β-methyl-3-(1-methylethyl)benzenepropanal

Phototransformation in air

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in air

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Study period:

16 October, 2019

Reliability:

4 (not assignable)

Guideline:

other: QSAR : AOP Program (v1.92) module of EPISuite (v4.11)

Principles of method if other than guideline:

QSAR evaluation :

Description taken from Introduction section of AOPWIN module in EPISuite (v4.11) : https://www.epa.gov/tsca-screening-tools/download-epi-suitetm-estimation-program-interface-v411

The Atmospheric Oxidation Program for Microsoft Windows (AOPWIN) estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals.  It also estimates the rate constant for the gas-phase reaction between ozone and olefinic/acetylenic compounds. The rate constants estimated by the program are then used to calculate atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone.

The estimation methods used by AOPWIN are based upon the structure-activity relationship (SAR) methods developed by Dr. Roger Atkinson and co-workers (Atkinson, 1985, 1986, 1987, 1991; Atkinson and Carter, 1984; Biermann et al, 1985; Kwok et al, 1992, Kwok and Atkinson, 1995; Kwok et al, 1996).   AOPWIN incorporates updated fragment and reaction values as cited in Kwok and Atkinson (1995).  In addition, Syracuse Research Corporation has derived some additional fragment and reaction values from new experimental data.

A journal article that discusses the Atmospheric Oxidation Program has been published (Meylan and Howard, 1993).

AOPWIN requires only a chemical structure to make these predictions.  Structures are entered into AOPWIN by SMILES (Simplified Molecular Input Line Entry System) notations.  A discussion of the encoding rules for SMILES Notation can be found in the on-line help document "A Brief Description of SMILES Notation".
 
Hydroxyl Radical Reaction Half-Life Estimation
Since a chemical in the troposphere is usually at a very low concentration and a steady-state concentration of OH radicals is produced by sunlight, the hydroxyl radical concentration can be treated as a constant so the reaction can be considered a pseudo first-order reaction.

The half-life in the troposphere, t½ = 0.693/kOH[OH]

   where kOH is the hydroxyl radical rate constant in units of cm3/molecule-sec and [OH] is the hydroxyl radical concentration in units of molecules (or radicals) per cm3.  Thus, to calculate the half-life in the troposphere, one needs the estimated or measured rate constant of the chemical as well as some average OH radical concentration. In a U.S. EPA review by Leifer (no date), the author concluded that the diurnally and annually averaged 12-h daylight hydroxyl radical concentration of 1.5 × 106 molecules (radicals)/cm3 should be used as the default in the AOPWIN program based upon data from Atkinson et al. (1990).  More recent reviews (Atkinson and Arey, 2003) have suggested 2.0 × 106 molecules (radicals)/cm3 12-hour daylight hydroxyl radical concentration.

Twelve hour daylight OH radical concentrations are reasonable for fast reacting chemicals but for chemicals that react more slowly (> a few days) 24 hours averages might be more appropriate. Atkinson (1985) suggested seasonally and diurnally 24 hour averaged hydroxyl radical concentrations at 298 K of:

 5 × 105 molecules/cm3 in the northern hemisphere and

 6 × 105 molecules/cm3 in the southern hemisphere

The AOPWIN program allows the user to select 12 or 24 hour time frames and any average hydroxyl radical concentrations, but the default is originally set at 1.5 × 106 molecules (radicals)/cm3 per 12-h of daylight.

GLP compliance:

no

Specific details on test material used for the study:

FLORHYDRAL :
SMILES Annotation : CCCCCOC(=O)c1c(O)cccc1

DT50:

0.251 d

Test condition:

Prediction of interaction with atmospheric Hydroxyl radicals.

Remarks on result:

other: Interaction with atmospheric Hydroxyl radicals. Based on 12-hours of daylight

Reaction with:

OH radicals

Rate constant:

0 cm³ molecule-1 s-1

Remarks on result:

other: Based on interactions with atmospheric Hydroxyl radicals and 12-hours of daylight per day

AOP Program (v1.92) Results:

===========================

SMILES : O=CCC(c1cccc(c1)C(C)C)C

CHEM  : FLORHYDRAL

MOL FOR: C13 H18 O1

MOL WT : 190.29

------------------- SUMMARY (AOP v1.92): HYDROXYL RADICALS (25 deg C) --------

Hydrogen Abstraction      = 31.6294 E-12 cm3/molecule-sec

Reaction with N, S and -OH =  0.0000 E-12 cm3/molecule-sec

Addition to Triple Bonds  =  0.0000 E-12 cm3/molecule-sec

Addition to Olefinic Bonds =  0.0000 E-12 cm3/molecule-sec

**Addition to Aromatic Rings = 10.9749 E-12 cm3/molecule-sec

Addition to Fused Rings   =  0.0000 E-12 cm3/molecule-sec

 

OVERALL OH Rate Constant = 42.6043 E-12 cm3/molecule-sec

HALF-LIFE =    0.251 Days (12-hr day; 1.5E6 OH/cm3)

HALF-LIFE =    3.013 Hrs

Conclusions:

OVERALL OH Rate Constant = 42.6043 E-12 cm3/molecule-sec

HALF-LIFE = 0.251 Days (12-hr day; 1.5E6 OH/cm3)
HALF-LIFE = 3.013 Hrs

Description of key information

QSAR Calculation - AOP Program (v1.92) Module of EPISuite (v4.11) :

OVERALL OH Rate Constant = 42.6043 E-12 cm3/molecule-sec

HALF-LIFE = 0.251 Days (12-hr day; 1.5E6 OH/cm3)

HALF-LIFE = 3.013 Hrs

Key value for chemical safety assessment

Half-life in air:

0.251 d

Degradation rate constant with OH radicals:

0 cm³ molecule-1 s-1

Additional information

QSAR Calculation - AOP Program (v1.92) Module of EPISuite (v4.11) :

OVERALL OH Rate Constant = 42.6043 E-12 cm3/molecule-sec

HALF-LIFE = 0.251 Days (12-hr day; 1.5E6 OH/cm3)

HALF-LIFE = 3.013 Hrs