Calcium cyanamide

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1986-07-23 to 1987-09-25

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

not applicable

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

2.5, 5 and 10 min after start of the reaction.

Buffers:

pH 1.2: Dissolve 2.0 g of sodium chloride in 7 mL hydrochloric acid and fill up to 1000 mL with deionised water
pH 5: Weigh 21.014 g citric acid into a 1000 mL volumetric flask, dissolve with 200 mL sodium hydroxide solution (c = 1 mol/L), and make up to a volume with deionised water. Mix 960 mL of this solution with 40 mL sodium hydroxide solution (c = 0.1 mol/L).

Estimation method (if used):

no estimation method

Details on test conditions:

Procedure:
Weigh 10 mg of Calcium cyanamide, technical grade (Kalkstickstoff) into a 100 mL beaker, add 50 mL buffer solution, and stir on a magnetic stirrer. At the specified time, stop the reaction by filtration through a folded filter and pipette 5 mL of the filtrate into a 10 mL volumetric flask. Add 4 mL sodium hydroxide solution, make up to volume with deionised water and mix thoroughly. Take 1.3 mL of this test solution and determine the hydrogene cyanamide content.

Duration:

10 min

Temp.:

23 °C

Initial conc. measured:

200 mg/L

Number of replicates:

2 per time point and pH.

Positive controls:

no

Negative controls:

no

Statistical methods:

not indicated

Preliminary study:

Preliminary studies were run at pH 1.2 and 5. At both pH conditions the results clearly show that under the test conditions of this test hydrogene cyanamide is quantitatively released from its calcium salt within a few minutes.

Test performance:

No problems with test performance reported.

Transformation products:

yes

No.:

#1

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

Calcium cyanamide, technical grade (Kalkstickstoff) is quantitatively hydrolysed to Hydrogen cyanamide within a few minutes.

% Recovery:

3.6

pH:

1.2

Temp.:

23 °C

Duration:

2.5 min

% Recovery:

3.3

pH:

1.2

Temp.:

23 °C

Duration:

5 min

% Recovery:

3.9

pH:

1.2

Temp.:

23 °C

Duration:

10 min

% Recovery:

8.1

pH:

5

Temp.:

23 °C

Duration:

2.5 min

% Recovery:

6.3

pH:

5

Temp.:

23 °C

Duration:

5 min

% Recovery:

4.4

pH:

5

Temp.:

23 °C

Duration:

10 min

Key result

pH:

5

Temp.:

23 °C

Remarks on result:

other: Already after 2.5 min only 8.1 % of the substance were still present.

Remarks:

It can be concluded that Calcium cyanamide is converted rapidly and practically quantitatively to hydrogen cyanamide within a few minutes.

Other kinetic parameters:

not reported

Details on results:

The results clearly show that under the test conditions of this test Hydrogen cyanamide is quantitatively released from its calcium salt within a few minutes.

Validity criteria fulfilled:

not specified

Conclusions:

The results clearly show that under the test conditions of this test hydrogen cyanamide is quantitatively released from its calcium salt within a few minutes.

Executive summary:

A hydrolysis study was performed using calcium cyanamide, technical grade (Kalkstickstoff) as starting material in strictly defined contact with acid solutions at pH values of 1.2 and 5, respectively. In order to get reliable and comprehensive information some preliminary studies were done followed by additional examinations under comparable conditions. From the results of all analytical examinations, it can be concluded that calcium cyanamide is converted rapidly and practically quantitatively to hydrogen cyanamide within a few minutes.

