A diazonium salt is an unstable organic compound containing an -N 2 + group, formed by reacting phenylamine with nitrous acid below 10 °C.

What reagents are used to prepare nitrous acid (HNO 2 ) in the first step of phenol production?

Sodium nitrite (NaNO 2 ) and dilute hydrochloric acid (HCl) are mixed while keeping the temperature below 10 °C using ice.

True or False? Benzenediazonium chloride is a stable compound that can be stored at room temperature.

False. Benzenediazonium chloride is very unstable and thermally decomposes when heated, which is why the temperature must be kept below 10 °C during its formation.

In step 2 of phenol production, phenylamine reacts with .......... to form an unstable .......... salt.

In step 2 of phenol production, phenylamine reacts with HNO 2 to form an unstable diazonium salt.

What happens in step 3 of phenol production from phenylamine?

The diazonium salt is heated and undergoes thermal decomposition to form phenol.

True or False? Phenols are characterised by an -OH group attached directly to a benzene ring.

True. The -OH group bonded directly to the benzene ring is the defining structural feature of phenols.

Why must ice be used during the preparation of nitrous acid in phenol production?

Nitrous acid (HNO 2 ) is so unstable that the temperature must be kept below 10 °C to prevent it from decomposing before it can react with phenylamine.

Phenol is produced from phenylamine by first forming .......... acid, then reacting it with phenylamine to give a .......... salt, which is then heated.

Phenol is produced from phenylamine by first forming nitrous acid, then reacting it with phenylamine to give a diazonium salt, which is then heated.

Phenol is an organic compound in which a hydroxyl (-OH) group is bonded directly to a benzene ring, giving it weakly acidic properties.

Define azo compound .

An azo compound is an organic compound in which two benzene rings are linked by a nitrogen bridge (-N=N-), formed from the reaction of a diazonium ion with phenol in alkaline solution.

Why does phenol react more readily with electrophiles than benzene does?

One of the lone pairs on the oxygen atom in the -OH group overlaps with the π bonding system of the ring, increasing electron density and making the ring more susceptible to electrophilic attack .

True or False? Phenol reacts with bromine water at room temperature to give a white precipitate of 2,4,6-tribromophenol.

True. The -OH group activates the ring so strongly that phenol decolourises orange bromine water without a catalyst, forming a white precipitate.

Phenol reacts with sodium hydroxide in an acid-base reaction to form a .......... salt and .......... .

Phenol reacts with sodium hydroxide in an acid-base reaction to form sodium phenoxide salt and water .

What positions does the -OH group in phenol direct incoming electrophiles to?

The -OH group directs electrophiles to the 2, 4, and 6 positions on the benzene ring.

True or False? Molten phenol reacts with sodium metal to produce hydrogen gas and a soluble salt.

True. This is an acid-base reaction. Phenol acts as the acid, donating a proton to sodium, producing sodium phenoxide (a soluble salt) and H 2 gas.

What colour is the product formed when phenol reacts with a cold diazonium ion in alkaline solution?

A yellow-orange solution or precipitate is formed, which is an azo compound containing two benzene rings linked by a nitrogen bridge.

Phenol undergoes .......... with dilute HNO 3 at room temperature to give a mixture of 2-nitrophenol and .......... .

Phenol undergoes nitration with dilute HNO 3 at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol .

Define electrophilic substitution .

Electrophilic substitution is a reaction in which an electrophile replaces a hydrogen atom on an aromatic ring, leaving the ring structure intact.

Define phenoxide ion .

A phenoxide ion is the conjugate base of phenol, formed when phenol loses a proton. The negative charge is delocalised across the entire ion, stabilising it.

Why is phenol a weak acid even though it contains an -OH group similar to alcohols?

One of the lone pairs on the oxygen atom overlaps with the delocalised π system of the ring. This stabilises the phenoxide ion formed, making phenol more likely to lose a proton than gain one.

True or False? Phenol is a stronger acid than ethanol.

True. Phenol has a pKa of 10 while ethanol has a pKa of 16. The lower pKa of phenol means it dissociates more readily and is a stronger acid.

In the phenoxide ion, the negative charge is .......... over the entire ion, which means H + ions are less likely to .......... the phenol molecule.

In the phenoxide ion, the negative charge is delocalised over the entire ion, which means H + ions are less likely to reform the phenol molecule.

Place ethanol, water and phenol in order of increasing acid strength and give their approximate pKa values.

Ethanol (pKa 16) < water (pKa 15.7) < phenol (pKa 10). Phenol is the strongest acid of the three.

True or False? The ethoxide ion is a weaker base than the phenoxide ion.

