Electrophilic aromatic substitution. Part 18. Protiodetritiation of anthracene, coronene (dibenzo[ghi,pqr]perylene), and triphenylene in anhydrous trifluoroacetic acid

Abstract

A method is described for determining aromatic hydrogen exchange rates in anhydrous trifluoroacetic acid for aromatic hydrocarbons of very low solubility. Kinetic runs, carried out on as little as 0.05 mg of aromatic compound, lead to the following partial rate factors (positions in parentheses): anthracene, 7 900(1); 1 135(2); 1.27 × 10⁷(9); coronene, 7 400(1); triphenylene, 620(1); 136(2). The corresponding σ⁺ values are –0.445. –0.35, –0.81, –0.44, –0.315, and –0.24. This, the first quantitative determination of the electrophilic aromatic reactivity of anthracene, shows that the 1- and 2-positions are more reactive than the corresponding positions in naphthalene, but these position are closer in reactivity than are those in naphthalene. Both effects are predicted by calculations which also correctly predict the reactivity of triphenylene and coronene; the exchange results confirm that the nitration of triphenylene gives anomalous rate data.