Reference 2

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Therefore, available data for the hydrolysis of hydrogen cyanamide in water are used in a read-across approach for the assessment of calcium cyanamide.
For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Reason / purpose for cross-reference:

read-across source

Preliminary study:

No preliminary study

Test performance:

No remarks

Transformation products:

no

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

Cyanamide was hydrolytically stable at 25 °C, regardless of the pH values. At higher temperatures cyanamide degraded at pH 9 with DT50 values of 7.2 hours at 80 °C and 302 hours at 50 °C. At pH 7 and pH 5 the hydrolysis was slower with estimated half-lives of 147 and 60.7 hours at 80 °C, respectively, and 563 and 1100 hours at 65/50 °C, respectively.

pH:

5

Temp.:

50 °C

Hydrolysis rate constant:

0 h-1

DT50:

1 100 h

Type:

(pseudo-)first order (= half-life)

pH:

5

Temp.:

80 °C

Hydrolysis rate constant:

0.01 h-1

DT50:

60.7 h

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

65 °C

Hydrolysis rate constant:

0 h-1

DT50:

563 h

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

80 °C

Hydrolysis rate constant:

0 h-1

DT50:

147 h

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0 h-1

DT50:

302 h

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

80 °C

Hydrolysis rate constant:

0.1 h-1

DT50:

7.2 h

Type:

(pseudo-)first order (= half-life)

pH:

5

Temp.:

22 °C

Hydrolysis rate constant:

0 h-1

DT50:

1 200 d

Type:

(pseudo-)first order (= half-life)

pH:

5

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

830 d

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

22 °C

Hydrolysis rate constant:

0 h-1

DT50:

2 300 d

Type:

(pseudo-)first order (= half-life)

Other kinetic parameters:

No other kinetic paramerters.
Due to

Details on results:

Test at 25 °C:
The concentration of cyanamide in the test solutions (pH 5, pH 7 and pH 9) at 25 °C remained nearly constant indicating that no degradation of cyanamide occurred at 25 °C, regardless of the pH value of the test solution. Therefore, additional tests were performed at higher temperatures (50/65 °C and 80 °C).
DT50 values for cyanamide:
The test substance hydrolysis is both pH and temperature dependent. The hydrolysis rate increased with increasing pH-value and temperature. Kinetic data was calculated using linear regression and assuming first-order kinetics. On the basis of the Arrhenius equation the rate constants and DT50 values at 22 °C and 25 °C were also calculated .

Hydrolytic degradation of cyanamide in sterile buffers at 50/65 °C and 80 °C:

pH	Temperature	Rate constant k [h^-1]	DT50 [hours]
5	50	0.00062	1100
	80	0.01141	60.7
7	65	0.00123	563
	80	0.00472	147
9	50	0.00229	302
	80	0.0966	7.2

Hydrolytic degradation of Cyanamide in sterile buffers at 22 °C and 25 °C, calculated on the basis of the Arrhenius equation:

pH	Temperature	Rate constant k [h^-1]	DT50 [days]
5	22	2.42 x 10^-5	1200
	25	3.48 x 10^-5	830
7	22	1.24 x 10^-5	2300
	25	1.77 x 10^-5	1630
9	22	3.55 x 10^-5	810
	25	5.93 x 10^-5	490

Validity criteria fulfilled:

yes

Conclusions:

Cyanamide was hydrolytically stable at 25 °C and pH values of 5, 7, and 9.
At higher temperatures cyanamide degraded at pH 9 with DT50 values of 7.2 hours at 80 °C and 302 hours at 50 °C. At pH 7 and pH 5 the hydrolysis was slower with estimated half-lives of 147 and 60.7 hours at 80 °C, respectively, and 563 and 1100 hours at 65/50 °C, respectively.

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Therefore, available data for the hydrolysis of hydrogen cyanamide in water are used in a read-across approach for the assessment of calcium cyanamide.
For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Executive summary:

The hydrolytic stability of cyanamide was studied in aqueous solutions buffered at pH values of 5, 7 and 9. Solutions containing cyanamide were prepared at nominal concentrations of 100 µg/mL and were incubated for up to 720 hours (30 days) at 25°C, 50°C or 65°C and 80°C under sterile conditions in the dark. Duplicate samples were analysed for each pH value. The rate of degradation of cyanamide was determined using linear regression assuming first-order reaction kinetics.

Cyanamide was hydrolytically stable at 25°C and pH values of 5, 7, and 9. Therefore, additional tests were performed at higher temperatures (50/65°C and 80°C). At higher temperatures cyanamide degraded at pH 9 with DT50 values of 7.2 hours at 80°C and 302 hours at 50°C. At pH 7 and pH 5 the hydrolysis was slower with estimated half-lives of 147 and 60.7 hours at 80 °C, respectively, and 563 and 1100 hours at 65/50 °C, respectively.