False. The ethyl group donates electron density to the oxygen in the ethoxide ion, making it more available to accept a proton. The ethoxide ion is therefore a stronger base than the phenoxide ion.

Why does the dissociation equilibrium of phenol lie further to the right compared to ethanol?

The phenoxide ion is more stable than the ethoxide ion because the negative charge is delocalised across the benzene ring. This makes phenol more likely to donate a proton.

Phenol is more acidic than ethanol because the .......... ion formed is stabilised by .......... of charge over the aromatic ring.

Phenol is more acidic than ethanol because the phenoxide ion formed is stabilised by delocalisation of charge over the aromatic ring.

pKa is a measure of acid strength: the smaller the pKa value, the stronger the acid and the more readily it donates a proton.

Define activating group .

An activating group is a substituent that increases the electron density of an aromatic ring, making it more reactive towards electrophilic substitution.

What reagents and conditions are needed to nitrate phenol, and how do these differ from benzene?

Phenol only requires dilute nitric acid at room temperature. Benzene requires a mixture of concentrated nitric acid and concentrated sulfuric acid, refluxed between 25 °C and 60 °C.

True or False? Phenol reacts with bromine water in the absence of a catalyst to give a white precipitate.

True. Unlike benzene, which needs pure bromine and an AlBr 3 catalyst, phenol reacts readily with bromine water at room temperature without any catalyst.

The -OH group in phenol is .......... and directs incoming electrophiles to the .......... and .......... positions.

The -OH group in phenol is electron-donating and directs incoming electrophiles to the 2, 4 and 6 positions.

What product forms when phenol is treated with concentrated nitric acid instead of dilute nitric acid?

2,4,6-trinitrophenol is formed when concentrated nitric acid is used.

True or False? The lone pair on the oxygen atom in phenol overlaps with the π system of the benzene ring, increasing electron density in the ring.

True. This overlap delocalises one of the oxygen lone pairs into the ring, activating it towards electrophilic substitution and directing electrophiles to the 2, 4, and 6 positions.

Why can phenol be brominated using bromine water, while benzene requires pure bromine and a catalyst?

The -OH group in phenol donates electron density into the ring, increasing it sufficiently to react with bromine water. Benzene is less electron-rich and requires a catalyst to polarise the Br 2 molecule.

Bromination of benzene requires .......... bromine and an .......... catalyst, but phenol only needs bromine water at room temperature.

Bromination of benzene requires pure bromine and an AlBr 3 catalyst, but phenol only needs bromine water at room temperature.

Define directing effect .

A directing effect is the influence a substituent has on determining which positions on an aromatic ring are attacked by an incoming electrophile during electrophilic substitution.

Define phenolic compound .

A phenolic compound is any organic molecule that contains a phenol functional group (-OH bonded directly to a benzene ring).

What structural feature makes 1-naphthol a phenolic compound?

1-naphthol contains an -OH group bonded directly to a benzene ring. The benzene ring is itself fused to a second benzene ring.

True or False? In 1-naphthol, electrophilic substitution can occur at the 6 position.

False. Substitution at position 6 is not possible because there is no hydrogen atom on that carbon. It is bonded to a carbon atom of the second benzene ring.

In 1-naphthol, the -OH group is .......... and directs electrophiles to the .......... and/or .......... positions.

In 1-naphthol, the -OH group is electron-donating and directs electrophiles to the 2 and/or 4 positions.

How does 1-naphthol react with electrophiles compared with phenol?

1-naphthol reacts in the same way as phenol. The -OH group activates the ring towards electrophilic substitution and directs incoming electrophiles to the 2 and/or 4 positions.

True or False? The -OH group in 1-naphthol activates the benzene ring towards electrophilic substitution.

True. Just as in phenol, the -OH group in 1-naphthol donates electron density into the ring, making it more reactive towards electrophilic attack.

What is the structural relationship between 1-naphthol and phenol?

1-naphthol has a phenol group (-OH attached to a benzene ring) which is fused to a second benzene ring, making it a bicyclic phenolic compound.

1-naphthol contains a .......... group attached to another .......... ring, and undergoes electrophilic substitution in a similar way to .......... .

1-naphthol contains a phenol group attached to another benzene ring, and undergoes electrophilic substitution in a similar way to phenol .

1-naphthol is a phenolic compound consisting of a phenol group fused to a second benzene ring. It reacts like phenol in electrophilic substitution, with substitution directed to the 2 and/or 4 positions.

A LevelChemistryCambridge (CIE)Flashcards32. Hydroxy CompoundsPhenol

Phenol (Cambridge (CIE) A Level Chemistry): Flashcards

Exam code: 9701

1/45

0Still learning

Know0

FrontProducing Phenol
diazonium salt

Was this flashcard helpful?

