Alcohol ROH Aldehyde Ketone Carboxylic Acid Ester by steepslope9876

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									Alcohol Reactions – Oxidations/Reductions

Movement of electron density towards carbon is a reduction of carbon. (Increasing
bonds to H, decreasing bonds to O, N, X)

Movement of electron density away from a carbon is an oxidation of carbon. (Increasing
bonds to O, N, X, decreasing bonds to H)

Functional Group Review:

Alcohol:              ROH
                           O

Aldehyde:             R            H

                           O
Ketone:
                      R            R

                                   O
Carboxylic Acid:
                           R           OH
                  O
Ester:
              R       OR

Oxidation or Reduction (or Neither)?

                                   O
    H    OH
    R     R                    R        R


    OH                                 Br




    O
                               H       OH
R        OH                 R          H

I. Oxidations:

         HO       H             [ox]        O
Oxidizing Agents:
      KMnO4, H2O
      CrO3, H2SO4, H2O
      Na2Cr2O7, H3O+
      PCC (pyridinium chlorochromate)

3º ROH – cannot oxidize:
                                           OH
                                   R            R
                                           R


2º ROH – always form ketones (with any of the reagents)

    OH                                 O
R        R
                               R           R
    H


1º ROH – can oxidize to an aldehyde OR to a carboxylic acid (via the aldehyde)

  OH                               O                    O
R   H
                               R           H        R       OH
  H


Oxidize up one oxidation state:

    OH        PCC              O
R     H
                           R       H
    H


Oxidize up two oxidation states:

  OH
                  any other            O
R   H
                  oxidizer
  H                                R           OH

Going one step further, any reagent that oxidizes a 1º alcohol to a carboxylic acid, does
so via an aldehyde oxidation state. Therefore, the same reagents would oxidize an
aldehyde to a carboxylic acid. More to come in Ch. 19…
Try these:
a.

             OH      PCC
b.
          OH
                        Na2Cr2O7, H3O+




c.
              OH            CrO3, H2SO4, H2O



d.

                              KMnO4, H2O
HO


II. Reductions:

     O             [H-]            HO        H



Reducing Agents:

         NaBH4 – Sodium Borohydride –
              reduces aldehydes and ketones only

         LiAlH4 – (LAH) Lithium Aluminum Hydride – reduces aldehydes, ketones,
         esters and carboxylic acids

     O                             HO        H
              NaBH4 or LAH




Mech:

     O                                                       HO   H
                                 O       H
                  H:-                               H+
                                                 (work-up)



Aldehydes and ketones reduce one oxidation state to form alcohols:
a.
          O
                        NaBH4
              H
b.
             O
                         LiAlH4



Carboxylic acids and esters reduce two oxidation states to form alcohols, when using
LiAlH4 (LAH):

         O
                      LiAlH4
             OCH3




Mech: (simplified)

         O                              O                         O
                       H:-
             OCH3                           OCH3                      H
                                        H


                                                            H:-

                                        OH                        O

                                            H     H+                  H
                                        H                         H
                                                (work-up)


Examples:
a.
         O
                      NaBH4
              OH


b.

             O
                             LiAlH4
                 OH

c.

     O                       O
                                             NaBH4
                                 OCH3
d.

     O                       O
                                                LiAlH4
                                 OCH3

								
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