8/3/2019 Redoks Alcohol HO
1/47
REDOX REACTIONS
8/3/2019 Redoks Alcohol HO
2/47
2
Oxidation is a loss of electrons a more positive oxidation
number a loss of hydrogen atoms the addition of oxygenatoms. more bonds to oxygen
CH3 CH3 CH3 CH2
OH
CH3 C H
O
CH3 C OH
O
CO2 H2O+
Alkane Alcohol (1) Aldehyde Carboxylic acid
1 Bond to O 2 Bonds to O 3 Bonds to O
[O] [O] [O][O]
Reduction is a gain of electrons a less positive oxidation
number a gain of hydrogen atoms the loss of oxygen atoms the loss of bonds tooxygen.
REDOX
8/3/2019 Redoks Alcohol HO
3/47
3
Oxidation numbers
Each C-H is a -1
Each C-O is a +1
Sum total C-H and C-O to determineOxidation Number
8/3/2019 Redoks Alcohol HO
4/47
4
Oxidation numbers
Each C-H is a -1
Each C-O is a +1
What are the oxidation numbers for
CH3
OH CH2
O
HCO2H
Hint: Write the expandedformula to determine thenumber of bonds to C
8/3/2019 Redoks Alcohol HO
5/47
1, 2, 3 Carbons
Chapter 11 5
=>
8/3/2019 Redoks Alcohol HO
6/47
6
OXIDATION REACTIONS
PrimarySecondaryTertiary
ALCOHOLS
8/3/2019 Redoks Alcohol HO
7/47
7
1 Alcohols are oxidized to either aldehydes or carboxylic acids,depending on the reagent.
Oxidation of 1 Alcohols
PCC = Pyridinium chlorochromate
8/3/2019 Redoks Alcohol HO
8/47
Oxidation of 1 Alcohols
8/3/2019 Redoks Alcohol HO
9/47
9
Oxidation of Secondary Alcohol
Secondary alcohol Ketone[O]
R1 CH
OH
R2[O]
R1 C
O
R2 H2O
R1, R2: alkylgroups
2 AlcoholKetone
Double bondsformsTwo hydrogen atoms removed
8/3/2019 Redoks Alcohol HO
10/47
10
Oxidation and Reduction
Any of the Cr6+ oxidants effectively oxidize 2 alcohols to ketones.
Oxidation of 2 Alcohols
8/3/2019 Redoks Alcohol HO
11/47
11
Metabolic example
Lactic aciddehyrogenase
Lactic acid Pyruvicacid
C H 3 C H
O H
C O H
O
C H 3 C
O
C O H
O
8/3/2019 Redoks Alcohol HO
12/47
12
Oxidation of Tertiary Alcohol
Tertiary alcohol No reaction[O]
R1, R2, R3: alkyl groups
3 Alcohol
ly one hydrogen atom, not the two required to be removed
R1-C-R2
R3
OH[O]
NR
8/3/2019 Redoks Alcohol HO
13/47
13
Alcohols are oxidized to a variety of carbonyl compounds.
Oxidation of Alcohols
8/3/2019 Redoks Alcohol HO
14/47
14
REDUCTION REACTIONSALCOHOLS
8/3/2019 Redoks Alcohol HO
15/47
Reduction of Alcohols
Dehydrate with conc. H2SO4, then add
H2
Tosylate, then reduce with LiAlH4
CH3CHCH3
OHH2SO4
CH2 CHCH3
H2
PtCH3CH2CH3
alcohol alkene alkane
alcohol
CH3CHCH3OH TsCl
CH3CHCH3OTs LiAlH4
alkane
CH3CH2CH3
tosylate
8/3/2019 Redoks Alcohol HO
16/47
Dehydration Mechanisms
CH3CHCH3
OHH2SO4
alcohol
CH3CHCH3
OH
H
CH3CHCH3
CH2 CHCH3H2O
8/3/2019 Redoks Alcohol HO
17/47
17
Dehydration of Alcohols to form Alkenes
During the dehydration of an alcohol, a Hand OH are removed from adjacentcarbon atoms of the same alcohol toproduce a water molecule. A double bond
forms between the same two carbonatoms to produce an alkene.
