Anthranilic acids

Other Names Anthranilic acid a-Aminobenzoic acid l-Aminobenzene-2-carboxylic acid 2-Aminobenzoic acid 2-Carboxyaniline 2-Carboxyphenylamine NSC 144 NSC 40929 Vitamin LI o-Aminobenzoic acid o-Anthranilic acid o-Carboxyaniline CA Index Name Benzoic acid, 2-amino-CAS Registry Number 118-92-3 Merck Index Number 422 Chemical Structure 

Chemical/Dye Class Fluorescent Molecular Formula C7H7NO2 Molecular Weight 137.14 pH Range 1.5-3.0 

Color Change at pH Non-fluorescence (1.5) light blue fluorescence (3.0) 

Light blue fluorescence (4.5) to dark blue fluorescence (6.0) 

Physical Form White to pale yellow crystalline powder 

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It is used as a first component in the preparation of azo-dyes, amlnoazo-dyes See azo-dyes, o-aminobenzoic acid See anthranilic acid. 

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

Prepared by the action of chloroethanoic acid upon anthranilic acid. It can also be prepared by the action of KCN and methanal on anthranilic acid, followed by hydrolysis with NaOH of the nitrile of anthranilic acid first produced. 

When treated with alkaline hypochlorite solution anthranilic acid is obtained. This reaction, the first stage in the indigo synthesis, is the most important commercial outlet for phthalimide. 

The first of the two experiments given below illustrates the separation of amino-acids, now an almost classic example of the use of paper chromatography the second illustrates the separation of anthranilic acid and iV-methylanthranilic acid. Both experiments show the micro scale of the separation, and also the fact that a mixture of compounds which are chemically closely similar can be readily separated, and also can be identified by the use of controls. 

Inspect the paper in ultraviolet light—conveniently in front on a Hanovia ultraviolet strip light—in a dark room. The acids show up as intense blue fluorescent spots. Mark with a pencil the positions of all spots. The position of the two spots arising from solution (C) should be compared with the single spots arising from solutions (A) and (B). It is probable that the solution (B) of pure N-methylan-thranilic acid may also reveal a faint spot corresponding to anthranilic acid still present in minute traces in the methylated acid cf. p. 223). 

Finally spray the paper with neutral 1% ethanolic ferric chloride solution the methylanthranilic acid spot develops a purple-brown coloration, whereas the anthranilic acid gives only a very faint pink coloration. 

Required Anthranilic acid, 20 g. anhydrous sodium carbonate, 7 5 g, sodium nitrite, 12 g. concentrated hydrochloric acid, 190 ml. crystalline copper sulphate, 50 g. concentrated ammonia, 85 ml, hydroxylamine hydrochloride, 14-5 g. (or hydroxylamine sulphate, 17-4 g.) acetic acid, 10-20 ml,... 

A) Diazotisation of Anthranilic Acid, Dissolve 20 g. of anthranilic acid in a solution of 7 5 g. of anhydrous sodium carbonate in 200 ml. of water contained in a 400 ml. beaker, (The mixture may be warmed very gently with stirring to obtain a solution more rapidly, and then cooled.) Add slowly 12 g. of sodium nitrite and cool the stirred solution below 10 , Pour this cold solution slowly on to a vigorously stirred mixture of 40 ml, of concentrated hydrochloric acid and 120 g. of crushed ice in a 600 ml. beaker. 

This preparation illustrates the use of dimethyl sulphate to convert a primary amino group into the secondary monomethylamino group, without the methy-lation proceeding to the tertiary dimethylamino stage. The methylation of anthranilic acid is arrested at the monomethylamino stage by using i-i molecular equiN alents of sodium hydroxide and of dimethyl sulphate. The reactions can be considered as ... 

The isolation of the. V-methylanthranilic acid is greatly facilitated by the fact that in cold water it is appreciably less soluble than anthranilic acid, and very much less soluble than A A -dimethylanthranilic acid. 

