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Author: Subject: preparation of α-nitronaphthalene
Magpie
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[*] posted on 18-5-2016 at 20:42
preparation of α-nitronaphthalene


Introduction
I used the procedure given in reference 1 to synthesize 11.8g of α-nitronapthalene. This procedure employs mixing naphthalene with acetic acid (as solvent) then adding the nitrating acid a step at a time while controlling the temperature:

nitronaphthalene.gif - 3kB

Prior to using this procedure I tried the one in Vogel (ref 2) but this turned out to be a disaster. More will be said about that under Discussion below.

Experimental
20g of naphthalene (Enoz Old-Fashioned Mothballs) was lightly ground in a mortar. This was added to 60ml of glacial acetic acid in a 2-neck 250ml RBF. This was then set up with an overhead mixer and thermocouple as shown below:

synthesis of a-nitronaphthalene.jpg - 129kB
Synthesis of α-nitronaphthalene

A second picture shows the controls and readouts for the stepper motor mixer and the temperature indicator (°C in red):

instrument room for a-nitronaphthalene synthesis.jpg - 196kB
mixer and thermocouple control/readouts

a. acid addition
The nitrating acid was made up using 30ml of con sulfuric acid (Rooto) mixed with 14ml of con nitric acid (70%). This was cooled to room temperature then added 2ml at a time to the RBF while stirring the product at 203.5 rpm. A cooling bath was at the ready beneath the RBF but was never needed. The temperature was to be kept at 60°-70°C. By the time all the acid had been added the temperature had just reached 70°C.


b. heating period followed by a cold water quench

The product was then kept at 70°-80°C for 30 minutes using a hot water bath. Following this the product was allowed to cool to ~40°C then dumped into 200ml of cold water. As α-nitronaphthalene has a mp of ~58°C and a density of 1.223 it settled on the bottom of the beaker as a dark brown oil. More will be said about this color in the Discussion below. A picture of this is shown below:

a-nitronaphthalene dumped in cold water.jpg - 115kB
α-nitronapthalene dumped in cold water

c. grinding followed by water washing
The solidified oil was removed in large chunks and placed in a mortar for grinding:

solidified a-nitronaphthalene from oil.jpg - 125kB
solidified α-nitronaphthalene from oil

After grinding the product was washed on a 7cm Buchner funnel 4-5 times with cold water. It was then placed on a plate to dry overnight:

a-nitronaphthalene ground and washed.jpg - 155kB
α-nitronaphthalene ground and washed

The mp of this crude product was was unacceptably low so I recrystallized it in 275ml of 90% ethanol. The recrystallized product is shown below where you can see that the color is much improved. Ideally it would be a light yellow.

a-nitronaphthalene recrystalized.jpg - 162kB
α-nitronaphthalene recrystalized

Results
After the first solidification the yield was 24.9g, or 92.1%. However the mp of 45°C, and the color, indicated that it was significantly contaminated. Therefore a recrystallization was performed. This yielded a product with a much improved mp of 51°-53°C. However, the yield then dropped to 11.8g, or 43.7%.

The mp for α-nitronaphthalene indicated in internet sources varies considerably from 53°-57°C (Sigma-Aldrich) to 61°-63°C (Jean-Claude Bradley).

Discussion & Conclusions
As indicated above I had earlier tried the synthesis found in Vogel's 3rd ed. This procedure specified addition of finely ground naphthalene to the nitrating acid a little at a time followed by vigorous shaking of the RBF. This approach is faulty from at least three aspects: (1) finely grinding smelly naphthalene is a PITA even though I used a coffee grinder instead of an open mortar, (2) the nitrating acid is always in excess, and (3) it is difficult to monitor and control the temperature when shaking the RBF. There is significant heat of reaction.

By far the biggest problem is item (2), ie, having the nitrating acid in excess throughout the reaction. This resulted in most of my product being dinitronaphthalene. This was confirmed by high mps of the product. The J. of Chem. Ed. procedure recognizes this liability by using a solvent and adding the nitrating acid a little at a time. With my apparatus the temperature was easily controlled to the procedure specifications.

