Carboneyels Flashcards
Aldehydes
Have the C=O bond at the end of the molecules
Ketones
The C=O bond is in the middle of the molecules
Oxidation of aldehydes
Can be oxidised to carboxylic acids when refluxed with acidified potassium dichromate. K2Cr2O7 / H2SO4
Reduction of carbonyls
Aldehydes and ketones are reduced to alcohols be NaBH4. The reaction is gently heated and the reducing agent is in an aqueous solution.
Reaction of carbonyl compounds with HCN
NaCN(aq) is added with H2SO4. A CN and OH group are added to the carbon atom and the C=O bond is lost.
Identifying a carbonyl group
Use 2,4 - dinitrophenylhydrazine. This is 2,4 DNP or Brady’s reagent. An orange precipitate will form if there is a carbonyl
Identifying a carbonyl by melting point
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.
Distinguishing between aldehyde or ketone
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
Solubility of carboxylic acids
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.
Redox reaction of carboxylic acid with metal
Forms hydrogen gas and a carboxylate salt, this is when the H of COOH is replaced with a metal.
Neutralisation reaction of carboxylic acid with metal oxide
Forms water and a carboxylate salt, where the H of COOH is replaced with a metal.
Neutralisation reaction of carboxylic acid with alkali
Forms water and a carboxylate salt, where the H of COOH is replaced with a metal. Ionic is H+(aq) + OH-(aq)–> H2O(l)
Neutralisation reaction of carboxylic acid with carbonate
Forms water, CO2 and a carboxylate salt, where the H of COOH is replaced with a metal.
Esterification
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
Reaction of acid anhydride with alcohol
Forms an ester and a carboxylic acid, the carboxylic acid gets both its oxygen from the acid anhydride
Acid hydrolyses of an ester
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
Alkaline hydolyses
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
Formation of acyl chlorides
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
Reaction of acyl chlorides with alcohols
Forms an ester and HCl, the acyl chloride effectively acts as the carboxylic acid
Reaction of acyl chlorides with phenols
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
Reaction of acyl chlorides with water
Forms a carboxylic acid and HCL. The OH of water replaces the Cl. A very violent reaction
Why are acyl chlorides useful in synthesis
Very reactive, can be converted into carboxylic acid derivatives with good yields. React with nucleophiles by loosing the chloride ion
Reaction of acyl chlorides with ammonia
Form primary amides where the nitrogen atom is attached to one carbon atom.
Why does Ammonia and amines act as nucleophiles
Ammonia and amines can act as nucleophiles by donating the lone pair of electrons on the nitrogen atom to an electron deficient species.
Reaction of acyl chlorides with amines
Form a secondary amide, the nitrogen is attached to two carbon atoms.
Acid anhydride
Where two carboxylic acids react together loosing a water molecule. Contains three oxygen atoms
How to distinguish between an alcohol, aldehyde and ketone
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
