Acetals reaction with bromine

The reaction of 2-amino-4(2-furyl)thiazole in acetic acid with bromine yields product 198 brominated on the furan ring (Scheme 126). The... 

The olefin of the Voc group is very susceptible to electrophilic reagents and thus is readily cleaved by reaction with bromine or mercuric acetate. 

It yields a characteristic reaction with bromine. If a few drops are, dissolved in 3 c.c. of glacial acetic acid and a little bromine vapour allowed to pass down the tube, a fine crimson colour forms which rapidly extends to the whole of the liquid and soon changes to violet and then to indigo blue with phosphoric acid, the acetic acid solution gives a rose madder colour at the junction of the liquids, and when the liquids are mixed, the colour changes to crimson and then slowly to violet. Baker and Smith consider that the sesquiterpene contains one double linkage. Semmler considers that it is a mixture of at least two bodies, one a bicyclic and the other a tricyclic sesquiterpene. 

Myristicin and isomyristicin are distinguished by their reactions with bromine. Myristicin, when treated with two atoms of bromine, yields an oily liquid, whilst isomyristicin yields a crystalline body melting at 109°. If the isomers are dissolved in acetic acid, and treated with bromine until no more is absorbed, the mixture being kept cold all the time, the following compounds are obtained —... 

Kinetic studies of molecular bromination have been carried out using a variety of solvents other than acetic acid. The bromination of 2-nitroanisole by bromine in water revealed that molecular bromine is the reactive species and that the tribromide ion is very unreactive191. By making allowance for the concentration of free bromine (which differs from the stoichiometric concentration through reaction with bromine ion), good second-order rate coefficients were obtained by application of equation (133) with k2 = 0.062 at 25 °C the dominance of the bimolecular mechanism is to be expected here in view of the trend observed on making acetic acid media more aqueous. 

If the bromination of phenylaminomethylenemalonates was carried out in acetic acid with bromine, only substitution of the aromatic ring occurred and, depending on the molar ratio and the reaction period, p-bromo or o,p-dibromo derivatives were obtained (57JIC817). From /V-(w-nitrophe-nyl)aminomethylenemalonate, only 3-nitro-6-bromoaniline was obtained. 

Procedure Weigh accurately about 0.2 g of ethacrynic acid, dissolve in 40 ml of glacial acetic acid in a 250 ml iodine flask. Add to it 20 ml of 0.1 N bromine and 30.0 ml of hydrochloric acid, immediately place in position the moistened stopper to the ffask, mix the contents vigorously and allow it to stand in a dark place for 60 minutes (to complete the reaction with bromine). Add to it 100 ml of water and 20 ml of KI Solution and titrate immediately with 0.1 sodium thiosulphate, employing freshly prepared starch solution as an indicator towards the end of the titration. Repeat an operation without the pharmaceutical substance (blank titration) thus the difference between the titrations represents the amount of bromine required by the ethacrynic acid. Each ml of 0.1 N bromine is equivalent to 0.01516 g of C13H12C1204. 

Mercuric acetate, reaction with cyclo-octatetraene, 50, 24 Mercuric oxide, use in oxidation of hydrazones, 50, 28 with 3-chlorocyclobutanecarboxylic acid and bromine to give 1-bromo-... 

Quadricyclane is a highly strained and reactive compound. It reacts readily with acetic acid to give a mixture of nortricyclyl acetate and exo-norbornyl acetate and with bromine to yield a mixture of 2,6-dibromonortricyclene and exo-5-anti-l-dihvo-monorbornene.3 Quadricyclane undergoes cycloaddition reactions with a variety of dienophiles to give 1 1 adducts.15 1 2 3 4 5 6 7... 

Thiophene is far more reactive than benzene in electrophilic substitution reactions. Reaction with bromine in acetic acid has been calculated to be 1.76 x 109 times faster than with benzene (72IJS(C)(7)6l). This comparison should, of course, be treated with circumspection in view of the fact that the experimental conditions are not really comparable. Benzene in the absence of catalysts is scarcely attacked by bromine in acetic acid. More pertinent is the reactivity sequence for this bromination among five-membered aromatic heterocycles, the relative rates being in the order 1 (thiophene) and 120 (furan) or, for trifluoroacetylation, 1 (thiophene), 140 (furan), 5.3 xlO7 (pyrrole) (B-72MI31300, 72IJS(C)(7)6l). Among the five-membered heteroaromatics, thiophene is definitely the least reactive. 

Hydroxyl groups are always protected prior to reaction with bromine radicals, and derived esters have proved suitable. Benzoates are particularly useful and are preferable to acetates, which are susceptible to methyl-group bromination, particularly when the acetoxyl groups are bonded to carbon atoms in the -relationship to carbon radicals. Conceivably, this susceptibility can be accounted for as follows. 

Later, Linda and Marino84, 90, 180 were able to compare the relative reactivities of all four fundamental systems (furan, thiophene, selenophene, and pyrrole) toward bromination by molecular bromine in acetic acid. Unfortunately, the comparison could not be made on the unsubstituted rings for the following reasons first, the rates of substitution for furan and pyrrole were too high to be followed by standard kinetic techniques second, furan and pyrrole undergo ring fission and/or polymerization under the influence of the hydrobromic acid formed in the reaction finally, furan tends to give addition as well as substitution products in the reaction with bromine.1818. 

The electron-donating ability of an amino group is moderated by acetylation. Only monobromination of acetanilide occurs on reaction with bromine in acetic acid (Scheme 8.5). Acetanilide behaves similarly on nitration. 

Aryl-4-(allylsulfanyl)quinazolines and 2-aryl-4-(prop-2-ynylsulfanyl)quinazolines 7 undergo quaternization at N3 and cyclization on reaction with bromine in glacial acetic acid to give... 

The conversion of 5a-cholestan-6/5-ol into the 6yS, 19-epoxide, by reaction with bromine and silver oxide, has been improved by the use of certain silver salts with bromine in pentane, in the dark. Silver acetate, carbonate, and... 

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