Oxidation of Aldehydes
- The carbonyl group in an aldehyde is always situated at the end of the chain
- When naming aldehydes, you do not include the '1' in the name, the carbonyl carbon is always number 1 on the chain
- The simplest aldehyde is methanal, HCHO, with the only carbon being that of the carbonyl group
- The carbonyl group in a ketone is always located within the chain
- The simplest ketone is propan-2-one, CH3COCH3, as you need an alkyl group either side of the carbonyl carbon in a ketone
Preparation of Aldehydes & Ketones
- Aldehydes and ketones can be prepared by oxidising primary and secondary alcohols as shown below
Further Oxidation
- During the oxidation of a primary alcohol to an aldehyde, the apparatus must be set up to distill off the aldehyde as it is produced
- Further oxidation of primary alcohols can then take place
- Aldehydes can be easily oxidised to form carboxylic acids
- To oxidise a primary alcohol straight to a carboxylic acid, you would heat the reaction mixture under reflux
- The aldehyde would still be produced, but as it evaporates it would condense and drop back into the reaction mixture, to be further oxidised to the carboxylic acid
- The oxidising agent used for all of the oxidation reactions be acidified potassium dichromate
- K2Cr2O7 with sulfuric acid, H2SO4
- Ketones are very resistant to being oxidised, so no further oxidation reaction will take place with secondary alcohols
- This is because ketones do not have a readily available hydrogen atom, in the same way that aldehydes (or alcohols) do
- An extremely strong oxidising agent would be needed for oxidation of a ketone to take place
- The oxidation will likely oxidise a ketone in a destructive way, breaking a C-C bond
Examiner Tip
In the exam you can simply say that ketones cannot be oxidised!