Cards in this collection (45)

diazonium salt
A diazonium salt is an unstable organic compound containing an -N₂⁺ group, formed by reacting phenylamine with nitrous acid below 10 °C.
What reagents are used to prepare nitrous acid (HNO₂) in the first step of phenol production?
Sodium nitrite (NaNO₂) and dilute hydrochloric acid (HCl) are mixed while keeping the temperature below 10 °C using ice.
True or False?
Benzenediazonium chloride is a stable compound that can be stored at room temperature.
False.
Benzenediazonium chloride is very unstable and thermally decomposes when heated, which is why the temperature must be kept below 10 °C during its formation.
In step 2 of phenol production, phenylamine reacts with .......... to form an unstable .......... salt.
In step 2 of phenol production, phenylamine reacts with HNO₂ to form an unstable diazonium salt.
What happens in step 3 of phenol production from phenylamine?
The diazonium salt is heated and undergoes thermal decomposition to form phenol.
True or False?
Phenols are characterised by an -OH group attached directly to a benzene ring.
True.
The -OH group bonded directly to the benzene ring is the defining structural feature of phenols.
Why must ice be used during the preparation of nitrous acid in phenol production?
Nitrous acid (HNO₂) is so unstable that the temperature must be kept below 10 °C to prevent it from decomposing before it can react with phenylamine.
Phenol is produced from phenylamine by first forming .......... acid, then reacting it with phenylamine to give a .......... salt, which is then heated.
Phenol is produced from phenylamine by first forming nitrous acid, then reacting it with phenylamine to give a diazonium salt, which is then heated.
phenol
Phenol is an organic compound in which a hydroxyl (-OH) group is bonded directly to a benzene ring, giving it weakly acidic properties.
Define azo compound.
An azo compound is an organic compound in which two benzene rings are linked by a nitrogen bridge (-N=N-), formed from the reaction of a diazonium ion with phenol in alkaline solution.
Why does phenol react more readily with electrophiles than benzene does?
One of the lone pairs on the oxygen atom in the -OH group overlaps with the π bonding system of the ring, increasing electron density and making the ring more susceptible to electrophilic attack.
True or False?
Phenol reacts with bromine water at room temperature to give a white precipitate of 2,4,6-tribromophenol.
True.
The -OH group activates the ring so strongly that phenol decolourises orange bromine water without a catalyst, forming a white precipitate.
Phenol reacts with sodium hydroxide in an acid-base reaction to form a .......... salt and .......... .
Phenol reacts with sodium hydroxide in an acid-base reaction to form sodium phenoxide salt and water.
What positions does the -OH group in phenol direct incoming electrophiles to?
The -OH group directs electrophiles to the 2, 4, and 6 positions on the benzene ring.
True or False?
Molten phenol reacts with sodium metal to produce hydrogen gas and a soluble salt.
True.
This is an acid-base reaction. Phenol acts as the acid, donating a proton to sodium, producing sodium phenoxide (a soluble salt) and H₂ gas.
What colour is the product formed when phenol reacts with a cold diazonium ion in alkaline solution?
A yellow-orange solution or precipitate is formed, which is an azo compound containing two benzene rings linked by a nitrogen bridge.
Phenol undergoes .......... with dilute HNO₃ at room temperature to give a mixture of 2-nitrophenol and .......... .
Phenol undergoes nitration with dilute HNO₃ at room temperature to give a mixture of 2-nitrophenol and 4-nitrophenol.
Define electrophilic substitution.
Electrophilic substitution is a reaction in which an electrophile replaces a hydrogen atom on an aromatic ring, leaving the ring structure intact.
Define phenoxide ion.
A phenoxide ion is the conjugate base of phenol, formed when phenol loses a proton. The negative charge is delocalised across the entire ion, stabilising it.
Why is phenol a weak acid even though it contains an -OH group similar to alcohols?
One of the lone pairs on the oxygen atom overlaps with the delocalised π system of the ring. This stabilises the phenoxide ion formed, making phenol more likely to lose a proton than gain one.
True or False?
Phenol is a stronger acid than ethanol.
True.
Phenol has a pKa of 10 while ethanol has a pKa of 16. The lower pKa of phenol means it dissociates more readily and is a stronger acid.
In the phenoxide ion, the negative charge is .......... over the entire ion, which means H⁺ ions are less likely to .......... the phenol molecule.
In the phenoxide ion, the negative charge is delocalised over the entire ion, which means H⁺ ions are less likely to reform the phenol molecule.
Place ethanol, water and phenol in order of increasing acid strength and give their approximate pKa values.
Ethanol (pKa 16) < water (pKa 15.7) < phenol (pKa 10). Phenol is the strongest acid of the three.
True or False?
The ethoxide ion is a weaker base than the phenoxide ion.
False.