Dissolve 2 g. of anthranilic acid in 12 8 ml. of 5% aqueous sodium hydroxide, or in 16 ml. of A -NaOH solution in a 50 ml. conical flask. (It is essential that the concentration of the hydroxide solution is accurately known.) Add i-6 ml. of dimethyl sulphate, and shake the securely-stoppered flask vigorously. 

This recrystallised acid is pure in the norm y accepted sense of the word, namely it has a sharp m.p. and gives on analysis excellent values for carbon, hydrogen and nitrogen. If however it is subjected to one-dimensional paper chromatography (p. 53), the presence of traces of unchanged anthranilic acid can be detected, and repeated recrystallisation is necessary to remove these traces. 

Anthranilic acid HaNCeH COOH Cinnamic acid CeHjCH.CHCOOH... 

Note. When this test is applied to amino-acids, e.g. glycine, anthranilic acid, ulphanilic acid, no odour is detected owing to the non-volatility of the acidic isocyanide in the alkaline solution. 

Diazotisation. Dissolve 0 2 g. of anthranilic acid in about 4 ml. of dil. HCl and cool in ice-water. To this solution, add slowly about I ml. of cold 20% sodium nitrite. solution and divide the cold diazonium solution thus prepared into two portions A and B. 

Heating with soda dime. See Test 2 for anthranilic acid (p. 383) and also Section 3, p. 327. 

An amino-acid, although insoluble in water (e.g., anthranilic acid), is usually soluble in excess of mineral acid in such a case it is important to make the solution only very slightly acid. This applies also to a mixture of a neutral and a basic substance, from which dil. HCl will extract an amino-acid the solution must then be carefully treated with NaOH to precipitate the amino-acid. 

The reaction is applicable to the preparation of amines from amides of aliphatic aromatic, aryl-aliphatic and heterocyclic acids. A further example is given in Section IV,170 in connexion with the preparation of anthranilic acid from phthal-imide. It may be mentioned that for aliphatic monoamides containing more than eight carbon atoms aqueous alkaline hypohalite gives poor yields of the amines. Good results are obtained by treatment of the amide (C > 8) in methanol with sodium methoxide and bromine, followed by hydrolysis of the resulting N-alkyl methyl carbamate ... 

An interesting coupling reaction with the diazonium salt derived from anthranilic acid leads to an excellent method for the preparation of dlphenic acid. The reaction occurs with cuprous salts in ammoniacal solution ... 

The valuable indicator methyl red (o-carboxybenzene-azo-dimethylaniline) is obtained by coupling diazotised anthranilic acid with dimethylaniline ... 

If crude anthranilic acid is employed, it should be titrated against standard alkali with phenolphthalein as indicator, and the weight adjusted in accordance with the purity. 

Anthranilic acid. This substance, the ortho amino derivative of benzoic acid, may be conveniently prepared by the action of sodium hypobromite (or sodium hypochlorite) solution upon phthalimide in alkaline solution at 80°. The ring in phthalimide is opened by hydrolysis to phthalamidic acid and the latter undergoes the Hofmann reaction (compare Section 111,116) ... 

Phenylglycine-o-carboxylic acid. In a 750 ml. round-bottomed flask, fitted with a reflux condenser, place 14 g. of anthranilic acid (Section IV,170), 10 g. of chloroacetic acid, 20 g. of anhydrous sodium carbonate and 200 ml. of water. Reflux the mixture for. 3 hours, then pour into a beaker, cool, render shghtly acid with concentrated hy dro-chloric acid, and allow to stand overnight. Filter off the crude acid and wash it with water. Recrystalhse from hot water with the aid of a little decolourising carbon, and dry the acid at 100°. The yield of phenyl-glycine-o-carboxyhc acid, m.p. 208°, is 12 g. 

Supplement 1951 1872-1928 Hydroxy-carbonyl amines, 233. Amino-carboxylic acids Anthranilic acid (o-aminobenzoicacid). 310. Amino-hydroxy-carboxylic acids, 577. Amino-sulphonic acids Sulphanilio acid, 695. 

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