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miamicanes
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Synthesis of isatin from indigo via ozone, HNO3 and others
A little while ago, I managed to find another (seemingly) straightforward way to synthesize isatin from indigo that I admittedly like a lot better
than the nitric acid method (mainly because it doesn't create picric acid as a waste product).
It looks like the reaction is:
C16H10N2O2 + O3 --> 2 C8H5NO2 + O (which I assume finds another oxygen fairly quickly to join and produce O2).
So... how might I go about actually getting this to work using a small ebay-ish ozone generator (like this one -- http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=2...)?
idea #1) dump 25g indigo into 1L filter flask and fill 1/3 with deionized water. Connect plastic tube and aquarium airstone to ozone generator
(passing through hole in the flask's rubber stopper) and insert airstone so it's bubbling ozone from the bottom of the beaker. Agitate and
swirl until the indigo seems to have completely oxidized into isatin.
idea #2) cover bottom of filter flask with thin layer of indigo. Run airstone's tube through hole in rubber stopper, with enough length to reach
the bottom of the flask. Insert the stopper into the flask and seal tightly. Connect another air tube to the filter flask's air hole and connect
the other end to the sink-mounted aspirator. Turn on the water and ozone generator. Hope that the ozone concentration gets high enough to actually
work.
Things I can think of that might go wrong:
* The reaction might be strongly exothermic and melt the airstone and/or air tube, and quite possibly blow the stopper out of the flask and boil over.
* The cheap ozone generator might be the equivalent of trying to turn the ocean yellow by peeing into the atlantic off a pier.
* It might be necessary to dissolve the indigo into a solution using some strong acid that would either dissolve the airstone and/or pipe, or react
violently with the ozone.
What do you think? Should I go ahead and order the sub-$50 ozone generator/air pump and hope for the best? Or will I really need to get one
that's a lot more powerful and expensive for it to work? Is it likely to be straightforward and easy to do, or (as was the case with the nitric
acid method) is there some major catch lurking in the shadows ready to cause major headaches with THIS method too?
[Edited on 14-10-2004 by chemoleo]
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neutrino
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There are chemical ways of making ozone that should be much cheaper than getting a generator and yeild much purer ozone. There was a thread about this
here, just search for it.
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miamicanes
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I saw the threads... the impression I got was that the various chemical methods proposed involved chemicals that were hard to get and/or dangerous to
work with & electronic (but not corona discharge) generators were the best compromise (not terribly efficient, but fairly cheap, convenient, and
generally adequate for the task)...
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miamicanes
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Whoops. It looks like I didn't get the reaction quite right. Apparently, the reaction's products are isatin and isatoic anhydride:
C16H10N2O2 + O3 --> C8H5NO2 + C8H5NO3
It looks like the reaction will still work reasonably well, yielding 1/2 mole of Isatin per mole of indigotin (plus 1/2 mole of isatoic anhydride). As
luck would have it, isatin is practically insoluble in water, and I'm assuming that by definition isatoic anhydride would immediately react with
the water to produce isatoic acid, which appears to be fairly tame and dump-down-the-sink-able (compared to picric acid). So hopefully, the outcome
would be isatin solids suspended in isatoic acid, ready to be filtered out.
From what I can tell, the Enaly 300U ozone generator looks like it might be good enough to do the trick. It's rated for 200-300mg/O3/hour and
comes with clear tubing and airstone. Plus, it even has an intake that can be fed pure O2 if nitrogen from the air becomes a problem.
Of course, there are still a few major questions to resolve... like how exothermic the reaction of the indigotin and ozone (or the isatoic anhydride
and water produced by the main reaction) will be. I suspect it'll be pretty tame, though... the book I saw referred to ozonating indigotin in
the context of sanitizing aquarium environments (I love Amazon.com's search inside... ) 
[Edited on 3-10-2004 by miamicanes]
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miamicanes
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Attempt #1 at isatin synthesis -- failed.
Well, I made my first attempt at synthesizing isatin from indigo using ozone tonight and failed miserably.
Procedure:
combined 5g synthetic indigo w/approx. 250mL distilled water in 1L flask and mixed into solution/suspension.
threaded plastic tube through 2-hole flask stopper and connected one end to ozone generator and other end to airstone.
lowered airstone into indigo+water and turned on ozone generator. watched it foam for 3 hours. When I finally ran out of patience, there was what
appeared to be a shiny yellow film atop a layer of purple foamy scum, but the bulk of the solution appeared to be unchanged, and after allowing the
liquid to settle down for 10 minutes after turning off the ozone generator and removing the airstone, most of the discernible top layer of scum was
gone.
