6.1.7: Reactions of carbonyl compounds Flashcards
What is a carbonyl functional group?
C=O
- If the functional group is on the end carbon atom, an aldehyde is formed.
- If the functional group is not at the end of a carbon chain, then a ketone is formed.
What do aldehydes form when they become oxidised?
A carboxylic acid
What are the reagents needed for the oxidation of an aldehyde and what do these reagents react in situ to form?
- Potassium dichromate, K2Cr2O7
- Sulfuric acid H2S04
- Reagents react in situ to form the oxidising species Cr2O7-, and H+.
What is the balanced ionic equation for the oxidation of ethanal to ethanoic acid?
3CH3CHO(l) +Cr2O7-(aq) +8H+(aq) –>
3CH3COOH(aq) + 2Cr3+(aq) + 4H2O(l)
What is the simplified balanced symbol equation for the oxidation of ethanal to ethanoic acid once the oxidising agent has been simplified to [O]?
CH3CHO + [O] –>CH3COOH
In a laboratory, how is an aldehyde oxidised to a carboxylic acid and what colour change will be observed?
- The reaction mixture is heated gently under reflux.
- As the reaction proceeds, a colour change is observed, from orange to green, due to the oxidation state of chromium changing.
What makes carbonyl compounds susceptible to nucleophilic attack?
- They have a dipole in the C=O functional group.
- This makes them susceptible to attack on the delta -ve carbon atom.
What happens when A nucleophile donates a lone pair of electrons to the electron deficient carbon in a carbonyl compound?
- Simultaneously, the pi-bond in the C=O breaks and a reactive intermediate is formed.
- The extra electron pair is is equally quickly donated to the neighbouring atom to form an alcohol group and the stable product.
Draw a general mechanism for nucleophilic addition on a carbonyl compound.
Check in book
What is sodium tetrahydridoborate(III) more commonly known as?
sodium borohydride
formula: NaBH4
What is sodium tetrahydridoborate(III) and what is it used for?
- A reducing agent commonly used in organic synthesis.
- This compound is made of a BH4- ion, which acts as a source of hyride ions, H-.
What is the hydride ion from sodium tetrahydridoborate(III) involved in?
The hyride ion is commonly used in the electrophilic addition and reduction of carbonyl compounds to alcohols.
What do aldehydes reduce to?
primary alcohols
What do ketones reduce to?
secondary alcohols
What is the simplified balanced chemical equation for the reduction of pentan-2-one, using [H] as the reducing agent?
CH3COC3H7 + 2[H] –> CH3CH(OH)C3H7
Draw the mechanism for the reduction of an aldehyde (propanal) by nycleophlic addition.
Check in book
What is hydrogen cyanide?
-A weak acid that will partially ionise in solution.
What happens when hydrogen cyanide partially ionises in water and what is the balanced symbol equation for this?
- A cyanide nucleophile with a negative charge on the carbon atom is formed.
- HCN + H2O CN- + H3O+
What are other sources of cyanide (not hydrogen cyanide)?
sodium cyanide, NaCN
The cyanide cannot react directly with carbonyl compounds. However, what happens when the reaction is acidified?
The carbonyl functional group becomes more reactive as polarity of the C=O bond increases.
Draw the mechanism for the reaction of hydrogen cyanide with propanone.
In the second step, where could the hydrogen also be obtained from?
- See book for mechanism
- Another small molecule in the reaction mixture such as ehanol.
What does the addition of a cyanide to an organic molecule allow?
-The addition of cyanide allows more carbon atoms to be added to the organic molecule.
Which important bi-product is produced as a result of the reaction to add more carbon atoms to an organic molecule?
-In this reaction, hydroxynitrile is formed, which is an important chemical used in many industrial processes. `
Why is the reaction between hydrogen cyanide and propanone completed in solution with an acidity no lower than pH4?
Because the addition of acid drives the cyanide equilibrium to the left and reduces the amount of nucleophiles.
