Isomerization aluminum bromide

Isomerization Aluminum bromide. Boron trifluoride-Hydrogen fluoride. Dimethyl sulfoxide. Formic acid. N-Lithioethylenediamine. Mercuric acetate. Perchloric acid. Potassium r-butoxide. Potassium hydride. Potassium hydroxide. Zinc dust. 

ISOMERIZATION Aluminum bromide. Aluminum chloride. Potassium f-butoxide. Silver fluoroborate. 

The intramolecular nature of most carbocationic isomerization was proved by means of labeling experiments. [l-13C]-Propane was isomerized in the presence of aluminum bromide promoted by hydrogen bromide to form [2-13C]-propane. None of the propane product contained more than one l3C atom per molecule.64 Similarly, very little label scrambling was observed in the isomerization of labeled hexanes over SbF5-intercalated graphite.65 Thus simple consecutive 1,2-methyl shifts can account for the isomerization of l3C-labeled methylpentanes (Scheme 4.3). 

Vigorous conditions have been found to cause similar skeletal rearrangements in adamantane itself. Thus, treatment of adamantane-2-14 C48) with aluminum bromide in carbon disulfide at 110° C for 8 hours gives rise to nearly 80 % net scrambling of the tertiary and secondary carbons 49 The mechanism for this degenerate isomerization possibly is similar to that depicted in Scheme 5. 

Brown, H. C., Jungk, H. The catalytic halides. XI. The isomerization of o- and p-xylenes and some related alkylbenzenes under the influence of hydrogen bromide and aluminum bromide the relative isomerization aptitudes of alkyl groups. J. Am. Chem. Soc. 1955, TT, 5579-5584. 

In support of this hypothesis it has been observed that when aluminum bromide is treated with oxygen a reaction occurs which liberates bromine,48 and further, the halogen atoms rather than the hydroxyl group are responsible for the catalytic activity of HOAlBr2. Thus when the compound DOAlBr2 is prepared, the hydrogen-deuterium exchange with n-butane is not at all proportional to isomerization.4 ... 

It is interesting that isomerization has been shown to occur even with propane. When this hydrocarbon, labeled with C13 in one end, is brought into contact with aluminum bromide, rearrangement occurs so as to move the heavy isotope into the central position 44... 

Parameters needed for the conformational analysis of the 10 isomeric monomethyldecalins are in Table XVI. The bridgehead methyl isomers are included for completeness, although they would not occur in the products of hydrogenation. Good agreement is shown between the computed equilibrium and one determined experimentally by isomerization with aluminum bromide-hydrogen bromide-hydrocarbon complex by the method described by Schneider e< al. (77). 

Isomerization. A Netherlands group14 found that diphenylacetylenc can be dimerized to 1.2.3-triphenylazulene in 10-15% yield by aluminum bromide purified... 

C (8) and n-butane-l-C (9) were contacted in the presence of aluminum bromide promoted with water. In the study however, of the liquid-phase isomerization of 2-methylbutane-l-C over an aluminum bromide catalyst... 

B.ii. Isomerization. There are several problems associated with Friedel-Crafts alkylation. The first occurs when primary and secondary halides are used, because the cations formed from these substrates are subject to rearrangement. Reaction of benzene with 1-bromopropane and aluminum bromide (AlBr3), for... 

The most important catalysts found for this reaction are aluminum chloride and aluminum bromide. The early investigators reported that these aluminum halides are catalysts for the isomerization of n-butane to isobutane later investigators found, however, that the reaction proceeds only when traces of water or hydrogen halide are used in conjunction therewith. More recent work indicated that under certain controlled conditions, even aluminum halides-hydrogen halides do not catalyze the isomerization of butanes unless traces of olefins or their equivalent are present. 

The isomerization of n-butane to isobutane and the reverse isomerization proceed in the presence of catalysts containing either aluminum chloride or aluminum bromide the latter, by virtue of its high solubility in hydrocarbons (Heldman and Thurmond, 1 Boedeker and Oblad, 2) and its higher activity, causes the isomerization of butanes to proceed at lower temperatures. 

The isomerization of butanes using a high vacuum technique for the purification and introduction of the reactants was investigated (Leighton and Heldman, 5). It was found that completely anhydrous aluminum bromide did not act as a catalyst for the isomerization at 85° the addition, however, of a small amount of hydrogen bromide to the reactants caused n-butane to isomerize. 

The Effect of Promoters upon the Isomerization of n-Butane in the Presence of Aluminum Bromide... 

Aluminum bromide-hydrogen bromide. The effect of olefins upon the isomerization of n-butane catalyzed by aluminum bromide-hydrogen bromide is summarized in Table III. 

