Sciencemadness Discussion Board - Synthesis of an omega-nitrostyrene

Synthesis of an omega-nitrostyrene

DiceTumbler - 8-3-2015 at 15:27

Hi all,

So today I decided to finally perform some real life practical chemistry. I'm quite well educated theoretically in Organic Chemistry, but as I'm an autodidact I never have had access to a real lab. My shiny new Chinese glassware came in and I wanted to do something exciting. In March's organic chemistry textbook I found a lead for a very interesting (different!) synthesis of phenylacetone going trough a omega-nitrostyrene intermediate (phenyl-2-nitropropene). I do not own a licence for synthesizing prohibited compound, but since reading Shulgin's work I've always be extremely interested by them, hence I focus on the precursors, which are here legal to synthesize and own.

March directed me to Vogel and so I grabbed my copy and looked it up (it is also online here: https://www.erowid.org/archive/rhodium/chemistry/nitrostyren...). The synthesis seemed reasonable easy for me to perform (note the synthesis in Vogel uses nitromethane but I figured it would work with nitroethane too). Just an ordinary nitroaldol reaction (Henry reaction) catalyzed by base. I guess that the resulting alcohol is easily dehydrated because of the conjugating effect between the benzene ring (and the carbonyl group) and the resulting olefin (the double bond).

Unfortunately, things didn't go so well as I had hoped :-). Practical things can look deceptively easy to the theorist!

I kept a journal for the synthesis to refer back to. Following is the transcription. I would greatly appreciate if you more practical guys could take a look at it and help me discover what went wrong (and why of course!).

00:00 - 53 mL of HCl (72.07g) were pipetted and deluded with 73 mL of water to obtain a 125 mL 4.00 molar solution. Slight irritation was noticed while proceeding, but they soon faded. Also noticed a bit of white dense fog coming from the stock solution (heavier than air).
00:25 - Added 31g of benzaldehyde (should have been 27g or 0.25 mole) and 19g of nitroethane to a clean three necked flask. The smell of the benzaldehyde was pleasant but overwhelming. 80 mL of methanol was added to the flask as solvent.
01:15 - After fumbling a bit with the saturated saline ice water solution that was prepared in advance (temperature around -23 °C) it was added to a glass bowl in which the three necked flask was emerged. A thermometer adapter was inserted which read 0 °C (i.e. the benzaldehyde, nitroethane, methanol mixture). 12g of NaOH was dissolved into an ice water mixture of around 150-200 mL (this should have been less but the ice melted rather quickly and I was uncertain about its temperature).
01:35 - The NaOH was added dropwise to the reaction mixture from a dropping funnel. The temperature remained in the 10-15 °C region.

By this time I knew I probably screwed up since no bulky white precipitate formed. The mixture was definitely white and cloudy but not viscous at all. I continued to see what I could make of it.

01:55 - The mixture was added to about 200 mL of ice water and then run from a dropping funnel into the previously prepared HCl solution (125 mL 4.00 molar solution). The mixture became blueish instead of forming the expected light orange precipitate. Over time the solution became progressively more orange. Little oily orange bubbles were noticed, almost like a oil in water emulsion. These settled to the bottom over time. I was also noticed that the benzaldehyde odor was still present (strongly).

Then the experiment was stopped since no orange precipitate appeared and the benzaldehyde odor made me uncomfortable. I did however check the pH of the orange oily bubbles (after decanting the cloudy liquid off) and it was < 1. So I thought that maybe neutralizing it would yield at least some product and I added some NaOH to it (I should have gone more slowly, but after a few drops it was already on pH > 12). Now some orange suspension became visible (no longer oily). However vacuum filtration did not leave any product so the product was probably still dissolved. I cleaned everything up.

So what went wrong? Also I the benzaldehyde smell was almost unbearable (the experiment was not done in a fumehood since I cannot afford one, but instead in a large well ventilated area). I wouldn't have thought that the benzaldehyde odor would be so pungent, then again the odor threshold is about 0.42 ppm so yeah. So two other question are:

- Do these benzaldehyde vapors pose any danger? I pursued this experiment since nothing needed to be heated (in fact cooling was even applied) and I judged that vapors wouldn't really be an issue (I also did not smell the methanol or nitroethane)
- And how about the HCl vapor I noticed at 00:00?

