Electrochemical Reduction of Metribuzin

Abstract

Metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one] is a widely used weed controlling agent. In aqueous solutions and in 30 % v/v acetonitrile/water solutions it is reduced in two two-electron steps. In both steps protonated forms of azomethine bonds are reduced, in the more positive the 1,6-bond, in the more negative (by about 0.4 V) the 2,3-bond. At pH > 7 the conjugated base is reduced at considerably more negative potentials in a one-electron step. Reduction of both azomethine bonds is accompanied by acid-base and hydration-dehydration equilibria. The 1,6-dihydrometribuzin, formed in the first reduction step, undergoes acid catalyzed hydrolysis. In many aspects the behavior of metribuzin resembles that of metamitron [4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one] investigated earlier. For analytical purposes waves between pH 2 and 4 are best suited.

Additions of water, hydroxide ions, alcohols and alkoxide ions to carbonyl and azomethine bonds

“…When the nucleophilic attack on C(5) is hindered or blocked by a bulky substituent, then the addition takes place at C (6) 105 . 1,2,4-Triazinium ions bearing no substituent at both C(5) and C(6) can undergo addition of two methoxide ions, with additions to both N(1)=C (6) and N(4)=C (5) (1) is so favored that the crystalline adduct has been isolated [119]. No crystalline products of these two compounds were isolated in the presence of i-PrOH, sec-BuOH and tert-BuOH and similarly no such adducts were isolated for 1,3-dimethyl-, 6-ethyl-93b and 6-phenyl-2,4-dioxo-1,3,5-triazines 93c 122 .…”

Electrochemical behavior of some triazine derivatives at glassy carbon electrode in non-aqueous media

“…Reduction in both steps involved the protonated from of azomethine bonds in 1,6-and 2,3-positions. In addition, similar reports [19,21,22] in relation with 2e-reduction of azomethine in triazine ring have been published. These processes involve the uptake of four electrons and one or two H + ions per herbicide molecule yielding non-aromatic products.…”

“…Therefore, it can be concluded that the first cathodic peak can follow the above EC mechanism, which is well defined in the reviewed literature. On the other hand, there are a few reports [18,19,[21][22][23] on the electrochemical reduction of 1,3,5-triazine derivatives involving reducible azomethine (C@N-) bonds. For example, Ludvik et al [18] studied electrochemical reduction of metamitron (4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one) on static mercury drop electrode (SMDE) in DMF and several other solvents.…”

“…Due to the importance of triazine compounds containing thiols and those without thiol groups such as metribuzin and metamitron in toxicological studies, chemical and food industries, and biomedical redox systems, these compounds have been extensively studied for many years [18][19][20][21][22][23][24]. However, triazine compounds including 4-amino-6-methyl-3-thio-1,2,4-triazine-5-one and 6-methyl-3-thio-1,2,4-triazine-5-one have rarely been studied especially at glassy carbon (Gc) electrode and in dimethylformamide (DMF) Medium.…”

Synthesis, spectroscopic and voltammetric studies of a novel Schiff-base of cysteine and saccharin

“…The reduction peak of azomethine center shows substantial drop in peak current and cathodic potential shift towards more negative values as the pH increases [47].…”