Vinyl acetate

Phototransformation in air

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in air

Type of information:

experimental study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline available

Principles of method if other than guideline:

The atmospheric reactivity of vinyl acetate to three main tropospheric oxidants (OH, NO3 and O3) has been experimentally determined and published.

GLP compliance:

no

Estimation method (if used):

PHOTOCHEMICAL REACTION WITH OH RADICALS
- Typical tropospheric concentration of radicals were used to determine tropospheric lifetimes (tau) of VAM: [OH] = 2x10^6 molecules/cm3; [NO3] = 2.5x10^8 molecules/cm; [O3] = 7.4 x 10^11 molecules/cm.
- Degradation rate constant: The rate constant of the OH-induced oxidation was determined by the relative rate technique using propene as a reference compound.
- Temperature for which rate constant was calculated: 293 ± 3 K

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

60

Details on light source:

Experiments performed in an evacuable environmental chamber consisting of a pyrex reactor surrounded by 40 fluorescent tubes (Philips TL05 and TL03) and 16 xeon arc lamps.

Details on test conditions:

Experimental setup:
Contained within the reactor were two multiple reflection optical systems interfaced with a Fourier transform IR spectrometer and a UV-Vis grating spectrometer. The FTIR spectrometer contained a glowbar as the mid-infrared source and was recorded with a resolution of 0.5 cm^-1 and a path length of 156 m.

For the rate determination of NO3 oxidation of VAM, the nitrate radical was monitored using the UV-Vis spectrometer. The detector in this setup was a CCD camera which covers a spectral range of ca. 60 nm and a maximum resolution of 0.15 nm.

OH and NO3 radical generation:
The hydroxyl radicals were generated by photolysis of methyl/isopropyl nitrites (previously prepared via addition of a dilute solution of sulphuric acid to a mix of sodium nitrate and the applicable alcohol. The nitrate radicals were generated from thermal decomposition of dinitrogen pentoxide.

Rate constant determination:
The rate constant of the OH-induced oxidation was determined by using a relative rate technique using propene as a reference substance. The rate constant for the ozonolysis was determined using an absolute rate technique. Both VAM and ozone were both monitored using FTIR spectrometry. The NO3 oxidation rate constant was determined by both relative and absolute rate techniques during the experiment.

Experimental procedure:
All of the experiments were conducted at atmospheric pressure and 293 +/- 3 K. Initial concentrations of reactants (i.e. VAM, propene and O3 (or N2O5 or alkyl nitrite)) were in the PPM range. For the OH oxidation, NO was added to the mixture to assist in minimising nitrate radical and ozone formation. For the ozonolysis experiments, CO was added as an OH scavenger (ca. 2000 ppm). As the CO concentration was high, more than 90% of the OH radicals are scavenged. During the experiments, compounds were monitored for IR every 5 minutes (totalling around 100 co-added interferograms). These were calibrated by flushing known amounts of these compounds.

Duration:

8 h

Temp.:

293 K

Reference substance:

yes

Remarks:

Propene

Preliminary study:

No preliminary test performed

Test performance:

Tropospheric lifetimes of VAM towards OH and NO3 radicals and ozone were estimated. From the mechanistic study the main products of OH, NO3 and O3 oxidation of VAM were detected.

Reaction with:

OH radicals

Rate constant:

0 cm³ molecule-1 s-1

Remarks on result:

other: Relative rate

Reaction with:

other: NO3

Rate constant:

0 cm³ molecule-1 s-1

Remarks on result:

other: Relative rate

Reaction with:

other: NO3

Rate constant:

0 cm³ molecule-1 s-1

Remarks on result:

other: Absolute rate

Reaction with:

ozone

Rate constant:

0 cm³ molecule-1 s-1

Remarks on result:

other: Absolute rate

Transformation products:

yes

Remarks:

Details provided in 'any other information on results incl. tables'.

Results with reference substance:

The rate constant for propene with OH has been taken as being equal to 2.9 x 10^-11 cm3 molecule-1 s-1

Yields of oxidation products of VAM by OH and NO3 radicals and by O3:

Reaction	Product	Yield (%)
VAM + OH	Formic acetic anhydride	75 ± 7
	Formaldehyde	96 ± 12
	Acetic acid	20 ± 3
	Formic acid	Secondary
	Carbon budget	90 ± 18
VAM + NO3	Formic acetic anhydride	44 ± 6
	Formaldehyde	46 ± 8
	Organic nitrates	Not quantified
	Carbon budget	44 ± 6
VAM + O3	Formic acetic anhydride	97 ± 8
	Formaldehyde	20 ± 6
	Formic acid	Not quantified
	Carbon budget	78 ± 7

Detailed reaction mechanisms can be located in the publication itself. Tropospheric lifetimes of VAM were estimated as 6 hours, 6 days and 5 days for TauOH, TauNO3 and TauO3, respectively. This demonstrates that the reaction with OH radicals is likely to be the main tropospheric loss process for VAM.

Validity criteria fulfilled:

not applicable

Conclusions:

The tropospheric life times of VAM towards OH/NO3 radicals and ozone were estimated using typical concentrations of three oxidants alongside degradation rate constants and yields. This demonstrates that the reaction with OH radicals is likely to be the main tropospheric loss process for VAM.

Reference 2

Endpoint:

phototransformation in air

Type of information:

calculation (if not (Q)SAR)

Remarks:

Migrated phrase: estimated by calculation

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, available in peer-reviewed literature, acceptable with restrictions

Principles of method if other than guideline:

Experimentally determined rate constant. Calculation to estimate atmospheric half-life

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
No data reported

Estimation method (if used):

No information on estimation method reported

Light source:

not specified

Details on light source:

No data reported

Details on test conditions:

No data reported

Preliminary study:

No data

Test performance:

no data

DT50:

14.6 h

Results with reference substance:

no data

Validity criteria fulfilled:

not applicable

Remarks:

estimation

Conclusions:

The atmospheric half-life of 14.6hrs has been estimated for vinyl acetate

Executive summary:

The atmospheric half-life of 14.6 hrs has been estimated for vinyl acetate. This value is used in the EU RAR.

Description of key information

The atmospheric half-life of 14.6 h has been estimated for vinyl acetate and the rate constant as 2.3x10^-11 cm2 molecule^-1S^-1. 

Key value for chemical safety assessment

Half-life in air:

14.6 h

Degradation rate constant with OH radicals:

0 cm³ molecule-1 s-1

Additional information

The study by Atkinson et al. (1987) is considered reliable and this value is used in the EU RAR. The study by Picquet et a. (2010) demonstrated that the reaction with OH radicals is likely to be the main tropospheric loss process for VAM.