Author Topic: Bromosafrole Made Easy  (Read 11686 times)

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hypo

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Re: Bromosafrole Made Easy
« Reply #40 on: April 25, 2001, 08:23:00 AM »


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?


You're overlooking something here: The oxidation potential of H2SO4 (or any oxidizer) depends on the activity, which itself depends on the concentration!

If you look at a table of standard potentials you will see that Cu is not oxidised by 1M (or was it 1N??) H2SO4, still you can dissolve Cu with conc H2SO4.

So the problem will not only be temperature but (and foremost?) concentration!


improv_chem

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Re: Bromosafrole Made Easy
« Reply #41 on: April 25, 2001, 10:27:00 AM »
Ok, say one has a pile of bromine and wants some HBr(g).  I don't have a copy of Vogel around but i think i remember reading something about this.  Do you just add sulfur and bromine to get HBr?  You can get bromine very easily by adding oxone to NaBr solution...
what about creating a small jet of hydrogen gas via electrolysis of water and placing the capillary tube with the hydrogen flame into the flask with the bromine?  Just light the hydrogen jet and then place it into the bromine.  (extreme caution should be taken when working with hydrogen gas.  Small scale only!) This should theoretically work right?  I don't know exactly how to set something like this up though, will probably explode if it isn't set up right.  Mabe you guys should check out festers method of bubbling HCl(g) into Safrole/GAA/48% HBr mix to cause dehydration of the acid.  Ritter says it works, SWIM tried it once but didn't bubble enough gas and used HBr that was too weak so no reaction took place.
Don't bang your heads against the wall too much with this one bees, SWIM has had many a head banging experience with this method!
-improv :)


--Preventing odors from escaping to nearby noses is essential.....

goiterjoe

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Re: Bromosafrole Made Easy
« Reply #42 on: April 25, 2001, 02:30:00 PM »
what conditions are needed to combine elemental hydrogen and bromine into HBr?  say, if one were to run an electrical current through a saturated solution of KBr in distilled water and pipe off the gas produced at the negative electrode, how hot would you have to get it for the two to combine, and would more than atmospheric pressure be needed?


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smiley_boy

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Re: Bromosafrole Made Easy
« Reply #43 on: April 25, 2001, 02:42:00 PM »
Good questions! Now we're getting somewhere. Okay, so what are we looking at as far as equilibria? Well, under aqueous conditions, with a mixture of Br2 and HBr, we have the following:

H-Br (hydrogen bromide) + H-O-H (H2O) <-> H3O+ (hydronium anion) + Br- (bromide cation)

Br-Br (elemental bromine) + H-O-H (H2O) <-> H-Br (hydrogen bromide) + HOBr (hypobromic acid)

and, we have the following reaction:

2 HOBr + (UV light) -> 2 HBr + O2

Now, when you add bromine to water, you get an equilibrium, where Bromine dissociates and reacts with one equivalent of water, forming one equivalent of hydrobromic acid, and one equivalent of hypobromic acid. After awhile, the HBr and HOBr react with each other, and the product is H2O and Br2. This goes on and on, back and forth, countless times in the solution, and its a relatively stable pattern.

Now if you shine some strong UV light source on the solution (like sunlight), something else happens. The light causes an irreversible reaction to happen,so that O2 gas and HBr evolve. Since the solubility of O2 in solution is only about 9 mg/L, it bubbles off quite quickly. However, like it was said before, a saturated HBr solution is 66% HBr, meaning you'd have to produce a hell of a lot of HBr before the solution wouldn't hold any more, and then you'd still have to separate HBr from the Br2 fumes. Also, you'd need a lot of light, or a lot of time, or both. In theory at least, it should work, but it sure sounds messy.

Hey, here's an idea:

NaBH4 + 4Br2 + 3H2O -> 7HBr + NaBr + B(OH)3

Now, to keep it relatively anhydrous (not completely anhydrous per se, since 3 equilvalents of water are used), we need a relatively innert solvent that will dissolve the starting materials well, but not the final products (well, at least not dissolve the HBr well, anyway.) Glyme or diglyme or even THF sound like fine candidates. If everything is kept relatively cold, perhaps by chilling  the NaBH4/glyme solution using ice and rock salt, then one could add elemental bromine with a pressure-equalized addition funnel. Perhaps by adding the bromine and water in series, the borohydride wouldn't have to compete for solvation against boric acid. Hmmm...

Step 1:

NaBH4 + 4Br2 -> 4HBr + NaBr + BBr3

Step 2:

BBr3 + 3H2O -> 3HBr + B(OH)3

It looks like this might work, but I have a funny feeling I'm overlooking something somewhere. To the other killer bees: does this look reasonable? Am I somehow forgetting some crucial side-reaction? I mean, this isn't all that great of an alternative, but would this work?

