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Klute
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Thanks alot for sharing Smuv, very interesting read. Alkyl halides are very usefull reagents and details several preparations is a very good idea.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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Siddy
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by mixing HCl and H2SO4, are you not creating Cl2 atleast in small concentration?
if so does this mean H2O2 could be replaced for H2SO4? Just and idea since you seem to be listing a few preparation methods.
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Nicodem
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| Quote: | Originally posted by smuv
@Nicodem
The only thread you posted that is pertinent to my question was the first one. In this thread 'Per' mixed hydrochloric acid with ethanol and
concentrated sulfuric acid and heated everything up; then stopped the operation because HCl gas was being produced; this hardly proved anything.
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Actually, in one of those threads there is a study on the EtCl preparation from EtOH where the conditions and acid catalyst were evaluated and
optimized, but I had no time to search for the specific post with the file attached. The yields can be increased above 50%, if I remember correctly.
Also, if you would have firstly formed ethanolic EtO-SO2-OH from EtOH and H2SO4 and then slowly added this to NaCl or conc. HCl, you might have
obtained better yields, at least in theory. Otherwise, nice experiment and pictures (I liked the burning thumb picture). Also, your liquid product is
quite probably a mixture containing some EtCl together with other volatiles.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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smuv
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AH! Ok, I interpereted your post much differently. I thought based upon the first link that you posted (I grazed through the others) that you were
saying it can't be done.
Yes, I am in the process of making potassium ethyl sulfate (I made the ethyl hydrogen sulfate already via EtOH and NaHSO4) and will try the dry
distillation of that with NaCl and possibly other chlorides. I have also been flirting of the idea of distilling ethyl chloride from a slurry of NaCl
and Potassium Ethyl sulfate in DMSO, or possibly NaCl, Ethyl hydrogen sulfate and DMSO. I am hoping I could help the reaction out with a good SN2
solvent.
On test tube scale I have already tried the reaction between ethyl hydrogen sulfate with ammonium bromide and Sodium chloride. With ammonium bromide
ethyl bromide is produced along with enough bromine to strongly color the mixture; with sodium chloride I got a lot of hydrogen chloride gas and
decided the dry distillation might be a more effective method (although I have no good reason to say that it didnt produce some ethyl chloride).
EDIT
The other day I did a run where I added (dropwise very slowly) a mixture of ethanol in a large excess of sulfuric acid to a large excess of sodium
chloride in a sury of water. The mixture of ethanol in sulfuric acid was allowed to sit for a day before addition. It didn't really work out, the
efluent gas did not smell as strongly like ethyl chloride as the previous run and I was having condensor issues, so I stopped the run after ca 1.2
hours, with no yield. I have more details at home if people are interested.
Also I agree about the impurities; but I first want to make Ethyl chloride on a reasonable scale before I deal with purification. I hate microscale
work-ups.
[Edited on 29-7-2008 by smuv]
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Panache
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| Quote: | Originally posted by 497
DCM has a water solubility about 10 times that of EtBr. That would be a pain in the ass though. Good luck. |
nice one! i have a liquid/liquid extractor, i'll get it going.
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Ullmann
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See at orgsyn:
orgsyn cv1p0025
[Edited on by Ullmann]
[Edited on by Ullmann]
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Sedit
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Ethyl Bromide synthesis
Molar Weights of reactants:
H2SO4 Molar mass 98.08 g/mol
NaBr Molar mass 102.894 g/mol
EtOH Molar mass 46.07 g/mol
Products
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C2H5Br Molar mass 108.97 g/mol * .5150 = 56.1195
H2O Molar mass 18.01528(33) g/mol * .5150 = 9.277
NaHSO4 Molar mass 120.06 g/mol
Reaction:
NaBr + H2SO4 = NaHSO4 + HBr
HBr + EtOH = EtBr + H2O
23.67ml or in other terms 30 grams of EtOH was placed into a cold water bath and 130 grams of 44% H2SO4(Liquid Lightning MSDS) was added slowly via dropper syringe over a 10 minute period in order to keep the temperature down.
While waiting for the flask to once again reach ambiant temperatures I weighed out 53 grams of Sodium Bromide(Brom Start MSDS) and prepared for addition.
