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
What is a derivative of a carboxylic acid?
A compound that can be hydrolysed to form the parent carboxylic a is. They all contain the acyl group.
What is the functional group of Ester
RCOOR
What is the acyl group
R-C=O
How do you name esters
Remove the “oic acid” and replace it with “-oate”
The alkyl chain that is attached to the oxygen atom of the C-OO, will be put as the first word.
How do you name acyl chlorides
Remove the “oic acid”
Replace it with “-oyl chloride”
How can you form acid anhydrides
Remove water from the 2 carboxylic acid groups and form an ethanoic anhydride.
What is an acid anhydride
It literally means without the water, so that’s exactly what you have to do.
Esterification
When you have an alcohol + carboxylic acids to form an ester.
Add concentrated sulphuric acid.
The esters are sweet smelling liquids.
Water is formed as a product.
PAG for making ethyl propanoate
- Pour 2cm3 of ethanol and 2cm3 of propanoic acid into a boiling tube
- Carefully, add a few drops of sulphuric acid (concentrated)
- Place it in a beaker of hot water for 50 degrees, for 5 minutes
- Pour it into a beaker of aq. Na2CO3 (which neutralises the acids, and gets rid of the carboxylic acid, making it easier to detect the ester.)
- If you notice you have oily drops of an ester floating on top of the water.
Hydrolysis of esters
There are 2 ways: acid hydrolysis and alkali hydrolysis (often called saponification).
Acid hydrolysis of esters
You heat the ester under reflux with dilute aqueous acid.
The ester is broken down using water into a carboxylic acid and an alcohol.
Saponification of esters
Heat the ester under reflux with aqueous OH- ions.
If you use NaOH, then you can produce CH3COO-Na+.
You create a salt and an alcohol.
What are acyl chlorides in terms of reactivity
They are the most reactive chemicals
How can you make acyl chlorides
Use their parent carboxylic acid chain.
Add thionyl chloride (SOCl2)
Creates SO2 and HCl as gases.
It should be carried out in a fumer cupboard.
Reactions of acyl chlorides
They are very reactive
They can be converted into carboxylic acid derivatives.
They react with nucleophiles by losing their Cl- ions whilst retaining their C=O double bond.
How do acyl chlorides form esters
Acyl chlorides + alcohol –> ester + HCl.
How do acyl chlorides react with phenols
Acyl chlorides + Phenol –> Phenol acyloate + HCl
How do acyl chlorides form carboxylic acids?
Acyl chlorides + water –> Carboxylic acid + HCl
This is a very violent reaction and fumes of HCl are released.
How do acyl chlorides react with amines and ammonia
Ammonia and amines can act as nucleophiles, by donating a lone pair of electrons on the nitrogen atom.
What is an amine?
NHx
What is ammonia?
NH3
What is ammonium?
NH4 +
Ammonia + acyl chloride
Primary amide + ammonium chloride
Acyl chloride + primary amine
Secondary amide + primary amine -Cl
Reactions of acid anhydrides
React the same way that acyl chlorides do with alcohols, phenols, water, ammonia, and amines.
Acid anhydrides are less reactive than acyl chlorides.
Acid anhydrides + alcohols
Ester + ethanoic acid
Acid anhydrides + water
2 carboxylic acids (one from either of the acid anhydride chains)
Acid anhydrides + phenol
An ester (called a phenyl alkynoate) and a carboxylic acid.
Reasons to use an acid anhydride rather than an acyl chloride, despite the fact that they have the same reactions?
Acid anhydrides are:
- cheaper
- safer to use ; less corrosive.
- doesn’t produce dangerous fumes of HCl.
How can you turn an acyl chloride into a carboxylic acid?
There are 2 main mechanisms for this:
- Nucleophilic addition
- Nucleophilic elimination
Uses of acylation reactions?
Used to make aspirin
Explain why an acyl chloride may be used rather than a carboxylic acid?
The reactions with a carboxylic acid are reversible, which gives a higher yield.
Explain why reflux is required for organic synthesis
A reflux is performed in a chemical reaction so that a solution may be heated to a boiling point without losing the solvent or products to evaporation.
