Organic Synthesis (Cambridge (CIE) A Level Chemistry): Flashcards
Exam code: 9701
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Define acyl chloride.
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Cards in this collection (27)
Define acyl chloride.
An acyl chloride is a carboxylic acid derivative in which the –OH group is replaced by –Cl, making it highly reactive towards nucleophilic addition-elimination reactions.
What reagents convert a carboxylic acid into an acyl chloride, and what by-products does each produce?
Three reagents work: PCl5 (solid) gives POCl3 and HCl; PCl3 (liquid, heat) gives H3PO3; SOCl2 (liquid) gives SO2 and HCl.
True or False?
Phenol reacts with carboxylic acids to form esters at a fast rate without any additional reagents.
False. The esterification of phenol with carboxylic acids is slow, so acyl chlorides are used instead to give a faster, higher-yield reaction.
Benzoic acid is produced from methylbenzene in two steps: first, refluxing with hot alkaline ..........; second, treatment with dilute ...........
Benzoic acid is produced from methylbenzene in two steps: first, refluxing with hot alkaline KMnO4; second, treatment with dilute HCl.
How are non-substituted and substituted amides distinguished by the reagent used with an acyl chloride?
A non-substituted amide is formed by reaction with ammonia (NH3). A substituted amide is formed by reaction with a primary amine, via nucleophilic addition-elimination.
Define electrophile.
An electrophile is an electron-pair acceptor, a species that attacks regions of high electron density such as the delocalised π system of arenes during electrophilic substitution reactions.
True or False?
Phenol reacts with bromine water at room temperature to form a white precipitate.
True. Phenol undergoes electrophilic substitution with bromine water at room temperature, forming a white precipitate of 2,4,6-tribromophenol.
When phenol reacts with dilute HNO3 at room temperature, the products are a mixture of ..........-nitrophenol and ..........-nitrophenol.
When phenol reacts with dilute HNO3 at room temperature, the products are a mixture of 2-nitrophenol and 4-nitrophenol.
What electrophile is involved in the nitration of benzene, and how is it generated?
The electrophile is the nitronium ion, NO2+. It is generated by mixing concentrated HNO3 and concentrated H2SO4, where the sulfuric acid protonates the nitric acid.
Define target molecule.
A target molecule is the desired product in an organic synthesis, whose structure guides the chemist in selecting starting materials, reagents and reaction steps.
Which reagent and reaction type converts a haloalkane into a nitrile, and why is this step useful in synthesis?
KCN in ethanol is used in a nucleophilic substitution reaction. It is useful because it increases the carbon chain length by one, allowing longer-chain target molecules to be reached.
A primary alcohol is oxidised to an aldehyde using ........../H2SO4 with distillation, then further oxidised to a carboxylic acid by heating under reflux.
A primary alcohol is oxidised to an aldehyde using K2Cr2O7/H2SO4 with distillation, then further oxidised to a carboxylic acid by heating under reflux.
True or False?
Nitrobenzene is reduced to phenylamine using tin and hydrochloric acid.
True. Nitrobenzene is reduced to phenylamine (aminobenzene/aniline) using Sn/HCl in a reduction reaction.
What reagents and reaction type convert an acyl chloride into a primary amide?
Ammonia (NH3) reacts with an acyl chloride in a nucleophilic addition-elimination reaction to form a primary amide and hydrogen chloride gas.
Define elimination reaction.
An elimination reaction is one in which atoms or groups are removed from adjacent carbons to form a double bond. For example, dehydration of an alcohol produces an alkene.
What reagents and conditions convert benzene into phenylethanone (acetophenone)?
CH3COCl and AlCl3 are used in a Friedel-Crafts acylation (electrophilic substitution). AlCl3 acts as a Lewis acid catalyst to generate the acylium ion RCO+.
An ester can be hydrolysed in two ways: acid hydrolysis with dilute acid gives a .......... ; alkaline hydrolysis with NaOH (aq) gives a carboxylate salt and an .......... .
An ester can be hydrolysed in two ways. Acid hydrolysis with dilute acid gives a carboxylic acid. Alkaline hydrolysis with NaOH (aq) gives a carboxylate salt and an alcohol.
True or False?
A ketone can be reduced to a secondary alcohol using NaBH4 in water.
True. Ketones are reduced to secondary alcohols using NaBH4 in water — the hydride ion acts as a nucleophile, reducing the C=O group.
Define synthetic route.
A synthetic route is a planned sequence of chemical reactions used to convert a starting material into a target product, specifying reaction types, reagents and conditions at each step.
When critically analysing a synthetic route, what three features must be evaluated at each step?
At each step you must evaluate: (1) the type of reaction, (2) the reagents used and (3) any possible by-products formed.
True or False?
H2 with a Pt catalyst will reduce both the benzene ring and the COOH group in a benzoic acid derivative.
False. Under hydrogenation conditions (H2/Pt or Ni), the benzene ring is reduced to cyclohexane. The –COOH group is typically not reduced under these conditions.
Oxidation of an alkyl side chain on benzene to a carboxylic acid requires refluxing with hot alkaline .......... followed by acidification with dilute .......... .
Oxidation of an alkyl side chain on benzene to a carboxylic acid requires refluxing with hot alkaline KMnO4 followed by acidification with dilute H2SO4.
Why is it more effective to synthesise an ester from an acyl chloride rather than directly from a carboxylic acid and alcohol?
The acyl chloride is more reactive, so the reaction goes to completion and gives a higher yield, whereas direct esterification with a carboxylic acid is reversible and slow.
What is the by-product when a carboxylic acid is reduced to a primary alcohol?
The by-product is water (H2O). The reduction of the –COOH group to –CH2OH removes an oxygen atom, which leaves as water.
True or False?
Alkaline KMnO4 followed by dilute H2SO4 can be used to oxidise an alkyl group attached to benzene.
True. Hot alkaline KMnO4 oxidises the alkyl side chain to a carboxylate salt; subsequent acidification with dilute H2SO4 gives the carboxylic acid.
A carboxylic acid is converted to an acyl chloride by reaction with liquid .......... . The other products are .......... and .......... .
A carboxylic acid is converted to an acyl chloride by reaction with liquid SOCl2. The other products are SO2 and HCl.
Define by-product.
A by-product is a secondary substance formed during a chemical reaction alongside the intended product, often produced because of the reagent or mechanism involved.
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