With minimal optimism, I filtered the solution through #2 whatman paper, and ended up with nothing more than a filter paper caked with indigo. No
trace of isatin. For the hell of it, I measured the pH -- 4.48.
So... does anyone have any idea as to what might have gone wrong? Was the indigo solution too strong? Too dilute? Do I need to heat the mixture? Would
using 40vol. hydrogen peroxide (12% w/v) instead of distilled water help (by providing more spare oxygen atoms), hinder (by aggressively cannibalizing
the ozone to create molecular oxygen, leaving nothing to oxidize the indigo), or make no real difference?
I just did some calculations now, and suspect my biggest problem might have been not waiting long enough. As far as I can tell:
1mol indigotin (C16H10N2O2) = 262.28g
5g indigotin = .019mol
1mol O3 = 48g
.019mol O3 = .91g
assuming 100% efficiency @ 200mg/hour, and one ozone molecule oxidizing one indigotin molecule, it looks like it will require at least 5 hours
(probably more like 10-24) to oxidize .019 mol indigotin using .019mol O3 to produce .019mol isatin precipitate and .019mol isatoic acid (presumably
aqueous and hopefully passable through a filter).
Is this a reaction that's safe to leave unattended for extended periods of time? Like, say, running in the shed in the back yard overnight and
maybe all day while I'm at work (theory: if it DOES blow up or something, at least it won't destroy the house too... though it would
definitely still suck if it happened...).
As far as I can tell it doesn't produce anything explosive... but I can't help wondering what mischief the handfull of nitrogen molecules
that get turned into NO2(?) by the ozone generator's corona and get injected into the solution along with the ozone might become...
Also, am I correct in assuming that I'll know when the indigo has been fully oxidized because it'll no longer be blue (I know Isatin is
yellow precipitate, but I'm not sure what color hydrated isatoic acid is.)
Also... is diluted isatoic acid safe to dump down the sink? In the back yard?
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miamicanes
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update:
It looks like ozone was a necessary, but not sufficient, component of the reaction. Apparently, ultraviolet light is also necessary.
So... it looks like tonight I'll get to go on a desperate scavenger hunt for a meaningful (yet not terribly expensive) source of ultraviolet
light.
I'm thinking that an aquarium-type setup might work best:
flask w/2-hole stopper filled with indigo + deionized water mixture -> outbound tube -> impeller-type aquarium or pond pump -> venturi tee
fed with output from ozone generator -> UV aquarium or pond sterilizer -> inbound tube -> flask
The idea being that the pump will slowly move water through the venturi tube (where ozonated air will get injected into it), then immediately pass
into the sterilizer chamber to get exposed to ultraviolet light before the isatin, isatoic acid, and unreacted indigo will return to the flask.
Things I'm open to suggestions on:
* IS C8H5NO3 "isatoic acid?"
* how watery should the mixture be?
* should the pump be slow (to maximize the amount of time the ozone-injected indigo mixture spends in the sterilizer tube after injection), or a bit
faster (if the UV will quickly break down the ozone before it passes far anyway)
* what is aqueous Isatoic acid (C8H5NO3) like? Will it pass through the filter paper (leaving behind the precipitated isatin)? I'm assuming that,
by definition of "hydration", hydrated C8H5NO3 will fully dissolve into water and not get caught in the filter paper.
* what grade of filter paper should I use (I have #2 whatman handy, but can get others today)?
* what does hydrated isatoic acid look like? I haven't been able to find a decent description anywhere online (everything refers to it in its
anhydrous form). What's its pH? General appearance (I'm assuming it's not blue, and probably falls somewhere between yellow and clear).
* is isatoic acid flammable, explosive, or toxic? What reagent acid is it comparable to with respect to reactivity (ie, citric acid? acetic acid?
hydrochloric acid? sulfuric acid? nitric acid? god forbid, picric acid?)
