6 10 acid catalyzed hydration of alkenes
Download
Skip this Video
Download Presentation
6.10 Acid-Catalyzed Hydration of Alkenes

Loading in 2 Seconds...

play fullscreen
1 / 30

6.10 Acid-Catalyzed Hydration of Alkenes - PowerPoint PPT Presentation


  • 133 Views
  • Uploaded on

6.10 Acid-Catalyzed Hydration of Alkenes. C. C. C. H. C. OH. Acid-Catalyzed Hydration of Alkenes. reaction is acid catalyzed; typical hydration medium is 50% H 2 SO 4 -50% H 2 O. +. H—OH. CH 3. H 3 C. H. 50% H 2 SO 4. CH 2 CH 3. CH 3. C. C. C. 50% H 2 O. H 3 C. CH 3. OH.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about '6.10 Acid-Catalyzed Hydration of Alkenes' - karim


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
acid catalyzed hydration of alkenes

C

C

C

H

C

OH

Acid-Catalyzed Hydration of Alkenes
  • reaction is acid catalyzed; typical hydration medium is 50% H2SO4-50% H2O

+

H—OH

follows markovnikov s rule

CH3

H3C

H

50% H2SO4

CH2CH3

CH3

C

C

C

50% H2O

H3C

CH3

OH

Follows Markovnikov\'s Rule

(90%)

follows markovnikov s rule1

CH3

50% H2SO4

CH2

50% H2O

OH

Follows Markovnikov\'s Rule

(80%)

mechanism

CH3

H3C

CH3

CH3

C

C

CH2

H3C

OH

Mechanism
  • involves a carbocation intermediate
  • is the reverse of acid-catalyzed dehydrationof alcohols to alkenes

H+

+ H2O

mechanism1

H

H3C

+

:

H

O

C

CH2

H3C

H

H

:

:

O

Mechanism

Step (1) Protonation of double bond

+

slow

H3C

+

+

C

CH3

H3C

H

mechanism2

H

H3C

+

:

:

+

O

C

CH3

H3C

H

fast

CH3

H

+

:

C

CH3

O

H

CH3

Mechanism

Step (2) Capture of carbocation by water

mechanism3

CH3

H

H

:

C

CH3

O

:

:

O

H

H

CH3

fast

CH3

H

..

+

:

:

H

C

O

CH3

O

H

H

CH3

Mechanism

Step (3) Deprotonation of oxonium ion

+

+

+

relative rates
Relative Rates

Acid-catalyzed hydration

  • ethylene CH2=CH2 1.0
  • propene CH3CH=CH2 1.6 x 106
  • 2-methylpropene (CH3)2C=CH2 2.5 x 1011
  • The more stable the carbocation, the fasterit is formed, and the faster the reaction rate.
principle of microscopic reversibility

CH3

H3C

CH3

CH3

C

C

CH2

H3C

OH

Principle of Microscopic Reversibility
  • In an equilibrium process, the same intermediates and transition states are encountered in the forward direction and the reverse, but in the opposite order.

H+

+ H2O

synthesis

OH

Synthesis

Suppose you wanted to prepare 1-decanol from 1-decene?

synthesis1

OH

Synthesis

Suppose you wanted to prepare 1-decanol from 1-decene?

  • Needed: a method for hydration of alkenes with a regioselectivity opposite to Markovnikov\'s rule.
synthesis2

1. hydroboration

2. oxidation

OH

Synthesis

Two-step reaction sequence called hydroboration-oxidation converts alkenes to alcohols with a regiochemistry opposite to Markovnikov\'s rule.

hydroboration step

H

BH2

C

C

C

C

Hydroboration Step

+ H—BH2

Hydroboration can be viewed as the addition ofborane (BH3) to the double bond. But BH3 is not the reagent actually used.

hydroboration step1

H

BH2

C

C

C

C

Hydroboration Step

+ H—BH2

Hydroboration reagents:

H

Diborane (B2H6)normally used in an ether- like solventcalled "diglyme"

BH2

H2B

H

hydroboration step2

H

BH2

C

C

C

C

••

+

O

BH3

Hydroboration Step

+ H—BH2

Hydroboration reagents:

Borane-tetrahydrofurancomplex (H3B-THF)

oxidation step

H

BH2

H

OH

C

C

C

C

Oxidation Step

H2O2, HO–

Organoborane formed in the hydroborationstep is oxidized with hydrogen peroxide.

example

1. B2H6, diglyme

2. H2O2, HO–

OH

Example

(93%)

example1

H

OH

1. H3B-THF

CH3

CH3

C

C

C

C

2. H2O2, HO–

CH3

H

Example

H3C

CH3

H3C

H

(98%)

features of hydroboration oxidation
Features of Hydroboration-Oxidation
  • hydration of alkenes
  • regioselectivity opposite to Markovnikov\'s rule
  • no rearrangement
  • stereospecific syn addition
example2

OH

Example

1. B2H6, diglyme

2. H2O2, HO–

(82%)

features of hydroboration oxidation1
Features of Hydroboration-Oxidation
  • hydration of alkenes
  • regioselectivity opposite to Markovnikov\'s rule
  • no rearrangement
  • stereospecific syn addition
syn addition

H

CH3

CH3

HO

H

H

syn-Addition
  • H and OH become attached to same face of double bond

1. B2H6

2. H2O2, NaOH

only product is trans-2-methylcyclopentanol(86%) yield

1 methylcyclopentene bh 3
1-Methylcyclopentene + BH3
  • syn addition of Hand B to double bond
  • B adds to less substituted carbon
add hydrogen peroxide
Add hydrogen peroxide
  • OH replaces B on same side
ad