To Agent_Smith: I just wanted to appologise again too, in case I sounded rude in my last response. I have to admit, sometimes I forget my manners. I'm sure you know that we're all on the same side of this terrible war. I took the time to give a thoughtful answer, which I genuinely hope you enjoy and find useful. I'd hate for that effort to go unappreciated, simply because of some of my bad choices in phrasology.

Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #44 on: April 25, 2001, 08:15:00 PM »
Fear not smiley_boy, I appreciate all your help, and I'm not fragile enough to be tweaked by tone.

I'll finally concede that the gaseous HBr bubbly method isn't hot shit, so my research into using aqueous HBr has borne this fruit:

Safrole (5.3 g.) added dropwise at 0C to 21 g. 70% HBr, the mixt. left 14hrs. at 0C, poured on ice, extd. with Et20,and the ext. distd. in vacuo yielded 97% 3,4-CH202C6H3CH2CHBrMe (I), n D-24 1.5634.

Chemical Abstracts 1961, column 14350, paragraph e (S.Biniecki &E.Krajewski) - Safrole + 70% HBr at 0C for 12hours produced 97% yield of bromosafrole.

Journal of Chromatographic Science, Vol. 29, april 1991, page 169: Bromination Reactions. Samples of sassafras oil or alkenes (5.0 g of safrole, isosafrole, eugenol, isoeugenol, etc.) in 48% HBr (25 mL) were stirred at room tempature for 7 days. The reactions were then quenched with the addition of crushed ice (25 mL) and extracted with ether (2 x 50 mL). The ether extracts were evaporated to dryness under reduced pressure and the resultant product oils analyzed directly.

FROM "The Journal of Chromatograpghy science, Vol 29, 1991, page 267-271:Bromination with 48% HBr (aqueuos). Stirred for 7 days @ room tempature. Quanities- 5 grams safrole, 25 mL 48% HBr. Quenched with 25 mL crushed ice and extracted with ether.

Wow, 97% yield without that DMSO crap.  Interesting.

Also, when making aqueous HBr, the H2SO4 and NaBr will work fine, right?


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terbium

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Re: Bromosafrole Made Easy
« Reply #45 on: April 25, 2001, 11:39:00 PM »

Also, when making aqueous HBr, the H2SO4 and NaBr will work fine, right?


According to Vogel, you want to keep the temperature below 75°C.


Osmium

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Re: Bromosafrole Made Easy
« Reply #46 on: April 26, 2001, 01:01:00 AM »
> Step 1:
>  NaBH4 + 4Br2 -> 4HBr + NaBr + BBr3

All that HBr formed in that first step will lower pH dramatically, which means the bulk of the NaBH4 will be lost to hydrolysis.
I don't think it will work.

Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #47 on: April 26, 2001, 05:03:00 AM »
Ok, keep it below 75C. 

How much water to use?  should I calculate an amount that will relate to a final 66% HBr sol'n (which I believe is the max).  Or should I dilute the stuff even more than that and then distill?


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smiley_boy

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Re: Bromosafrole Made Easy
« Reply #48 on: April 26, 2001, 07:24:00 AM »
Os,

Thanks for your input. Actually, I thought about the hydrolysis problem, which was why I suggested diving the reaction up into two steps - the first being the reduction of Br2 with NaBH4 under anhydrous conditions, followed by quenching with H2. If the conditions are kept anhydrous during the addition of Br2 to NaBH4, then hydrolysis isn't possible. In other words, Br2 is added to an anhydrous solution of NaBH4 in some inert solvent; perhaps the reaction could even be done hetergeneously to minimize the amount of solvent needed. After all of the Br2 has been allowed to react with NaBH4 (indicated by the absence of Br2's characteristic color), the solution is then hydrolyzed by careful addition of water. So, step 1 is the treatment of one equivalent of NaBH4 with 4 equivalents of Br2, yielding 1 equivalent of NaBr, 1 equivalent of BBr3, and 4 equivalents of HBr. Step 2 is the hydrolysis of BBr3 with 3 equivalents of water or alcohol, yielding the final 3 equivalents of HBr. What do you think?

smiley_boy

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Re: Bromosafrole Made Easy
« Reply #49 on: April 26, 2001, 07:44:00 AM »
Huh?! I don't get it; in some posts, you sound like you're a early-yet-promising beginner, but in posts like this, you sound like a flaskjockey who's been doing this for awhile - what's the dealio? Is there more than one person posting on this account?

The safrole and 70% HBr looks interesting, except that 70% HBr isn't the easiest or cheapest thing to come by. ACtually, I think that article has been discussed at length here on the Hive in the past.

