Author Topic: Borane/diborane  (Read 200 times)

Tsathoggua

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Borane/diborane
« on: February 21, 2012, 10:56:08 AM »
According to wikipedia, diborane is a reducing agent on a par with LiAlH4.....

Will it reduce a nitro group to the corresponding amine? and will the presence of the nitro group, being strongly electron-withdrawing, prevent addition across a double bond in the case of a nitroalkene?

One is wondering weather diborane/borane or the adducts with either THF or (one presumes such an adduct forms, given the lone pair of triphenylphosphine and electron-deficiency of (di)borane), P(Ph3) would reduce an aliphatic nitroalkene, as resulting from a knoevanagel/henry condensation rxn. One imagines that the adducts of borane are somewhat easier to handle, particularly in the case of TPP.

Looks like diborane and friends might be fun to play with. And yes, he is aware that B2H6 is pyrophoric. BH3 itself dimerises to diborane, according to wikipedia, quite quickly and is obtainable only in the gaseous state. How quickly does this take place? slowly enough to bugger around with borane itself to attempt formation of adducts with various ligands, or is it so unstable that the rapidity of the dimer formation is such that one will end up with just plain ol' diborane?

Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

Wizard X

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Albert Einstein - "Great ideas often receive violent opposition from mediocre minds."

atara

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Re: Borane/diborane
« Reply #2 on: February 21, 2012, 10:29:11 PM »
Whenever "borane" is cited as a reducing agent, you can be sure that the rxn actually uses diborane. Mono-borane is unknown under ordinary conditions. Diborane itself is produced rapidly from a borohydride and dry phosphoric acid. Be very careful if you attempt that, for obvious reasons.

Diborane reduces nitro groups, not to amines, but to hydroxylamines:

http://en.wikipedia.org/wiki/Reduction_of_nitro_compounds#Reduction_to_hydroxylamines
http://pubs.acs.org/doi/abs/10.1021/jo01020a002

As the hydroxylamines are themselves active, diborane provides an interesting route to a novel class of compounds. Interesting as in explosive. Caveat emptor!

Tsathoggua

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Re: Borane/diborane
« Reply #3 on: February 22, 2012, 12:35:44 AM »
What are interesting as explosives? hydroxylamines? Toady was aware of certain issues with hydroxylamine itself, without any substitution. Or were you speaking of ring-substituted phenyl-subsituted hydroxylamines in particular? Could you PM toady with the info you have about hydroxylamines being trouble in this way? He is aware of the the issues with hydroxylamine itself, but is STRONGLY under the impression that it likes to up in smoke so to speak, while freebase is being distilled, which is particularly the case for those industrial units that suddenly found themselves emerging feet-first from chinese and australian toilets at a very high impulse speed, accompanied by a sound that sounded like 'scraaapppeeekkhhhshitohshitfuckfuckfuckfuckfuckfuckfuckjesusmyspleenbloodychrist!!'

NH3OH HCl is, to the best of his knowledge, quite stable, and nonexplosive.

Question: when the reduction of a nitroalkEne is taking place, is there any chance of rearrangement to an oxime where that double bond is taking place? and will the aliphatic double bond find itself reduced also? At any rate he is more concerned with the fate of his precious aldehydea than any possibility of taking the house out and leaving a smoking crater. He will be working on a gram scale at most.

       Any mention of 2C-D hydroxylamine on the Books?

Toady will of course read that paper...if he can get it (fucking free information!)
Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

RoidRage

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Re: Borane/diborane
« Reply #4 on: February 22, 2012, 02:34:08 AM »
Tsathoggua, here is the paper in question:


Diborane Reduction of Nitro Salts. A New Synthesis of N-Monosubstituted Hydroxylamines

H. Feuer, R. S. Bartlett, B. F. Vincent Jr., R. S. Anderson
J. Org. Chem., 1965, 30 (9), pp 2880–2882
DOI: 10.1021/jo01020a002


Tsathoggua

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Re: Borane/diborane
« Reply #5 on: February 22, 2012, 10:50:36 AM »
Much appreciated, roidrage. And as it would be...there is useful data to be scrounged from the bottom bit of the previous article (not provided...any chance of that article, if you have it? please) , in that borane will reduce an oxime to its amine. Handy.

Roasting boric acid should first, after melting it, dehydrate it to metaboric acid: H3BO3 ? HBO2 + H2O and then to pyroboric acid: 4 HBO2 ? H2B4O7 + H2O  (at 170 C and 300 degrees C respectively. Easily accomplished with a propane torch, driving off the formed moisture in the process.)

It states on wikipedia that further dehydration, to boron trioxide, B2O3 occurs, but not what temperature. Tsathoggua is thinking that presumably, a thermite type reaction would serve to obtain free elemental boron from either the trioxide, or possibly the pyroboric acid itself.