After evolution of heat some 15 minutes later or so the flask was placed in an ice bath followed by the slow addition of Sodium Bromide. The mixture
quickly took on a red orange color with some Sodium Bromide resting on the bottom.
The flask was allowed to set for 15-20 minutes and the arranged for simple distillation.
The reciever flask was filled about a quarter of the way full of cold spring water and as you can see in the picture above the recieving flask was
placed in an icebath as to not allow the formed Ethyl Bromide to evaporate.
After reaching 58*C at the still head the formed Ethylbromide started to distill over pretty rapidly and the contents of the flask boiled rapidly. The
EtBr droped to the bottom of the reciever with a milky white color. This was sustained for about 25 minutes at which point the rapid frothy boiling
stopped and the color of the mixture was not noticebly darker. The sound the boiling made now was completely different and unusual. Everytime a bubble
would form it would do so with a sharp tinny sound to it. It sounded as though it was being boiled in a metal container but I think this may due to
the EtBr forming and rapidly vaporizing in the solution resulting in the strange sound because the bubbles where forming in the middle of the flask
instead of around the sides like normal. It was at this point that the distillate started to take on a slightly orange tinge to it and the distillate
took on a dirtier look to it no doubt carrying some EtOH with it as it made the top H2O layer slightly milky looking until more H2O was added to crash
the EtBr out. The remainant of the reaction vessle has now lightened to a pale shade of yellow/orange and after cooling the Sodium hydrosulfate
crystalized filling up the vessle.
After about 45 minutes to an hour the distilling was stopped because a bad lightning storm was comming and I am working right next to a large open
garage door. The distillate was noticed to be only slightly more dirty the the first half of distilling so I just decided to mix both together. This
is where one of the notable things happened. When the two distilling flask where added together as soon as the cloudy EtBr hit the air it would
release puffs of dense white vapors with the consistancy of smoke. Im pretty sure that its HBr fumes after watching the final product clear up after
sitting for an hour.
The yeild prepurification yeilded roughly 30ml or 44.1 grams equaling 78.5% yeilds with more then likely a small amount still in the mother liquid of
slightly milky white EtBr with exact weight still to be determined.
I post more tommorow after I am hopefully able to purify it. But the initial conclusion is that this is a very easy synthesis to pull of and the
yeilds are not bad either. As smvu said there was no hint of odor until the end and I started to move the contents between flask. After speaking with
Arrhenius recently I decided to add excess H2SO4 and EtOH to the mixture to ensure complete digestion of the NaBr.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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UnintentionalChaos
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I spoke briefly with smuv via PM and the problem with my iPrBr synthesis is probably my lack of water in the reaction mixture. I used NaBr which is
more or less insoluble in conc. H2SO4, preventing reaction, where smuv used NH4Br. I'll run this again later with some water in the mix and report
back with pictures.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Sedit
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I tryed a small scale run with 98% H2SO4 and did not get really anything of use. The NaBr has poor solubility in Alcohols so I think the H2O helps
everything stay mobile also keeping the HBr down in the reaction where it belongs.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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jon
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you know i was wondering could this type of bromination be performed owing to the possibility of aromatic sulfonation side reactions on aklanols
bering aryl, indoyl substitutents etc?
wht about lucas reagent? then there's the friedel crafts side reactions so that leaves only pbr3?
input appreciated.
seems like you could get by with just a small amount of h2so4 and nothing bad would happen.
in light of this tosylates seems the route of choice.
[Edited on 8-7-2009 by jon]
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DJF90
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I dont think a phenyl ring will have side reactions with this method as bromide, dil. H2SO4 and HBr (formed in situ) don't react with benzene. You may
encounter problems with activated rings and those with sensitive functionalities. Lucas' reagent forms the chloride, not the bromide. You could also
use the appel reaction, which is very mild, and usually works even on sensitive substrates. I would be suprised if the CCl4 used could not be
substituted with CBr4 or CI4 to yield the respective alkyl halides.
[Edited on 8-7-2009 by DJF90]
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entropy51
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Sedit, are you sure you didn't get those images off a DEA website?
Save up for some glassware dude! EtBr is less toxic than MeI, but still...
I'm looking forward to your next installment: the beer bottle Grignard.
[Edited on 8-7-2009 by entropy51]
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Sedit
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LOL, what are you saying entropy.
