Adapted from Chemcases.com

Silicones

Background

Silicates are silicon-containing compounds / minerals built around Si-O bonds.

SiO

SiO

SiO

O O

O O

O O

O

SiO O

O

90% of the earth’s crust is made of silicates!

What’s the Chemistry?

Tetraethylsilane synthesis: SiCl4 + 2Zn(C2H5)2 → 2ZnCl2 + (C2H5)4Si

Si-C bonds are stable, unlike Si-F, Si-Cl, Si-Br, or Si-I ones.

Tetraphenylsilane synthesis: SiCl4 + 2Zn(C4H6)2 → 2ZnCl2 + (C4H6)4Si

Boiling point 154 °C

Boiling point 530 °C

Frederic Stanley Kipping found that he could replace the chlorines in SiCl4 sequentially.

Diethyldichlorosilane (C2H5)SiCl3 + MgBr(C2H5) → MgBrCl + (C2H5)2SiCl2Triethylchlorosilane (C2H5)2SiCl2 + MgBr(C2H5) → MgBrCl + (C2H5)3SiClTetraethylsilane  (C2H5)3SiCl + MgBr(C2H5) → MgBrCl + (C2H5)4Si

and that the remaining chlorines could be easily reacted with H2O.

Triethylhydroxysilane (C2H5)3SiCl + H2O  → (C2H5)3SiOH + HCl

Moar Silicon

2(C2H5)3SiOH → (C2H5)3SiOSi(C2H5)3 + H2O

Kipping also found that these hydroxysilicon compounds could react with themselves.

He tried the same reaction with diethyldichlorosilane, and characterized his products as “glue-like and unimportant”.

After 40 years of research, he told an audience…

“We have considered all the known types of organic derivatives of silicon . . . the prospect of any immediate and important advance in this section of chemistry does not seem very hopeful".

Some more Background

James Franklin Hyde thought Kipping was on to something.

As electricity became commonplace, a need for high quality insulation for wires arose.

Cotton and asbestos were the original materials used.

Kipping: (C2H5)2SiCl2 + H2O → something glue-like and unimportant

Hyde: n(C2H5)(C4H6)SiCl2 + nH2O → O Si

C2H5

C6H4

O Si

C2H5

C6H4 n

When Hyde took his product and heated it, he got a rubbery mass with insulating properties up to 180 °C, first Class H insulators.

Improving It

O Si

C2H5

C6H4

O Si

C2H5

C6H4 n

Downsides: 1) too many steps to synthesize2) not atom-economical3) yield sucks

Scientists at Corning decided to invite GE scientists to take a look, and Winton Patnode and his buddy Eugene Rochow took notice of the problem.

"I was busy with several . . . problems at the time, but kept thinking about Patnode's (ideas) and Hyde's silicone. The questions and answers went like this.

(Q) What is really needed? (A) A flexible inorganic insulation that will stand at least 200 or 300 Celsius in service.

(Q) If we have to admit some of the enemy into the camp, what form should it take? (A) It should constitute an absolute minimum of the whole and it should have no carbon-carbon bonds, lest it end up as C-C-C-C-C conducting resins in the motor."

The Proposed Idea

O Si

CH3

CH3

O Si

CH3

CH3 n

Successful chemists think by analogy!

Rochow knew that 2Si + 6HCl → 2HSiCl3 + 2H2

It turns out that a Cu impurity in his Si catalyzed the desired reaction!

So he did Si + 2H3CCl → (CH3)2SiCl2

(CH3)2SiCl2 + nH2O → [(CH3)2SiO]n + nHCl

In 1940, Rochow was able to confirm this one step process of making silicone polymers.

Preparation of Silicon

Turns out reacting carbon and sand is how Si metal is produced.

2C + SiO2 → 2CO + Si

  C SiO2 CO Si∆H° (kJ / mol) 0 -911 -110 0∆S° (J / mol K) 6 42 198 19∆G° (kJ / mol) 0 -856 -137 0

Is this even reasonable or spontaneous???

∆H° = ∆H°products – ∆H°reactants = +691 kJ / mol highly unfavorable enthalpically∆S° = ∆S°products – ∆S°reactants = +367 J / mol K highly favorable entropically∆G° = ∆G°products – ∆G°reactants = +586 kJ / mol whoa this won’t be spontaneous at 298 K

What T is needed for the reaction to be at equilibrium?

∆G = 0 = ∆H – T∆S, and solve for T. T is 1850 K!

This explains why Si is prepared by reacting sand and carbon in a high temperature electric arc reactor.

Engineering!

Once a chemist figures something out, it’s up to chemical engineers to make it actually useful.

The exothermic reaction has an activation energy of up to 300 °C!

Medical Implants Jaw, finger, and other joint implants. Long term contraceptives.

Silicones are Everywhere

Electronics Insulation, tapes, basically most of the silicon

Automotives Heat, oil, and fuel-resistant rubber sealants

Cookware Coatings on bakewares

Medicine Medical-grade tubing

Home Products Glues, caulks, sealants

Personal Care Lotions, deoderants, shaving cream, makeup.

Military Gaskets to stabilize vibration sensitive items

Implants

Silicone implants were extremely successful in treating difficult medical problems.

Thousands of children suffering hydrocephalus were saved with silicone shunts.

There did not appear to be any medical side effects!

So in 1960, plastic surgeons Thomas Cronin and Frank Gerow developed silicone breast implants for women who had undergone mastectomies.

Silicone breast implants became big.

Around the same time the government began testing the effects of polymers in the body.

In 1977, a woman won a lawsuit claiming her implant leaked, and the FDA started to pay attention.

Controversy!

In the early 1980s, the FDA started to reclassify implants as a “Class III” device.

Between then and 1992, juries awarded several women millions of dollars because implant leakage was determined to be the cause of their new autoimmune disorders.

One of the women stated in court that her disorder was “like having the flu”.In 1992, Dow Corning stopped producing implants in response to an FDA moratorium.

Saline breast implants became the standard.

Only in 1976 did the FDA require that a manufacturer of a device prove to that the device was "safe and efficacious," that it both do no harm and that it would work as intended.

Breast implants were grandfathered in because there weren’t any problems before then.

Fallout

In 1998, a court-appointed scientific panel found that there were no proven links between silicone implants and any disease.

In early 1998, Dow Corning agreed to a 3.2 billion dollar settlement, and by that point was already bankrupt from fighting hundreds of lawsuits.

Three conclusions could be drawn from the data…1) Implants rupture on occasion and leak silicone fluid into the body.2) Some silicone fluid leaks through the walls of an intact implant.3) Autoimmune disease occurs in women with implants.

In 2005 and 2006, the FDA re-approved silicone gel-filled implants produced by Allergan and Mentor.

Discussion Maybe?

These types of debates happen everyday over new medicines, treatments, and even nanotechnology.

How responsible is a company for the medical conditions of a minority of consumers?

How much financial responsibility should the company have

if they are found liable?