3.5- Dinitrobenzoic acid, preparation

The melting points of these esters are usually much lower than those of the corresponding 3 5 dinitrobenzoates their preparation, therefore, offers no advantages over the latter except for alcohols of high molecular weight and for polyhydroxy compounds. The reagent is, however, cheaper than 3 5 dinitrobenzoyl chloride it hydrolyses in the air so that it should either be stored under light petroleum or be prepared from the acid, when required, by the thionyl chloride or phosphorus pentachloride method. 

Dinitrobenzoic acid. This acid may be prepared by the nitration of benzoic acid with a mixture of concentrated sulphuric acid and fuming nitric acid under special conditions (see also Section VII,22) ... 

Dinitrobenzoyl chloride reacts readily with water and it should be kept in sealed tubes or under light petroleum. When required for qualitative organic analysis it is usually best prepared from 3 5 dinitrobenzoic acid immediately before use (see Section 111,27,2). 

Cognate preparations. 3,5-Dinitrobenzoyl chloride. Place a mixture of 30 g (0.141 mol) of 3,5-dinitrobenzoic acid (Expt 6.160) and 33 g (0.158 mol) of phosphorus pentachloride in a round-bottomed flask fit a reflux condenser, and heat the mixture in an oil bath at 120-130°C for 75 minutes. Allow to cool. Remove the phosphorus oxychloride by distillation under reduced pressure (25 °C/20mmHg) raise the temperature of the bath to 110 °C. The residual 3,5-dinitrobenzoyl chloride solidifies on cooling to a brown mass the yield is quantitative. Recrystallise from carbon tetrachloride the yield is 25 g (77%), m.p. 67-68 °C, and this is satisfactory for most purposes. Further recrystallisation from a large volume of light petroleum, b.p. 40-60 °C, gives a perfectly pure product, m.p. 69.5 °C. 

B) 2,5-Dinitrobenzoic Acid.—A suspension of 20 g. (0.12 mole) of the air-dried 2-nitroso-5-nitrotoluene in 100 cc. of water is prepared in a 500-cc. Erlenmeyer flask, and to it is added 50 g. (0.17 mole) of powdered potassium dichromate (Note 5). The flask is placed in an ice-salt bath, and the mixture is stirred vigorously by means of an efficient stirrer. When the temperature has dropped to 5°, 175 cc. of concentrated sulfuric acid is added in a thin stream (Note 6), while the temperature is not allowed to exceed 35°. After all the sulfuric acid has been added the mixture is stirred and heated to 50°. The source of heat is removed, and the temperature is maintained between 50° and 55° by cooling in an ice bath as the exothermic reaction takes place (Note 7). After twenty minutes the temperature is raised to 65° 3°, and held there for one hour longer. 

Dinitrobenzoic acid has been prepared by nitration of o-nitrobenzoic acid and fractional crystallization of the acids as the barium salts 1 and by oxidation of 2,5-dinitrotoluene.2... 

Dinitrobenzoic acid has been prepared by nitration of benzoic acid with sulfuric acid and fuming nitric acid 1 by nitration of 3-nitrobenzoic acid 2 and by oxidation of 3,5-dinitrotol-uene.1, 3 It has been obtained along with other products by the action of nitric acid upon 1,5-dinitronaphthalene.4... 

Figure 12.1 Dinitrobenzoylated-aminopropyl-silica. This phase is prepared by a catalysed reaction of 3,5-dinitrobenzoic acid with aminopropyl-silica. Retention takes place through charge transfer interactions when an analyte containing an electron-rich n-electron system interacts with the electron-deficient dinitrobenzoyl- system.

G) Identification of Monohydroxy Compounds. The evolution of hydrogen chloride, when acetyl chloride or phosphorus trichloride is added to a compound, indicates the possible presence of a hydroxy group. For identification purposes a derivative should be prepared. 3, 5-Dinitrobenzoic acid forms crystalline derivatives with hydroxy compounds. The melting points of the esters are utilized for identification. 

DinitrobenzoyI chloride. Place in an eight-inch tube 2 g of 3,5-dinitrobenzoic acid and 4 g of phosphorus pentachloride. Heat in the hood with a small smoky flame for five minutes. In the beginning the tube is heated to start the reaction and thereupon the flame is removed until the reaction has subsided. Then the flame is adjusted so that the vapors condense at about the middle of the tube. Allow to cool for one minute and pour carefully into a small evaporating dish. Cool and transfer the sohd to a paper drying disc or to several filter-paper circles. Press with the spatula so as to force the phosphorus oxychloride into the absorbent medium. After ten minutes transfer the crude 3,5-dinitrobenzoyl chloride into a small bottle or tube. The crude material is satisfactory for the preparation of derivatives of the lower hydroxy compounds. 

The reaction of chlorine gas and aqueous sodium hydroxide with 4-hydroxy-3,5-dinitrobenzoic acid can be used to prepare chloropicrin (Simandi and Soos, 1986). 

Dinitrobenzoic acid. This acid may be prepared by the nitration... 

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