3.3.9- Carboxylic acids and derivatives (PAPER 2) Flashcards
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
Draw general equation for reaction of an oil with methanol and KOH catalyst to produce glycerol and methyl ester
O
H //
H C O C - R
O
//
H C O C- R + 3CH3OH —> (KOH)
O
//
H C O C - R
H
H O
H- C- OH //
H- C -OH + 3 H3C O C - R
H- C- OH
H
Where do aspects in methyl ester come from in the reaction?
CH3O from methanol, C=O- R from oil
What are acyl/acid chlorides and how are they named?
Have the functional group -COCl which contains acyl group C=O Cl
Named by finding longest C chain and adding -oyl chloride to the end- C on acyl group is always C 1
Draw the structure of ethanoyl chloride
H
H C - C =O
H Cl
COCl group on end
Draw the structure of 3,4-dihydroxy-2-methylbutanoyl chloride
OH on 3rd and 4th carbon, CH3 on 2nd carbon COCl on end
What is the mechanism for nucleophilic addition- elimination reaction between ethanoyl chloride and H2O?
Addition: curly arrow from lone pair on O to d+ C, curly arrow from double bond to O , double bond breaks and H2O joins to the C, new O has + charge, old O has lone pair
Elimination: double bond reforms as curly arrow from new lone pair on old O to C-O bond, curly arrow from C-Cl bond to Cl, negative Cl removed
Curly arrow from lone pair on Cl to one H joined to O, curly arrow from H-O bond to O+
ethanoic acid and HCl formed
What is ethanoic acid known as?
Acetic acid
What is the mechanism for nucleophilic addition-elimination between ethanoyl chloride and NH3?
Addition: curly arrow from lone pair on N of NH3 to d+ C, curly arrow from double bond to O, double bond breaks and NH3 joins to the C, O has lone pair, N has + charge
Elimination: double bond reforms as curly arrow from lone pair on O to C-O bond, curly arrow from C-Cl bond to Cl, negative Cl removed
H ion removed from ammonia either by chloride ion or ammonia molecule
Chloride ion: curly arrow from lone pair to H, curly arrow from N-H bond to N to form HCl. HCl immediately reacts with excess ammonia- NH3 + HCl —–> NH4Cl
Ammonia: curly arrow from lone pair on N to H, curly arrow from N-H bond to N, H joins to extra ammonia molecule
ethanamide produced and either NH4Cl or NH4+
What is the mechanism for nucleophilic addition-elimination between ethanoyl chloride and ethanol/ an alcohol?
Addition: curly arrow from lone pair on O from alcohol to d+ C, curly arrow from double bond to O, double bond breaks and O joins to the C (with H and CH3CH2), new O has + charge, old O has lone pair.
Elimination: double bond reforms as curly arrow from lone pair on O to C-O bond, curly arrow from C-Cl bond to Cl, negative Cl removed
Curly arrow from lone pair on chloride ion to H joined to O from alcohol, curly arrow from O-H bond to positive O
ethyl ethanoate and HCl produced
What is the mechanism for nucleophilic addition-elimination between ethanoyl chloride and ethylamine/ a primary amine?
Addition: curly arrow from lone pair on N from ethylamine to d+ C, curly arrow from double bond to O, double bond breaks and N joins to the C (with H, H, CH3Ch2), N+, O has lone pair
Elimination: double bond reforms as curly arrow from lone pair on O to C-O bond, curly arrow from C-Cl bond to Cl, negative Cl removed
H ion removed from N either by chloride ion or another ethylamine molecule
Chloride ion: curly arrow from lone pair on Cl to one H joined to N, curly arrow from H-N bond to N. HCl immediately reacts with excess ethylamine- CH3CH2NH2 + HCl —> CH3CH2NH3Cl
Ethylamine: curly arrow from lone pair on N to one H joined to N, curly arrow from H-N bond to N. CH2CH3NH3+ produced
ethylammonium chloride produced
What are acid anyhydrides and how are they named?
Molecules made from 2 carboxylic acids which are the same.
Named by using half the molecule: one of the carboxylic acids and removing the -acid and adding -anyhydride.
Draw the structure of ethanoic anhydride
O
//
H3C - C
\
O
/
H3C - C
O
What is produced when an acid anhydride reacts with water? Eg ethanoic anhydride with H2O equation
2 of the carboxylic acid
slower reaction, acid anhydrides are not as reactive as acyl chlorides
(CH3CO)2O + H2O ——> 2CH3COOH
What is produced when an acid anhydride reacts with an alcohol? Eg ethanoic anhydride with ethanol
ester + carboxylic acid
(CH3CO)2O + CH3CH2OH —-> CH3COOCH2CH3 + CH3COOH
ethyl ethanoate + ethanoic acid
What is produced when an acid anhydride reacts with ammonia? Eg ethanoic anhydride with ammonia
ester + amide
(CH3CO)2O + 2NH3 —-> CH3CONH2 + CH3COONH4
ethanamide and ammonium ethanoate
What is produced when an acid anhydride reacts with a primary amine? Eg ethanoic anhydride with methylamine
N-substituted amide and carboxylic acid
(CH3CO)2O + CH3NH2 —-> CH3CONHCH3 + CH3COOH
N-methylethanamide and ethanoic acid
How will excess methylamine form a salt with ethanoic acid?
CH3COOH + CH3NH2 —> CH3COO- +NH3CH3
methylammonium ethanoate
What is the functional group of amides?
-CONH2
What is the reaction to produce aspirin?
Ethanoic anhydride + salicylic acid —-> aspirin + ethanoic acid
Why is ethanoic anhydride used instead of ethanoyl chloride?
Less corrosive so safer
Does not produce harmful HCl gas
Less expensive
Does not react rigorously with water
