FireLion3
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Accidentally made benzyl bromide! Ouch My eyes! What happen? Need advice!
I have a small fume-tent set up with a 500cfm fan running attached to a carbon scrubber. I walked to another area and came back, and the
entire outside of the fume area had the lachyrmeter stench. My carbon scrubber is not absorbing the benzyl bromide! Why not? It absorbs everything
else? It absorbs bromine and every other odor I have put through it. That tent is perfect at containing odors, so why not benzyl bromide
I step into the tent and its unbearable! I rapidly unplug everything and quickly swap out the adapters of the flask to close them off. The tent is
still ventilating but the activated charcoal does not seem to be absorbing the odor! What am I to do?
Luckily I was only working with a 20g batch.... but I could really use some advice right now.
I was experimenting with some DBDMH that I picked up from the store. It behaves in mechanism similar to NBS. I was under the impression that benzyl
bromide only forms via the Bromine radical and that only forms with a radical initiator present.
I was attempting to brominate toluene on the ring. I've worked with many ring halogenated products and none of them give such intense eye watering
effects. Nor has bromine or chlorine. The bromine on DBDMH should react with water to form hypobromous acid which would go on to brominate toluene
ring; alternatively DBDMH could potentially exchange directly with the hydrogen on the toluene ring.
How exactly did benzyl bromide form without a radical initiator? And why didn't my carbon scrubber work? Is there any advice on how I can neutralize
this benzyl bromide quickly? It's in the flask closed off right now, with a lot of water, and the temperature is 70-80 degrees and cooling. How
quickly would the benzyl bromide decompose?
[Edited on 22-7-2014 by FireLion3]
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FireLion3
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The odor seems to have mostly cleared up. Benzyl Bromide must be a strong lachrymator at very low concentration and some must have escaped from the
tent.
I went to clean one of my thermometer adapters and there may have been a dab of the stuff on there and just holding it in my gloved hand made my eyes
pour out water until I was able to soak it down with water.
Now I just need to figure out how I can neutralize this while having my flask opened for the utmost minimal amount of time.
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Crowfjord
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As with other alkyl halides you can neutralize with ammonia, or an amine. Not sure about the free radical initiation, maybe an impurity in the
toluene? Good luck, and be careful!
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FireLion3
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Good point..... but this is urgent and I cannot afford to be waiting a week for a response by posting in a old thread.
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subsecret
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Benzyl bromide can be neutralized with any hydroxide (via SN2), depending on what you have lying around.
Fear is what you get when caution wasn't enough.
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FireLion3
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I've got plenty of reagents laying around. I've got some R-Napthylethylamine laying around that I'm never going to use. Already have plenty excess
loading in a addition funnel. This should take care of any excess halogen gas and the benzyl bromide
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Magpie
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If your brominating agent works like NBS then it would form benzyl bromide. See http://en.wikipedia.org/wiki/N-Bromosuccinimide
Maybe your carbon bed is saturated and needs to be regenerated. Or maybe, as you say, just any small amount of the benzyl bromide is enough to
irritate your eyes.
The single most important condition for a successful synthesis is good mixing - Nicodem
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FireLion3
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Hehe it was thanks to one of your post I found out about these other alternatives. When I was researching this reaction, almost all google occurences
I could find about Benzyl Bromide, Toluene, and bromosuccinimide all mentioned the use of a radical initiator. I guess a radical initiator just
accelerates the reaction, and isn't required.
In any case, I'm just glad I cleared this up.
Feel free to lock this thread Mods
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Magpie
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I think I was wrong here. I have never actually worked with NBS and I didn't read the Wiki very accurately. It says a radical initiator is used.
Maybe you had enough sunlight or other light to initiate the reaction.
I wouldn't lock this thread - you have presented experimental results. This might well save someone else from lachrymatory pain. 
Where did you get the DBDMH? Is it OTC?
Edit: Nevermind, I found your post on Brilliance Spa Sanitizer.