Brother im a single father with 3 young children that warrent my money much more then a set of glassware. I would have had one sometime ago but a
hobby can never take precedence over them.
I started playing with chemistry when I was a kid unable to buy my own stuff so I chose to make what I needed and got pretty good at it. Now that im
older its common habit and theres a good chance I would be lost with a good set of glass. The idea of toxicity may play into my favor because I am so
worryed about it that someone using proper equipment maynot focus on safety half as much as I do. The synthesis was performed right next to a giant
open garage door. Once every thing was running smoothly I kept my distance. Gloves and long sleaves where worn the whole time even though it was 97
degrees outside.
Thats the reason that I have never posted any pictures and such before because people have gotten in there heads that fancy glassware , rotary
evaporator, ect... make you a great chemist. I do believe they can make you a better chemist due to ease of use but being able to afford Sigma Aldrich
does not make someone a chemist. Being able to perform the work and idealize the synthesis before hand gives someone more of an advantage then money
not to mention the amount of fun that you get along the way. Lets face it, Im not the only fellow here that don't have good glassware but I may be the
only one that don't mind showing it.
Beer bottle Grignard eh... Hmm now thats an idea. I got the Ethyl bromide and
if im able to get the Grignard to take off in my setting I don't want to here complaints from anyone how hard it is to work with a Grignard reagent.
Reaction note:
Overnight the EtBr cleared up nicely to a very slightly tinted yellow fluid.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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entropy51
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Just kidding, not dissing. No need to be ashamed if it works! It's taken me over 40 years to accumulate my lab supplies. I'm glad you're trying to
ventilate things.
I can't follow your stoichiometry either. Was your EtOH 95%? I think you started with less than 0.4 mol of EtOH, which I think is limiting, and
ended up with 0.4 mol of EtBr. Did I mess up my math? And don't forget that you may have water and/or EtOH in your product before purification. Do
you plan to dry and distill it?
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Sedit
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Na... no offense taken I knew I was gonna get ragged on before I even posted them pictures. It works good. One of my goals is to give people hope that
don't have the best equipment and is scared off by these sort of things.
The EtOH came from window de-icer as it was a by product of extracting the Ethylene Glycol. It was distilled, dryed with MgSO4 and the first few ml
and last few that came over where discarded. This was repeated once again until I was satisfied that it was not a mixture of Ethylene Glycol and EtOH.
Next time I would use either vodka or Ever clear over this anyday but it was what I had laying around so I used that. In doing so I would also use a
more concentrated H2SO4 instead of 45% to help compensate for the H2O in the alcohol.
The total amount of EtOH I used was 30 / 46.07 = .65 mol because I wanted to have excess to ensure completion as much as possible. The limiting
reagent was the NaBr so the whole synthesis was based around 53 grams of NaBr or .515 mol. Excess H2SO4 and EtOH where added though for reasons stated
above.
I will distill this much slow next time I try it to ensure that HBr is not being lost and to get higher yeilds. Does anyone know how much H2O this
reaction can tolerate? It seems that the more there is the more the HBr will stay in solution but im sure there has to be a point where the dilution
works against you more then the small amount of HBr loss right?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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entropy51
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Sedit, you said "23.67ml or in other terms 30 grams of EtOH". But the density of EtOH is only about 0.8, and 23.67 ml x 0.8 gm/mL = 18.9 gms EtOH.
If you have the 95% azeotrope, then I think you had 18.9 x 0.95 = 18 gm EtOH or 0.39 mols EtOH. If so, EtOH is limiting.
Am I missing something?
Speaking of possible losses of EtBr, did you use ice water in your condenser?
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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Sedit
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The condenser has a hose that comes streight from the well. It is cold and can handle a heavy flow of water thru it. I had it cranked open pretty well
while distilling to make sure the condenser stayed chilled and after a while condensation could be seen on the outside of the condenser.
