Henry's Law Constants of Some Environmentally Important Aldehydes

The Henry's law constants of seven aldehydes have been determined as a function of temperature by bubble-column and by head-space techniques. The compounds were chosen for their potential importance in the polluted troposphere and to allow structure-reactivity patterns to be investigated. The results (at 25 °C) are as follows (in units of M atm^-1): chloral, 3.44 X 10⁵glyoxal, ≥3 X 10⁵methylglyoxal, 3.71 X 10³formaldehyde, 2.97 X 10³benzaldehyde, 3.74 X 10¹hydroxyacetaldehyde, 4.14 X 10⁴acetaldehyde, 1.14 x 10¹A plot of Taft's parameter,Σσ*, vs log H* (the apparent Henry's law constant) gives a straight line with a slope of 1.72. H* for formaldehyde is anomalously high, as expected, but the extremely high value for hydroxyacetaldehyde was unexpected and may indicate that α-hydroxy-substituted aldehydes could have an unusually high affinity for the aqueous phase. The intrinsic Henry's law constants, H, corrected for hydration, do not show a clear structure-reactivity pattern for this series of aldehydes.