I could definitely use a few links to online articles google missed regarding hydrated isatoic acid, as well as anything that discusses in depth the
reaction between nitric acid and indigotin (I still might get desperate and try that route tomorrow... but not until I feel confident that I've
got a really good understanding about the whole reaction from start to finish. There's no way in hell I'm going to just blindly start adding
nitric acid to indigo and hope it doesn't explode...).
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chemoleo
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I had a look around, and found this:
http://employees.csbsju.edu/hjakubowski/classes/ch331/oxphos...
are you using indigo carmine? (which presumably is the sulphonic acid form)? Presumably the acid form is easier to isolate, as it will produce
precipitable salts.
Anyway, more importantly, have a look at this:
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0327
It describes isatin as large brown-red crystals which melt at 196–197°, when recrystallised in glacial acetic acid. Also, there is a large
reference section on the preparation of isatin from indigo via oxidation. This may be most helpful to you.
Regarding your experimental difficulties, what means do you have to identify the isatin? Anymore than 'a yellow liquid'? Did you weigh the
indigo before and after the reaction? Any change?
Also, it seems a basic solution brings the isatin into solution, while acidifying it leads to its precipitation. Maybe thats the way forward to
identify it.
What do you want the isatin for?
PS the preparation of isatin from aniline and hydroxylamine actually seems quite simple, once you have anilin.
[Edited on 8-10-2004 by chemoleo]
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neutrino
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If you want UV, just leave the thing running in the sun. 
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miamicanes
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Well, round #2 is underway, with slightly refined hardware.
Procedure so far:
approx. 3/4 gallon sodium-free distilled water (I couldn't find actual deionized+distilled, so I had to settle for the best compromise available)
added to new, clean plastic bucket.
aquarium powerhead submerged in water in bucket.
enlay OZX-300U ozone generator (rated for 200-300mg/hour) attached to powerhead's venturi air intake to inject ozone into water.
powerhead's output connected to Turbo-Twist 6X UV sterilizer (18w cf UV, with spiral internal water path to increase exposure time).
sterilizer's output dumped back into bucket to marinate further and repeat the trip.
turned on powerhead. Verified no leaks.
turned on ozonator. Observed bubbles.
turned on sterilizer and allowed to run for 15 minutes. No explosions, no unusual heat.
Added 10mg indigotin (C16H10N2O2, CAS 482-89-3, MW 262.27)
Observed closely for 1 hour to make sure it didn't look like it was going to suddenly become wildly exothermic. Nowhere close.
Observed casually for another hour. Still looks quite under control. Shiny, metallic-looking scum over most of the liquid's surface in the
bucket. It might be contamination, but I saw a few distinctly yellow shiny flakes. Dare I say, "Isatin?"
It looks like it's going to take AT LEAST 8-12 hours to get anywhere close to oxidizing all the indigo into isatin and waste. The exact outcome
is still anybody's guess... I found about 9 sources online (5 or 6 via amazon.com's "look inside" that referred to oxidizing indigotin with ozone, with three different opinions as to
the outcome:
1) C16H10N2O2 + 2 O3 + water --(uv)--> 2 C8H5NO2 + H2O2 [this is obviously the one I like, since it transforms all the indigotin into isatin with
no hazardous wastes.
2) C16H10N2O2 + O3 --> C8H5NO2 + C8H5NO3 [1 Isatin, 1 isatoic anhydride that would probably end up hydrated since the reaction is taking place in
water)
3) indigotin + O3 --> isatin + anthranilic acid + O2. God knows where this one came from... I only saw it listed in one source, but remember
scratching my head wondering what the hell the author was thinking. As far as I can tell, anthranilic acid isn't another name for hydrated
isatoic acid.
Anyone care to speculate as to which one might be most likely?
Anyway, getting back to why I think it's going to be a
L O N G ...
reaction, I pulled out the calculator for the first equation:
1 mole indigotin = 262.27g
I used 10g = .038mol
1mol O3 ~= 48g
.038mol O3 = 1.83g
but according to equation 1, I need two O3 molecules for each indigotin, so that means I'll need 2x.038mol = 1.83g x 2 = 3.66g O3.
At the most optimistic rate (300mg/hour, 100% utilization), that translates into 12 hours. At 200mg/hour, that translates into 18 hours. I have no
idea what the actual ozone utilization efficiency might be, but I'm going to assume that 100% is wildly optimistic and figure that it'll
take at least 50% longer to complete the reaction. Of course, if one of the single-ozone-reagent equations applies, that would cut the time roughly in
half.
does this rationale seem correct?
