Oxidation of propanol to propanal VID 1592052479220

High School Chemistry
The oxidation of a primary alcohol to an aldehyde can be problematic in a school chemistry lesson.
One part of the problem is that it is more difficult to oxidise the alcohol to the aldehyde, than it is to oxidise the aldehyde to the corresponding carboxylic acid.
Thus, it is recommended to distil off the aldehyde as soon as it is formed to prevent it from oxidising further.
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This is easier said than done.
The boiling points of propanol, propanal and propanoic acid are as follows
Boiling point propan-1-ol 97 C
Boiling point propanal 49 C
Boiling point propanoic acid 141 C
It is also recommended to use an excess of the alcohol relative to the oxidising agent in the reaction mixture.
We used 2ml of propanol to 10ml of oxidising agent.
The oxidising agent was prepared by dissolving 1g sodium dichromate in 10ml of dilute sulfuric acid, 1M.
This is described as generating chromic acid in situ
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We also cooled down the oxidising agent in an ice/water bath before adding the propanol to it. This slows down the initial rate of reaction, allowing the distillation apparatus to be assembled before heating.
One could heat with a water bath. This would be a safer option.
We chose to heat carefully with a Bunsen burner for greater control of the heating process.
We aimed to maintain a temperature reading of between 80 to 85 C on the thermometer in the distillation arm of the apparatus.
The reaction seems to be exothermic. Initially, the reaction mixture turned brown in colour, but on further heating during distillation, developed a dark green colour.
1 to 2ml of clear liquid was obtained as a distillation product.
The product mixture gave a silver mirror on heating with Tollen's reagent, indicating the presence of an aldehyde.
We used microscale Quickfit apparatus in this experiment.
We aim to compare this with carrying out the experiment in a boiling tube, which offers lower cost and greater simplicity.