Carboxylic Acids and their Derivatives (DONE) Flashcards
What is the order of acidity of the following. Put into increasing acidity
- Ethanoic Acid
- Ethanol
- Phenol
- Water
Ethanol is the least acidic
Water is neutral
Phenol is a very weak acid
Ethanoic acid is a weak acid
Why is ethanoic acid acidic?
(2 marks)
- The OH bond in carboxylic acids is the weakest bond, so more protons (aq) are produced.
- The carboxylate ion is given extra energetic stability by delocalisation from one of the lone pair electrons, which spreads its charge across both oxygens. This gives partial pi character.
Why are lower chained carboxylic acids soluble in water, but long chained carboxylic acids are not?
- Able to form hydrogen bonds between molecules of water and other carboxylic acids
- At longer chains, the hydrocarbon chain gets in the way of forming hydrogen bond and instead weaker van der waals forces are made between molecules.
Describe a test to distinguish phenol from a carboxylic acid.
(3 marks)
- Aqueous sodium carbonate (Na₂CO₃) or aqueous sodium hydrogencarbonate (NaHCO₃)
- Only carboxylic acid will be able to liberate CO₂ as an effervescence (bubbles), which turns limewater milky in a separate flask
- The phenol does not produce an effervescence
How can benzoic acid be formed by oxidation of alkyl side chains?
- Give reagents and conditions
- Show the equation for the reaction
4 marks
- alkaline aqueous potassium manganate (VII) as an oxidising agent
- Heat under reflux
- Subsequent acidification by dilute acid
(poly)BENZOIC ACID IS ALWAYS FORMED
C₆H₅CH₃ + 3[O] -> C₆H₅COOH + H₂O
How would you be able to turn a carboxylic acid directly into an alcohol.
- Give reagents and conditions
- Show the equation for the reaction (using ethanoic acid)
(3 marks)
- LiAlH₄ / Lithium Aluminium Hydride
- Anhydrous conditions as LiAlH₄ reacts violently with water
CH₃COOH + 4[H] -> H₂O + CH₃CH₂OH
How is decarboxylation of carboxylic acids carried out?
- Give the reagents and conditions used
- The reaction of the reagent with carbon dioxide
- The overall reactions using carboxylic acid and carboxylate salt
- Which method is preferred
(5 marks)
- Sodalime (NaOH solid) + heat
- 2NaOH + CO₂ -> Na₂CO₃ + H₂O
With CARBOXYLIC ACID
CH₃COOH + 2NaOH -> CH₄ + Na₂CO₃ + H₂O
WITH CARBOXYLATE SALT
CH₃COONa + NaOH -> CH₄ + Na₂CO₃
- Using the sodium salt is preferred as it is generally more effective as there is ionic bonding in the salt. Whereas, with the normal carboxylic acid the molecules rapidly vaporize as there is only weak intermolecular forces between molecules.
Show the reaction of the hydrolysis of an acid chloride using ethanoyl chloride.
Ethanoyl chloride + Water -> Ethanoic acid + Hydrogen chloride (gas)
Show the three different methods of obtaining an acid chloride from carboxylic acids and state which is the preferred method.
State conditions required.
(5 marks)
- RCOOH + SOCl₂ -> RCOCL + SO₂ (g) + HCl (g)
- 3RCOOH + PCl₃ -> 3RCOCl + H₃PO₃
- RCOOH + PCl₅ -> RCOCL + POCl₃ + HCl
Anhydrous conditions and rtp is required
Method with SOCl₂ is preferred as the by-products are both gases and there much more easier to separate.
Which of the following react with phenol to make esters?
- Acid chloride
- Carboxylic acids
Acid chlorides
How is an ester formed from carboxylic acid?
- Give reagents and conditions
- Give a general formula of the equation
- State how the ester can be isolated
(6 marks)
- Concentrated sulfuric acid (dehydrating agent as well as a catalyst) + heat + distill as ester forms
- Alcohol + Carboxylic Acid <–> ester + water (low yield)
Separation:
- Separating funnel and aqueous sodium hydrogencarbonate is added + shaken to remove acidic impurities
- Organic layer is run off
- Ester is dried over anhydrous calcium chloride which removes water and any alcohol
- Ester is re-distilled noting its boiling point
What is an alternative catalyst for making esters with carboxylic acids and why?
- HCl (g)
- Prevents alkene formation that the concentrated sulfuric acid catalyst can lead to (dehydrates alcohols)
How is an ester formed from an acid chloride?
- Give reagents and conditions
- Give a general formula of the equation
- State the disadvantages and advantages of this method in relation to carboxylic acid
- No catalyst + rtp + anhydrous conditions
- Acid chloride + alcohol -> ester + hydrogen chloride
ADVANTAGES
- One way reaction therefore better yield as it goes to completion
- No heating or catalyst
DISADVANTAGES
- Toxic corrosive HCl gas is produced
- Acid chloride is more expensive
How is Acid hydrolysis of esters carried out?
- Give reagents and conditions
- Show a general equation
(3 marks)
- Heat under reflux
- Excess dilute HCl/H₂SO₄ (represented as H+) catalyst
Ester + Water <–> Carboxylic acid + alcohol
How is alkaline hydrolysis of esters carried out?
- Give reagents and conditions
- Show a general equation
(3 marks)
- Heat under reflux
- Excess dilute NaOH (aq) acts as a reagent NOT catalyst
- Ester + NaOH (aq) -> Sodium carboxylate salt + Alcohol
