Chlorinated pesticidesHydrocarbons combined with chlorine are among the most effective insecticides known. Most familiar of this group is DDT (dichlorodiphenyl-trichloroethane). DDT is termed a "hard" insecticide because it can exist in soil and water systems for months or even years. Other hard insecticides include Aldrin, Dieldrin, and Lindane. Their use is severely re-
stricted. Although they successfully eradicate disease-transmitting insects and crop predators, they are also hazardous to humans. Many herbicides are also halogenated hydrocarbons. The most widely used is a wheat herbicide.
Recordsare made largely of PVC, with the addition of plasticizers to make the records flexible. PVC is one of the best-known and most widely used of the vinyl polymers. In its rigid, un-plasticized form it is used for pipes and guttering. In its flexible, plasticized form, it is used for pliable sheeting, electrical insulation, nonflammable upholstery coverings, floor tiles, and clothing.
Alcohol(ethanol) has long been made by fermentation. During this process, enzymes from yeast cells (shown highly magnified, right) bring about the breakdown of starch or sugar into alcohol and carbon dioxide. The process is still the basis of the brewing industry for beer and lager and for the production of spirits such as whiskey (far right).
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| -CH3
| | •
| -CH2 1
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| 1 -CH
| | O
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-c-
| | The boiling pointsof primary alcohols (red line) are higher than the boiling points of their isomeric counterparts. Secondary isomers lie along the purple line. Tertiary isomers he along the orange line. These secondary and tertiary isomers have the same molecular weight and lie on the same vertical line on the diagram as their primary alcohols.
(*C) *CF)
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| Ethanol • O*
^r 2-propanol
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Alcohols
Alcohols are some of the most common and widely used chemicals. Methanol (methyl alcohol) is the simplest. It has been used for many years as a solvent in dissolving other substances and as a fuel. Another well-known alcohol is ethanol, or ethyl alcohol. It has been used for thousands of years as an intoxicating ingredient in alcoholic beverages such as wine, spirits, mead, and ale. Ethanol is also important industrially as a solvent and as a reaction medium, which acts on other substances to form further substances.
Date: 2015-12-11; view: 1277
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