Potassium cyanate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

from 2009-12-11 to 2009-12-16

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

13 April 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Version / remarks:

Regulation 440/2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were diluted with buffer and water to fit the calibrated range. The pH value if the diluted samples was adjusted to pH 4.5. 2-aminobenzoic acid and then hydrochloric acid solution was added and the solution was thermostated.

Buffers:

All buffers were diluted with ultra-pure water and adjusted with 0.2 M Sodium hydroxide.
pH 4.0: 0.2 M Potassium hydrogen phthalate
pH 7.0: 0.2 M Potassium dihydrogen phosphate
pH 9.0: 0.2 M Boric acid and Potassium chloride

Details on test conditions:

Temperature: 50 °C ± 0.5 °C
Light and oxygen: the reaction was carried out using a dark thermostat to avoid photolytic effects. Nitrogen was bubbled into the water for 5 minutes before the preparation of the solutions in order to exclude oxygen.
All glassware, water and buffer solutions were sterilised.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

ca. 305 mg/L

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

ca. 381 mg/L

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

ca. 377 mg/L

Number of replicates:

five

Negative controls:

yes

Remarks:

control buffer

Statistical methods:

Calculation and construction of the calibration curves were carried out using "EXCEL for Windows".

Preliminary study:

The hydrolysis rate of the test item was found to be 47 % at pH 9 and approximately 100 % at pH 4 and 7. For the latter concentrations were below the detection limit after 5 days.

Transformation products:

not measured

% Recovery:

0

pH:

4

Temp.:

50 °C

Duration:

5 d

% Recovery:

0

pH:

7

Temp.:

50 °C

Duration:

5 d

% Recovery:

53

pH:

9

Temp.:

50 °C

Duration:

5 d

Key result

pH:

7

Temp.:

50

DT50:

< 5 d

Type:

not specified

Analysis of Samples

The content of potassium cyanate in the different pH buffer samples was determined at the beginning and the end of hte test periods. Three samples were taken and analysed at the starf of the study. Five samples were taken from five separate tubes of the hydrolysis test and were anaylsed after 120 hours. Sample volume was 1 mL. This was diluted fivefold at the start of the study. At the end of the preliminary test the samples of buffer solution pH 9 were diluted fivefold. The samples of buffer solution pH 4 were analysed without dilution. The samples of buffer solution pH 7 were diluted twofold. One sample was taken from the control vessel anddiluted in the same way as the samples.

 

Measured data at a temperature of 50 °C at the start and after 120 hours

pH	Sampling time (hour)	Concentration of potassium cyanate  (mg/L )			Hydrolysis (%)	Measured pH
		Test vessels	Mean withthe 95% confidence intervals
4	Start	Control buffer			-	4.00
		293	305 ± 16.5		-	4.05
		316				4.05
		306				4.10
	120	Control buffer			-	4.05
		< LOQ	< LOQ		100	4.42
		< LOQ				4.44
		< LOQ				4.42
		< LOQ				4.44
		< LOQ				4.40
7	Start	Control buffer			-	7.00
		372	381 ± 10.9		-	7.02
		383				7.02
		387				7.03
	120	Control buffer			-	7.04
		< LOQ	< LOQ		100	7.25
		< LOQ				7.30
		< LOQ				7.28
		< LOQ				7.30
		< LOQ				7.25
9	Start	Control buffer			-	9.00
		390	377 ± 33.1		-	8.98
		391				8.98
		351				8.99
	120	Control buffer			-	8.98
		198		198 ± 2.3	47	9.01
		204				9.03
		197				9.02
		201				9.02
		193				9.03

 

Validity criteria fulfilled:

yes

Conclusions:

Based on the results of the preliminary test the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %.

Executive summary:

Purpose

The purpose of this study was to evaluate the hydrolysis of potassium cyanate in different pH buffer solutions.

Results:

Based on the results the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

from 2008-12-02 to 2009-06-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Water solubility (IUCLID section 4.8)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
water solubility: 96.4 g/L

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis.
1.0 mL of the diluted sample was mixed with 1.0 mL of 0.02-molar anthranilic acid and kept at 40 °C for 10 minutes. Then, 2 mL HCl 37% were added, the solution was heated to 100 °C for 1 minute and then left to cool down to room temperature.

Buffers:

Deionised water (conductivity below 0.1 µS/cm and TOC below 5 ppm) was used for the test (commercially available doubly distilled water guarantees conductivity as large as 5 µS/cm).

Details on test conditions:

In a water solubility study also hydrolysis was observed and recorded at 20 °C.

Duration:

7 d

Temp.:

20 °C

Initial conc. measured:

97.06 mg/L

Number of replicates:

2 Experiments with different sampling times (one sample each).

Positive controls:

no

Negative controls:

no

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

Qualitative analysis of the remaining solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time.

Key result

pH:

10

Temp.:

20 °C

DT50:

7 d

Type:

not specified

Other kinetic parameters:

Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20 °C. This DT50 corresponds to 13 days at 12 °C.

Day	Absorption diluted sample	Concentration in flask	Difference to previous sample	pH
#	310 nm	g/L	%	---
3	0.93045	90.6	---	approx. 10
4	0.79955	78.0	-14.0	approx. 10
5	0.69131	67.5	-13.4	approx. 10
6	0.57957	56.7	-16.0	approx. 10
7	0.47523	46.6	-17.8	approx. 10

 

Validity criteria fulfilled:

not applicable

Conclusions:

Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20 °C. This DT50 corresponds to 13 days at 12 °C.

Executive summary:

In a water solubility study also hydrolysis was observed and recorded at 20 °C. Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis. Qualitative analysis of the solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time. Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20 °C. This DT50 corresponds to 13 days at 12 °C.

Description of key information

Based on the results of the preliminary test the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %. From a water solubility study with the structural analogue sodium cyanate a DT50 of 13 d at 12 °C could be extrapolated. This value is used as worst case value in the risk assessment.

Key value for chemical safety assessment

Half-life for hydrolysis:

13 d

at the temperature of:

12 °C

Additional information

In a screening study (Gaal, 2010), the hydrolysis of potassium cyanate in different pH buffer solutions was evaluated. Based on the results of the test, the hydrolysis rate of potassium cyanate was found to be 47 % at pH 9 after 5 days at 50 °C. Hydrolysis rates at pH 4 and pH 7 were approximately 100 %. This finding is supported by the study of Hartley (1983), where it could be shown that potassium cyanate is hydrolyzed to ammonia and potassium bicarbonate.

In a water solubility study with the structural analogue sodium cyanate also hydrolysis was observed and recorded at 20 °C. Samples were taken and measured after 2, 4, 7.5, 24 and 30 hours and on days 4, 5, 6 and 7 in order to collect information about the kinetics of hydrolysis. Qualitative analysis of the solution showed presence of ammonia, which could not be detected in a freshly prepared solution of the test item. Literature also describes hydrolysis of cyanates to ammonia and carbon dioxide with time. Cyanates decompose in aqueous solutions forming ammonia and carbonate. This process started after the sampling of day three. A DT50 of 7 days could be estimated from the measured concentrations at 20 °C. This DT50 corresponds to 13 days at 12 °C.

Taking all available data together a worst case DT50 of 13 d at 12 °C could be concluded