Preparation of 3,5-Dinitrobenzoates

5-Dinitrobenzoyl chloride releases hydrochloric acid upon hydrolysis, so avoid contact of this reagent with your skin. If contact occurs, immediately flood the area with water and rinse it with 5% sodium bicarbonate solution. Wear latex gloves when handling this reagent. 

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Method A. A/ofe 3,5-Dinitrobenzoyl chloride is reaotive toward water it should be used immediately after weighing. Take oare to minimize its exposure to air and to keep the bottle tightly closed. 

6 mL of the alcohol with about 0.2 g of 3,5-dinitrobenzoyl chloride and 0.2 mL of pyridine in a small round-bottom flask equipped for magnetic stirring and for heating under reflux with protection from atmospheric moisture. Gently heat the mixture under reflux for 30 min, although 15 min is sufficient for a primary alcohol. Cool the solution and add about 5 mL of 0.6 Maqueous sodium bicarbonate solution. Cool this solution in an ice-water bath, and collect the crude crystalline product. Recrystallize the product from aqueous ethanol, using a minimum volume of solvent. 

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When good quality 3,5-dinitrobenzoyl chloride is not obtainable in sealed glass ampoules, it may be prepared in a condition suitable for the preparation of 3,5-dinitrobenzoates of alcohols and phenols, in the following manner. 

The preparation of 3,5-dinitrobenzoates is advantageous even when the alcohol is available in the form of a dilute aqueous solution. Derivatives are prepared by shaking an aqueous solution of alcohol with a solution of 3,5-dinitrobenzoylchloride in a mixture of ether and benzene in the presence of pyridine. The aqueous phase should be saturated with potassium carbonate. 

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. 

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.

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. 

Second series of derivatives. It is convenient when a second series of derivatives can be prepared from the derivatives in a simple way, and when the identification constants of the second series prove definitely the identity of the tested substance. For example, alcohols are identified as esters of 3,5-dinitrobenzoic acid, and these give addition compounds with 1-naphthylamine, etc. 

The most suitable method for the detection and identification of alcohols is the utilization of the reaction with 3,5-dinitrobenzoyl chloride the reaction has been very thoroughly studied and it can be used in combination with paper chromatography for simultaneous detection and identification. As they serve for identification purposes, the esters of 3,5-dinitrobenzoic acid were prepared from a maximum number of alcohols. Another advantage consists in the possibility of preparing these derivatives even when the alcohols are available only in the form of their aqueous solutions. 

A suitable substitution of the aromatic nucleus of benzoyl chloride (nitration, bromination), or the use of chlorides of naphthalene-carboxylic adds, or, especially, anthraquinone-carboxylic acids, results in their esters being solid substances, even when prepared from aliphatic alcohols. The most popular derivatives for the identification of alcohols are, however, the esters of 3,5-dinitrobenzoic acid. 

Dinitrobenzoates give crystalline complexes with aromatic amines. 1-Naphthylamine is especially suitable for identification purposes. Complex compounds are prepared by mixing both components in a mixture of alcohol and ether. These complexes crystallize well and serve as a second series of derivatives. They can also be used for the purification of 3,5-dinitrobenzoates which do not crystallize well. 

The ether (0.05 ml), 3,5-dinitrobenzoic acid anhydride (0.05 g) [for the preparation see (5)], and 1 ml of a 0.5 m SnCl4 solution in benzene (prepared from 6 ml of SnCl4 and benzene to make a total volume 100 ml) are introduced into an ampoule which is then sealed and heated at 120 °C for 30 min. After cooling, the ampoule is opened and the benzenic solution is spotted directly onto a strip of chromatographic paper, where solutions of aut-enthic samples of esters of 3,5-dinitrobenzoic acid are also applied (see p. 154). Chromatography is carried out in dimethylformamide or formamide/ /hexane. For thin-layer chromatography on silica gel G the system cyclohexane-carbon tetrachloride-ethyl acetate (10 75 15) is used. 

Procedure 10 ml of the reagent are added into a 20-ml test tube containing 0.2 ml of diethyl acetal, and the mixture is allowed to stand for 1 hr. The separated 2,4-dinitrophenylhydrazone is filtered off and dried. Yield, 45 mg mp, 157—158 °C. After crystallization from 8 ml of ethanol 30 mg of pure product were obtained, mp 159—160 °C. After the isolation of the hydrazone the filtrate is transferred into a distillation flask, diluted with 10 ml of water, and distilled. Ten milliliters of the condensate are collected and the distillate is worked up as described on p. 150, preparing a 3,5-dinitrobenzoate. Yield, 98 mg mp, 91 °C,... 

Formation of, -dinitrobenzoates. Aliphatic ethers are broken up by heating with ZnClg, and a 3,5--dinitrobenzoate of the residue can then be prepared. This is suitable only for symmetrical ethers. 

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. 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

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) ... 

Diethylene glycol method. Place 0-5 g. of potassium hydroxide pellets, 3 ml. of diethylene glycol and 0 5 ml. of water in a 10 or 25 ml. distilling flask heat the mixture gently until the alkali has dissolved and cool. Add 1-2 g. of the ester and mix well. Fit the flask with a thermometer and a small water-cooled condenser in the usual way. Heat the flask over a small flame whilst shaking gently to mix the contents. When only one liquid phase, or one hquid phase and one solid phase, remains in the flask, heat the mixture more strongly so that the alcohol distils. Identify the alcohol in the distillate by the preparation of the 3 5 dinitrobenzoate (Section 111,27,2). 

Irradiated ergosterol was found not to be as antirachitic in the chick as in the rat, whereas the chick could be protected by direct kradiation. The provitamin in cholesterol was shown not to be ergosterol. Rygh (14) in 1935 found that 1 rat unit of cod Hver oil was 100 times more potent in chicks than 1 rat unit of vitamin D2. Brockmann (15) in 1936, prepared the pure crystalline 3,5-dinitrobenzoate derivative of vitamin D obtained from tuna Hver oil... 

Mori reported an improved synthesis of (3S,4P,6 ,10Z)-faranal (37), the trail pheromone of the Pharaoh s ant (Monomorium pharaonis) [84]. As summarized in Scheme 55, the key-reaction was the coupling of iododiene A with iodide E. The geometrically pure A was prepared by the zirconocene-mediated carbo-alumination reaction, and E was prepared from B by the asymmetric cleavage of its epoxy ring to give C (77% ee), which could be purified via its crystalline 3,5-dinitrobenzoate D. 

Marans and co-workers used pentaerythritol trinitrate (81) to synthesize a number of aryl and alkyl esters, including the formate, propionate (84), oxalate, succinate, benzoate (85), 3,5-dinitrobenzoate (86), and ortho-, meta-, and para- (87) nitrobenzoate esters. The para-nitrobenzoate ester (87) has also been prepared from the nitration of pentaerythritol monobenzoate with mixed acid. ... 

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