The jury's still out, but one or two of the sources mentioned needing to heat the reacted mixture prior to filtering to make the new isatin
molecules crystallize. Anyone have any suggestions regarding time & temperature?
----------------
responding to questions...
no, it's not indigo carmine. it's indigotin (aka "indigo blue" and synthetic indigo. This is the active molecule that actually
matters).
I knew about the sulphonic acid form, but skipped over it for now until I first verify that the experiment works with normal, plain isatin. I suspect
the sulphonic acid form won't work. Now, if I knew how to turn THAT into pure isatin... ;-)
the purpose? a few weeks ago I tripped across a formula for a novel hair dye that was discovered about 20 years ago, but never marketed (I'm
guessing because by its very nature it has to have a volatile alcohol base, which probably freaked out their liability lawyers. Not to mention it
probably violates California and New York clean air regulations for VOC.). Its big appeal is that it apparently has minimal affinity for skin, but
develops rapidly in contact with hair (something in hair acts as a catalyst).
One interesting bit of trivia... apparently, someone discovered the isatin-in-hair reaction more than a century ago and found the color to be both
permanent and offensive. I think this was before the discovery of aniline dyes, so it never occurred to him to try adding one (like p-aminophenol) to
the equation (apparently, p-aminophenol nudges the color towards medium-dark brown w/yellow undertones. yay! no red!)
What's really sad is that if Isatin were readily available for purchase by individuals in its pure form, the formula itself is pretty trivial...
1.5g isatin + 1g p-aminophenol dissolved in 30mL ethanol, then 70mL water + some small amount of gum arabic or similar agent added for viscosity.
[Edited on 9-10-2004 by miamicanes]
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miamicanes
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pH update...
at t=3 hours, I had a *hell* of a time trying to get anything resembling a stable pH reading using the digital pH meter.
The frothy scum seemed to have a pH of approximately 6, +/- .5
The stream of fluid coming out of the return tube (having just made the trip through the uv sterilizer after its ozone injection) had a pH of
approximately 5, +/- .25
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miamicanes
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t=12h update
My initial impression was disappointment. The solution doesn't appear to have lightened or otherwise changed color since last night.
HOWEVER... the pH has definitely dropped. The liquid coming from the return tube is down to a fairly stable 3.7 (3.5 to 3.8), and the liquid in the
bucket itself has pH~= 4 (3.65-4.8).
There's also a crusty dark purple scum along the surface at the bucket's walls. I'm torn between trying to scrape it off & try to
heat and filter it (on the chance it's isatin + isatoic acid), and rinsing it down into the pail with the rest using a wash bottle (on the
likelihood that it's just splashed indigotin that had water evaporate since it's quite dark purple).
I suspect that the reaction will probably speed up rapidly once the color begins to lighten. Right now, the dark violet indigotin is probably
absorbing and blocking the UV from passing more than a millimeter or two, so it can only break up ozone molecules that are close to the lamp. OTOH, as
the solution clarifies (I hope), the UV will be able to make it farther -- affecting ozone molecules farther away and increasing the effect on the
reaction.
I'm tempted to try slowing down the powerhead. Last night I cranked it to max in case the reaction inside the UV sterilizer got too active and
threw off too much heat. Seeing how that hasn't happened, it might help to give the fluid more time inside to interact with the UV (from the
smell, I can tell that lots of ozone is emerging from the sterilizer intact).
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chemoleo
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Isn't UV absorbed by aromatics of any nature regardless? A normal phenhydroxy group absorbs nearly up to 300 nm... so isatoic acid is bound to
absorb itself too. So a reaction is bound to occur, as you say, only for 1-2 mm into the mixture.
In addition, did you check whether your glass is UV transmissible? Maybe you'd need a quartz container anyway to make this work 
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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miamicanes
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The UV is provided by a Turbo-Twist 6X aquarium/pond sterilizer. It's basically a UV compact fluorescent (18w) inside a watertight glass cylinder
(which presumably doesn't block the UV), inside a larger black plastic cylinder through which the liquid being exposed to the UV passes.
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Marvin
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According to what little Ive been able to find isatoic acid is not a required byproduct.
