Diamminediisocyanatozinc

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

until 1992-09-08

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

chosen conditions most relevant (authentic) for environmental assessment, and suitable for health assessment, too

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

Official Journal of the European Communities (English edition) legislation L251 Vol 27 September 1984 pages 199 一 211.

Deviations:

not specified

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

none, distilled water only

Details on test conditions:

Hydrolysis Experiments
The conditions used in these experiments were based on the modified MITI biotic biodegradation test. Thus either ca. 100mg of DBZ was added to 1 litre of distilled water or ca. 50mg DBZ was added to 500 mls of distilled water. The distilled water had a pH between 6.15 and 7.02. Most data was obtained with water of pH 7.02 but no difference in hydrolysis was noted with water of pH 6.15.
Most hydrolysis experiments were undertaken in stoppered conical flasks although one experiment used an open beaker. The solid was dispersed in the water by submitting the flasks or beaker to five minutes treatment in a ultrasonic bath except where stated. The temperature at which the hydrolysis occurred was 22 ± 2°C. The stoppered flasks were left for 18-20 hours before analysis was undertaken. The open beaker was left for one week.

Duration:

18 h

pH:

7.02

Temp.:

22 °C

Initial conc. measured:

100 mg/L

Remarks:

18-20h, pH 6.15 - 7.02, 22±2°C, stoppered flasks

Duration:

1 wk

pH:

7.02

Temp.:

22 °C

Initial conc. measured:

100 mg/L

Remarks:

pH 6.15 - 7.02, 22±2°C, open beaker

Number of replicates:

2 x 2

Positive controls:

no

Negative controls:

no

Preliminary study:

No preliminary study was carried out.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

No.:

#6

No.:

#7

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

- Formation and decline of each transformation product during test:
Zn(NCO)2 (NH3)2 + 2H2O ―> Zn(OH)2 + 2NH3 + 2HNCO
These interim products undergo further decay:
Zn(OH)2 ―> ZnO + H2O / ZnCO3 + CO2 + H2O
2HNCO ―> 2CO2 + 2NH3
For details, please refer to free text fields below and reaction scheme.

pH:

7.02

Temp.:

22 °C

Duration:

>= 18 - <= 20 h

Remarks on result:

other: No indications for residual parent compount given. (besides residual isocyanate complex being present as aqueous insoluble products)

Remarks:

stoppered flasks

pH:

7.02

Temp.:

22 °C

Duration:

1 wk

Remarks on result:

other: No indications for residual parent compount given. (besides residual isocyanate complex being present as aqueous insoluble products)

Remarks:

open beakers

Remarks on result:

other: DT50 not available, as the whole DBZ appears to be totally decomposed at the concentration of the MITI test after the shortest examination time of 18h.

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): none stated

MAJOR TRANSFORMATION PRODUCTS (Ultimate transformation products)
Zinc oxide / oxozinc / 1314-13-2 / 215-222-5
Zinc carbonate / zinc carbonate / 3486-35-9 / 222-477-6
Ammonia / ammonia / 7664-41-7 / 231-635-3
Water / Water / 7732-18-5 / 231-791-2
Carbon dioxide / carbon dioxide / 124-38-9 / 204-696-9

PATHWAYS OF HYDROLYSIS
- Description of pathways: See below
- Figures of chemical structures attached: Yes

RESULTS

(A) Aqueous Insoluble Hydrolysis Products

(A).1 Mass of recovered product

During the hydrolysis process the fine DBZ powder never seemed to dissolve in the water. Application of ultrasonic treatment gave a milky appearance to the water and during these forcing conditions bubbles appeared around the larger lumps or aggregates of DBZ. No effervescence at all was detected by simply adding the DBZ to water and no smell of ammonia was detected at any time in any experiments.

Flocculant behaviour was evident on leaving the flask to stand and within eighteen hours a sediment had formed on the flask's floor leaving a clear liquid above.

The recovered dried solid was a fine, off-white powder and consistently weighed between 43 and 50% of the starting weight, including the experiment conducted in an open beaker left for one week. See table below

 

TableTypical weights of recovered dried aqueous insoluble hydrolysis product

 

Original weight of DBZ	Volume of water	Weight of recovered dried solid	Recovered wt.of dried solid as%of starting wt of DBZ
97mg	1 litre	42mg	43%
54mg	500 ml	23mg	43%
48mg	500 ml	24mg	50%
113mg	1 litre	59mg	44%

*      Experiment using open beaker instead of stoppered conical flask.

 

The solid hydrolysis product was then subjected to further analysis一DSC, IR.,mass spectroscopy and elemental analysis.

 

 

(A). 2 Elemental Analysis

The zinc, carbon, nitrogen and hydrogen contents were all determined with the oxygen content obtained by difference. Table below shows the analyses on the starting material and solid hydrolysis products. The experiments differed in the time they were subjected to ultrasonic treatment• "1st MITI hydrolysis product" received <2 mins ultrasonic treatment whilst the "2nd MITI hydrolysis product received 5 mins. treatment". The theoretical values for purestarting material are also presented.

