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Author: Subject: Synthesis of isatin from indigo via ozone, HNO3 and others
neutrino
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[*] posted on 13-10-2004 at 19:16


Picric acid is not a liquid at room temperature, although there's a chance you might have a solution of it. I think that the odd results are due to not using enough acid. If the pH = 3, either you had some incredible stroke of luck and get exactly stoichiometric amounts, or (much more likely) there was a lack of acid. With some inorganic reactions at least, you need at least one reactant in slight excess before the products become visible at all.
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[*] posted on 13-10-2004 at 19:38


I read somewhere that the principal product of nitration of indigo is picric acid. I don't know under which conditions that is supposed to hold, but that was one of the reasons why I purchased indigo a long time ago.
However, looking at your conditions, you may have gotten a di or mono nitrophenol.
I don't think you can argue on the basis of solubility, as phenol nitration on its own doesnt result in the immediate precipitation of picric acid. This in fact only happens after dilution with ice-cold water.

Anway, this thread is merged with the existing isatin threads (this is now the THIRD ONE). Miamicanes, there is no NEED to create a new thread for every other experimental method you try. Unless there are masses of posts on each method (therefore justifying a thread in each case).

[Edited on 14-10-2004 by chemoleo]




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[*] posted on 13-10-2004 at 20:24


Well, in this case, I thought it justified a new thread because it's an entirely different reaction (vs ozone... same ultimate goal, different set of problems and complications).

So... COLD water increases the likelihood/quantity of picric acid? Sigh. I thought it was the other way around (keeping the reaction slow, cold, and dilute to minimize the amount of picric acid produced).

Does anybody actually have a college textbook (probably pre-1965, when colleges wouldn't have been scared shitless of liability and would have actually let students do it) that describes in some reasonable detail how to properly oxidize indigo using nitric acid?

Confession: this was actually my third attempt with nitric acid. The first ended with the destruction of $25 or so worth of glassware because I got impatient, went overboard with the non-dilute nitric acid, and wound up with a mini-volcano-in-a-flask spewing black tar above what was obvious picric acid. The second time around, I was too cautious, over-diluted the nitric acid, and ended up with what felt like a ticking time bomb (90% dilute nitric acid, 10% indigo sludge, pH of .95, with the flask sitting in a bowl of ice water. I chickened out and dumped the solution after mulling what might happen once the solution hit room temperature with that much acid waiting to spring into action...). This time I tried to go for the happy medium... minimal water, 70% acid straight from the bottle, but only adding it one drop at a time. With occasional squirts of cold water into the solution if the reaction seemed to be speeding up too much, and getting ready to form volcano #2 & ruin another flask.

[Edited on 14-10-2004 by miamicanes]
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[*] posted on 13-10-2004 at 20:34


No, what I was saying is that the reaction conditions (highly acidic, hot) don't favour the potential precipitation of picric acid, and mono/di-nitro derivatives. It only becomes apparent when it is diluted with ice cold water, afaik.
Therefore you cannot judge whether you got picric acid (or not) just by looking at whether it is soluble in your reaction mixture or not. That's all.
What is '90% dilute nitric acid'? Is it in fact 10% (10 g HNO3 and 90 g H2O)?
Anyway.. I am sure there are some patents/preps around as to how to prepare picric acid from indigo. I guess these are the conditions you'd exactly try to avoid!!!!!!

PS if everyone started posting a new thread for each method for the same final product (i.e. sodium), we'd have at least 5 times the number of threads we have now. Honestly, do you think that'd make sense?

PPS Interesting anyway that you got a runaway. I can't remember this happening when I tried it. But at least it didn't explode. I think someone even did a study once to deliberatly cause runaways, and see whether one'd achieve detonation. They never did. So don't worry too much. Runaway, yes (lots of NO2, heat etc), but detonation, NO (at least these guys couldn't trigger it, neither did anyone seem to in the existing forums). So it looks like you are physically safe, as long as you are upwind.

[Edited on 14-10-2004 by chemoleo]




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[*] posted on 13-10-2004 at 21:00


Quote:
'90% dilute nitric acid'?

about 10mL of indigo + water, 90mL of 70%/16M nitric acid diluted 10:1 with water.

