Week 1: Oxidation, reduction, hydrogenation Flashcards
Describe LiALH4
More reactive than LiBH4 as Al-H is weaker than B-H.
can also reduce aldehydes, ketones, esters plus amides.
Reduces carboxylic acids slowly
Can reduce amides to aldehydes as well
What is chemoselectivity, regioselectivity and stereoselectivity
Chemoselectivity: Which functional group will react
Regioselectivity: Where it will react
Stereoselectivity: How it will react (stereochemistry of products)
Describe NaBH4
Mild reagent, easier to handle
Mainly reduces only aldehydes and ketones
Needs protic solvent or electrophilic cations
Explain TPAP
Mild oxidising agent for 1º to aldehydes
Explain Swern oxidation
1º to aldehyde by using oxalyl chloride and DMSO.
Makes biproducts Me2S, CO, CO2 and HCl.
Define reactivity regarding steric and electronics
- Sterics: Space and hinderance
e. g. Aldehyde is more reactive than ketone as it is on the end of a molecule. - Electronics: Due to electrons and electronegativity
e. g. Ester is less reactive than ketone due to having a resonance structure and thus spread out electrons.
Explain KMnO4
Used for over-oxidation for 1º or aldehydes to carboxylic acids.
Can also use Cr(VI) or Mn(VII).
Will not stop at aldehyde.
Explain dess martin periodinane
Mild oxidising agent for 1º to aldehyde. Also good for sensitive alcohols.
Name the reagents of carbonyl reduction
NaCNBH3 NaBH4 LiBH4 LiAlH4 BH3 DIBAL
List the reagents of carbonyl oxidation
Jones oxidation Swern oxidation PDC TPAP Dess-Martin periodinane KMnO4 PCC
What is the hierarchy of carbonyl reactivity as electrophiles
Aldehyde (most reactive) Ketone Ester Amide Carboxylate (least reactive)
Explain lindlers catalyst
Hydrogenation of an alkyne to an alkene.
H2, Pd, CaCO3 and Pb(OAc)2. Does not hydrogenate alkenes to alkanes due to the Pb deactivating the catalyst to make reduction of the alkene slow.
Describe BH3
Reduces amides and carboxylic acids
aldehydes, ketones and esters very slowly
Describe LiBH4
More reactive than NaBH4 so can also reduce aldehydes, ketones + esters.
Describe the process of catalytic hydrogenation
Always needs a H2 source which is bubbled onto a catalyst. Then the alkene coordinates to it and Hs delivered to same face (syn)
Chemoselective for C=C because weaker than C=O so more reactive
Describe NaCNBH3
Reduces imine to amine
Explain the rosenmund reaction
Hydrogenation of acyl chlorides to aldehydes.
Use H2, Pd and BaSO4 (the support stops reduction to alcohol by allowing products to escape catalyst, CaCO3 also).
Describe DIBAL
Converts esters to an aldehyde
Could also do this in 2 steps by reducing to alcohol with LiAlH4 and then Cr(VI) to convert to aldehyde
Explain PCC:
Used if alcohol is acid sensitive (means it would eliminate to form an alkene) to retain the alcohol.
Does not work in H2O as hydrate acts as alcohol and oxidises to carboxylic acid.
Must be an organic solvent like dichloromethane.
List the catalysts of hydrogenation for an alkene and an aromatic
Alkene: Pd, Pt or Ni
Aromatic: Pt, Rh or Ni (under high pressure)
Explain PDC
1º to aldehyde
Explain jones oxidation
(Na2Cr2O7, H2SO4, acetone
Oxidises 2º to a ketone
Explain what a protic and lewis acid is
Protic acid: Bronsted acids, thus, electrophiles that can donate protons
Lewis acid: Electrophiles that accept a pair of electrons
