Phenanthrene, bromination

The relative rates of bromination from the above and additional studies yielded the following relative rates with partial rate factors for the indicated position in parentheses. These rates were mostly obtained by extrapolation of observed rates to those expected in 50% aqueous acetic acid and therefore probably contain small errors benzene, 1.0 (1.0) biphenyl, 1.54 x 103(4-,4.34 x 103) naphthalene, 1.24 x 105(1 -, 1.84 x 10s 2-, 1.86 x 103) phenanthrene, 7.43 x I03(9—, 2.23 x 10s) f uoranthrene, 2.30 x 106(3 —,6.90x 106) chrysene,... 

The fusion of a second aromatic ring results in subtle changes in reactivity. Halogenation of naphtho[l,2-c]-l,2,5-thiadiazole (42) occurs either by 4,5-addition of chlorine (43a) or by 5,6-substitution (44) by bromine. This heterocyclic analog of phenanthrene behaves like phenanthrene in that it gave the 4,5-addition product (43b) when treated with Br2 in glacial acetic acid (Scheme... 

Previously, diphenaldehyde has been made by the Ullman coupling of o-iodobenzaldehyde,6 6 by bromination of o/Z-bitolyl and hydrolysis of the resulting tetrabromo compound,7 and by lithium aluminum hydride reduction of the N-methylanilide of diphenic add.8 These methods involve more steps and give poorer yields than ozonolysis of phenanthrene. 

The resonance energies of fused systems increase as the number of principal canonical forms increases, as predicted by rule 6 (p. 35).75 Thus, for benzene, naphthalene, anthracene, and phenanthrene, for which we can draw, respectively, two, three, four, and five principal canonical forms, the resonance energies are, respectively, 36, 61, 84, and 92 kcal/mol (152, 255, 351, and 385 kJ/mol), calculated from heat-of-combustion data.76 Note that when phenanthrene, which has a total resonance energy of 92 kcal/mol (385 kJ/mol), loses the 9,10 bond by attack of a reagent such as ozone or bromine, two complete benzene rings remain, each with 36 kcal/mol (152 kJ/mol) that would be lost if benzene was similarly attacked. The fact that anthracene undergoes many reactions across the 9,10 positions can... 

Write the five Kekule-type resonance structures of phenanthrene and show how these structures can account for the fact that phenanthrene, unlike benzene, adds bromine, but only across the 9,10-positions. 

There are principally two different approaches of correlating experimental rate data of electrophilic substitution with reactivity indices (1) Correlating the index with the rate data of a given reaction, e.g. bromination. For example, a satisfying correlation of Dewar reactivity numbers with the log of rate constants of the bromination of benzene, naphthalene (1- and 2-position), biphenyl (4-position), phenanthrene (9-position), and anthracene (9-position) has been observed [55]. In correlations of this type the reactivity index corresponds to the reactivity constant in the Hammett equation while the slope of the linear correlation corresponds to the reaction constant (see also Sect. 3) (2) correlating the index with experimental a values. 

A much more deep-seated photorearrangement than in the dibenzo[2.2.2] systems occurs in the dibenzo[3.2.1] compound 55 with chloride or bromine as nucleofugal group at C-8 (equation 49)229. 9-Functionalized phenanthrenes are formed, supposedly also by way of photoinduced intramolecular electron transfer in the (triplet) excited state. 

As noted above, the first definition of "aromaticity" was in terms of substitution rather than addition. This is certainly true for many benzene derivatives. However, it must be used with some care since thiophene is by most criteria about as "aromatic" as benzene, but when treated with chlorine or bromine it gives an addition product. The latter is, however, the kinetically controlled product, for when heated or treated with base it loses hydrogen halide and gives the 2-halothiophene.20 Compounds such as anthracene and phenanthrene, which are recognized as having considerable resonance stabilization, also undergo addition reactions. 

Treatment of 2,9-dibromophenanthrene with Pt (Et3P)4 followed by bromine-nitrate exchange gave the desired 60° tecton, 2,9-6/i [/ra 5 -Pt(PEt3)2(N03)]phenanthrene, which with different linear connectors afforded a series of self-assembled supramolecular triangles <03JA5193>. A series of related binuclear metallomacrocycles [Cd(N03)2L]2, where L is an angular exo-bidentate, such as 4-(4 -pyridinyl)(2-pyridinylethynyl) benzene, have been reported... 

From ortho-Brom Benzyl Bromide.—From this constitution for phenanthrene and its similarity to the constitution of anthracene, both being made up of three benzene nucleii, it will not be surprising that the same synthesis will yield the two compounds. This is the synthesis from ortho-brom benzyl bromide (p. 794), which by the loss of two molecules of hydrobromic acid and two atoms of bromine, by heating with alkali, yields both compounds. 

