Chapter 15 Notes - Alcohols
Sources of Alcohols
- natural sources
- fermentation of sugars makes ethanol
- wood alcohol - methanol
- many natural products are more complex alcohols or polyols
- industrial preparations
- CO + 2 H2 --(cat)--> CH3OH
- hydration of alkenes (from petroleum)
- laboratory preparations (review)
- hydration of alkenes (Markovnikov)
- hydroboration-oxidation of alkenes (anti-Markovnikov)
- hydrolysis of alkyl halides
- Grignard additions to carbonyl compounds
- Grignard additions to epoxides
- reduction reactions that generate alcohols
- from aldehydes or ketones - H2 + catalyst, LiAlH4, or NaBH4
- from carboxylic acids or esters - LiAlH4
- preparation of vicinal diols
- alkene + tBuOOH (OsO4 cat)
Reactions of Alcohols
- substitution reactions (review)
- ROH + HX --> RX
- ROH + SOCl2 --> RCl
- ROH + PBr3 --> RBr
- ROH + TsCl --> ROTs (tosylate ester)
- ROH --(H2SO4)--> alkene (elimination)
- formation of ethers
- acid-catalyzed dehydration
- formation of esters
- Fischer esterification - ROH + R'COOH <==(H+)==> R'COOR
+ H2O
- ROH + R'COCl --> R'COOR + HCl
- ROH + (R'CO)2O --> R'COOR + R'COOH
- inorganic esters (sulfates, sulfonates, phosphites, phosphates,
nitrates, etc.)
Alcohol Oxidation Reactions
- chromium (VI) oxidants:
CrO3, H2CrO4, K2Cr2O7
- oxidation involves intermediate chromate ester
- 1° alcohol to carboxylic acid with any Cr(VI) reagent,
e.g., CrO3
- 1° alcohol to aldehyde with PCC (avoids further oxidation)
- 2° alcohol to ketone with any Cr(VI) reagent
Glycol Oxidation Reactions
- periodic acid, H5IO6
(or HIO4·2H2O)
- C-C bond is cleaved and alcohols are oxidized
- intermediate is a cyclic periodic ester
- common degradation reaction for sugars
Thiols
- Preparation of thiols
- RX + NaSH --> RSH
- RX + thiourea --> RSH
- Acidity: thiols are stronger acids than alcohols ( pKa about
10 )
- Oxidized forms of sulfur are common
- 2 RSH --> R-S-S-R (disulfide)
- sulfoxide, sulfone, sulfenic acid, sulfinic acid, sulfonic
acid