[Edited on 22-7-2014 by Magpie]
[Edited on 22-7-2014 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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chemrox
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Hey magpie you lucky guy I have to drive 45 miles to buy NaOH, HCL and H2SO4 or wait 5 days for shipping.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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FireLion3
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Quote: Originally posted by Magpie  | I think I was wrong here. I have never actually worked with NBS and I didn't read the Wiki very accurately. It says a radical initiator is used.
Maybe you had enough sunlight or other light to initiate the reaction.
I wouldn't lock this thread - you have presented experimental results. This might well save someone else from lachrymatory pain.
Where did you get the DBDMH? Is it OTC?
Edit: Nevermind, I found your post on Brilliance Spa Sanitizer.
[Edited on 22-7-2014 by Magpie]
[Edited on 22-7-2014 by Magpie] |
I found some other studies that showed when NBS is used with toluene, a majority (70-80%+) form benzyl bromide, where as the other things formed were
ring halogenations. There definitely was no sunlight and maybe 26w of room light going through thick plastic sheeting.
Magpie you may be interested, but in my other thread about this:
http://www.sciencemadness.org/talk/viewthread.php?tid=31843
I recently found great utility using DBDMH for ring bromination (and Trichloroisocyanuric acid for ring chlorination). I also found out that mixing
and halide anions with these causes the formation of the halogen gas. When Sodium Bromide touched DBDMH, dry, bromine gas evolved, and the same was
for Trichloroisocyanuric acid, except chlorine. These compounds with structures similar to NBS, functioning on the same exact mechanism, are
brilliant, especially since they are over the counter. Using them alone without any added halides allowed me to get ring halogenation without any
colored evolution of halogen gasses.
As I understand it the multiple carbonyls polarize the Nitrogen-Halogen bond, making it behaves as a persistent radical and/or electrophile. Both
behaviors have been observed in their usage.
| Quote: Originally posted by chemrox | | Hey magpie you lucky guy I have to drive 45 miles to buy NaOH, HCL and H2SO4 or wait 5 days for shipping. |
Unlucky you! I found all of those things in large containers with no contaminants at my local hardware store. I've actually found a ton of very pure
and useful reagents at local stores. Do you live in a small town?
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Chemosynthesis
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As you've noticed, NBS definitely yields some benzyl bromide. I believe use of a catalytic quantity of iodine almost exclusively produced the para
ring chlorinated toluene.
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FireLion3
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| Quote: Originally posted by Chemosynthesis | | As you've noticed, NBS definitely yields some benzyl bromide. I believe use of a catalytic quantity of iodine almost exclusively produced the para
ring chlorinated toluene. |
I wasn't specifically trying to achieve a halogenated ring on Toluene. I just had an abundance of toluene and a small quantity of the other compounds
that I wished to use in other synthesis. I intended to use toluene solely for testing the experiment fist. I recall toluene has been used successfully
in other ring halogenations such as the one with oxone, alongside the anisole and dimethoxybenzene that I was working with in the past, so I figured
it might be a good candidate. At least now I know to use a different cheap aromatic if ever doing this experiment.
I read a quote by someone on here the other day saying that no sane man ever seeks to repeat his encounter with Benzyl Bromide. Oh how much I agree. I
experienced accidental dust clouds of paraformaldehyde before, and that's a blindingly unpleasant lachrymator... but it is nothing compared to benzyl
bromide. A small amount of paraformaldehyde is perfectly bearable. A benzyl bromide smudge on an adapter being held in the hand is enough to cause
excruciating eye pain, as I found out yesterday. I felt like I was going to pass out and almost broke my the adapter by quickly tossing it into the
sink, flicking the water on and the fan on and leaving with the door closed behind me. Luckily the lachrymatory effects were gone the moment I left
the room with that thing.
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zed
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Benzyl Chloride is extremely unpleasant to work with. Is Benzyl Bromide a worse lachrymator than Benzyl Chloride?
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FireLion3
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| Quote: Originally posted by zed | | Benzyl Chloride is extremely unpleasant to work with. Is Benzyl Bromide a worse lachrymator than Benzyl Chloride? |
I assume they are both fairly unpleasant, due to their high degree of reactivity.
