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Author: Subject: Benzyl Chloride Distillation Problems :(
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[*] posted on 8-1-2019 at 07:27
Benzyl Chloride Distillation Problems :(


Hello !!
So i made Benzyl chloride reacting benzyl alcohol and HCl (70 ml, 450ml respectively) wash it with NaHCO3 and distill H2O, then try to Fractionally distill the product, and for the F**k third time it polymerized :( It gives off HCl gas, and end up polymerizing. The last time i knew it was possible FeCl3 contaminationbut these time i wash it good and it still polymerized, i don't know what to do with it, i changed my HCl supplier and it still happens. What am i Doing wrong ?
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AvBaeyer
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[*] posted on 8-1-2019 at 19:14


You need to provide more details. How concentrated was your HCl? How were trying to distill the benzyl chloride? Was there unreacted benzyl alcohol in your crude product?

I have posted detailed procedures for making benzyl chloride using benzyl alcohol and hydrochloric acid.:

https://www.sciencemadness.org/whisper/viewthread.php?tid=71...

Take a look.

AvB
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[*] posted on 9-1-2019 at 02:58


Quote:
Hello !!
So i made Benzyl chloride reacting benzyl alcohol and HCl (70 ml, 450ml respectively) wash it with NaHCO3 and distill H2O, then try to Fractionally distill the product, and for the F**k third time it polymerized :( It gives off HCl gas, and end up polymerizing.

It also happened to me (or rather to my benzyl chloride).
It is rather polycondensation, but effect is the same.
More than 50% of input turn to polystyrene-like mass, however not so hard but impossible to remove mechanically....:mad:
Conclusions:
Crude b.ch. should be prefectly acid-free - I recommend 24 hours treatment (stirring) with CaCO3.
Distillation should be as quick as possible.
Two-step purification: first with the steam (just distillation with water, hydrolysis is very, very slow), drying with CaCl2, then normal distillation.

The best solution is distillation under vacuum, even not high (as in AvBaeyer's experiments)




Klaszczę w dłonie, by było mnie więcej....
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[*] posted on 9-1-2019 at 07:13


Hi AvBaeyer

Thanks for The link's, I did not titrate my HCl but know that is concentrated,i did reflux the reaction and HCl gas was given off, so HCl is above 21%. I will do the reaction on heating at 60-70°C Its more safe :) Thanks for that !!

And hi kmno4

I will have the precaution of drying and eliminating HCl with MgCO3 for overnight or 5hs at least [i don't have CaCO3] Then CaCl2 :) I will be honest, i will try distillation of dry Benzyl Chloride because i don't have a fume hood to deal with Hydrolysis.

Thank you very much guys :D
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[*] posted on 9-1-2019 at 13:57


If you acid is contaminated with metallic chlorides then actuate like catalist and autopolimerise benzyl chloride and evolve ClH gas.

You are used muriatic ( industrial) or Chlorhydric?


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[*] posted on 10-1-2019 at 07:19


HiGaratGhost !!
Yes i know that metal chlorides like FeCl3 catalyzes the polymerization, i did get a supplier that sels very very cristal clear HCl :) To be more sure that i eliminate any Fe present, i will wash with Bicarbonate for at least 30 min.
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[*] posted on 11-1-2019 at 06:38


Hi, so reporting on my once again failure :( and Success :)
So i did the synthesis at 70-75°C for 2hs, wash with H2O, then H2O and MgCO3 suspension for 30 min, H2O again, Dry with pure lab grade CaCl2 overnight, and attempted to Fractionally distill the Product. But it once again give of HCl and started to polymerize :/ I think the fractionation column was a little bit wet (yea F**k me xD) So i stop it and add water to try to Steam distill it, and IT WORKED :) Apparently hydrolysis is in fact slow, Thanks very much kmno4 for your suggestion :) my yield was bad but because a great deal polymerized, from now on i will do Steam distillation for these synthesis :)
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[*] posted on 11-1-2019 at 07:19


Quote: Originally posted by Chem Science  
Hi, so reporting on my once again failure :( and Success :)
So i did the synthesis at 70-75°C for 2hs, wash with H2O, then H2O and MgCO3 suspension for 30 min, H2O again, Dry with pure lab grade CaCl2 overnight, and attempted to Fractionally distill the Product. But it once again give of HCl and started to polymerize :/ I think the fractionation column was a little bit wet (yea F**k me xD) So i stop it and add water to try to Steam distill it, and IT WORKED :) Apparently hydrolysis is in fact slow, Thanks very much kmno4 for your suggestion :) my yield was bad but because a great deal polymerized, from now on i will do Steam distillation for these synthesis :)

