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The pKa for N-methylaniline is 4.848 at 25 deg C indicating that some of the molecule is ionized (e.g, 10% at pH 5.8) at the acidic end of the environmental pH range. N-Methylaniline is susceptible to oxidation and photooxidation in solution as is evidenced by its turning brown on exposure to air. Algae-induced phototransformations of anilines is believed to involve superoxide ions. In a laboratory study, the half-life of N-methylaniline in a photoreactor illuminated with 20 W fluorochemical lamps (radiation between 300 and 400 nm with a maximum at 350 nm) was 1.5 hr.

N-Methylaniline has a vapor pressure of 0.453 mm Hg at 25 degC and therefore in the atmosphere, it will exist primarily as the vapor. In the atmosphere, vapor-phase N-methylaniline reacts with photochemically-produced hydroxyl radicals with an estimated rate constant of 43.9E-12 cu cm/molecule-s. Assuming a hydroxyl radical concn of 5E+5 radicals/cu cm, the half-life of N-methylaniline in the atmosphere would be 8.8 hr (SRC). The structurally similar chemical, aniline, has a strong UV absorption band at 285 nm which extends beyond 290 nm and therefore N-methylaniline which would be expected to have similar UV absorption and could be subject to direct photolysis.