Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: the_negro_puppy on July 03, 2006, 11:33:41 PM

Title: What reagents are required to complete this is 3 or less steps?
Post by: the_negro_puppy on July 03, 2006, 11:33:41 PM
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg82.imageshack.us%2Fimg82%2F2460%2Fquestion34ru.jpg&hash=186619f4532f0751e689749a0ab4f7a2)

What reagents are required, and in what order for this reaction?

Thanks very much for your input and *delete me*
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: Donaldson Tan on July 04, 2006, 12:08:07 AM
1-propyl-cyclohexane -> 1-cyclohexyl-prop-2-ene (dehydrogenation)

1-cyclohexyl-prop-2-ene -> required product (using a very weak oxiding agent, such as chromate(VI) in alkali)
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: the_negro_puppy on July 04, 2006, 12:25:22 AM
Thanks for the reply!

Would a reagent such as AlCl3 be approriate for dehydrogenation?
Or would FeCl3 be more appropriate?

Thanks
Title: Re: What reagents are required to complete this in 3 or less steps?
Post by: swati on July 04, 2006, 02:47:30 AM

1-cyclohexyl-prop-2-ene -> required product (using a very weak oxiding agent, such as chromate(VI) in alkali)


1-cyclohexyl-prop-2-ene -----> 1-cyclohexyl-propane-2,3-diol (using a very weak oxiding agent, such as chromate(VI) in alkali)

But the required product is 1-cyclohexyl-ethane-1,2-diol
Title: Re: What reagents are required to complete this in 3 or less steps?
Post by: the_negro_puppy on July 04, 2006, 05:48:36 AM

1-cyclohexyl-prop-2-ene -> required product (using a very weak oxiding agent, such as chromate(VI) in alkali)


1-cyclohexyl-prop-2-ene -----> 1-cyclohexyl-propane-2,3-diol (using a very weak oxiding agent, such as chromate(VI) in alkali)

But the required product is 1-cyclohexyl-ethane-1,2-diol


I dont understand, thats not what he said at all.
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: Albert on July 04, 2006, 12:00:36 PM
Yes, I'd say swati is right. the_negro_puppy, could you check whether or not you correctly copied the structures?
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: wereworm73 on July 04, 2006, 12:12:50 PM
The product in your diagram is 1-cyclohexyl-ethane-1,2-diol.


 CH2--CH2     OH  OH
 /       \    |   |
CH2     CH----C---C-H
 \       /    |   |     
 CH2--CH2     H   H


If it was 1-cyclohexyl-propane-2,3-diol, then it would be this...



 CH2--CH2      H   OH  OH
 /       \     |   |   |
CH2     CH-----C---C---C-H
 \       /     |   |   | 
 CH2--CH2      H   H   H


Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: the_negro_puppy on July 04, 2006, 08:25:19 PM
The product in your diagram is 1-cyclohexyl-ethane-1,2-diol.


 CH2--CH2     OH  OH
 /       \    |   |
CH2     CH----C---C-H
 \       /    |   |     
 CH2--CH2     H   H


If it was 1-cyclohexyl-propane-2,3-diol, then it would be this...



 CH2--CH2      H   OH  OH
 /       \     |   |   |
CH2     CH-----C---C---C-H
 \       /     |   |   | 
 CH2--CH2      H   H   H


Thanks for the input. The structures i drew are correct, but i cant see anywhere in this thread where anyone mentioned the name of the final product, so im not sure what your talking about.

The problems is completing that synthesis in 3 or less steps, that is:

1-propyl-cyclohexane -> 1-cyclohexyl-prop-2-ene (dehydrogenation) --------> 1-cyclohexyl-ethane-1,2-diol. (Using weak oxidising agent such as Cr(IV) in alkali.

My question is, what exact substances should i use for both the dehydrogenation and weak oxidation.

At the moment im thinking of AlCl3 or FeCl3 for dehydrogenation, and possibly PCC as the weak agent?


Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: Will on July 04, 2006, 09:41:26 PM
Thanks for the input. The structures i drew are correct, but i cant see anywhere in this thread where anyone mentioned the name of the final product, so im not sure what your talking about.

The problems is completing that synthesis in 3 or less steps, that is:

1-propyl-cyclohexane -> 1-cyclohexyl-prop-2-ene (dehydrogenation) --------> 1-cyclohexyl-ethane-1,2-diol. (Using weak oxidising agent such as Cr(IV) in alkali.

I think after you get allylcyclohexane (1-cyclohexylprop-2-ene) you will need to do something like ozonolysis with a work-up with NaBH4 to get MeOH and 2-cyclohexylethanol and then elimination (dehydration with H2SO4) to get vinylcyclohexane which you can oxidise with OsO4 (or epoxidise with meta-chloroperoxybenzoic acid for example and then react with HO-) to your diol (1-cyclohexylethane-1,2-diol).
Unfortunately that is (at least) four 'steps' :(. Somewhere in your synthesis you must remove a carbon atom from your propyl chain; I don't know what would be the best way of doing it, sorry!

Sorry to correct you but the suggested Chromate(VI) changed to Cr(IV)! ;)
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: the_negro_puppy on July 06, 2006, 12:40:32 AM
Please help my exam is tomorrow
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: Will on July 06, 2006, 08:19:27 AM
Hi guys, its 12 hours to my final exam and i really need help with this question. I have posted this in a previous thread but forgot to add the Br!

I need to complete this synthesis using any reagents in 3 steps or less

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg207.imageshack.us%2Fimg207%2F6963%2Fquestion38gk.jpg&hash=40926d37ebe869999717e17db7805ed5)

Thanks very much for your help.

Hmm... that's ever so slightly easier!! ;)
In fact you could probably use the information in the thread here to apply it to the correct question; all you needed to know is how to do the elimination step.

But...
:) 

1.)  1-bromo-2-cyclohexyl ethane -----------> 1-cyclohexyl ethene
       Dehydrohalogenation using NaOEt and EtOH

2.)  1-cyclohexyl ethene ---------------> 1-cyclohexyl ethane-1,2-diol
       Hydroxylation using following reagents
         (i) Cold aqueous alkaline KMnO4
                         OR
        (ii) OsO4 followed by hydrolysis
I think that the first step is not so great. Although NaOEt is fine if the primary bromide was more hindered, I just think it isn't hindered enough so you may get a SN2 reaction instead, or both SN2 and E2 reactions. Bases like DBN, DBU, KOCEt3 and KOt-Bu would be better as they are hindered nucleophiles.

Also I would name the product of the first reaction vinylcyclohexane or at least cyclohexylethene; there is no need for the spaces between the cyclohexyl bit and the ethane/ethene bit.

(the_negro_puppy: please stick to one thread for one 'topic (http://www.chemicalforums.com/index.php?topic=9579.0)', and good luck in your exam! :))
Title: Re: What reagents are required to complete this is 3 or less steps?
Post by: swati on July 06, 2006, 09:01:13 AM

Also I would name the product of the first reaction vinylcyclohexane or at least cyclohexylethene; there is no need for the spaces between the cyclohexyl bit and the ethane/ethene bit.


I agree with your statement & hence modified it as vinylcyclohexane  :)

I think that the first step is not so great. Although NaOEt is fine if the primary bromide was more hindered, I just think it isn't hindered enough so you may get a SN2 reaction instead, or both SN2 and E2 reactions. Bases like DBN, DBU, KOCEt3 and KOt-Bu would be better as they are hindered nucleophiles.

Also changed the reagents of first reaction.