Pyrene, bromination

Pyrene is a common PAH contaminant and may occur in drinking water. Chlorination of water with or without bromide that may be present in coastal environments has been examined. Both chlorinated and brominated pyrenes with halogen substituents at the 1,3-, 1,6-, and 1,8-positions were found, and could putatively be produced by reaction of pyrene with hypochlorous acid and hypochlorite (Hu et al. 2006). 

Tetrabromomethane shows two types of n-bonding with aromatic donors that are contrasted in Fig. 8a and b, showing over-the-rim coordination to the aromatic C-C bond and over-the-center coordination to the benzene ring. The over-the-rim coordination is generally similar to that observed in the dibromine complexes but the C - Br distance in the former is longer, in agreement with weaker acceptor abilities of tetrabromomethane. Note that picryl bromide shows similar bromine coordination to the outer pyrene C-C bond with Br - C distances of 3.35 and 3.39 A [83]. A second type of coordination was reported earlier in ihc p-xylcnc complex [80] and recently in the associate with dimethylnaphtalene [53]. 

Figure 5.16. Plot of data for the external heavy-atom quenching of pyrene fluorescence in benzene at 20°C. Polaro-graphic half-wave reduction potentials Ein are used as a measure of the electron affinity of the quencher containing chlorine (O), bromine ( ), or iodine (3). From Thomaz and Stevens<148) with permission of W. A. Benjamin, New York.

This procedure is described by Lock 2 a modification using a small amount of phenol has been published.3 The patent literature discloses the use of a tertiary amine, such as pyridine, and its combination with other solvents for the monobromination of pyrene with elemental bromine.4 Brominating agents, such as N-bromosuccinimide5 and N-bromohydantoins,6 have also been used. 

A different synthetic route involves halogenation (bromination, chlorination) of pyrene 77, which is thus converted to the tetrahalogen derivative. Oxidation with sulfuric acid to form a diperinaphthindandione with subsequent oxidation, once again in a sodium hydroxide solution [7], yields the tetra sodium salt of naphthalene tetracarboxylic acid 78 ... 

When methyl bromide was heated to 550 °C in the absence of oxygen, methane, hydrobromic acid, hydrogen, bromine, ethyl bromide, anthracene, pyrene, and free radicals were produced (Chaigneau et al, 1966). 

Fig. 6 Generated (l-pyrenyl)diphenylmethylcarbenium ion, 1,6- and l,8-bis(diphenylmethylenium)-pyrene dications, and the brominated analogs.

It is instructive to look at the refractive indices for a variety of chemical structures (Table 3.1.) What one quickly sees is that polar compounds are not the same as polarizable compounds. Indeed, polarizability is more related to chemical structure features like overall size (higher homologs within a compound family have greater polarizabilities), and presence of conjugated electron systems (benzene is more polarizable than hexane polarizability increases in the order benzene < naphthalene < pyrene). Finally, molecules with large atoms containing nonbonded electrons far from the nucleus (e.g., bromine, iodine) are generally more polarizable. After this brief diversion, now we continue to use refractive indices to estimate polarizabilities. 

N-Bromoacetamide (NBA) is also a useful positive bromine equivalent Thus NBA in the presence of H2O or LiOAc/HOAc has resulted in the functionalization of 11,12-dihydrobenzo[e]pyrene (Scheme 69).135 NBA has also been employed in conjunction with H2O for the regio- and stereo-selective hydro-bromination of the 10,11 double bond of avermectin Bla, a complex antibiotic containing five double bonds.136... 

Little is known of the actual mechanism. A mode of reaction is possible, in which the oxygen atom at the top of the ozone molecule with a formal positive charge (p. 230) reacts with an electron pair, not localized in a bond but on one carbon atom, and in which the ozone therefore reacts by an electrophilic mechanism (Wibaut, Sixma and Kampschmidt). However, in order to explain the differences between the reaction course for ozonization and for other electrophilic reactions, e.g., bromination and nitration with pyrene, these authors assume also an interaction of one of the other oxygen atoms with the adjacent carbon atom. The net result is, however, about the same as that predicted by the bond localization hypothesis. 

In a SOO-ml, three-necked, round-bottomed flask fitted with a stirrer, a reflux condenser, and a dropping funnel are placed 8.08 g. (0.040 mole) of pyrene (Note 1) and 80 ml. of carbon tetrachloride (Note 2). A solution of 2.0 ml. of bromine (6.24 g., 0.039 mole) (Note 3) in 30 ml. of carbon tetrachloride is added dropwise over a period of 2-3 hours. The resulting orange solution is stirred... 

