Sciencemadness Discussion Board

Wurtz Reaction in Alkanes....

sankalpmittal - 16-1-2013 at 07:53

Ok , so I have a doubt regarding wurtz reaction. Ok , so in wurtz reaction , we prepare alkanes having even number of carbon atoms and its not convenient to use it to prepare odd number of alkanes.

Lets consider a wurtz reaction :

3CH3Cl + 6Na + 3C2H5Cl ----> 6NaCl + C4H10 + C2H6 + C3H8

So there are many possibilities ( A reason why Wurtz reaction is not suitable for preparing odd number of alkanes.)

Now here is my question :

In the reaction (above) which I stated , which one will be major product : C4H10 or C2H6 or C3H8 ?

Or there will be no major product and there will be formation of all of these in equal proportion ?

Also , I have been told by a teacher that cross product (in this case C3H8) will be the maor product. If so why ? I asked this to the teacher and he said that there is no reason. Its just as it is !!

Please help !!

Thanks in advance... :)

sankalpmittal - 19-1-2013 at 08:31

Does this thread needs to be transferred to organic chemistry ? I get no answer/reply.

Again this doubt needs to be clarified. 48 views but no reply... Please help !!

I found something here : http://www.deepdyve.com/lp/de-gruyter/the-wurtz-cross-coupli...

I can not read its whole article as I fail to understand from there... May be anyone can clarify from there....



[Edited on 19-1-2013 by sankalpmittal]

Hexavalent - 19-1-2013 at 08:43

"Although the Wurtz reaction can be used to prepare unsymmetrical hydrocarbons by reaction two alkyl halides with sodium [...] the yields are generally low due to the nearly statistical distribution of RR, R'R', as well as RR'."

No, the thread is fine where it is. Just because 48 people have seen it, that doesn't mean that they are experts in this field or could be bothered answering a question to someone who is desperate for answers ("48 views but no reply... Please help !!")

BTW, if you ever need a full article but don't want to pay for it, you could try your luck asking in the "References" sub-forum.

Hexavalent

sankalpmittal - 19-1-2013 at 08:48

Quote: Originally posted by Hexavalent  
"Although the Wurtz reaction can be used to prepare unsymmetrical hydrocarbons by reaction two alkyl halides with sodium [...] the yields are generally low due to the nearly statistical distribution of RR, R'R', as well as RR'."

No, the thread is fine where it is. Just because 48 people have seen it, that doesn't mean that they are experts in this field or could be bothered answering a question to someone who is desperate for answers ("48 views but no reply... Please help !!")

BTW, if you ever need a full article but don't want to pay for it, you could try your luck asking in the "References" sub-forum.

Hexavalent


But which one will be the major product out of RR, R'R'and RR' ?

That is what I asked...

[Edited on 19-1-2013 by sankalpmittal]

Hexavalent - 19-1-2013 at 08:55

My teacher told me that "statistical distribution" means a generally equal amount of the products are formed...so I guess that RR, R'R', and RR' will be formed in equal amounts.

However, how true the former fact is, I'm not sure; I can only go based upon what I am taught.

BTW, is this reaction theoretical or do you intend to carry it out? If the latter, you could analyse the products and find out experimentally the answer to your question.

[Edited on 19-1-2013 by Hexavalent]

sankalpmittal - 20-1-2013 at 00:18

Quote: Originally posted by Hexavalent  

BTW, is this reaction theoretical or do you intend to carry it out? If the latter, you could analyse the products and find out experimentally the answer to your question.

[Edited on 19-1-2013 by Hexavalent]


This reaction is theoretical (i.e. my question). I am just a student. I was just asking to clear up the doubt. While one teacher say that there will be major product , three people (including you) say that there will be statistical distribution.

Hexavalent - 20-1-2013 at 07:00

Ask your teacher on what grounds he said a) there would be a major product, and b) why specifically the propane.

Boffis - 20-1-2013 at 16:49

No this is a free radiacl reaction and if the 2 possible radiacals are of similar size and stability the possible rections are:

AA, AB, BA, BB but since AB=BA you will get 25% AA, 50% AB and 25% BB

The reaction, however, is more complex because occasionally a free radical will react with a product molecule, creating potentially hydrogen, methane or longer molecules.

