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基础有机化学-常见还原剂
2012-12-17 14:28:58 来源:有机化学网 浏览:24178

Reducing Reagents

Reagent Preferred Solvents Functions Reduced Reaction Work-up
Sodium Borohydride
    NaBH4
ethanol; aqueous ethanol
15% NaOH; diglyme
avoid strong acids
aldehydes to 1º-alcohols
ketones to 2º-alcohols
1,2-reduction of enones is favored by CeCl3
inert to most other functions
1) simple neutralization 
2) extraction of product
Lithium Aluminum Hydride (LAH)
    LiAlH4
ether; THF
avoid alcohols and amines
avoid halogenated compounds
avoid strong acids
aldehydes to 1º-alcohols
ketones to 2º-alcohols
carboxylic acids to 1º-alcohols
esters to alcohols
epoxides to alcohols
nitriles & amides to amines
halides & tosylates to alkanes
most functions react
1) careful addition of water
2) dissolve aluminum salts
3) extraction of product
Lithium tri t-Butoxyaluminohydride
    LiAlH(Ot-C4H9)3
ether; THF
avoid alcohols and amines
avoid halogenated compounds
avoid strong acids
fast:
acid chlorides to aldehydes
(at -78 ºC)
3º-amides to aldehydes (at -78 ºC)
nitriles to aldehydes (at -78 ºC)
slower:
aldehydes to 1º-alcohols
ketones to 2º-alcohols
1) careful addition of water
2) dissolve aluminum salts
3) extraction of product
Diisobutylaluminum Hydride
    AlH[CH2CH(CH3)2]2
THF; toluene
avoid alcohols and amines
avoid halogenated compounds
avoid strong acids
fast:
acid chlorides to aldehydes
(at -78 ºC)
3º-amides to aldehydes (at -78 ºC)
nitriles to aldehydes (at -78 ºC)
slower:
aldehydes to 1º-alcohols
ketones to 2º-alcohols
1) careful addition of water
2) dissolve aluminum salts
3) extraction of product
Diborane
    B2H6 = 2 BH3
ether; THF
sulfide complex in CH2Cl2
complexes with amines
avoid alkenes & alkynes
carboxylic acids to 1º-alcohols
aldehydes to 1º-alcohols
ketones to 2º-alcohols
nitriles to amines
esters & epoxides slowly reduced
1) dilute acid or H2O2 
2) extraction of product
Hydrogen & Catalyst
    H2 & Pt, or Pd, or Ru, or Ni



Modified (poisoned) Catalyst
alcohols, ethers, hydrocarbons
or carboxylic acids
alkenes & alkynes to alkanes (fast)
nitro groups to amines (fast)
imines to amines (fast)
aldehydes & ketones to alcohols (slow)
nitriles to amines (slow)
may remove benzylic groups
alkynes to alkenes
acyl chlorides to aldehydes
filter to remove catalyst
Reactive Metals
    Na, or Li, or K 



   Mg or Al or Zn or Fe
liq. ammonia & ether co-solvents
or alcohols or amines



water, alcohols, acetic acid
or aqueous mineral acid
ketones to 2º-alcohols
alkynes to alkenes
conjugated π-systems
  (e.g. aromatic rings, dienes & enones)
cleaves C-X and benzylic groups
cleaves activated substituents
nitro groups to amines
C=O (aldehyde/ketone) to CH2
1) quench with NH4Cl
2) extract product


extract product from salts
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