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Topic: 1 bromobutane synthesis query  (Read 2692 times)

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Offline Discosucks

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1 bromobutane synthesis query
« on: December 02, 2015, 08:21:32 AM »
Hello , new to this forum but looking forward to exploring it .

I have a strange query regarding a practical experiment I recently did in college , the results of which are kinda confusing .

what I expected to happen was:

 Butan 1 ol + Sodium bromide   :rarrow: H2SO4  :rarrow: 1 bromobutane + h20

we used :

13.5ml of butan 1 ol ( denisty 0.81 g/cm3 )
18.5g of sodium bromide
and i cant remember the amount of  H2SO4 we used but im pretty sure it was more than enough

So the theoretical yield was around 20 g of 1 bromobutane , after a 15 mins of reflux and then a distillation we recovered around 4 grams of what was expected to be 1 bromobutane .

But when we did a test with the refactometer the refractive index came up as 1.338 , not the expected 1.4399 .

when i looked up 1.338 i got this compound https://en.wikipedia.org/wiki/Cryolite

So as you can imagine im pretty confused to what happened .

Could anyone shed some light on what may have happened? im not sure how detailed the questions need to be on this but if there is anything i have left out please feel free to ask .

thanks  :)

Offline orgopete

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Re: 1 bromobutane synthesis query
« Reply #1 on: December 02, 2015, 08:35:55 AM »
But when we did a test with the refactometer the refractive index came up as 1.338 , not the expected 1.4399.


Hint, isn't 1.4399 the refractive index of pure 1-bromobutane?
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Offline Discosucks

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Re: 1 bromobutane synthesis query
« Reply #2 on: December 02, 2015, 11:13:03 AM »
But when we did a test with the refactometer the refractive index came up as 1.338 , not the expected 1.4399.


Hint, isn't 1.4399 the refractive index of pure 1-bromobutane?

Ahh I see .

I considered this,  the rest of the class got the expected refractive index and I felt the method was followed very well.


Offline Enthalpy

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Re: 1 bromobutane synthesis query
« Reply #3 on: December 03, 2015, 02:23:10 PM »
When i looked up 1.338 i got this compound https://en.wikipedia.org/wiki/Cryolite

There are only <10,000 different refractive indices written with 3 places, but many many more known chemical compounds, so a refractive index fits many pure compounds. And then, mixtures, sure. Same for density, boiling point, melting point and so on.

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