The only downside I can see for the J. of Chem. Ed. procedure is the formation of tar. This discolored the product and made its purification wasteful. Still, I much prefer it over the procedure in Vogel, and it gave me the intended product.

edit:

I should note that the Vogel procedure also produced some tar. This may be an unavoidable consequence when using con sulfuric acid. Tars tend to be taken up in oils. And there was some of this dark solidified oil produced in the Vogel procedure. I just didn't recognize at the time what this was and discarded it.

References
1. “CONGO RED,” by E. R. Kline, Journal of Chemical Education, pp. 129-130, (1938), (see DJF90's post in this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=65706#...)
2. “α-NITRONAPHTHALENE,” Textbook of Practical Organic Chemistry, by A. I. Vogel, 3rd Ed, (1958), p. 526. (see forum library)

Questions, suggestions, and comments are welcomed.











[Edited on 19-5-2016 by Magpie]




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[*] posted on 19-5-2016 at 02:13


Very nice!
As for multiple nitration, since the nitro group is a -M group, maybe this would need a higher temperature than the mono-nitration (this definitely happens for benzene, but probably not for naphthalene, which has a more extended conjugation that can make it more prone to have a second nitration). Which is a shame, because monitoring temperature would have been fairly easy if it made any difference. In that case...

...as you said, adding nitric acid slowly and in stoichiometric amounts would hopefully lead to reaction with unreacted naphthalene, somewhat more electron-rich than the product.


While 1-nitration is clearly favoured for naphthalene, is the proportion of 2-nitrated product lower than, say, 5%?




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[*] posted on 19-5-2016 at 07:04


Quote: Originally posted by Eddygp  


While 1-nitration is clearly favoured for naphthalene, is the proportion of 2-nitrated product lower than, say, 5%?


I don't think there is much dinitro product. The J. Chem Ed article says that the yield of α-nitro product is very near quantitative. My yield of 92.1% before recrystalization confirms this.

There was a minor amount of strange looking (fluffy, fibrous) light yellow by-product, however. I removed this from the supernate from the quench water and discarded it.





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[*] posted on 19-5-2016 at 23:36


I ran the Vogel procedure a number of years ago and I ended up with a fair amount of dinitronaphthalene isomers which had a melting point above 200 Celsius. Any plans for the 1-nitronaphthalene? I have been doing some work with heptafluoro-2-naphthylamine, somewhat scary due to the bad reputation of 2-napthylamine for being a carcinogen.



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[*] posted on 20-5-2016 at 08:17


benzylchloride1 thanks for this confirmation of my troubles with Vogel's procedure.

Yes, I will be making napthionic acid, then Congo Red. I will avoid the scary α-naphthylamine intermediate by using the Piria reaction (ref 2 of my OP).




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[*] posted on 20-5-2016 at 10:34


I mean, before recrystallisation the "extra" yield is not 1-nitronaphthalene, because otherwise it would have neatly recrystallised with the rest of it. Whatever it is, it has to be either initial reagents (doubtful) or some side reaction (my guesses: 1,x-dinitronaphthalene and 2-nitronaphthalene).



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[*] posted on 20-5-2016 at 10:43


Yes, I suppose there is some minor amount of 2-nitrophthalene. How much? I have no clue.

I attribute the loss in yield at recrystallization to α-nitronaphthalene still in the supernate.

For the extraction I heated the solution up to about 40°C (no higher to avoid oil formation) then placed the flask in ice water.

I still have the supernate and may place it in the freezer to see if I can recover more of the α-.

[Edited on 20-5-2016 by Magpie]




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[*] posted on 21-5-2016 at 07:57


Nice experimental. If you were running the experiment a few times, you could likely recombine all of the supernate and then concentrate to recover a good bit more material. I have found that often getting a second crop if much tougher with only one batch. Or if you ran the remaining material through a quick plug of silica gel, often that will all you to remove the greasy crud by washing with hexane, which might not elute the product, then waste with ethyl acetate and you can likely elute the nitronaphthalene without all of the other more polar materials, like dinitros and polymers. I find that often doing a quick silca gel plug gives me very nice recrystallization yields or I can sometimes crystallize most of the material, and then recover the rest with a simple column. Just depends how valuable the material is. In many cases, 40-50% yield is fine and sufficient, if the SM are all cheap.
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[*] posted on 21-5-2016 at 12:15


Thanks Dr Bob for those tips on removing contaminants. I have silica gel but it is only flower shop grade. I do have some chromatography grade aluminum oxide (neutral). Might that work as well?

