Carbonyls, carboxylic acids, esters and other acyl groups Flashcards
What type of reaction and what is the product of the reaction of an aldehyde and Cr2O72-
oxidation. Carboxylic acid is produced
Describe the mechanism for the reaction of a carbonyl and NaBH4
- The lone pair of electrons from :H-(nucleophile), is attracted and donated to the + carbon in the C=O.
- Dative covalent bond is formed between hydride ion and C=O.
- The pi bond in C=O breaks by heterolytic fission forming negatively charged intermediate.
- O of the intermediate donated lone pair to H in water. Intermediate has been protonated to form an alcohol.
Describe the mechanism for the reaction of a carbonyl compound and NaCN/H+
- Lone pair of electrons from -:CN is attracted and donated to + carbon in the C=O. Dative covalent bond forms.
- The pi bond in C=O breaks by heterolytic fission forming negatively charged intermediate.
- Intermediate is protonated by donating lone pair of electrons to H+ to form product.
- Product is hydroxynitrile
How does 2,4-dinitrophenylhydrazine detect presence of carbonyl group
NH2 group adds across the C=O and water is removed (condensation reaction) forming a yellow/orange precipitate
How can you use 2,4-dinitrophenylhydrazine to identify the carbonyl.
The precipitate is filtered and solution left over is recrystallised. Bp is found and compared to known values of 2,4-DNP derivatives to find specific carbonyl.
What will form when an aldehyde reacts with tollens reagent
carboxylic acid/silver mirror
Why can’t tollens reagent react with a ketone
can not oxidize to form a carboxylic acid so no silver mirror formed
Equation for the reaction of Ag in tollens reagent
Ag+(aq) + e- -> Ag(s)
Are carboxylic acids soluble in water
Carboxylic acids with up to 4 carbon atoms are soluble in water because C=O and O-H bonds are polar so hydrogen bond is formed.
Trend in solubility for carboxylic acids
as the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.
Products of reaction between carboxylic acids and metals
hydrogen gas and carboxylate salt
Observation for reaction between carboxylic acids and metals
metal disappears and effervescence
Products of the reaction between carboxylic acids and metal oxides/alkalis
carboxylate salt (aq) and water
Products of the reaction between carboxylic acids and carbonates
carboxylate salt, water and carbon dioxide. If carboxylic acid solid carbonate should disappear
How can you distinguish carboxylic acids from other organic compounds
only organic compound that is sufficiently acidic enough to react with carbonates
What is esterification
the reaction of an alcohol and a carboxylic acid to form an ester
What are the products for the reaction between an alcohol and carboxylic acid
ester and water
What are the conditions for esterification
concentrated sulfuric acid(catalyst) and heat
Products of the reaction between acid anhydride and alcohol
ester and carboxylic acid
Define hydrolysis
Chemical breakdown of a compound in the presence of water or in aqueous solution
Conditions needed for acid hydrolysis
ester heated under reflux with dilute aqueous acid (catalyst). Ester broken down by water.
State a difference between alkaline and acid hydrolysis
acid hydrolysis is a reversible reaction, alkaline hydrolysis is irreversible
What are the products of acid hydrolysis
carboxylic acid and alcohol
Conditions needed for alkaline hydrolysis
ester heated under reflux with aqueous hydroxide ions
What are the products of alkaline hydrolysis
carboxylate ion and an alcohol
Preparation of acyl chloride
carboxylic acid + SOCl2 (thionyl chloride) -> acyl chloride + SO2 + HCl
Why are acyl chlorides useful in organic synthesis
very reactive. Easily converted into carboxylic acid derivatives with good yields. They react with nucleophiles by losing Cl- whilst retaining C=O.
Why can acyl chloride react with phenol and carboxylic acids can’t
acyl chloride is more reactive
Reaction of acyl chloride to form esters
acyl chloride + phenol/alcohol -> ester + HCl
Products of the reaction between acyl chloride and water
carboxylic acid and HCl
What is a primary amide
Nitrogen is attached to one carbon
What is a secondary amide
Nitrogen attached to 2 carbons
Products of reaction between acyl chloride and ammonia
primary amide and ammonium chloride
Products of reaction between primary amine and acyl chloride
secondary amide and -chloride
Acyl chloride functional group
O=C-Cl
How to name an acyl chloride
Remove -oic acid from the carboxylic acid and add -oyl chloride
Acid anhydride functional group
O=C-O-C=O
Naming acid anhydrides
remove -acid from the carboxylic acid name and replace with anhydride
Naming esters
From the carboxylic acid remove -oic acid and replace with -oate. For the alcohol remove the -anol and replace with -yl
How to form tollen’s reagent?
Add AgNO3 to sodium hydroxide in a clean test tube until a brown precipitate forms (Ag2O). Add dilute ammonia until the precipitate dissolves to form a clear colourless solution.
