Laser-based studies of NO3 radical reactions with selected aromatic compounds in aqueous solution

The reactivity of the nitrate radical towards selected aromatic compounds in aqueous solution has been investigated using a laser photolysis/long-path laser absorption technique (LP-LPLA). The reactions of NO3 radicals with (1) phenol, (2) 4-nitrophenol, (3) 2,4-dinitrophenol, ( 4) ortho - and (5) para-cresol, (6) 2-nitro-p-cresol, (7) 2,6-dinitro-p-cresol, (8) benzoic acid, (9) 4-hydroxybenzoic acid, (10) 3-nitrobenzoic acid, (11) 4-nitrobenzoic acid, (12) 4-cyanobenzoic acid, (13) 4-methoxybenzoic acid, (14) 4-methylbenzoic acid and (15) 4-methyl-3-nitrobenzoic acid were investigated at T = 298 K. The following rate coefficients were obtained: k(1) = (1.9 +/- 0.3) x 10(9) M-1 s(-1), k(2) = (7.1 +/- 0.4) x 10(7) M-1 s(-1), k(3) = (5.3 +/- 0.6) x 10(7) M-1 s 1, k(4) = (1.1 +/- 0.2) x 10(9) M-1 s(-1), k(5) = (8.2 +/- 0.3) x 10(8) M-1 s(-1), k(6) = (1.0 +/- 0.1) x 10(8) M-1 s(-1), k(7) = (1.4 +/- 0.2) x 10(8) M-1 s(-1), k(8) = (6.5 +/- 1.3) x 10(7) M-1 s(-1), k(9) = (5.0 +/- 1.3) x 10(8) M-1 s(-1), k(10) = (2.0 +/- 0.6) x 10(7) M-1 s(-1), k(11) = (2.0 +/- 0.9) x 10(7) M-1 s(-1), k(12) = (2.7 +/- 1.5) x 10(7) M-1 s(-1), k(13) = (6.9 +/- 3.2) x 10(8) M-1 s(-1), k(14) = (6.0 +/- 0.8) x 10(8) M-1 s(-1), k(15) = (3.3 +/- 1.4) 10(7) M-1 s(-1). Moreover, the effect of temperature on the reaction of NO3 with (1) phenol, (5) para-cresol, (8) benzoic acid and (14) 4-methylbenzoic acid was studied leading to the Arrhenius expressions k(1)(T) = (1.4 +/- 0.2) x 10(12) exp [(2100 +/- 500) K/T] M-1 s(-1), k(5)(T) = (3.8 +/- 0.2) x 10(15) exp [(4600 +/- 1000) K/T] M-1 s(-1), k(8)(T) = (4.9 +/- 0.2) x 10(9) exp [(1300 +/- 400) K/T] M-1 s(-1), and k(14)(T) = (1.6 +/- 0.3) x 10(12) exp [-(2400 +/- 500) K/T] M-1 s(-1), respectively. Based on the results the possible reaction pathways are discussed. The influence of ionic strength on the reaction rate for the reactions of NO3 with phenol and benzoic acid was studied by varying the electrolyte concentration of the aqueous solution. From these experiments limiting rate constants for zero ionic strength and for I --> infinity could be determined. Additionally, the in uence of pH on the reaction of NO3 with selected aromatics was studied. From the derived data the limiting rate constants for the reaction of NO3 with the undissociated aromatic compound and its anion were determined.