Alcohols

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					      Chapter 10
Structure and Synthesis
      of Alcohols
      Structure of Alcohols




• Hydroxyl (OH) functional group
• Oxygen is sp3 hybridized.
                                   =>
           Classification
• Primary: carbon with –OH is bonded to one other
                 H
  carbon.
             H3C    C    OH
                    H
• Secondary: carbon with –OH is bonded to two other
                  H
  carbons.
                H3C      C       OH
                         CH3

• Tertiary: carbon with –OH is bonded to three other
                      CH3
  carbons.
                   H3C       C     OH
                             CH3
• Aromatic (phenol): -OH is bonded to a benzene ring.

                                 OH
            Classify these:

      CH3                    CH3
CH3   CH CH2OH         CH3   C OH
                             CH3



             OH               OH
                       CH3    CH CH2CH3   =>
    IUPAC Nomenclature

• Find the longest carbon chain
  containing the carbon with the -OH
  group.
• Drop the -e from the alkane name,
     add - ol.
• Number the chain, starting from the end
  closest to the -OH group.
• Number and name all substituents. =>
             Name these:

      CH3
                                      OH
CH3   CH CH2OH
                           CH3        CH CH2CH3
2-methyl-1-propanol
                                 2-butanol
            CH3                                  OH
      CH3   C OH
            CH3
                                 Br        CH3
  2-methyl-2-propanol
                        3-bromo-3-methylcyclohexanol
                                                  =>
       Unsaturated Alcohols

  • Hydroxyl group takes precedence over
    double and triple bonds.
  • Assign carbon with –OH the lowest number.
  • Use alkene or alkyne name.
                  OH
      CH2   CHCH2CHCH3      4-penten-2-ol (old)

       pent-4-ene-2-ol
(1997 revision of IUPAC rules)
                            =>
          Common Names
• Alcohol can be named as alkyl alcohol.
• Useful only for small alkyl groups.
• Examples:
        CH3                 OH

  CH3   CH CH2OH      CH3   CH CH2CH3

  isobutyl alcohol
          CH3
                              OH
    CH3   C OH
          CH3
           Naming Diols

• Two numbers are needed to locate the two
  -OH groups.
• Use -diol as suffix instead of -ol.


      HO                     OH

            1,6-hexanediol

                                             =>
               Glycols
• 1, 2 diols (vicinal diols) are called glycols.
• Common names for glycols use the name of
  the alkene from which they were made.

    CH2CH2                 CH2CH2CH3
    OH OH                  OH OH

  1,2-ethanediol          1,2-propanediol

  ethylene glycol         propylene glycol
           Naming Phenols
 • -OH group is assumed to be on carbon 1.
 • For common names of disubstituted phenols,
   use ortho- for 1,2; meta- for 1,3; and para- for
   1,4.
 • Methyl phenols are cresols.
                                                 OH
           OH


                                    H3C
      Cl                            4-methylphenol
3-chlorophenol                        para-cresol
                                                      =>
meta-chlorophenol
     Physical Properties

• Unusually high boiling points due to
  hydrogen bonding between molecules.
• Small alcohols are miscible in water, but
  solubility decreases as the size of the
  alkyl group increases.

                                       =>
Boiling Points
Solubility in Water




         Solubility decreases as the size
         of the alkyl group increases.

                                     =>
Commercially Important Alcohols
          -Methanol
   • “Wood alcohol”
   • Industrial production from synthesis gas
                Catalyst
    CO + 2H2               CH3OH
                High T
    3C + 4H2O              CO2 + 2CO + 4H2
   • Common industrial solvent
   • Common starting material for other chemicals
   • Fuel at Indianapolis 500
               Ethanol
• Fermentation of sugar and starches in grains
               yeast enzymes
     C6H12O6              2C2H5OH + 2CO2
•   12-15% alcohol, then yeast cells die.
•   Distillation produces “hard” liquors
•   Azeotrope: 95% ethanol, constant boiling
•   Denatured alcohol used as solvent
                    High T,P
            + H2O
                      catalyst     OH
• Gasahol: 10% ethanol in gasoline
          2-Propanol

• “Rubbing alcohol”
• Catalytic hydration of propene

                   100-300 atm, 300°C
CH2 CH CH2 + H2O                        CH3 CH CH3
                        catalyst
                                           OH



                                                =>
      Acidity of Alcohols

• pKa range: 15.5-18.0 (water: 15.7)

               + B-
    OH                                    -   + BH
                                        O

• Acidity decreases as alkyl group length
  increases.
• Halogens increase the acidity.
• Phenol is very acidic (carbolic acid) 100 million
  times more acidic than cyclohexanol!
Table of Ka Values


       CH3   OH




                     =>
 Formation of Alkoxide Ions

 React alcohol with sodium metal (redox
  reaction).
                                               1
CH3CH2OH +       Na      CH3CH2O        Na   + /2 H2

  React less acidic alcohols with more
  reactive potassium.
  (CH3)3C OH +    K      (CH3)3CO   K    + 1/2 H2
Formation of Phenoxide Ion

Phenol reacts with hydroxide ions to form
 phenoxide ions - no redox is necessary.
           O H               O
                 +   OH
                                 +     HOH
                                     pKa = 15.7
pKa = 10


