One of the reactants for the formation of previously identified transi
tory product in the gas-phase ozonolysis of C2H4 was shown to be HCOOH
. The most probable structure of this compound is HOO-CH2-O-CHO. Its c
oncentration increased with the addition of HCOOH but decreased with t
he addition of HCHO which had previously been assumed as one of the re
actants. This compound slowly decomposed to formic acid anhydride and
water.