carboxylic acids and esters

what is the structure of carboxylic acid and ester

RCOOH. carboxyllic acid

esters RCOOR

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how do you form an ester

Carboxylic acids and alcohols react, in the presence of an acid catalyst, to give esters.

the reaction is reversible and water is always the by-product 

carboxylic acid and alcohol will determine the ester made. e.g. butanol + ethanoic acid will make butylethanoate and water.

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what happens when reacting with carbonates with ca

 will liberate CO2 from carbonates. form salt, water and CO2

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how strong are carboxylic acids

weak 

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what are the physical properties of carboxylic aci

  • OH bond in carboxyllic acids form hydrogen bonding and so they have relatively high MP and BP than other similar sized alkanes 
  • COOH group is very soluble in water due to hydrogen bonding but the hydrocarbon chain of a carboxyllic acid is non-polar and is insoluble. short chain carboxyllic acuds dissolve easily but longer ones is less soluble because the hydrocarbon chain is longer the sollubility of COOH is cancelled out by the insolubility of the hydrocarbon chain
  • they have very distinguished melting points and so can be used to distinguish between different carboxylic acids
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what are the common uses of esters

solvents

plasticiser (makes plastic more flexible)

perfumes

food flavourings (like pear drops)

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what can esters be hydrolysed in and what do they

Esters can be hydrolysed in acid to form carboxyllic acids and alcohol 

alkaline conditions to form a salt of carboxyllic acids and alcohol. this will leave the equilibrium to the right as there are less carboxyllic acids to form esters again.

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what can vegetable oils and animal fats be hydroly

Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol.

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what is biodiesel

Biodiesel is a mixture of methyl esters of long-chain carboxylic acids.

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how is biodiesel produced

Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst.

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why is there an increased use of biofuels

  • to conserve crude oil supplies 
  • to reduce the amount of CO2 released to atmosphere 
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base hydrolysis

Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol.

has to be refluxed 

the carboxyllic acid salts dissociate in water 

RCOONa --> RCOO- + Na+

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how does soap work

Hydrophobic ends of soap molecule all attach to the oil. Hydrophilic ends stick out into the water. This causes a drop of oil to form

These drops of oil are suspended in the water. This is how soap cleans a surface - it causes drops of grease and dirt to be pulled off it and suspended in water. These drops are washed away when you rinse with more water.

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how can you identify an ester

Students could identify an ester by measuring its boiling point, followed by hydrolysis to form the carboxylic acid, which is purified by recrystallisation, and determine its melting point.

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how could you m are an ester

Students could make esters by reacting alcohols with carboxylic acids, purifying the product using a separating funnel and by distillation.

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how are Biodiesel made

fatty acids formed from hydrolysis of triesters are used to create a new ester with methanoic acid

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