Phenanthrene, ozonization

The reaction of ozone with an aromatic compound is considerably slower than the reaction with an alkene. Complete ozonolysis of one mole of benzene with workup under non-oxidative conditions will yield three moles of glyoxal. The selective ozonolysis of particular bonds in appropriate aromatic compounds is used in organic synthesis, for example in the synthesis of a substituted biphenyl 8 from phenanthrene 7 ... 

Phenanthrene Diozonide. Ct 4 Hj 0 (03 )2, colorl crysts, very expl. Prepd by passing ozone thru a cooled chioroformic phenanthrene soln Refs 1) Beil 5,670 [583] 2) C.D. Harries... 

Yoshikawa, T., L.P. Ruhr, W. Flory, D. Giamalva, D.F. Church, and W.A. Pryor. 1985. Toxicity of polycyclic aromatic hydrocarbons. I. Effect of phenanthrene, pyrene, and their ozonized products on blood chemistry in rats. Toxicol. Appl. Pharmacol. 79 218-226. 

The rate should be sufficiently great to cause considerable agitation of the suspended phenanthrene. As the reaction proceeds, the reaction vessel should be shaken frequently in order to maintain good contact between the phenanthrene and ozone. For smaller runs a reaction vessel that includes a stirrer is advantageous (Note 5). 

Unreacted ozone starts passing through to the potassium iodide trap toward the end of the reaction. However, it is best to continue the reaction until all the suspended phenanthrene has disappeared. This usually requires a total of 1.1-1.3 mole-equivalents of ozone. Unless all the phenanthrene has reacted, difficulty is encountered in the crystallization and/or recrystallization of the dialdehyde. 

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... 

The double-bond character of the 9,10 bond in phenanthrene is particularly evident in ozonization. This bond is attacked preferentially, which leads to the formation of a dialdehyde when the ozonide is reduced with iodide ion ... 

A finely divided suspension (Notes 1 and 2) of 10.0 g. (0.056 mole) of phenanthrene (Note 3) in 200 ml. of dry methanol (Note 4) is placed in a standard ozonolysis vessel (Note 5). The reaction mixture is cooled in a Dewar flask by an acetone-Dry Ice mixture to about —30° (Notes 6 and 7), and ozone (Note 8) is passed through at a rate of about 20 1. per hour (Note 9) until all the phenanthrene has reacted (Note 10). 

The UV /ozone process removed nearly 100% of the influent phenanthrene after 5 min at pH around 7 furthermore, the UV/ozone process removal rate was virtually identical to that of ozone alone, with only slight variations occurring after about 3 min. Evidence of the buildup of scavengers can be seen... 

Beltran et al. (1995) concluded that (1) the UV/ozone oxidation process can achieve high removal rates of fluorene, phenanthrene, and acenaph-thene, with total efficiencies being near 100% in some cases (2) neutral pH of 7 yields the highest removal rate of fluorene in solution and (3) the greater the bicarbonate concentration added to fluorene, the lower the removal efficiency becomes. When an excess of ozone is present in the reaction mixture, the degradation rate of anthracene, phenanthrene, and pyrene can be given as ... 

The results obtained in AOP-treatment of pyrene in aqueous solutions were quite similar to those of anthracene and phenanthrene. For pyrene, ozonation has been more effective at lower pH values than at neutral pH values. The half-lives of pyrene at pH 3,7, and 9 are 17,24, and 42 s, respectively however, the half-life of pyrene increased in the series of 03 < UV/03 < 03/H20 < UV/ 03/H202 (Trapido et al., 1995). The UV degradation of pyrene is quite fast the half-life is only 69 s (Trapido and Veressinina, 1995). Figure 14.23 illustrates the oxidation kinetics of anthracene and pyrene in neutral media. 

AOPs have also been applied for phenanthrene degradation in acidic and basic media, as shown in Figure 14.24. The results are similar to those obtained in neutral media. Ozonation alone was shown to be the most effective for destruction of phenanthrene. Table 14.19 provides the half-lives of phenanthrene under various AOP systems (Trapido and Veressinina, 1995). Figure 14.24 illustrates the degradation kinetics of phenanthrene with the UV/03/H202 system. 

Degradation kinetics of phenanthrene with UV/ozone/H202 system. (From Trapido, M. and Veressinina, Y., Environ. Technol., 16, 729-740, 1995. With permission.)... 

Trapido M, Yeressinina J, Munter R. Ozonation and advanced oxidation process (AOP) treatment of phenanthrene in aqueous solutions. Ozone Sci Eng 1994 16 475-486. 

The ozonolysis of phenanthrene in methanol leads to the eight-membered ring peroxide (137).140,141 When phenanthrene is ozonized in the presence of water, it gives the cyclic dihydroxyperoxide (138), which is also formed from diphendialdehyde and hydrogen peroxide.142... 

The breakdown of the benzene ring to aldehydes is extremely rare and has been achieved only by ozone. A historical and classical example is the disintegration of o-xylene to a mixture of glyoxal, methyl glyoxal, and diacetyl (butanedione) in the predicted ratios [104]. From the preparative point of view, the conversion of phenanthrene into 0,0 -diformyl-biphenyl (diphenaldehyde) [1123] or o-formylbiphenyl-o -carboxylic (diphenaldehydic) acid [1124] is more important (equation 154). 

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