3,5,5-trimethylhexanoic acid

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-06-07 to 2018-06-11

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:

Adopted May 1981

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EU method A.25

Version / remarks:

COMMISSION REGULATION (EU) 2017/735 of 14 February 2017, amending COMMISSION REGULATION (EC) No 440/2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Dissociating properties:

yes

No.:

#1

pKa:

4.74

Temp.:

20 °C

Remarks on result:

other: Run 1

No.:

#2

pKa:

4.96

Temp.:

20 °C

Remarks on result:

other: Run 2

No.:

#3

pKa:

4.84

Temp.:

20 °C

Remarks on result:

other: Run 3

No.:

#4

pKa:

4.8

Temp.:

20 °C

Remarks on result:

other: mean value of run 1 to 3

Tables 1 to 3 present the raw data generated during this test. These data were plotted (abscissa: volume base added; ordinate: measured pH) and graphically evaluted to determine the end point volume, 1/2 endpoint volume and pKa based on pH at 1/2 of the endpoint volume. See the attached figure for an example evaluation.

Included in the tabulated data below are the end point volumes for each titration and the pH at half of the end point volume (equivalent to the pKa value).

iso-Nonanoic acid (3,5,5-Trimethylhexanoic acid) was determined to have a pKa value of 4.8 (mean of 4.7, 5.0 and 4.8). The repeatability of ± 0.1 units satisfied the requirement of the test method.

Table1:            Dissociation Constant Results for Run 1

Titre (mL)		pH
0.000	5.534	3.792	9.809
0.010	5.758	3.793	9.978
0.020	6.030	3.794	10.144
0.030	6.340	3.798	10.275
0.166	6.724	3.846	10.415
0.460	7.138	3.968	10.520
0.822	7.626	4.115	10.633
1.214	8.132	4.259	10.729
1.626	8.678	4.415	10.800
2.032	9.290	4.547	10.875
2.470	9.912	4.740	10.946
2.846	10.544	4.886	10.996
3.226	11.228	5.069	11.051
3.534	11.910	5.247	11.096
3.812	12.614	5.441	11.139
4.048	13.328	5.643	11.176
4.238	14.058	5.871	11.213
4.332	14.790	6.017	11.243
4.414	15.540	6.154	11.276
4.554	16.284	6.484	11.302
4.592	17.044	6.490	11.324
4.606	17.816	6.624	11.350
4.616	18.580	6.624	11.355
4.626	19.400	6.650	11.391
4.638	20.000	6.652	11.399
5.132		9.252
5.194		9.377
5.206		9.415
5.226		9.455
5.356		9.632

End point volume, V = 4.86 mL ½ V = 2.43 mL pH at ½ V =4.74 pKa= 4.74

Table2 :           Dissociation Constant Results for Run 2

Titre (mL)		pH
0	7.432	4.039	10.791
0.010	7.976	4.036	10.880
0.020	8.548	4.042	10.963
0.030	9.142	4.043	11.030
0.104	9.776	4.048	11.086
0.786	10.446	4.387	11.101
1.138	11.232	4.524	11.197
1.462	11.854	4.654	11.237
1.856	12.482	4.807	11.250
2.256	13.212	4.956	11.310
2.666	13.890	5.132	11.341
3.046	14.630	5.326	11.370
3.356	15.382	5.519	11.382
3.612	16.182	5.722	11.418
3.802	16.924	5.730	11.449
3.842	17.672	5.968	11.456
3.852	18.450	5.974	11.489
3.862	19.196	5.982	11.501
4.022	19.996	6.246	11.523
4.176	20.002	6.249	11.529
4.958		9.692
4.968		9.702
4.980		9.710
5.078		9.854
5.246		10.013
5.478		10.171
5.768		10.326
6.104		10.462
6.496		10.588
6.936		10.696

End point volume, V = 4.57 mL ½ V = 2.28 mL pH at ½ V = 4.96 pKa = 4.96

Table 3:            Dissociation Constant Results for Run 3

Titre (mL)		pH
0	6.382	3.943	10.481
0.010	6.794	3.944	10.590
0.020	7.274	3.947	10.695
0.030	7.792	3.951	10.793
0.328	8.338	4.099	10.871
0.680	8.934	4.250	10.942
1.028	9.560	4.390	11.007
1.422	10.206	4.539	11.065
1.828	10.874	4.695	11.112
2.232	11.572	4.840	11.161
2.650	12.270	5.008	11.205
3.044	12.980	5.191	11.250
3.384	13.690	5.370	11.278
3.702	14.442	5.582	11.312
3.930	15.184	5.786	11.330
4.078	15.966	5.958	11.362
4.196	16.716	6.133	11.381
4.288	17.496	6.274	11.407
4.448	18.260	6.622	11.426
4.490	19.040	6.928	11.452
4.500	19.804	6.921	11.473
4.510	20.000	6.921	11.478
5.164		9.689
5.238		9.800
5.250		9.801
5.270		9.833
5.424		9.997
5.638		10.144
5.734		10.208
6.026		10.350

End point volume, V = 4.74 mL ½ V = 2.37 mL pH at ½ V = 4.84 pKa = 4.84

Conclusions:

pKa (OECD 112; titration method): 4.8 at 20°C, based on acidic functionality

Executive summary:

The pKa for 3,5,5 -trimethyhexanoic acid was determined in a reliable study performed according to OECD 112 compliant with GLP, following the potentiometric titration method.

Three titration runs were performed, each consisting of at least 49 titration steps, with the following results:

Run 1: pKa 4.74 (20 +/- 1 °C)

Run 2: pKa 4.96 (20 +/- 1 °C)

Run 3: pKa 4.84 (20 +/- 1 °C)

In conclusion, iso-nonanoic acid (3,5,5 -trimethylhexanoic acid) was found to have a pKa (acidic functionality) value of 4.8 at 20ºC (mean value of three runs). The repeatability of ± 0.1 units satisfied the requirement of the test method.

Description of key information

pKa (OECD 112; titration method): 4.8 at 20°C, based on acidic functionality

Key value for chemical safety assessment

pKa at 20°C:

4.8

Additional information

The pKa for 3,5,5 -trimethyhexanoic acid was determined in a reliable study performed according to OECD 112 compliant with GLP, following the potentiometric titration method.

Three titration runs were performed, each consisting of at least 49 titration steps, with the following results:

Run 1: pKa 4.74 (20 +/- 1 °C)

Run 2: pKa 4.96 (20 +/- 1 °C)

Run 3: pKa 4.84 (20 +/- 1 °C)

In conclusion, iso-nonanoic acid (3,5,5 -trimethylhexanoic acid) was found to have a pKa (acidic functionality) value of 4.8 at 20ºC (mean value of three runs). The repeatability of ± 0.1 units satisfied the requirement of the test method.