2.3- Benzoquinoline, acridine

Acridine (2,3-benzoquinoline) [260-94-6] M 179.2, m 111° (sublimes), b 346°, pK 5.58 (pK of excited state 10.65). Crystd twice from benzene/cyclohexane, or from aqueous EtOH, then sublimed, removing and discarding the first 25% of the sublimate. The remainder was again crystd and sublimed, discarding the first 10-15% [Wolf and Anderson 7Am Chem Soc 77 1608 7955]. 

The reaction network for 5,6-benzoquinoline [101] has been proposed in a more detailed level than that of acridine. In this network, conversely to acridine network, only one primary hydrogenation product, l,2,3,4-tetrahydro-5,6-benzoquinoline, was identified, and in contrast to the quinoline case however, no aniline derivatives were detected. 

Scheme 52 explains the [(Cp )Rh(MeCN)3]2+-assisted regioselective hydrogenation of pyridines, benzoquinolines, acridines as well as indoles and benzothiophene.258 The relative hydrogenation rates were attributed to both electronic and steric effects, the rate generally decreasing with increasing basicity and steric hindrance at the nitrogen atom. 

As a general trend, six-membered mononuclear N-heteroaromatics such as pyridine and derivatives are much less prone to undergo hydrogenation than bi-and trinuclear N-ring compounds (e.g., quinolines, benzoquinolines, acridines) due to their higher resonance stabilization energy. 

The o values of rings annelated to pyridine in systems such as quinoline, isoquinoline, benzoquinolines, acridine, and phenanthridine and determined by the basicity of the ring nitrogen atom are predicted186 and found to be small.33,34 This is an important point stressed and elucidated previously,181 and demonstrating the validity of the basic assumptions of the Hammett equation. 

As already mentioned, quinoline is one of the major nitrogenated compounds found in heavy oils, and with its pyridine and benzene rings is a good representative of the other nitrogenated impurities. These two facts explain why its HDN has been extensively used as model reaction by different research groups, mainly Satterfield et al. (MIT),31 Katzer et al. (Delaware),32 and by Schultz etal.,33 Vlugter etal.,34 and Flinn etal.3Sa Some studies have also been published on benzoquinolines,36 acridine,32 and indole.35b... 

Several homogeneous systems have been reported to catalyze the hydrogenation of polynuclear N-heterocycles efficiently the regioselective reduction of the N-containing ring in quinoline, isoquinoline, indole, benzoquinolines, acridine and other related molecules can be achieved with relative ease and under moderate conditions of temperature and pressure. A number of metals are known to be active (Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir) but most of the published work has concentrated on ruthenium and rhodium precursors [95-100] as shown in Table 3.3. 

The hydrogenation of other polynuclear N-heterocycles was also reported by Rosales group, by use of the same Ru(II) catalyst precursor operating at 125° C and 3 atm. H2. The reactivity order acridine > quinoline 5,6-benzoquinoline > 7,8-benzoquinoline > indole > isoquinolinc was in line with other trends previously observed, reflecting steric and electronic effects. A kinetic analysis of the hydrogenation of acridine reveals a different, second order, rate law -d[A]/dr = consistent... 

Transition metal complexes of other relevant organonitrogen compounds such as isoquinoline, 5,6-benzoquinoline, 7,8-benzoquinoline, acridine, and phenanthridine are also known, and they contain theN-ligand coordinated in either the p fN) or the tl -arene fashion [49, 69, 70]. The triosmium cluster Os3(CO),o(CH3CN)2 reacts with polyaromatic N-heterocycles such as 5,6-benzoquinoline and phenanthridine in an analogous manner to Py and Q, yielding J.3, n (N,C,C) complexes [69]. 

The relationship between cationic ionization and antibacterial activity, as demonstrated above in the acridine series, is valid also for at least seven other series, namely the three series of benzoacridines 10,9) to (10.11) of which 16 examples were studied, the phenanthridines (10,12), six examples, and the three series of benzoquinolines (10,13) to (10.15) of which 21 examples were studied (Albert, Rubbo and Burvill, 1949). Some of these examples are given in the first half of Table 10.10 (p. 407). 

H-1-Benzopyran, 2-oxo-. SeeCoumarin Benzo[b]pyridine. See Quinoline Benzo(c)pyridine. See Isoquinoline Benzopyrene 1,2-Benzopyrone Benzo-a-pyrone. SeeCoumarin Benzopyrrole 1H-Benzo[b]pyrrole 2,3-Benzopyrrole. See Indole Benzoquin. See Hydroquinone benzyl ether 2,3-Benzoquinoline. See Acridine 5,6-Benzoquinoline. See Benzo (f) quinoline Benzo (b) quinoline. See Acridine Benzo (f) quinoline CAS 85-02-9 UN 8027... 

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