Ok I think this thread got a bit sidetracked because I just wasn't able to shut up (as usual, but where else can you talk to someone about OUR interests?) So I believe its time to post something reasonable.
nitrostyrene->amine with Pd/C/amm formate CTH pseudo-one-pot style, this is how SWIA does it:
100mmol (16,3 gram) nitrostyrene (P2NP, HIGH purity)
150mmol (5,7 gr) borohydride (NaBH
4)
115 ml IPA
45 ml H
2O
some xx ml 60% acetic acid (didn't measure)
~2 ml GAA
500mmol (~31g) NH
4COOH
4,2 grams Pd/C 10% (bought, not homemade)
a)
Borohydride reduction First SWIA dissolved 5,7g borohydride in 115ml IPA and 45ml water with good stirring. After it had dissolved he added his nitropropene in small portions so that rxn didn't become too violent (gas/heat evolution made this necessary). The addition took 20 minutes, every portion nitropropene caused a color change to yellow which faded to almost white very quickly. After the addition everything was stirred for another 30 minutes, then ~5ml water was added, followed by small amounts of 60% AcOH (to destroy excess borohydride) until gas evolution had ceased completely and the mixture had become almost colorless, then a last 2ml was added. The rxn mixture was decanted from some white, sticky borate goo at the bottom, saturated with NaCl and the resulting upper alcohol layer (slightly yellowish) was separated and washed again with brine.
b)
Pd/C CTH Next, SWIA weighed out 4,2 grams of 10% Pd/C (one half of it was already used and reactivated, and the other half was fresh from the bottle), put them in a 250ml RBF (bit too small
), added the IPA/nitropropane solution gotten from the borohydride reduction and introduced ~31 grams ammonium formate. This was stirred violently for 5 minutes to dissolve as much formate as possible and then a reflux condenser was attached and temp. was slowly raised to 65°C on a water bath. When this temp was reached 45 minutes had passed already, but the rxn had just started to evolve lots of CO
2 and apparently hydrogenation had just begun, so SWIA decided to let it run at least another 45 mins. In the end, he waited until gas evolution had nearly ceased (to be sure hydrogenation was complete), took 3 hours in total (from additon of formate until heat was removed and the condenser was disconnected). After 1,5hrs 2ml GAA were added to prevent bicarbonate clogging in the condenser. After rxn had cooled down to RT it was filtered (very nice, clear, bright yellow soln, smelled alot ammonia) and saturated with NaCl. The resulting alcohol layer was separated, aeq. phase extracted once with 50ml toluene and the extraction and alc. layer combined, washed with sat. NaOH and then brine in order to remove ammonia (smelled still like household cleaner
). Then, SHOCK! SWIAs only drying agent at hand is CaCl
2, not suited for drying amines, nor alcohols. Well, SWIA thought, perhaps the water will bee removed azeotropically when I distill away some solvent (thinking of dean-stark traps), so he cooled, added solid NaCl until soln. became clear, and distilled almost all solvent away and was left with a dark yellow, oily residue with a strong amine smell.. (perhaps vac. dist. would've been better here, before applying heat the color was WAY brighter, obvioulsy something got decomposed; but SWIA has only ONE tap, no pump, hence he can only distill, reflux OR vac.filter, none of these at the same time
)
The residue was dissolved in 4x its volume IPA, H
2SO
4 98% was added in 0,1ml aliquots, everytime the solution got slurried with crystals SWIA added a few ml's Et2O and filtered. The crystals were washed with more Et2O (2x) until they had a shiny white color. Yield: 5,4 grams (phenyl-2-aminopropane)
2*H
2SO
4, 29% of theory (based on starting material phenyl-2-nitropropene) But SWIA suspects yields would've been higher if he had used REALLY anhydrous solvents for crystallization...
And he's very sure that without his attempt to dry a solution by azeotrope distillation, the salt obtained would've been very pure (without washing), as the crude amine soln. had a very pale yellow color (really nice appearance for freebase!)
But more important: it works simple, fast and WITHOUT having to isolate the intermediate nitropropane!
Next time SWIA will try it with KCOOH to see if rxn time can perhaps be shortened..
greetz A
Oh I forgot: in SWIAs opinion there was no need to do an A/B because normally, after ABing/extracting his non-polar has the same color like the post-rxn solution he got this time, so he assumed that there were very few side products (besides they don't really interfer when making the sulfate - opposed to water
). And furthermore the very strong ammonia smell convinced SWIA that the mixtr. was already basic enough to release its goodies upon Xtraction.. with KCOOH that's perhaps not the case - or is it perhaps decomposed to KOH? Then there would bee no need to basify, too, right?
S. Ram & R.E. Ehrenkaufer report the use of a somewhat similar procedure: "..the catalyst was removed by filtration through a celite pad and washed with dry methanol (10ml). The filtrate was evaporated either under reduced or at normal pressure. The resulting residue was triturated with water (10-25ml), product was extracted with an organic solvent (i.e. ether, DCM or chloroform) and dried over Na
2SO
4. The organic layer on evaporation gave the desired amino derivative.
Some products were directly converted into the HCl-salt with ethereal-HCl without evaporation of ether layer."
(from:
A General Procedure for Mild and Rapid Reduction of Alipathic and Aromatic Nitro Compounds Using Ammonium Formate as a Catalytic Hydrogen Transfer Agent, Tetrahedron Letters 25(32), 3415-3418 (1984))
And the idea of azeotropically drying a solution with an apropriate solvent (toluene, benzene etc.) isn't that wierd like SWIA first thought: its in this thread, Barium uses it here
Post 384333
(Barium: "Dare I say quantitative yield", Novel Discourse) to remove water from post-cth mixture with toluene, but he used a rotovap, seems as if normal distillation does no good to freebase amphetamines in this case...
Barium, do you think that not acidifying before removing the solvent/alcohol reduces yield? (->steam distillation?)
Or perhaps basifying everything bee4 the first extraction would be good? SWIA was under the impression that the mixtr. was nearly saturated with ammonia, but I think the yield could be raised quite a bit with some modifications... freebase looked REALLY nice, clean, bright - BEFORE SWIA reduced the volume of its solution...
and I think the procedure could surely be modified to give good purity AND good yields - but how?
To Ganesha: Scrape matchbooks, hm?