This information is used in a read-across approach in the assessment of the target substance.

For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Reference 3

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Therefore, available data for the stability of hydrogen cyanamide in acdic and basic media are used in a read-across approach for the assessment of calcium cyanamide.
For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Reason / purpose for cross-reference:

read-across source

pH:

0

Temp.:

25 °C

Hydrolysis rate constant:

0.002 min-1

DT50:

ca. 310.8 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Half-life calculated for cyanamide in 1 M nitric acid (strong acid)

pH:

0

Temp.:

25 °C

Hydrolysis rate constant:

0.002 min-1

DT50:

ca. 297.5 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Half-life calculated for cyanamide in 1 M perchloric acid (strong acid)

pH:

0

Temp.:

25 °C

Hydrolysis rate constant:

0.002 min-1

DT50:

ca. 320.3 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Half-life calculated for cyanamide in ca. 1 M nitric acid (strong acid). Concentration of cyanamide 0.214 M

pH:

1.5

Temp.:

85 °C

Hydrolysis rate constant:

0 s-1

DT50:

ca. 77 min

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Half-life calculated for the formation of urea from cyanamide in 0.02 M sulphuric acid (pH ca. 1.5). Concentration of cyanamide 0.02 M

pH:

12.5

Temp.:

20 °C

DT50:

ca. 11.5 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: 8 measured cyanamide concentrations in an alkaline solution (pH 12.2 - 12.4) at a temperature of 18 - 24 °C were used to calculate the half-life

Remarks:

The R add-on package mkin was used assuming a first-order reaction

Validity criteria fulfilled:

not applicable

Conclusions:

The evaluated literature confirms that cyanamide is hydrolytically instable at low pH and not stable in alkaline solution.

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Therefore, available data for the hydrolysis of hydrogen cyanamide in water are used in a read-across approach for the assessment of calcium cyanamide.
For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Executive summary:

The evaluated literature confirms that cyanamide is hydrolytically instable at low pH. It is postulated that cyanamide is converted to urea and eventually to carbon dioxide and ammonia in an acid-catalysed reaction. The decomposition of urea to carbon dioxide and ammonia (occurring at a much lower rate than the formation of urea from cyanamide) is considered the rate-determining step of the overall reaction. At a temperature of 25 °C and a concentration of strong acids of ca. 1 M (pH 0), half-lives in the range 310 – 320 min were derived for the hydrolysis of cyanamide. At pH ~1.5, a hydrolysis half-life of ~77 min at a temperature of 85 °C was observed.

Further, cyanamide is not stable in alkaline solution according to experimental results. The main reaction is the formation of dicyandiamide (dimerisation) from cyanamide. An estimated half-life at 18 - 24 °C of ca. 11.5 d for cyanamide can be calculated when using 8 measured concentrations in an alkaline solution (pH 12.2 - 12.4) within a period of 28 days.

This information is used in a read-across approach in the assessment of the target substance.

For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Reference 4

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2019-02-22

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD Series on Testing and Assessment No. 29: Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Version / remarks:

23 July 2001

Principles of method if other than guideline:

The test substance calcium cyanamide technical grade was dispersed in water to get a 10% aqueous suspension. Filled in a bottle this suspension was agitated on a shaker for defined times at ambient conditions. For each sampling date a separate bottle was prepared. At each sampling date the suspension was filtrated and the filtrate was analyzed for cyanamide, dicyandiamide, calcium and pH-value. The total period of the test was 28 days with 8 sampling dates (1, 2, 3, 4, 7, 14, 21 and 28 days).

