CH4: Alcohols and Ethers Flashcards
3 membered ring ether called
Oxirane
4 membered ring ether called
Oxetane
Ether vs alcohol vs hydrocarbon BP, Solubility
BP: HC=Ether
Acid-catalyzed hydration
An alkene + water with HA leads to an alcohol.
Alkene + H2O 1) HA
There is a carbocation intermediate which may rearrange. Markovnikov addition.
Everything is in equilibrium.
Not a stereoselective reaction, leads to a racemic mixture.
Alcohols from alkenes
1) Acid-catalyzed hydration
2) Oxymercuration-demercuration
3) Hydroboration-oxidation
Oxymercuration-demercuration
Water + Alkene with 1) Hg(Oac)2/THF 2) NaBH4/NaOH.
Not a stereoselective reaction, markovnikov addition.
Hydroboration-oxidation
1) BH3/THF 2) H2O2, NaOH
Antimarkovnikov. Syn addition.
How to make an alkoxide
Alcohol and strong base ex. NaNH2
Can organometallic reagents be used with alcohols
NO! They will react and form alkoxides
Alkyl halides from alcohols
1) Hydrogen halides
2) PBr3
3) SOCl2
Hydrogen halides and alcohol
Reactivity: HI>HBr>HCl>HF
Alcohol: Only 3, 2, allylic, and benzyllic
SN1 rxn
SN2 rxn can take place with 1
Lewis-acid catalyst and 1+2 alcohols
ZnCL3 or FeCL3 etc can be used with primary and secondary alcohols to form alkyl halides
SOCl2 + PBr3
These convert primary and secondary alcohols into alkyl halides with no rearrangement via the SN2 rxn. They make OH- a good L.G.
SOCl2 is done with pyridine/imadazole to mop HCl
Tosylates, mesylates and trifylates
Create good L.G.
Put on to create an ester. When it is attacked via SN2 it inverts, when it is originally put on it doesn’t invert. This is done with Ts/Tf/Ms + Cl
What is special about trifylate
It can cause vinylic carbons to go through SN1
3 ways to make ethers
1) Intermolecular dehydration
2) Williamson ether
3) Alkoxymercuration-demercuration
Intermolecular dehydration
2 symmetrical alcohols and 2 moles of acid ex. 2HBr cleaves an ether via SN2
It must be done at a lower temp so that elim doesn’t occur. It is also only done with primary alcohols.
Williamson ether synthesis
Can be done with 2 unsymmetrical ethers. Alkoxide attacks a primary alkyl halide via SN2.
To form the alkoxide we can use NaNH2 etc.
Must be a good L.G. on the primary alkyl halide ex Br or I
Alkoxymercuration-demercuration
1) Hg(OAC)2, R-OH 2) NaBH4, NaOH
Alcohol gets used instead of water forming an ether.
T-butyl ethers
T-butyl ethers are good protecting groups for primary alcohols against organometallic reagants
1) H2SO4 2) CH2=C(CH3)2
They are removed with dilute acid H3O+/H2O
Silyl ether protecting group
Protecting group against organometallic
Primary alcohol + TBDMSCl…must have imidazole or pyrimidine in DMF.
Removed with TBAF or Bu4N+F-
TBDMSCl
TBAF
Silyl ether protecting group
Removal of the group (Bu4N+F-)
Ether cleavage
Acyclic ethers are typically unreactive, however, with 2 moles of strong acid they are cleaved via SN2
Epoxide
3 membered ring
