3.3.9- Carboxylic acids and derivatives (PAPER 2) Flashcards
(44 cards)
What are carboxylic groups and how are they named?
Weak acids with the carboxyl (-COOH) functional group which contains carbonyl C=O and hydroxyl group OH
Carboxyl group is always Carbon 1 at the end of the molecule- add -oic acid to name
How are carboxylic acids produced?
From the oxidation of primary alcohols under reflux.
How do carboxylic acids dissociate in water? Eg CH3COOH
They are weak acids so partially dissociate to form a carboxylate ion and a H+ ion
CH3COOH ⇌ CH3COO- + H+
Equilibrium lies to left
How do acids react with carbonates?
To form a salt, carbon dioxide gas and water
Difference in reaction between ethanoic acid and sodium carbonate- ethanoic acid and sodium hydrogencarbonate
ethanoic acid and sodium carbonate
2CH3COOH (aq) + Na2CO3 (aq) —-> 2CH3COONa (aq) + CO2 (g) + H2O (l)
ethanoic acid and sodium hydrogencarbonate
CH3COOH (aq) + NaHCO3(aq) —–> CH3COONa (aq) + CO2 (g) + H2O (l)
What are esters and how are they named?
Derived from carboxylic acids- COOH group but H is replaced by a type of hydrocarbon
first section of name from alcohol, second section from carboxylic acid ( -oate)
Draw the structures of methyl butanoate and propyl methanoate
methyl butanoate- CH3CH2CH2COOCH3, methyl group on end
propyl methanoate- CH3CH2CH2OCOCH, propyl group on end C=O, H , O joined to propyl group
How are esters made from carboxylic acid and alcohol?
Esters are produced when carboxylic acids are heated with alcohols in the presence of an acid catalyst (usually sulfuric)
General formula
RCOOH + R’OH ⇌ RCO(OR from alcohol) + H ( 1 from alcohol) 2O
Write the equation for ethyl ethanoate from ethanoic acid and ethanol
CH3COOH + CH3CH2OH ⇌ CH3COOCH3CH2 + H2O
What are esters used for?
They are used commercially and in industrial processes:
Perfumes and food flavourings- some have sweet smells like pear drops
Solvents- they are polar so other polar compounds will dissolve readily in esters, low boiling points and evaporate easily so good as glue
Plasticisers- make plastics more flexible in polymerisation process, can leach out over time so plastic becomes brittle
How does acid hydrolysis of esters occur? reacting with water
Use dilute acid such as sulfuric or hydrochloric acid to split ester into carboxylic acid and alcohol, conduct reaction under reflux.
What is the equation for the hydrolysis of methyl propanoate using an acid?
CH3CH2COOCH3 + H2O ⇌H+ CH3CH2COOH (propanoic acid) + CH3OH (methanol)
How to make the reaction as complete as possible due to its reversible nature?
You would have to use an excess of water. The water comes from the dilute acid, so mix the ester with an excess of dilute acid.
How does base hydrolysis of esters occur?
Use dilute base like sodium hydroxide to split ester into carboxylate ion and an alcohol, reaction conducted under reflux.
What is the equation for the hydrolysis of methyl propanoate using a base?
CH3CH2COOCH3 + NaOH —–> CH3CH2COONa (sodium propanoate) + CH3OH (methanol)
What are the advantages to using dilute alkali instead of dilute base for ester hydrolysis?
The reactions are one-way instead of reversible so reaction goes to completion and the products are easier to separate: with an excess of NaOH, there will be no ester left and alcohol can easily be distilled off.
What is IUPAC name for glycerol? Draw the structure
propane-1,2,3-triol
H H- C- OH H- C -OH H- C- OH H
What happens when glycerol reacts with fatty acids(carboxylic acids)?
An ester is produced which makes fats and oils
Glycerol reacts with long chain fatty acids which can be saturated (no double bonds) or unsaturated (at least 1 double bond)
Draw the general equation for reversible reaction between glycerol and 3 fatty acids to show esterification and hydrolysis
H
H- C- OH
H- C -OH + 3- R-COOH ⇌ esterif/ hydroly
H- C- OH
H
H H- C- O- C - R1
//
H O H- C - O - C - R2 + 3H2O
//
H O H- C - O - C - R3
H //
O
Which part is the ester link?
O-C=O
What occurs during base/ alkaline hydrolysis of animal fats and vegetable oils?
A salt of a carboxylic acid is formed which is found in soap and an alcohol is produced- this is known as saponification.
What is the equation for saponification of a typical fat/ oil to produce glycerol and sodium salt?
O
H //
H C O C (CH2)16CH3
O
//
H C O C (CH2)16CH3 + 3NaOH
O
//
H C O C (CH2)16CH3
H
—–> H
H- C- OH
H- C -OH + 3CH3(CH2)16COO-Na+
H- C- OH
H
What is the difference between fats and oils?
Oils have unsaturated (DOUBLE BONDS) hydrocarbon chains which are not straight so chains cannot pack as tightly together- lower VDW’s and melting point, fats have saturated hydrocarbon chains that are straight and can pack tightly together, higher VDW’s and melting point.
What is biodiesel?
A type of fuel made from vegetable oils- by reacting the oils with methanol and potassium hydroxide as a catalyst.
Mixture of fatty acids made from methyl esters- can be made from rapeseed oil