Indigo oxidised with dilute nitric acid in the cold is supposed to go to isatin and nothing else. If the acid is hot it also produces some
nitrosalicylic acid or picric acid but kept dilute and cold these are not supposed to form.
The isatin formed is supposed to be yellow and insoluable but it should be easy to tell from nitration products if the acid you use is too
concentrated.
I would be inclined to skip the ozone method.
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miamicanes
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How sure are you that dilute, cold nitric acid will react with indigo blue to form isatin with little/no picric acid? I was under the impression that
the two pretty much went hand-in-hand as byproducts of oxidation via nitric acid. If you're right and I'm wrong I'll definitely be
happy and you'll have made my day
It's weird.... supposedly, the reaction between nitric acid and indigo was one of the first to be studied and documented two centuries ago, but
if you look for details on the internet, you'd barely know it even existed except as a historical footnote. I guess it's not an experiment
really suitable for inclusion in a glossy, lavishly illustrated college chem class lab manual with step-by-step instructions that put most cookbooks
to shame 
Also, what would you define as "dilute" (I have a liter of 70% (16M?) technical-grade nitric acid available to dilute. I'm just
paranoid as hell about going anywhere near TNP for a few reasons, including:
* TNP residue is the most dangerous part of all. I suspect there's going to be lots of dried residue on the filter paper, buechner funnel, stir
rods, and just about everything that comes in contact with the solution at some point in time.
* Ultimately, this is something that's going to wind up in hair... I have no idea how much damage a tiny crystal of TNP can do, but I suspect its
reaction during a potential future encounter with hydrogen peroxide probably wouldn't be pleasant.
* Just about every reference I've seen to TNP mentions TNT in the next sentence -- the one chemical that's probably earned a Darwin Award
for more home chemists than any other...
Mitigating the fear (slightly) is the fact that TNT's main danger comes from the fact that the reaction can easily accelerate out of control
(boom), not from the actual power of intentionally-detonated TNT itself (which I suspect is where the two are really comparable). Also, I can't
help wondering how garment makers managed to oxidize indigo with nitric acid to make picric acid for use as a yellow dye for nearly half a century
before anyone even realized it IS explosive...
I'll admit that I can't help but suspect that the reaction most businesses, schools, and government agencies seem to have upon discovering
an old jar of picric acid might be just a wee bit excessive, fueled more by the perception that going WAY overboard and treating it like
plutonium-laced plastic explosive is the normal, rational way to handle it...
[Edited on 9-10-2004 by miamicanes]
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neutrino
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TNT isn't really that dangerous. I have never heard of a runaway reaction causing an explosion for one simple reason: it can't. TNT is a
secondary explosive, which means that it is very hard to detonate, requiring powerful blasting cap. Even if you pound on it with a hammer, you’re
unlikely to get a detonation. If you light it, it will only burn. In short, there’s no way the TNT will ever explode, especially with the tiny
batches you’re working with.
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miamicanes
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Oops. I meant nitroglycerine (which can definitely accelerate out of control if you're not incredibly careful and lucky).
I'm also starting to have second thoughts as to just how dangerous random, scattered picric acid residue might be. I'm starting to suspect
that a single crystal the size of a grain of salt might produce an effect comparable to the quasi-firecrackers that consist of some a rock coated with
some chemical wrapped in a piece of tissue paper that detonate when you throw them on the ground. Unlike, say, a jar of picric acid with crystals
around the lid, there's no reservoir of picric acid a few inches away ready to get detonated as well.
Still, I think having intimate bodily contact with detonating picric acid -- even a crystal the size of a grain of salt -- wouldn't be pleasant,
even if it weren't necessarily fatal or even serious. Probably comparable to having a glob of molten solder fall from a soldering iron onto your
leg (been there, done it circa 7th grade. Still have the scar.)
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vulture
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DON'T POST A NEW THREAD FOR EVERY ATTEMPT!!! 
-----------------------------------------------------
Attempt #2 at isatin synthesis -- not yet.
Well, it's been 18 hours, and the solution is just as dark as it was yesterday. No visible isatin precipitate, either.
Sigh. It looked so elegantly simple on paper... bring ozone into contact with the indigo and watch the isatin precipitate out as the ozone gives up an
oxygen atom and neatly cleaves the indigotin molecule in half...
