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Author: Subject: p-Aminobenzoic Acid - routes to it
un0me2
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[*] posted on 3-2-2010 at 23:56
p-Aminobenzoic Acid - routes to it


There a few OTC-friendly options that I can see, other than the nitration of phenylalanine/cinnamic acid, which aren't cheap, or the Hoffman on the monoamide of Terephthalic acid, I see nothing...

So...

Anyone got any ideas on forming the monoamide of terephthalic acid, presumably one could start from the monoammonium salt and dehydrate it. If that is the case, then it would be a piece of piss to make from PET.

[Edited on 4-2-2010 by un0me2]
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Picric-A
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[*] posted on 4-2-2010 at 00:13


I have written a thread on the TPA-> AHTPA -> 4ABA --> PABA route you mention.

Nitrate toluene, seperate p isomer, reduce to amine, protect, oxidise to carboxylic acid, deprotect.
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[*] posted on 4-2-2010 at 07:04


It is easier than that;

Nitrate toulene, separate p isomer, oxidise to the acid, reduce to the amine.

I have saved you three steps!

Oops, I meant two steps!

[Edited on 4-2-2010 by ScienceSquirrel]
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Picric-A
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[*] posted on 4-2-2010 at 10:03


I have always thought you could do that and save the whole protection however just about every prep for it states protection is neccesary, i guessed the carboxylic acid is easily reducable or something, i just dont see why...
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[*] posted on 4-2-2010 at 10:09


Carboxylic acids generally are not easy to reduce. Nitro groups on the other hand are easily reduced; the reaction should go fine, especially if you use Sn/HCl (chemoselective reduction); the only issue I could see with this is ipso substitution of the carboxylic acid group, but the nitro group is in the wrong position to effect this so it should be no hassle. Its likely that hydrogenation over Pd/C will also yield the same result, but in a somewhat cleaner fashion.
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[*] posted on 4-2-2010 at 12:52


Quote: Originally posted by Picric-A  
I have always thought you could do that and save the whole protection however just about every prep for it states protection is neccesary, i guessed the carboxylic acid is easily reducable or something, i just dont see why...


The standard lab and industrial prep for it does not use protection.
Wherever possible working organic chemists try and use reaction order to avoid protection / deprotection steps as they waste material and time.
In this case, the nitro group is tough as old boots so you can hit the methyl group hard to oxidise it to the carboxylic acid.
The carboxylic acid group is then really resistant to reduction from dissolving metals, catalytic hydrogenation etc so no need to worry as you take the nitro group to the amine.
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[*] posted on 4-2-2010 at 14:08


Modern industrial organic chemistry is very demanding when it comes to incorporating as many atoms in the starting materials as possible in the finished product and using as little as possible in energy and producing little or no waste.
Look at the process that makes acetic acid and other products from natural gas and air.

http://www.platinummetalsreview.com/pdf/pmr-v44-i3-094-105.p...

For acetic acid the reaction is pretty much;

2CH4 +2O2 -> CH3COOH + 2H2O

I forgot the two before the oxygen molecules!


[Edited on 4-2-2010 by ScienceSquirrel]
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[*] posted on 4-2-2010 at 15:05


Also if you look at this article you will realise that methane, water, and oxygen from the air can be converted into methanol and carbon monoxide to feed the industrial process to make acetic acid.
http://en.wikipedia.org/wiki/Methanol
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[*] posted on 4-2-2010 at 15:54


Quote: Originally posted by ScienceSquirrel  
Modern industrial organic chemistry is very demanding when it comes to incorporating as many atoms in the starting materials as possible in the finished product and using as little as possible in energy and producing little or no waste.


If this so called "Green Chemistry" principle is to be applied then mono nitro toluenes are ideal candidates to get amino benzoic acids by "Intra-molecular Redox Reaction"

CH3-C6H4-NO2 -------> HOOC-C6H4-NH2

100 % utilization of available atoms! :)

Seriously speaking though, one reads often about this rearrangement, but is there a published procedure for it?

gsd
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[*] posted on 5-2-2010 at 17:03


Nothing at all on the use of the PET component, terephthalic acid and the monoamide thereof? I mean, on an amateur forum, nobody is interested in making p-aminobenzoic acid via the Hoffman degradation of the amide of plastic waste?:o

Granted, I'm having a hard time finding references to forming the monoamide, although one would assume, like most amides, it could be made from the ammonium terephthalate salt via dehydration...

As to the nitration of toluene, yeah, it would work, but why waste oxidants and nitric/sulfuric acid when it can be, apparently, obtained via such a simple process....
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[*] posted on 5-2-2010 at 21:10


Quote: Originally posted by unome  
Nothing at all on the use of the PET component, terephthalic acid and the monoamide thereof? I mean, on an amateur forum, nobody is interested in making p-aminobenzoic acid via the Hoffman degradation of the amide of plastic waste?:o

Granted, I'm having a hard time finding references to forming the monoamide, although one would assume, like most amides, it could be made from the ammonium terephthalate salt via dehydration...