It was mainly the pH reading of .95 that spooked me. I think the straight nitric acid was less acidic (1.65, from what I remember). I kind of envisioned a metaphorical scene in a cheezy action film where somebody finds himself in a pit filled with groggy crocodiles on ice... rapidly melting ice. And really, really hungry crocodiles...

So... do you think the isatin is just in solution with whatever the oily-looking-but-highly-miscible-yellow-orange liquid is, or do you think the Isatin precipitated out, then ended up getting destroyed by continued exposure to the oxidant (like it apparently did with the ozone attempt)?

[Edited on 14-10-2004 by miamicanes]
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[*] posted on 14-10-2004 at 00:46


Indigo plus nitric or chromic acid apparently produces isatin plus anthranilic acid, plus a bunch of other degradation and condensation products.

This is probably why isatin has not been commercially produced from indigo anytime in the twentieth century, because other syntheses are much more practical.

You probably are producing isatin plus a mix of other stuff. To answer the question of what to do next probably have to go back to the original 19th-century German references or other papers based on them.

This project does seem like mad, mad science given that you can buy 100g of isatin online for less than you already spent on the experiment.

http://www.sciencelab.com/page/S/PVAR/10416/SLI1291
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[*] posted on 14-10-2004 at 04:34


Working with an indigo sludge and adding drop wise is not ideal. More likley to over oxidise, you need a suspension in a large volume of nitric acid and as soon as you start to see any yellow forming stop adding and filter the moment its complete.

How fine a powder is the indigo you are working with btw? Since both indigo and isatin are insoluable I would think youd need a very very fine powder.

You could also think about trying cold very dilute and *neutral* potassium permanganate as an oxidising agent.

I would bet sizable amounts a large fraction of your yellow oil is isatin with enough impurities to render it liquid. Try a purification step.

You dont need to be scared of the nitration mixture exploding, NO2 is the nastiest thing it will do, have good ventillation (and you NEED good ventillation). You're jumpy mainly due to lack of lab experience I think.

Isatin isnt made from indigo industrially because indigo is made from isatin like compounds so its production would be a step backwards. The preperation interest is only historical becuase its how the structure of indigo was determined well enough for chemical syntheses to be devised, before this it had to be extracted at great cost from plants.

I'm wrong about being unable to repair the carbon chain in anthanillic acid without cyanides. Treatment with chloroacetic acid forms phenylglycine-o-carboxlylic acid and then fusion with alkali forms a carbon-carbon bond giveing indoxylic acid. Loss of carbon dioxide from this forms indoxyl which then goes rapidly back to indigo.
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[*] posted on 14-10-2004 at 04:53


Quote:
This project does seem like mad, mad science given that you can buy 100g of isatin online for less than you already spent on the experiment.


I tried placing an order from their "other" site (labdepotinc.com) for 500g and got (several days later) an email claiming that it wasn't available and the order was cancelled. I interpreted that as, "we won't sell it to individuals, but don't want to look like assholes so we'll just lie and offer a lame excuse instead."

I'm happy to say that I have found someone apparently willing to sell it, but I'm holding off on dismantling the lab until I have it in my hands. In the meantime, I'd still like to get it successfully synthesized at least once, if only to have something to show for all of my efforts ;)
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[*] posted on 15-10-2004 at 23:17


Victory at last! Well... kind of.

I finally got visible, measurable Isatin. That's the good news.

After 4 grams of indigotin, around 5mL of 70%/16M nitric acid, and a little over 4 hours of work (not counting drying time for the filter paper), I ended up with 0.15g/Isatin. That's the bad news.

Well... it's a start. Next time, I'll double the nitric acid and let it work longer. I ended up with a LOT of sludge due to unoxidized indigo.

How I did it:

measured 4g indigotin into pyrex measuring cup (I wasn't about to risk another $8 flask this time around).

Slowly added approximately 5mL of straight 70%/16M nitric acid a few drops at a time until the powder no longer looked blue. In retrospect, it was still quite blue... but it looked greenish brown at the time because of the layer of oxidized indigotin floating on top.

Added 500mL distilled sodium-free water and brought to a rolling boil.

