N-[3-(triethoxysilyl)propyl]ethylenediamine

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline followed

Principles of method if other than guideline:

It should be able to differentiate very short half lives from half lives of several hours at rather low concentrations, as required by the general OECD guideline 111 for hydrolysis studies, which asks for measurements at a concentration of 0.01 mol/l, or ½ of the solubility, what ever is the lower concentration.
The method finally identified for this purpose, was 1H-NMR spectroscopy.

GLP compliance:

no

Transformation products:

not measured

pH:

4

Temp.:

25 °C

DT50:

15 min

Type:

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

pH:

7

Temp.:

25 °C

DT50:

165 min

Type:

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

pH:

9

Temp.:

25 °C

DT50:

14 min

Type:

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

The individual samples are prepared by the following procedure: Approximately 10 mg of the respective silane are weighed into a dry glass container. Then the necessary quantity of the necessary buffer solution (pH 4: citrate buffer, pH 7: phosphate buffer and pH 9: bo-rate buffer) with deuterated water D2O as solvent is added to reach a concentration of 0.01 mol/l. Usually this is a quantity of 5 – 10 g of D2O-buffer solution. Immediately after mixing, approximately 0.5 – 1 ml of the solution is transferred into a 5 mm NMR tube which then directly is introduced into the NMR-magnet and the NMR-data acquisition is started. The whole procedure till the begin of the measurement takes 1 to three minutes. The use of D2O instead of non-deuterated water as solvent has advantages for the NMR measurements; especially since it prevents the occurrence of a huge H2O-signal in the 1H-NMR spectrum which would make the evaluation of the signals from the silane and its hy-drolysis products at a concentration of 0.01 mol/l very complicated. The D2O itself is not visible in the 1H-NMR spectrum. The reaction rate of the silanes with D2O is expected to be very similar to the reaction rate with H2O; if ever, the reaction with D2O would be a little slower. Each 1H-NMR spectrum stored for later evaluation is generated by accumulating 16 indi-vidual spectra in the time domain which takes 54 seconds with the acquisition parameters set. Thus, one of the spectra - which are the Fourier-Transformation of the accumulated time domain spectra - shown in the following sections represents the average spectra of a time period of approximately 1 minute.

For the first 10 minutes after the transfer of the sample into the magnet, one spectrum generally was measured directly one after the other; for slower hydrolysis reactions, addi-tional spectra were measured individually after specified periods of time (some times after hours or days). The time shown in the upper left corner of the individual spectra in this re-port indicates the period passed since the mixing of the substance with the water. For evaluation of the data the signal intensities of the chosen signals (see details in the sections on the individual compounds) are determined by integration. The signal intensities in 1H-NMR spectra are directly related to the concentration of the structure originating the signal in the spectrum, independent of the substance where this structure is present. This allows the straight-forward calculation of the percentage of the original product on the sum of the concentrations of the original product (e.g. the alkoxy-moiety) and the hydrolysis product (e.g. the alcohol). Half lives then are determined by the slope of the regression line through the determined values in a semi logarithmic Arrhenius plot.

The regression of the Arrhenius plot in this case results in a half life of the original com-pound of 165 minutes at pH 7 and a concentration of 0.01 mol/l.

For the other pH values studies the calculated half lives again are even shorter.

Estimated hydrolytic half life of N-(3-triethoxysilyl-propyl)-ethylenediamine (0.01 mol/l):

pH 4 :15 min

pH 7 : 165 min

pH 9 : 14 min

Description of key information

Half-life approx. 165 min at 25 °C and  pH 7

Key value for chemical safety assessment

Half-life for hydrolysis:

165 min

Additional information

The hydrolysis of N-(3-triethoxysilyl-propyl)ethylenediamine (CAS 5089 -72 -5) was determined in a study with 1H-NMR spectroscopy (Gerhards, 2006). This method is able to follow the hydrolysis of the various alkoxy and acetoxysilanes. During the course of the hydrolysis the corresponding alkyl alcohols or acetic acid are formed. 1H-NMR-spectroscopy is used to differentiate the alkoxy structure from alcohol structure, or the acetoxy from the acid structure. At the same time 1H-NMR-spectroscopy can be used to quantify products with a molecular weight typical of the studied products at a concentration of 0.01 mol/L without severe problems.

For determining the hydrolysis rate in this case the signal of the CH2-group attached to the oxygen in the ethoxy-group or to the OH-group in ethanol is used. The regression of the Arrhenius plot in this case results in a half-life of the original compound of 165 minutes at pH 7 and a concentration of 0.01 mol/L. For the other pH values studies the calculated half-lives are even shorter with a DT50 of 15 min for pH 4 and 14 min for pH 9.

The initial hydrolysis products are N-(3-(trihydroxysilyl)propyl)ethylenediamine and ethanol.