Chapter 26 - Carbonyl Compounds and Carboxylic acids Flashcards
What is the carbonyl functional group
C=O
What is the functional group for an aldehyde
COH
What is the functional group for a ketone
RCOR’
What is the simplest ketone
Propanone
Naming aldehydes
Ends in -al
The C=O is always designated as carbon-1
Naming ketones
Ends in -one
What are the main reactions an aldehyde can go through
Oxidation
Turned into alcohols
Addition reactions
Why can aldehydes and ketones react?
Because the C=O is polar. A nucleophile is attracted to the partially positive C.
What is a nucleophile
An electron pair donor.
What are the main reactions a ketone can go through
Turned into an alcohol
Addition reactions
Oxidation of aldehydes
This is when you turn an aldehyde into a carboxylic acid.
So, you would reflux the aldehyde with H+ / CR2O7 2- and it would turn into a carboxylic acid.
Colour change for the oxidation of aldehydes
Orange to green
Aldehydes to a primary alcohol (+ equation)
NaBH4 acts as a reducing agent to aldehydes to turn them into primary alcohols.
Generally, the equation for the reaction is
Aldehyde + 2[H] –> Primary alcohol
(above arrows: NaBH4/ H20).
Ketones to a secondary alcohol (+ equation)
NaBH4 acts as a reducing agent to ketones to turn them into secondary alcohols.
Generally, the equation for the reaction is:
Ketone + 2[H] –> Secondary alcohol
(Above arrow : NaBH4 / H20)
Aldehydes + ketones to a hydroxynitrile
It’ll react with HCN and H2SO4 / NaCN to create a hydroxynitrile.
It’s useful because it increases the length of the carbon chain.
What type of reaction is turning an aldehyde/ketone into a hydroxynitrile
An addition reaction
Mechanism for nucleophilic addition of carbonyl compounds to turn them into alcohols
Firstly, a Hydride ion (H-) will attack the C=0 bond by being attracted to the C.
Then, the C=O bond will break by HETEROLYTIC FISSION.
DRAW THE PARTIAL CHARGES.
Then, the O will donate it’s free pair of electron to the H in a water molecule.
DRAW THE PARTIAL CHARGES ON THE WATER MOLECULE.
Then, there is an OH bond that’ll form where the O used to be, and there will be an OH- made as well.
Mechanisms for nucleophilic substitution of carbonyl compounds to turn them into hydroxynitriles
The CN- will attack the C=O by being attracted to the C. There should be a lone pair of electrons on the C of the CN.
Break the C=O bond by HETEROLYTIC FISSION.
The O will donate its lone pair of electrons to a H+. There will be a OH formed where there used to be an O.
How can you identify for aldehydes and ketones
Add 2,4-dinitrophenylhydrazine.
It’ll turn yellow/ orange precipitate in the presence of a C=O bond.
Testing for a carbonyl group in an aldehyde
- Add 5cm of depth of 2,4 DNP to a test tube
- Use a dropping pipette, add 3 drops of the other unknown compound. Leave to stnad.
- If no crystals form, add a few drops of sulfuric acid.
- Yellow/ orange precipitate is formed. C=O is present.
Distinguishing between aldehydes and ketones
You can use a fresh sample of the unknown compound and Tollen’s Reargent.
An aldehyde will form a silver mirror
How can you create Tollen’s Reagent
It has a short shelf life and shoul dbe made up immediately before the test.
- In a clean test tube, add 3cm of depth of (Aq) AgNO3.
- Add NaOH(aq) to the AgNO3, until a brown precipitate of Ag2O is formed.
- Add dilute ammonia solution until the brown precipitate dissolves to form a clear colourless solution.
Testing for an aldehyde
- Pour 2cm depth of the unknown compound into a test tube.
- Add an equal amount of Tollen’s Reagent
- Leave the test tube to stand in a beaker of warm water at 50 degrees for 10-15 mins.
- If silver mirror is made, then aldehyde is present.
How does the aldehyde test work?
There is a redox and oxidation reaction happening.
Ag(aq) + +e –> Ag(s)
The aldehyde + [O] –> carboxylic acid.
Identifying an aldehyde/ ketone by melting point
The 2,4 DNP precipitate can be analysed to identify the C=O compound.
1. The impure yellow/ orange solid is filtered.
2. The solid is recrystallised to produce a sample of crystals
3. The melting point of the purified 2,4 DNP is measured.
Then you can compare the data using a data book.
What are the 2 groups making up a carboxyl group
Carbonyl and hydroxyl group.
Solubility of carboxylic acids
Because C=O and O-H, they allow to make hydrogen bonds with water molecules.
Carboxylic acids with upto 4 C atoms are soluble in water.
Any more than 4C atoms, and the solubility decreases as the non-polar C- chain has a greater effect on the polarity as a molecule.
Dicarboxylic acids and their solubility
They will readily dissolve in water.
Carboxylic acids and their reactions
Generally,
this happens:
HCOOH H+ + HCOO-
What reactions can carboxylic acids go through?
In redox reactions with metals
and neutralisation reactions with bases (alkalis, metal oxides and carbonates)
They both create carboxylate salts
Carboxylic acids and redox reactions with metals
Forms hydrogen gas and carboxylate salts.
Observe the metal disappearing
Effervescence as H2 gas.
Carboxylic acids and neutralisation reactions with bases
Forms salt and water.
The products are examples:
(CH3COO-)2Ca2+
Carboxylic acids and neutralisation reactions with alkalis
Forms salt and water
No reaction may be seen
May form: CH3COO-Na+
Carboxylic acids and neutralisation reactions with carbonates
CO2 gas is made
If carboxylic acid is in excess, the solid will disappear.
Tests for the carboxyl group
Carbonates will only react with carboxylic acids.
Salicylic acid
2 - hydroxybenzoic acid
What is nylon
A polyamide
What is a compound with 2 carboxylic groups called
Oxalis acid
What is oxalic acid called
Ethanedioc acid
Who can you test for a carbonate
Add sodium carbonate and it should fizz