I placed the supernate in my freezer (-20°C) for ~2hrs and recovered a 2nd crop as shown below. This weighed 3.9g which would increase my yield from 43.7% to 58.1%. It has an mp of 49°-50°C so is not as pure as the 1st crop. It has a somewhat darker color also I think.

2nd crop of a-nitronaphthalene).jpg - 119kB




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[*] posted on 21-5-2016 at 13:20


I did this same prep a couple of weeks ago(based on the same paper), on a 2x scale. The crude product looked essentially like dirt, so I recrystallized a small portion from ethanol first to see how well that worked. What followed was several hours screwing around, trying various ways of recrystallizing it to prevent it from oiling out(originally I thought that a bit of the product which was oiling out was tar), and trying to maximize recovery. I ended up with four different products, all different colors and MPs, totaling around 35% yield, and another 10-15g of dark solid product which oiled out and needs to be recrystallized again. I believe that methanol is a slightly better solvent than ethanol due to it's lower boiling point, but Purification of Laboratory Chemicals 6<sup>th</sup> Edition recommends heptane or ethanol. The procedure on PrepChem is interesting, as it recommends xylene or high boiling ligroin. Seems like I've got another several hours of trying various solvents to see.:(

Let me know how the Piria reaction goes. I've tried it once already with some of the crude product to get a feel for it. After two hours of refluxing, the nitro compound had fully dissolved, so I cooled and acidified it, but nothing came out of solution. There was a substantial color change though, to a darker red color. I've been meaning to try it again, but haven't had time as of yet, I was planning on doing it next week sometime if I have time.




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[*] posted on 21-5-2016 at 15:22


Quote: Originally posted by gdflp  
I ended up with four different products, all different colors and MPs, totaling around 35% yield, and another 10-15g of dark solid product which oiled out and needs to be recrystallized again.


Now that is unexpected!! How pure was the naphthalene that you used?




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[*] posted on 21-5-2016 at 15:26


In the Kline procedure for Congo Red it says to use the solidified oil directly as precursor for the naphthionic acid. Based on this it seems that the α-nitronaphthalene purity is not that important. But further on it states that the yield of naphthionic acid will only be in the 20-30% range. Therefore I decided it would likely be a good plan to do some purification of the α-nitronaphthalene.



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[*] posted on 21-5-2016 at 20:57


Quote: Originally posted by Eddygp  
Quote: Originally posted by gdflp  
I ended up with four different products, all different colors and MPs, totaling around 35% yield, and another 10-15g of dark solid product which oiled out and needs to be recrystallized again.


Now that is unexpected!! How pure was the naphthalene that you used?

I just used crushed moth balls, I didn't bother to recrystallize them(though naphthalene crystallizations are really pretty). The different colored product was due to varying amounts of solidified oil(which is drastically darker than the crystals)/impurities in the product from the different temperatures of recrystallization, solvents, etc.




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[*] posted on 8-6-2016 at 10:58


A long time ago, (about 23 years ago), I did perform nitration of mothbal naphtalene with HNO3 69% only.
Thus without H2SO4.

I did put the ball into a test tube, and I added about 4 times the volume of HNO3 69%.
The mothbal was floating on top (test tube was thus about half full)

Then I allowed a common 75W lightbulb (yes one of those old tungsten wire ones) to heat it up from above by holding the tube close to the lamp (with a woden clamp).
When molten the naphtalene was a clear transparent liquid (so T° was above 80°C (the mp of Naphtalene) but below the boiling point of 69% HNO3).
I did put a cap on top when hot to avoid too much smell of the sublimating naphtalene.
While heating the HNO3 was turning the clear phase above it yellow...then after a good while (1 hour), it turned deeper yellow.