The ethyl group donates electron density to the oxygen in the ethoxide ion, making it more available to accept a proton. The ethoxide ion is therefore a stronger base than the phenoxide ion.
Why does the dissociation equilibrium of phenol lie further to the right compared to ethanol?
The phenoxide ion is more stable than the ethoxide ion because the negative charge is delocalised across the benzene ring. This makes phenol more likely to donate a proton.
Phenol is more acidic than ethanol because the .......... ion formed is stabilised by .......... of charge over the aromatic ring.
Phenol is more acidic than ethanol because the phenoxide ion formed is stabilised by delocalisation of charge over the aromatic ring.
Define pKa.
pKa is a measure of acid strength: the smaller the pKa value, the stronger the acid and the more readily it donates a proton.
Define activating group.
An activating group is a substituent that increases the electron density of an aromatic ring, making it more reactive towards electrophilic substitution.
What reagents and conditions are needed to nitrate phenol, and how do these differ from benzene?
Phenol only requires dilute nitric acid at room temperature. Benzene requires a mixture of concentrated nitric acid and concentrated sulfuric acid, refluxed between 25 °C and 60 °C.
True or False?
Phenol reacts with bromine water in the absence of a catalyst to give a white precipitate.
True.
Unlike benzene, which needs pure bromine and an AlBr₃ catalyst, phenol reacts readily with bromine water at room temperature without any catalyst.
The -OH group in phenol is .......... and directs incoming electrophiles to the .......... and .......... positions.
The -OH group in phenol is electron-donating and directs incoming electrophiles to the 2, 4 and 6 positions.
What product forms when phenol is treated with concentrated nitric acid instead of dilute nitric acid?
2,4,6-trinitrophenol is formed when concentrated nitric acid is used.
True or False?
The lone pair on the oxygen atom in phenol overlaps with the π system of the benzene ring, increasing electron density in the ring.
True.
This overlap delocalises one of the oxygen lone pairs into the ring, activating it towards electrophilic substitution and directing electrophiles to the 2, 4, and 6 positions.
Why can phenol be brominated using bromine water, while benzene requires pure bromine and a catalyst?
The -OH group in phenol donates electron density into the ring, increasing it sufficiently to react with bromine water. Benzene is less electron-rich and requires a catalyst to polarise the Br₂ molecule.
Bromination of benzene requires .......... bromine and an .......... catalyst, but phenol only needs bromine water at room temperature.
Bromination of benzene requires pure bromine and an AlBr₃ catalyst, but phenol only needs bromine water at room temperature.
Define directing effect.
A directing effect is the influence a substituent has on determining which positions on an aromatic ring are attacked by an incoming electrophile during electrophilic substitution.
Define phenolic compound.
A phenolic compound is any organic molecule that contains a phenol functional group (-OH bonded directly to a benzene ring).
What structural feature makes 1-naphthol a phenolic compound?
1-naphthol contains an -OH group bonded directly to a benzene ring. The benzene ring is itself fused to a second benzene ring.
True or False?
In 1-naphthol, electrophilic substitution can occur at the 6 position.
False.
Substitution at position 6 is not possible because there is no hydrogen atom on that carbon. It is bonded to a carbon atom of the second benzene ring.
In 1-naphthol, the -OH group is .......... and directs electrophiles to the .......... and/or .......... positions.
In 1-naphthol, the -OH group is electron-donating and directs electrophiles to the 2 and/or 4 positions.
How does 1-naphthol react with electrophiles compared with phenol?
1-naphthol reacts in the same way as phenol. The -OH group activates the ring towards electrophilic substitution and directs incoming electrophiles to the 2 and/or 4 positions.
True or False?
The -OH group in 1-naphthol activates the benzene ring towards electrophilic substitution.
True.
Just as in phenol, the -OH group in 1-naphthol donates electron density into the ring, making it more reactive towards electrophilic attack.
What is the structural relationship between 1-naphthol and phenol?
1-naphthol has a phenol group (-OH attached to a benzene ring) which is fused to a second benzene ring, making it a bicyclic phenolic compound.
1-naphthol contains a .......... group attached to another .......... ring, and undergoes electrophilic substitution in a similar way to .......... .
1-naphthol contains a phenol group attached to another benzene ring, and undergoes electrophilic substitution in a similar way to phenol.
Define 1-naphthol.
1-naphthol is a phenolic compound consisting of a phenol group fused to a second benzene ring. It reacts like phenol in electrophilic substitution, with substitution directed to the 2 and/or 4 positions.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:AlcoholsNext:Carboxylic Acids