Desmedipham

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-10-18 to 2012-12-06

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

no

Principles of method if other than guideline:

UV/VIS — absorption spectrum of the dissociated and undissociated forms of the chemical substance. In the particular case, described in the OECD Test Guideline 112, the test item is behaving as an acid or base, and the determination is most conveniently done by determining the different extinction coefficients (absorption) of ionised and unionised forms of the test item and the pH of the solution.
Dissociation is the reversible splitting into two or more chemical species which may be ionic by
RX <-> R+ + X-

The concentration equilibrium constant governing the reaction is
K= [R+][X-] /[ RX]

GLP compliance:

yes

Dissociating properties:

yes

No.:

#1

pKa:

0

Temp.:

23 °C

Remarks on result:

not determinable

Table 2: Details of experiment A

Experiment	Volume and concentration of added I-ICI	Resulting pH value
		5.82
	0.5 mc- 1.0 mol/L	1.95

An overlay plot of the UV/VlS-spectra is given in Section 8, Figure 1

This means (according to Section 4.2) that no dissociation equilibrium occurred for Desmedipham, pure substance in the pH range 2 < pH < 6.

This result is equivalent to the conclusion that Desmedipham, pure substance, showed no pKa value in the range 2 < pKa < 6.

Conclusions:

The result is acceptable. No dissociation constant pKa was found in aqueous solution of Desmedipham (AE B038107), pure substance, in the pH-range of 2 < pH < 6.

At pH values above pH 7 a rapid hydrolysis of Desmedipham takes place.

Executive summary:

Test Guideline: Based on OECD Test Guideline 112, US EPA Product Properties Test Guideline OCSPP 830.7370

The dissociation constant of Desmedipham was examined using a spectrophotometric method based on the OECD-Guideline 112 and the US EPA Product Properties Test Guideline OCSPP 830.7370.

Due to the lack of stability above pH 7, the UV/VIS spectra of the test item were recorded at pH 1.95 and pH 5.82 at room temperature (approx. 23°C).

The UV/VIS spectra were almost congruent, taking the UV absorption of aqueous hydrochloric acid into account. No relevant difference was found between the UV/VIS absorption at the examined pH values.

Result:

No dissociation constant pKa was found in aqueous solution of Desmedipham, pure substance, in the pH-range of 2 < pH < 6. At pH values above pH 7 a rapid hydrolysis of Desmedipham takes place

This finding corresponds to the result that Desmedipham, pure substance, shows no acidic or basic properties in the range of approximately 2 < pKa < 6.

Description of key information

No dissociation constant pKa was found in aqueous solution of Desmedipham, pure substance, in the pH-range of 2 < pH < 6. At pH values above pH 7 a rapid hydrolysis of Desmedipham takes place