1-[(4-chlorophenyl)methyl]-1-cyclopentyl-3-phenylurea

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-11-17

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA OPPTS 830.7370 (Dissociation constants in water)

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

no

Principles of method if other than guideline:

According to the OECD Guideline for Testing of Chemicals No. 112 and the EPA Product Properties Test Guideline OPPTS 830.7370, the spectrophotometric method is applicable to compounds having appreciably different UV / VIS – absorption spectra for the dissociated and un-dissociated forms.
The technique used in this study is able to deduce pKa values with high accuracy even if the absorption spectra of the reacting species are very similar.
A multi-wavelength spectrophotometric approach was developed by Sirius Analytical Instruments Ltd. to determine acid dissociation constants (pKa -values) of compounds with low solubility.
The pKa results are determined from changes in wavelength and absorption as a function of pH. A method called target factor analysis was applied to deduce the pKa values from the multi-wavelength UV absorption data recorded at different pH values.

UV absorption spectra data of the solution are acquired using a versatile device based on a fibre optics dip probe, a light source and a photodiode array detector. The pH of the chemical system is changed precisely by means of a commercially available titrator (at a constant ionic strength).

The optical system consists of a continuous deuterium lamp with fiber optics output, and a UV-VIS 256-element photodiode array detector. This combination offers a spectral range of 190 - 735 nm.

GLP compliance:

no

Remarks:

Spectrophotometric method performed. Although not performed to GLP, considered to have no impact on the overall result as modelling software predicts the same result.

Dissociating properties:

not determined

The dissociation constant of Pencycuron (NTN 19701) was examined by using a spectrophotometric screening method based on the OECD Guideline 112 and EPA Product Properties Test Guideline OPPTS 830.7370.

 

An instrument for pKa screening measurements – Instrument type GLpKa with D-Pas (Dip Probe Absorption Spectroscopy) provided by Sirius Analytical Instruments Ltd. (UK) was used.

Result:No dissociation constant of Pencycuron could be detected in the range between 2 < pKa < 12.

Conclusions:

No dissociation constant of Pencycuron could be detected in the range between 2 < pKa < 12.

Executive summary:

The dissociation constant of Pencycuron (NTN 19701) was examined by using a spectro-photometric screening method based on the OECD Guideline 112 and EPA Product Properties Test Guideline OPPTS 830.7370. The experimental work was performed by Dr. M. Kaußmann (PT - Analytics Monheim). An instrument for pKa screening measurements from Sirius Analytical Instruments Ltd (UK) was used (type GLpKa with D-Pas, Dip Probe Absorption Spectroscopy).

Result: No dissociation constant of Pencycuron (NTN 19701) could be detected in the range between 2 < pKa < 12.

Description of key information

No dissociation constant in the range pH 2 to 12