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Topic: What reagents are required to complete this is 3 or less steps?  (Read 9799 times)

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Offline the_negro_puppy

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

Thanks very much for your input and *delete me*
« Last Edit: July 04, 2006, 12:04:49 AM by geodome »

Offline Donaldson Tan

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #1 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)
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline the_negro_puppy

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #2 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

Offline swati

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Re: What reagents are required to complete this in 3 or less steps?
« Reply #3 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

Offline the_negro_puppy

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Re: What reagents are required to complete this in 3 or less steps?
« Reply #4 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.

Offline Albert

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #5 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?

Offline wereworm73

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #6 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



Offline the_negro_puppy

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #7 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?



Offline Will

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #8 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)! ;)

Offline the_negro_puppy

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #9 on: July 06, 2006, 12:40:32 AM »
Please help my exam is tomorrow

Offline Will

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #10 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



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', and good luck in your exam! :))

Offline swati

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Re: What reagents are required to complete this is 3 or less steps?
« Reply #11 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.
« Last Edit: July 06, 2006, 09:21:09 AM by swati »

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