Silicones
Matt Hermes

 

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Chemical Concepts
Let's introduce a new and important chemical concept
6. Catalysts lower Activation energy and speed the rates of chemical reactions

Dr. Eugene Rochow observed the catalytic action of copper metal..

Silicones and Patents
The ChemCases unit on Gatorade discusses United States patents.  You might read the patent section on the invention of Gatorade.

7221.jpg (26476 bytes)

General Electric did take one action with Rochow's first methyl silicones.  They filed patents, differentiating them in their patent claims from the ethylphenyl silicones made at Corning.  These patents led to a controversy between the two companies; Corning, having introduced their silicone work to GE, then  sued GE in the patent courts claiming GE's methyl silicone were obvious in light of Corning's own work.  Corning lost, the methyl silicones became GE's sole property.

Observation and Science

The powers of observation serve science well. See Aeneas the King, here struck by an arrow. Victory and defeat, the founding of Rome, hang in the balance. You might read of a victory for observation from Virgil's Aeneid, Book XII, lines 438-587.
And you might think about the headline on the Obituary page of the Bay Area Reporter on August 13, 1998. "No Obits" the headline read. No deaths for more than a week from AIDS and its related diseases in the San Francisco area. A respite from grief occasioned by new science, chemical discovery.

OBSERVATION

Aeneas the King, Virgil the Poet,
Had Rome no beginning lest the magic appear?
The warrior king, struck mortally in combat,
Tears at the wound, begs to the gods.

Venus in motion bears to his healer
The potion she
knows will answer his pleas.
Extract of dittany, flowering purple,
Laved to his thighs, the King is restored.

Somewhere lies buried the bones of the poet
Who brought us the news of this classical science.
For Virgil and Venus watched dittany heal
The fever of goats laid open with shafts.

No bones for a week writes Bay Area Reporter!
New classical science, protease inhibitors
Our Virgils and Venus bring to the healers
Who chart for the wounded a new battle plan.

The gods of this craft and their chemical legion
See the trace of disease in the cells of confusion.
Microscopic, molecular, manipulating the foe.
Had Rome no beginning lest the magic appear?

Matt Hermes

 

 

Heat and Chemical Resistant Silicone Rubber
6.(CH3)
2SiCl2

Eugene Rochow set out to make methylsilicone polymer.  This is what chemists do.

Rochow stumbled through the magnesium-based synthesis scheme introduced first by Kipping then studied by Hyde.  By starting with CH3MgBr, he made  (CH3)2SiCl2 (9)and then attempted to make the resins he called methyl silicones:

(CH3)MgBr   +  SiCl4  -->  (CH3)SiCl3  +  MgClBr

(CH3)MgBr   +  (CH3)SiCl3  -->   (CH3)2SiCl2(9)   +  MgClBr

Rochow reacted (9) with water just as Hyde had done with (7). He obtained sticky fluids.   But when he heated them, they hardened to clear, resinous materials, certainly methylsilicones of the structure shown below:

               CH3
           |
                              (-Si-O-)
n           
           |
                CH
3

But Dr. Rochow needed a better method to make the methylsilicones - some pathway that could be converted to a low cost, commercial process. Successful chemists think by analogy.   Dr. Rochow remembered the work of Dr. Alfred Stock, in Germany.  Stock believed that a H- atom attached to silicon was just the first member of a like-behaving series of alkyls: CH3-, C2H5-, etc.

Rochow knew that he could make trichlorosilane, HSiCl3, by reacting:

2Si + 6HCl  -->  2HSiCl3   +  2H2

Suppose he reacted silicon with methyl chloride, CH3Cl.   He would  expect to obtain CH3SiCl3, right?  If so, could he adjust the ratio of Si and CH3Cl and obtain the critical intermediate to methyl silicones, (CH3)2SiCl2?

beaker4.wmf (6082 bytes) Successful chemists must be observant. Well, Rochow went to the laboratory and treated silicon with CH3Cl.   The experiment was disappointing at first.  But when Rochow was cleaning up his flasks with water he noticed the flask had a slippery feel - as if a film of his methylsilicone polymer had formed on its surface!

Successful chemists tend to work long hours.   On a spring morning in May, 1940, Eugene Rochow prepared a new experiment.

 He planned to pass a stream of methyl chloride gas along with some hydrogen chloride across a bed of silicon at high temperature.  (From left to right in the accompanying sketch). But this morning he set up using a source of silicon that contained copper metal.  He heated a tube containing the Cu-Si to 370 degrees Celsius and ran the gases over the hot silicon all day.  He shut the chemical reaction down just before 5PM.  But Rochow did not go home. 

labsetup.jpg (6240 bytes)
From Silicon and Silicones, Eugene G. Rochow, Springer-Verlag, Berlin, 1987, p.80.

He found a pool of liquid in the cooled flasks (on the right in the sketch) and treated the liquid with water.  "The end result is a clear, resinous body I believe is methyl silicone," Rochow wrote in his laboratory notebook late that night. The chemical reaction to make (9) was a simple one:

2CH3Cl  +  Si -->  (CH3)2SiCl2 (9)

It turns out, the hydrogen chloride gas served only to etch the surface of the Cu-Si that day.  What was more important was the copper.   Copper served as a catalyst for the reaction between methyl chloride and silicon.  

rochow.jpg (12239 bytes)
Rochow Repeating his First Effective Synthesis
Silicones Under the Monogram, H. A. Liebhafsky, John Wiley and Sons, NY, 1978, p.92

You may remember (or you will learn) that a catalyst participates in a chemical reaction by lowering the activation energy for the chemical reaction.  Activation energy is the energy required to form the "activated complex" through which all chemical reactions must go on the pathway from starting materials to products.   Lowering the activation energy increases the rate of a chemical reaction at any specific temperature - it allows reactions to proceed at practical rates at lower temperatures than without the catalyst.

When Rochow added the water, he made his methyl silicone:

n(9)  +  nH2O   -->  n[(CH3)2SiO]n    +  nHCl

In 1940, Eugene Rochow  demonstrated a one step method to make silicone polymers.  Much more would need to be done to make Rochow's process practical for the manufacture of high-temperature insulation.

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