Oxidation of substituted triazines by sulfate radical anion (SO S 4 ) in aqueous medium: a laser flash photolysis and steady state radiolysis study P. Manoj, 1 K. P. Prasanthkumar, 1 V. M. Manoj, 1 Usha K. Aravind, 1 T. K. Manojkumar 2 and C. T. Aravindakumar 1 * 1 School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala, India 2 Indian Institute of Information Technology and Management-Kerala, Technopark Campus, Thiruvananthapuram 695 581, Kerala, India Received 13 July 2006; revised 24 October 2006; accepted 27 October 2006 ABSTRACT: Laser flash photolysis has been used to determine the bimolecular rate constants and the spectral nature of the intermediates obtained by the reaction of sulfate radical anion (SO S 4 ) with 1,3,5-triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT), 2,4-dioxohexahydro-1,3,5-triazine (DHT), and 6-chloro N-ethyl N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine, AT). The rate constants determined were in the range 4.6 T 10 7 –3 T 10 9 dm 3 mol S1 s S1 at pH 6. The transient absorption spectra obtained from the reaction of SO S 4 with T, TMT, DHT and AT has an absorption maximum in the region 320–350nm and was found to undergo second-order decay. The intermediate species is assigned to N-yl C(OH) radical of T (TOH  ), carbon centered neutral radical of TMT, an OH-adduct of AT and an N-centered radical in the case of DHT. The interpretations on the experimental results obtained from TMT are supported by DFT calculation using Gaussian 03. Steady state radiolysis technique has also been used to investigate the degradation of AT induced by SO S 4 . The degradation profile indicated that about 99% of AT has been decomposed after an absorbed gamma-radiation dose of 7.5kGy. The degradation yield of AT (expressed as G(-AT)) was found to be 0.26 m mol J S1 . The degradation reactions initiated by SO S 4 may thus be employed as a potential alternative for  OH-induced degradation of triazines. Copyright # 2007 John Wiley & Sons, Ltd. KEYWORDS: triazine; sulfate radical anion; laser flash photolysis; radiation chemical; DFT calculation; radical cation; pollutant INTRODUCTION The production of radical cations in aqueous solution by radiation chemical or photochemical method relies mainly on the use of oxidizing species such as SO  4 , Cl  2 , Br  2 , Tl 2þ , or photo-excited quinones. 1–4 Among these, the sulfate radical anion, SO  4 (E 0 ¼ 2.5–3.1 V vs. NHE) is commonly used and it can be generated both radiolytically and photolytically. 5 It can be produced by the laser flash photolysis of S 2 O 2 8 with laser light of 248 or 266 nm. The reactions of radiolytically produced hydrated electron (e  aq ) and  H with S 2 O 2 8 is another method for its production. 6 It is reported that the reaction of SO  4 with several aromatic compounds results in the production of hydroxyl cyclohexadienyl radicals. 7 But in the case of methoxy derivatives, radical cations of the aromatic compounds have been observed. 8 It results decarboxylation with several carboxy derivatives, leading to the production of phenyl radical. 9 The hydroxyl cyclohexadienyl radical can be formed either by the addition of SO  4 to the benzene ring followed by hydrolysis 7 or by direct electron transfer from the aromatic ring to SO  4 followed by hydroxylation with water or OH  . 10 The radical cations from anisole can be obtained by direct electron transfer or via addition followed by elimination. 8 Decarboxylation can occur through direct oxidation of the carboxyl group, as is the case with aliphatic carboxylic acids. 7 The reactions of SO  4 is also important in the radical chemistry of nitrogen heterocyclic compounds like purines and pyrimidines. The selectivity of this radical to produce radical cations of purines and pyrimidines has been used to obtain valuable information about the direct effect of the ionizing radiation on DNA. 6 This means, SO  4 is very useful to understand the underlying chemistry of the fate of the radical cations of different heterocyclic systems in aqueous medium. Triazine (a nitrogen heterocyclic compound)-based herbicides are among the most widely used pesticides. Because of the large and prolonged use of these JOURNAL OF PHYSICAL ORGANIC CHEMISTRY J. Phys. Org. Chem. 2007; 20: 122–129 Published online 5 February 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/poc.1134 *Correspondence to: C. T. Aravindakumar, School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala, India. E-mail: CT-Aravindakumar@rocketmail.com Copyright # 2007 John Wiley & Sons, Ltd. J. Phys. Org. Chem. 2007; 20: 122–129