CHEM 2 - Alcohols

Primary alcohols are easily oxsidised to aldehydes 

Secondary alcohols are oxidised to ketones and no further

Tertiary alcohols are not easily oxidised due to C-C bond instead of C-H being broken

Ethanal

Use dilute acid and less potassium dicrhromate (IV) than is needed for oxidation to carboxylic acid

• Use excess alcohol so there isn't enough oxidising agent for further oxidation
• Ethanol vapourises and distils of as soon as it is formed to prevent further oxidation.

Ethanoic acid

Use concentrated acid and excess dichromate ions to ensure full oxidation

• Heated under reflux

Alcohols can be used as intermediates in the chemical industry

Ethanol via crude oil

Ethanol is made by reacting ethene (from crude oil - naphtha fraction) with steam using phosphoric acid (H3PO4) as a catalyst

Ethanol via fermentation of sugars

Glucose ---> 2C2H5OH + 2CO2

• Compromise of 35 degrees is made
• Air kept out of fermentation vessels to prevent ethanol --> ethanoic acid
• Ethanol via fermentation is carbon-neutral: 6CO2 in via respiration, 2CO2 out via fermentation and 4CO2 out via combustion

• Aldehydes and ketones both have a C=O group which is called a carbonyl

• Aldehydes: RCHO
• Ketones: RCOR'

Tollens' (silver mirror) test

• Tollens' reagent (silver nitrate in aqueous ammonia) oxides aldehydes but not ketones. Silver ions are reduced from colourless to metallic if aldehyde

Benedict's test

• Benedict's reagent contains blue Cu(II) ions which will oxidise aldehydes but not ketones. Blue solution changes to red if aldehyde

- OH group and a hydrogen from the next carbon is removed from the alcohol.

Elimination in the context of alcohols is always dehydration

• Alcohol vapour is passed over excess hot sulfuric acid/aluminium oxide
• Alkene is formed
• Dehydration of longer-chained alcohols may produce a mixture of alkenes including E-Z isomers