26. Carbonyls and Carboxylic Acids Flashcards
How are aldehydes and ketones oxidised?
Ketones CAN NOT BE OXIDISED
Aldehydes are oxidised to carboxylic acids when refluxed using potassium dichromate and H2SO4
What is the nature of the C=O bond in carbonyls?
The C=O bond is polar (O has delta negative charge and C has delta positive) this means they can undergo nucleophilic addition reactions. The double bond is made up of bath a sigma bond and a pi bond.
How are aldehydes and ketones reduced?
They can both be reduced to form an alcohol when using NaBH4 as a reducing agent (water is also needed)
Why’s the reaction of carbonyls with HCN so important?
It increases the length of the carbon chain to form a hydroxynitrile.
What is a nucleophile?
An atom that is attracted to an electron deficient centre where it DONATES A PAIR OF ELECTRONS to form a covalent bond
What is an electrophile?
An atom which is attracted than electron rich centre where it ACCEPTS A PAIR OF ELECTRONS to form a covalent bond
How do you test for a carbonyl group?
Use Bradys reagent (2,4 DNPH) - if a yellow / orange precipitate forms when unknown compound is added then a C=O bond is present
How do you distinguish between aldehydes and ketones?
Test using tollens reagent - aldehydes will react to form a silver mirror precipitate and ketones will not
Are carboxylic acids soluble?
Yes, they can form hydrogen bonds with water (shorter carboxylic acids are more soluble)
What are acyl chlorides?
They have the same structure as carboxylic acids except the -OH group is replaced with a -Cl group
What are acid anhydrides?
They are formed by the removal of water from two of the same carboxylic acid
What is esterification?
The reaction of an alcohol with a carboxylic acid to form an ester
How is acid hydrolysis of an ester carried out?
The ester is heated under reflux with dilute acid and water which produces a carboxylic acid and an alcohol (opposite of esterification)
How is alkaline hydrolysis of an ester carried out?
Ester is heated under reflux with aq hydroxide ions which forms a salt ion and alcohol. (salt ion = carboxylic acid but instead of having an -OH its has an -O^-)
How are acyl chlorides prepared?
A carboxylic acid is reacted with thionyl chloride (SOCl2) to produce the acyl chloride + HCl + SO2