I don't think I've seen that J.Chrom.Sci. article before. It looks nice; the reaction time is a little long, but reasonable. 47% HBr is something obtainable (readly obtainable from KBr and H2SO4, which can be followed up by distillation to get a reagent of very high purity.) I'm kinda wondering about this, since safrole and aqueous HBr solution isn't going to mix well.

smiley_boy

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Re: Bromosafrole Made Easy
« Reply #50 on: April 26, 2001, 07:57:00 AM »
This reduction of bromine with elemental sulfur certainly sounds clever! I'm guessing that the stoichiometry would go something like this:

S + 3H2O + 2Br2 -> 4HBr + H2SO3

or,

S + 4H2O + 3Br2 -> 6HBr + H2SO4

It sounds a little smelly and dangerous, since undoubtedly a little H2S will also be generated due to incomplete oxidation. Maybe if the sulfur is added to an excess of Br2? Hmmm...

Bwiti

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Re: Bromosafrole Made Easy
« Reply #51 on: April 26, 2001, 08:50:00 AM »
In Total Synthesis 2(page 255-256), Strike shows an HBr synth she found in Vogel's "Practical Organic Chemistry":

"48% HBr: Method 3 (from bromine and sulphur)
A 1-litre three-necked flask is charged with 27g of flowers of sulphur and 550ml of H2O. The flask is equipped with a dropping funnel(with tip below the surface of the water), a water sealed mechanical stirrer and an Allihn reflux condenser; Ground glass joints are preferable, but used rubber stoppers are generally satisfactory. The flask is immersed in a bath of water at 60*C, the mixture stirred vigorously and, when the temp. inside the flask is about 50*C, 400g(125.5ml) bromine are introduced from the dropping funnel during about 20 minutes. The temp. of the reaction mixture rises rapidly as the reaction proceeds; the flask is cooled momentarily in a bath of cold water if the condensed bromine vapour  is near the top of the condensor. When all the bromine has been added, the mixture is heated on a boiling water bath for 15 min.. The reaction product is cooled, and filtered from residual sulphur and other solid matter through a sintered glass funnel. The filtrate is distilled and the constant b.p. hydrobromic acid collected at 125-126*C/760mm. The yield is 805g.

Note: The reaction between bromine and sulphur in the presence of water may b represented by the equation:

3Br2 + S + H2O = 6HBr + H2SO4

It is rather slow at moderate temps. and the hydrobromic acid formed in the initial stages of the reaction inhibits it's further progress. Bt carrying out the reaction at 50-70*C or above in the presence of a large excess of water, the inhibition observed at lower temps. does not occur."
-----------------------------------------------------------
  To me, the above synth seems pretty fucking useless for making a concentration above 48%, so right now I'm thinking that bubbling anhydrous HCl through 48% HBr/safrole is the best way to go(at least 2nd in line to the DMSO method) Is any other solvent that can be used in place of that smelly-ass DMSO?
  Getting back to my earlier idea: H2SO4 + 48% HBr that is saturated with NaCl creates bromine and HBr - If this gas could be passed over a dry material that binds bromine, but not HBr, then I'd be all set.
  By the way, if dibromo
safrole is heated with methylamine/alcohol in a pipe-bomb, would the product have any CNS-activity comparable to the serotonin-boosting effects of E, or would it just be a chunk of neurotoxic shit? If bees have been putting their trust in Strikes method for making bromosafrole, then yields are low, which has given the pipe-bomb method the rep it has today. :P


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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #52 on: April 26, 2001, 09:07:00 PM »
No no, only one person posting, and I am a beginner.  I have a good amount of chemistry education under my belt though, but I never really liked it. So, for exmaple, when I got flamed for missing the importance of the dissociation constants of HCl vs HBr, I'm fully capable of making those calculations and understanding them, I just fail to make the intial connections 'cuz I never took much time to understand the "why this is important", but rather just focused on "how do I get an A?"

I was wondering about the sassy and HBr(aq) phases myself.  I read somewhere that when the reaction is complete, the solution becomes one-phased and turns red...?

One thing I would like to lnow is how does the rate of this reaction proceed?  Logic to me dictates that it proceeds quickly at first then slows as time progresses (since rate is based on concentration of reactants).  So if it takes 7 days to completely brominate safrole with 48% HBr, at 3.5 days, the yield is >50% ?  Or is the progression linear?


