Condensing benzaldehyde

[Boomer]

Looking for things to do with my newly acquired benzaldehyde, in the Rhodium achieve there was found a synth for phenyl-2-nitropropene (P2NP) going like this:

 

Benzaldehyde + nitroethane ---(methylamine catalyst)---> phenyl-2-nitropropene + water.

 

It says after 6 hours of heating an oil will form, which on cooling overnight gives yellow crystals with mp 60-65C.

There is also a follow-up like:

 

P2NP ---(urushibara Ni + Al/HCl + H2SO4)---> amphetamine sulfate.

 

These reactions are interesting, but I am not a meth cook, so instead of EtNO2 I used MeNO2 for the condensation, staying perfectly legal. The second modification was using MeNH2.HCl + NaOH instead of MeNH2(aq). I used 25 mmol aldehyde, 35 mol nitroalkane and 10mmol catalyst (prep. in 2ml water) in 30ml denat. spirit, reacting at 65C with overhead stirring.

 

The problem is instead of 6 hours, the reaction took only 30 minutes; and instead of an oil it gave a suspension of some brown gunk. On cooling and filtering, it gave 2.3 grams of a dark brown shit (literally) that solidifies at RT and gets somewhat kneadable in the warm hand. It has a slight but hard to describe odour. Every attempt to get crystals via different solvents has so far failed, except for a little (presumably) NaCl left from the prep. of the aq. methylamine catalyst. I suspect the m.p. to be ca. 20C lower than for the nitropropene analogue, and with some impurities this would explain the shit-like consistency. All I know is that the reaction did went to completion, since the marzipan smell was completely gone in the end.

 

Does anybody know whether phenethylamine is easier to recognise that phenyl-2-nitroethene (which is what I think should have come out of the condensation)? I might try some reductions (Fe/HCl, Al/Hg) on it. The amine should form salts, so be easy to purify to get a melting point etc.

BTW PEA is inactive in man, legal to buy, and without having other groups from the start (3,4,5-trimethoxy anyone?), it is not a drug precursor. This just had to be said, I’m not going to blow up my brain instead of some steel plates any time soon.

 

Oh, anyone ever made ethyl bromide? Gotta put my sodium nitrite to some use… (joke)

[Boomer]

Not a pyro topic eh? Well this is general chem after all. Is capsaicin pyro? OK it does burn...

 

And will the NaOH lead to the alcohol, even if it was barely sufficient to convert the amine HCl? It should all be NaCl, since the MeNH2.HCl was in slight excess.

 

 

But anyway, thanks for the tips.

BTW making a *non-active* compound was the whole purpose of this experiment. Otherwise this would belong on the hive, wetdreams etc!

[Nitric63]

I agree that it's a porblem with using MeNH2.HCl and NaOH as the catalyst. It does seem a little strange that it's a problem if you're certain the NaOH is fully neutralized. Still though, the brown gunk sounds like what I got once when I heated a Henry reaction involving anisaldehyde(p-methoxybenzaldehyde). Normal procedure for a Henry reaction is slow addition of the NaOH to a well cooled solution of the aldehyde and nitroalkane in alcohol. Very high yields of quite pure nitrostyrene may be obtained with a carefully done Henry reaction.

 

Zn/HCl makes for a nice, clean reducing method for nitrostyrenes to PEAs. I've gotten yields of 70% or more. From what I've read, it doesn't work on alpha-methyl nitrostyrenes(which would reduce to amphetamines) though.

 

I have also synthed EtBr from ethanol(well, denatured alcohol anyway), H2SO4, and NaBr. Yields were very unsatisfactory. I blame the very low purity of the denatured alcohol. Using iPOH to prepare iPBr, my yields were much higher(first and only attempt). Using pure EtOH(water is an acceptable impurity), high yields ought be achievable.

[Douchermann]

This isn't a pyro topic, but before/if this gets locked:

It shouldn't get locked as he explained that he is not trying to make meth, he changed one of the precoursers to keep from doing that.

 

This is actually an interesting reaction, I looked into it multiple times. I also looked into the difficult synthesis of P2P

Benzyl chloride + alkali cyanide ----> Benzyl Cyanide

Benzyl Cyanide + Sodium Ethoxide + Ethyl acetate ---> a-Phenylacetoacetonitrile

a-PAA + H2SO4 ----> Phenyl-2-Propanone (P2P)

 

The first reaction must be completely anhydrous. No, I don't want to make meth. I just want to try that synthesis because it looks challenging. Or at least procuring all of the precursors will be hard.

[Boomer]

Bright colours eh? Finally the brown shit dried out anough to crumble, and you can see there's definitely some yellow/orange crystals in it.

 

Encouraged by this, I tried Al/Hg reduction anyway (Fe/AcOH or Zn/HCl will NOT give a ketone since I started with MeNO2. No secondary nitro - no keto group unfortunately).

