Author Topic: Bromosafrole Made Easy  (Read 25057 times)

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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #20 on: April 22, 2001, 10:56:00 PM »
I apologize, I forgot to mention in this post that my NaBr was mixed with a slightly smaller molar amount of dichloro-s-triazinetrione.  I still maintain, however, that gaseous HBr will be difficult to produce with the H2SO4 and NaBr method. ( 2HBr (g) + H2SO4 (l) --> Br2 (g) + SO2 (g) + 2H2O (l) )

Nevertheless, I'd love to make it work as much as the next guy, so I've obtained 99% NaBr and will give the H2SO4 method a shot tommorrow, and let ya'll know how it goes.


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Osmium

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Re: Bromosafrole Made Easy
« Reply #21 on: April 23, 2001, 02:32:00 AM »
I still doubt that adding HCl to NaBr will produce HBr. At best you will end up with a 50:50 mixture of HCl and HBr.

Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #22 on: April 23, 2001, 05:33:00 AM »
I posted this in the chem forum "HBr bubbly bubbly", thought it would be of interest to this thread:

"Okeeeokdeee, a small amount of NaBr (99%) was placed in a beaker, and covered with conc. H2SO4.  This immediately foamed and released a creamy orange gas (sorta the color of orange sherbert).  After 30 seconds the reaction began producing more orange gas, until at about t=60seconds the beaker issued a lot of bromine and apparently little HBr.  Probably 'cuz things heated up.

This worked only slightly better than the previous experiment with the triaz. mixed in.  Will try again with chilled reactants, although given the heat of the beaker after this trial was over, I'm not sure ice water is gonna cut it, this seems very exothermic.

Since to get good yields the HBr should be bubbled slowly, I still like the HCl method better, it *seems* less exothermic, and keeping the H2SO4 method cold for a long time is gonna be a pain.  I'll try to find a reference for the HCl and NaBr reaction.

Chilled H2SO4 test to come..."

Os, why do you think 50/50?


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Bwiti

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Re: Bromosafrole Made Easy
« Reply #23 on: April 23, 2001, 07:51:00 AM »
In "Total Synthesis 2" --> 240g potassium bromide is dissolved in 400ml water. After this is chilled, 180ml H2SO4 is slowly added, keeping the temp. below 75*C to prevent the formation of bromine, and this is distilled to give 48% hydrobromic acid.
----------------------------------------------------
Here's my idea: Saturate the 48% HBr with sodium chloride, and slowly drip H2SO4 from a sep funnel to produce slightly damp HBr. This could be lead into a chilled flask of acetic acid until it can't hold anymore HBr. A little water won't hurt just as long as the HBr's concentrated enough to be of use in producing bromosafrole. So, what do ya think? :P


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smiley_boy

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Re: Bromosafrole Made Easy
« Reply #24 on: April 23, 2001, 09:21:00 AM »
Hiya,

I should have mentioned something earlier, but I just never got around to it. Please, do yourself a favor, and put your energy towards something that will work. You're banging your head against a wall with this one, since you are not going to be able to produce gaseous HBr this way, no matter what. Period. Sure, sulfuric acid and KBr will give you aqueous hydrobromic acid, but you'll never be able to produce hydrogen bromide, the gas. The little KBr/H2SO4 technique is the laboratory preparation method of choice for aqueous HBr, as outilined in Inorg. Syn. 1, 155 (1939), but there is a reason why the only preparations for anhydrous HBr involve the fusion of elemental hydrogen and bromine at elevated temperatures, or the bromination of Tetralin(R) - and the reason isn't that they had nothing better to do with their time. Its not that they're gluttons for punishment or exceptionally anal about purity, its just the only way that works. It all comes down to dissociation constants and the competing ion effect.

Let it go, for your own good... ;)

Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #25 on: April 23, 2001, 12:56:00 PM »
I disagree...  a reaction obviously occurs when H2SO4 and NaBr are anhydrous or nearly so.  Thus, any HBr is given off as a gas. 

Purity is a big problem here though, thats why HBr gas is produced in the manners you say. 


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foxy2

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Re: Bromosafrole Made Easy
« Reply #26 on: April 23, 2001, 04:14:00 PM »
can you not just brominate it to the dibromo safrole and then decompose this with heat???

Solves all the problems


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terbium

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Re: Bromosafrole Made Easy
« Reply #27 on: April 23, 2001, 07:00:00 PM »

Os, why do you think 50/50?


Allow me to be a bit presumptuous and answer for Osmium:
Because HBr is extremely soluble in water just like HCl. There is nothing to drive the equilibrium in one direction or another. All that you will end up with is a flask of water containing Na+, H+, Cl- and Br- ions in aqueous solution.


Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #28 on: April 23, 2001, 07:15:00 PM »
I remind you that everything I've discussed here is anhydrous, the water form adding HCl (aq) is negligable, once saturated with HCL OR HBr, it fumes off the rest.


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Bwiti

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Re: Bromosafrole Made Easy
« Reply #29 on: April 23, 2001, 07:40:00 PM »
Jesus Fucking Christ! What does a guy have to suck to get some fucking HBr!? Alright, lets say you made some 48% HBr that's contaminated with a little Br. Add some sulfur to this and apply heat, which will convert the Br to HBr. Add some more sulfur, so that while dripping H2SO4 if Br's created from over-heating, it'll be converted back to HBr. Just to be safe, have the HBr go through another flask containing sulfur, then lead it to the acetic acid? Would H2SO4 react with sulfur?
  Or, could the impure HBr be bubbled into the acetic acid, then sulfur be added without anything fucked-up happening? 8)


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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #30 on: April 23, 2001, 08:00:00 PM »
This aint hard... all these mthods make HBr, pick you poison:

H2SO4 and NaBr:  makes HBr but risk high Br2 formation, and thus dibromo.  cooling reduces br2 formation

HCl and NaBr:  make HBr but also HCl giving bromo and chlorosafrole mix (light on the chloro)

buy 48% HBr:  bromosafole can still be made with the aqueous stuff, see

http://rhodium.lycaeum.org/chemistry/halosafrole.txt




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terbium

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Re: Bromosafrole Made Easy
« Reply #31 on: April 23, 2001, 09:53:00 PM »

I remind you that everything I've discussed here is anhydrous, the water form adding HCl (aq) is negligable, once saturated with HCL OR HBr, it fumes off the rest.


Sigh, you just don't listen. Hydrochloric acid is hardly anhydrous. Reread my last post and try to pay attention to what is being said. But, if you don't want to, then I wish you much happy windmill tilting.


Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #32 on: April 24, 2001, 04:57:00 AM »
Terbium:

I don't want to be confrontational, however if you read Os's post, he said the GASES are 50/50, so your presumption that no HBr(g) is produced... I can't believe it.

Also, I aknowledge, quantitatively, youre correct, 33% HCl brings roughly 100ml H2O/mole HCl and produces 80.9g HBr/mole HCl upon reaction with NaBr.  Since HBr is almost 200g/100ml soluble, you're correct that all the HBr could dissolve. 

Qualitatively, however, experimental procedures reveal that this reaction does in fact produce gas, and lots of it.  I could measure the volume of gas to show that more gas is produced that could be theoretically all HCl, however, even you must agree that that isn't the case:

Another quantitative analysis shows that HCl is 62g/100ml soluble, so 33% HCl is only 1/2 the way to saturation.  As such, there would be plenty of water to dissolve all the HCl produced as well.  By these numbers, there should be NO gas at all, and that is certainly not the case.

I conclude that this reaction produces:

a) lots of gas (which quantitatively, it shouldn't)
b) at least a fraction of it is HBr

That's my thinking, seems sound to me...?


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Osmium

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Re: Bromosafrole Made Easy
« Reply #33 on: April 24, 2001, 06:12:00 AM »
As someone said before, you will end up with a solution containing Na+, H+, Cl-, and Br-.
The question now is: since this solution is above saturation, which molecule will be given off? Since HBr is less volatile than HCl, I would expect the HCl to be the mayor component of the gasses. What means mayor? How much? I don't know, that's why I said 50:50. Probably the HCl content will be even higher.
Those solubility numbers you gave up there don't mean much, they are for the pure gasses in pure water.
What we have here is a multi-component mixture, with the Na anions being non-volatile, so whatever happens, they will of course stay in solution. Which gas composition will be given off is hard to say, but it will most certainly be a mixture of both gasses, and the HCl will be the main component.

I'm not trying to discourage anybody, but if you want to try the HBr route, then steer yourself to the serious chemistry forum, and search for the procedure I posted there, which gives over 90% bromosafrole. There is a reason why this HBr shit isn't used widely on these boards.

Osmium

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Re: Bromosafrole Made Easy
« Reply #34 on: April 24, 2001, 06:14:00 AM »
> can you not just brominate it to the dibromo safrole and
> then decompose this with heat???

No, doesn't work. Even if that was a clean reaction this would split off HBr from the molecule, and you will end up with a double bond somewhere.

smiley_boy

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Re: Bromosafrole Made Easy
« Reply #35 on: April 24, 2001, 07:32:00 AM »
Agent_Smith,

Like I said, it won’t work. I’m trying to figure out where to begin clarifying, but I'm overwhelmed.

