Flashcards · 9620 · A Level Topic 27

Carboxylic acids and derivatives (A Level) flashcards

13 cards on A Level Topic 27, subtopics 3.3.9.1 to 3.3.9.2. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 13 cards

For a quick read-through or printing. Cover the right-hand side to test yourself.

Carboxylic acids: strength and reaction with carbonates: Weak acids (only partly dissociated), but they still liberate CO₂ from carbonates. 2CH₃CH₂CH₂COOH + CaCO₃ → (CH₃CH₂CH₂COO)₂Ca + CO₂ + H₂O
How are esters made from carboxylic acids?: Warm the acid with an alcohol and an acid catalyst (concentrated H₂SO₄). Reversible: acid + alcohol ⇌ ester + water.
Name the ester HCOOCH₂CH₂CH₂CH₂CH₃: Pentyl methanoate (from methanoic acid and pentan-1-ol).
Acid vs alkaline hydrolysis of an ester: Acid (dilute acid, reflux): carboxylic acid + alcohol; reversible. Alkaline (NaOH(aq), reflux): carboxylate salt + alcohol; goes to completion because the carboxylate ion does not react with the alcohol.
Uses of esters: Solvents, plasticisers, perfumes and food flavourings.
Making soap from a fat or oil: Fats and oils are triesters of propane-1,2,3-triol (glycerol). Heating with NaOH(aq) hydrolyses them: 1 mol fat + 3 mol NaOH → 3 mol soap (carboxylate salt) + 1 mol glycerol.
Biodiesel: A mixture of methyl esters of long-chain carboxylic acids, made by reacting vegetable oils with methanol in the presence of a catalyst (glycerol is also formed).

Products of acyl chlorides with water, alcohols, ammonia and primary amines: Water: carboxylic acid. Alcohol: ester. Ammonia: amide (–CONH₂). Primary amine: N-substituted amide (–CONHR). The by-product is HCl (or an ammonium/alkylammonium chloride with excess NH₃ or amine).
Acyl chloride vs acid anhydride as acylating agents: Same organic products, but the by-product from an acid anhydride is a carboxylic acid instead of HCl.
Outline of the nucleophilic addition–elimination mechanism with an acyl chloride: Lone pair (on O or N) attacks the δ+ carbonyl C; C=O electrons move to O. Then the O⁻ lone pair re-forms C=O and Cl⁻ leaves. Finally H⁺ is lost from the positive O or N.
Ethanoyl chloride with excess butylamine: equation and product name: CH₃COCl + 2CH₃CH₂CH₂CH₂NH₂ → CH₃CONHCH₂CH₂CH₂CH₃ + CH₃CH₂CH₂CH₂NH₃Cl Product: N-butylethanamide.
Why does industry use ethanoic anhydride, not ethanoyl chloride, to make aspirin?: It is cheaper, less corrosive, less readily hydrolysed by moisture, reacts less vigorously (easier to control) and gives no hydrogen chloride gas.
Required practical 10: recrystallisation and purity check: Dissolve in the minimum hot solvent, filter hot, cool, collect crystals by vacuum filtration, rinse with a little cold solvent, dry. A pure solid melts sharply at the data-book value; an impure one melts lower and over a range.