Cyanamide

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1990-03-03 until 1990-08-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: BBA Merkblatt Nr. 55 I

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

no

Details on sampling:

No sampling

Buffers:

Buffers in pH 5, pH 7 and pH 9

Estimation method (if used):

The rate of degradation of Cyanamide was determined using linear regression assuming first-order reaction kinetics.

Details on test conditions:

- 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.

Duration:

720 h

Initial conc. measured:

100 other: µg/mL

Number of replicates:

Duplicate samples were analysed for each pH value.

Positive controls:

no

Negative controls:

no

Statistical methods:

Not applicable

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)

Key result

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 parameters.

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:

At 25 °C Cyanamide was hydrolytically stable at the investigated 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.

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, regardless of the pH values, 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.

Description of key information

It was shown in one hydrolysis study that the hydrolytic degradation of cyanamide under sterile conditions is both temperature and pH dependent. At 25 °C cyanamide was hydrolytically stable at the investigated pH values of 5, 7 and 9. At lower pH cyanamide hydrolyses while dimerization takes place at higher pH values.

Additional information

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.

The hydrolytic degradation of cyanamide under sterile conditions is both temperature and pH dependent. At 25 °C cyanamide was hydrolytically stable, regardless of the pH values, therefore, additional tests were performed at higher temperatures (50/65 °C and 80 °C). With increasing temperature and pH value of the buffer solutions cyanamide was degraded with DT50 values of 1100 h (pH 5), 563 h (pH 7), 302 h (pH 9) at 50 °C and 60.7 h (pH 5), 147 h (pH 7) and 7.2 h (pH 9) at 80 °C, respectively. The hydrolysis results are given in more details in the following table:

 

Guideline / Test method	pH	Temperature [°C]	Initial TS concentration, C0	Rate constant, K [h-1]	Half-life, DT50 [h]	Coefficient of correlation, r2	Reference
BBA Merkblatt Nr. 55 I; EPA-FIFRA 161-1	5	50	100 µg/ml	0.00062	1100	0.77	Eskötter, H. (1990)
		80		0.01141	60.7	0.98
	7	65		0.00123	563	0.97
		80		0.00472	147	0.99
	9	50		0.00229	302	0.96
		80		0.0966	7.2	0.99

In a supporting literature review (Höhne 2019) several publications were evaluated regarding the hydrolysis at acidic and alkaline pH values. 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.

 

According to experimental results cyanamide is not stable in alkaline solution. The main reaction is the formation of dicyandiamide (dimerisation) from cyanamide. An estimated half-life at 18 – 24 °C of 11.48 days can be calculated when using 8 measured cyanamide concentrations in an alkaline solution (pH 12.2 – 12.4) within a period of 28 days.