Metal diborides, analogous to carbides such as CaC2? give diborane(6) when protonated. Rxn of HCl with aluminium diboride yields diborane (or rather, borane, as far as he is aware, which then dimerises to diborane(6), which should be watched carefully, as it is both toxic, and pyrophoric.

Toxicity wise...its extremely toxic stuff. NIOSH guidelines state a calculated (from rat, guinea pig and hamster lethal time-weighted lethal concentrations) concentration of 15ppm as immediately dangerous to life or health. Scrubbing shouldn't be too difficult though seeing as its reactive with H2O to form boric acid.

Tsathoggua has more to post on this, but for now he is going to sleep for the day.


Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

RoidRage

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Re: Borane/diborane
« Reply #6 on: February 22, 2012, 12:24:05 PM »
Much appreciated, roidrage. And as it would be...there is useful data to be scrounged from the bottom bit of the previous article (not provided...any chance of that article, if you have it? please)

Which paper are you talking about ? I've reread the thread rapidly and I've only seen the paper I posted being referenced...

salat

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Re: Borane/diborane
« Reply #7 on: February 22, 2012, 04:39:11 PM »
Someone requested a whole lot of reference articles about boron chemistry last year.   There's a thread devoted to it in the reference section separate from normal reference requests.   I don't think the reference section is indexed for searching though so you might have missed them.

The thread is
hxxps://www.thevespiary.org/talk/index.php/topic,1206.0.html

Salat

Salat

Tsathoggua

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Re: Borane/diborane
« Reply #8 on: February 23, 2012, 01:15:47 PM »
Roidrage-I meant the paper you posted. The snippet of the previous article in that journal..its got data on oxime reduction via diborane.

Salat-I will point toady in the direction of that boron chemistry reference thread.

If the reference section isn't indexed for searching...we could do with a way to search it,for those who have access. It surely wouldn't be too difficult a task to code the script for that, would it? for those with experience with PHP etc. Seeing as the only credentials needed are a post count above...what is it? 10? the restriction never affected toady seeing as he posts regularly enough.

One thing he isn't too happy about is those nitronates......we all know what the Na/K salts of nitromethane or nitroethane are like.......Presumably, in solution, those problems are rendered less relevant? Toady is just concerned..because we also know what certain agencies are trying to get him for.

Looking at th NIOSH data, and MSDS sheets for diborane, its way beyond just  'toxic', its bloody vicious stuff, causing pulmonary oedema in a similar manner to phosgene. Anyone know the correct gas mask cartridge type for B2H6? Presumably the risk is at least mitigated by its tendency to be pyrophoric and ignite spontaneously. Is that in response to moist air? or merely right when it hits O2?

This is outside chemistry, of course......but he wouldn't want to poison one of his two sets of neighbours:P (shes cute....so sue me):D so presumably an argon blanket would be needed for bubbling diborane into ether or THF. THF should form a complex with it, should it not? that has the same reducing properties with those nitronate salts?


Ol' toady seems to be having quite the run of luck with his labware aquisitions lately. His new hotplate w/mag stirring arrived today...no more pillar drill now, and no more competing with his father for mechanical stuff involving a hotplate, or competing with himself for his own non-scientific uses for the old, bog standard kitchen type hotplate....not only that, but instead of the stir bar promised for free...the place he bought it from sent him two.

Whilst there is much sense in anonymizing outgoing links, and to govt. websites especially, but....is there ANY point at all in doing so for internal hyperlinks?

Speaking of govt. .....boy is toady ever glad that the weather patterns are screwed up.....he keeps getting cold weather payments for heating bills he doesn't have to pay in the first place, living rent free. More like govt. reagent and glassware payments. He thinks...maybe this one will go on copper salts and hydrazine :D
Nomen mihi Legio est, quia multi sumus

I'm hyperbolic, hypergolic, viral, chiral. So motherfucking twisted my laevo is on the right side.

salat

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Re: Borane/diborane
« Reply #9 on: February 23, 2012, 02:26:08 PM »
is there ANY point at all in doing so for internal hyperlinks?

I haven't been posting a lot lately and am a bit foggy on which rules apply where so don't assume there is any "sense" involved. 

What chemistry I've been attempting lately is breaking the rule books for "weird results"

Salat
Salat

RoidRage

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Re: Borane/diborane
« Reply #10 on: February 23, 2012, 07:22:10 PM »
Roidrage-I meant the paper you posted. The snippet of the previous article in that journal..its got data on oxime reduction via diborane.

Here you go!

