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Environmental fate & pathways

Phototransformation in air

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Description of key information

Half life in presence of NO: 15hrs
Half life in presence of OH only: 75hrs by measurement and QSAR. 96 hours by QSAR

Key value for chemical safety assessment

Additional information

In a study that was primarily investigating the photodegradation of organochlorocompounds, the degradation of ethyl acetate was also examined. In the presence of the initiator NO and under artificial sunlight irradiation 2.6x the strength of normal sunlight, the half life for degradation was determined to be around 15 hours at a concentration of 10ppm.  Another study examined the potential for photochemical degradation of ethyl acetate and established that it is stable to degradation through the action of UV at wavelengths that reach the troposphere in the absence of sensitisers. Degradation can proceed quite rapidly at environmentally relevant UV wavelengths in the presence of sensitisers. SO2 is a relatively weak sensitiser and does not function at environmentally relevant concentrations. At 500ppm NO2, the estimated half life for degradation is 17 hours. At 100ppm degradation occurs but is slow (days to DT50).  In a reliable review of available measured data on the reaction rate of ethanol with hydroxyl radicals, 3 studies were identified, all reporting reasonably consistent values for this parameter, a typical value of which at 298K was of which was 31.7 x10E-12cm3/(mol.sec), which leads, assuming typical average hydroxyl radical concentrations, to a predicted half life of around 75 hours.

A study to clarify the relative reactivities of a number of hydrocarbon and oxygenated substances established that the reactivity of ethyl acetate was amongst the lowest hydrocarbons studied in respect of the rate of depletion of a NOx initiator. Under light irradiation, there was no evidence of any ozone formation. Ethyl acetate can be considered to have a low reactivity with NOx and therefore a low photochemical ozone formation potential.

A study using a QSAR approach predicted that the rate constant for indirect photolysis of ethyl acetate (reaction with OH radicals) is 1.4x10^-12cm3/(molecule.sec) and that degradation primarily occurs through H abstraction from the methylene carbon. The resultant half life is predicted to be 92 hours assuming typical hydroxy radical concentrations.  The calculated Rate constant (for indirect photolysis) of ethyl acetate using a modern QSAR method is : 1.70 E-12 cm³/(molecule*sec) which leads to a predicted half life, assuming typical hydroxyl radical concentrations, of 75 hours.

In conclusion, Ethyl acetate will react with photochemically-produced hydroxyl radicals. Clean atmosphere half-life is 8.3 days and moderately-polluted atmosphere half-life can be estimated as around 2.1 days (both values based on a 12 hour sunlit day).  With a typical tropospheric OH concentration of 1 x 106 molecule cm-3, the estimated trophospheric lifetime for ethyl acetate was 7 days.  Effective pseduo-first order rate constant; results suggested that H-atom abstraction takes place at the alkoxy end of the molecule.