BromintUion of aromatics. When a solution of the hydrocarbon in carbon tetrachloride is refluxed with the reagent, anthracene affords 9-broraoanthracene in 99% yield and pyrene affords 1-bromopyrene in 94% yield. Bromination of anthracene in nitrobenzene at 210 afforded 9,10-dibroraoanthracene in low yield. ... 

Mol. wt. 204.18, m.p. 296°. The reagent was prepared by condensation of cyclohexane-1,4-dione with malononitrile, bromination, and dehydrobromination with pyridine. The compound has properties similar to those of tetracyanoethylene and is a TT-acid of comparable strength. The equilibrium constant for ir-complex formation with pyrene is 78.4 as compared to 29.5 for the tetracyanoethylene-pyreno complex. 

It is reported that 1,4-dibromonaphthalene can be formed selectively and in 90% yield by irradiation of naphthalene and 1-bromonaphthalene with stoichiometric amounts of bromine and with the minimum amount of CH2CI2 as solvent at —30 to — SO C. In contrast, l,2,3,4,5-pentabromo-l,2,3,4-tetrahyd-ronaphthalenes result from irradiation of 1-bromonaphthalene in CCI4 at — 30°C, whereas at 77°C only 1,5-dibromonaphthalene is formed and in 80% yield. Two of the more unusual examples of the photoinduced introduction of groups into aromatic rings which have been described within the year are the formation of 1-cyanopyrene in a yield of up to 73% from irradiation at the interface of a solution of pyrene and 1,4-dicyanobenzene in propylene carbonate and an aqueous solution of NaCN in a polymer microchannel chip, and the addition of a variety of groups e.g. NH2, OMe, CN, and CO2H) to coronene by irradiation of arene-ice mixtures at low temperature and pressure." The latter work provides the first experimental evidence that such functionalized arenes, which are detected in primitive meteorites and interplanetary dust particles, may have arisen, at least in part, from photochemistry in ice. 

Polynuclear arenes from metacyclophanes. A few years ago, Japanese chemists reported that [2.2]metacyclophane (1) is converted into tetrahydro-pyrene (2) in 100% yield by treatment with bromine and iron. In an extension of this reaction to (4), pyridinium hydrobromide perbromide was used to obtain... 

In the Hoechst process, pyrene reacts with bromine to yield 1,3,6,8-tetrabromo-pyrene this is oxidized with sulfuric acid, to produce the intermediate 2,7-di-bromo-l,2,3,6,7,8-hexahydro-l,3,6,8-tetraoxopyrene subsequent oxidation in an alkaline medium yields the tetra-sodium salt of 1,4,5,8-naphthalenetetracarboxylic acid. 

HC f lithium hydride, methyUsocyanate, toluene diisocyanate, 2,4,6-trinitrotoluene (TNT), tri-o-cresylphosphate, vinyl chloride... 

The influence of halogen substitution on the interaction energy between PAH molecules has also been investigated. Unlike the anthracene + pyrene mixture system, bromine substitution on anthracene induces a different kind of interaction in the pyrene (1) + 9,10-dibromoanthracene (2) mixture system, which also results in non-idealities in solid-liquid equilibrium (see Figure 8). The surface area and volume of the 9,10-dibromoanthracene molecule is much larger than that of pyrene. 

The phase behaviors of binary PAC mixtures are complicated and non-ideal. Mixtures with large PAHs, such as benzo[a]pyrene, can exhibit a gap between the thaw curve and liquidus curve. Halogen substitution (bromine substitution) also has significant effect on the thermochemical behaviors of binary PAC mixtures. Bromine substitution on anthracene results in non-ideal phase behavior in pyrene + 9,10-dibromoanthracene and anthracene + 2-bromoanthracene systems. 

Two important polycycles produced prior to 1920 were perylene 19 (Fig. 1.2a) and pyrene 7, both of note as parent structures for numerous fused benzenoid analogs produced in the following decades. In 1910, Scholl, Seer, and Weitzenbock first produced perylene from an AlCls-mediated cyclization of naphthalene and/or 1,1 -binaphthyl under heat in low yield [19]. A subsequent success with improved yield occurred via treatment of 1,8-diiodonaphthalene with Cu powder. Weitzenbock was responsible for the first synthesis of pyrene in 1913 [20]. The five-step synthesis began with bromination of o,o -ditolyl followed by conversion into dicar-boxylic add 20 via a dinitrile intermediate (Scheme 1.7). Cyclization and Zn-dust distillation afforded the tetra-fused structure in a well-designed synthesis, confirming its structure through intermediate analysis. 

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