Branches of Chemistry. Organic Chemistry

In an achievement regarded as a milestone in synthetic organic chem­istry, two research groups in 1994 announced development of techniques for the total synthesis of the anticancer drug taxol. Originally isolated from the Pacific yew tree, taxol was regarded as a promising treatment for a variety of cancers, including those of the ovary, breast, and lung. At first, obtaining taxol in quantity had been expected to require the cutting and processing of thousands of trees, leading to concern about destruction of yew forests. The shortage in supply set off a worldwide race among organic chemists to obtain the molecule from other sources, yet its total synthesis from simple starting materials proved to be one of the most elusive goals of the past decade. The taxol molecule is large and complex, built from an unusual system of four rings extremely difficult to recreate in the laboratory.

The two techniques to taxol synthesis are different and were devel­oped by separate research groups. Robert A. Holton and co-workers of Florida State University used ordinary camphor as a starting material and proceeded with a " linear" strategy to assemble each component of the molecule one piece after another. By contrast, K.C. Nicolaou and co-workers of the Scripps Research Institute, La Jolla, Calif., and the University of California at San Diego used a " convergent" strategy in which two large parts of the taxol molecule are synthesized separately, and then joined.

Neither synthesis was expected to have an immediate impact on the commercial supply of taxol, which no longer was scarce. Taxol was be­ing made in a semi-synthetic process from chemical precursors collected from yew needles and twigs, which can be harvested without killing trees. But scientists said that the work could have the way for a simpler total synthesis and that it had expanded knowledge about synthesizing com­plex molecular structures.

Natural gas, best known as a fuel for home heating and cooking, is typically 85-90% methane (CH₄). Researchers long have sought cheaper and better ways for exploiting the methane in natural gas as a raw mate­rial for making industrial chemicals that currently must be made from petroleum. Doing so has proved difficult because methane does not readily undergo the proper chemical reactions.

During the year AyusmanSen and Minren Lin of Pennsylvania State University reported developing a single-step process that converts meth­ane into acetic acid (CH₃COOH) under mild conditions. An addition to, being the acid in vinegar, acetic acid is a key raw material of the chemical industry, used in the manufacture of plastics, Pharmaceuticals, pesticides, dyes, and other products. Most industrial acetic acids has been obtained from petroleum. Sen and Lin's process requires only methane, carbon monoxide (CO), oxygen (O₂), and a catalyst, rhodium chloride (RhCl₃), which is dissolved in water to promote the conversion of methane. The reaction, which can be summarized as gives high yields and produces only methanol and formic acid as by­products. Importantly, the reactions require temperatures of only 100°C (212°F), the boiling point of water. By contrast, a process used for manufacturing acetic acid from methane requires three costly steps, consumes much energy, and requires hazardous organic solvents that must be con­tained or recycled. The researches regarded the new process as an impor­tant first step toward exploiting the methane in natural gas.

Chemists were devoting increased research attention to molecular self-assembly, a phenomenon in which complex molecules form sponta­neously from simple components. Some scientists suggested that life on Earth originated in such a way, with simple chemical components spon­taneously growing more complex and developing the ability to replicate. In an advance in the understanding of self-assembly, chemists at the University of Birmingham, England, announced discovery of a mole­cule that pieces itself together in a previously unrecognized way. J. Fraser Stoddart and David Amabilino synthesized the new molecule, which was dubbed olympiadane because its five underlinked molecular rings resemble the logo of the Olympic Games. Many organic compounds are formed from ringlike arrays of atoms that are attached by chemical bonds between atoms. Olympiadane's rings, however, are interlocked mechan­ically without bonds. Stoddart and Amabilino encouraged the self-as­sembly by careful control of temperature, pressure, and other conditions during synthesis. During assembly, chains of atoms thread together one inside the other, much like the links on a chain, ending with five inter­locked rings.

Bleach additives in laundry detergent powders work by oxidizing fabric stains through the action of hydrogen peroxide. Laundry deter­gents usually contain a berborate compound that forms hydrogen per­oxide when the detergent powder comes into contact with water. Hy­drogen peroxide, even when aided by detergent additives that lower the water temperature needed for acceptable bleaching activity, does not bleach effectively unless the water temperature is above 40°C (104°F). Many consumers, however, want to do laundry in cooler wa­ter in order to conserve energy and avoid damaging modern fabrics. Chemists thus have searched for low-temperature oxidants that bleach in cooler water.

Ответьте на вопросы по тексту:

1. What did two research groups announce in 1994?

2. What was regarded as a promising treatment for a variety of cancers?

3. What is natural gas?

4. What did AyusmanSen and Minren Lin of Pennsylvania State University report?

5. What is the most industrial acetic acids obtain from?

6. What kind of discovery was announced at the university of Birmingham?

7. Why do many consumers want to do laundry in cooler water?

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