So in your example a methyl radical might react with propane giving methane and a propyl radical, the latter might then react with another propane giving hexane and a hydrogen radical and so on. Statistically the AB combimation should be most abundant but less than 50%

Re: Wurtz Reaction in Alkanes.

sankalpmittal - 21-1-2013 at 02:17

Quote: Originally posted by Hexavalent  
Ask your teacher on what grounds he said a) there would be a major product


Ok I asked the teacher. He said while its not necessary for you to understand the reasoning , but since you're asking this is due to probability factor. Probability of forming mixed product always exceeds the formation of other products in wurtz reaction.
Quote:

, and b) why specifically the propane.


He said : Well you have your specific reaction balanced as :

3CH3Cl + 6Na + 3C2H5Cl ----> 6NaCl + C4H10 + C2H6 + C3H8

Now notice that you have 3 moles of methyl chloride and 3 moles of ethyl chloride. Now probability of forming propane is 3x3=9. Now if you form ethane , then you have to react methyl chloride among themselves only. Thus your probability of forming ethane (and same is the case with butane) is less than 9 because you have total 3 moles ingredient to form it , and for propane , 6 moles of ingredient.

sankalpmittal - 21-1-2013 at 02:21

Quote: Originally posted by Boffis  
No this is a free radiacl reaction and if the 2 possible radiacals are of similar size and stability the possible rections are:

AA, AB, BA, BB but since AB=BA you will get 25% AA, 50% AB and 25% BB

The reaction, however, is more complex because occasionally a free radical will react with a product molecule, creating potentially hydrogen, methane or longer molecules.

So in your example a methyl radical might react with propane giving methane and a propyl radical, the latter might then react with another propane giving hexane and a hydrogen radical and so on. Statistically the AB combimation should be most abundant but less than 50%


Yes , that's what my teacher said , except , he said that AB will be 70% formed , and AA and BB will be 15% each. (Not AB: 50%, AA and BB : 25% each.)

BTW , is it not obvious from my reaction that 1 mole each of butane , propane and ethane being formed , 1:1:1 ratio , no ?

[Edited on 21-1-2013 by sankalpmittal]

kavu - 21-1-2013 at 03:00

Quote: Originally posted by sankalpmittal  

Ok I asked the teacher. He said while its not necessary for you to understand the reasoning , but since you're asking this is due to probability factor.


You have one VERY odd teacher.

sankalpmittal - 21-1-2013 at 08:53

Quote: Originally posted by kavu  
Quote: Originally posted by sankalpmittal  

Ok I asked the teacher. He said while its not necessary for you to understand the reasoning , but since you're asking this is due to probability factor.


You have one VERY odd teacher.


Why did you say that ? Any reason ?

Well I asked my classmates today , and many of their coaching teachers gave the same answers as the teacher to whom I asked today. Now , will you say that all those 2-3 teachers are VERY odd ?

[Edited on 21-1-2013 by sankalpmittal]

kavu - 21-1-2013 at 09:05

This is just my oppinion, but to me a teacher saying stuff like "There is no reason. It's just as it is!" and "it's not necessary for you to understand the reasoning" is an odd one indeed. Curiosity and questions should not be smothered, quite the opposite!

[Edited on 21-1-2013 by kavu]

sankalpmittal - 22-1-2013 at 02:02

Quote: Originally posted by kavu  
This is just my oppinion, but to me a teacher saying stuff like "There is no reason. It's just as it is!" and "it's not necessary for you to understand the reasoning" is an odd one indeed. Curiosity and questions should not be smothered, quite the opposite!

[Edited on 21-1-2013 by kavu]


Now this is off topic for sure. Organic chemistry is so complex. While one teacher give a reply , the other teacher give just the opposite and both claim they are correct.

Seriously !!
Either let me know if the teacher is correct or not , or just discuss the validity of his point , pertaining to this particular topic. I'm sure this is not the personality discussion section.

Please give scientific replies pertaining to this topic , else don't post off topic.

Note : I asked you why Odd teacher. But this question should have not come into account.