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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Start of the test period: 26.09.2016 End of the test period: 05.12.2016 Report date: 02.01.2017
Reliability:
1 (reliable without restriction)
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
Deviation from the OECD guideline was needed due to the fact that the reaction of CaH2 with water is very fast.
Principles of method if other than guideline:
- Brief description of the test procedure:
A glass reactor (total volume 1100 ml) was filled with 600 ml of an aqueous buffer solution (see below for details of the buffers). The water phase (600 ml) as well as the gas phase (500 ml) of the reactor was saturated with hydrogen gas at atmospheric pressure. In order to prevent the sample from reacting with air humidity the sample container (a small shuttle made of Polypropylene) was put onto the balance and flushed with Argon. The sample was weighed into the shuttle which was immediately put into the reactor. While the shuttle was swimming on the water surface the reactor was tightly closed and the pressure sensor installed. The hydrolysis reaction started when the shuttle went down into the water phase by vigorously stirring.
- The test was performed at three different pH values (4 / 7 / 9), each at temperatures of 20 °C, 40 °C and 50 °C. An additional test was performed, simulating physiologically significant conditions at 37 °C and pH 1,2.
GLP compliance:
no
Remarks:
this is a physical chemical study not requiring GLP. The institute has an adequate qulaity control system.
Test material information:
Composition 1
Specific details on test material used for the study:
- Test substance: Calcium hydride K, <2 mm, Batch no. 75552
- Molecular weight calculated: 42,094 g/mol (formula CaH2 assumed)
- The test substance was supplied by the customer as a grey powder. From data of a certificate of analysis (provided by the customer) a purity of 89,5 % may be calculated.
Radiolabelling:
no
Analytical monitoring:
yes
Buffers:
Preparation of the buffer solutions:
- Buffer for pH 1,2:
Hydrochloric acid (0,2 mol/l) + Potassium chloride (0,2 mol/l); pH measured: 1,3
- Buffer for pH 4:
Acetic acid (2 mol/l) + Sodium acetate (2 mol/l); pH measured: 4,1
- Buffer for pH 7:
Potassiumdihydrogenphosphate (0,026 mol/l) + Sodiumhydrogenphosphate (0,041 mol/l); pH measured: 7,1
- Buffer for pH 9:
Glycin (0,039 mol/l) + Sodium hydroxide (0,012 mol/l) + Sodium chloride (0,088 mol/l); pH measured: 9,0
Details on test conditions:
- Equipment for recording the pressure: data logger Ahlborn Almemo 710; pressure sensor Ahlborn FDAD3302A
Duration:
1 s
pH:
4.1
Temp.:
19.2 °C
Initial conc. measured:
ca. 0.251 other: g/600 mL
Duration:
1 s
pH:
7.1
Temp.:
19.5 °C
Initial conc. measured:
ca. 0.251 other: 9/600 mL
Duration:
1 s
pH:
9
Temp.:
20.3 °C
Initial conc. measured:
ca. 0.252 other: g/600mL
Duration:
1 s
pH:
1.3
Temp.:
36.7 °C
Initial conc. measured:
ca. 0.257 other: g/600mL
Duration:
1 s
pH:
4.1
Temp.:
39.9 °C
Initial conc. measured:
ca. 0.26 other: g/600mL
Duration:
1 s
pH:
7.1
Temp.:
40 °C
Initial conc. measured:
ca. 0.255 other: g/600mL
Duration:
1 s
pH:
9
Temp.:
40.3 °C
Initial conc. measured:
ca. 0.258 other: g/600mL
Duration:
1 s
pH:
4.1
Temp.:
50.1 °C
Initial conc. measured:
ca. 0.253 other: g/600mL
Duration:
1 s
pH:
7.1
Temp.:
50.2 °C
Initial conc. measured:
ca. 0.256 other: g/600mL
Duration:
1 s
pH:
9
Temp.:
49.9 °C
Initial conc. measured:
ca. 0.252 other: g/600mL
Number of replicates:
No replicates
Positive controls:
no
Negative controls:
no
Preliminary study:
No
Transformation products:
yes
Remarks:
Calcium hydroxide
No.:
#1
Reference substance:
Composition 1
Details on hydrolysis and appearance of transformation product(s):
Metal hydrides react quickly with water, forming metal hydroxide and hydrogen gas.
% Recovery:
0
Duration:
< 1 s
Remarks on result:
other: Calcium hydride reacts instantly with water.
Key result
pH:
4.1
Temp.:
19.2 °C
Hydrolysis rate constant:
< 1 s-1
Remarks on result:
other: Hydrolytically unstable

Calcium hydride results:

 Test no.  1 2 3  4 5  6  7  8  9  10
 T°/C°  19.2 19.5  20.3  36.7  39.9  40.0  40.3  50.1  50.2  49.9 
 pH  4.1 7.1  9.0  1.3  4.1  7.1  9.0  4.1  7.1  9.0 

Sample

(m0/g)

 0.251 0.251  0.252  0.257  0.260  0.255  0.258  0.253  0.256  0.252 
 Sample (mol)  0.006 0.006  0.006  0.0061  0.0062  0.0061  0.0061  0.006  0.0061  0.006 
 Pressure increase (kPa)  50.8 51.0  53.0  56.1  55.4  55.2  55.5  54.7  54.9  54.2 
 reaction time (s)  <=1   <=1   <=1   <=1   <=1   <=1   <=1  <=1    <=1   <=1
 c(Ca) (mg*l-1)  404.3 404.1  403.9  406.2  409.2  405.8  408.0  404.9  406.2  403.6 
 recovery (%)  112 112  111.5  110.1  109.7  110.8  110.2  111.4  110.5  111.4 
 k/s-1  >=2.2   >=2.2   >=2.2   >=2.2   >=2.2   >=2.2   >=2.2  >=2.2   >=2.2    >=2.2
 T0.5/s   <=0.3    <=0.3   <=0.3     <=0.3   <=0.3      <=0.3   <=0.3      <=0.3  <=0.3    <=0.3
Validity criteria fulfilled:
yes
Conclusions:
As a final conclusion of all data it can be stated that the test substance Calcium hydride is hydrolytically extremely unstable at all conditions of temperature and pH. This compound will never be found in aqueous phase or environmental water.

Description of key information

As a final conclusion of all data it can be stated that the test substance Calcium hydride is hydrolytically extremely unstable at all conditions of temperature (from 19.2 to 50.2°C) and pH (1.3; 4.1; 7.7; 9.0) This compound will never be found in aqueous phase or environmental water.

Key value for chemical safety assessment

Additional information