How should I branch out the two methyl groups here and why:
(CH₃)₂CHCH₂COOCH₂CH₂CH₂CH(CH₃)₂?
Give name of esther.
- Keep one in chain and drop one down.
- Make sure there is no CH3 in MIDDLE OF THE CHAIN, because this means the CH3 is bonded to 2 carbons so, C would incorrectly have 5 bonds!
- Name: 4-methylpentyl-3-methylbutanoate.
Spot what’s incorrect!
CH₃COOCH(CH₃)CH₃
- We can’t have (CH₃) group sandwiched in middle of the chain because C atom incorrectly has 5 bonds!
- Needs to be:
CH₃COOCH(CH₃)₂
How do I number the alcohol part of esther (ie. right-hand side?)
- Start numbering from O, O essentially needs to be PART of the chain ie. the hydrocarbon chain in straight line to the O.
- First C after O = carbon 1.
How do I number the carboxylic acid part of esther (ie. left-hand side?)
- From right to left.
- 1st C is the C involved in the esther link.
What are carboxylic acids?
- Weak acids that will react with carbonates to form carbon dioxide.
What does it mean when we say “carboxylic acids are weak acids?”
- They dissociate partially to form carboxylate and H+ ion.
Give equation for dissociation of carboxylic acid. Where does equilibrium lie in this reaction and why?
- RCOOH – (reversible reaction sign) > RCOO⁻ + H⁺
- (minus is on O that was originally OH in the carboxyl group.)
- Equilibrium: left as dissociates poorly.
Give equation for reaction between sodium carbonate and ethanoic acid. Give name of salt produced.
- 2CH₃COOH (aq) + Na₂CO₃(s) –> 2CH₃COONa(aq) +H₂O(l) + CO₂(g)
- Salt: sodium ethanoate.
Give equation for reaction between sodium hydrogen carbonate and ethanoic acid. Name salt produced
- CH₃COOH (aq)+ NaHCO₃(s)–>CH₃COONa (aq) + H₂O (l) + CO₂ (g)
- Salt: sodium ethanoate.
CH₃COONa. What bond is between O and Na? What would displayed formula look like?
- Ionic bond.
- CH₃-C - ONa (inc. double bond from C to O!)
Which 3 reactions will form esters? Write 3 equations.
- Carboxylic acid + alcohol –(reversible reaction sign/ H+ catalyst) –> ester + water.
- Acid anhydride + alcohol –> ester + carboxylic acid
- Acyl chloride + alcohol –> ester + HCl
What are the conditions for esterification reaction between carboxylic acid and alcohol?
- Sulphuric acid catalyst.
Name this ester.
CH₃CH(CH₃)COOCH₂CH₃
What alcohol/ carboxylic acid formed this ester?
- ethylmethylpropanoate
- Ethanol + methylpropanoic acid
Name ester formed
From reaction between ethanol and propanoic acid.
- CH₃CH₂COOCH₂CH₃
- Ethyl propanoate.
What are esters used in?
- Perfumes/ food flavourings: some esters have sweet smells.
- Solvents: polar so other polar compounds dissolve readily.
- Used as plasticisers: make plastic more flexible.
What are the two ways we can speed up an ester hydrolysis reaction?
- Use base: base hydrolysis.
- Use acid: acid hydrolysis.
Conditions of acid hydrolysis of ester
- Dilute acid (either sulphuric/ hydrochloric.)
- Under reflux.
How do we form carboxylic acid / alcohol in ester acid hydrolysis reaction?
- Carboxylic acid: OH from water joins.
- Alcohol: H from water joins.
In acid hydrolysis of ester, what does adding more water do?
- Shifts eqilibrium to right, more product produced.
True or False
Acid/ base-hydrolysis reactions of esters are single-way reactions.
- False.
- They are both reversible reactions.
Write general equation for acid hydrolysis of ester.
Ester + water – (reversible reaction sign/ H+ on top arrow as catalyst) –> Carboxylic acid + alcohol
Write general equation for base hydrolysis of ester?
Ester + OH- –(reversible reaction sign) –> carboxylate ion + alcohol.
Conditions for base hydrolysis of ester.
- Dilute base (KOH/ NaOH.)
- Under reflux
What does carboxylate ion look like
C=OO-