As to the nitration of toluene, yeah, it would work, but why waste oxidants and nitric/sulfuric acid when it can be, apparently, obtained via such a simple process....


There's a thread on exactly this. look harder.




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[*] posted on 6-2-2010 at 21:29


Quote: Originally posted by unome  
Nothing at all on the use of the PET component, terephthalic acid and the monoamide thereof? I mean, on an amateur forum, nobody is interested in making p-aminobenzoic acid via the Hoffman degradation of the amide of plastic waste?:o

Granted, I'm having a hard time finding references to forming the monoamide, although one would assume, like most amides, it could be made from the ammonium terephthalate salt via dehydration...

As to the nitration of toluene, yeah, it would work, but why waste oxidants and nitric/sulfuric acid when it can be, apparently, obtained via such a simple process....


Converting PET in to aminobenzoic acid will require potassium hydroxide, sulphuric acid for the hydrolysis, ammonia to make the salt, possibly a dehydrating agent and then bromine and sodium or potassium hydroxide or sodium hypochlorite for the Hoffmann reaction.
None of these grow on trees!
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unome
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[*] posted on 7-2-2010 at 00:35


Sodium hydroxide will also do the trick, the glycol is useful in itself, ammonia based fertilizers are cheap as shit and hypochlorite bleach (or Calcium Hypochlorite) is cheap and non-dangerous to purchase. I "CAN" get Nitric Acid in very small quantities, mixed with crap and it costs a fortune. Sulfuric acid, other than that from batteries, is not able to be purchased here, it has to be made. Waste PET, ammonium fertilizers, caustic soda and hypochlorite are unnoticeable.

[Edited on 7-2-2010 by unome]
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[*] posted on 7-2-2010 at 11:02


I can obtain all the chemicals relatively easily and there are published procedures for making PABA from toluene.
Making it up as you go along which is what you would have to do to make it from PET is a lot harder than following a recipe.
The other thing is that you will have not any analytical apparatus apart from maybe melting point so you could spend weeks going nowhere.
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[*] posted on 7-2-2010 at 16:12


I don't think so, the easiest way to determine if I have the acid is still going to be to use bicarbonate to end-point (anything that is not an acid at this point, ie. post-Hoffman, is going to be the diamine) if the substance is an acid, and can form an ester, then whether or not it forms an acetate/oxalate salt will let me know if it is aminoester, knowing what is in the pot and what is not, the use of basic analytical chemistry will solve the issue.

Insofar as that is a bitch to perform, I personally suspect that the separation of the nitrotoluene isomers would be every bit as enjoyable.

[Edited on 8-2-2010 by unome]
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[*] posted on 7-2-2010 at 16:39


Off you go then, plough your own furrow.
I suspect you have little or no experience of organic synthesis and its trials and tribulations.
Really good literature procedures are the result of hundreds of experiments that optimise reaction conditions. Organic chemistry is harder than you think.
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[*] posted on 7-2-2010 at 17:04


Quote: Originally posted by ScienceSquirrel  
Off you go then, plough your own furrow.
I suspect you have little or no experience of organic synthesis and its trials and tribulations.
Really good literature procedures are the result of hundreds of experiments that optimise reaction conditions. Organic chemistry is harder than you think.


Yet your basing this assumption on what now? His unwillingness to follow a cook book or his desire to find another means of synthesis from a ready avalible material worldwide?

I suspect he is correct in so being that seperation of the isomers could be a royal pain in the ass and analysis can be performed at home with ease. You people and your NMR machines ect are just down right spoiled. Go get some TLC plates, various reagents and do some real analysis already.





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[*] posted on 9-2-2010 at 04:50


Might I presume to suggest Ozonelabs try it out?:P I mean, they have already produced at least one local anesthetic, and this is the basic precursor to so many of the locals... There are literature procedures on using the diamide to form the phenylenediamine and from that the polyimide.... I wonder just how hard it would be to form the monoamide...
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[*] posted on 10-2-2010 at 02:12


The problems that I see with the TPA acid route revolve around getting the monoamide.

What is the Ka values for the two carboxylates on the TPA? If they're too close then you're faced with the possibility of having significant amounts of the diammonium salt mixed in with the monoammonium salt.

Then there's the issue of relative solubilities of the diacid, both ammoinium salts, monoamide, and diamide in the reaction mix. If the diacid, diammonium salt, diamide, or more than one of those, is significantly lower that the desired compound(s) then they will precipitate from the reaction mix and drive it away from forming the monoamide.

And there's the possibility of forming imides from even pure monoamide; this could well give oligomers and even polymers.

However, as you said, the source reagents are cheap and easy to come by. This could make an interesting bit of home research, as macro quantities can be used simple traditional methods can be used to identify products along the way.