The Reduction of Oximes with Diborane. A New Synthesis of N-Monosubstituted Hydroxylamines
H. Feuer, B. F. Vincent Jr., R. S. Bartlett
J. Org. Chem., 1965, 30 (9), pp 2877–2880
DOI: 10.1021/jo01020a001

pyramid

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Re: Borane/diborane
« Reply #11 on: July 02, 2012, 02:20:53 AM »
Hello,

This is the closest thread I could find related to borane. This is not exactly free borane being used but the formation of BH3*THF in situ, which I'm sure many have heard about, but there is hardly any experimental information around. Well, the method works alright and what follows is its application in the synthesis of Aleph, 4-methylthio-2,5-dimethoxyphenylaminopropane. The synthesis of some of the precursors is also included. 2,5-dihydroxythiophenol was made from 5-hydroxy-1,3-benzoxathiol-2-one, this information is available elsewhere. 

The yield on methylation was lower than reported in the Me3PO4 thread because it was done through the night and stirring had stopped as the RM became too thick. At least that is my theory.

2-methylthio-1,4-dimethoxybenzene

In a 250ml 3-neck RBF w/stirbar, condenser, thermometer, Ar inlet and bubbler was added trimethyl phosphate (4eq, 400mmol, 56g) and there was added in a single portion 2,5-dihydroxythiophenol (14.22g, 100mmol) and this stirred until dissolution. A pale yellow solution resulted. In a single portion there was added anhydrous, powdered K2CO3 (3.1eq, 310mmol, 42.84g) which resulted in a very strong exotherm and foaming, but it stayed under control, it should be added in a few portions for safety.
The greenish slurry was heated overnight (~8h) on a boiling water bath. The next day the thick, unstirrable, light brown mass was cooled transferred to a sep funnel with the aid of 250ml H2O.

The mixture was extracted with EtOAc (3x50ml), the organic layer washed with H2O (100ml), 5% aq NaOH (2x 50ml), H2O (2x100ml) and finally brine (50ml). The solvent was filtered through a plug of silica (30g) which removed much color. The orange filtrate was evaporated to give an amber oil weighing 16.19g, MW 184, 88mmol, 88% yield.

4-methylthio-2,5-dimethoxybenzaldehyde

The above substituted benzene was transferred to a 500ml RBF with the help of AcOH (150ml). With stirring there was added hexamethylenetetramine (2eq, 176mmol, 24.64g) and this stirred to dissolution, the flask was heated to about 50C to achieve this. After cooling to 15C in an ice bath there was added dropwise during about 10 minutes conc. H2SO4 (4eq, 352mmol, 34.5g) taking care to not allow clumping which occurs if it is added too quickly.
A thick white ppt formed and the bath was removed, then the flask heated to reflux. The mixture became yellow as reflux temperature was reached, then the mixture foams a little and the ppt dissolved within 10 minutes to give a deep red, yellow staining solution.
After 1 hour of reflux the heat was removed and the still hot mixture poured into H2O (250ml) that was warm and kept stirring. The transfer was completed using additional H2O (50ml). 
After stirring overnight the white precipitate was filtered, washed with H2O (100ml) and portions of cold MeOH (~40ml total).

The resulting product was dried to give 14.67g of white, fine crystals with a slight sulfide/onion odor that is not strong or irritating. MW 212.26, 78.5% yield. Mp 100-103C

4-methylthio-2,5-dimethoxyphenylnitropropene

To a 100ml 3-neck RBF containing a stirbar and fitted with thermometer, condenser and drying tube was added 4-methylthio-2,5-dimethoxybenzaldehyde (5.30g, 25mmol) followed by iPrOH (25ml) and this stirred and heated to 60C to dissolution. There was then added  nitroethane (2eq, 50mmol, 3.58ml), AcOH (800ul) and finally ethylenediamine (170ul, ~10mol%).
This solution was stirred at 75-80C for 1 hour and 10 minutes (ppt occurs at 1h mark) then heat turned off and the flask left stirring (minus water bath, just over the plate) for a further 30 mins.
The flask was then cooled in the freezer for 30 minutes and the crystals filtered and washed with cold iPrOH.

Recrystallization is probably not necessary as the mp is spot on at this point at 137-138C. 
The "crude yield" was 5.867g, MW 269.31, 87% yield. The orange product was recrystallized from 150ml iPrOH together with several ml EtOAc to bring all solids into solution, and hot filtered through a cotton plug. After cooling overnight and standing in the freezer for an hour the product is filtered, washed with some iPrOH and dried to give 5.154g of orange needles, mp the same. 76.5% yield after reX.

4-methylthio-2,5-dimethoxyphenylaminopropane hydrochloride

The following reaction was conducted under argon in a closed system (bubbler) with a tube venting outside to remove any free borane that escapes and to prevent an explosion. The dry iodine can be made by melting crude I2 made from an iodide salt under conc H2SO4, decanting the acid and sublimating. 

