UNDER-FLAME REACTION OF SULFUR-CONTAINING AMINO-ACIDS BY A HYDROGEN-OXYGEN FLAME

Methionine was subjected to a flame-induced reaction in water or in an aqueous formic acid solution by using a hydrogen (50%)-oxygen (50%), hydrogen (87%)-oxygen (13%) and hydrogen diffusion flame. Besides the already-known stepwise oxidation by a hydroxyl radical, the contributi on of a hydrogen atom from the flame to the reaction was recognized wh en the hydrogen-rich mixtures were employed. Homoserine was obtained u nder all the reaction conditions employed here, and glutamic acid when employing aqueous formic acid as a solvent. A common intermediate, th e 3-carboxy-3-aminopropyl radical, appeared to exist in the reaction p athway. A coupling reaction of this radical with a hydrogen atom, hydr oxyl radical and hydroxycarbonyl radical afforded 2-aminobutyric acid, homoserine and glutamic acid, respectively. Lanthionine and S-methylc ysteine underwent the same reactions. Increasing the hydrogen content of the fuel and adding formic acid to the solvent resulted in retardin g the reaction rate. The latter modification of the reaction system al so brought about greater stability of the reaction products.