Carboneyels

Question 1

Aldehydes

Answer 1

Have the C=O bond at the end of the molecules

Question 2

Ketones

Answer 2

The C=O bond is in the middle of the molecules

Question 3

Oxidation of aldehydes

Answer 3

Can be oxidised to carboxylic acids when refluxed with acidified potassium dichromate. K2Cr2O7 / H2SO4

Question 4

Reduction of carbonyls

Answer 4

Aldehydes and ketones are reduced to alcohols be NaBH4. The reaction is gently heated and the reducing agent is in an aqueous solution.

Question 5

Reaction of carbonyl compounds with HCN

Answer 5

NaCN(aq) is added with H2SO4. A CN and OH group are added to the carbon atom and the C=O bond is lost.

Question 6

Identifying a carbonyl group

Answer 6

Use 2,4 - dinitrophenylhydrazine. This is 2,4 DNP or Brady’s reagent. An orange precipitate will form if there is a carbonyl

Question 7

Identifying a carbonyl by melting point

Answer 7

The 2,4 DNP precipitate is filtered to separate it from the solution. The solid is then recrystalised to produce a pure sample of crystals. The melting point is then measured and recorded. It is then compared to a data base of known melting points to identify the original carbonyl compound.

Question 8

Distinguishing between aldehyde or ketone

Answer 8

Tollens reagent is added and a silver mirror effect is observed if there is an aldehyde. This is because the aldehydes are oxidised to a carboxylic acid which reduces the silver ions to silver to create the effect

Question 9

Solubility of carboxylic acids

Answer 9

The C=O and O-H bonds in a carboxylic acid are polar allowing the carboxylic acid to form hydrogen bonds with water molecules. As length of chain increases solubility decreases as the polar head has less effect on the overall polarity of the molecule.

Question 10

Redox reaction of carboxylic acid with metal

Answer 10

Forms hydrogen gas and a carboxylate salt, this is when the H of COOH is replaced with a metal.

Question 11

Neutralisation reaction of carboxylic acid with metal oxide

Answer 11

Forms water and a carboxylate salt, where the H of COOH is replaced with a metal.

Question 12

Neutralisation reaction of carboxylic acid with alkali

Answer 12

Forms water and a carboxylate salt, where the H of COOH is replaced with a metal. Ionic is H+(aq) + OH-(aq)–> H2O(l)

Question 13

Neutralisation reaction of carboxylic acid with carbonate

Answer 13

Forms water, CO2 and a carboxylate salt, where the H of COOH is replaced with a metal.

Question 14

Esterification

Answer 14

Reaction of carboxylic acid with alcohol in the presence of an acid catalyst to form an ester. The alcohol contributes to the first part of the name. I.e. propanoic acid and ethanol make ethyl propanoate. Water is also formed

Question 15

Reaction of acid anhydride with alcohol

Answer 15

Forms an ester and a carboxylic acid, the carboxylic acid gets both its oxygen from the acid anhydride

Question 16

Acid hydrolyses of an ester

Answer 16

An ester is heated under reflux with dilute aqueous acid, the ester is broken down by water with the acid acting as a catalyst. A carboxylic acid and alcohol is formed

Question 17

Alkaline hydolyses

Answer 17

An ester reacts with an alkali ie NaOH to form a carboxylate salt, where the H of COOH is replaced by the metal. An alcohol is also formed

Question 18

Formation of acyl chlorides

Answer 18

When a carboxylic acid reacts with thionyl chloride (SOCl2). The other products of the reaction are SO2 and HCl which leave as gases, leaving the acyl chloride. Example is propanoyl chloride which is made from propanoic acid

Question 19

Reaction of acyl chlorides with alcohols

Answer 19

Forms an ester and HCl, the acyl chloride effectively acts as the carboxylic acid

Question 20

Reaction of acyl chlorides with phenols

Answer 20

Forms an ester and HCl, the acyl chloride effectively acts as the carboxylic acid. Done because carboxylic acids are not reactive enough to react with phenols and acyl chlorides are very reactive

Question 21

Reaction of acyl chlorides with water

Answer 21

Forms a carboxylic acid and HCL. The OH of water replaces the Cl. A very violent reaction

Question 22

Why are acyl chlorides useful in synthesis

Answer 22

Very reactive, can be converted into carboxylic acid derivatives with good yields. React with nucleophiles by loosing the chloride ion

Question 23

Reaction of acyl chlorides with ammonia

Answer 23

Form primary amides where the nitrogen atom is attached to one carbon atom.

Question 24

Why does Ammonia and amines act as nucleophiles

Answer 24

Ammonia and amines can act as nucleophiles by donating the lone pair of electrons on the nitrogen atom to an electron deficient species.

Question 25

Reaction of acyl chlorides with amines

Answer 25

Form a secondary amide, the nitrogen is attached to two carbon atoms.

Question 26

Acid anhydride

Answer 26

Where two carboxylic acids react together loosing a water molecule. Contains three oxygen atoms

Question 27

How to distinguish between an alcohol, aldehyde and ketone

Answer 27

Put 10ml if each solution into its own test tube. Add 10ml 2,4 DNP to each of the three solution, the compound which does not give a orange precipitate is an alcohol. Take fresh samples of the compounds which gave an orange precipitate. Add tollens reagent to each compound in a 50 degrees water bath. The compound that gives a silver mirror is an aldehyde Ag + e- —> Ag(s). The ketone will not have reacted