 

Table Elemental analysis as%weight of each element

Sample	Zinc	Carbon	Hydrogen	Nitrogen	Oxygen
'Pure'DBZ(theoretical)	35.65	13.08	3.3	30.5	17.47
DBZ	36.5	12.26	3.11	28.66	19.47
1stMITI Hydrolysis product	64.4	2.06	1.31	0.42	31.81
2ndMITI Hydrolysis product	70.4*	1.38	0.93	0.054	27.24

*Small sample ±2%error

 

The data shows that the starting material is not a pure material and that the length of time the sample is submitted to ultrasonic treatment can influence the resulting hydrolysis products.Subsequent data obtained and discussed in this report is based on material treated in an identical fashion to that described in the experimental section for the2ndMITI test. These conditions are very similar to an earlier study made on the hydrolysis of DBZ².

 

(A). 3 Mass Spectroscopy

Attempts to identify the molecular mass of the solids using mass spectroscopic techniques proved unsuccessful. Electron impact and soft ionisation techniques (chemical ionisation and fast atom bombardment) produced no spectra. Introducing the sample into the mass spectrometer using thermal desorption did not yield a spectrum either. It has been concluded that the nature of the sample is such that it is not volatile enough to produce a mass spectrum.

 

(A). 4 Infra Red Spectroscopy

Infra red spectra were obtained from the original DBZ and the product of hydrolysis. The spectra of zinc carbonate, oxide and hydroxide, which are likely hydrolysis products, were obtained for comparison.

 

(A). 5 Differential Scanning Calorimetry

Thermograms were obtained from samples of DBZ, the solid hydrolysis product, zinc carbonate, hydroxide, oxide and peroxide.

 

(B) Aqueous Soluble Hydrolysis Products

(B ).1 pH changes

The initial pH of the distilled water was determined as was the final pH, ie after ultrasonic treatment and being left to stand for ― 20 hrs.

Typically the pH increased as shown in Table below

 

 Table Change in pH of water

Initial pH (distilled water)	Final pH
6.70 6.15 7.02	8.30 8.08 8.29

 

 

B,2      Evaporation to dryness and weight of resulting product

The aqueous filtrate was vacuum distilled on a rotary evaporator at 700 nun Hg and at temperatures of 40°C, 55°C and 70°C. Very little solid was obtained under any conditions but that which was obtained had a slight blue hue to it. These small solid particles were smeared around the flask and it proved impossible to recover all the solid, but 1.5mg was recovered. Between 2-3mg of such solid per 100mg of DBZ hydrolysed is estimated to be formed.

Validity criteria fulfilled:

not specified

Conclusions:

The study was conducted under EU method C.7 of 1984, and is sufficiently documented to conclude that the study was properly performed and so, the results can be considered reliable.
The rate of hydrolysis of DBZ is influenced by the amount of ultrasonic treatment it receives but it is a relatively rapid process and DBZ appears to be totally decomposed at the concentration of the MITI test.
The aqueous insoluble hydrolysis products have been quantified albeit in the case of zinc hydroxide and zinc oxide, within a range rather than given exact values.
The aqueous soluble products have not been specifically identified but the circumstantial evidence is consistent with the products being ammonia and carbon dioxide.
To obtain more information on the aqueous phase components it might be possible to repeat the evaporation of the aqueous portion many times and bulk the residues together in order to get a larger quantity of material for analysis. However, the value of doing this is questionable.
The gases released from the aqueous portion during evaporation may be trapped, eg. CO2 in soda-asbestos trap although the effect of trying to trap mixed weakly basic and acidic gases is not known by the author. Also the laboratory is not suitably equipped for these types of experiments.
Summarizing, after the shortest test duration of 18-20h, the product was found to be hydrolyzed (besides residual isocyanate complex being present as aqueous insoluble products), and the actual required time could be also way shorter.

Executive summary:

The products resulting from hydrolysis of diammine biscyanato-N-zinc (DBZ) under conditions similar to the MITI biotic biodegradation test (Official Journal of the European Communities (English edition) legislation L251 Vol 27 September 1984 pages 199 - 211.) need to be determined to help gain registration for this product.

Under stated conditions DBZ hydrolyses to yield aqueous insoluble, or slightly soluble, products and aqueous soluble products. Zinc oxide and zinc carbonate have been identified as aqueous insoluble products. There is also evidence for zinc hydroxide and residual isocyanate complex being present as aqueous insoluble products.

The aqueous soluble products are urea and most probably ammonia and carbon dioxide. Evidence for ammonium salts - carbonate, carbamate and bicarbonate was not found.

A route by which hydrolytic degradation of DBZ occurs is proposed.

Description of key information

The products resulting from hydrolysis of diammine biscyanato-N-zinc (DBZ) under conditions similar to the MITI biotic biodegradation test (Official Journal of the European Communities (English edition) legislation L251 Vol 27 September 1984 pages 199 - 211.) need to be determined to help gain registration for this product.

Under stated conditions DBZ hydrolyses to yield aqueous insoluble, or slightly soluble, products and aqueous soluble products. Zinc oxide and zinc carbonate have been identified as aqueous insoluble products. There is also evidence for zinc hydroxide and residual isocyanate complex being present as aqueous insoluble products.

The aqueous soluble products are urea and most probably ammonia and carbon dioxide. Evidence for ammonium salts - carbonate, carbamate and bicarbonate was not found.

A route by which hydrolytic degradation of DBZ occurs is proposed.

The rate of hydrolysis of DBZ is influenced by the amount of ultrasonic treatment it receives but it is a relatively rapid process and DBZ appears to be totally decomposed at the concentration of the MITI test. After the shortest test duration of 18-20h, the product was found to be hydrolysed (besides residual isocyanate complex being present as aqueous insoluble products), and the actual required time could be also way shorter.