VAPOR-PRESSURES AND RELATIVE VOLATILITY OF ETHYL AND METHYL PARATHION

Vapor pressures of ethyl parathion (O, O-diethyl O-(p-nitrophenyl)phosphorothioate) and methyl parathion (O, O-diethyl O-(p-nitrophenyl)phosphorothioate) were measured using a gas saturation technique and polyurethane foam vapor traps. The vapor pressure, in mmHg, of ethyl parathion was linearly related to reciprocal temperature by the equation log P = 12.66 - (5274/T). With methyl parathion, apparently heat of vaporization changes at the melting point of 35.2-35.4 °C and the equations log P = 14.37 - (5700/T) and log P = 10.61 - (4543/T) describe the vapor pressure-temperature relationship below and above the melting point, respectively. The vapor flux of ethyl and methyl parathion at 25 °C from nonadsorbing surfaces was 0.210 and 0.435 µg (cm2)-1 h-1 respectively, which is directly proportional to their relative vapor pressures. Vapor loss rates from soil-incorporated methyl parathion were much lower than those from glass surfaces. © 1979, American Chemical Society. All rights reserved.