First off, let’s scrap this nonsense about HCl + HBr making HBr. Compare, if you will, the pKa’s of the two acids. Oh, you can’t find those numbers? Well, let your good friend Smiley_Boy help you out (the pKa for HBr can be surprisingly elusive when you’re first starting.) The pKa for HBr is around –8.6, and the pKa for HCl is near -7.4 (or so IUPAC would have us believe.) Notice something? Yes, the pKa of HBr is lower, meaning that in fact HBr is about 20 imes more acidic, and indicating that in a mixture the cation (Br-) will generally stay ionic, and that HCl will generally be in far higher concentrations than HBr. To rephrase this, you're not going to get a lot of HBr this way.

Let’s also clear up the matter with ammonia fumes.  I have some doubts about the way this experiment was performed, since both HCl and HBr  form salts with ammonia. The fact that you got nothing certainly doesn’t indicate that HBr was produced. Rather, the fact that you got nothing indicates the test was performed in a manner that it was not intended.

Moving on, let’s straighten this business out with Osmium, and your quotation of him. Not once in his message did he use the word 'gases', and 50/50 'at best' was what he suggested. He was being polite, but at the same time, he was trying to tell you this is a dead end. Osmium is a nice guy, but parroting him certainly isn’t exactly the stuff of science. Why 50/50? You tell me. Oh, you can’t? Well, neither can I; as far as I can tell, Osmium pulled this number out of thin air, in an effort to explain the reason why the best-possible-scenario with this procedure is still unacceptable.

Now, let’s get into the meaty part:


Another quantitative analysis shows that HCl is 62g/100ml soluble, so 33% HCl is only 1/2 the way to saturation.  As such, there would be plenty of water to dissolve all the HCl produced as well.  By these numbers, there should be NO gas at all, and that is certainly not the case.



Wow, this makes me nervous.

Okay, let’s go through this, step-by-step. Now what is that whole “%” all about? It’s the percentage of how much of the weight of the solution is made up by HCl. How do we calculate it? Well, let’s say that water weighs about 1 g/ml (certainly close enough for this demonstration.) That means that the solution weighs 162 grams (62 g HCl, plus 100 g H2O). Now, calculate:

(62 g HCl)/(162 g solution)*(100%) = 38.2%

Which, according to the Merck Index, is actually about as much HCl as water can hold under ambient conditions (BTW, if you haven’t picked up a copy of it, do so. It will save you a lot of grief and energy - and chemicals.) Incidentally, a saturated HBr solution is made up of 66% HBr.

I want to make sure you know I don’t mean this at all in a discouraging manner; though I think your understanding of theory could use some polishing, you’ve shown a great deal of promise in practical lab technique. The fact that you went out and actually took some carefully measured direct observations -- that's impressive. I really look forward to seeing your progression.

I hope this helps...


smiley_boy

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Re: Bromosafrole Made Easy
« Reply #36 on: April 24, 2001, 08:45:00 AM »
...Plus, I can't imagine that the bromine is going to stay away from that benzene ring for very long, in particular the 6-position.

goiterjoe

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Re: Bromosafrole Made Easy
« Reply #37 on: April 24, 2001, 10:05:00 AM »
how about these apples.  bubble H2S into cold water until it is saturated.  next, drip sulfuric acid onto NaBr or KBr and bubble the resultant fumes into the H2S saturated cold water.  that way, any HBr produced will stay in the water, and the Bromine that passes over will react with the H2S to form HBr.  should work in theory, works for HI production.

oh yeah, wear SCBA gear if you want to be able to carry on with the bromination procedure.


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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #38 on: April 24, 2001, 01:23:00 PM »
Ok, ya got me :)  Thanks to everyone for keeping the "flames low"... 

To head back to reality now, does anyone have any data for ratio of Br2 to HBr production at various temperatures with the H2SO4 method?

Ok, I just thought of something, so I'll hafta diverge a little bit back to the imaginary.  I see that Br2 reacts with H2O to form a mix of HBr and HBrO (and heating or exposing HBrO to sunlight gives HBr) (

http://www.ucc.ie/ucc/depts/chem/dolchem/html/elem/elem035.html

.  If gaseous HBr and Br2 is bubbled into H2O, I know that you'll get HBr acid (aqueous).  However, since the Br2 is reacting with the water, would the water be consumed fast enough to release the HBr from solution as a gas? I know this one is far fetched.


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Bwiti

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Re: Bromosafrole Made Easy
« Reply #39 on: April 25, 2001, 07:05:00 AM »
Check this out:

http://l2.espacenet.com/dips/viewer?PN=GB551789&CY=gb&LG=en&DB=EPD


Pat. GB551789
Process for preparing hydrobromic acid  8)


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