H OH
H+, heat
H-C-C-H H-C=C-H + H2O
H H H H
alcohol (ethanol) alkene (ethene)
8/3/2019 Redoks Alcohol HO
18/47
18
Saytzeffs Rule
The dehydration of a secondary alcoholcan result in the formation of either of twoproducts.
Saytzeffs rule
THE POOR GET POORERrule
8/3/2019 Redoks Alcohol HO
19/47
19
Saytzeffs Rule
The major product is the one that results
when the hydrogen is removed from thecarbon atom with the smallest number ofhydrogen atoms. The poor get poorer
H
OH
H+
Heat
+H2O
+H2O
2-Butene (major product: 90%)
1-Butene (minor product: 10%)2-Butanol
2H
3H
THE MOST SUBSTITUTED C=C IS THE MAJOR PRODUCT
8/3/2019 Redoks Alcohol HO
20/47
Alkenes
Oxidative Cleavage of Alkenes
Oxidative Without Cleavage of Alkenes
8/3/2019 Redoks Alcohol HO
21/47
21
Addition of Water to Alkenes:Hydroboration
Herbert Brown (HB) invented hydroboration (HB)
Borane (BH3) is electron deficient is a Lewis acid.
Borane adds to an alkene to give an
organoborane.
C CB
H
H H
Borane
+BH2H
Organoborane
8/3/2019 Redoks Alcohol HO
22/47
22
BH3 Is a Lewis Acid
Six electrons in outer shell
Coordinates to oxygen electron pairs in ethers
O id ti With t Cl f Alk
8/3/2019 Redoks Alcohol HO
23/47
23
Addition of H-BH2 (from BH3-THF complex) to threealkenes gives a trialkylborane
Oxidation with alkaline hydrogen peroxide in waterproduces the alcohol derived from the alkene
Hydroboration-Oxidation Alcohol Formation fromAlkenes
Oxidative Without Cleavage of Alkenes
8/3/2019 Redoks Alcohol HO
24/47
24
Orientation in Hydration viaHydroboration
Regiochemistry is opposite to Markovnikovorientation
OH is added to carbon with most Hs
H and OH add with syn stereochemistry, to thesame face of the alkene (opposite of anti addition)
CH3BH3
THF
H
CH3
H
B
HH -
OH
H2O2
H
CH3
H
OH
1-methylcycopentene Alkylborane intermediate trans-2-methylcyclopentanol(85%)
8/3/2019 Redoks Alcohol HO
25/47
25
Mechanism of Hydroboration
Borane is a Lewisacid
Alkene is Lewis base
Transition stateinvolves anionicdevelopment on B
The components of
BH3 are across C=C
8/3/2019 Redoks Alcohol HO
26/47
26
Hydroboration, Electronic Effects Give Non-Markovnikov
More stable carbocation is also consistentwith steric preferences
8/3/2019 Redoks Alcohol HO
27/47
27
Hydroboration - Oxygen InsertionStep
H2O2, OH- inserts OH in place of B
Retains syn orientation
8/3/2019 Redoks Alcohol HO
28/47
28
Epoxidation is the addition of a single oxygen atom to an
alkene to form an epoxide.Epoxidation is typically carried out with a peroxyacid.
Epoxidation
E id ti
8/3/2019 Redoks Alcohol HO
29/47
29
Epoxidation occurs via syn addition of an O atom to either side of aplanar double bond. Thus, a cis alkene gives an epoxide with cissubstituents. A trans alkene gives an epoxide with trans substituents.
Epoxidation
Epoxidation is stereospecific because cis and trans alkenes yield differentstereoisomers as products.
8/3/2019 Redoks Alcohol HO
30/47
30
Dihydroxylation is the addition of two hydroxy groups to a double bond,forming a 1,2-diol or glycol.
Depending on the reagent, the two new OH groups can be added to theopposite sides (anti addition) or the same side (syn addition) of thedouble bond.
Dihydroxylation
Dih d l ti
8/3/2019 Redoks Alcohol HO
31/47
31
Anti dihydroxylation is achieved in two stepsepoxidation,
followed by ring opening with OH or H3O+.
Dihydroxylation
8/3/2019 Redoks Alcohol HO
32/47
32
Syn hydroxylation results when an alkene is treatedwith either KMnO4 or OsO4.
Dihydroxylation
Dih dro lation
8/3/2019 Redoks Alcohol HO
33/47
33
Each reagent adds two oxygen atoms in a syn fashion.
