June 16, 2024, 01:49:03 PM
Forum Rules: Read This Before Posting


« previous next »
Pages: [1] 2   Go Down

Topic: THF!!!  (Read 7256 times)

0 Members and 1 Guest are viewing this topic.

Offline tomhall15

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-1
THF!!!
« on: December 12, 2010, 01:34:19 PM »
hello...can someone show me the mechanism of how to turn 1,4-butanediol to THF....thank you :)
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #1 on: December 12, 2010, 02:33:01 PM »
 I left off some arrows at the dehydration/cyclization. Can you fill them in?
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

Offline tomhall15

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-1
Re: THF!!!
« Reply #2 on: December 12, 2010, 03:11:21 PM »
okay im not really sure but are the missing arrows: 1) the OH2 coming off of the chain and 2) the other OH group moving to the new empty spot???
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #3 on: December 12, 2010, 03:33:00 PM »
Yep. The question I was getting at is: does a primary cation form as an intermediate or does the alcohol at the other end of the molecule react at the carbon with the C-OH2 as water leaves?
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

Offline tomhall15

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-1
Re: THF!!!
« Reply #4 on: December 12, 2010, 03:37:13 PM »
hmmmm im not sure but I would guess that it would occur in one reaction...so there would be no carbocation intermediate?
Logged

cupid.callin

  • Guest
Re: THF!!!
« Reply #5 on: December 12, 2010, 03:41:42 PM »
Why would it occur in one step?

Dehydration is one step and then attack or carbocation on O is second. I have no reason but this method works because wiki says this is the industrial process to produce THF
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #6 on: December 12, 2010, 03:45:32 PM »
It would work that way because a primary carbocation is  a very unstable species. The alcohol could come in at the same time water leaves because it would donate electron density to the partially positive carbon, thus adding stabilization.
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

cupid.callin

  • Guest
Re: THF!!!
« Reply #7 on: December 12, 2010, 03:59:56 PM »
but this is very unsatisfactory.

I've read thousands of rxn where this kind of mechanism donot happen. 1degree converts into 2 degree.
Logged

Offline tomhall15

  • Regular Member
  • ***
  • Posts: 12
  • Mole Snacks: +0/-1
Re: THF!!!
« Reply #8 on: December 12, 2010, 04:04:21 PM »
thank you for helping me MissPhosgene!!
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #9 on: December 12, 2010, 04:08:53 PM »
Quote from: cupid.callin on December 12, 2010, 03:59:56 PM
but this is very unsatisfactory.

I've read thousands of rxn where this kind of mechanism donot happen. 1degree converts into 2 degree.

It doesn't form a secondary carbocation when THF is formed. Formation of 5 membered rings in this manner is favored, see Baldwin's rules. 5-exo-tet.

Water leaving and ether formation probably occur asynchronously hence the formation of THF and not a different product.
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

cupid.callin

  • Guest
Re: THF!!!
« Reply #10 on: December 12, 2010, 04:15:30 PM »
AHHH i see!!

Sorry for my useless complaint!!!
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #11 on: December 12, 2010, 04:22:47 PM »
Quote from: cupid.callin on December 12, 2010, 04:15:30 PM
AHHH i see!!

Sorry for my useless complaint!!!

Not like that. What you said makes sense, but in this case, it seems that rearrangement to the more highly carbocation does not happen. For other cases, you are right, such as dehydration of cyclohexanemethanol.

Do you see why? It could be explained using kinetics.
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

cupid.callin

  • Guest
Re: THF!!!
« Reply #12 on: December 13, 2010, 07:16:13 AM »
You know out of every chemist on chemical forum, you are really patient
Logged

Offline MissPhosgene

  • Chemist
  • Full Member
  • *
  • Posts: 364
  • Mole Snacks: +23/-5
  • Gender: Female
Re: THF!!!
« Reply #13 on: December 13, 2010, 10:22:35 AM »
Thanks. Maybe you wouldn't say so if you read my post bitching about my advisor.
Logged
Stereograms of the 32 crystallographic point groups: little bike wheels of cold, hard, pure rationality.

cupid.callin

  • Guest
Re: THF!!!
« Reply #14 on: December 13, 2010, 05:12:02 PM »
:D  :o well i don’t know about that but you are the most patient i came across since i joined this website
Logged
Pages: [1] 2   Go Up
« previous next »
Sponsored Links