Preparation & Reactions of Aldehydes and Ketones, RHO & ROR'

A couple of key points:

  • Aldehydes and Ketones both contain a carbonyl group, but are also less reactive than acid chlorides.
  • They do NOT react with organocopper reagents and weak hydride donors (as these weak reagents are involved in their own synthesis).
  • The reactions are addition rather than substitution as there is no leaving group.
  • They have one less bond to an electronegative atom than acid chlorides (no chlorine!).
Aldehyde & Ketone

Aldehyde & Ketone

They can be formed through reduction of Acid Chloride:

Aldehyde & ketone synthesised with Bu3SnH and R'2CuLi

Aldehyde & ketone synthesised with Bu3SnH and R

If an aromatic ring is being substituted then we must use friedel crafts acylation.

For Acid Chloride to Aldehyde we use Bu3SnH as a source of weak Hydride ions which displace a Cl-. We do not use a more obvious source such as LiAlH4 as this will result in the over reduction of the aldehyde into a primary alcohol.

For Acid Chloride to Ketone we use R’2CuLi as a source of nucleophilic R’ group.

and via reactions with Alcohols:

Simply, Primary alcohols lead to Aldehydes and secondary alcohols lead to Ketones when reacted with PCC. This is oxidation.

Aldehyde & Ketone synthesised from Alcohols

Aldehyde & Ketone synthesised from Alcohols

and finally with Alkanes:

Alkanes are just as simple as alcohols – just add O3 then PPh3 for an easy reaction!

Simple alkenes lead to aldehydes and more complex lead to ketones.

Aldehyde  Ketone synthesised from Alkenes

Aldehyde Ketone synthesised from Alkenes

Synthesis Summary:

In short:

REDUCTION
From Acid Chloride to Aldehyde – Bu3SnH (as a source of H-)
From Acid Chloride to Ketone – R2CuLi (as a source of R)

OXIDATION
From Alcohol to Aldehyde/Ketone – PCC
From Alkene to Aldehyde/Ketone – O3 then PPh3

– Reactions with Carbon Nucleophiles and Hydride Donors

As mentioned earlier, aldehydes and ketones do not react with weak hydride donors (eh Bu3SnH) or organocopper reagents (eg R2CuLi) – they need more powerful reagents.

These come in the form of Grignard reagents (eg RMgBr) and powerful halide donors (eg LiAlH4).

TBF

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