Suggest a method which could be used to separate the desired product from the reaction mixture
Fractional distillation
Explain why ethanoic anhydride is often used, rather than ethanol chloride
Ethanoyl chloride may produce a reversible reaction, which gives a higher yield, but it forms fumes of HCl.
Ethanoic acid forms a reversible reaction and a lower yield.
Ethnic anhydride has a high yield, and the by-product is only an irritant. It is also cheaper than acyl chloride and not as easily hydrolysed as the acyl chlorides.
How do you name an acyl chloride with 3 Carbon atoms
Propanoyl chloride, NOT propyl chloride
Explain why it may be hard to identify a product in a fractional distillation
Because it is rare for all the reactants to be used up in the reaction. Also, the boiling point for the desired product may be close to others as well.
Reactions of the carbonyl group
The slightly positive Carbon is attacked by nucleophiles.
What reaction is an aldehyde/ ketone to a hydroxynitrile
An addition reaction
Where do aldehydes and ketones differ
Aldehydes have a H atom attached to the carbonyl group, which makes it easier to oxidise. Because the ketones have the carbonyl compounds attached to a C. It is a lot harder (and requires more energy) to break a C-C bond, in comparison to a C-H bond.
At what temperature does ethanal boil at?
Close to room temperature.
Their boiling points increase as the molecules get bigger (due to increased London forces)
For the same number of C atoms, does an alkane have a higher b.p or an aldehyde, or an alcohol
Alcohols have the highest b.p because they have hydrogen bonding, London forces and Permanent dipoles. Then is aldehydes because they have Dipole-dipole interactions, and London forces, as the alkane only has London forces.
What does NaBH4 do to aldehydes/ ketones?
NaBH4 acts as a reducing agent.
Electron half for the reduction of dichromate ions when they react with the aldehydes?
Cr207 2- + 14H+ + 6e- -> 2Cr 3+ + 7H20.
Overall equation for the oxidation of an aldehyde (like actual equation)
3RCHO + Cr2O7 2- +8H+ –> 3RCOOH + 2Cr3+ + 4H2O.
Carboxylic acid + sodium carbonate
2CH3COOH + Na2CO3 —>2CH3COONa + H2O +CO2
Carboxylic acid + sodium hydrogen carbonate
CH3COOH + NaHCO3 — > CH3COONa + H2O + CO2
Ethanoic acid + ammonia
CH3COOH + NH3 —> CH3COONH4
Wha this 2,4 DNP
2, 4 dinitrophenylhydrazine
What is Brady’s reagent
2,4 DNP with methanol and sulphuric acid.
Hydroxylamine structure
NH2OH
What is 2,4 DNP + propanone
Propanone- 2,4 dinitrophenylhydrazone
Basically the entire thing is the same, just the NH2NH2 part changes - here the H2 comes off, and a double bond between the Carbonyl chain in the aldehyde or ketone bonds onto it, where the O used to be.
When you reduce an aldehyde or ketone to an alcohol, do you get water?
NO!
you don’t get water being formed.
What is the name of NaBH4
Sodium tetrahybridoborate
Why does the (III) after NaBH4 show
It shows the oxidation state of the boron.
Is water formed when turning an aldehyde into a carboxylic acid
Yes.
Reactions of the acyl chlorides reacting with ammonia
It may need to react with 2NH3, to produce the primary amine and the ammonium chloride.
Pretty much just one of the hydrogens is removed from the NH3, and it is attached to where the C- Cl used to be.
Reaction between Phenylamine + methanol chloride
CH3COCl + 2C6H5NH2 —> CH3CONHC6H5 + C5H5NH3Cl
Creating, Phenylethanamide and phenylammonium chloride.
What happens when a carboxylic acid and sodium carbonate react
Effervesce, and the white solid disappears
Explain why all aldehydes except for methanal will produce enantiomers when they react with the cyanide ion.
C=O is planar.
The nucleophiles can attack from above or below the plane.
For an asymmetrical ketone, there will be a chiral carbon, but methanol doesn’t because two of the resulting groups will be carbon will be hydrogen atoms.
Why is using TLC better than melting point
TLC is generally more sensitive to temperature changes.