"Dry with pure lab grade CaCl2 overnight, and attempted to Fractionally distill the Product. But it once again give of HCl and started to polymerize :"
CaCl2 isn't as strong an acid as FeCl3, but it seems it's good enough...
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[*] posted on 11-1-2019 at 09:30


HI UNIONISED
Sorry, i filtered off the CaCl2 before Fractionally distilling xD. i forgot to tip that down
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[*] posted on 11-1-2019 at 10:26


I'm willing to bet that at least some dissolved.
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[*] posted on 11-1-2019 at 11:08


I've done this reaction numerous times. I stir benzyl alcohol with seven volumes of concentrated HCL and as much bone-dry CaCl2 as the stirrer can handle. I use a heavy-walled filtration flask with a sealed sidearm and stopper it tightly. Stir at ambient temperature very vigorouslyfor 3 hours. Gaseous HCl will slightly pressurize the vessel. Decant or filter and separate layers. Wash crude BC with an equal volume of H2O and then twice with aqueous NaHCO3. Put a bubbler on it*. Stir until no more CO2 is evolved. I then distill under aspirator vacuum through a long Vigeraux column without drying. Any water comes over in the forerun. Yields are excellent and I find essentially no polymerization. It's always easier and better to wash out trace acid with a solution of base than using a solid base.

The two factors that seem to matter the most are vigorous stirring and an aqueous base wash. Vacuum distillation helps, but is not a necessity. You can distill at 760 mm but it works better at 10 mm or so as shown in the picture.

Distillation setup is shown below.

*A bubbler on what you ask? The RB flask in which I stir for 30 minutes before separating layers.

[011268].jpg - 1.3MB

[Edited on 1/11/2019 by Dan Vizine]





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[*] posted on 11-1-2019 at 18:00


Hi Dan Vizine, well i indeed may use soluble bases next time, unfortunately i don't have access to a Vacuum Fractionation apparatus :( I is strange, because the very first time i did these, i didn't have any problems,for know i will stick with the steam distillation :) i can finally replenish my Benzyl chloride stock to continue research. Ow and btw Awesome set up, I wish i could have one some day :)
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[*] posted on 11-1-2019 at 19:02


I believe one of the important steps in the procedure I posted (see above) is that the product was dissolved in hexanes before distillation. This minimizes the amount of water and residual benzyl alcohol in the product. It also helps the CaCl2 drying agent remove any residual water and benzyl alcohol. This adds an extra step (removal of hexanes) but is probably help to a purer product. I have used my method many times and have never experienced any polymerization or HCl outgassing.

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[*] posted on 12-1-2019 at 08:07


The problem is that i don't have access to Hexanes. I was saving some of the used hexanes in the University lab i work but my boss is not very convinced yet xD
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26-1-2019 at 04:18
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[*] posted on 9-3-2019 at 18:33


Does the Benzyl chloride form an azeotrope with any side products of this reaction?
Yesterday I made Benzyl chloride from 250ml conc. HCl and 32,5ml of Benzyl alcohol.
Over night I dried the separated and NaHCO3 washed Benzyl chloride layer with some anhydrous CaCl2.
Now I wanted to distill it, but it's stated to have a boiling point of 179°C. So I put a beaker under there for collecting the lower boiling fraction and eventually at 164°C something began to distill over: A (in the condenser) clear distillate, that got milky in color, when it dripped in the slightly wet beaker.
I was waiting a long time for a higher boiling fraction to come over, but now I'm at just a bit more than 20ml of distillate that came over at 164°C and nothing more wants to come over.

The boiling flask has some high boiling yellow liquid in it, so it also doesn't seem to have any Benzyl chloride left:o
I used an old alcohol Thermometer, that was in a distillation kit from deschem around five years ago - maybe the thermometer just doesn't work that good at this high temperature?
Does anybody have experience with either the deschem thermometers at high temperatures or a lower boiling Benzyl chloride product?

*edit*
But I have to say, that I didn't had any problems with degassing HCl from the condenser or any polymerization - maybe because of the well dried glassware(except the beaker:D) and dry product?

[Edited on 10-3-2019 by Tellurium]

[Edited on 10-3-2019 by Tellurium]
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