Halogenation of Naphthalene?
AS
1) An experiment to brominate naphthalene failed, I wonder why:
30g NaBr was dissolved in 150ml water. This was gassed with a molar excess
of chlorine, and the solution turned deep red with some liquid bromine
appearing at the bottom.
At this point, .6g of finely powdered Iron was added to the solution, which
was hopefully going to form FeBr3 in situ and act as a catalyst for the
upcoming bromination. The Fe quickly reacted, and filled much of the
beaker with a "chunky" suspension. The suspended solid seemed lighter than
the red liquid.
This didn't seem right, but references supported in situ formation of the
catalyst in this manner, so some crushed naphthalene was added.
No reaction seemed to take place. None of the expected HBr gas was
observed. Anyone know why? Is this reactyion slow? I was under the
impressionb that it proceded quickly? Does it need to be heated (bromine
vapor, ugh..)?
2) Why does tetrahydronaphthalene brominate without a catalyst? What are
some other materials (what is THN? just a hydrogenation aromatic? Is there
another name?) that brominate without the use of a catalyst?
3) If the bromination of naphthalene can't be done in the manner described
in 1), are there any aromatics that can? benzene for example?
Thanks, any help is appreciated.
AS
news:Xns90CF9608E4F...@207.126.101.100:
I wanted to add that the failed experiment I described was left alone for
posterity. After several hours, it had separated into some kinda of 3
phased mixture! Some of the naphthalene (the larger bits) has floated to
the top and appeared yellow (may have just been covered in bomine). The
top layer was a light orange. The middle layer appeared the red of the
original solution. The bottom layer was very dark, nearly black, and
looked to be solid. FeBr3?
What's the deal here?
I'm wondering if the solution wasn't over saturated? The presence of the
liquid bromine when gassing seemed to indicate that things might be getting
"full". FeBr3 is supposed to be soluble, so if the solid at the bottom is
indeed the ferric bromide, then it looks like there wasn't anough water.
Would success result if this was repeated with more water and less NaBr to
begin with?
AS
Oops, one more. I saw a ref where the bromination of tetrahydronaphthalene
was used to produce HBr for the bromination of an allylbenzene. Does the
bromination of benzene or naphthalene release HBr fast enough, and with
enough pressure to make it a viable procedure for the preparation of HBr?
Uncle Al
>
> Hi guys, I'm new here, but I could use some of your expertise.
>
> 1) An experiment to brominate naphthalene failed, I wonder why:
>
> 30g NaBr was dissolved in 150ml water.
That's a good start for failure.
AS a SWAG, naphthalene + bromine dissolved in nitrobenzene, add
an equivlaent of anhydrous FeBr3 or powdered metallic iron
(you'll need more bromine) and heat until HBr evolves. Or do a
phase transfer catalysis with bromine into cold (Bu4N)+ OH-/NaOH
to make hypobromite
Or do the unthinkable and look up a literature prep.
--
Uncle Al
http://www.mazepath.com/uncleal/
http://www.ultra.net.au/~wisby/uncleal/
(Toxic URLs! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
AS
news:3B3CEDE8...@hate.spam.net:
Can you elbarote on why it was a good starts for a failure? I didn't have
any bromine at the moment, so I improvised. I didn't anticipate any
problems with the NaCl in the bromine water. Does the reaction need to be
anhydrous? How high must it be heated? Thanks
Uncle Al
You don't know sufficient organic chemistry. You are winging it,
badly. Hydrated iron bromide is not much of a Lewis acid -
certainly not in this application.
AS
> AS wrote:
>>
>> Uncle Al <Uncl...@hate.spam.net> wrote in
>> news:3B3CEDE8...@hate.spam.net:
>>
>> Can you elbarote on why it was a good starts for a failure? I didn't
>> have any bromine at the moment, so I improvised. I didn't anticipate
>> any problems with the NaCl in the bromine water. Does the reaction
>> need to be anhydrous? How high must it be heated? Thanks
>>
>> > AS wrote:
>> >>
>> >> Hi guys, I'm new here, but I could use some of your expertise.
>> >>
>> >> 1) An experiment to brominate naphthalene failed, I wonder why:
>> >>
>> >> 30g NaBr was dissolved in 150ml water.
>> > [snip]
>> >
>> > That's a good start for failure.
>> >
>> > AS a SWAG, naphthalene + bromine dissolved in nitrobenzene, add
>> > an equivlaent of anhydrous FeBr3 or powdered metallic iron
>> > (you'll need more bromine) and heat until HBr evolves. Or do a
>> > phase transfer catalysis with bromine into cold (Bu4N)+ OH-/NaOH
>> > to make hypobromite
>> >
>> > Or do the unthinkable and look up a literature prep.
>> >
>
> You don't know sufficient organic chemistry. You are winging it,
> badly. Hydrated iron bromide is not much of a Lewis acid -
> certainly not in this application.
>
Yes, well, I'm learning... a simple "Yes, it must be anhydrous" would have
sufficed.
Uncle Al
The factoid is not important. That you have no conceptual
framework is important. You do not know what you are doing. You
cannot incrementally improve a model that does not exist. Your
first step is to look up a literature synthesis, e.g., Beilstein
for something so elementary - possibly authered by Friedel or
Crafts. Your zeroeth step is to see if Aldrich sells what you
want to make.
Planar polyhalogenated aromatics tend to be accumulative
lipophiles and toxic, both as carcinogens and as
cryptoestrogens. Cloracne is not a subtle thing, nor is it
clinically reversible.
One can postulate wildly heterodox science that flies in the face
of orthodox expectation yet is consistent with all observation
and can only be decided by conservative experimentation,
http://www.mazepath.com/uncleal/eotvos.htm
It still needs footnotes. (It still needs quantification -
Petitjean's and Avnir's software for calculating geometric
chirality. In the Fall.)
AS
Relax big guy, theres more than one way to learn... look how much I've
learned from your charming discourse already!
Regardless of your rudeness, thanks for your help.
Mark Thorson
You need to understand it's an exchange. You got the answers
to some questions, and Uncle Al got the amusement of belittling
your knowledge, experience, and problem-solving skills. Sort
of like the Roman Coliseum, but without the lions.
Bill Walker
supervision?
"Go formylate something with ZnCl2 and liquid HCN...."
yeah, great.
AS: Go get Vogel's Practical Organic Chem. It's a great book for
beginners.
Bill
enehaf...@gmail.com
Krzysztof Mitko
(in article<b30f6fe7-78eb-46bb...@googlegroups.com>):
> Pls what is the mechanism for the halogenation of naphthalene
--
Chemical engineers do it in packed beds.