2,2-dimethyl-1,3-dioxolan-4-ylmethanol

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 8 November 2013 to 5 February 2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study performed according international guidelines. No deviation from the guidelines was observed during the test.

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 830.7370 (Dissociation constants in water)

Deviations:

no

GLP compliance:

yes

Dissociating properties:

yes

No.:

#1

pKa:

> 6.4 - < 6.64

Temp.:

20 °C

Remarks on result:

other: Value obtained with basic titration

No.:

#1

pKa:

> 6.32 - < 6.42

Temp.:

20 °C

Remarks on result:

other: Value obtained with acid titration

Previous testing with the test substance in reagent water (~0.01 M) indicated the test substance was very water soluble and possessing a slightly acidic pH. The test substance was a clear, colorless liquid with no suspended material noted. Prior to sample weighing, the test substance was mixed via inversion.

The definitive test solutions were checked for the Tyndall effect – none was noted in any of the samples.

Two titration schemes were performed; each gave a unique dissociation constant. Each basic titration dissociation constant value (pKa) was calculated using fifteen data points prior to each equivalence point. The data obtained for different sample (with basic titration) are shown below:

Sample I.D. Number (411C-108-)	Nominal concentration (moles/L)	Water Bath temperature (°C)	Equivalence point (pH)	Titrant volume (mL)	pKa	Mean pKa	Standard deviation
3	0.00941	20.0	8.139	2.600	6.531	6.52	0,12 (CV= 1,83%)
4	0.00944	20.0	8.008	2.200	6.6874
5	0.00940	20.0	7.759	2.700	6.3718
7	0.00928	20.0	7.882	2.500	6.5603
8	0.00923	20.0	8.051	2.800	6.4495

Each acidic titration dissociation constant value (pKa) was calculated using six data points prior to each equivalence point.

The data obtained for different sample (with basic titration) are shown below:

Sample I.D. Number (411C-108-)	Nominal concentration (moles/L)	Water Bath temperature (°C)	Equivalence point (pH)	Titrant volume (mL)	pKa	Mean pKa	Standard deviation
12	0.00931	20.0	5.967	1.000	6.3723	6.37	0,05 (CV= 0.71%)
14	0.00919	20.0	6.127	1.000	6.4188
15	0.00922	20.0	5.928	1.000	6.3288

With both titration schemes, the number of data points was limited due to the solution pH being so close to the pKa. This was especially evident with the acidic titration testing. Although a pKa value was determined for both the acidic and basic titrations, due to the native solution pH of the test substance being slightly acidic, the basic titration should take precedent. Additionally, the basic titrations had significantly more data points used to determine its pKa value. The mean values generated from each titration scheme are for all practical purposes, statistically equivalent.

Conclusions:

The dissociation constant value (pKa) of the test substance at 20°C is 6.52.

Executive summary:

The dissociation constant value (pKa) was performed according to OPPTS 830.7370,OECD guideline 112 and GLP. No deviation from the guidelines was observed during the test.

Before the determination of pKa for the test substance, a reference substance was used for instrument verification. The calculated pKa for the reference substance was consistent with literature values. So, the apparatus was considered acceptable for use.

The titration method was used to determine the dissociation constants K of the test substance in reagent water. Based on the native slightly acidic pH of the test substance, a solution of the test substance in water was titrated both with a standardized base (sodium hydroxide) and a standardized acid (hydrochloric acid). The pH of the test solution was monitored and plotted as a function of titrant volume added to the test solution. The titration was continued through the equivalence points of the dissociation reactions of the test substance. The dissociation constant is equal to the pH of the test substance at the half-neutralization point, where the concentrations of the ionized and unionized species of the test substance were equivalent. Prior to use, all of the reagent water used in the study was degassed with nitrogen to remove carbon dioxide.

Although a pKa value was determined for both the acidic and basic titrations, due to the native solution pH of the test substance being slightly acidic, the basic titration should take precedent. The dissociation constant value (pKa) of the test substance at 20°C is 6.52.

Description of key information

Experimental value of pKa at 20°C: 6.52 +/- 0.12 (1.83%)

Key value for chemical safety assessment

pKa at 20°C:

6.52

Additional information

The dissociation constant value (pKa) was performed according to OPPTS 830.7370,OECD guideline 112 and GLP. No deviation from the guidelines was observed during the test.

Before the determination of pKa for the test substance, a reference substance was used for instrument verification. The calculated pKa for the reference substance was consistent with literature values. So, the apparatus was considered acceptable for use.