carboxylic acid derivatives

• weak acids

  -carb. acids with fewer than 6 carbon atoms are water soluble - h2o can form H bonds with functional group

  -in aq soln - partially ionised

  -produces carboxylate ions and H+

  -pos of equm lies to the left, conc of H+ is smaller than conc of carb. acid
• preparation of esters

  -formed by condensation reaction between alcohol and carb. acid in the presence of conc strong acid catalyst

  -esterification

  -involves the elimination of a small molecule
• esters

  -carboxylic derivative -COO-

  -remove -oic acid from suffix and replace with -oate

  -alkyl chain attached to oxygen atom of the COO- group

  eg. ethanoic acid ---> methyl ethanoate
• uses of esters - fragrances and flavouring

  -esters have a fruitier and sweeter smell than aldehydes

  -ketones are responsible for many natural flavour scents and flavouring

  -synthetic esters can also be used as artificial fruit flavours in confectionary products

  -aromas and tasters are often due to complex mixtures of different esters
• uses of esters - plasticisers

  -poly(chloroethene), PVC is a strong rigid polymer suitable for making drainpipes and guttering

  -plasticisers which are additives mixed into polymers to increase the flexibility of the polymer

  -when a suitable plasticising ester is added, it can be made into cling film

  -ester plasticiser works by penetrating between the polymer chains which increases the distance between them

  -This then weakens the polar effects of the carbon-chlorine bond and the rigidity of the 3D structure if reduced allowing the polymer chains to slide over one
• uses of esters - solvents

  -commonly used as solvents for organic compounds

  -ethyl ethanoate is a common solvent which has beneficial properties of low toxicity and low volatility and well as being relatively cheap

  -ideal solvent for use in glues, fragrance and nail polish
• naturally occurring esters

  -triglycerides found in animal fat and olive oil are naturally occurring

  -they are tri-esters of glycerol and fatty acids such as stearic acid
• Biodiesel

  -made form renewable vegetable oils rather than non sustainable petrochemicals

  -natural triglyceride oils are converted to esters of methanol which makes them less viscous
• eg. biodiesel made from rapeseed oil

  -produced by transesterification

  -triglyceride is transesterified into less viscous fatty acid methyl ester using methanol

  -acids and alkalis can both be used as a catalyst

  -acid protonates carbonyl group

  -alkali deprotonates the alcohol

  -more common to use NaOH or KOH

  -a reversible reaction, so XS methanol is used to drive equm right

  -can produce very successful yield
• transesterification reaction

  triglyceride + methanol --NaOH--> fatty acid methyl esters + glycerol
• ester hydrolysis - acid

  -reverse of esterification is hydrolysis

  -creates biodegradable plastics

  -esters hydrolysed to reform carb. acid and alcohol or salt of carb. acid using dilute acid

  -ester heated under reflux with acid an equm mixture is established - hydrolysis reaction is not complete
• ester hydrolysis - alkaline

  -heating ester under reflux with dilute alkali is an irreversible reaction - ester is fully hydrolysed reaction goes to completion

  -carb. acid produced reacts with XS alkali to form carb. salt and alcohol

  -the carboxylate salt requires further acidification to turn into a carboxylic acid
• ester hydrolysis - acid VS alkaline


  ACID:

  -equm established - doesnt go to completion

  -heat under reflux and dilute acid eg. HCl or H2SO4

  -carb. acid and alcohol produced

  ALKALINE:

  -reaction is irreversible - goes to completion

  -heat under reflux and dilute alkali eg. NaOH

  -carboxylate salt and alcohol produced
• making soap


  -veg oil and animal fat can be hydrolysed in alkaline conditions with aq NaOH to form soap

  -saponification

  -soaps are carboxylate salts of long chain carboxylic acids, known as fatty acids

  -when triglycerides are hydrolysed in hot alkaline conditions - products is a mixture of glycerol and salts