Reaction mass of divinylbenzene and ethylstyrene

Phototransformation in air

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in air

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Study period:

March 2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Remarks:

Acccepted estimation method, with predictive accuracy demonstrated for structural analogs

Justification for type of information:

QSAR prediction

Principles of method if other than guideline:

Estimation of gas-phase indirect photolysis reaction rate constants with ozone and hydroxyl radical, based on a series of structure-fragment reactivity coefficients determined from correlations of an extensive experimental dataset.

GLP compliance:

no

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Predictions were performed for two structural analogs, styrene and ethylbenzene, which have experimentally-derived rate constants for indirect photolysis, to demonstrate predictive accuracy of the QSAR for the DVB and EVB components.
Styrene: c(cccc1)(c1)C=C
Ethylbenzene: c(cccc1)(c1)CC

Estimation method (if used):

AOPWIN v1.92a (June 2008), as described in the cited publication by Meylan and Howard, with subsequent modifications.

Light source:

sunlight

Details on light source:

Simulated reaction with photochemically-generated hydroxyl radical and ozone in the troposphere. The assumed concentrations of these sensitizers are 500,000 molecules/cm3 OH radical, and 700,000,000,000 molecules/cm3 ozone averaged over a 24-hr photoday

DT50:

6.3 h

Remarks on result:

other:

Remarks:

Estimated atmospheric half-life is 6.3 hours (represents longest predicted half-lives for reaction of substance components with both OH radical and ozone.

Transformation products:

not measured

Results with reference substance:

Styrene:
Predicted OH rate constant = 2.81E-11 cm3/molecule*sec
Measured OH rate constant = 5.80E-11 cm3/molecule*sec
Predicted Ozone rate constant = 2.10E-17 cm3/molecule*sec
Measured Ozone rate constant = 2.17E-17 cm3/molecule*sec

Ethylbenzene:
Predicted OH rate costant = 5.95E-12 cm3/molecule*sec
Measured OH rate constant = 7.10E-12 cm3/molecule*sec
Ozone rate constant not predicted, due to lack of unsaturated functional group

Conclusion: the applied QSAR results in predicted rate constants for OH radical and ozone which are within a factor of approximately 2 of measured values.
References for measured values:
Atkinson, R.  1989.  Kinetics and mechanisms of the gas-phase reactions of the hydroxyl  radical with organic compounds. J. Phys. Chem. Ref. Data Monograph No. 1.  NY: Amer. Inst. Physics & Amer. Chem Soc
Kwok, E.S.C. and Atkinson, R.   1995.   Estimation of Hydroxyl Radical Reaction Rate Constants for Gas-Phase Organic Compounds Using a Structure-Reactivity Relationship: An Update.   Atmospheric Environment 29: 1685-95.  [adapted from Final Report to CMA Contract No. ARC-8.0-OR, Statewide Air Pollution Research Center, Univ. of CA, Riverside, CA 92521].

Predicted second-order rate constants and associated half-lives for reaction of DVB and EVB isomers with OH and ozone:

o- DVB:

Predicted rate constant with OH radical = 5.43E-11 cm3/molecule*sec

Predicted rate constant with ozone = 4.20E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 3.4 hours

m- DVB:

Predicted rate constant with OH radical = 5.43E-11 cm3/molecule*sec

Predicted rate constant with ozone = 4.20E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 3.4 hours

p- DVB:

Predicted rate constant with OH radical = 5.43E-11 cm3/molecule*sec

Predicted rate constant with ozone = 4.20E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 3.4 hours

o-EVB:

Predicted rate constant with OH radical = 3.20E-11 cm3/molecule*sec

Predicted rate constant with ozone = 2.10E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 6.3 hours

m-EVB:

Predicted rate constant with OH radical = 3.20E-11 cm3/molecule*sec

Predicted rate constant with ozone = 2.10E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 6.3 hours

p-EVB:

Predicted rate constant with OH radical = 3.20E-11 cm3/molecule*sec

Predicted rate constant with ozone = 2.10E-17 cm3/molecule*sec

Overall half-life for combined reaction with OH (500,000 molecules/cm3) and ozone (7E11 molecules/cm3) = 6.3 hours

Validity criteria fulfilled:

yes

Conclusions:

The estimated atmospheric half-life for the DVB-HP, -63, and -55 substances is 6.3 hours, representing the longest predicted half-lives for reaction of the substance components with both OH radical and ozone. The substances therefore will have a short lifetime in the atomosphere, and low potential for long-range transport.

Executive summary:

The second-order rate constants for reactions of divinylbenzene and ethylvinylbenzene isomers with photochemically-generated hydroxyl radical and ozone were estimated using the U.S. EPA AOPWIN v1.92a software. The model indicated no difference in reactivity among the o-, m-, and p-isomers of the DVB and EVB components, and that reactions with EVB had the longest predicted half-lives among the DVB and EVB substances. The QSAR model was shown to give estimted reaction rate constants which were within a factor of approximately 2 of measured rate constants for structural analogs, styrene and ethylbenzene. The overall atmospheric half-life for the DVB-HP, -63, and -55 substances is estimated to be 6.3 hours.

Description of key information

The overall atmospheric half-life for the DVB-HP, -63, and -55 substances is estimated to be 6.3 hours.

Key value for chemical safety assessment

Half-life in air:

6.3 h

Additional information

The second-order rate constants for reactions of divinylbenzene and ethylvinylbenzene isomers with photochemically-generated hydroxyl radical and ozone were estimated using the U.S. EPA AOPWIN v1.92a software. The model indicated no difference in reactivity among the o-, m-, and p-isomers of the DVB and EVB components, and that reactions with EVB had the longest predicted half-lives among the DVB and EVB substances. The QSAR model was shown to give estimated reaction rate constants which were within a factor of approximately 2 of measured rate constants for structural analogs, styrene and ethylbenzene. The overall atmospheric half-life for the DVB-HP, -63, and -55 substances is estimated to be 6.3 hours. Although the components of the substance can be expected to absorb sunlight at wavelengths > 290 nm, there is no evidence to suggest that direct photolysis would be a more important or more rapid process, than estimated for these indirect photolytic reactions.