Alcohols — common mistakes

In exam questions about the oxidation of primary alcohols, pay close attention to the conditions. 'Distil' or 'distillation' implies the product is an aldehyde. 'Reflux' or 'heat strongly' implies the product is a carboxylic acid. If no conditions are given, assume complete oxidation to the carboxylic acid.

For unsymmetrical secondary or tertiary alcohols, dehydration can lead to more than one possible alkene product, depending on which adjacent carbon atom loses a hydrogen. You may be asked to draw all possible isomers.

In an alcohol, the hydroxyl (–OH) group is attached to a saturated carbon atom (part of an alkyl group). In a phenol, the –OH group is attached directly to a carbon atom within a benzene ring. This difference leads to significantly different chemical properties, particularly in terms of acidity.

Yes, potassium manganate(VII) ($KMnO_4$) is a powerful oxidising agent and will oxidise primary and secondary alcohols. The colour change is from purple ($MnO_4^-$) to colourless ($Mn^{2+}$). However, it is less selective than dichromate(VI) and can easily cause cleavage of C-C bonds, especially under harsh conditions. For A-Level purposes, acidified potassium dichromate(VI) is the standard reagent you should refer to unless specified otherwise.

Esterification is a slow, reversible reaction. The strong acid catalyst (e.g., concentrated $H_2SO_4$) serves two purposes: it speeds up both the forward and reverse reactions, allowing equilibrium to be reached faster. It also acts as a dehydrating agent, removing the water produced, which shifts the equilibrium position to the right (according to Le Chatelier's principle), increasing the yield of the ester.