3- Alkoxy-1,2,4-triazine 1-oxides

The reaction of triazine oxides 73 with acetone cyanohydrin yields triazine carbo-nitriles 74 (X = CN). Reacting 73 with potassium cyanide in alcohols results in the isolation of alkoxy products 74 (X = OR) which are also formed by treating the nitriles with alcohols <97MC66>. 

Deoxygenative autoaromatization was reported to occur in the reaction of 3-amino-1,2,4-triazine 2-oxides 42 with alcohols in the presence of HCl or acetyl chloride. In this case the intermediate cr -adducts undergo elimination of water or acetic acid, resulting in 6-alkoxy-3-amino-l,2,4-triazines 75 (77JOC3498). 1,2,4-Triazine 1-oxides do not react with alcohols under these conditions (77JOC3498). 

Paudler observed alcohol addition to the N( 1)—C(6) bond of 1,2,4-triazine 2-oxides unsubstituted at the 6-position (96) in the presence of hydrogen chloride. Elimination of water followed, leading to 6-alkoxy-1,2,4-triazines (97) (77JOC3489). 

Direct photolysis of aqueous solutions of the 2-chloro-.v-iriaz.ine herbicides (atrazine, simazine, propazine) proceeds via excitation of the triazine molecule, followed mainly by dechlorination and hydroxylation to form the corresponding hydroxytriazine (Pape and Zabik, 1970 Khan and Schnitzer, 1978 Chan et al, 1992 Lai et al, 1995 Schmitt et al, 1995 Sanlaville et al, 1997 Torrents et al, 1997 Texier et al, 1999b Hequet et al, 2001). This observation - plus the fact that when 2-chloro-v-triazine herbicides are photolyzed in methanol, ethanol, and n-butanol, the respective 2-alkoxy derivatives are formed - indicates a mechanism involving photochemical solvolysis rather than the involvement of hydroxyl radicals. This conclusion is supported by the fact that the rate of oxidation of atrazine was unaffected by the presence of either bicarbonate ion (Beltran et al, 1993) or ferf-butanol (Torrents et al, 1997), both strong hydroxyl radical scavengers. 

The specific nature of 1,2,4-triazine /V-oxides discussed in Section II,C is also manifested in the SNH reactions. Treatment of 1,2,4-triazine 2-oxides containing electron-donating groups at C-3 with methanol, ethanol, or isopropanol in the presence of hydrochloric acid results in 6-alkoxy-substituted 1,2,4-triazines 137 (Scheme 77) (77JOC3498). The reaction is proposed to involve the addition of alcohol to C-6 of the hydroxy-1,2,4-triazinium cation 135, followed by elimination of water. The presence of an electron-donating group at C-3 seems also to be important because it contributes considerably to the stabilization of the intermediate cationic species 136 (Scheme 77). 

---