Benzenesulfonamide, N-[2-[[(phenylamino)carbonyl]amino]phenyl]-

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2022-02-08

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Version / remarks:

1981

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Dissociating properties:

yes

No.:

#1

pKa:

7.6

Temp.:

20 °C

Spectra of the pH 2.9 (unionised form) and pH 10.1 (ionised form) test solutions was examined in 282-292 nm range. Greatest difference between the absorbance curves was found at 286.5 nm, therefore this wavelength was chosen for the evaluation.

The pH and absorbance values corresponding to 286.5 nm were tabulated and plotted.

pKa was calculated with the following formula:

pK_a= pH – log (A_HA-A)/(A-A_A-)

 

where      pK_a         negative base-10 logarithm of the acid dissociation constant

                  pH          pH measured for the test solution

                  A            absorbance measured for the test solution

                  A_HA         absorbance measured for the unionised form

                  A_A-          absorbance measured for the ionised form

 

Absorbance of the test solutions and the calculated pKa values are summarised in the following table.

pH	Absorbance	pKa
6.84	0.433	7.54
7.05	0.432	7.76
7.24	0.534	7.65
7.44	0.625	7.64
7.57	0.694	7.63
7.76	0.759	7.69
7.90	0.868	7.60
8.32	1.011	7.63
Mean		7.64
Standard deviation		0.06

Conclusions:

The dissociation constant of the test item in water was determined to be 7.64 at 20 °C.

Executive summary:

A study was conducted according to OECD Guideline 112 to determine the dissociation constant of the test item using the spectrophotometric method. A volume of 2.5 mL of the stock solution (0.5 mg/mL; dissolved in acetonitrile) was added to 25 mL of the various buffer solutions. UV absorption spectra of all the test solutions were recorded in 190 – 400 nm wavelength range. Control solutions containing acetonitrile were used as the reference. Spectra of the pH 2.9 (unionised form) and pH 10.1 (ionised form) test solutions was examined in 282-292 nm range. Greatest difference between the absorbance curves was found at 286.5 nm, therefore this wavelength was chosen for the evaluation. The dissociation constant of the test item in water was determined to be 7.64 at 20 °C.

Description of key information

The dissociation constant of the test item in water was determined to be 7.64 at 20 °C.

Key value for chemical safety assessment

pKa at 20°C:

7.64

Additional information

A study was conducted according to OECD Guideline 112 to determine the dissociation constant of the test item using the spectrophotometric method. A volume of 2.5 mL of the stock solution (0.5 mg/mL; dissolved in acetonitrile) was added to 25 mL of the various buffer solutions. UV absorption spectra of all the test solutions were recorded in 190 – 400 nm wavelength range. Control solutions containing acetonitrile were used as the reference. Spectra of the pH 2.9 (unionised form) and pH 10.1 (ionised form) test solutions was examined in 282-292 nm range. Greatest difference between the absorbance curves was found at 286.5 nm, therefore this wavelength was chosen for the evaluation. The dissociation constant of the test item in water was determined to be 7.64 at 20 °C.