Question

Today's Reaction vanillin KBrO3 / HBr -----------> acetic acid 6-bromovanillin or 5-bromovanillin or 2-bromovanillin Bromination of the benzene ring is typically carried out with elemental halogen (Br2) and a Lewis Catalyst such as FeBr3. Bromine is a volatile liquid that can cause serious burns to the eyes and skin in both gas and liquid form. It is potentially severe to fatal irritation of the respiratory system. For this reason, bromine should not be frequently used in the undergraduate laboratory. However, brominated aromatic compounds and electrophilic aromatic substitutions are important to and frequently used by the organic synthetic chemist. Rather than using elemental bromine, you will use a safer and greener procedure where the brominating species will be formed in situ (meaning inside the reaction mixture) according to complex reactions involving potassium bromate, hydrobromic acid and acetic acid. For our purposes (and to simplify an otherwise complex mechanism) we will consider this mixture a source of bromonium ions, Br+. Experiment Procedure Work with a partner. 1) Place 3.0 mL of glacial acetic acid, and a spin vane into a 5-mL conical vial 2) Add 1.5 mmol of vanillin. Begin stirring the solution at room temperature. 3) Add 0.09 g of potassium bromate, followed by 0.3 mL of hydrobromic acid (this does not need to be exact-approximate using a plastic pipet.) 4) Stir the mixture 40 minutes. 5) Pour the mixture into 25 mL of water, add a stirring bar and stir for an additional 5 minutes. 6) Isolate the white solid obtained by vacuum filtration. 7) Wash with 0.5 mL of ice cold water, and oven dry (do not use plastic) at 80°C for 10 minutes. Cool. Weigh. Record. If your mass has changed, dry again for 5 minutes and recheck mass. Dry until mass is stable. 8) Weigh the product and determine percent yield

Today's Reaction

vanillin
KBrO3 / HBr
----------->
acetic acid

6-bromovanillin or 5-bromovanillin or 2-bromovanillin

Bromination of the benzene ring is typically carried out with elemental halogen (Br2) and a Lewis Catalyst such as FeBr3. Bromine is a volatile liquid that can cause serious burns to the eyes and skin in both gas and liquid form. It is potentially severe to fatal irritation of the respiratory system. For this reason, bromine should not be frequently used in the undergraduate laboratory. However, brominated aromatic compounds and electrophilic aromatic substitutions are important to and frequently used by the organic synthetic chemist.

Rather than using elemental bromine, you will use a safer and greener procedure where the brominating species will be formed in situ (meaning inside the reaction mixture) according to complex reactions involving potassium bromate, hydrobromic acid and acetic acid. For our purposes (and to simplify an otherwise complex mechanism) we will consider this mixture a source of bromonium ions, Br+.

Experiment Procedure

Work with a partner.
1) Place 3.0 mL of glacial acetic acid, and a spin vane into a 5-mL conical vial
2) Add 1.5 mmol of vanillin. Begin stirring the solution at room temperature.
3) Add 0.09 g of potassium bromate, followed by 0.3 mL of hydrobromic acid (this does not need to be exact-approximate using a plastic pipet.)
4) Stir the mixture 40 minutes.
5) Pour the mixture into 25 mL of water, add a stirring bar and stir for an additional 5 minutes.
6) Isolate the white solid obtained by vacuum filtration.
7) Wash with 0.5 mL of ice cold water, and oven dry (do not use plastic) at 80°C for 10 minutes. Cool. Weigh. Record. If your mass has changed, dry again for 5 minutes and recheck mass. Dry until mass is stable.
8) Weigh the product and determine percent yield

Today's Reaction

vanillin
KBrO3 / HBr
———–>
acetic acid

6-bromovanillin or 5-bromovanillin or 2-bromovanillin

Bromination of the benzene ring is typically carried out with elemental halogen (Br2) and a Lewis Catalyst such as FeBr3. Bromine is a volatile liquid that can cause serious burns to the eyes and skin in both gas and liquid form. It is potentially severe to fatal irritation of the respiratory system. For this reason, bromine should not be frequently used in the undergraduate laboratory. However, brominated aromatic compounds and electrophilic aromatic substitutions are important to and frequently used by the organic synthetic chemist.

Rather than using elemental bromine, you will use a safer and greener procedure where the brominating species will be formed in situ (meaning inside the reaction mixture) according to complex reactions involving potassium bromate, hydrobromic acid and acetic acid. For our purposes (and to simplify an otherwise complex mechanism) we will consider this mixture a source of bromonium ions, Br+.

Experiment Procedure

Work with a partner.
1) Place 3.0 mL of glacial acetic acid, and a spin vane into a 5-mL conical vial
2) Add 1.5 mmol of vanillin. Begin stirring the solution at room temperature.
3) Add 0.09 g of potassium bromate, followed by 0.3 mL of hydrobromic acid (this does not need to be exact-approximate using a plastic pipet.)
4) Stir the mixture 40 minutes.
5) Pour the mixture into 25 mL of water, add a stirring bar and stir for an additional 5 minutes.
6) Isolate the white solid obtained by vacuum filtration.
7) Wash with 0.5 mL of ice cold water, and oven dry (do not use plastic) at 80°C for 10 minutes. Cool. Weigh. Record. If your mass has changed, dry again for 5 minutes and recheck mass. Dry until mass is stable.
8) Weigh the product and determine percent yield

Added by Manuela E.

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