GLP compliance:

no

Specific details on test material used for the study:

Calcium cyanamide technical grade

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: 8 sampling dates (days 1, 2, 3, 4, 7, 14, 21 and 28)
- Sampling method: For each sampling date a separate test bottle was prepared. At the relevant sampling date the bottle was carefully opened and the solid and the solution were separated by filtration. The filtrate was used for further analysis
- Sampling intervals/times for pH measurements: Days 1, 2, 3, 4, 7, 14, 21 and 28

Duration:

1 d

pH:

12.2

Remarks:

See Table 1 for further results

Duration:

2 d

pH:

12.1

Remarks:

See Table 1 for further results

Duration:

3 d

pH:

12.1

Remarks:

See Table 1 for further results

Duration:

4 d

pH:

12.2

Remarks:

See Table 1 for further results

Duration:

7 d

pH:

12.1

Remarks:

See Table 1 for further results

Duration:

14 d

pH:

12.2

Remarks:

See Table 1 for further results

Duration:

21 d

pH:

12.3

Remarks:

See Table 1 for further results

Duration:

28 d

pH:

12.4

Remarks:

See Table 1 for further results

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

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

Calcium cyanamide technical grade is tramsformed into cyanamide upon dissolution in water.
Cyanamide and dicyandiamide formed thereof are the main dissolved species formed from a calcium cyanamide technical grade in contact with water because of the high pH.

Other kinetic parameters:

An estimated half-life of ca. 11.5 d can be calculated for cyanamide when using the 8 measured concentrations of cyanamide in alkaline solution (pH 12.2 - 12.4) within a period of 28 days.

Details on results:

Table 1 shows the results of the different sampling dates from day 1 to day 28. Listed are the concentrations of cyanamide, dicyandiamide, calcium and the pH-value of the filtrate. Further species as result of side- or secondary reactions (such as urea, ammonia, N-cyanourea) have not been analysed.
The analysis results show, that cyanamide and dicyandiamide formed thereof are the main dissolved species formed from calcium cyanamide technical grade in contact with water. Side reactions of both species, forming urea, ammonia and others (not quantitatively determined in this study) account for the decrease of the sum of cyanamide and dicyandiamide.
Based on an initial calcium cyanamide content of 67.7% in the test item, only approx. 20% are still present after 28 days as cyanamide. As expected, the majority is dimerized to dicyandiamide.
The pH value of the filtrate remains almost constant at approx. 12 over the whole period of the test.
The calcium concentration fluctuates in the first week between 11 and 17 g/L, and decreased continuously to 4.6 g/L in the next 3 weeks. The reason has not been investigated, but it is probably the effect on solubility of calcium ions of hydrogen cyanamide, dicyandiamide and the other substances generated.

Table 1: Results for the transformation of test item in aqueous media as a function of time

Sampling date [days]	Cyanamide [g/L]	Dicyandiamide [g/L]	Calcium [g/L]	pH-value
1	35.3	2.49	12.8	12.2
2	32.2	4.96	16.9	12.1
3	29.1	7.32	14.9	12.1
4	26.5	9.17	14.1	12.2
7	21.8	12.9	11.4	12.1
14	15.0	17.0	7.4	12.2
21	11.0	19.3	6.0	12.3
28	7.76	20.5	4.6	12.4

Validity criteria fulfilled:

not applicable

Conclusions:

The analysis results show, that cyanamide and dicyandiamide formed thereof are the main dissolved species formed from calcium cyanamide technical grade in contact with water. Based on an initial calcium cyanamide content of 67.7% in the test item, only approx. 20% are still present after 28 days as cyanamide. As expected, the majority is dimerized to dicyandiamide.

Executive summary:

The intention of the test was to determine the solubility of calcium cyanamide technical grade in aqueous media. Due to the fact that calcium cyanamide reacts immediately with water, a determination of water solubility of the substance in its proper definition is not possible.

The test substance was dispersed in water to get a 10% aqueous suspension. Filled in a bottle this suspension was agitated on a shaker for defined times at ambient conditions. For each sampling date a separate bottle was prepared. At each sampling date the suspension was filtrated and the filtrate was analyzed for cyanamide, dicyandiamide, calcium and pH-value. The total period of the test was 28 days with 8 sampling dates (1, 2, 3, 4, 7, 14, 21 and 28 days).