I let the all test tube cool down and repeated the heating of the same test tube from time to time one day on two days, then cooled again.

After about 3 treatments (one week --> about 3 hours), the solid was nearly orange and had a very distinctive smell totaly different from initial naphtalene...from which smell had disapeared (or was covered/masked).
This orange waxy solid was heavier than the initial naphtalene...almost sinking into the used HNO3.
It was very different solid...with a different kind of crystalinity so to speak.

It was washed with boiling water and hot bicarbonate water and dried then used with KClO3/NaClO3 for Cheddite experiments.

What is interesting here is that just like for my toluen experiment (yielding nitrotoluen and nitrobenzoic acid), no H2SO4 nor concentrated HNO3 was used ...only 69% azeotropic HNO3!
Nothing else could have been formed since only mononitration can occur in such media and naphtalene is like benzene quite resistant to oxydation (less than C6H6 of course but more than C6H5-CH3).

Sadly I didn't perform at that time a sublimation test to be sure there was no more naphtalene present inthere nor did I made a melting point testing.

If I have time and no ex-girlfriend at home (sadly can take monthes), I want to redo that fast experiment and confirm those old datas with more detailled results.


[Edited on 8-6-2016 by PHILOU Zrealone]




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[*] posted on 18-6-2016 at 06:33


The napthalene mothballs have finally arrived !

Let's see if i can replicate Magpie's experiment.




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[*] posted on 28-6-2016 at 12:13


Sorry for the long delay - I've been meaning to comment on this for while now but haven't had the opportunity to find sufficient time to write a comprehensive and coherent reply.

Quote: Originally posted by Magpie  

The nitrating acid was made up using 30ml of con sulfuric acid (Rooto) mixed with 14ml of con nitric acid (70%). This was cooled to room temperature then added 2ml at a time to the RBF while stirring the product at 203.5 rpm. A cooling bath was at the ready beneath the RBF but was never needed. The temperature was to be kept at 60°-70°C. By the time all the acid had been added the temperature had just reached 70°C.

I have two trains of thought on this, but both involve dropwise addition of the nitrating acid rather than portionwise addition. The first idea is to perform the addition with cooling in an ice bath. This may minimise/eliminate the formation of tarry material, but may allow for accumulation of nitrating acid and potential (although unlikely) exothermic runaway when cooling is removed. This leads me to the second idea - to pre-heat the naphthalene suspension/solution before dropwise addition of nitrating acid (further comment on this later). I'm not sure if/how this might affect the formation of tarry material.

Quote: Originally posted by Magpie  

The product was then kept at 70°-80°C for 30 minutes using a hot water bath. Following this the product was allowed to cool to ~40°C then dumped into 200ml of cold water. As α-nitronaphthalene has a mp of ~58°C and a density of 1.223 it settled on the bottom of the beaker as a dark brown oil.

Did you check for the complete consumption of starting material before quenching the reaction? I'm not sure if you have access to TLC plates, but I think that would be the easiest and most appropriate way. You say that you had a dark brown oil separate out after drowning the reaction mixture in water, but make no mention of solidification on cooling? I assume this was an accidental omission, but should be added for clarity.

Quote: Originally posted by Magpie  

After grinding the product was washed on a 7cm Buchner funnel 4-5 times with cold water. It was then placed on a plate to dry overnight

Given that you have access to mechanical stirring, you might consider adopting the workup provided on PrepChem (melting the crude product under water, agitating, allowing to settle and cool, then decant the aqueous supernatant and repeat). I suspect you'll find it more efficient at removing residual acids compared to washing on the filter, but I appreciate it is more involved. If you confirm complete consumption of naphthalene prior to quenching, then you can omit the steam distillation. I would certainly advice recrystallisation; more of that below.

Quote: Originally posted by Magpie  

The recrystallized product is shown below where you can see that the color is much improved. Ideally it would be a light yellow.

...yielded a product with a much improved mp of 51°-53°C. However, the yield then dropped to 11.8g, or 43.7%. The mp for α-nitronaphthalene indicated in internet sources varies considerably from 53°-57°C (Sigma-Aldrich) to 61°-63°C (Jean-Claude Bradley).