Again, I would really appreciate if someone with more experience in practical organic chemistry could gave me some insightful answers to my question.

With nothing but love,
DiceTumbler.

Sulaiman - 8-3-2015 at 17:25

Hello, I'm new here and also fairly new to chemistry,
I would say your first mistake was to change the recipe,
I've noticed that even apparently simple substitutions can cause unexpected results,
maybe if you try the 'correct' ingredients first to test your experimental skills
and familiarise yourself with what should happen at each stage
then use your theoretical knowledge to modify the procedure?
I'm way too inexperienced and have negligible organic chemistry skills
(I hope to slowly improve) and no knowledge of this particular reaction
so my comments are just general observations.
Other more experienced chemists here may give better guidance.

You mentioned 72.07g of HCl = 53 ml ... density = 1.36
What kind of HCl were you using that has a density of 1.36?

I'm also curious how you got your ice/salt bath to -23C?
(I don't think that adding salt to ice from a domestic freezer would achieve this, though I'm often wrong
or did you cool the salt/ice mixture in a freezer after mixing?)

[Edited on 9-3-2015 by Sulaiman]

CuReUS - 9-3-2015 at 08:28

Quote: Originally posted by DiceTumbler

So what went wrong?

this

Quote:

I pursued this experiment since nothing needed to be heated (in fact cooling was even applied)

why are you trying to come up with your own synthesis when this has been done since time immemorial.just google nitropropene and you will get the synthesis
this thread might help you(notice that they use an aliphatic amine as catalyst)
http://www.sciencemadness.org/talk/viewthread.php?tid=30621

- Do these benzaldehyde vapors pose any danger?
this question has a mixed opinion
http://en.wikipedia.org/wiki/Benzaldehyde#Safety
drug related questions are generally not tolerated in SM.But the reason I am helping you is because I really appreciate it that you did some practical chemistry instead of just reading books.There are many other organic reactions that you can try out
don't feel sad if you failed.I also screwed up my first nitration

DJF90 - 9-3-2015 at 08:54

Quote: Originally posted by CuReUS

Quote: Originally posted by DiceTumbler

So what went wrong?

this

Quote:

I pursued this experiment since nothing needed to be heated (in fact cooling was even applied)

why are you trying to come up with your own synthesis when this has been done since time immemorial.

Actually, it looks pretty similar to the OrgSyn prep, with the OP substituting nitroethane for nitromethane. See http://www.orgsyn.org/demo.aspx?prep=cv1p0413

[Edited on 9-3-2015 by DJF90]

DiceTumbler - 9-3-2015 at 09:29

Quote: Originally posted by CuReUS

Quote:

I pursued this experiment since nothing needed to be heated (in fact cooling was even applied)

Thanks for your reaction. The synthesis was taken from Vogel, which is a very well established book in practical organic chemistry (arguable THE book). The only adaption I made was swap nitromethane for nitroethane as I saw no objection to that and reduce the stoichiometric amount from 1 mole to 0.25 mole, which I think is not unreasonable considering it indeed went wrong and so I wasted less reagent.

Sure it is a drug related synthesis, but I don't see any objection arising from that. I'm fascinated with pharmaceuticals and their chemistry but would never consider synthesizing them without a proper license (Shulgin had a DEA licence people!). Pharmaceutics is arguable (after petrochemical chemistry) the most important field within organic chemistry. I loved reading "An Introduction to Medicinal Chemistry" by Patrick and am still looking for more advanced stuff about the subject.

Bronstein - 10-3-2015 at 00:05

I have done this synthesis with nitromethane, and it did indeed crystallize almost immediately as I dripped it into the HCl. But your product, phenylnitropropene is (I heard) a bit hard to crystallize, and maybe it just oiled out instead of precipitating. Next time try to put the oil into some alcohol and keep it in a freezer for some days and see if it crystallizes.