Giving the foil lots of time in the HgCl2 sln, I barely had time to rinse it in H2O and alcohol before it started steaming and nearly burned my hand. (BTW can this shit ignite?)

 

After 5 hours of bubbling at 60C (IPA, external heat), and subsequently little sleep, it is currently waiting for separation from the alu sludge. The 'clear yellow overhead' is present, but a vac buchner is not. Happy filtering!

 

**Double good day ** This should be 100 posts and my first Al/Hg on a single day. Anyone donate some piperonyl acetone for the party?

[Boomer]

You were right, no PEA came out of it as far as I can tell. The post-reduction mix was basified, extracted with Et2O/pentane, solvents evaporated to leave brown gunk again. Trying to dissolve some amine out with 10% HCl, then evaporating left a yellow residue, but no crystals whatever.

 

Is it even possible to get a HCl salt of PEA this way? I remember the non-methylated phenylisopropylamine is hard to obtain as the hydrochloride, even through gassing in dry ether. That's why the sulphate salt is the common form.

 

What about a "reductions" thread? I still don't get it that on one and the same substrate, Hg/Al does shit, Zn/HCl gives the ketone, and Urushibara Ni the amine, not to mention Hi/P and the classics Pt/Pd... confusing stuff, even on paper !

[Boomer]

Tried it the cold way with NaOH. Found this on OrgSyn:

 

1. Procedure

In a 6-l. wide-mouthed bottle, packed in a pail with a freezing mixture of ice and salt and fitted with a mechanical stirrer, a thermometer, and a separatory funnel, are placed 305 g. (5 moles) of nitromethane (p. 401), 530 g. (5 moles) of benzaldehyde (Note 1), and 1000 cc. of methyl alcohol. A solution of sodium hydroxide is prepared by dissolving 210 g. (5.25 moles) of sodium hydroxide in approximately an equal volume of water and cooling. It is then diluted to 500 cc. with ice and water, poured into the funnel, and added with stirring to the nitromethane mixture at such a rate that the temperature is kept at 10–15° (Note 2) and (Note 3).

A bulky white precipitate forms rapidly during the addition of the alkali. The mixture gets so thick that stirring becomes difficult and it may be advisable to add 100 cc. more of methyl alcohol. After fifteen minutes' standing, the pasty mass is converted to a clear solution by the addition of 3–3.5 l. of ice water containing crushed ice (Note 4). Hydrochloric acid (made by diluting 1000 cc. of concentrated hydrochloric acid with 1500 cc. of water) is placed in a 15-l. mixing jar and the reaction mixture run into this from the separatory funnel at such a rate that the stream just fails to break into drops (Note 5). A pale yellow crystalline mass separates almost immediately as the alkaline solution comes in contact with the acid. After the stirring is stopped, the solid settles to the bottom of the jar. The major part of the cloudy liquid layer is removed by decantation, and the residue filtered by suction and washed with water until free from chlorides. This product is freed from all but a negligible amount of water by melting in a beaker immersed in hot water. Two layers are formed, and on cooling again the lower layer of nitrostyrene freezes; the water may then be poured off. The crude nitrostyrene is purified by dissolving in 420 cc. of hot ethyl alcohol (Note 6), filtering the solution into a warm suction flask to remove solid impurities, and then cooling until crystallization is complete. The yield of crude product melting at 56–58° is 650–670 g. The yield of recrystallized nitrostyrene melting sharply at 57–58° is 600–620 g. (80–83 per cent of the theoretical amount). The whole procedure, including purification, can be done in a day.

 

The only difference I made was using 50 mmol (1/100 amounts), and using distilled nitro fuel for both the MeOH and MeNO2, which led to about a quarter more volume at step one due to too little nitro content. Guess what: *NO* white precipitate formed, and on diluting with ice water, instead of a clear solution it got milky with oil drops. How can 1/4th more volume prevent crystallisation, if otherwise you get a thick slurry

 

I did the second step (excess HCl crush) anyway, but instead of yellow crystals a yellow oil separated. Is that the nitro alcohol then, or just unreacted BzHO? The marzipan smell did *not* disappear as it did using amine catalyst. Above text also states:

 

Note 5. The alkaline solution must be added slowly to the acid, for the reverse procedure always forms an oil containing a saturated nitro alcohol. A large excess of acid at room temperature is used, conditions which facilitate the formation of the desired unsaturated nitro compound.

 

But I *did* add it slowly, drop wise from a syringe with fine needle. Strange...

[Boomer]

Did an Al/Hg in IPA on the liquid anyway, after basifying extracted with toluene (dried with freshly heated CaCl2 before), added HCl and evapped to a thiick syrup. Then 2 days in a desicator over sulfuric gave a yellow rystal slush, washing successively with 3, 2 and 1ml acetone, then 1ml ether gave snow white crystals!

 

I hope it's enough to get a m.p., looks like 150mg at most! Where should PEA.HCl be in that respect?