                                             =>
      Organometallic Reagents

 • Carbon is bonded to a metal (e.g. Na, Mg or
   Li).                                -  +
CH3   C C H + NaNH2            CH3   C C: Na      + NH3


 • Carbon is nucleophilic (partially negative).
 • It will attack a partially positive carbon.
      C - X
      C = O
 • A new carbon-carbon bond forms.
                                         =>
      Grignard Reagents

• Formula RMgX (reacts like R- +MgX)
• Stabilized by anhydrous ether
• May be formed from any organic halide
  primary
  secondary
  tertiary
  vinyl
  aryl                              =>
Some Grignard Reagents

        Br
                                   ether            MgBr
             +           Mg



  Cl                                             MgCl
                                      ether
CH3CHCH2CH3          +        Mg               CH3CHCH2CH3


CH3C CH2
                                       ether
   Br            +            Mg                 CH3C CH2    =>
                                                    MgBr
       Reaction with Carbonyl

    • R- attacks the partially positive carbon in the
      carbonyl.
    • The intermediate is an alkoxide ion.
    • Addition of water or dilute acid protonates the
      alkoxide to produce an alcohol.

R
         C O          R C O                   R C OH
                                 HOH
                                                        OH
                                                   =>
   Synthesis of 1° Alcohols

Grignard + formaldehyde yields a primary
 alcohol with one additional carbon.
   CH3      H           H                       CH3            H
H3C C CH2   C   MgBr        C O         CH3     CH CH2   CH2   C O   MgBr
                       H
    H       H                                                  H

                             CH3            H
                                                         HOH
                       CH3   CH CH2   CH2   C O H
                                            H




                                                                      =>
        Synthesis of 2º Alcohols

 Grignard + aldehyde yields a secondary
  alcohol.
   CH3      H          H3C                        CH3            CH3
H3C C CH2   C   MgBr         C O         CH3      CH CH2   CH2   C O    MgBr
                        H
    H       H                                                    H

                               CH3            CH3
                                                           HOH
                       CH3     CH CH2   CH2   C O H
                                              H




                                                                       =>
    Synthesis of 3º Alcohols

 Grignard + ketone yields a tertiary alcohol.
   CH3      H          H3C                     CH3            CH3
H3C C CH2   C   MgBr         C O         CH3   CH CH2   CH2   C O   MgBr
                       H3C
    H       H                                                 CH3

                              CH3            CH3
                                                        HOH
                       CH3    CH CH2   CH2   C O H
                                             CH3




                                                                    =>
           Grignard + Acid
             Chloride (1)
• Grignard attacks the carbonyl.
• Chloride ion leaves.
               H3C                      CH3
 R   MgBr            C O            R C O        MgBr
               Cl
                                        Cl
     CH3                         CH3
R C O       MgBr              R C       +     MgBrCl
                                    O
     Cl
                           Ketone intermediate          =>
   Second step of reaction
• Second mole of Grignard reacts with the
  ketone intermediate to form an alkoxide ion.
• Alkoxide ion is protonated with dilute acid.
                      CH3                    CH3
     R   MgBr   +   R C                 R C O      MgBr
                          O
                                             R
                                       HOH
                                CH3
                              R C OH
                                R                         =>
Grignard Reagent + Ethylene
          Oxide
 • Epoxides are unusually reactive ethers.
 • Product is a 1º alcohol with 2 additional
   carbons.
                        O                     O     MgBr

       MgBr   +                            CH2CH2
                  CH2       CH2


                                           HOH
                                     O H
                                  CH2CH2
                                           =>
   Reduction of Carbonyl

• Reduction of aldehyde yields 1º alcohol.
• Reduction of ketone yields 2º alcohol.
• Reagents:
  Sodium borohydride, NaBH4
  Lithium aluminum hydride, LiAlH4
  Raney nickel, Ni

                                       =>
    Sodium Borohydride
• Hydride ion, H -, attacks the carbonyl
  carbon, forming an alkoxide ion.
• Then the alkoxide ion is protonated by
  dilute acid.
• Only reacts with carbonyl of aldehyde or
  ketone, not with carbonyls of esters or
  carboxylic acids.
             O         H       O         H        O H
         C                 C         +       C
             H                     H3O
H                              H                 H
                                             =>
Lithium Aluminum Hydride

• Stronger reducing agent than sodium
  borohydride, but dangerous to work with.
• Converts esters and acids to 1º alcohols.
          O      LiAlH4         H       O H
      C                     +       C
          OCH3   LAH      H3O
                                        H     =>
    Comparison of
   Reducing Agents

• LiAlH4 is stronger.
• LiAlH4 reduces more
  stable compounds
  which are resistant
  to reduction.
                      =>
  Catalytic Hydrogenation

• Add H2 with Raney nickel catalyst.
• Also reduces any C=C bonds.
    OH               O                  OH

           NaBH4         H2, Raney Ni




                                         =>
    Thiols (Mercaptans)

• Sulfur analogues of alcohols, -SH.
• Named by adding -thiol to alkane name.
• The -SH group is called mercapto.
• More acidic than alcohols, react with
  NaOH to form thiolate ion.
• Stinks!


                      SH
             Thiol Synthesis


    SH           + -OH             -
                                         + H2O
                                   S
pKa = 10.5



             _                                  _
    H S             R X        R       SH + X



                                                    =>

				
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