December 01, 2020, 10:30:09 PM
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Topic: How to remove 1-pentanol from 1-bromopentane?  (Read 945 times)

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Offline lukas.stib

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How to remove 1-pentanol from 1-bromopentane?
« on: November 08, 2020, 04:49:58 AM »
Hello chemists,

can you advise me how to remove 1-pentanol from 1-bromopentane? I made about 100 ml of 1-bromopentane, and I'm sure it also contains 1-pentanol.

Thank you, Lukáš S.

Offline Traumatic Acid

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #1 on: November 10, 2020, 11:35:50 PM »
Aparently 1-bromopentane is practically insoluble in water while 1-pentanol is reasonably soluble in water. You could give your product a few water washes. Put your product into a separatory flask and add about 150ml clean (preferably distilled if you have it) water and give it a good mix. Don't shake it or you could form an emulsion which will be a pain to separate, just invert the flask repetativly for a few minutes.
Then drain off the lower layer (your 1-bromopentane). You can do that as many or as few times as you feel necessary.


I was suprised at the low solubility of 1-bromopentane, so I'll leave this here:

https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6336015.htm
https://pubchem.ncbi.nlm.nih.gov/compound/1-bromopentane#section=Solubility

Good luck!

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #2 on: November 11, 2020, 09:37:30 AM »
OK, thank you very much!  ;)

Offline Babcock_Hall

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #3 on: November 11, 2020, 11:44:38 AM »
Do you think a distillation would be successful?  Why or why not?

Offline Guitarmaniac86

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #4 on: November 11, 2020, 11:51:07 AM »
If you think it still contains the alcohol, why not just resubmit it to the reaction and fully convert it? Would be easier than trying to separate them.
Don't believe atoms, they make up everything!

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #5 on: November 11, 2020, 12:59:10 PM »
Because both substances have a close boiling point, so they cannot be easily separated by distillation.

Offline Babcock_Hall

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #6 on: November 11, 2020, 01:34:15 PM »
Because both substances have a close boiling point, so they cannot be easily separated by distillation.

I agree.  Although a careful fractional distillation might give some separation, I would not be very optimistic.

Offline AWK

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #7 on: November 11, 2020, 04:55:38 PM »
I'm guessing lucac.stib was doing a synthesis with HBr (KBr + H2SO4) and probably has a mixture containing 20-30% pentanol. He did not provide any data on the synthesis, processing of the reaction mixture, and the distillation product. We can only guess. It knows nothing about the possible formation of azeotropic mixtures. We do not know about its distillation capabilities (vacuum - although from a water pump, distillation column, etc.). Before lukas.stib starts any synthesis, he should prepare it well (I already pointed it out to him).
It is probably possible to save this synthesis and obtain quite pure 1-bromopentane, but we need to know all its previous procedures and possible his technical and analytical possibilities.
AWK

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #8 on: November 12, 2020, 10:24:27 AM »
Hello chemists,

I performed the synthesis using concentrated HBr, H2SO4 and pentanol. Weighed everything according to the instructions and refluxed for 3,5 hours, then distilled the mixture of water and bromopentane, stored the lower layer, rinsed with water, HCl, water, NaHCO3 solution, water and distilled. My thermometer showed a distillation temperature of 128°C, so it held on to the end of distillation. I guess it's a thermometer fault that's from China.

And as I mentioned, I think 1-bromopentane contains the alcohol, because I smell the "musty" smell of pentanol +  smell of bromopentane.



Offline Babcock_Hall

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #9 on: November 12, 2020, 11:24:39 AM »
Did you use a fractional or simple distillation?  Have you checked the product by NMR?

Offline AWK

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #10 on: November 12, 2020, 12:07:37 PM »
The quality of the thermometer is easy to check - distill some distilled water (this will allow you to check not only the thermometer but the correct position of the mercury bulb also).
Also, check the boiling point of your alcohol (add 2 cm3 of water to 10 ml of alcohol) - this way you will check the boiling point of the azeotrope and alcohol at the same time and compare it with any correction measured during the distillation of water (watch the lower end of the cooler - the azeotrope will stratify (drops of water) and alcohol), pure alcohol will be a homogeneous liquid).

Where does the procedure for your synthesis come from?
What can you learn about the quality of your amyl alcohol (eg: 98%, pure, extra pure, lab-grade, for synthesis, for analysis)?
Is your distillate colorless or yellowish? Does washing with a little water still acidify the water?
What is the solubility of n-pentanol in the water?
What is the boiling point of the n-pentanol-water azeotrope and what is its composition? What is the boiling point of 2-bromopentane? What were your temperature constant points during the distillation? Do you have the possibility of vacuum distillation with a water pump?

I suppose 1-Bromopentane is likely to form an azeotrope with n-pentanol (although a simple internet search gives nothing, I expect a boiling point of ~ 125°C).

If you do all of this with understanding, you will probably understand the idea of ​​splitting your mixture (but ask beforehand).
AWK

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #11 on: November 12, 2020, 01:01:59 PM »
I used simple distillation because high-boiling substances do poorly distillation.
1-Pentanol is 99% for analysis.
My distillate is colourless, and i wash H2O.
No, vacuum not possibility.
Distillation comes from 90°C in little drops, then everything distilled at about 118 - 120°C.
Thank you for your tips of quality my thermometer.
After that distillation, I rinsed everything H2O, dried it, and next time I will try to perform a simple distillation again.
NMR haven´t.

Offline AWK

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #12 on: November 12, 2020, 01:30:46 PM »
Binary azeotrope 1-pentanol-water boils at 95.8°C and contains 45.6 wt. % of n-amyl alcohol.  Add 15-20 ml of water to your mixture/ The first fraction below 100°C will contain n-pentanol, next fraction - water, at about 115°C maybe a few drops of 2-bromopentane (if it occurs), and above 125 - pure 1-bromopentane.

In this volume of water, the pentanol solubility will be less than 0.5 g, so you can separate the alcohol and measure its volume to estimate the alcohol content of your product.
AWK

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #13 on: November 12, 2020, 02:22:34 PM »
OK, thank you very much for your informations. I add water to my bromopentane and distill.
Should I use mixing? I do not use mixing, just a large number of small and large pieces of porcelain for good boiling.

Offline lukas.stib

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Re: How to remove 1-pentanol from 1-bromopentane?
« Reply #14 on: November 14, 2020, 05:18:09 AM »
OK, I tested the accuracy of the thermometer when I was boiling pure water, and the thermometer showed 100°C, so it's probably accurate.

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