CARBON

GEORGE A. OLAH, UNIVERSITY OF SOUTHERN CALIFORNIA

Carbon is the key element not only of terrestrial life but also of minerals (carbonates) and fossil fuels (oil, gas, and coal), and it is a minor but essential component of our atmosphere. Carbon is produced in the stars by nuclear synthesis from hydrogen that originated from the initial Big Bang. Over the eons, asteroids hitting Earth may have carried carbon to our planet.

Elemental carbon is found in nature as its allotropes--diamond and graphite--which are of vastly differing abundance and thus also of differing value. In the 1980s, a new group of allotropes called fullerenes or buckyballs--named after R. Buckminster Fuller, who designed famous geodesic domes resembling soccer balls--was recognized, first spectroscopically (for which Robert F. Curl Jr., Sir Harold W. Kroto, and Richard E. Smalley received the 1996 Nobel Prize in Chemistry) and later produced in electric discharge devices using carbon electrodes (Donald R. Huffman and Wolfgang Krätschmer). These new carbon allotropes promise significant applications.

Carbon has a remarkable ability to bind with itself to form chains, rings, and complex structures. The variety of carbon compounds with bound hydrogen (hydrocarbons) and other elements (oxygen, nitrogen, and phosphorus, for example), which are generally called organic compounds, is practically unlimited.

CARBON AT A GLANCE
Name: From the Latin carbo, coal.
Atomic mass: 12.01.
History: Known since ancient times.
Occurrence: Carbon occurs naturally as crystalline graphite or diamond, or amorphously in charcoal, carbon black, coke, and white carbon. A new molecular allotrope, C60, or buckminsterfullerene, was discovered in 1985.
Appearance: Nonmetal solid. Graphite is black or silver-black. Diamond comes in various colors.
Behavior: Not volatile. Readily bonds with many elements and itself, forming millions of compounds.
Uses: Essential component of all organic molecules, including nucleic acids, proteins, and carbohydrates. The C-14 isotope is used for carbon dating. Graphite is used as a lubricant and in pencils. In addition to being valued as a gem, diamond is often used as an abrasive. Carbon dioxide has numerous uses, including refrigeration.
8136element.carbon
C60
The very heart and essence of chemical transformations and hence of modern chemistry is an understanding of chemical reactions and their intermediates. Carbocations (the positive ions of carbon compounds) and related electron-deficient species represent the most important intermediates in all of chemistry. I was fortunate to have discovered ways to observe carbocations as persistent, long-lived species.

The related development and use of superacids, billions of times stronger than sulfuric acid, and superelectrophiles have changed the field of chemistry. The realization that carbon, in many of its electron-deficient species, including carbocations, can simultaneously bind (coordinate) to five, six, and even seven neighboring atoms or groups is significant. This has extended Kekulé's concept of the limiting four valency of carbon to higher coordinate carbon compounds and has opened up new fields of hypercarbon chemistry.

My discoveries also provided insights into the electrophilic activation of C–H and C–C single bonds and formed the basis of the development of new and improved hydrocarbon transformations. These have significant applications in the petroleum and chemical industries for improved production of high-octane gasoline (via alkylation and isomerization) and the direct conversion of methane (natural gas) to methanol and higher hydrocarbons without producing syngas.

From plant life over the ages, new fossil fuels can be formed. The process is so slow, however, that within our human life span we do not have time for nature to replenish what we are rapidly using up. A challenging new approach that we are pursuing is to reverse the process and produce hydrocarbons from carbon dioxide and water via methanol, thus chemically recycling carbon dioxide. In the laboratory, we already know how to do this, and progress is being made toward bringing about the feasibility of such an approach. The limiting factor is the energy needed for generating hydrogen from water. Using alternative energy sources--but first of all atomic energy, albeit improved and made safer--will eventually give us needed energy.

Much is said these days about a "hydrogen economy," emphasizing hydrogen as the clean, inexhaustible fuel of the future. However, the safe handling and dispensing of volatile hydrogen--for which no infrastructure exists--is difficult and costly.

I believe a much preferable way of storing hydrogen is in the form of methyl alcohol ("methanol economy"). Methanol is a convenient liquid that can be produced by reduction of carbon dioxide in the atmosphere. It can be catalytically converted into ethylene and propylene and through them to higher hydrocarbons. This can provide an inexhaustible source of hydrocarbon products and fuels, which are now obtained from oil and gas. Furthermore, in recent years, with colleagues at California Institute of Technology and the Jet Propulsion Laboratory, we have also developed a new, direct methanol fuel cell that produces electric power without the need of hydrogen. Thus, methanol is both a fuel and a source of hydrocarbons. By recycling excess CO2 into methanol instead of just storing or sequestering it, we can also mitigate global warming. It is to this effect that a major research effort, with my colleagues associated with the Loker Hydrocarbon Research Institute at the University of Southern California, is directed.


George A. Olah is a professor of chemistry and director of the Loker Hydrocarbon Research Institute at the University of Southern California. He won the 1994 Nobel Prize in Chemistry for his work on carbocation and hydrocarbon chemistry.

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