1. Experiment is contained in the WACKER's Experimental Kit.

No

 2. Experimental procedure has been modified

/

 3. A separate experimental procedure has been devised

Yes

 4. Video clip available

No

 5. Flash animation available

No

Hydrolysis of Triacetoxymethylsilane

TopDown 1 Materials, Chemicals, Time Needed
  • Watchglass
  • Dropping pipet


The experiment takes less than five minutes.

TopDown 2 Procedure and Observations

In a fume cupboard, add about 20 drops of water to about 10 drops of triacetoxymethylsilane on a watchglass.

Observe the white “strings” in the liquid that form a few seconds after the water has been added. When the liquid has evaporated, a thin hazy layer remains firmly stuck to the watchglass and is highly water repellent.

TopDown 3 Discussion of Results

The triacetoxymethylsilane hydrolyzes in water to form a methylsilicone resin and acetic acid.

If the product from the experiment “Synthesis of triacetoxymethylsilane” is used, the acetic anhydride still contained in it must be completely converted to acetic acid. That is why the water is added in excess.
The silicone resin produced by the hydrolysis adheres well to silicate glass and is hydrophobic (see also the experiment "Hydrophobic properties of silicone fluid").

TopDown 4 Tips and Comments

  • This experiment is of relevance to everyday life. It may be performed on silicone bought from a DIY (Do it yourself) store instead of the triacetoxymethylsilane that you have produced (see 5 Supplementary Information).
  • Acetoxysilanes are much more easily hydrolyzed than esters, such as ethyl acetate. They hydrolyze as easily as acetic anhydride. This could be developed into a topic that also deals with the mechanism of ester hydrolysis (see also 6 References).

TopDown  5 Supplementary Information

The typical vinegar odor smelled when silicone sealants from DIY stores are used stems from the reaction above. The commercial tubes contain silicone material whose macromolecules have a fairly high content of acetoxy groups. When the sealant is squeezed from the tube into the air, the macromolecules undergo hydrolytic crosslinking in the atmospheric moisture, and acetic acid is released.
TopBottom  6 References
M. Tausch, M. von Wachtendonk (editors), CHEMIE S II, STOFF-FORMEL-UMWELT, C.C. Buchner, Bamberg (1993), (1998), S. 267 - 269
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