General Description
Colorless crystals that discolor on exposure to light and air.
Reactivity Profile
P-AMINOBENZOIC ACID is incompatible with ferric salts and oxidizing agents.
Hazard
Questionable carcinogen.
Chemical Properties
White to off white crystalline powder
Originator
Pabalate,Robins,US,1949
Definition
ChEBI: An aminobenzoic acid in which the amino group is para to the carboxy group.
Indications
PABA preparations absorb UVL between 280 and 320 nm. This acid will
stain white fabrics, especially cotton. The esters of PABA are slightly less
effective and do not stain as much. Cross-sensitization can occur with some
sunscreens. In particular, PABA and its derivatives may cross-react with
sulfonamides, benzocaine, procaine, paraphenylenediamine, and azo dyes.
Padimate-O, the ester form of PABA, is also used for UVB protection.
Preparation
4-Aminobenzoic acid synthesis method: add 38.0g of p-nitrobenzoic acid, 200mL of water, 20mL of tetrahydrofuran, 0.4g of sodium dodecyl sulfonate and 1.9g of Raney nickel to the autoclave, nitrogen replacement Three times, fill with hydrogen, adjust the pressure to 0.9±0.1MPa, adjust the temperature to 100±2°C, and keep the reaction under pressure for 4h to complete. After the reaction, the catalyst was recovered by filtration, left to stand for stratification, the water layer was directly applied mechanically, the tetrahydrofuran layer was distilled and recovered and applied mechanically, then 1.5 g of activated carbon was added to the 4-aminobenzoic acid mother liquor, and under nitrogen protection, heating and refluxing for decolorization for 20min, Filtration, cooling and crystallization of mother liquor, filtration, drying under vacuum at 80-85 °C to obtain 30.3 g of 4-aminobenzoic acid with a yield of 97.2%, a melting point of 187.1-187.6 °C, and a content of 100.2% (permanent stop titration method) .
Manufacturing Process
The following example illustrates in detail the preparation of amino benzoic
acids from the hot reaction product obtained by the oxidation of a xylene and
containing a mixture of salt, amide salt and diamide of a phthalic acid.
800 cc of hot aqueous oxidation product, obtained from the oxidation of pxylene
with ammonium sulfate, hydrogen sulfide and water are boiled and agitated for 4 hours to remove carbon dioxide, hydrogen sulfide and
ammonia, sufficient water being added to maintain a constant volume. The
mixture is filtered to remove a precipitate containing elemental sulfur. 12
grams of activated charcoal are added to the filtrate and the mixture held at a
temperature of 180°F for 20 minutes. Filtration through diatomaceous earth
removes color bodies formed during the oxidation process and yields a pale
yellow filtrate. The filtrate is acidified with sulfuric acid to a pH of 3 or less to
precipitate approximately 49 grams of white solid, comprising a mixture of
terephthalic acid and amides of terephthalic acid, which are removed by
filtration. This solid is then washed with water at 200°F and redissolved in 200
cc of water containing 28.6 grams of sodium hydroxide.
A mixture of sodium hypochlorite and sodium hydroxide is prepared by adding
27.5 grams of chlorine to a vessel equipped with cooling means and
containing a solution of 50 grams of sodium hydroxide in 375 cc of water,
thereafter adding sufficient water to produce 500 cc of solution. 190 cc of this
cold solution are slowly added to the acid-amide solution previously prepared
so as to keep the temperature of the mixture below 55°F. The mixture is
stirred for 15 minutes and then heated rapidly to 200°F and maintained at
that temperature for one hour. 2 grams of sodium thiosulfate are added to
consume excess sodium hypochlorite. The solution is acidified to a pH of 3 or
less and filtered hot. The filter cake, comprising about 26.9 grams of
terephthalic acid, is then suspended in 300 cc of dilute sulfuric acid of pH
about 2, heated to 200°F and filtered hot.
The filtrates are combined, cooled, and extracted with three successive 200 cc
portions of ether. The pH of the filtrate is then raised to 3.5 with sodium
hydroxide and the filtrate extracted with six successive 200 cc portions of
ether to yield the balance of the product. The crude p-aminobenzoic acid
product is recovered by evaporation of ether and is suspended in hot benzene,
cooled and filtered to remove benzoic and toluic acids together with small
amounts of impurities soluble in the filtrate. Recrystallization of the product
from 200 cc of water yields 14.5 grams of light tan needles of p-aminobenzoic
acid having an acid number of 411 (theoretical value 409).
Aminobenzoic acid can be then purified and decolorized by a process
described in US Patent 2,735,865.
Brand name
RVPaba Lipstick (ICN).
Therapeutic Function
Sunscreen agent, Antirickettsial
Biological Functions
4-Aminobenzoic acid is one of the most important aromatic amino acids. It is an important part of the substances necessary for the growth and division of body cells. It has an irreplaceable role in the metabolism of life. It is used in yeast, liver, bran and malt. The content is very high. 4-Aminobenzoic acid can relieve anemia caused by lack of red blood cells, viral anemia, sprue and anemia during pregnancy. 4-Aminobenzoic acid is a high-efficiency nutritional product with the main ingredient - vitamin B-100, which can effectively improve the three major metabolisms of the human body, comprehensively combat fatigue and relieve stress. The compatibility of 4-aminobenzoic acid with penicillin or streptomycin can effectively improve the bacteriostatic effect.
Flammability and Explosibility
Nonflammable
Purification Methods
Purify p-aminobenzoic acid by dissolving it in 4-5% aqueous HCl at 50-60o, decolorising with charcoal and carefully precipitating it with 30% Na2CO3 to pH 3.5-4 in the presence of ascorbic acid. It can be recrystallised from water, EtOH or EtOH/water mixtures. [Beilstein 14 IV 1126.]
