3,3'-sulphonyldianiline

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24 August 2011 - 17 November 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study has been performed according to an OECD guideline and in compliance with GLP principles.

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:

3.1

Remarks on result:

other: calculated value based on molecular structure; basic group: RC6H4NH3+.

Remarks:

Temperature is not specified.

No.:

#2

pKa:

2.18

Remarks on result:

other: calculated value based on molecular structure; basic group: RC6H4NH3+.

Remarks:

Temperature is not specified.

Search for spectra of the pure molecule and the pure anion

Attempts were made to determine the pK_avalues of the separable–NH₂group in the test substance, thus a basic group.

 

The spectra recorded at pH 4 till pH 13 were comparable. The spectra recorded at pH 0, pH 1, pH 2 and pH 3 had different forms and are therefore called intermediate spectra. It was concluded that spectra recorded at pH>4 are of the non-ionized test substance, whereas spectra recorded at pH<4 are a combination of the ionized test substance and its non-ionized form.

Choice of an analytical wavelength

From comparing the spectra of the ionized substance with the spectra of the non-ionized substance, it was concluded that the difference in optical absorbance is maximal at 305 nm. Hence 305 nm was chosen as the analytical wavelength.

 

Only one wavelength could be selected though two pKa’s have to be determined which only differ by approximately 1 log unit. In principle, two specific wavelengths are required, one for each dissociation reaction. In order to test the applicability of the method, the study was continued.

Search for an approximate pK_avalue

The optical absorbances at 305 nm were determined. As well as the actual pH values of the test solutions and actual pH values of the reference solutions. From these absorbances and the actual pH value, the approximate pK_avalue was calculated. Actual pH values and optical absorbances at 305 nm.

actual pH values of the reference solutions	actual pH values of the test solutions	Absorbance for the test solution [units]	pKavalue
0.19	0.19	0
1.02	1.05	0.020	1.99
2.17	2.16	0.072	2.39
3.11	3.13	0.149	2.61
4.11	4.12	0.184	2.86
5.08	5.09	0.184	3.83
6.12	6.11	0.192	4.13
7.13	7.13	0.186	5.76
8.01	8.06	0.193	5.77
9.06	9.07	0.184	7.81
10.02	10.03	0.186	8.66
10.84	10.84	0.186	9.47
11.65	11.68	0.189	10.10
12.81	12.85	0.194

No approximate pK_avalue could be calculated from above results because the pK_avalues were not within ±0.1 log units as required. This is probably caused as the results were influenced by two pKa values which are close together. Since a specific wavelength was not found for each dissociation reaction, the spectrophotometric method cannot be used for the determination of the dissociation constants of 3,3’-DDS.

 

Due to the low water solubility of 3,3’-DDS, the titration method is also not feasible for this test substance. Therefore, the calculated pK_avalues will be given as the final result.

 

Using the Perrin calculation method, the following pK_avalues in the logarithm range of 1 - 14 for acidic and basic groups in the molecular structure of the test substance were calculated:

acidic: none

basic:

RC6H4NH3+ : pKa 3.10

RC6H4NH3+ : pKa 2.18

Conclusions:

The pKa value for 3,3’-DDS could not to be determined using the spectrophotometric method. In view of the relatively low water solubility of the substance, the titration method was also considered to be not feasible to perform. Alternatively, the calculation method was used to estimate possible pKa values. In the logarithm range of 1 - 14 two pKa values for a basic group in the molecular structure of the test substance were calculated: 3.10 and 2.18.

Description of key information

DETERMINATION OF PHYSICO-CHEMICAL PROPERTIES OF 3,3’-DDS, project 496966, 2011
Dr. Ir. E. Baltussen.
Study performed according to an OECD guideline 112 and in compliance with GLP principles.

Additional information

In the logarithm range of 1 - 14 two pKa values for a basic group in the molecular structure of the 3,3'-DDS were calculated : 3.10 and 2.18.