Aluminum bromide. When aluminum bromide was used as a catalyst in the absence of air, n-butane did not isomerize even when the solution was exposed to sunlight for 8 hours and then allowed to stand in the dark for an additional 500 hours. The isomerization proceeded, however, when 0.06 mole air per 100 moles n-butane was added and the mixture was kept in the dark for 192 hours the yield of isobutane produced was 7.5%. Nitrogen alone did not cause the isomerization under similar conditions. 

Reaction of Aluminum Bromide with Water, and Isomerization of n-Buiane in the Presence of the Resulting Reactioii Product... 

The complex resulting from the action of water on aluminum bromide, freed from any noncombined hydrogen bromide, was used as a catalyst for the isomerization of n-butane. It was found that by contacting n-butane at 25 for 20 hours with the catalysts, isomerization occurred when the molal ratio of water-aluminum bromide was 1, 2, or 3 (Table IX, B). When the ratio was 4, slight isomerization occurred at 25°, but appreciably more occurred at 80°. With a ratio of 6, no isomerization occurred. No appreciable evolution of hydrogen bromide was noticed in these experiments. The results obtained demonstrate that the isomerizing catalyst formed by the action of water on aluminum bromide is not equivalent to an aluminum bromide catalyst, inasmuch as the latter requires hydrogen bromide and traces of olefins to cause the isomerization of n-butane. 

The effect of water upon the isomerization of n-butane that contains aluminum bromide also has been studied. These experiments are not comparable with those described above, as the hydrogen bromide formed was not removed from the reaction zone. It was found that aluminum bromide promoted by water, in spite of the free hydrogen bromide present, is a less active catalyst (Table X) than the corresponding catalyst described... 

Aluminum chloride. The reaction of aluminum chloride with water is, to some extent, similar to the one of aluminum bromide namely, the more water added, the less hydrogen chloride liberated. With a 1 molal ratio of water to aluminum chloride, 0.71 mole hydrogen chloride was formed when the water-aluminum chloride ratio was increased to 2, only 0.29 mole hydrogen chloride was generated per mole aluminum chloride reacted (Table XI). The catalysts produced from the actioii of water on aluminum chloride were less active than those obtained from aluminum bromide and therefore the isomerization experiments were carried out at 80-100°. Unlike aluminum chloride, catalysts produced by the action of water on aluminum chloride did not require the presence of olefins or hydrogen chloride to promote the isomerization of 7i-butane. 

In order to test the validity of the postulated mechanism of isomerization, deuterium bromide-aluminum bromide instead of hydrogen bromide-aluminum bromide was used as an isomerization catalyst (Pines and Wackher, 23). The reactions were carried out under controlled conditions using a high-vacuum technique. The experimental conditions are summarized in Table XIV. 

It was found that by treating either n-butane or isobutane with 10 mole % deuterium bromide-aluminum bromide catalyst for 20 hours at 25°, no isomerization of the butanes occurred and only 6 and 9.5% of the deuterium exchanged with n-butane and isobutane, respectively. When, however, 0.1 mole % butenes was added to n-butane and the isomerization reaction was carried out under the same experimental conditions, over 40% of the butane isomerized to isobutane and 92% of the deuterium underwent an exchange reaction. These results indicate clearly that olefins take an active part in isomerization. The results obtained are in agreement with the proposed mechanism of isomerization. 

Effect of oxygen. Two hypotheses were proposed to explain the effect of oxygen upon the isomerization of n-butane in the presence of either aluminum chloride or aluminum bromide (Pines and Wackher, 8). Both hypotheses assume the formation of hydrogen halide and alkyl halide the latter acting as a chain starter for isomerization. 

Recent experiments (Beeck el al., 25a) on the isomerization of propane-1-C to propane-2-C further demonstrate that the isomerization proceeds through an intramolecular rearrangement. No propane containing more than one C carbon atom per molecule was foimd. These experiments were made by contacting vapors of propane at approximately 25 and 450 mm. pressure with a catalyst prepared by the addition of 0.023 g. water to 0.40 g. anhydrous aluminum bromide for periods of time varying from 0 to 1074 hours. It was found that the rate of isomerization of propane-1-C to propane-2-C is comparable to the rate of isomerization of n-butane to isobutane under similar conditions. The equilibrium distribution of the propanes-l-C and -2-C was found to be statistical, that is, propane-l-OVpropane-2-C = 2. 

It has been shown that the isomerization of n-pentane in the presence of aluminum chloride or aluminum bromide containing catalysts was accompanied by side reactions, characterized by the formation of butanes and tarry material. These side reactions can be inhibited by the use of hydrogen or organic additives. 

The action of aluminum bromide on n-hexane using purified material and controlled conditions was studied (Grummit et al, 42). In the absence of a promoter aluminum bromide does not isomerize n-hexane at room... 

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