Bromide tropylium

Tropylium bromide was first prepared but not recognized as such m 1891 The work was repeated m 1954 and the ionic properties of tropylium bromide were demon stated The ionic properties of tropylium bromide are apparent m its unusually high melt mg point (203°C) its solubility m water and its complete lack of solubility m diethyl ether... 

Stabilisation, through delocalisation, can also occur through aromatisation. Thus l-bromocyclohepta-2,4,6-triene(tropylium bromide, 6),... 

G. Merling had obtained tropylium bromide in 1891 by brominating cycloheptatriene but could not guess its structure tropylium was discovered when prepared again via the same route by W. E. Doering and L. H. Knox in 1957, i.e., 66 years later.23... 

Perhaps the most significant of the numerous applications of radiotracers in chemistry has been the study of chemical reaction mechanisms. In fact, most of the proposed reaction mechanisms have been verified by means of a radiotracer study. One of the simplest mechanistic experiments using radiotracers is to test the equivalence of various atoms in molecules in chemical reactions. An example of this type of study is the work of Volpin et al. (1959) on the equivalence of the seven carbon atoms in the tropylium ring. Volpin et al. reacted labeled diazomethane with benzene and brominated the cyclohepatriene product to form a labeled tropylium bromide, as shown below ... 

Then the tropylium bromide was subjected to a Grignard reaction and the product oxidized to give a labeled benzoic acid. Thus, one had... 

The infrared and Raman spectra of tropylium bromide in hydrobromic acid solution have no common bands, which means that the cation exists in a highly symmetrical form in this solution (see Section 9-8), At higher pH, reversible formation of the hydroxy compound occurs ... 

A further example of the synthesis of an organometallic derivative of 16 by oxidation of 18 is provided by the reaction of 18 with tropylium bromide [Eq. (13)] (41). 

On the academic side, W. H. Perkin made mention of unsuccessful experiments directed towards the preparation of benzocyclobutene in 1888. This compound was eventually prepared by H. Finkelstein, a student of J. Thiele, in 1909, as reported in his long-unknown Ph.D. thesis. Benzocyclobutene and biphenylene were also reported by Lothrop in 1941. Tropylium bromide was synthesized in 1891 by Merling, but its structure was only established in 1954 by Doering and Knox. The isolation and structure determination of the aromatic steroids estrone, estriol, and estradiol arrived only in 1929 (E. A. Doissy, A. Bute-nandt), 1931 (G. F. Marian), and 1935 (E. A. Doissy), respectively, with the advent of X-ray crystallography. 

Aryl tellurium trihalides accept halide ions from tropylium bromide, ammonium halides, phosphonium halides, arsonium halides, sulfonium chlorides, telluronium chlorides, and diphenyl iodonium chloride to form aryltetrahalotellurates(lV)1-5. 

Tropylium aryltetrahalotellurates can be prepared from tropylium bromide and an aryl tellurium trihalide. A more convenient procedure avoiding the laborious preparation of the tropylium bromide uses cycloheptatricne and triphenylmethyl perchlorate2. The product of this reaction can then be converted to the tetrahalotellurate by treatment with hydrohalic acids. 

In certain cases, the carbocations are so stable that their solid salts have been isolated. For example, triphenylmethyl perchlorate (2.1) exists as a red crystalline solid and tropylium bromide (2.2) has been isolated as a yellow solid. Tropylium bromide (2.2) is stabilized by aromatization as the tropylium cation is planar and has 6tt electrons like benzene. 

In contrast, it is the resonance-stabili/ed cation derived from cyclo-hep tatriene that possesses the aromatic sextet of Jt-electrons. Tropylium bromide is formed by the addition of bromine to cycloheptatriene and... 

The ylidic carbon atom of a number of acylylides reacted with tropylium bromide to give tropylarsonium salts (23), which decomposed by elimination of triphenylarsine to give jS-acylstyrenes and j -acyl-j -tropylstyrenes. Triphenylarsonium benzoylylide was also alkylated with 1-p-nitrobenzoylaziridine in boiling toluene to give 24 . 

Dehydrogenation [1,127, at end.] The hydrocarbon (3) was obtained by condensation of tetraphenylcyclopentadienyl sodium (1) with tropylium bromide (2).8a Dehydrogenation to tetraphenylsesquifulvalene (4) was accomplished by refluxing with chloranil. An initial deep red solution deposited greenish black needles having a metallic luster, m.p. 250°. dec. 

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