I'm open to suggestions as to what to try tomorrow. Here are some of my random thoughts:
* I should get a new bucket -- saving today's solution in the old one -- and tomorrow try adding today's solution to water a little bit at a
time. The general theory being that the reduced concentration will expand the reach of the UV and let it work harder on the smaller amount.
* I need to find a way to expose the ozonated solution to direct sunlight. There's plenty of ozone (quite a bit is NOT getting destroyed by the
pass through the UV sterilizer), but the solution just isn't getting enough of a dose from the 18w sterilizer.
Of course, I'm having a few darker thoughts... like the possibility that nothing short of an industrial-strength ozonator and several hundred
watts of UV (comparable to direct sunlight) will really do the job.
Sigh.
[Edited on 10-10-2004 by miamicanes]
--------------------------------------------------------
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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vulture
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Again, from yet another new thread about this!
---------------------------------------------------
Attempt #3 at isatin synthesis... working!!!
I couldn't wait until the sun came up tomorrow to try exposing the ozonated indigotin+water mixture to sunlight, so I tried something a bit
different -- massively diluting the mixture to see whether decreasing the concentration would let the UV rays reach farther and influence more ozone
molecules.
So far, it seems to be (slowly) working. I'm seeing tiny yellow flecks appear in the mixture. It's not much yet, but it's a start.
A little more good news. Yesterday, the tube connecting the ozone generator to the powerhead got stained blue about 8 inches in from the end when
indigo-containing water got blown up into it by the powerhead when I briefly turned off the ozone generator. As of 5 minutes ago, it's now
YELLOW! yay! finally, tangible evidence that the ozone is actually doing something :-)
1,000,000 indigo molecules down, 20,474,800,000,000,000,000,000 to go
Bringing one of my other posts into the current discussion, I went out to home depot and bought two coils of plastic tubing. One is translucent frosty
white polyethylene; the other is clear vinyl. I'm thinking about mounting a big spiral using one of them on a piece of plywood to put in direct
sunlight to take advantage of the massively more intense UV coming from the sun during the day.
Which one is likely to offer the least resistance to UV-B radiation? On one hand, somebody mentioned that polyethylene food wrap has a single bond and
should offer little resistance. As I said, one of the tubes is polyethylene... but I guess the fact that it's frosty white is leading me to
believe that it won't have quite the same effect as hair-thin clear saran wrap. The other is clear, but I think vinyl has a double bond, which
someone else said will block UV.
I'd rather return all the stuff to Home Depot if neither tube is likely to help matters (I blew another thirty bucks there tonight), but on the
other hand I'll definitely implement one (or both!) if anyone thinks one or both will let a useful amount of solar UV through.
Hmmm. If nothing else, the vinyl one will probably absorb lots of heat and raise the fluid's temperature a few degrees. Maybe sending the
ozonated mixture into the UV chamber 10-25 degrees hotter might help, too...
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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miamicanes
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Last night, I was happy. After running the apparatus all day with diluted indigo, it finally turned yellow.
One problem, though... the Isatin appears to be gone. More online research suggests the reason why, as well as the reason for the divergence of
opinion as to the products of the indigo + ozone + uv reaction:
ozone + uv oxidizes indigo into isatin, but continued exposure of isatin to ozone + uv apparently transforms it into anthranilic acid
(ortho-aminobenzoic acid). In other words, I went too far.
sigh.
So... can anyone suggest a way to reduce anthranilic acid back down to isatin?
[Edited on 11-10-2004 by miamicanes]
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miamicanes
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For what it's worth, here are some details about the first batch.
Initially, the mixture was green-yellow with visible specks of unoxidized indigotin remaining. I heated 1L to some point with visible heat-induced
currents just short of boiling (no thermometer. oops.) and let it cool, then filtered it through #2 whatman paper. While the first batch was drying, I
repeated the procedure with the second half of the first batch (a little under 1L).
No red or yellow precipitate was observed on the filter paper. A bit of indigo residue, but that's about all. The filtered liquid was now
yellow-green.
18 hours later (after work today), I decided to make one last try at finding isatin in the liquid. This time, I only filled the pyrex measuring cup
1/3 (to give plenty of room for foam, etc) and heated it to a rolling boil. I let it boil for 10 minutes, then let it cool for 2 hours.
No precipitate. Just clear yellow-green liquid.
I decided to compare the pH of the three groups:
the first batch to be heated (but not boiled) and filtered: 5.44
what was left of the second batch to be heated (but not boiled): 5.15.