CuReUS - 10-3-2015 at 01:27

I checked up on the reaction after my last post and I am very sorry for my reply.you are right,this reaction is done without any heating
but in the source I referred to,the molarity of the NaOH used was 5 M ,whereas you have used 1.5 M,so the mistake could lie there
here is the procedure,from strike's total synthesis 2

Quote:

In Pihkal, Alexander Shulgin mentions that the preparation of
MDP-nitropropene can be carried out in cold methanol with aque-
ous sodium hydroxide as the base. In fact, this method is even
more reliable, and gives higher yields than the other method ad-
vocated by the dear doctor in his book.

15g of piperonal was dissolved in 40ml of methanol under stirring
in a 250ml Erlenmeyer flask. When all of the piperonal had dis-
solved, 7.1g nitroethane was added to the solution. The flask was
put in a ice/salt-bath with magnetic stirring, and when the tem- perature of the solution had dropped to 0°C, an ice-cold solution of
4g of NaOH in 20ml dH20 was added at such a rate that tem-
perature never rose above 10°C.
A white precipitate formed at the
bottom of the flask during this addition, which was broken up with
a glass rod. The stirring was continued for another hour, while the
temperature of the solution was never allowed to rise above 5°C,
and at the end of this time, 100 ml of ice-cold dH20 was added to
the solution, which caused even more precipitation of white solid.

The whole slurry was poured into 100 ml of ice-cold 2M HCI solu-
tion in a 500ml Erlenmeyer flask, which was gently swirled, and
there was a slight bubbling and fizzing, with the color of the solu-
tion shifting from white to blue to green to yellow in under a min-
ute. Quite spectacular! When the fizzing had subsided, the
solution was once again placed in an ice-bath with magnetic stir-
ring. When the temperature had dropped to about 5°C, the solu-
tion was clear with yellow granules of crude product at the bottom.
The granules were filtered with suction, and recrystallized from
IPA. After air-drying, the canary-yellow crystals amounted to a
yield of 65-70% of theory.

This nitropropene should be used within a week, or stored in the
cold, as the color fades to a slight orange over a couple of weeks
in room temperature, which is a sign of decomposition.

[Edited on 10-3-2015 by CuReUS]

DiceTumbler - 10-3-2015 at 05:53

Quote: Originally posted by Bronstein

I have done this synthesis with nitromethane, and it did indeed crystallize almost immediately as I dripped it into the HCl. But your product, phenylnitropropene is (I heard) a bit hard to crystallize, and maybe it just oiled out instead of precipitating. Next time try to put the oil into some alcohol and keep it in a freezer for some days and see if it crystallizes.

Thanks. Yes I heard these things too. How do the reaction conditions have influence on whether a certain product remains "oily" or is crystallized. I'm guessing that the white precipitate did not form because I used much more ice water than was stated to begin with. Also the benzaldehyde odor was still strongly present, perhaps used too much benzaldehyde? But I've done the calculations correctly it seems, so IDK for sure.

Chemosynthesis - 10-3-2015 at 07:43

First, I want to say you clearly are using good texts, seem to have a well kept notebook, and do appear educated in the theory as you state. Commendable. It was also good preparatory practice to work in micro scale.

In the absence of any experience with this specific reaction, I do suspect you have made a theoretical oversight, though your intuition seems pretty sound. I would first compare your reaction molarity with that of your source material and consider the impact on kinetics. Now consider how this correlates with the hue you noted in lieu of what was expected. This may be compounded by a second issue. If you go back through the mechanism of your reaction with LeChatelier's Principle in mind, you may see something stick out at you. These two conjectures may lead to a hypothesis that, in conjunction with the excess of benzaldehyde, can explain the olfactory intensity and lack of expected observations.

DiceTumbler - 10-3-2015 at 13:36

Quote: Originally posted by Chemosynthesis

First, I want to say you clearly are using good texts, seem to have a well kept notebook, and do appear educated in the theory as you state. Commendable. It was also good preparatory practice to work in micro scale.

In the absence of any experience with this specific reaction, I do suspect you have made a theoretical oversight, though your intuition seems pretty sound. I would first compare your reaction molarity with that of your source material and consider the impact on kinetics. Now consider how this correlates with the hue you noted in lieu of what was expected. This may be compounded by a second issue. If you go back through the mechanism of your reaction with LeChatelier's Principle in mind, you may see something stick out at you. These two conjectures may lead to a hypothesis that, in conjunction with the excess of benzaldehyde, can explain the olfactory intensity and lack of expected observations.