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Bwiti

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48% HBr + P2O5
« Reply #53 on: April 27, 2001, 02:31:00 PM »
If you own Uncle Fester's "Secrets of Methamphetamine Manufacture", then check out pages 166 & 167. Dry HBr is produced by dripping 48% HBr onto phosphorus pentoxide..I'm not sure if that's good news, because I can't find a source for this. The best I could find was phosphorus oxychloride, and I doubt this would be of any use?  :P


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Rhodium

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Re: 48% HBr + P2O5
« Reply #54 on: April 27, 2001, 03:07:00 PM »
48% HBr on POCl3 would result in the water in the acid reacting with the POCl3 like this: POCl3 + 3 H2O => H3PO4 + 3 HCl

With P2O5, the water would react like this: P2O5 + 6 H2O => 2 H3PO4


http://rhodium.lycaeum.org


Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #55 on: April 27, 2001, 04:06:00 PM »
Okeedokee, in classic Agent_Smith fashion, I'm gonna charge ahead with a reaction without accounting for all the parameters.

Heres what my dream will be:

103g 99% NaBr will be dissolved in 169ml of dH2O.  Then, about 103g of my "concentrated H2SO4" will be added. 

This will make 81g or so of HBr in 169ml of H2O is around a 48% sol'n.  There will also be 120g or so of NaHSO4 in sol'n, but I'm not gonna distill, I'm just gonna ignore that.

So then my ~48% HBr will be put in a champagne bottle, and 30g of safrole will be added.  This will be sealed and placed on the swirler for 7 days. 

Good idea, eh?  If all goes well, the mix should turn red and homogenize, as is reported by other similar reactions.


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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #56 on: April 27, 2001, 05:52:00 PM »
Ok, dropped in the H2SO4 to the chilled (~5 degrees C) NaBr sol'n.  It heated itself up and was placed in the freezer to cool it down.  Gas emitted was minimal. 

When removed from freezer, it was a nice clear sol'n, and ~30g sassy was added.

Interestingly, during the sassy addition, a bunch of white precip was noticed about the bottom of the bottle...  A lot!  A small amount of the acid was placed in a beaker, and swirled around, and wherever the acid evap.ed, a crystaline something was left behind... hmmm, NaHSO4 perhaps?  That's probably whats in the bottom of the bottle as well.  No matter, it's still in there when the bottle was sealed, don't forsee any probs.

So now the bottle will be swirled for 7 days or so... so far so good, only that white precip. seems to be non-bueno.

UPDATE:  The bottle showed no reaction when left sit for a few hours.  After it was placed on the swirler, the oil layer appeared to turn red (dark bottle makes it hard to tell, but the oil changed to a dark color) in about 10 minutes.  Also, the HBr seems to have turned cloudy, but this may be suspended oil.  The crystaline suspected-NaHSO4 remained in a solid chunk at the bottom of the bottle, and is unaffected by siwrling.  How does this sound?


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goiterjoe

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Re: Bromosafrole Made Easy
« Reply #57 on: April 28, 2001, 01:57:00 AM »
nice waste of sassafras oil there.  sulfuric acid bonds to 2 molecules, forming Na2SO4.  that probably means you added too much sulfuric acid.  sassafras oil decomposes upon exposure to sulfuric acid, which accounts for the dark red you noticed.  next time distill it.


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Agent_Smith

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Re: Bromosafrole Made Easy
« Reply #58 on: April 28, 2001, 08:52:00 AM »
Damn. But please help me learn here:


sulfuric acid bonds to 2 molecules, forming Na2SO4


I expected it to form a salt, however I didn't think it would be a problem.  Althought I predicted NaHSO4, why do you say Na2SO4?  Not much gas at all was given off in this reaction, and since I used about a mole of everything, there certainly wasn't any gas in an amount similar to the amount of H that'd be released when Na2SO4 was formed. 


that probably means you added too much sulfuric acid


I calc'd a slight excess of NaBr, if anything, I thought I added too little H2SO4.


sassafras oil decomposes upon exposure to sulfuric acid, which accounts for the dark red you noticed


I believe sassafras decomposes on exposure to any strong acid, doesn't it?  I noticed the same dark red color when I bubbled the HBr/HCl mix into it in a previous experiment

If it means anything, the sassy is slowly being digested into the HBr layer, and the HBr layer is turning darker, even after all the oil is left to settle.  That seems like things are progressing correctly...?



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goiterjoe

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Re: Bromosafrole Made Easy
« Reply #59 on: April 28, 2001, 10:03:00 AM »
there will be no hydrogen evolution during this reaction.  it goes as such:

                heat
2NaBr + H2SO4 ---------> 2HBr + Na2SO4
                water

if you calculated a slight excess of NaBr, but used a 1:1 molar ratio to base your calculations on, then there was too much sulfuric.  sulfuric acid forms a diatomic(?) salt with bases, meaning that each molecule of sulfuric bonds to 2 molecules of the base.

as far as sassafras decomposing on exposure to all strong acids, the only two I suspect a problem with would be sulfuric and maybe concentrated hydriodic. 


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