I really need to construct a fume hood inside my fume tent, because these Benzyl Halides are extremely reactive making them very versatile, and in
spite of the lachrymatory hazards, I am itching to try a few substitution reactions with them.
I didn't mention this, but when I used my chiral R-Napthylethylamine I had laying around, which smelled like straight vomit by the way, to react with
the benzyl bromide, the product that resulted was a almost-pleasant minty-smelling compound. The reaction was very quick, complete in almost seconds
of adding it, with no noticeable exothermic evolution.
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Chemosynthesis
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| Quote: Originally posted by zed | | Benzyl Chloride is extremely unpleasant to work with. Is Benzyl Bromide a worse lachrymator than Benzyl Chloride? |
It appears that benzyl halides follow the general rules of the chlorides being more volatile than the bromides due to mass, which likely equates to
greater lachrymatory characteristics through increased exposure. Both are definitely unpleasant.
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FireLion3
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| Quote: Originally posted by Chemosynthesis | | Quote: Originally posted by zed | | Benzyl Chloride is extremely unpleasant to work with. Is Benzyl Bromide a worse lachrymator than Benzyl Chloride? |
It appears that benzyl halides follow the general rules of the chlorides being more volatile than the bromides due to mass, which likely equates to
greater lachrymatory characteristics through increased exposure. Both are definitely unpleasant. |
That is true, Benzyl Chloride would be more volatile, but I wonder if the lachrymatory effects are also caused by the lability of the bond. No doubt
the close-conjugation of the ring has some effect on the reactivity. Benzyl Halides are all reactive, but I think they get more reactive Cl -> Br
-> I. The reactivity may be directly correlated with the lachrymatory effects.
I know paraformaldehyde is quite reactive, volatile, and small, and its lacrymatory effects are no picnic either... Being in a cloud of
paraformaldehyde just makes your eyes tear up for the most part. Benzyl Halides seem to have those same effects, but a much greater emphasis on the
body. Benzyl Bromide makes you feel like that but also almost like you are losing consciousness.
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Chemosynthesis
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| Quote: Originally posted by FireLion3 |
That is true, Benzyl Chloride would be more volatile, but I wonder if the lachrymatory effects are also caused by the lability of the bond. No doubt
the close-conjugation of the ring has some effect on the reactivity. Benzyl Halides are all reactive, but I think they get more reactive Cl -> Br
-> I. The reactivity may be directly correlated with the lachrymatory effects. |
I definitely think that's a valid assumption, and would think that estimating a ratio of pKa or summed heat of dissociation with vapor pressure, and
kinetics of reaction would be sensible, but if asked for an empirical measure, I am not sure how easily the two could be compared. Obviously self
reporting is flawed and unethical when comparing equimolar direct application, and I wouldn't suspect galvonic sensors or estimates of tissue damage
to be stringent enough to distinguish between the two. In the absence of such a scenario, I presume the differences in vapor pressure are enough to
alter exposure levels sufficiently to render reactivities negligible, much as chloro vs. bromo pharmaceutical derivatives can be estimated as
equipotent in molarity.
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Dr.Bob
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Carbon filters work best on polar chemicals and some smaller molecules. They don't absorb a lot of hydrocarbons well. And it only takes ppm of
BnBr to burn your eyes a bit. At least it is not likely persistent once you remove the source. There are traces of free radicals everywhere, and
any light source will generate some, which is why most chemicals are stored in dark bottles. But glass filters out much of the UV. But NBS can
react with some activated compounds without much help, and toluene may be active enough, or it may autocatalyze the reaction with some Br2 or HBr that
forms in the reaction. And benzyl bromides are more reactive than chlorides in most cases I have seen.