Thank-you for your words. I do not exactly understand what you are saying in your second paragraph? I don't really see any objection why a nitroaldol reaction could not happen. I cannot imagine that the steric hindrance of the nitromethane versus nitroethane would render this reaction impossible. Could you please clarify? Must thanks in advance!

Chemosynthesis - 10-3-2015 at 13:59

My suspicion is that by diluting the reaction, you reduced the kinetics and may have needed to run your reaction for a longer duration. This could account for the time lag in observing an orange tint rather than instantaneously. This should be simple to estimate with a plug and chug rate equation. Additionally, in a Henry nitroaldol, you are eliminating water (which you are clearly aware of). With this in mind, if you have a large excess of water in your reaction vessel already, this will shift your equilibrium if not removed.

It seems likely some product was formed at both stages, but small impurities can dramatically influence color, so how much the yield may have been impacted is difficult to say without some more data.

zed - 10-3-2015 at 14:09

Dice Tumbler,

Now, about 40 years ago, when the world of chemistry was a less encumbered with regulations, I attempted the synthesis you described. It doesn't work. The why of it, I didn't trouble with much. I just moved on. Lots of easy, low tech, high yield ways to produce Nitropropenylbenzenes.

As to the current regulatory climate, I feel I should comment. In the USA, and many other countries.....attempting to combine benzaldehyde and nitroethane, as you did...is not legal. Benzaldehyde is a listed material. Nitroethane is a listed material. And, combining the two to produce Beta-nitropropenyl-benzene (an amphetamine or p2p precursor) well, that could land you in the slammer.

If you wish to continue your experiments, I suggest you find some non-regulated analog to play with. Vanillin might produce one, but I couldn't swear to it. O-methoxybenzaldehyde used to be OK, but that may have changed. Since, O-methoxy-methamphetamine, was OTC, and therefore not illegal to make, its precursors were not illegal to make. Long ago, this material was withdrawn from the over the counter designation, and laws may have been changed accordingly. Or, not. I Don't know.

As for the dangers of Benzaldehyde. Small amounts added to poppyseed muffin batter, produce a very tasty almond flavored muffin. Likewise, a small amount when added to stewed apricots, produces almond flavored apricots. A very tasty treat.

Effects of ingestion of Nitroethane can be pretty serious. So, it ain't the snakes that you can easily see, that usually bite you.

[Edited on 10-3-2015 by zed]

DiceTumbler - 10-3-2015 at 15:24

Quote: Originally posted by zed

Dice Tumbler,

Now, about 40 years ago, when the world of chemistry was a less encumbered with regulations, I attempted the synthesis you described. It doesn't work. The why of it, I didn't trouble with much. I just moved on. Lots of easy, low tech, high yield ways to produce Nitropropenylbenzenes.

As to the current regulatory climate, I feel I should comment. In the USA, and many other countries.....attempting to combine benzaldehyde and nitroethane, as you did...is not legal. Benzaldehyde is a listed material. Nitroethane is a listed material. And, combining the two to produce Beta-nitropropenyl-benzene (an amphetamine or p2p precursor) well, that could land you in the slammer.

If you wish to continue your experiments, I suggest you find some non-regulated analog to play with. Vanillin might produce one, but I couldn't swear to it. O-methoxybenzaldehyde used to be OK, but that may have changed. Since, O-methoxy-methamphetamine, was OTC, and therefore not illegal to make, its precursors were not illegal to make. Long ago, this material was withdrawn from the over the counter designation, and laws may have been changed accordingly. Or, not. I Don't know.

As for the dangers of Benzaldehyde. Small amounts added to poppyseed muffin batter, produce a very tasty almond flavored muffin. Likewise, a small amount when added to stewed apricots, produces almond flavored apricots. A very tasty treat.

Effects of ingestion of Nitroethane can be pretty serious. So, it ain't the snakes that you can easily see, that usually bite you.
[Edited on 10-3-2015 by zed]

Thanks Zed for your comment. I live in Western Europe (so not the DEA ruled US) currently and benzaldehyde and nitroethane can be easily purchased by any chemical supplier. Even in large quantities. I have no intentions of reducing this nitrostyrene to amphetamine. I'm just researching some precursors, which to my best of knowledge are legal here to have, albeit suspicious (they probably won't believe I'm only interested as far as I can go legally, but it is strictly speaking not illegal here).

