Chapter 26 - Carbonyls and carboxylic acids Flashcards
describe the oxidation of aldehydes
they can be oxidised to carboxylic acids when reflux with acidified dichromate ions
do ketones undergo oxidation reactions?
no
what type of reaction is common in carbonyls?
nucleophilic addition
aldehydes can be reduced to form what?
Primary alcohols
what is used to detect carbonyls and what will be the positive result?
Brady’s Regent and a yellow/orange precipitable forms
what is used to distinguish between aldehydes and ketones?
tollen’s reagent
how do you make tollen’s reagent?
add aqueous sodium hydroxide to 3 cm of aqueous silver nitrate until a brown precipitate of silver oxide is formed, then add dilute ammonia until the brown precipitate dissolves
what is the positive test for aldehydes?
A silver mirror will form
what two groups does the carboxyl group contain?
A carbonyl group and a hydroxyl group
why are carboxylic acids soluble?
The C-O and O-H bonds are polar allowing them to form hydrogen bonds with the water
What is the maximum number of carbons a carboxylic acid can have before it becomes insoluble?
four
are carboxylic acids strong or weak
Weak
what are the two main reactions that carboxylic acids undergo?
redox and neutralisation
what are the products when an aqueous solution of carboxylic acid reacts with a metal?
Hydrogen gas and the carboxylate salt
what are the products when a carboxylic acid reacts with a metal oxide?
a Salt and water
what are the products when a carboxylic acid reacts with an alkali?
a Salt and water
What are the products when a carbonate reacts with a carboxylic acid?
a salt, water and carbon dioxide
What is a derivative of a carboxylic acid?
A compound that can be hydrolysed to form the parent carboxylic acid
give four examples of derivatives of carboxylic acids
Estes, acyl chlorides, acid anhydrides and amides
how is an ester named?
Remove the oic acid suffix from the parent carboxylic acid and replace with oate. The chain attached the oxygen atom of the COO group is an added at the start.
how is an acyl chloride named?
remove oic and replace it with oyl chloride
how is an acid anhydride formed?
By the removal of water from two carboxylic acid molecules
what is esterification?
The reaction of an alcohol with a carboxylic acid to form an ester
what conditions are needed for esterification?
warm with a small amount of concentrated sulphuric acid which acts as a catalyst
what two chemicals can esters be hydrolysed by?
Aqueous acid or alkali
What is acid hydrolysis of an ester the reverse of?
Esterification
describe the acid hydrolysis of an ester
The Ester is heated under reflux with dilute aqueous acid. Ester is then broken down by water with the acid acting as a catalyst.
which one out of acid hydrolysis and hydrolysis is reversible?
Acid hydrolysis
how can acyl chlorides be prepared and what are the other products of this reaction?
they can be prepared directly from their parent carboxylic acid by reaction with thionyl chloride, the other products of this reaction SO2 and HCL are evolved as gases.
why are acyl chlorides useful?
they are very reactive and in organic synthesis can be easily converted into carboxylic acid derivatives with good yields
what kind of compound do acyl chlorides react with?
nucleophiles
acyl chlorides react with alcohols to form what?
esters
why can’t carboxylic acids react with phenols to form esters?
They are not reactive enough
acyl chlorides and acid anhydrides can react with phenols to form what?
phenyl esters
What happens when water reacts with acyl chlorides?
A violent reaction takes place with the evolution of dense steamy hydrochloric acid fumes. A carboxylic acid is also formed.
Acyl chlorine react with ammonia form what?
A primary amide
A primary amine reacts with an acyl chloride to form what?
a secondary amide
Why are acid anhydrides useful?
they react in a similar way to acyl chlorides but are less reactive