The portion of the second batch that was heated to a rolling boil today: 5.26.
The pH readings were fairly stable, +/- .02.
The difference between the first batch to be heated and the second batch to be heated can be partially explained by the fact that the fluid comprising
the second batch had an additional 3 hours of ozonation and UV exposure (more intense than usual, because half of the original quantity was gone from
the system, so each bit was getting sent through the loop twice as often).
I'm not really sure why the unboiled liquid is more acidic than the boiled liquid, unless I was REALLY boiling away more of the presumably acidic
mystery liquid than the water diluting it.
Any ideas as to what the yellow liquid might be? It's obviously acidic, but not terribly reactive. I've had lots of casual
bodily contact with it... no burns, tingling, rash, or even an itch. It's not odorless, but I can't really think of anything to compare it
to. Given a choice between smelling it and not smelling it I'd rather not smell it, but the smell isn't bad enough to motivate me to really
try avoiding or reducing it if I randomly encountered it somewhere.
I can think of two obvious possibilities:
* hydrated isatoic anhydride (isatoic acid?)
* anthranilic acid
I doubt there's any significant amount of Isatin dissolved in the liquid. For one thing, Isatin is practically insoluble in cold water, and
minimally soluble in hot water. From what I've read, if there were any Isatin in there, it should have fallen out as crystals when the
aggressively boiled liquid cooled.
If it's hydrated isatoic anhydride or anthranilic acid, is there any straightforward way to react it back into isatin?
I want to think it might be possible to reduce isatoic acid into isatin precipitate by bubbling hydrogen gas diluted with helium (to keep the reaction
from getting too violent) into the liquid in the hope that the extra oxygen that makes the difference between isatin and isatoic anhydride might
prefer to be the backbone of a water molecule instead of a mere cling-on to a big organic molecule... but that assumes I could actually talk someone
at Airgas or some other company into actually selling a cylinder of hydrogen diluted with helium. Seriously doubtful.  As a practical matter, I'd probably wind up having to drop a penny into a flask,
pour the liquid into a tall, narrow container with a tube leading to an airstone at the bottom, and run the other end of the tube through a rubber
stopper capable of fitting tightly over the penny-containing flask, add acid, plug the opening, and run for cover...
If there's some straightforward way to turn the mystery liquid into isatin precipitate, this method will be perfect because it'll mean I can
let "most" of the indigo oxidize, then simply filter out all the remaining indigo before doing the final reaction against the
"clean" liquid...
On the other hand, I just might get desperate enough to try using nitric acid tomorrow night. One question, though.. what, exactly, constitutes
"dilute" nitric acid (relative to 16M/70% non-fuming)?
[Edited on 12-10-2004 by miamicanes]
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Marvin
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"If it's hydrated isatoic anhydride or anthranilic acid, is there any straightforward way to react it back into isatin? "
If its gone this far its destroyed, youve broken a carbon chain and they dont fix easily. The only way I see to go backwards from anthranilic acid
for example would involve cyanide.
Hydrogen tends to be used as a rather specific reducing agent and most people very sensibly avoid it. Helium is much much more expensive than
hydrogen and if dilution was needed it would be done with 2 tanks, say hydrogen and argon with a mixer tap. Mostly hydrogen reductions do not go
easily and need high pressure and/or high temperature. They do produce a lot of heat when they do go though, you're right. I cant think of any
hydrogen reduction that links 2 unlinked carbon atoms.
When it comes to making isatin I have no idea at all what 'dilute' would indicate. I would suggest you try a few test tube scale reactions,
few mg of indigo, and start with say 10 or 20% and see how concentrated to make it go yellow in a fairly short space of time without heating. If you
make any quantities of picric acid by accident on this scale there really is no hazard unless you drink it. Just pour the solutions down the sink.
If you can do an accurate melting point this would confirm you have what you think you have, maybe after a single purification stage.
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miamicanes
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Well, last night I found out that there is a way to turn anthranilic acid into isatoic anhydride, but it's utterly out of the question --
reacting it with phosgene. Argh.
I assume that you mean that even if the spurious oxygen in isatoic anhydride were to join a nearby H2 molecule drifting by, the two carbons previously
bonded to the oxygen wouldn't just bond with each other and close the ring automatically.
