see also Dox366). The decomposition temperature of dibenzoyl peroxide is higher than that of 2,2 -azoisobutyrodinitrile, and about 30° above the boiling point of CC14. 

EXPLOSION and FIRE CONCERNS nonflammable NFPA rating (not rated) explosive reaction with crown ethers or potassium hydroxide violent reaction with lithium, sodium-potassium alloy, acetone, or bases incompatible with metals, caustic alkali, and strong oxidants decomposition emits highly toxic gases and vapors (such as hydrogen bromide and bromine) use dry chemical, carbon dioxide, water spray, fog or foam for firefighting purposes. 

These unsaturated bromo-acids are soluble without decomposition in sodium carbonate solution, but aqueous potassium hydroxide decomposes them, forming benzaldehyde and removing the bromine and phosphorus radicals. The first bromo-acid also gives a small yield of dibenzal acetone, the use of alcoholic potassium hydroxide increasing the yield of unsaturated ketone to 25 per cent. the reaction taking place is probably as follows ... 

While the evidence on bromination of acetone merely confirmed a mechanism that was already considered highly likely on other grounds, the deuterium isotope effect contributed very importantly to work on the mechanism of oxidation of isopropyl alcohol by chromic acid (Westheimer and Nicolaides, 1949). The isotope effect was 6.7 when the hydrogen on the carbinol carbon was replaced by deuterium. Other evidence had indicated that a chromate ester of isopropyl alcohol was an intermediate. The isotope effect showed that its decomposition to acetone and a lower valence state of chromium was the slow step [Eq. (28) ] ... 

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