Organic Chemistry II
	Professor Carl C. Wamser
Chem 335 - Winter 2005	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

Balancing Organic Redox Reactions

There are a variety of methods for balancing redox reactions - if you already use one that works well for you, use it

The following is a particularly straightforward method that works well for organic reactions

It uses H atoms rather than electrons as a means of tracking oxidation and reduction changes

• create two half-reactions (an oxidation and a reduction) and balance them separately
• balance carbon by inspection (same for metals and other atoms besides H and O)
• balance charge using H+ (in acid) or OH- (in base)
• balance O using H2O
• balance H using H atoms
• combine the two half-reactions so that the H atoms cancel out

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