The analysis results show, that cyanamide and dicyandiamide formed thereof are the main dissolved species formed from a calcium cyanamide in contact with water. Side reactions of both species, forming urea, ammonia and others (not quantitatively determined in this study) account for the decrease of the sum of cyanamide and dicyandiamide.

Based on an initial calcium cyanamide content of 67.7% in the test item, only approx. 20% are still present after 28 days as cyanamide. As expected, the majority is dimerized to dicyandiamide.

The pH value of the filtrate remains almost constant at approx. 12 over the whole period of the test.

The calcium concentration fluctuates in the first week between 11 and 17 g/L, and decreased continuously to 4.6 g/L in the next 3 weeks. The reason has not been investigated, but it is probably the effect on solubility of calcium ions of hydrogen cyanamide, dicyandiamide and the other substances generated.

 

Description of key information

Upon dissolution in water calcium cyanamide is fast transformed to hydrogen cyanamide. Therefore, available data for the hydrolysis of cyanamide are used in a read-across approach for the assessment of calcium cyanamide. For detailled description where read across is used/recommended and where it is preferrable to refain from read across, please see section 13.2 "read across justification for environmental endpoints" and "Scientific rationale for not using cyanamide as read-across substance for calcium cyanamide on toxicological endpoints"

Cyanamide is hydrolytically stable at 25 °C and pH 5,7, and 9 (Eskötter 1990). However, at low pH values cyanamide is hydrolysed to urea and eventually to carbon dioxide and ammonia in an acid-catalysed reaction, with half-lives of 310 – 320 min at pH 0 and 25 °C, or ~77 min at pH ~1.5 and 85 °C (Höhne, 2019). In alkaline solution (pH 12.2-12.4), cyanamide dimerises to dicyandiamide (Wildenauer, 2019) with an estimated half-live of 11.5 d at temperatures of 18-24 °C (Höhne, 2019).

Additional information

The transformation of calcium cyanamide to hydrogen cyanamide is experimentally confirmed by the study from Rust (1987). Results from the hydrolysis study at pH 1.2 and 5 clearly show that hydrogen cyanamide is quantitatively released from its calcium salt within a few minutes.

Available data for cyanamide show that the substance was hydrolytically stable at 25 °C and pH values of 5, 7, and 9. At higher temperatures cyanamide degraded at pH 9 with DT50 values of 7.2 hours at 80 °C and 302 hours at 50 °C. At pH 7 and pH 5 the hydrolysis was slower with estimated half-lives of 147 and 60.7 hours at 80 °C, respectively, and 563 and 1100 hours at 65/50 °C, respectively (Eskötter, 1990).

The study conducted by Wildenauer (2019) investigates the dissolution behaviour of calcium cyanamide technical grade in water. The test substance was dispersed in water to get a 10% aqueous suspension and samples were taken for up to 28 days. At each sampling, samples were filtered, and the filtrate was analysed for cyanamide, dicyandiamide, calcium and pH-value. The pH value of the filtrate remains almost constant at approx. 12 over the whole period of the test. The analysis results show, that cyanamide released from calcium cyanamide dimerizes to dicyandiamide in alkaline solution. Side reactions of both species (cyanamide and dicyandiamde), forming urea, ammonia and others (not quantitatively determined in this study) account for the decrease of the sum of cyanamide and dicyandiamide. From the 8 measured concentrations in an alkaline solution (pH 12.2 - 12.4) reported by Wildenauer (2019), an estimated half-life at 18 - 24 °C of ca. 11.5 d for cyanamide can be calculated (Höhne, 2019).

Besides, information on the hydrolysis of calcium cyanamide transformation product cyanamide at low pH is available (see Höhne, 2019): Cyanamide is converted to urea and eventually to carbon dioxide and ammonia in an acid-catalysed reaction. At a temperature of 25 °C and a concentration of strong acids of ca. 1 M (pH 0), half-lives in the range 310 – 320 min were derived for the hydrolysis of cyanamide. At pH ~1.5, a hydrolysis half-life of ~77 min at a temperature of 85 °C was observed.