26) Carbonyls and carboxylic acids Flashcards
What is the carbonyl functional group and where are they commonly found?
C=O
on aldehydes and ketones
What type of reaction does the polar bond of the carbonyl functional group enable?
nucleophilic addition (with some nucleophiles)
What are the reagents, conditions and organic product in the oxidation of aldehydes?
K2Cr2O7/H2SO4
reflux
carboxylic acid
What are the typical organic products of carbonyl compounds with aqueous NaBH4?
aldehyde -> primary alcohol
ketone -> secondary alcohol
What acts as the nucleophile in NaBH4?
hydride ion, :H-
Where are the curly arrows on the nucleophilic addition mechanism for the reaction of carbonyl compounds with NaBH4?
from the hydride ion to the partially positive carbon
from the C=O bond to the partially negative oxygen
from the lone pair of e- on the negative oxygen to the partially positive H of a water molecule
from the O-H bond of the water molecule to the partially negative O
Why is hydrogen cyanide, HCN, made in situ and what with?
toxic
H2SO4 and NaCN
What is the purpose of reacting carbonyl compounds with hydrogen cyanide?
provides a means of increasing the length of the carbon chain
Where are the curly arrows in the nucleophilic addition mechanism of carbonyl compounds with hydrogen cyanide?
from the :CN- to the partially positive carbon
from the C=O bond to the partially negative oxygen
from the :O- to a proton
What type of organic product is formed from the reaction of carbonyl compounds with hydrogen cyanide?
a hydroxynitrile / cyanohydrin
How can you test for a carbonyl compound and what would you observe?
Brady’s reagent / 2,4-DNP
forms a yellow/orange precipitate (or pale orange solution when dissolved in methanol and sulfuric acid)
Describe the steps to identify a carbonyl compound by melting point analysis
1) filter 2,4-DNP derivative crystals under reduced pressure
2) recrystalise using the minimum amount of hot solvent
3) measure the melting point and compare to a database of known compounds
How can you test to distinguish between an aldehyde and a ketone? What would you observe?
Tollen’s reagent (solution of silver nitrate in aqueous ammonia)
aldehyde will produce a silver mirror (and be oxidised to form a carboxylic acid)
What two functional groups do carboxylic acids contain?
carbonyl C=O group
hydroxyl OH group
Describe the solubility of carboxylic acids and the effect of the length of the carbon chain increasing
polar C=O and O-H bonds form hydrogen bonds
solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity
carboxylic acid + metal ->
carboxylate salt + hydrogen
redox reaction
carboxylic acid + metal oxide ->
salt + water
neutralisation reaction
carboxylic acid + alkali ->
salt + water
neutralisation reaction
carboxylic acid + carbonate ->
salt + water + carbon dioxide
neutralisation reaction
Define carboxylic acid derivative
compound that can be hydrolysed to form the parent carboxylic acid
What is the electronegative atom/group of an ester, carboxylic acid derivative?
-OR
What is the electronegative atom/group of an acyl chloride, carboxylic acid derivative?
-Cl
What is the electronegative atom/group of an acid anhydride, carboxylic acid derivative?
-OC(R)
What is the electronegative atom/group of an amide, carboxylic acid derivative?
-NH2
Define esterification
a reaction in which a carboxylic acid (warmed with a small amount of conc. sulfuric acid) reacts with an alcohol to form an ester and water
Define hydrolysis
the chemical breakdown of a compound in the presence of water or in aqueous solution
What are the organic products of alkaline hydrolysis of an ester (+OH-(aq), reflux)?
carboxylate ion and alcohol
If NaOH is the alkali responsible for the alkaline hydrolysis of an ester, what salt will be formed?
sodium _oate, RCOO-Na+
What are the organic products of acid hydrolysis of an ester (+H20, reflux with dilute aqueous acid)?
carboxylic acid and alcohol
Write an equation for the preparation of acyl chlorides
parent carboxylic acid + thionyl chloride, SOCl2 -> acyl chloride + SO2(g) + HCl(g)
in a fume cupboard
acyl chloride + alcohol ->
ester + HCl
acyl chloride + phenol ->
phenyl ester + HCl
acyl chloride + water ->
carboxylic acid + HCl
acyl chloride + ammonia ->
primary amide + ammonium chloride, NH4Cl
acyl chloride + primary amide ->
secondary amide + _yl ammonium chloride _NH3+Cl-
Acid anhydrides react in a similar way to acyl chlorides. Are they more or less reactive?
less reactive
Suggest why an alcohol would be heated under reflux with K2Cr2O7/H2SO4 rather than the reaction mixture being distilled to form a carboxylic acid
to ensure the carboxylic acid has fully formed
