What Is Para-Aminobenzoic Acid?

Para-aminobenzoic acid (PABA) is a compound formed by replacing the para (4-position) on the benzene ring of benzoic acid with an amino group.

On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization initially compiled the reference, and p-aminobenzoic acid was included in the list of Class 3 carcinogens. ^[1]

Chinese name: P-aminobenzoic acid
English name: 4-aminobenzoic acid
nickname: 4-aminobenzoic acid
Chemical formula: C7H7NO2
Molecular weight: 137.14

CAS Registry Number: 150-13-0
EINECS registration number: 205-753-0
Melting point: 187 188
Water soluble: Slightly soluble
Density: 1.374 (25 ° C)

Introduction to Paraben

Para-aminobenzoic acid is one of the constituents of folic acid, which is necessary for the growth and division of the body's cells. It is synthesized by the shikimic acid pathway via branched acids. The first reaction step is the reaction of a branched acid with ammonia to form 4-amino-4-deoxy branched acid, which is catalyzed by an amino deoxy branched acid synthetase. The 4-amino-4-deoxy branched acid then eliminates one pyruvate and is aromatized to p-aminobenzoic acid. The second-step reaction in bacteria is catalyzed by aminodeoxybranching lyase, and a similar enzyme is likely to be present in plants, but has not yet been found.

Physicochemical properties of p-aminobenzoic acid

Traits: colorless needle-like crystals. Turns pale yellow in air or light. With moderate toxicity. Irritates skin and mucous membranes. Rinse immediately with water after contact with skin. ^[2]

P-aminobenzoic acid structural formula

Melting point: 187 ~ 187.5 ^[3]

Density: 1.374 g / mL at 25 ° C

Solubility: Easily soluble in hot water, ether, ethyl acetate, ethanol and glacial acetic acid, hardly soluble in water and benzene, insoluble in petroleum ether.

Ethanol use

Used in dyes and pharmaceutical intermediates. Used in the production of reactive red M-80, M-10B, reactive red violet X-2R and other dyes, and the production of cyanobenzoic acid to produce p-carboxybenzylamine. Para-aminobenzoic acid can be used as a sunscreen, its derivative octyl dimethylcarbamate, is an excellent sunscreen, trade name Padimate O. Preparation or source

(1) Derived from p-nitrobenzoic acid.

(2) It is prepared from p-nitrotoluene through oxidation reduction.

(3) It is prepared from p-methylaniline through acetylation, oxidation and reduction.

Under the catalysis of dihydrofolate synthase, p-aminobenzoic acid synthesizes dihydrofolate with dihydropteridine pyrophosphate and glutamic acid or dihydropteridine pyrophosphate and p-aminobenzoylglutamic acid. Dihydrofolate is then reduced to tetrahydrofolate under the catalysis of dihydrofolate reductase. Tetrahydrofolate is further synthesized to obtain coenzyme F, which provides a carbon unit for bacteria to synthesize DNA bases. Sulfonamides, as derivatives of p-aminobenzenesulfonamide, have similar structures, molecular sizes, and charge distributions as the substrate p-aminobenzoic acid, so they can replace p-aminobenzoic acid in the synthesis of dihydrofolate and block the synthesis. This causes the folic acid synthesis of the microorganisms to be blocked and life cannot be continued.

The p-aminobenzoic acid in the cytoplasm is reversibly converted to glucuronide under the catalysis of glucuronyl transferase, so all or most of the p-aminobenzoic acid in the plant is esterified, which may be the p-amino A form of storage and transportation of benzoic acid.

Production method of p-aminobenzoic acid

1. Add water, sodium chloride, and hydrochloric acid in this order. ^[4] Start stirring and heat up to 50-60 ° C, add 9/10 quantity of iron powder, continue to heat up to 98-102 ° C, hold for 1h, stop heating, slowly add p-nitrobenzoic acid at 95 ° C, about 1 -1.5h after adding, add iron powder, keep it at 98-102 for 1h, let cool to 80 , add 30% liquid alkali to adjust pH = 8.5-9, press filter, wash with a small amount of water, combine the filtrate with a small amount of washing , Press into an acid precipitation pot, cool to 30-34 ° C, add insurance powder to decolorize, and filter. Add acid to the filtrate to adjust pH = 3.5-4, continue to cool to below 10 ° C, shake the water and dry to obtain the finished product. Yield was 84-88%.

2. Catalytic hydrogenation of p-nitrobenzoic acid to obtain industrial p-nitrobenzoic acid and water in a 1000ml beaker, adjust the pH = 6-7 with 22% sodium hydroxide under stirring, and then add Raney nickel With stirring, the feed liquid is pumped into a swinging autoclave, respectively with hydrogen; nitrogen is replaced twice each; refilled to 3.43 MPa, pressure 3.43-2.54 MPa; reaction at temperature 134-140 for about 5 hours, The end of hydrogen pressure does not decrease. After the reaction, it was filtered and dried to obtain the finished product. The yield is over 80%.

Para -aminobenzoic acid storage and transportation characteristics

Storage conditions: 2-8 ° C. It should be protected from heat, moisture and sunlight during storage. Store in a cool, ventilated and dry place. ^[2]

Overview of the dangers of p-aminobenzoic acid

Skin contact: Remove contaminated clothing and rinse with running water.

Eye contact: Raise eyelids and rinse with running water or saline. Seek medical attention.

Inhalation: Remove to fresh air. If breathing is difficult, give oxygen. Seek medical attention.

Ingestion: Drink plenty of warm water and induce vomiting. Seek medical attention.

Ethanol fire protection measures

Hazardous characteristics: Combustible in case of open flame and high heat.

Hazardous combustion products: carbon monoxide, carbon dioxide, nitrogen oxides.

Fire fighting methods: Firefighters must wear gas masks and full-body firefighting suits to extinguish fire in the upwind direction. Fire extinguishing agent: mist water, foam, dry powder, carbon dioxide, sand.

Emergency treatment for p-aminobenzoic acid leakage

Emergency treatment: Isolate leaking contaminated areas and restrict access. Cut off the fire. It is recommended that emergency handlers wear dust masks (full-face masks) and wear protective clothing. Avoid dust, sweep up carefully, transfer to a safe place in a bag. If a large amount of leakage, cover with plastic cloth, canvas. Collect, recycle or transport to waste disposal site for disposal.