Esters Flashcards
Preparation
Produced by the reaction of a carboxylic acid with an alcohol and sulfuric acid catalyst (esterification), Ester is isolated from mixture using distillation, equilibrium reaction, K value is close to 1
Melting and boiling point
Most esters are liquids at room temperature, Lower than alcohols and carboxylic acids of similar molecular mass (removes consideration of dispersion forces) as esters can’t form hydrogen bonds, Higher than alkanes of similar size
Solubility in water
Small esters are soluble in water, As size of the ester increases, solubility decreases as it can’t form hydrogen bonds, Most esters are insoluble in water
Solubility in organic solvents
Most esters are soluble in organic solvents as they can form dispersion forces, As size increases, solubility increases
Esters are powerful solvents
Reactions
Undergo combustion, In acidic conditions, undergo hydrolysis to reform the carboxylic acid and alcohol (original reactants), In basic conditions, forms a salt of carboxylic acid and alcohol (occurs in two steps and reaction goes to completion, important for soap production)
Biodiesel
Biofuel, Made from biomass- plant or animal oils (plant oils), Usually methyl or ethyl esters, Dominant IMF of dispersion forces, Carbon neutral, Renewable, Only 7% of worlds diesel requirements are met from biodiesel, Australia consumes 400 ML biodiesel and the rest is petrodiesel (23 000 ML)
Why are straight-chain esters better
More biodegradable
Acid catalysed esterification with alcohol
Least used method, Conversion of a long chain fatty acid to a methyl or ethyl ester using acid catalyst, Produces a non-volatile ester, CH3(CH2)18COOH + CH3OH –H2SO4–> CH3(CH2)18COOCH3 + H2O
Conversion of oils to fatty acids and then alkyl esters via acid catalysis
Not very popular, preferred, Hydrolysis of an oil (ester) to a fatty acid, Conversion to a methyl or ethyl ester via acid catalysis (esterification)
Base catalysed transesterification with alcohol
Predominant method of biodiesel, Uses raw material of vegetable oil from sources such as soya bean, canola or palm oil, Recycled vegetable oil or animal fats can be used, Reaction goes to completion, R’OH (commonly methanol) is in excess about 6:1 giving a 98% conversion, Occurs at 60 degrees so that everything is liquid (methanol boils at 64 degrees), R’OH + RCOOR’’ –base (KOH/NaOH)–> R’‘OH + RCOOR’
Saponification
Base hydrolysis of an ester (triglycerides), Fats and oils are naturally occurring esters based on the alcohol glycerol and 3 long chains of saturated and/or unsaturated carboxylic acids known as fatty acids
How are soaps made
Fat or oil is boiled with a strong base (need 3 moles to break 3 ester bonds) such as sodium hydroxide or potassium hydroxide, each ester linkage is split to give a salt of a fatty acid and glycerol
Limitations of soap
Surfactant (surface acting agent) which works by making dirt and grease soluble in water, Limited effectiveness in hard water as it precipitates and forms scum with calcium and magnesium ions, In hard water: poorly washed clothes, blocked drains, grey scum in wash tubs, stains around basins and taps
Detergents
Soapless cleaning agents, Work in hard water, Work similarly to soaps
Manufacturing detergents
Make alkylbenzene sulfonic acid from an alkylbenzene, Alkylbenzene sulfonic acid is neutralised with sodium hydroxide producing sodium alkylbenzene sulfonate