A dry, 250ml 3-neck RBF containing a stirbar was fitted with thermometer, condenser, drying tube, bubbler, Ar inlet and septa and the setup flame dried under a stream of Ar. There was added THF (anhydrous, dist. from LiAlH4, 20ml) and NaBH4 (4.6eq, 46mmol, 1.74g) and this stirred in a salt ice bath to below 0C.
Once at this temperature, dry Iodine (2eq, 20mmol, 2.54g) In THF (15ml) was added carefully, dropwise, over 30 minutes keeping the temp at or below 0C.
Once the addition was complete, the white mixture was stirred without cooling for 30 minutes longer. After this time a solution of the nitropropene (10mmol, 2.69g) in THF (35ml used, with occasional warming to keep in solution) was added during 10 minutes at RT, then the mixture heated to reflux for 5h at which point the color is gone. 

Very carefully via syringe there was added dropwise with good stirring/cooling H2O (50ml). At first it is added slowly dropwise, letting the vigorous reaction settle. Then there is added over a few minutes a mixture of conc HCl in H2O (10/40ml) which results in some bubbling. This is then stirred at reflux for 2h to destroy the complex, the THF evaporated in vacuo, and the aqueous solution washed with PhMe (2x 15ml) which removed minimal color. The solution was then basified with excess NaOH solution which precipitated a white product, and it was extracted with PhMe (3x 50ml) and the organic layer washed with H2O (2x 100ml) then brine (30ml).
The slightly cloudy organic layer was filtered though 2cm of Na2SO4 and the solvent removed in vacuo. The thick pale yellow oil was taken in 20ml 96% EtOH, neutralized with conc HCl and diluted with Et2O (80ml) and left for 3h at RT.
The crystals were freed and triturated, left another 30 minutes and filtered, washing with 80ml Et2O. There remained 1.176g of fine, snow white crystals. MW HCl salt: 277.81, 4.2mmol, 42% yield, Mp 200-203 (lit 204-205), bioactivity confirmed.

--------

So it works, yield is not huge, but I have seen many procedures using BF3*Et2O with NaBH4 that do not yield too high (40-60%). Just another method to apply if you need. It would be very interesting to try a similar procedure utilizing H2SO4 instead of iodine which also reportedly can create BH3*THF.

lomg john

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Re: Borane/diborane
« Reply #12 on: September 25, 2012, 07:47:45 PM »
This is from elsewhere, but it mentions boron trifloride in ether:

Synthesis of phenylalkylamines by reduction of nitrostyrenes
Amphetamine HCl and the 1-phenylpropan-2-hydroxylamine HCl impurity were prepared using the method of Varma and Kabalka

NaBH 4 (1.10 g, 29.1 mmol, 4.75 eq) and BF 3-Et2O (5.22 g, 36.8 mmol, 6 eq) in THF (66 ml) were stirred at 0°C for 10 min. At
room temperature 2-nitro-1-phenylprop-1-ene (3a) (1.0 g, 6.13 mmol, 1 eq) in THF (15 ml) was then added dropwise and the reaction mixture heated at re?ux for 3 h. The reaction mixture was left to cool at room temperature then water (75 ml), and HCl 1M (75 ml) were added. The reaction mixture was then heated at 80-85°C for 3h. The aqueous layer was washed with diethyl ether; sodium hydroxide was added until the solution was basic, NaCl solution was added and the product was extracted into diethyl ether and dried (MgSO 4). Evaporation of the solvent gave pale yellow oil which was dissolved in propan-2-ol, acidi?ed and diluted with diethyl ether. Evaporation gave a yellow oil (0.82 g, 4.78 mmol, 78%). 1H NMR spectroscopy showed the presence of amphetamine 80%) and 1-phenylpropan-2-hydroxylamine HCl (20%)

letters

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Re: Borane/diborane
« Reply #13 on: September 26, 2012, 08:33:28 AM »
Varma and Kabalka's NaBH4/BF3 to generate BH3 species insitu works adequately for a variety of nitrostyrenes.
by choosing the correct stoichiometry you can either reduce all the way to the amine or partially to the n-hydroxylamine.
Nitrogen/Argon atmosphere's a must for good yields.

)

Adrenaline

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Re: Borane/diborane
« Reply #14 on: September 26, 2012, 09:56:34 AM »
This is an extract from Strike`s "Total Synthesis".

lomg john

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Re: Borane/diborane
« Reply #15 on: January 13, 2013, 09:12:06 PM »
So how can we make BH3-THF without BF 3-Et2O (Boron Trifluoride in ether) safely.