I'd recommend including a carbon treatment into the recrystallisation from ethanol. You should observe a suitable improvement in the colour of your product. As the product is a low-melting solid, I'd dissolve it in minimal solvent around the expected melting point (should minimise/prevent oiling out), add 0.1 wt of activated carbon, heat to reflux for a short period and filter whilst still hot. As the solution cools to saturation point (around the expected meltng point) you should observe crystallisation rather than oiling out. You may also consider the use of aqueous alcohol to improve the recovery of the material, assuming solubility in water is lower than that in ethanol. You may also consider the use of isopropanol as a substitute for ethanol, either with or without the presence of water.

The difference in literature values might be explained by different polymorphs. You might be able to check this by looking at the crystal structures under a microscope (e.g. platelets, needles, prisms). Sometimes it is found that the use of a different solvent for recrystallisation affords a different polymorph. It may be that the lower value you have observed is obtained when ethanol is used as solvent, but the higher value (as mentioned on the PrepChem page) is observed when xylenes or ligroin is used. It certainly wouldn't surprise me if this was the case. When you're making a melting point determination, you're really looking for the sharpness of the transition as opposed to the actual value, which can depend on rate of heating, accuracy of thermometer etc. That being said, there are some compounds known to give broad, poorly-defined melting points, but I don't think this is one of them.

Quote: Originally posted by Magpie  

...finely grinding smelly naphthalene is a PITA even though I used a coffee grinder instead of an open mortar...

I'd address this issue by recrystallising the mothballs. This will ensure that the naphthalene is of good purity before use, and also provides a finely divided material (assuming you stir during cooling). Alternatively, if the reaction is preheated before addition of the nitrating acid then the solubility of naphthalene should be high enough to afford full dissolution (wikipedia states 111g/100g AcOH at 60 *C)

A final point to address is one that PHILOU Zrealone has brought up - it might not even be necessary to use sulfuric acid and it may afford a cleaner reaction/less tarry material. Certainly worth a go on small scale, and I'd probably recommend employing the "preheated method" that I suggested above in this case.

[Edited on 28-6-2016 by DJF90]
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[*] posted on 28-6-2016 at 13:43



Quote: Originally posted by DJF90  

Did you check for the complete consumption of starting material before quenching the reaction? I'm not sure if you have access to TLC plates, but I think that would be the easiest and most appropriate way. You say that you had a dark brown oil separate out after drowning the reaction mixture in water, but make no mention of solidification on cooling? I assume this was an accidental omission, but should be added for clarity.


I don't have TLC plates.
The oil did solidify, as recorded in my notebook.

Quote: Originally posted by Magpie  

The recrystallized product is shown below where you can see that the color is much improved. Ideally it would be a light yellow.


Quote: Originally posted by DJF90  

I'd recommend including a carbon treatment into the recrystallisation from ethanol. You should observe a suitable improvement in the colour of your product. As the product is a low-melting solid, I'd dissolve it in minimal solvent around the expected melting point (should minimise/prevent oiling out), add 0.1 wt of activated carbon, heat to reflux for a short period and filter whilst still hot. As the solution cools to saturation point (around the expected meltng point) you should observe crystallisation rather than oiling out. You may also consider the use of aqueous alcohol to improve the recovery of the material, assuming solubility in water is lower than that in ethanol. You may also consider the use of isopropanol as a substitute for ethanol, either with or without the presence of water.



I agree that efforts to obtain a pure product here are worthwhile as long as yield is acceptable.


Quote: Originally posted by Magpie  

...finely grinding smelly naphthalene is a PITA even though I used a coffee grinder instead of an open mortar...


Quote: Originally posted by DJF90  

I'd address this issue by recrystallising the mothballs. This will ensure that the naphthalene is of good purity before use, and also provides a finely divided material (assuming you stir during cooling). Alternatively, if the reaction is preheated before addition of the nitrating acid then the solubility of naphthalene should be high enough to afford full dissolution (wikipedia states 111g/100g AcOH at 60 *C)


Enoz claims 99.95% purity and the mothballs are dazzling white crystals.





[Edited on 28-6-2016 by Magpie]




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