C26 - Carbonyls and Carboxylic acids Flashcards
What is the carbonyl functional group and what compounds is it seen in?
C=O
Ketones, aldehydes and carboxylic acids
What reactants can be used in place of HCN, why would this be useful?
H2SO4 and NaCN (provides HCN in situ)
HCN is poisonous and gas slightly above room temperature (so difficult and dangerous to use)
Why is the reaction of carbonyls with HCN useful?
Increases length of the carbon chain
What reagent is used to detect C=O bonds (2 names) and what does a positive test look like?
2,4-DNP or Brady’s reagent
yellow or orange ppt formed
How can you distinguish between aldehydes and ketones?
Tollen’s reagent (silver nitrate and aq ammonia) acts as oxidising agent
Silver mirror formed (for aldehydes)
No reaction for ketones
After reacting a carbonyl with Brady’s reagent, how could you check whether it was a ketone or aldehyde?
Recystralise and purify ppt
Measure melting point
Compare to known values
What is the strength of carboxylic acids?
Weak acids
Partially dissociate in water
Carboxylic acid + metal –>
carboxylate salt + hydrogen
Carboxylic acid + metal oxide–>
carboxylate salt + water
Carboxylic acid + alkali–>
carboxylate salt + water
Carboxylic acid + carbonate –>
carboxylate salt + water + carbon dioxide
For an ester written in structural formula, which reactant is shown first?
Carboxylic acid section then alcohol section
For an ester, which order is the IUPAC name written?
alcohol (eg. methyl) carboxylic acid (eg. methanoate)
When forming an ester, the side product is water. Where do each of the atoms come from?
OH from alcohol
H from carboxylic acid
What is an acyl chloride?
Carboxylic acid but with Cl in place of OH
R-C=O
|
Cl
Why are acyl chlorides used in place of carboxylic acids?
Cl is a better leaving group than OH
Forming an ester with a carboxylic acid, the reaction is reversible, conditions = under reflux with H2SO4 catalyst. With acyl chloride, rtp no catalyst
How do you form an acyl chloride?
Carboxylic acid + SOCl2 –> acyl chloride + SO2 +HCl
Equation for hydrolysis of an ester in acid conditions
ester + H2O –(h+)–> carboxylic acid + alcohol
Equation for hydrolysis of an ester in acid conditions. Name of type of reaction.
ester + OH- –> carboxylate ion + alcohol
Saponification
What is an acid anhydride?
2 carboxylic acids that have reacted together (and released water)
