What molecule am I?
p-Aminobenzoic acid (PABA) is a bifunctional aromatic molecule that occurs naturally via bacterial production in animals’ digestive systems and plants’ chloroplasts. It is particularly abundant in baker’s yeast and brewer’s yeast in concentrations ranging from 5 to 100 ppm.
PABA was mentioned in the chemical literature as early as 1900, by British chemist Walter J. Elliott in an article on reactions of its isomer o-aminobenzoic acid1. The same year, it was alluded to by Marston Taylor Bogert and August Henry Gotthelf at Columbia University (New York City), also in connection with the ortho isomer. It is not clear how PABA was discovered or first synthesized, other than that it has been known since 1863.
In 1959 US Patent 2,878,281, inventors William G. Toland and Charles D. Heaton at the now-defunct California Research Corp. (San Francisco) synthesized PABA by first oxidizing p-xylene2 to terephthalic acid3 and its mono- and diamides, and then heating the mixture with sodium hydroxide and sodium hypochlorite. The next year, in US Patent 2,947,781, Louis Spiegler at DuPont (Wilmington, DE) took another approach; he used catalytic hydrogenation to reduce p-nitrobenzoic acid4 to PABA. These and similar methods are used currently , along with ones that begin with methyl 4-formylbenzoate5 and some fermentation processes.
PABA was once called “vitamin B10” or “vitamin Bx”; but it is no longer considered a vitamin because microorganisms in the body generate it. Similarly, it has been sold as a nutritional supplement, although few people have PABA deficiencies.
Uses of PABA include the synthesis of its esters, azo dyes, and folic acid. (It is an intermediate in the biosynthesis of folic acid and its derivatives.) It was formerly used as an ingredient in sunscreens; but this this use was discontinued because of possible cellular damage caused by UV absorption and for associated allergic reactions.
1. CAS Reg. No. 118-92-3; aka anthranilic acid.
2. CAS Reg. No. 106-42-3.
3. CAS Reg. No. 100-21-0.
4. CAS Reg. No. 62-23-7.
5. CAS Reg. No. 1571-08-0.
p-Aminobenzoic acid
hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 4 | H302—Harmful if swallowed |  |
| Skin corrosion/irritation. category 2 | H315—Causes skin irritation | |
| Skin sensitization, category 1 | H317—May cause an allergic skin reaction | |
| Serious eye damage, category 2A | H319—Causes serious eye irritation | |
| Specific target organ toxicity, single exposure, respiratory tract irritation, category 3 | H335—May cause respiratory irritation | |
| Long-term (chronic) aquatic hazard, category 3 | H412—Harmful to aquatic life with long-lasting effects | |
*Compilation of multiple safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
Winter Remedy Molecule
Many Asian cultures use various forms of ginger (Zingiber officinale) in traditional medicine, particularly as a ginger tea. Ginger components such as former Molecules of the Week gingerol1 and shogaol2 are claimed to be remedies for cough, sore throat, and the common cold; but the US Food and Drug Administration has not approved them for medical use and, like many herbal medicines, has placed them under restrictions.
Paradol3, also found in ginger, has a chemical structure similar to those of gingerol and shogaol. In 1917, E. K. Nelson at the US Department of Agriculture comprehensively described gingerol and paradol, the latter of which was extracted from grains of paradise (Aframomum melegueta)4, a member of the ginger family. Paradol is the prime flavor component of A. melegueta and is used to add spiciness to foods.
In 2001, Kwang-Kyun Park and colleagues at Yonsei University (Seoul) and Seoul National University reported that paradol significantly reduced the incidence and multiplicity of skin tumors in laboratory mice.
1. CAS Reg. No. 23513-14-6.
2. CAS Reg. No. 555-66-8.
3. CAS Reg. No. 27113-22-0.
4. Nelson’s terms were “paradise” and “Amomum melegueta”. The plant is also called Guinea pepper.
Winter Remedy Molecules
Throughout January, MOTW is featuring key components of natural substances that people use when they have coughs or runny noses.—Ed. See this week's winter remedy.
This molecule was suggested by a reader. We present almost all of the molecules suggested by our readers. If you have a molecule you would like us to consider, please send us a message. And thank you for your interest in Molecule of the Week! —Ed.
p-Aminobenzoic acid fast facts
| CAS Reg. No. | 150-13-0 |
| SciFindern name | Benzoic acid, 4-amino- |
| Empirical formula | C7H7NO2 |
| Molar mass | 137.14 g/mol |
| Appearance | White crystals or powder |
| Melting point | 188–189 ºC |
| Water solubility | 5.9 g/L (25 ºC) |
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