3'-(trifluoromethyl)acetophenone

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

16 Oct to 05 Nov 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

GLP compliance:

yes

Dissociating properties:

no

The absorbance spectra recorded in 0.1 M hydrochloric acid, phosphate buffer solution and 0.1 M sodium hydroxide are identical. The same two characteristic absorbance maxima occur at 239 nm and 277 run in all three spectra, clearly demonstrating that there is no change in the absorption behaviour of the molecule and, consequently, that there can be no protonation or deprotonation of the test substance within the range pH 1.1 to pH 12.7.

Conclusions:

The test item does not have a dissociation constant within the pH range 2 to 12.

Executive summary:

A study was carried out in accordance with the OECD guideline number 112, dissociation constants in water, to assess the dissociation constant of the test substance.

A stock solution of the test substance was prepared in methanol with a concentration of 207.2 mg/L.

To obtain the spectra of the test substance in neutral solution, 5.0 mL of the stock solution were diluted to 100.0 mL with phosphate buffer solution pH 7.0 (composition: 0.041 M disodium hydrogen phosphate and 0.028 M potassium dihydrogen phosphate). The measured pH value of the prepared test solution was 7.0. To obtain the spectra in acidic solution (pH 1) and in basic solution (pH 13) 5.0 mL of the stock solution were diluted, as appropriate, to 100.0 mL with 0.1 M hydrochloric acid and 0.1 M sodium hydroxide. The measured pH values of these test solutions were 1.1 and 12.7 respectively.

The final concentration of the test substance in all three test solutions was 10.4 mg/L.

To record the spectra a Hitachi U-3200 spectrophotometer was used with quartz cells of 10 mm path length.

For each test solution absorption spectra were recorded in the range 200 nm to 400 nm.

The absorbance spectra recorded in 0.1 M hydrochloric acid, phosphate buffer solution and 0.1 M sodium hydroxide are identical. The same two characteristic absorbance maxima occur at 239 nm and 277 run in all three spectra, clearly demonstrating that there is no change in the absorption behaviour of the molecule and, consequently, that there can be no protonation or deprotonation of the test substance within the range pH 1.1 to pH 12.7.

Description of key information

A study was carried out in accordance with the OECD guideline number 112, Dissociation constants in water, to assess the dissociation constant of the test substance.

A stock solution of the test substance was prepared in methanol with a concentration of 207.2 mg/L.

To obtain the spectra of the test substance in neutral solution, 5.0 mL of the stock solution were diluted to 100.0 mL with phosphate buffer solution pH 7.0 (composition: 0.041 M disodium hydrogen phosphate and 0.028 M potassium dihydrogen phosphate). The measured pH value of the prepared test solution was 7.0. To obtain the spectra in acidic solution (pH 1) and in basic solution (pH 13) 5.0 mL of the stock solution were diluted, as appropriate, to 100.0 mL with 0.1 M hydrochloric acid and 0.1 M sodium hydroxide. The measured pH values of these test solutions were 1.1 and 12.7 respectively.

The final concentration of the test substance in all three test solutions was 10.4 mg/L.

For each test solution absorption spectra were recorded in the range 200 nm to 400 nm.

The absorbance spectra recorded in 0.1 M hydrochloric acid, phosphate buffer solution and 0.1 M sodium hydroxide are identical. The same two characteristic absorbance maxima occur at 239 nm and 277 run in all three spectra, clearly demonstrating that there is no change in the absorption behaviour of the molecule and, consequently, that there can be no protonation or deprotonation of the test substance within the range pH 1.1 to pH 12.7.