Reactions of Alcohols 2021-22

• A chain of carbon atoms can be represented by R when drawing the structure. This is referred to as an R group.

• R group can either be an alkyl or an aryl.

• Primary (1°) alcohols have one R group attached to the carbon to which the OH group is attached.

  
  

• Secondary (2°) alcohols have two R groups attached to the carbon to which the OH group is attached.

  
  

• Tertiary (3°) alcohols have three R groups attached to the carbon to which the OH group is attached.

  
  

• Primary alcohols can be oxidized to aldehydes by an oxidizing agent such as an aqueous solution of acidified potassium dichromate(VI).

• When the symbol equation is written, the oxidizing agent is represented by [O]

• Aldehydes contain a carbonyl group (C=O) at the end of the carbon chain, and are named using the suffix –al.

• When aldehydes are prepared by the reaction of a primary alcohol with acidified potassium dichromate(VI), the aldehyde is distilled off and collected, preventing further oxidation.

• If primary alcohols are reacted with an excess of oxidizing agent and refluxed, they can be oxidized to aldehydes and then oxidized further to carboxylic acids.

• Carboxylic acids contain a carbonyl group (C=O) at the end of the carbon chain, with a hydroxyl group (OH) attached to the carbonyl carbon.

• Carboxylic acid are named using the suffix –oic acid.

• Secondary alcohols can be oxidized to ketones by an oxidizing agent such as an aqueous solution of acidified potassium dichromate(VI).

• Ketones contain a carbonyl group (C=O) attached to any carbon in the chain except a terminal carbon atom, and are named using the suffix –one.

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• Esterification involves refluxing a carboxylic acid and an alcohol with a concentrated sulfuric acid catalyst.

• The names of esters have two parts: the first is an alkyl group (from the alcohol) and the second is a carboxylate group (from the carboxylic acid).

• For example, methanol and ethanoic acid react to form methyl ethanoate.

• Esters can be hydrolysed by heating under reflux with

  either an acid or a base.

• Refluxing with an acid simply reverses the preparation of the ester from an alcohol and a carboxylic acid.

• The acid catalyses the reaction.

• The reaction is reversible and an equilibrium mixture is established.

• In acid hydrolysis, there are always both reactants (ester + water) and products (carboxylic acid + alcohol) present after the reaction.

• When an ester is refluxed with an alkali (a

  soluble base), such as aqueous sodium hydroxide, it is fully hydrolysed.

• Unlike acid hydrolysis, this is not a

  reversible reaction, so all the ester present can be broken down by excess alkali.

• An alcohol and the sodium salt of the carboxylic acid are formed.

• Aldehydes and ketones can be reduced by a reducing agent, such as sodium borohydride (NaBH₄), to form alcohols.

• When the symbol equation is written, the reducing agent is represented by [H].

• Aldehydes are reduced to primary alcohols.

• Ketones are reduced to secondary alcohols.

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• In the lab, dehydration of ethanol can be achieved by passing ethanol over a hot aluminum oxide catalyst. Ethene gas is collected by displacement.

• Alcohols undergo complete combustion to form carbon dioxide and water.

• Denatured alcohol is ethanol that has been made toxic and undrinkable by the addition of other chemical additives.

• A traditional additive was methanol, which formedmethylated spirits (meths): 90% ethanol and 10% methanol.

• Denatured alcohol is a useful portable fuel (e.g. for camping stoves) as, unlike LPG, it does not need to be transported in heavy, specialized containers. It is also used as a solvent.

• Primary, secondary and tertiary alcohols all react with phosphorus(V) chloride to form a chloroalkane.

• Adding solid phosphorous(V) chloride to an alcohol at room temperature produces white HCl fumes, as well as the chloroalkane.

• This reaction can be used as a test for alcohols (the OH group), as well as a method of producing halogenoalkanes.