Jackson - 27-5-2018 at 12:39
Hi,
I am trying to work out a route to synthesize silicone rubber. One Component I think I need for the silicone rubber is Vinyl Silane. The only reaction
I found to make Vinyl Silane is between Triphenylsilyl hydride and Phenylacetylene. The problem is that I can't find much info on its synthesis. The
closest I have gotten is the reaction between Ethoxytriphenylsilane and Diisobutylaluminum Hydride. I can't find any info on the synthesis of
ethoxytriphenylsilane and the small ammount of info on Diisobutylaluminum does not specify some of the reagents for the synthesis.
If you guys could tell me if i'm on the right track for what I need for the silicone rubber and let me know how to synthesize the chemicals that I
can't find much info on that would be helpful and much appreciated.
Thanks,
Jackson
12thealchemist - 29-5-2018 at 11:02
The simplest silicone is polydimethylsiloxane, (Me2SiO)n, which can be made by hydrolysing dimethyldichlorosilane,
SiMe2Cl2. This compound is usually an oil, depending on the length of the polymer.
Silicones with higher melting points, closer to solid rubber, could be made by one of two ways. One would be to dramatically increase the size of the
sidechain, for example to octyl or phenyl or some such. The exact same hydrolysis reaction could then be carried out. The other route is to use
crosslinking. This would entail using trichloroalkylsilanes, and hydrolysing those. The result would be a 3D network of siloxane with alkyl groups.
To synthesise these alkyl silanes is quite difficult, and I put a deal of thought into it some time ago. The industrial route is pass e.g. methyl
chloride over a heated mixture of silicon and copper powders, and fractionally distil the resulting mixture of isomers of alkylchlorosilanes. As with
most industrial processes, this is quite difficult to enact on a hobby scale. Hence, a different approach is required. My reckoning was to use
Grignard reagent with some sort of "precursor" like silicon tetrachloride or tetraethoxysilane (aka tetraethyl orthosilicate). The former is
synthesised by combination of the elements, but has a notoriously low yield. I do not know how readily available it is for purchase.
Tetraethoxysilane (which will now be referred to as TEOS) can be made through a more roundabout route I recently posted here. Unfortunately, I cannot give a yield as yet due to the experimental state of the synthesis. However, this can be purchased if one is willing
to hunt around; Applied Science mentioned he bought his TEOS and TMOS in his video on aerogel.
The next step after acquiring either SiCl4 or SiOEt4 is to react them with either a substoichiometric amount of the desired
Grignard to synthesise the monoalkylsilane or two equivalents for the dialkylsilane. Admittedly, this does yield a mixture of isomers, and I do not
know what yields are like, though I plan to investigate this process in detail in future. Since it sounds like you're doing it for the science, the
overall yield isn't massively important, though high yields are always good to aim for. Anyway, once you've performed the Grignard reaction, the
desired isomer can be distilled out of the reaction mixture, though if you want to quench the reaction you're going to want to use ethanolic acid
rather than aqueous because the product is water-sensitive. After the distillation, the product can then be hydrolysed to generate the final silicone
product.
As a side note, the distillates could be used to investigate organosilicon chemistry if one were interested in exploring that field.
wg48 - 29-5-2018 at 12:21
Don't forget the green route to methylsiloxanes see:
Attachment: cheng2000.pdf (275kB)
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