Chapter 26 - Carbonyls and Carboxylic Acids Flashcards
What is a carbonyl group?
C=O
What is an aldehyde?
The carbonyl functional group is found at the end of the chain
What is a ketone?
The carbonyl group is found in the middle of the chain
Suffix for aldehyde
-al
Suffix for ketone
-one
What is produced when aldehydes are refluxed with acidified dichromate ions?
Carboxylic acids
How do you produce carboxylic acids from aldehydes?
Reflux the aldehyde with acidified dichromate ions
What is produced when ketones are refluxed with acidified dichromate ions?
No reaction
What two bonds are found in the C=O bond?
Sigma and pi bonds
Why do carbonyls not react in the same way as alkenes?
The C=O bond is polar
Why do nucleophiles react with carbonyls?
There is a positively charged carbon atom
Which compound is used as a reducing agent?
NaBH4 - must be heated
What is produced when aldehydes are reduced?
Primary alcohols
How are primary alcohols produced?
Reduction of aldehydes
What is produced when ketones are reduced?
Secondary alcohols
Why is the reaction of carbonyls and HCN useful?
It is a way of extending the carbon chain
What conditions are needed for carbonyls to react with HCN?
Sodium cyanide and sulphuric acid
Describe the mechanism of the nucleophilic addition of carbonyls with NaBH4
The lone electrons from the H- ion is donated to the carbocation
This forms a dative covalent bond
The pi bond breaks by heterolytic fission, forming an intermediary
The oxygen atom of this molecule donates an electron pair to a hydrogen atom in a water molecule
This forms an alcohol
Describe the mechanism of the reaction of carbonyls with NaCN
The lone pair of electrons on the CN- is donated to the carbocation of the carbonyl, forming the dative covalent bond
The pi bond in the C=O bond breaks by heterolytic fission
The intermediate donated an electron pair to a hydrogen ion
Which compound is used to identify the a carbonyl group?
2,4-DNP
What is the positive test for a carbonyl group?
An orange precipitate forms
Which test distinguishes between aldehydes and ketones?
Using Tollens’ reagent
What will happen when Tollens’ reagent is mixed with an aldehyde?
A silver mirror effect is produced
What will happen when Tollens’ reagent is mixed with a ketone?
No reaction
Why are carboxylic acids soluble?
The C=O bond and O-H bonds are polar so form hydrogen bonds with water molecules
Up to what number of carbon atoms are carboxylic acids soluble?
4
Why does the solubility of carboxylic acids decrease with increasing chain length?
The non-polar carbon chain has a greater effect on solubility than the polar bonds
What strength are carboxylic acids?
Weak
What is produced when carboxylic acids react with metals?
Hydrogen gas and the carboxylate salt
What is produced when carboxylic acids react with metal oxides?
A salt and water
What is produced when carboxylic acids react with alkalis?
A salt and water
What is produced when carboxylic acids react with carbonates?
Carbon dioxide, water and a salt
How can you test for a carboxylic acid?
Add carbonate
Carboxylic acids are the only organic compounds acidic enough to react with them
What are the four carboxylic acid derivatives?
Ester
Acyl chloride
Acid anhydride
Amide
How to name an ester
The carboxylic acid becomes the -oate
The alkyl chain attached then becomes the first word
How to name an acyl chloride
Remove the -oic acid suffix from the carboxylic acid an replace with -oyl chloride
What is an acid anhydride?
Water is removed from two carboxylic acid molecules
Describe the process of esterification
An alcohol is warmed with a carboxylic acid
H2SO4 catalyst
Ester functional group
COO
Acyl chloride functional group
COCl
Amide functional group
CONH2
Describe the acid hydrolysis of esters
Ester is heated under reflux with dilute acid catalyst
Ester is hydrolysed into a carboxylic acid and an alcohol
Is acid hydrolysis or alkaline hydrolysis reversible?
Acid
Describe the alkaline hydrolysis of esters
Ester heated under reflux with hydroxide ions (e.g. NaOH)
Alcohol and sodium salt formed
What compound is used to make acyl chlorides?
SOCl2
What two gases are created when an acyl chloride is made?
SO2 and HCl
How do esters react with nucleophiles?
They retain the C=O bond but lose the chloride ion
What is produced when acyl chlorides react with alcohols?
Esters
What is produced when acyl chlorides react with phenols?
Phenyl esters
Which compound is made when an acyl chloride forms either an ester or carboxylic acid?
HCl
What is produced when carboxylic acids react with water?
Carboxylic acids
What is produced when an acyl chloride reacts with ammonia?
Primary amide and NH4Cl
What is produced when an acyl chloride reacts with an amine?
Secondary amide and the chloride salt