Filtered slightly-less-than-boiling mixture through #2 whatman into buechner funnel and filter flask w/vacuum pump. Prayed to multiple deities that the black ooze wouldn't harden onto the filter or flask and ruin them (it didn't... it stayed soft and mushy & wiped right off at the end.)

cleaned sludge from measuring cup and washed it. poured liquid from flask into measuring cup to cool off.

watched Isatin crystals form along the top of the liquid.

filtered liquid through #2 whatman paper again. Rinsed profusely with distilled-sodium-free water.

Allowed filter paper and isatin to dry. Weighed paper: .5g (but some paper got torn off when scooping it out of the filter funnel using a metal spatula). The paper used to weigh .4g. Giving myself the benefit of doubt for the chunk of paper that was lost, I'll pretend it weighed .35 grams. .5g - .35g = .15 grams.

Now I just need to figure out how to get the Isatin out of the filter paper. I'm thinking about putting it back in the buechner funnel, putting my finger over the bottom hole, and adding a few mL of everclear to see whether I can dissolve the isatin into it that way then drain it.
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[*] posted on 17-10-2004 at 19:19
Success!


Having (mostly) gotten over my fear that the reacted solution is going to spontaneously explode, I conducted my most aggressive experiment to date -- INTENTIONALLY seeking to maximize the amount of red in the final product.

Up to now, I was deathly afraid of the red product because I thought it was picric acid. It turns out, the deep-red reacted product is the Isatin.

Procedure:

Added 5mL 70%/16M nitric acid to 1L pyrex measuring cup

Measured 6g Indigotin onto paper scoop, then slowly sprinkled the indigotin powder onto the nitric acid pooled in the bottom of the measuring cup. The initial reaction was pretty violent -- lots of visible gas, deeply blood-red product.

Continued to add powder as reaction settled down until all powder was added to solution.

When reaction mostly stopped, began to slowly swirl the mixture around the bottom of the measuring cup by tilting the cup towards the corner until all sides had a chance to be exposed to the full power of the acid.

Added more acid a few drops at a time and repeated the slow swirling until all visible powder was gone. At this point, I'd estimate that there were about 40mL of intensely orange-red solution.

Added approximately 500mL of distilled, sodium-free water. The red isatin solution instantly solidified and bonded with the remaining traces of unoxidized indigotin into blobs of tarry scum.

Put cup on stove at medium-high heat and allowed to come to a rolling boil. Made initial attempt to stir, but abandoned further efforts because too much tar (and isatin bound up with it) stuck to the plastic spoon and was wasted.

Allowed solution to boil until all traces of red were gone from black tarry blobs.

filtered solution through #2 whatman paper into filter flask. Set filter flask on burner on low heat to keep warm for a few more minutes.

discovered that tarry gunk had hardened and could not be removed from measuring cup. filled measuring cup with water and brought to a boil, then used spatula to scrape now-softened tarry gunk from the measuring cup's sides. Dumped tar-filled water into back yard, then quickly wiped residue from cup with paper towel immediately afterward.

poured liquid from filter flask into now-clean measuring cup. Allowed it to cool for 3 hours. Liquid was orange-red, but didn't have much visible precipitate along the surface. Panicked, but decided to go through with the filtering anyway.

Filtered liquid using buechner funnel with #2 whatman paper back into filter flask (this time, with suction). As I neared the last of the liquid to be filtered, I was relieved to see that lots of it was settled along the bottom of the measuring cup.

Filtered the last of the liquid. Rinsed the measuring cup with distilled/sodium-free water.

Admired the nearly solid coppery film impregnating the filter paper.

Allowed the filter paper to dry for 3 hours, then got impatient and decided to try something different.

Dumped water from wash bottle and replaced it with 151 proof Everclear (cheaper than paying hazmat shipping for ethanol, almost as pure. If Florida weren't so anal retentive and allowed 190+ proof alcohol to be sold, it would have probably been purer...)

added ~20mL everclear to filter funnel (other end over small beaker) and slowly swirled alcohol over filter paper until most of the isatin dissolved into the alcohol and passed through the paper into the beaker below.

I won't know for sure until tomorrow night (when most of the alcohol will have evaporated), but based upon the weight of the beaker, 10mL pure everclear, and the weight of the beaker with 30mL everclear and dissolved Isatin in it, it looks like I now have approximately 2.5-3g/Isatin to play with. :)
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