I am not basing my calculations on the 95% azeotrope because the Ethyl alcohol came from window de-icer and was distilled twice over MgSO4. Possibly
Im wrong but im pretty sure this should lead to a much lower percentage of H2O in the EtOH then 95%. When adding the drying agent even the first time
it never clumped up and flowed freely so im left to assume that there is little H2O in the EtOH if any at all. So for simplicitys sake I calculated no
H2O in the Ethyl alcohol but figured in the H2O from the sulfuric instead.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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UnintentionalChaos
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Quote: Originally posted by Sedit  | | Does anyone know how much H2O this reaction can tolerate? It seems that the more there is the more the HBr will stay in solution but im sure there has
to be a point where the dilution works against you more then the small amount of HBr loss right? |
I ran this again last night, and not thinking, used a lot of water. 65g of 90-93% H2SO4 and 95g of water to completely dissolve the NaBr (about 52g
IIRC) I was using. There was no bromine evolution at all and the product that distilled is water clear. However, yield appears to be about 50% The
distillate was barely acidic, so plenty of HBr is still in the reaction flask. I'm going to add some more iPrOH and reflux for maybe two hours, then
redistill to try to salvage some of my bromide.
[Edited on 7-8-09 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Sedit
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After washing with H2O 2x times the water extracts where combined and set aside overnight. I smelled them to see if they contained any Ethyl bromide
dissolved but instead was greated with a different smell, Ether. I wounder if as the reaction loses water thru distillation and the concentration of
excess H2SO4 goes up the chances of EtO2 formation should go up as well. This is making me rethink the idea of excess H2SO4 a little bit. Maybe a
little excess H2SO4 but to much will result in the formation of ether. It can't be a large amount as there is no ether layer on the top but never the
lest its there and it more then likely cuts into ones yeilds a bit.
@UC Im not sure refluxing is needed and a slow distill may just suffice. As Arrhenius stated the reaction is not favored as much until the iPrBr
distills off. The addition of iPrOH may just push the reaction over to IPrBr by simply distilling it.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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entropy51
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I used to make alkyl bromides by generating the HBr in situ using NaBr + H2SO4. Then I discovered the preps using HBr. They're much cleaner, just
check the literature.
HBr is not hard to make. Here's a prep I posted last week:
https://www.sciencemadness.org/whisper/files.php?pid=156645&...
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UnintentionalChaos
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My question though, is what do the yields look like entropy? Perhaps for a valuable alcohol, HBr may be cleaner, but what if it's something rather
cheap like ethanol or isopropanol? That prep you gave produces 85% of azeotropic HBr based on the bromide salt. Then, that percentage yield must be
compounded with the percentage yield from the soup of SN1 and SN2 reactions that generate the alkyl bromide. Assuming the bromide salt is our most
valuable ingredient, which prep is cheaper and easier?
Also, if I had to guess volumes from looking at a sep funnel, I'd get an F. I was way off from the 50% I guessed before. At any rate, I refluxed the
remainder of the reaction mixture with an additional 51mL of dry isopropanol for an hour, then distilled it. Overall yield after washing with NaHCO3
and conc. H2SO4 was 55% with density matching the literature values.
moral of the story- the amount of water when using NaBr is critical.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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entropy51
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UC, my yields for isopropyl and ethyl bromide run around 80% for the HBr prep, sometimes 90% or so. I never personally achieved those yields with
NaBr + H2SO4 when the product was purified and redistilled.
Once you have the HBr prepared there is a lot less futzing aroung with the reaction and workup. I don't think the HBr method produces the ethers that
you get with lots of H2SO4 in the mix. I haven't tried to figure out the economics of it. I'm an amateur doing it for fun. But you need an excess
of HBr by either method and you can recover the excess HBr by distilling off the azeotrope after the R-Br comes over. I don't think you can do that
with NaBr + H2SO4, so the economics might be favorable.
[Edited on 9-7-2009 by entropy51]
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Nicodem
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Isopropanol is way cheaper and more widely available than NaBr, so it would make more sense to use its excess instead of using HBr or NaBr/H2SO4 in
excess. My yield of isopropyl bromide using NaBr/H2SO4 was 76% and I think it is not worthy trying to improve its yields given the reaction uses no
particularly expensive reagents.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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garage chemist
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Whether the alkyl bromide produced contains any ether can be determined easily by measuring its density and comparing it to the literature value of
the density of the pure alkyl bromide.
Ether can be removed from the product by shaking it with conc. H2SO4.
It protonates the ether to the oxonium salt, which dissolves in the H2SO4.
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entropy51
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Yes, a H2SO4 extraction will do that. But it's second on my list of things I rather hate to shake in a sep funnel:
1. NaCN in DMSO
2, Conc. H2SO4
3. BnCl
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