I'm still going to experiment with the mystery fluid... there's a tiny chance that if it IS (mostly) isatoic acid instead of anthranilic
acid, it might still do Isatin's job. I doubt it, but at this point I've gone through so much work to make it, I might as well play with it
a little more to see what happens when it's brought together with 1% w/v p-aminophenol.
One other possibility that I haven't had time to explore yet is whether it might be straightforward (if it's anthranilic acid) to reduce it
to aniline by stealing away the COOH, then try using the aniline to build a new isatin molecule. I vaguely remember reading about a synthesis reaction
involving aniline at some point over the past few days, but wrote it off because I didn't have aniline available anyway.
God, I really wish I could just buy the stuff. So far I've spent close to $400 trying to synthesize something that's not even restricted or
toxic and costs about 35 cents/gram to buy if you're a commercial research lab.
[Edited on 12-10-2004 by miamicanes]
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miamicanes
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Just to conclude this thread in case anybody wants to try ozonating indigo to get Isatin -- it doesn't work.
Ozone + UV-B does neatly cleave indigo molecules into two isatin molecules. Unfortunately, it doesn't stop there. Continued
exposure to Ozone + UV-B causes the isatin to decompose into anthranilic acid. Herein lies the catch... by the time the last of the indigo gets cut
in half and transformed into isatin, most of the isatin will have been destroyed.
Thus, ozone + UV is feasible as a method for decomposing indigo into isatin and anthranilic acid as long as your goal is to be rid of the indigo, but
it's NOT feasible as a method for synthesizing isatin from indigo if you need to actually preserve the isatin once it's created.
On top of that, the amount you can process at any given moment in time is ridiculously small... in a system consisting of a pump, tank, ozone
generator capable of 200-300mg/hour, and 18w UV sterilizer whose total operating capacity is one gallon of water, you can MAYBE process a whole
whopping gram of indigo at a time before the indigo itself begins to block too much UV... and you're looking at 24-48 hours of running time just
to get that far.
On the other hand, if your ultimate goal is extremely dilute anthranilic acid, this system works beautifully because it's totally safe. But for
Isatin, forget about it.
Well, there is one possibility I didn't bother to explore due to cost feasibility... imagine a system built into a large igloo cooler with
high-power fluorescent UV tubes (say, 2 to 4 40w+ tubes w/10% min efficiency @ UV-b), a BIG ozone generator capable of generating 1000mg/hour, and a
pump with ultrasonic mister that sprays a fine mist of indigo solution into the ozone-rich air inside the cooler directly beneath the UV tubes. In
such a system, it might be possible to fry enough of the indigo quickly enough to avoid destroying too much isatin. But this little experiment will
realistically cost you AT LEAST $500 to try... and quite possibly won't work either. So think carefully before pulling out your visa card and
hitting eBay...
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miamicanes
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Isatin synthesis via Nitric acid and Indigo
OK, I bit the bullet tonight and decided to try oxidizing the indigo using nitric acid despite my misgivings about the safety of doing so. 
The good news: I didn't end up with a black tarry mess, nor did anything blow up.
The bad news: I'm not entirely sure what I ended up with.
Ingredients:
4g synthetic indigo blue ("indigotin", mixed with small amount of
distilled+deionized water to make thick paste.
approximately 8 mL 70%(16M) technical grade nitric acid, added a couple of drops at a time over the span of 3 hours.
It took about 5 mL of nitric acid to see any visible reaction.
At first, yellow precipitate formed and rose to the surface. It looked like this was going to be pretty easy to do after all...
...Then, it turned into an oily orange-yellow liquid that I ended up skimming off the top using a pipette and filtered through #2 whatman paper.
Its massively diluted (approx. 20 parts water to one part oily liquid) pH is approximately 3.0. Despite the oily appearance, it appears to have
dissolved thoroughly into the water. It doesn't smell particularly acidic, but there seems to be WAY too much of it to be Isatin (plus, I vaguely
remember reading somewhere that Isatin is minimally soluble in water).
I'm hoping it's not picric acid. I suspect it is.
The gunk in the filter paper looks like unoxidized indigo. No apparent yellow crystals or precipitate.
Any suggestions what to do next? Or ideas as to what the hell the oily yellow-orange liquid I now have a (highly-diluted) liter of is?
[Edited on 14-10-2004 by miamicanes]
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