If obtaining nitrates was not an issue, I would suggest rather than nitrating toluene instead nitrate polystyrene in DCM solution. The steric effects of the backbone and adjacent phenyls gives a ration of about 75% para, 15% ortho, and 10% meta. Oxidation of the backbone gives the nitrobenzoic acids. These can be separated by first slowly heating the free acids to ~150 C where the o- and m- acids melts and can be drained off as a mix with some dissolved p-; then dissolving the remaining solids in aqueous alkali and precipitating the para isomer by controlled acidification. The o- isomer has a pKa of around 2,16 and the p- around 3,41; the meta is a tiny bit weaker than the para - pKa ~3.5 so it needs to be mostly removed by the melt method or some other means first.

The backbone can be oxidised with KMnO4, by O2/air in acetic or butyric acid with a transition metal (Co, Mn, V) catalyst and a bit of LiBr, or by dilute nitric acid. See US patents 3978117 & 3978118 for the nitration process and HNO3 oxidation, as well as references to related processes bsed on polystyrene.

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[*] posted on 10-2-2010 at 04:13


Yeah, I was considering trying to form the mono-ester, then the amide from that... There are articles on the use of a Hoffman to transform reclaimed terephthalic acid to the diamine, so the solubility issue seems to be well in hand... I must request the articles I'm thinking of (when I remember where I saw them, JACS I think). I'm presuming that they do things differently to what would be expected to avoid contaminating the process stream with overly large amounts of the monoamide. Reversing that will give access to the monoamide:D
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[*] posted on 10-2-2010 at 06:18


There is no reason to presume that heating monoammonium terephthalate would give 4-carbamoylbenzoic acid (terephthalamic acid) selectively. Neither is this the case if heating with urea. There is more reason to believe it would give a mixture of terephthalamide, 4-carbamoylbenzoic acid and unreacted terephthalic acid together with other possible side products (if amides forms at all!).

In the literature there are examples where 4-carbamoylbenzoic acid is made from terephthalic acid, but nearly all examples start with the esterification to the dimethyl ester which can be selectively hydrolysed to the potassium monomethyl terephthalate. This is then ammonolysed to the 4-carbamoylbenzoic acid. One such example is described in J. Org. Chem., 42, 3118-3123 (the Hofmann degradation to 4-aminobenzoic acid is also described). Another such route to 4-carbamoylbenzoic acid is described in JP51008232 (the only difference is in the ammonolysis method):
Quote:
Abstract: Di-Me terephthalate (I) was partially hydrolyzed with alc. KOH and the mono-Me ester treated with aq. NH4OH to give terephthalamic acid (II). Thus, I was refluxed with KOH in MeOH for 2 hr. The solid was dissolved in H2O, stirred with 35% HCl for 0.5 hr, and treated with 28% aq. NH4OH at 30 for 7 hr to give 98.5% II.


The reason in why you can get hydrolyse dimethyl terephthalate to its monomethyl ester with such high selectivity is in the electronic effect the carboxylate group has on the rate of monomethyl ester further hydrolysis to the diacid (this effect is nicely explained in the Organikum book on the example of malonate esters. In the case of direct synthesis of terephthalamic acid from terephthalic acid there is not much to rely on this effect and not surprisingly I could find no such example in the literature using any method.

I think the idea of starting by nitrating styrene is better. Just three steps from the polymer to 4-aminobenzoic acid. 4-Nitrobenzoic acid is a nice crystalline solid and thus the ortho and meta isomers can be simply removed using just a recrystallization and no fancy isolation techniques (as is the case with nitrotoluenes).




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[*] posted on 13-2-2010 at 01:30


And this from a paper I have just requested:

Hydrolysis of Dimethyl Terephthalate for the Production of Terephthalic Acid

Myungsang Sim and Myungwan Han

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN
Vol. 39 (2006) , No. 3 pp.327-333
DOI: 10.1252/jcej.39.327 : JOI JST.JSTAGE/jcej/39.327

Abstract

Hydrolysis of dimethyl terephthalate (DMT) to produce terephthalic acid (TPA) was studied using a batch reactor. Zink acetate was used as a catalyst to promote the reaction rate. We found that the reaction consists of two reactions: from DMT to mono methyl terephthalate (MMT) and then MMT to TPA. The first reaction is relatively fast and irreversible while the second reaction is relatively slow and reversible. A kinetic equilibrium constant for the second reaction decreases with reaction temperature. A kinetic model consisting of the two reactions for the hydrolysis fitted well with the experimental data.

That is true, but Nitric acid isn't cheap, and I suspect forming the diester, then hydrolysis of the same to the same will be relatively low-brow compared to nitrating styrene.
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[*] posted on 21-2-2010 at 22:11


Ftw I know this is about this compound's synthesis, but if you're just looking for a source of it PABA is sold for really cheap as a dietary supplement.
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