menchaca
Hazard to Self
Posts: 80
Registered: 12-3-2003
Member Is Offline
Mood: No Mood
|
|
better way to benzyl bromide
Hi, im interested in the better way to obtain benzyl bromide.I , ve read that can be as simple as reflux toluene and bromine in prsence of Mn(IV)oxide
is that correct?can somebody help me in temperatures, times of refluxing, etc..?
Thanks!!
|
|
|
evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
|
|
N-bromosuccinimide is the best brominating agent for toluene, and the best catalyst is sunlight. Why I say NBS is the best is because all you get is
the alpha brominated product. For sheer simplicity boiling toluene in the bright midday sunlight and slowly dripping in your bromine is the way to go.
Coupla pointers... be sure to pre-distill your toluene first to eliminate as many metal ions as possible... those metal ions promote nuclear
substituted products. When you get ready to do the reaction, simply boil some of the toluene off in the reaction flask which will dry everything out.
Be sure to dry your bromine by adding an equal volume of H2SO4 to it as well. Adding in an excess of toluene is not a bad idea also as it will prevent
the formation of benzal bromide (you'll end up with some regardless). Keep your condensor wrapped in aluminum foil as well, as this will keep the
toluene from reacting when cool (promotes nuclear substitution). Be sure to vent off the HBr formed into water to recycle back into bromine for later
(calcium cloride drying tube wouldn't hurt either to keep things nice and dry).
|
|
|
Flip
Hazard to Others
Posts: 116
Registered: 7-12-2005
Member Is Offline
Mood: No Mood
|
|
I'll back that up, and NBS is certainly the safest way to go, but reagents cost $$$. If you want to go with aq. Br, sunlight is all that you need.
I've seen it done with expensive lamps and such at certain wavelengths, and by chemical catalysis, but the truth is that sunlight is all you really
need. If you go the easy way, just make sure to take good care how you handle the bromine and especially how you store it when not in use.
I had never heard that about the foil around the condenser... instead of insulating it though, why not just control the temperature of the liquid in
the cooling jacket...?
|
|
|
evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
|
|
The reasoning behind insulating the condensor with aluminum foil is not to protect it from thermal irradiation, but to attempt to insulate it from
photo irradiation.
|
|
|
menchaca
Hazard to Self
Posts: 80
Registered: 12-3-2003
Member Is Offline
Mood: No Mood
|
|
well i thought that bromine could be stored diluted in methylene chloride, then add toluene and reflux. Will methylene chloride interfere in the
reaction? or its low boiling point will make reaction not possible??
I would like to make it as simple as possible!! thanks!!
|
|
|
menchaca
Hazard to Self
Posts: 80
Registered: 12-3-2003
Member Is Offline
Mood: No Mood
|
|
ouch!! i forgot it
How expensive is order N-Br-succinimide for Spain I´ve asked my chemsupplier about it and has no idea..and i´ve never ordered a chemical..
|
|
|
evil_lurker
National Hazard
Posts: 767
Registered: 12-3-2005
Location: United States of Elbonia
Member Is Offline
Mood: On the wagon again.
|
|
I think the free radicals formed would brominate the methylene chloride as well as the toluene.
And there is no need to store bromine in methylene chloride anyways. Just get a good glass bottle with PTFE cap and put in the freezer.
|
|
|
Ephoton
Hazard to Others
Posts: 463
Registered: 21-7-2005
Member Is Offline
Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.
|
|
yes methylene bromide comes to mind when using methylene chloride as a solvent
e3500 console login: root
bash-2.05#
|
|
|
MagicJigPipe
International Hazard
Posts: 1554
Registered: 19-9-2007
Location: USA
Member Is Offline
Mood: Suspicious
|
|
I've never put my bromine in the freezer (only I2). I keep my freezer very cold, around -20*F (-28*C). Wouldn't that freeze the Br2 and cause
possible breakage? I mean, even a normal freezer might if it's below -7*C, right? Or does Br2 not expand when it freezes?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
|
|
|
syntelman
Harmless
Posts: 31
Registered: 26-8-2007
Location: Europe
Member Is Offline
Mood: Tired
|
|
No, solid bromine has a higher density than in liquid form (as do most compounds except water).
If bottled properly bromine doesn't need to be stored in the freezer really, just keep it in a well ventilated area. In order to minimize vaporization
just cool it in some ice before use.
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
I hope that anyone trying to make benzyl bromide has the good sense to do it in a fume hood. If not, they will be sorry.
Nasty stuff.
Sic gorgeamus a los subjectatus nunc.
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
The toluene + halogen method for production of benzyl bromide and chloride is far from optimal for the laboratory- careful fractionation is needed to
get a reasonably pure product, and you can never completely ensure absence of ringchlorinated impurities.
I make my benzyl chloride from benzyl alcohol and concentrated HCl. There is a method on Rhodium- you simply heat BzOH with an excess of fuming HCl
under stirring, the BzCl separates as an organic phase. Separate, wash with water, dry, and distill.
This gives very pure BzCl since benzyl alcohol today is made from benzaldehyde in a completely chlorine-free process.
The only impurity in BzCl prepared this way is BzOH, which can be removed by fractionation, or converted to BzCl by heating and bubling in HCl gas.
|
|
|
Siddy
Hazard to Self
Posts: 81
Registered: 8-10-2007
Member Is Offline
Mood: No Mood
|
|
But how can Benzyl Alcohol be obtained OTC?
[Edited on 23-12-2007 by Siddy]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