Bromination of anthracene or phenanthrene takes place at the 9-position. (9-Bromophcnanihrenc is a useful intermediate for the preparation of certain 9-substituted phenanthrenes.) In both cases, especially for anthracene, there is a... 

The procedure described for the preparation of 9-bromo-phenanthrene is an adaptation of that described by Henstock, who effected the bromination at various temperatures and in different solvents but gave little experimental detail. Other methods of preparation involve the formation and isolation of phenanthrene dibromide and its subsequent conversion to 9-bromophenanthrene by heating. 

Crude bromophenanthrene prepared by the bromination of technical (90%) phenanthrene and purified by distillation only was used by the submitters in this preparation. The an-thracene-9-aldehyde, which may be formed from the anthracene present as an impurity in 90% phenanthrene, does not form a sodimn bisulfite addition product and so will not contaminate the phenanthrene-9-aldehyde. The checkers used 9-bromophe-nanthrene, m.p. 54-56° (p. 20), exclusively, but without any advantage in yield. The submitters report yields of 55-60% from pure 9-bromophenanthrene. 

When the resonance stabilization which can be gained by elimination of a proton is small, however, subsequent addition of an anion occasionally does occur. Phenanthrene, for example, can be brominated in the dark to give either 9,10-dibromophenanthrene 1 or 9-bromophenanthrene (see p. 247). 

The fact that both phenanthrene and phenanthrene dibromide react at the same rate in the presence of iodine and bromine to give 9-bromo-phenanthrene23 suggests that the same intermediates are involved in... 

Although a stable dibromide cannot be isolated for a similar study of the bromination of benzene, the kinetics of the iodine catalyzed bromina-tion of benzene is identical with that of phenanthrene.26 Consequently it is very probable that the mechanism of the halogenation of benzene is the same as that proposed for phenanthrene. The kinetics of chlorination,27 bromination,28 and iodination by iodine chloride29 are also in agreement with this interpretation. The halogenation of phenols, however, appears to be a different, more complex process. 0... 

Phenanthrene-9-carbonitrile, prepared by bromination of phenanthrene to the 9-bromo derivative54 and its transformation by cuprous cyanide in dimethylform-amidess, served as starting material for the needed phenanthrene-9-acetonitrile (86). By the same sequence of steps as when converting phenanthrene- 1-carbonitrile (72a) to (81) the 9-carbonitrile was converted to (86), giving an overall yield of 60%. The standard procedure leads very smoothly to the triphenylenes (57) ... 

One pathway to benzo(c)phenanthrene by the cyclization-elimination method has been outlined already (Section III., B. 2.) and another we will see later. A synthesis by benzannelation should start with phenanthrene-4-acetonitrile or with phenanthrene 3-acetonitrile (88) as the one component. For steric reasons the preparation of the first has only poor chances, but (88) is readily available 3-methylphenanthrene, mp. 62—63°56), obtained by hydrolysis and decarboxylation from the nitrile (72 b) (Section III., C. 3.) in an overall yield of 92% was side-chain brominated by N-bromo-succinimide in CC14, and the 3 bromomethylphenanthrene, mp. 116—117° (67%), converted to (88), mp. 82-83° (91%). 

The preparation of phenanthrene-9-aldehyde starts with crude 9-bromophenan-threne obtained by bromination of technical phenanthrene (90%) and purified only by distillation (m.p. 54-56° crystalhzation gives pure material, m.p. 65-66°). The magnesium (50.3 g.) is placed in a 5-1. flask provided with a stirrer, a 500-ml. separatory funnel, a nitrogen-inlet tube, and a large reflux condenser fitted at the top with a 1-1. separatory funnel. The crude bromophenanthrene (514 g.) is vMgBr CHlOCjHs) CHO... 

Bromination of a-codeimethine methyl ether in chloroform leads to bromohydroxydihydro-a-codeimethine methyl ether, which affords 3 6-dimethoxy-4-acetoxyphenanthrene on acetolysis [48], and in like manner the e-isomer can be degraded to 3 8-dimethoxy-4-acetoxy-phenanthrene [48]. 

Hofmann degradation of N-methylthebenine dimethyl ether methiodide or methomethylsulphate, which result from the complete methylation of thebenine, affords 3 4 8-trimethoxy-5-vinylphenan-threne [vn], the 4-methoxyl group of which is so readily hydrolysed that boiling with acetic acid or alcoholic hydrogen chloride results in formation of methebenol and bromination in formation of bromo-methebenol [8], 3 4 8-Trimethoxy-5-vinylphenanthrene can be reduced to 3 4 8-trimethoxy-5-ethylphenanthrene, identical with a specimen prepared from 2-nitroveratric aldehyde and 2-methoxy-5-ethylphenyl-acetic acid by the Pschorr phenanthrene synthesis [11]. 

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