Organic Synthesis (Edexcel International A Level (IAL) Chemistry): Flashcards

To convert an ester to a carboxylate salt and an alcohol, NaOH (aq) is used in an alkaline hydrolysis reaction.

Acidified potassium dichromate(VI) (K₂Cr₂O₇/H₂SO₄) with heat. The alcohol is oxidised and the orange dichromate is reduced to green Cr³⁺.

True.

A haloalkane must first be converted to a nitrile (by KCN), then the nitrile is hydrolysed with dilute acid to give the carboxylic acid.

SOCl₂ (thionyl chloride) converts a carboxylic acid to an acyl chloride in a chlorination reaction.

Reducing an aldehyde with NaBH₄/H₂O gives a primary alcohol.

Step 1: nitrate benzene with conc. HNO₃/H₂SO₄ to give nitrobenzene.

Step 2: reduce with Sn/conc. HCl, then add NaOH to give phenylamine.

A Grignard reagent is an organomagnesium compound of the form RMgX, prepared by reacting a halogenoalkane with magnesium in dry ether. The R group behaves as a nucleophile.

The halogenoalkane is dissolved in dry ether and reacted with magnesium. Dry conditions are essential as Grignard reagents react with water.

A Grignard reagent reacts with methanal then dilute acid to produce a primary alcohol.

A tertiary alcohol is produced. The R group from the Grignard adds to the carbonyl carbon of the ketone, and acid hydrolysis releases the alcohol product.

True.

The Grignard adds to CO₂ to form an intermediate carboxylate salt, which is then hydrolysed by dilute acid to give a carboxylic acid with one more carbon than the original R group.

Butan-2-ol is formed, a secondary alcohol. The ethyl group from the Grignard adds to the carbonyl carbon of ethanal.

In Grignard reactions, an initial addition reaction with the carbonyl compound is followed by hydrolysis with dilute acid.

Aldehydes (other than methanal): the Grignard adds to the aldehyde to give a secondary alcohol after hydrolysis. Methanal gives primary alcohols and ketones give tertiary alcohols.

Heating under reflux is a technique in which a reaction mixture is heated with a vertical condenser attached so that vapours condense and return to the flask, keeping all reactants and products inside the vessel.

Many organic chemicals are flammable. An electric heating mantle provides controlled, safer heating without an open flame that could ignite the vapours.

In distillation apparatus, cooling water enters the condenser at the bottom and exits at the top to maximise heat exchange.

Anti-bumping granules promote smooth, even boiling, preventing sudden bursts of vapour (bumping) that could cause the mixture to splash out of the flask.

Steam distillation is used to separate an insoluble liquid from an aqueous solution. Steam is bubbled through the mixture, allowing the organic compound to distil below its normal boiling point.

False.

Simple distillation separates compounds by boiling point. Compounds with lower boiling points distil first.

The product is distilled off as soon as it forms. The aldehyde has a lower boiling point than the alcohol (no hydrogen bonding) so it can be removed before further oxidation occurs.

When heating under reflux, the condenser is clamped vertically to ensure vapours condense and flow back into the reaction flask.

Recrystallisation is a purification technique for impure solids. The solid is dissolved in the minimum volume of hot solvent and as the solution cools, the purified solid crystallises out while impurities remain in solution.

Using excess solvent dissolves too much of the product, reducing the yield of purified crystals recovered on cooling.

After recrystallisation, crystals are recovered by filtration under reduced pressure using Buchner apparatus.

Solvent extraction separates an organic product from an aqueous mixture by transferring it into an immiscible organic solvent. A separating funnel is used to allow the layers to separate.

Add a small amount of water to the separating funnel. The layer that increases in volume is the aqueous layer.

Drying agents are anhydrous inorganic salts (such as anhydrous CaCl₂ or MgSO₄) added to an organic liquid to absorb traces of water by hydrating, leaving a dry organic product.

True.

The drying agent clumps when it absorbs water. More drying agent should be added until some remains as a fine powder, indicating all water has been removed.

Sodium carbonate solution can be added during extraction to neutralise acidic impurities and remove them in the aqueous layer.

True.

Each recrystallisation step removes more impurities but also dissolves some product in the solvent, so the yield of purified solid decreases with each cycle.

A melting point range is the temperature interval from when a solid first begins to melt to when it melts completely. A narrow range indicates high purity; a wide range indicates impurities.

Impurities lower the melting point and broaden the melting point range, because they disrupt the crystal lattice and cause the solid to begin melting at a lower temperature.

A pure substance has a sharp melting point, whereas an impure substance melts over a broad temperature range.

The measured melting point is compared to the literature value. A close match to the data book value, combined with a narrow range, confirms both identity and purity.

A pure liquid boils at a single sharp temperature matching the literature value. An impure sample may boil at a higher temperature or over a range of temperatures.

False.

Impurities generally lower the melting point and widen the melting point range, as they disrupt the regular crystal lattice.

1. Use a finely powdered, dry sample

2. Heat the sample very slowly for accuracy

3. Repeat at least three times to get a reliable range

4. Compare the result with the literature value

Boiling point is determined by distilling the sample gently and recording the temperature at which it boils.