Oxidizing Methoxybenzyl alcohol to methoxy benzaldehyde using phase transfer catalysis

OCHEM II LAB FINAL

What is the oxidizing agent in this experiment?

sodium hypochlorite

What is the phase transfer catalyst?

tetrabutylammonium hydrogen sulfate

What is oxidation?

occurs when oxygen is added to or hydrogen is lost from an organic molecule

Chromate

• CrO42-

• used in acidic, aq condition

• Turns primary OH —> carboxylic acid

Dichromate

• Cr2O72-

• used in acidic, aq conditions

• turns primary OH —> carboxylic acid

Chromium Trioxide

• CrO3

Collins Reagent

• toxic complex composed of one molecule of CrO3 and two molecules of pyridine

• contains no water

• oxidize primary OH to aldehyde w/o further oxidation to a carboxylic acid

  • b/c no water used

• all reagents are toxic and tertiary OH are not oxidized

What does KMnO4 do?

• potassium permanganate

• used in basic conditions to oxidize primary alcohols to potassium carbonate salts

• strong acid is added (ex: dilute acid) —> carboxylic acid

• also reacts w/ double + triple bonds so not used to oxidize an alcohol w/ those

• not normally used to oxidize secondary alcohols to ketones b/c many ketones react further

Mn + 7 —>

MnO2 (Mn +4)

What does sodium hypochlorite do?

• oxidizes aromatic + aliphatic secondary alcohols —→ ketones and primary alcohols to aldehydes

• sub for collins reagent

• primary aliphatic alcohols oxidize very slowly

• selectively oxidizes secondary alcohols in the presence of primary alcohols

What is the main problem in this reaction?

• starting alcohol is soluble in organic solvent

• NaOCl is soluble in water, not in organic solvents

• need to bring water soluble NaOCL and ethyl acetate soluble alcohol together to react

How can we bring NaOCl + ethyl acetate soluble alcohol together to react?

• need to use phase transfer catalyst

  • tetrabutylammonium hydrogen sulfate

  • 4 alkyl groups help make it soluble in ethyl acetate

  • TBAS is salt so water soluble

  • acts as a shuttle, moving back and forth between the aq. layer + organic layer

  • can exchange HSO4- counter ion for ClO- forming

  • TBAS transfers ClO- into ethyl acetate layer so it can react w/ alcohol

When using ethyl acetate what safety measures should be observed?

• not using the chemical near flames or other heat sources must be observed

When using dichloromethane what safety measures should be observed?

• wearing goggles and gloves must be observed as well as using the chemical in the fume hood

What does a disubstituted aromatic compound that has a 740 cm IR absorptions look like?

• ortho

• IR range for ortho is 735-770

What is the purpose of this experiment?

to oxidize methoxybenzyl alcohol to methoxybenzaldehyde using sodium hypochlorite and tetrabutylammonium hydrogen sulfate as the phase transfer catalyst.

• helps turn a primary alcohol into an aldehyde

• determine the starting alcohol as either ortho, meta, or para

What are the reactions?

What are the steps of the experiment?

1. methoxy benzyl alcohol + ethyl acetate + TBAS into rbf w/ stir bar

2. bleach added slowly every 5 seconds while stir bar kept stirring

3. rxn stirred for 45 min —> two layers

4. solution added to sep. funnel w/ ethyl acetate, sat. NaCL, + ethyl acetate again —> both ether layers removed from the top

5. added to sep. funnel + washed w. 5% NaOH

6. extracted again with NaCl

7. ethyl layer into Erlenmeyer flask + dried/ MgSO4 then decanted into RBF + evaporated

The major peak in the aldehyde that is absent in the alcohol is ?

carbonyl at 1686.26 cm-1

The major peak in the alcohol that is absent in the aldehyde is ?

broad strong peak at 3330 cm-1 range

How can the crystals of methoxybenzoic acid can be isolated from the NaOH solution?

• add heated HCl to neutralize solution

• will reprotonate the solution which will form crystals

• after solution is cooled, crystals will form and vacuum filtration can be used to isolate the crystals

How can the TLC be used to monitor the reduction of methoxybenzaldehyde to methoxybenzyl alcohol?

• use NaBH4 as reducing agent

• silica gel is polar and NaBH4 will increase bonds to hydrogen and decrease bonds to oxygen

• methoxybenzyl alcohol will move a shorter distance due to polar nature