Chemosynthesis - 10-3-2015 at 15:51

As for future chemical health concerns, other than the obligatory perusal (preferably hardcopied) MSDS for each reagent, here is an example of health information on benzaldehyde with good citations (toxnet, ATSDR, EPA)
http://www.odh.ohio.gov/~/media/ODH/ASSETS/Files/eh/HAS/Benz...

And before anyone corrects me, I meant elimination of water through the nitroaldol, not in. It's important for me to be specific with my language, and dehydration is not part of the actual Henry reaction itself, though often appended.

CuReUS - 10-3-2015 at 23:41

you didn't pay attention to the procedure I posted.It clearly says to keep the temp below 10'C

Quote: Originally posted by DiceTumbler

01:35 - The NaOH was added dropwise to the reaction mixture from a dropping funnel. The temperature remained in the 10-15 °C region.

Quote:

4g of NaOH in 20ml dH20 was added at such a rate that tem-
perature never rose above 10°C..... The stirring was continued for another hour, while the temperature of the solution was never allowed to rise above 5°C

DJF90 - 11-3-2015 at 00:02

Quote: Originally posted by CuReUS

you didn't pay attention to the procedure I posted.It clearly says to keep the temp below 10'C

Quote: Originally posted by DiceTumbler

01:35 - The NaOH was added dropwise to the reaction mixture from a dropping funnel. The temperature remained in the 10-15 °C region.

Quote:

And you didn't pay attention to the OrgSyn procedure I linked to, which is peer reviewed and thus replicable. There are even footnotes discussing temperature control during the addition (2, 3).

I have to say that the biggest problem with the OP's attempt to perform the reaction was the lack of reaction monitoring. This is a,common problem with less experienced chemists, assuming that because the reference says the reaction is done in an hour, it is. In reality the chemist should use this as a guideline for when to IPC the reaction (TLC or otherwise) in order to check for completion. If starting material is found to remain, the chemist can then make an informed decision as to whether the reaction needs to be left for longer/heated/ reagents recharged or whether the residual starting material can be removed during work-up or purification.

CuReUS - 12-3-2015 at 01:33

nitroethane is harder to deprotonate than nitromethane,so maybe a stronger conc of base should be used.

PkA of MeNO₂ is 10.2 whereas for EtNO₂ it is 8.6,so just follow the new procedure instead of fighting over the reliability of the source
and DFJ90,you still haven't told me how to make propylene oxide from propylene glycol

DJF90 - 12-3-2015 at 02:30

Quote: Originally posted by CuReUS

nitroethane is harder to deprotonate than nitromethane,so maybe a stronger conc of base should be used.

There is hardly a difference between the two nitroalkanes in terms of acidity. Sodium hydroxide is more than sufficient for this, and even sodium carbonate would likely be adequate. Concentration is a minor factor here - its acid/base strength thats important.

Quote: Originally posted by CuReUS

PkA of MeNO₂ is 10.2 whereas for EtNO₂ it is 8.6

This bit surprised me. I believed that the pKa of nitromethane was about 10, and expected nitroethane to be similar. A quick pKa predicion using MarvinSketch gave 8.3 for nitromethane, and 8.7 for nitroethane. This is about the difference in acidity that I was expecting, but the absolute value is less than what I expected based on pKa tables. I currently cannot account for this discrepancy.

Quote: Originally posted by CuReUS

just follow the new procedure instead of fighting over the reliability of the source

What new procedure? As a chemist I know I'd rather do a reaction that is reliable and from a respectable source that struggle trying to reproduce something that is flawed. Been there, done that. Even experimentals from journal articles can be difficult to reproduce, see BlogSyn for examples. At least OrgSyn experimentals have already been independantly reproduced, and in my honest opinion represent one of the best sources of experimental data for the (amatuer) chemist.

