Oxidation – Carbonyl Compounds

00:01 Okay. Oxidation. Aldehydes, as we’ve seen before, are readily oxidised and ketones are oxidised with considerable difficulty. If we go back to when we were looking at alcohols, we showed that it was possible to oxidise the alcohol first up to an aldehyde, if it was primary, and then all the way up to a carboxylic acid. If on the other hand we had a secondary alcohol, we could get it as far as the ketone, but we couldn’t oxidise it any further. If we look at aldehydes, there are a number of different ways in which you can convert it to a carboxylic acid. Exhaustive oxidation with potassium permanganate, shown on the top, potassium dichromate and also, in this particular case, a silver diamine nitrate which is otherwise known as Tollen’s reagent which is a characteristic test for the presence of aldehydes since the silver+ becomes reduced and then coats the inside of the tube in the presence of an aldehyde.

01:02 The oxidation can only occur in the case of ketones under severe conditions to give a mixture of acids which are of little synthetic use since you effectively split the entire molecule apart. Let’s have a look at reduction. We’ve already seen chemical reduction using sodium borohydride and lithium aluminium hydride.

01:21 However, it is also possible to reduce ketones and aldehydes via catalytic amounts of nickel, platinum or palladium shown here as Ni, Pt or Pd in the presence of hydrogen gas. And these are able to reduce ketones and aldehydes down to alcohols.

01:44 This is of particular importance when you don’t necessarily want to use an aggressive reducing agent which may perhaps reduce another part of your molecule which you want to keep and hydrogenation can be the best choice when you have other groups that would react with a more aggressive hydride-based reducing agent like lithium aluminium hydride or sodium borohydride.

02:08 Carbonyl compounds are reduced to alcohols and in this particular case, ketones would be reduced to secondary alcohols and aldehydes would be reduced to primary alcohols.