Acetylene- Champion of Unintended Consequences

Jack Dini
Livermore, California

(From a series on Unintended Consequences)

Acetylene could perhaps take the prize for how knowledge, intuitiveness, serendipity, and a mix of unintended consequences all came together in various parts of the world at different times to produce a variety of unexpected materials. In 1892, Canadian researchers Thomas Willson and James Morehead, attempted to produce aluminum in an electric furnace. They started with a mixture of coal tar and lime reasoning that the lime would be converted to calcium which, in turn, would strip the oxide away from aluminum oxide leaving pure aluminum. Upon opening the furnace they saw a dark residue, not the shiny aluminum they were expecting. When the mixture was thrown into a stream near their lab (this was long before the days of environmental concerns and regulations), bubbles formed and a plume of water shot into the air. They had discovered calcium carbide and acetylene. (1) On the other side of the world, Henri Moissan, a Frenchman trying to make artificial diamonds also discovered calcium carbide and acetylene. (2) But these scientists weren’t the first in this area of invention. Friedrich Wohler, a professor of chemistry at the University of Gottingen, had made calcium carbide around 1862 by heating calcium with charcoal to a high temperature. He observed that it formed acetylene when it reacted with water. However, his method of making the materials wasn’t efficient, so the discovery lay dormant until the 1890s, the era of the gaslight. (1) When it was realized that acetylene burned with a far more brilliant flame than kerosene, and efficient ways of making carbide were available, a vast new market opened up. As Joe Schwarcz reports, “By 1895 Thomas Willson had founded the company that eventually became Union Carbide, one of the biggest chemical companies in the world. Soon consumers were able to purchase lamps based on calcium carbide, clever devices in which water dripped into a container of carbide and generated acetylene gas. This gas, in turn, flowed to a nozzle where it could be ignited. A mirrored surface behind the flame increased the intensity of the light.” (3)

Then Thomas Edison came along with his electric light and the bottom dropped out of the acetylene market. Enter Fritz Klatte, working in Stuttgart at Greisham Electron. He was trying to find a material for weatherproofing aircraft wings. Working with a mixture of acetylene, hydrogen chloride, and mercury, he was unsuccessful, and set the mixture on a sunny window sill. Later he noticed that it formed a milky sludge which eventually turned solid. He convinced his firm to file a patent on the mixture and they did, but nothing was done to commercialize the discovery. In 1925 the patent lapsed. (4) It should also be noted, that as with acetylene, PVC had originally been discovered long before Klatte came along. French physicist Henri Victor Regnault was the original discoverer in 1835 but nothing was done with the product.

Back to Klatte. A year after his patent expired (1926), an American chemist, Waldo Semon, working at B. F. Goodrich, independently reinvented PVC. He envisioned that this material would make a perfect shower curtain so he and his colleagues at Goodrich patented the process (Klatte’s team apparently never filed for a patent outside Germany). It turns out PVC was much more than shower curtain material. It became the forerunner of many plastics without which modern industrialized nations could no longer function. (5)

These days PVC is everywhere. It’s one of the most widely used plastics in the world. It is also the cheapest and probably the most versatile plastic. Some uses include pipe and pipe fittings (the largest scale use), floppy computer discs, garden hose, building sidings, wire and cable insulation, food packaging, automobile seat covers, shower curtains, and many other household uses. (6)

Other Uses For Acetylene

In 1895, the same year Willson established his company, French chemist Henry-Louis Chatelier, discovered that when acetylene was burned with an equal volume of oxygen, a flame with a temperature over 3000 C was obtained. This temperature, high enough to melt steel, was much higher than achievable with any other gas and introduced the concept of welding. Oxyacetylene welding was a boon to the construction industry and is widely used today.

Joe Schwarcz adds, “About half of all acetylene produced today goes towards the production of other organic chemicals. Adding hydrogen cyanide to acetylene, for example, yields acrylonitrile, which is used in the production of acrylic fibers. Acetylene can also be converted into vinyl acetylene, which is the raw material needed for the manufacture of neoprene, one of the most useful synthetic rubbers.” (7) But once again, this wasn’t a finding that came easily or was predictable. Wallace Carothers, a chemist at Du Pont challenged one of his assistants, Arnold Collins, to make synthetic rubber. You guessed it—acetylene was the key starting material. Reacting it with hydrochloric acid produced something they called vinylacetylene, and one weekend when a mixture was left setting in a flask, by the following Monday it had turned into a tiny, cauliflower-type mass. Sharon Bertsch McGrayne notes, “Collins stuck a wire into the glass vessel and fished a few cubic centimeters of the substance out. It felt strong, resilient, and elastic, much like vulcanized rubber. Almost without thinking, Collins threw the mass against his laboratory bench. It bounced like a golf ball. Collins had made chloroprene in his test tube, and over the weekend it had spontaneously polymerized into the high-grade synthetic rubber that Du Pont would market as Neoprene.” (8)

DuPont promoted it cleverly as a specialty rubber, more durable than natural rubber and more resistant to oil, gasoline, solvents, sunlight, and heat. Neoprene was also great for making balloons, like the ones used in Macy’s Thanksgiving Day parade. It also gave chemists the impetus to develop other synthetic rubbers. (7)

So from experiments originally intended to produce aluminum in one case and cheap diamonds in another, acetylene, a key player in the plastics, chemistry, and metallurgical industries, was discovered. This then led to PVC and other plastics, many organic chemicals, and oxyacetylene welding. Besides all this, both acetylene and PVC had been discovered a number of times before their value was really known. Is there any doubt why this should not put acetylene at, or near the top of the unintended consequences list?

References

1.Joe Schwarcz, The Genie in the Bottle, (New York, Henry Holt & Company, 2002), 154

2.James Burke, Connections, (Boston, Little, Brown & Company, 1978), 209

3.Joe Schwarcz, The Genie in the Bottle, 155

4.James Burke, Circles, (New York, Simon & Schuster, 2000), 220

5.“Poly(vinyl chloride),” http://www.pslc.ws/mactest/pvc.htm

6.Royston M. Roberts, Serendipity, (New York, John Wiley & Sons, 1989), 185

7.Joe Schwarcz, The Genie in the Bottle, 156

8.Sharon Bertsch McGrayne, Prometheans in the Lab, (New York, McGraw-Hill, 2001), 131