Ochem presentation possible questions

Why is this considered a multi-step synthesis?

Because the final product is not made in a single reaction, each step produces and intermediate that is used in the next reaction

What type of reaction occurs in week 1?

A haloform oxidation reaction, where methyl ketone is oxidized to a carboxylic acid using sodium hypochlorite under basic conditions

Why is NaOCl (bleach) used? And what is the role of NaOH?

NaOCl acts as the oxidizing agent, converting the methyl ketone group into a carboxylic acid. NaOH provides basic conditions necessary for the haloform reaction to proceed

Why do you add acetone at the end?

Acetone reacts with and destroys excess NaOCl, preventing unwanted side reactions

Why is HCl added to pH 2?

To protonate the carboxylate ion, forming 4-nitrobenzoic acid, which precipitates out of solution

Why does a solid form after acidification?

Because the neutral carboxylic acid is less soluble in water than its ionic form

What type of reaction is involved in week 2?

A fischer esterification, where a carboxylic acid reacts with an alcohol to form an ester

What is the role of sulfuric acid?

It acts as a catalyst, promoting the Fischer esterification reaction by protonating the carboxylic acid, which increases its reactivity with the alcohol.

Why is excess ethanol used?

Excess ethanol is used to drive the reaction towards ester formation and improve yield by shifting the equilibrium.

Why is the reaction refluxed?

Refluxing the reaction maintains a steady temperature, allowing the reaction to proceed efficiently while preventing evaporation of the volatile components, thus ensuring higher yields of the ester.

Why does the product precipitate when poured into ice water?

The ester is less soluble in cold water, so it crystallizes out

In week 3, what functional group is being reduced?

the nitro group (-NO2) is reduced to an amine (-NH2)

Why use iron and acetic acid?

They form a mild reducing system that selectively reduced the nitro group without affecting the ester

Why is celite filtration used?

To remove iron and metal salts from the reaction mixture

Why is NaOH added to pH 10?

to make benzocaine less soluble in water so it precipitates

Why might extraction with ether be needed?

If no precipitate forms, benzocaine can be extracted into and organic solvent due to its nonpolar nature

Why is the nitro group reduced last instead of first/

The nitro group is more stable than the amine group formed during reduction, thus it is reduced last to prevent undesired side reactions.

Why does NaOCl selectively oxidize a methyl ketone to a carboxylic acid rather than over-oxidizing other parts of the molecule?

NaOCl selectively oxidizes a methyl ketone to a carboxylic acid due to the specific reactivity of the methyl group, which allows the oxidation to occur without affecting other functional groups.