Maui3
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Ethyl Bromide Synthesis Question
I am sorry if this question has been asked before. I am wondering if ethyl bromide can be prepared by reacting 48% HBr with 93% Ethanol in a lot of
calcium chloride, and then distilling the ethyl bromide off.. similar to how isopropyl chloride can be prepared.
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bnull
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I don't think so. If it works at all, you may end up with a mixture of ethyl bromide and chloride. You need another dehydrating agent (sulfuric acid,
for example).
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Maui3
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Thanks, bnull! I am not the best chemist - as probably evident by this post - so I would like to learn why it might not even generate ethyl bromide
:-)
If you swap out HBr for HCl and Ethanol for Isopropanol you get isopropyl chloride, so I did not see why it wouldn't work with ethyl bromide.
I am trying to make phenacetin from paracetamol. If I get a mix of ethyl bromide and chloride couldn't I use that? Since chloride will probably also
work for that reaction.. If I am not completely wrong. Also, I am in EU so sulfuric acid is very hard for me to get.. I have sodium sulfate, but I
assume that won't work either
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bnull
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| Quote: | | I am not the best chemist |
Neither am I. 
| Quote: | | If you swap out HBr for HCl and Ethanol for Isopropanol you get isopropyl chloride, so I did not see why it wouldn't work with ethyl bromide.
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It's not so simple. Primary alcohols are less reactive than secondary alcohols with respect to the substitution of a hydroxyl by a halogen. HBr is
more reactive than HCl, but I think that is not enough to promote the reaction. There is probably something very obvious that I'm forgetting.
| Quote: | | I am trying to make phenacetin from paracetamol. If I get a mix of ethyl bromide and chloride couldn't I use that? Since chloride will probably also
work for that reaction.. If I am not completely wrong. |
That's a good question.
| Quote: | | Also, I am in EU so sulfuric acid is very hard for me to get.. I have sodium sulfate, but I assume that won't work either |
Oops, I forgot that. Sodium sulfate won't do. You need a strong acid since the reaction involves the protonation of the carbon to which the hydroxyl
is attached. If I'm not mistaken, of course. Sodium bisulfate* may work, or phosphoric acid if it hasn't been restricted yet.
*: With an "a". Sometimes people confuse it with bisulfite, with an "i", which may lead to bizarre
argumentations.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Dr.Bob
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I don;t know that the calcium chloride will help at all. I would just try a small vial of about 50:50 ethanol and 48% HBr. I know that this works
well with tBuOH, and isoPrOH as they mostly go via a SN2 reaction, but you may be able to get it to go with ethanol if you let it go long enough and
perhaps carefully heat it. Either way, you would see a lower layer form if any EtBr formed. So not hard to tell if it works.
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Keras
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The best way is to use red phosphorus as a source of in-situ PBr₃, of course.
If I’m not mistaken, the SN¹ reaction is possible with HBr, but needs refluxing for a while. The key here is that ethyl bromide is not soluble in
water, it separates as an upper layer, which somehow impedes the reverse reaction to take place.
Don’t take my word for it, though.
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Maui3
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Hey again everybody. I think I'll try with sodium BIsulfate, since that is used as a substitue for sulfuric acid in some reactions, and can easily be
completely dry, since it's a powder. I'll try that, thank you!
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bnull
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Make a concentrated solution of sodium bisulfate and add it to the alcohol (see Merck Index, 1972). Then add HBr. Filtration/decantation may be not necessary; sodium sulfate is quite inert.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Maui3
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How long do you think the reaction will take.. do I need to reflux?
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bnull
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Ah, crap. I have just found the procedure in Vogel's Textbook of Practical Organic Chemistry (in the Library), pages 278-279. My PDF printer is a little sassy today, so I'll attach snapshots of the paragraphs.
If you haven't already read Vogel's, I recommend you do it.
 
Edit: The procedure uses concentrated sulfuric acid. With bisulfate as replacement, it will probably take longer and require reflux. There will be a
little ether along with the ethyl bromide, which is not easy to remove since their boiling points differ by 5 °C or so. Just take more care than
usual.
[Edited on 4-11-2024 by bnull]
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Maui3
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Thank you so much bnull! This helps me a lot. I will keep you updated on how it goes.
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Maui3
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So far so good. Looks like this method is actually working. This is suprising me. I'll probably make a seperate post about this. It's a good idea I
did it, so more people can make alkylating agents without theu se of sulfuirc acid.
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