Quote: Originally posted by CuReUS

DFJ90,you still haven't told me how to make propylene oxide from propylene glycol

I didn't realise you had asked. I'd suggest something akin to www.orgsyn.org/demo.aspx?prep=cv1p0294 for the conversion to chlorohydrin (regioselectivity doesnt matter due to subsequent epoxide formation) and www.orgsyn.org/demo.aspx?prep=cv1p0233 for conversion to the epoxide.

morganbw - 12-3-2015 at 11:59

Gentlemen, please do not piss on this thread, it is refreshing.

CuReUS - 13-3-2015 at 01:30

Quote:

and even sodium carbonate would likely be adequate

no my dear,sodium carbonate wont be able to dehydrate the nitro aldol formed

Quote: Originally posted by DJF90

I didn't realise you had asked

http://www.sciencemadness.org/talk/viewthread.php?tid=61390&...

so,your method of making propylene oxide is 2 step,so is my method of making allyl bromide,so I guess we are even
also,I think in your method,when you are going to use propylene glycol,there is going to be some dehydration too

[Edited on 13-3-2015 by CuReUS]

DJF90 - 13-3-2015 at 08:26

Quote: Originally posted by CuReUS

Quote:

and even sodium carbonate would likely be adequate

no my dear,sodium carbonate wont be able to dehydrate the nitro aldol formed

I was talking about deprotonation of the nitroalkane; we were discussing pKas, remember...

Quote: Originally posted by CuReUS

so,your method of making propylene oxide is 2 step,so is my method of making allyl bromide,so I guess we are even
also,I think in your method,when you are going to use propylene glycol,there is going to be some dehydration too

It was simply a suggestion on how to make propylene oxide from the glycol. A Reaxys search may provide a more elegant method.

Dehydration does not appear to be a competing pathway when glycerol is used, and I suspect propylene glycol will behave similarly.

CuReUS - 13-3-2015 at 20:57

that's what,DFJ90 ,when glycerol is used,there is an OH on every carbon,so it will not be that easy to dehydrate,but that's not the case with propylene glycol.but I may be wrong,so please correct me

Chemosynthesis - 13-3-2015 at 21:33

You usually get hydroxyacetone and acrolein, but what does this have to do with the original thread?

Darkstar - 14-3-2015 at 05:23

Quote: Originally posted by Chemosynthesis

You usually get hydroxyacetone and acrolein

I'm guessing it's also possible for propylene glycol to undergo a similar pinacol rearrangement/hydride shift under dehydrating conditions to give acetone and propanal?

Quote:

what does this have to do with the original thread?

Nothing. It was a reference to their discussion in that 1-(2-Thienyl)acetone? thread.

[Edited on 3-14-2015 by Darkstar]

Chemosynthesis - 14-3-2015 at 12:43

Ah. Perhaps we should move discussion back there? A mod could move relevant posts or post portions, perhaps. CuReUS, why bring this up here? I would try to stick to the OP and relevant discussion creep, out of respect for the thread starter. This doesn't seem relevant.

DarkStar, good catch. If I were paying attention to context I wouldn't have mentioned it. Applied Catalysis A: General
27 December 2012, Vol.449:59–68, doi:10.1016/j.apcata.2012.09.034

Given that DFJ was citing what became an industrial process (Kirk-Othmer) that probably doesn't have any real scaling issues, I would lean to that. It can't have too many issues. Full disclosure: I was considering using it for something else awhile back.

If something less conventional were desired, perhaps US 4410501 with peroxide would be utilizable, though I still find the chlorohydrin process more desirable.

I don't think CuReUS' concern on yields or byproducts is going to be a big deal.
"Meanwhile it was proven that high reaction tempera- ture was necessary for the dehydration of glycerol, since no acrolein formation was detected at 250oC, 34.5 MPa using sulfuric acid as a catalyst [6]."
Journal of Environmental Protection, 2010, 1, 201-205 1 doi:10.4236/jep.2010.12024
Comparison with US 2501042 A, if believable, using HCl and sulfuric, requires high temperatures for 1,2 propylene glycol.

Uh, back to the original topic? Comparing the two threads, it is great that DiceTumbler did requisite research prior to starting his reaction. I wish more members came as prepared, or at least open to being as prepared with a little pointing towards some chemistry resource threads.

morganbw - 15-3-2015 at 10:24

@DiceTumbler
Post up if you have success please. Interesting stuff.
I would try the same except it does not seem legal here.