Reactions of Alcohols

Reactions of Alcohols – Basic Features

  • Alcohols, chemical compounds containing a hydroxyl (-OH) group, are reactive and undergo a range of transformations.
  • The reactivity of alcohols relates to the presence of the polar hydroxyl group and the carbon chain’s nature influenced by functional group.
  • Primary (1°), secondary (2°), and tertiary (3°) alcohols differ in their reactivity because of the types and amounts of alkyl groups bonded to the carbon atom holding the hydroxyl group.

Alcohol Oxidation

  • Primary alcohols are oxidised in two steps. At first step, an alcohol is transformed into an aldehyde with mild oxidation agents, and subsequent strong oxidation leads to the formation of a carboxylic acid.
  • Secondary alcohols are oxidised to ketones using either mild or strong oxidising agents, but they cannot be further oxidised.
  • Tertiary alcohols can’t be oxidised due to the lack of hydrogen atoms on the carbon attached by the alcohol group.

Alcohol Dehydration

  • Alcohols undergo dehydration to produce alkenes. In the presence of acid catalysts, such as concentrated sulphuric acid, the -OH group and a hydrogen atom from the adjacent carbon atom are removed forming a carbon-carbon double bond (alkene).
  • The order of reactivity of alcohols in dehydration reactions is 3° > 2° > 1°.

Esterification

  • Alcohols can react with carboxylic acids in the presence of concentrated sulfuric acid to form esters.
  • This reaction, known as esterification, is reversible and is often driven to completion by removing the water produced during the reaction.
  • Esters are significant in the fragrance and flavourings industry due to their sweet smells.

Roles of Alcohol in Medicine

  • Disinfection: Alcohols such as isopropyl alcohol and ethanol are effective disinfectants, used for general surface cleaning and skin antiseptics.
  • Drug Formulation: Certain alcohols, like ethanol and propylene glycol, serve as solvents in pharmaceutical products. They help in enhancing the solubility of poorly soluble drugs.
  • Induce Sleep: Alcohol can induce sleep, but too much interrupts the sleep cycle and can lead to alcohol dependence or addiction. Consequently, it loses its effectiveness as a sleep aid.

Potential Negative Consequences

  • Alcohols such as methanol and ethylene glycol are included in the category of ‘toxic alcohols’. They can cause serious poisoning if ingested, leading to blindness or even death in the case of methanol and acute kidney injury in the case of ethylene glycol.
  • Overconsumption of ethanol leads to various health problems, including liver damage and nervous system disorders.