Hydrolysis of the cyclic intermediate cleaves the metal oxygenbonds, forming a cis-1,2-diol.
Dihydroxylation
8/3/2019 Redoks Alcohol HO
34/47
34
Dihydroxylation can also be carried out by using a catalytic
amount of OsO4, if the oxidant N-methylmorpholine N-oxide(NMO) is also added.
In the catalytic process, dihydroxylation of the double bondconverts the Os8+ oxidant into an Os6+ product, which is thenre-oxidized by NMO to Os8+.
Dihydroxylation
8/3/2019 Redoks Alcohol HO
35/47
35
Oxidative cleavage of an alkene breaks both the and bonds
of the double bond to form two carbonyl compounds. Cleavagewith ozone (O3) is called ozonolysis.
Oxidative Cleavage of Alkenes
8/3/2019 Redoks Alcohol HO
36/47
36
Addition of O3 to the bond of an alkene forms an unstableintermediate called a molozonide, which rearranges to anozonide in a stepwise process.
The unstable ozonide is reduced to afford carbonylcompounds. Zn (in H2O) or dimethylsulfide (CH3SCH3) are two
common reagents used to convert the ozonide into carbonylcompounds.
Oxidative Cleavage of Alkenes
8/3/2019 Redoks Alcohol HO
37/47
37
Ozonolysis of dienes or other polyenes results in oxidativecleavage of all C=C bonds.
It is important to note that when oxidative cleavage involves adouble bond that is part of a ring, the ring opens up affording asingle chain with two carbonyls at the carbons where the
double bonds were originally.
Oxidative Cleavage of Alkenes
8/3/2019 Redoks Alcohol HO
38/47
38
Examples of Ozonolysis of Alkenes
Used in determination of structure of anunknown alkene
8/3/2019 Redoks Alcohol HO
39/47
39
Permanganate Oxidation of Alkenes
Oxidizing reagents other than ozone alsocleave alkenes
Potassium permanganate (KMnO4) can produce
carboxylic acids and carbon dioxide if Hs arepresent on C=C
+ KMnO4
O
O
H
O
O H
+
8/3/2019 Redoks Alcohol HO
40/47
40
Cleavage of 1,2-diols
Reaction of a 1,2-diol with periodic (per-iodic)acid, HIO4 , cleaves the diol into two carbonyl
compounds
Sequence of diol formation with OsO4 followed
by diol cleavage is a good alternative toozonolysis
8/3/2019 Redoks Alcohol HO
41/47
41
Mechanism of Periodic Acid Oxidation
Via cyclic periodate intermediate
8/3/2019 Redoks Alcohol HO
42/47
42
Reduction of Alkenes: Hydrogenation
Addition of H-H across C=C
Reduction in general is addition of H2 or its
equivalent
Requires Pt or Pd as powders on carbon andH2
Hydrogen is first adsorbed on catalyst
Reaction is heterogeneous (process is not in
solution)
8/3/2019 Redoks Alcohol HO
43/47
43
Hydrogen Addition- Selectivity
Selective for C=C. No reaction with C=O, C=N
Polyunsaturated liquid oils become solids
8/3/2019 Redoks Alcohol HO
44/47
44
Mechanism of Catalytic Hydrogenation
Heterogeneous reaction between phases
Addition of H-H is syn
8/3/2019 Redoks Alcohol HO
45/47
Other Oxidation Reagents
Collins reagent: Cr2O3 in pyridine
Jones reagent: chromic acid inacetone
KMnO4 (strong oxidizer)
Nitric acid (strong oxidizer)
CuO, 300C (industrialdehydrogenation)
Swern oxidation: dimethylsulfoxide,with oxalyl chloride and hindered
base, oxidizes 2alcohols to ketones45
8/3/2019 Redoks Alcohol HO
46/47
46
ethanol orange Acetic acid green
Breathalyzer test forsuspected drunk driversCH3 CH2
OH
CH3 C H
O
Cr6+[O]
+ + Cr3+O
CH3 CH2
OH
CH3 C H
O
CO2H
2O
+
Oxidation of Alcohol in the body[O][O]
8/3/2019 Redoks Alcohol HO
47/47
Oxidation of 1 Alcohols
Figure 12.10
Blood alcohol screening
Top Related