Author Topic: P-Aminobenzoic Acid?  (Read 2472 times)

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  • Guest
P-Aminobenzoic Acid?
« on: June 21, 2002, 09:01:00 PM »
Just out of curiousity, does anyone know of a substance from which useful quantities (say, a couple of grams without too much trouble) of p-aminobenzoic acid can be extracted?

I've looked all over for it, and all I can find are references to syntheses that require precursors that are just as ecclectic, and, as we all know, none of the major supply houses will deal with individuals, and none of the smaller supply houses that WILL deal with individuals seem to stock many organics...

Thanks in advance!  :)


  • Guest
You could also work backwards from one of its ...
« Reply #1 on: June 21, 2002, 09:40:00 PM »
You could also work backwards from one of its esters, that's if you only want a few grams of the stuff.

p-aminobenzoic acid apparently occurs in yeast !

Other than that you will either have to prepare it from p-nitrobenzoic acid by reduction, or from acet-p-toluidide by oxidation to p-acetylaminobenzoic acid and subsequent hydrolysis of the acetyl radical.

John Lennon - Working Class Hero


  • Guest
Re: You could also work backwards...
« Reply #2 on: June 21, 2002, 10:12:00 PM »
Thanks for the quick reply, though, as dumb as it may sound, I'm trying to have some quick and legal fun in the lab by synthesizing some of these esters (e.g. benzocaine).

For the record, though, in case anyone else is ever interested, I actually did manage to find a page after looking around some more in the last hour or so here that discusses a number of substances that one could possibly extract this substance from, as follows, although I was sort of hoping that there might have been a naturally occuring source of the chemical, or perhaps that it would be present in a simpler mixture that is not quite as troublesome with respect to extraction as I imagine a lot of these creams would be.

• Lipsticks
• Self-Browning Creams
• Covering Creams and Sticks
• Moisturizing Creams, Lotions and Emulsions
• Face, Body and Hand Creams
• Hair Cures and Hair Care Agents
• Hair Setting Lotions, Styling Gels, Hair Sprays
• Deodorants
• Eye Wrinkle Creams
• Multivitamin Preparations
• Preparations for the Treatment of Hair and Nail Diseases
• Tonics Marketed Towards the Geriatric Market

Apparently the prevalence of PABA in such products has something to do with the fact that it is an excellent blocker of ultraviolet light.

Most of these sound pretty nasty from the point of view of doing an extraction on them, but I would guess that a few of the afforementioned products occur in liquid form, and, thus, are more appropriate for a polar/nonpolar or acid/base extraction?


  • Guest
« Reply #3 on: June 23, 2002, 11:59:00 PM »
..the esters of PABA are used as preservatives, not as UV-blockers!
Upon the extraction....these esters are used in such tiny amounts (usually about 0.5 %) in creams or lotions loaded with emulsifiers, so I wouldn't bother about extracting may not even work.
Try to obtain PABA itself or one of the esters (methylparabene or propylparabene) and saponify it to PABA. Buying an ester of PABA should arouse no suspicion, as these are the most used preservatives worldwide. Or try the route from toluene via nitration, separation of p-nitrotoluene, oxidation to p-nitrobenzoic acid and the already mentioned reduction of the nitro group with iron filings/HCl.

Quidquid agis, prudenter agas et respice finem!


  • Guest
« Reply #4 on: June 24, 2002, 05:05:00 PM »
Synthesis of benzocaine from p-aminobenzoic acid? Funny you should mention that, because I've been looking to do exactly the same. PABA can be had quite easily as it is a dietary supplement. Go to your local chemist/druggist/health food/supplement store. Look for the "great wall of pills" which is built of dietary supplements such as amino acids and vitamins and the like. There should be a product range there that consists of single supplements rather than mixed coctails, and they should sell PABA. metwurst has here a bottle of 100 x 500mg PABA tablets which cost about US$7. They're obviously mixed with binders, but not too much. They taste vaguely acidic if sucked, and are really soft pills, and how hard the PABA is to extract is yet to be proven, but judging from the syntheses in chem classes all over the net, it should be a piece of cake. Health food stores are finally good for something!


  • Guest
PABA and more!!!
« Reply #5 on: June 25, 2002, 08:12:00 AM »
Yes also look for dimethylaminoethanol and get your novocaine precursors all in one shot, (the health food place)
Why complicate shit, it's complicated already.
I like to keep things simple as possible, and explain it the same way.
Some people like to explain things in such a complicated  context it pisses me off!


  • Guest
bucket experimentation
« Reply #6 on: June 26, 2002, 03:50:00 PM »
The 500mg PABA tablets metwurst had were determined to average 700mg each, and since metwurst is still several weeks away from aquiring equipment and consumables for TLC, he decided some bucket chemistry was in order.
35g of PABA tablets were added to 250mL 95% ethanol, and stirring was commenced.
When the pills were broken up entirely after about 30 minutes, the mixture was vacuum filtered yielding a clear yellow ethanolic solution of PABA and whatever component of the filler, if any, dissolved in the alcohol.
25mL conc. sulfuric was added and the mixture was refluxed for 75 minutes.
The resultant acidic yellow-brown mixture was taken to about pH 8  with sodium bicarbonate solution, which turned the mixture to a light beige color, and some precipitate was evident.
600mL of water was added causing immense precipitation.
This white precipitate was vacuum filtered and washed with water.
The mildly damp precipitate weighed 27.4g, and is still drying.
In the absence of any proper diagnostic equipment, and having read on the applications and dosage of benzocaine in medicine, a small amount (about two poppy seeds in size) was applied to the tip of the tongue. Mild anaesthesia of the tongue tip resulted, and from the taste, perhaps a tiny quantity of PABA is left. 100mg was smeared on a one inch square section of skin. Blunting of the pain response resulted within ten minutes, and lasted perceptibly for about 35 minutes.
Anaesthetic throat lozenges routinely contain 6.5mg of benzocaine.

If doing this, you might wish to test that you are not sensitive to benzocaine, as some people experience an irritation of the skin when benzocaine is applied. metwurst's only known chemical sensitivity is to a particular antibiotic agent, which might explain some of his nonchalance with regards to taste testing the product of this esterification.

This stuff obviously needs to be cleaned up properly, and metwurst would like to know how pure the product was to start with. More fun.


  • Guest
« Reply #7 on: June 26, 2002, 07:24:00 PM »
Benzocaine is much easier to extract from burn ointment then produce.  They have a number that come in spray cans with minimum contaimination.  In a life and time far far away,  I recall someone playing a nasty trick on a drug deprived cocaine addict using benzocaine extracted from one of those spray ointments.

Anyway, you seem more interested in the PABA.  Equipment for basic LC is filter paper, iodine and a solvent.

Variations include:
a) dissolving the sample in the solvent (wasteful)
b) taping a solid sample above the solvent line (contaimination from tape glue).
c) putting a single drop of the sample above the solvent line (best).

1) Suspend said paper with just the end in the solvent.
2) Allow the solution to wick up the paper.
3) Place the paper in a closed container with iodine crystals to allow it to develop.

The exact paper length is a matter of trial and error.  The solution should wick to the end of the paper. Not all organics respond to this method but the percentage is high enough.

For this to work the chemicals to be analyzed must be soluble in the solvent and they must turn brown on exposure to concentrated iodine vapor.

If all of the chemicals are not soluble then the separation procedure should be obvious.  Not many organics are completely inert to iodine vapor.

Liquid Chromotagraphy should be some mystical science.  It should be a working part of every potential chemists toolkit.  This is the way they do it in beginning organic chemistry.