7.2.3 Alcohols

Alcohols contain the functional group -OH and are characterised by the general formula R-OH, where R represents a hydrocarbon group. The first four members of the homologous series of alcohols are methanol, ethanol, propanol, and butanol.

Alcohols, such as ethanol, can be represented either by their molecular formula (CH₃CH₂OH), or in the following form:

When alcohols react with sodium, a displacementThe forced removal of people from their land. reaction occurs where hydrogen gas is evolved, and sodium alkoxide is formed. For example, with ethanol (CH₃CH₂OH):

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂

When alcohols burn in air, they undergo combustion reactions, similar to other hydrocarbons. The alcohol is oxidised to produce carbon dioxide and water. For example, with ethanol:

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O

Alcohols can be added to water, forming a homogeneous mixture. This process is called solvation or hydration. The alcohol molecules interact with water molecules through hydrogen bonding.

When alcohols react with oxidising agents, they can be oxidised to produce various products. The specific products depend on the oxidising agent used. For example, ethanol can be oxidised to ethanal (acetaldehyde) by mild oxidising agents like acidified potassium dichromate (K₂Cr₂O₇) or to ethanoic acid by stronger oxidising agents like acidified potassium permanganate (KMnO₄).

The main uses of these alcohols include:

• Methanol: Used as a solvent, antifreeze, and in the production of formaldehyde and other chemicals.
• Ethanol: Used as a solvent, fuel additive, in the production of alcoholic beverages, and in many industrial processes.
• Propanol: Used as a solvent, intermediateAny structure in the reaction profile which is connected by two transition states and is an energy minima. Although intermediates are energetically disfavoured they are stable and can sometimes be isolated. in chemical synthesisCombining information from more than one text to show comparison., and in cosmetics and personal care products.
• Butanol: Used as a solvent, fuel additive, and in the production of butyl rubber and other chemicals.

Aqueous solutions of ethanol are produced through the process of fermentation. Fermentation occurs when sugar solutions, such as those derived from fruits or grains, are exposed to yeast. The yeast converts the sugars into ethanol and carbon dioxide through anaerobic respiration.