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FireLion3
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| Quote: Originally posted by Dr.Bob | | Carbon filters work best on polar chemicals and some smaller molecules. They don't absorb a lot of hydrocarbons well. And it only takes ppm of
BnBr to burn your eyes a bit. At least it is not likely persistent once you remove the source. There are traces of free radicals everywhere, and
any light source will generate some, which is why most chemicals are stored in dark bottles. But glass filters out much of the UV. But NBS can
react with some activated compounds without much help, and toluene may be active enough, or it may autocatalyze the reaction with some Br2 or HBr that
forms in the reaction. And benzyl bromides are more reactive than chlorides in most cases I have seen. |
Interesting, when I was testing out my filters ability I tested it specifically with smelly hydrocarbons. Toluene, Xylene, and similar related
compounds. Usually having a bottle of these opened is enough to stink up a room easily. I was able to keep bottles of 3 different ones open inside an
enclosed air filtered room with the fan at max speed, for 10 hours, and the smell never penetrated outside, but one step into the room and the smell
was very obvious.
This could just be because the molecules were quite bulky, and may not work for hydrocarbons like methane. In my reading research it was revealed to
me that activated charcoal can be superb at absorbing things like Toluene and similar molecules.
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Nectarine
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benzyl bromide is terrible - I've had to leave the lab crying from it simply from the distance from my fume hood to the rotovap (about 4 feet) in a
RBF.
The stuff just lingers around for a long time...
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CuReUS
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| Quote: Originally posted by Chemosynthesis | | As you've noticed, NBS definitely yields some benzyl bromide. I believe use of a catalytic quantity of iodine almost exclusively produced the para
ring chlorinated toluene. |
dont you mean para ring brominated toluene?
zed and chemosynthesis ,benzyl bromide is more lachrymatory than benzyl chloride and iodide is the worst ,but the choride is the most toxic .read the
"war gases" book in the sciencemadness libraryhttp://www.sciencemadness.org/library/books/the_war_gases.pd...
fire lion ,if toluene is treated with TCCA,you will get benzyl chloride not chlorobenzene under some conditions ,read this thread http://webcache.googleusercontent.com/search?q=cache:KO1xrl5...
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I Like Dots
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MY EYES :'(
I decided to make this today, and I can conform sunlight initiates the reaction. quickly. Now knowing this is a strong irritant, and potential
carcinogen I read all the info I could find on the reaction. including this youtube video, which shows a smooth, gentle conversion: https://www.youtube.com/watch?v=6yKFkJbG9UU
Today was a cool, sunny, breezy day so i decided this is a great time to try something with my newly generated bromine! I go outside and measure 5ml
bromine, and added this to 42 ml toluene (1:2 molar ratio) with a pipette. A slight effervescence was observed, then quickly the whole thing started
vigorously and uncontrollably evolving HBr in a continuous white fog. Obviously there was a small amount of Benzyl Bromide vaporized, because
here I am.. 30 minutes later and my eyes are just starting to stop stinging.
So let me save you some time if you try this.
1.Make sure both reagents are cold.
2.Make sure both reagents are absolutely dry. my toluene was not. BnBr is water sensitive, releasing HBr slowly on contact. I keep having to "burp" my
reagent bottle.
3. I would suggest doing this in the shade.
4. Be prepared for the HBr gas. I was not.
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I Like Dots
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My benzyl bromide turned pink overnight, trying to figure out what it may be. There are also some orange oily droplets on the glass.
I think it may just be some condensation products, or the bromine oxidized the toluene to some sort of phenol. I've had phenol solutions turn this
shade of pink before. Or maybe it just does that normally, but I couldn't find any literature on it.
[Edited on 2-11-2014 by I Like Dots]
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Chemosynthesis
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1. I only have data for the chlorination, but presume bromination is the same except for kinetics. Since I don't have data to confirm, I am abstaining
from stating so definitively.
2. Thanks. I haven't seen that book mentioned in a long time. While that is very informative correlating lachrymatory effect to vapor density, the
dose disparity doesn't address my particular interest; I wonder what quantitative effect molar equivalent doses (thus adjusted concentration for vapor
density) to the mucous membranes from direct application, varying the amount in an enclosed space to equilibrate vapor pressures, or aerosolization
has, and what research has been done on the subject elsewhere, if applicable. I have yet to see any data on that aspect.
[Edited on 3-11-2014 by Chemosynthesis]
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