Science and Technology for UPSC Examinations [Chemistry] Part 17- Alcohols
Alcohols are compounds which contain carbon, hydrogen and oxygen. Alcohols can be derived from alkanes, if a hydrogen (–H) in alkane is replaced by a hydroxyl group (–OH). For example,
Generally alcohols are represented as R–OH where R is an alkyl group and –OH is the functional group and the general formula of alcohol is given as CnH2n + 1 OH, where ‘n’ is the number of carbon atoms. There are two ways of naming organic compounds namely Common and IUPAC system. The common names of alcohols are derived when the last letter ‘-ane’ in the name of the parent hydrocarbon is replaced by ‘-yl’ and it is combined with the word ‘alcohol’.
According to IUPAC system, the last letter ‘-e’ in the name of the parent hydrocarbon is replaced by ‘ol’.
Alcohols are classified into primary, secondary (sec), and tertiary (tert), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl group. The primary alcohols have general formulas RCH2OH; secondary ones are RR’CHOH; and tertiary ones are RR’R”COH, where R, R’, and R” stand for alkyl groups. Ethanol and n-propyl alcohol are primary alcohols; isopropyl alcohol is a secondary one.[table id=32 /]
Common Applications of Alcohols
Alcoholic beverages, typically containing 5% to 40% ethanol by volume, have been produced and consumed by humans since pre-historic times.
A 50% v/v (by volume) solution of ethylene glycol in water is commonly used as an antifreeze.
Ethanol can be used as an antiseptic to disinfect the skin before injections are given, often along with iodine. -based soaps are becoming common in restaurants and are convenient because they do not require drying due to the volatility of the compound. Alcohol based gels have become common as hand sanitizers.
Some alcohols, mainly ethanol and methanol, can be used as an alcohol fuel. Fuel performance can be increased in forced induction internal combustion engines by injecting alcohol into the air intake after the turbocharger or supercharger has pressurized the air. This cools the pressurized air, providing a denser air charge, which allows for more fuel, and therefore more power.
Alcohol is often used as a preservative for specimens in the fields of science and medicine.
Alcohols have applications in industry and science as reagents or solvents. Because of its relatively low toxicity compared with other alcohols and ability to dissolve non-polar substances, ethanol can be used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In organic synthesis, alcohols serve as versatile intermediates.