5 - distillation

What is produced when a primary alcohol is partially oxidised?

An aldehyde

Reagent and conditions for partial oxidation of a primary alcohol

• Potassium dichromate solution and dilute sulfuric acid

• Warm gently and distil the aldehyde out as it forms

Safety when using solid potassium dichromate

Wear gloves as it is highly toxic and an irritant. Avoid inhaling any dust

Method for partial oxidation of propan-1-ol

1. Place about 10cm3 of dilute H2SO4 in a round-bottomed flask and add about 3g K2Cr2O7 and anti-bumping granules. Shake contents

2. Add 1.5cm3 of propan-1-ol in drop from a dropping pipette and shake flask

3. Assemble distillation apparatus - clamp flask over electric heater, add bung with integrated thermometer + Liebig condenser

4. Gently heat and slowly distil - collected sample at boiling point of the desired product

What is produced when a primary alcohol is fully oxidised?

A carboxylic acid

Reagents and conditions for full oxidation of primary alcohol

• EXCESS potassium dichromate solution and sulfuric acid

• EXCESS k2Cr2O7, heat under reflux

Method for full oxidation of propan-1-ol

1. Measure 5cm3 water and add 6g sodium dichromate - shake to dissolve (if u have solid K2Cr2O7)

2. Put about 1.5cm3 propan-1-ol into a 50cm3 round bottomed flask and add anti-bumping granules

3. Put a condenser on the flask, vertically

4. Add 2cm3 conc H2SO4 and excess K2Cr2O7 (acidified potassium dichromate)

5. Heat eg with heating mantle until colour change

6. Distil to separate the ketone from the mixture

During reflux, why shouldn’t you seal the end of the condenser?

Build up of gas pressure could cause the apparatus to explode

Why are anti bumping granules used?

Prevents vigorous, uneven boiling by making small bubbles form instead of large bubbles