Solubility of Picric Acid in Water

The most versatile derivative from which the free base can be readily recovered is the picrate. This is very satisfactory for primary and secondary aliphatic amines and aromatic amines and is particularly so for heterocyclic bases. The amine, dissolv in water or alcohol, is treated with excess of a saturated solution of picric acid in water or alcohol, respectively, until separation of the picrate is complete. If separation does not occur, the solution is stirred vigorously and warmed for a few minutes, or diluted with a solvent in which the picrate is insoluble. Thus, a solution of the amine and picric acid in ethanol can be treated with petroleum ether to precipitate the picrate. Alternatively, the amine can be dissolved in alcohol and aqueous picric acid added. The picrate is filtered off, washed with water or ethanol and recrystallised from boiling water, ethanol, methanol, aqueous ethanol, methanol or chloroform. The solubility of picric acid in water and ethanol is 1.4 and 6.23 % respectively at 20°. 

Solubility of Picric Acid in Water Solubility of Picric Acid in Nitric Acid... 

Solubilty. Doliriski [41] gave the following figures for the solubility of picric acid in water at various temperatures (Table 109) (see also Findlay [41a]). 

If the amine is soluble in water, mix it with a slight excess (about 25 per cent.) of a saturated solution of picric acid in water (the solubility in cold water is about 1 per cent.). If the amine is insoluble in water, dissolve it by the addition of 2-3 drops of dilute hydrochloric acid (1 1) for each 2-3 ml. of water, then add a sUght excess of the reagent. If a heavy precipitate does not form immediately after the addition of the picric acid solution, allow the mixture to stand for some time and then shake vigorously. Filter off the precipitated picrate and recrystaUise it from boiling water, alcohol or dilute alcohol, boiUng 10 per cent, acetic acid, chloroform or, best, benzene. 

Washings are collected in special wooden tanks for settling. The spent acid is also added to the washings so as to bring the H2S04 content to 10-30% as in such an acid water the solubility of picric acid is at its lowest. The water is decanted from time to time and disposed off into the river, after being neutralized, while the settled picric acid is collected from the bottom of the tank. 

Mercuric oxide (8-4 grams) is shaken for several hours with a solution of 15 grams of picric acid in 800 c.c. of water at 80° C., when orange-yellow needles separate. If this mixture is then boiled the anhydride results. It yields small, pale yellow crystals which are only slightly soluble in the usual solvents and decompose without melting. In aqueous solution it is a non-electrolyte, and with dilute hydrochloric acid the ehloro-... 

Oxazines can form salts with strong acids. The salts vary with regard to their solubility and stability. Some of the hydrochlorides are hydrolyzed by water. Some less common salts are known e.g., dichromates and ferrocyanates, " chloroplatinates and chloroaurates. Sometimes the picrates can also be used to identify the 1,3-oxazine derivatives. " In some instances a special procedure is required to form the picrates, as the heterocyclic ring can open under the action of picric acid. " ... 

The mixture is then chilled in an ice bath for at least 3 hours, and the olive-brown precipitate of the sparingly soluble copper complex of imidazole derivatives is filtered. The product is washed with about 500 ml. of cold water, suspended while moist (Note 4) in 11. of water, and rendered just acid to litmus by the addition of concentrated hydrochloric acid (about 40 ml.). Hydrogen sulfide is then passed into the suspension, with frequent shaking, until precipitation of the copper is complete (2-3 hours). The precipitate is filtered and extracted with 500 ml. of hot water in two or three portions. The clear, light brown to reddish brown filtrate and washings are boiled for 15 minutes, and then 60 g. (0.26 mole) of picric acid is added with stirring heating is continued until solution is complete. 

Picric acid is a strong acid, very toxic, soluble in hot water, alcohol, ether, benzene and acetone, and is a fast yellow dye for silk and wool. It attacks common metals, except for aluminium and tin, and produces salts which are very explosive. The explosive power of picric acid is somewhat superior to that of TNT, both with regard to the strength and... 

Ammonium picrate is soluble in water, alcohol and acetone, and is practically insoluble in ether. It is prepared by saturating an aqueous solution of picric acid with ammonia a red form is formed first which passes into the stable yellow form in the presence of water vapor, on prolonged storage or by recrystallization from water. Ammonium picrate has been employed as an explosive in military charges. 

C. 1.2 g of picric acid is soluble in 100 g of cold v/ater and 7.2 g in 100 g of hot water soluble in alcohol, ether or benzene. It forms picrates, which are sensitive to shock and friction, in combination with lead, iron, copper or other salts. 

Trinitrophenol is known by the common name picric acid. Picric acid is a solid but is readily soluble in water. In solution it is used as a biological tissue stain. As a solid, it is also known to be unstable and may explode. In this way it is similar to 2,4,6-trinitrotoluene (TNT). Draw the structures of picric acid and TNT. Why is picric acid readily soluble in water whereas TNT is not ... 

It is a strong acid, forming well crystallised yellow salts, which detonate violently when heated, some of them also by percussion. The potassium salt, C 6 H 2 (NO 2 ) 3 OK, crystallises in long needles very slightly soluble in water. The sodium, ammonium, and barium salts are, however, easily soluble in water. Picric acid, when heated, bums with a luminous and smoky flame, and may be burnt away in large quantity without explosion but the mere contact of certain metallic oxides, with picric acid, in the presence of heat, develops powerful explosives, which are capable of acting as detonators to an indefinite amount of the acid, wet or dry, which is within reach of their detonative influence. The formula of picric acid is... 

Potassium Picrate [KC 6 H 2 (N0 2 ) 3 0]. When a strong solution of picric acid is neutralised by carbonate of potash, this salt is thrown down in yellow crystalline needles, which require 260 parts of cold or 14 parts of hot water for their solution. In alcohol it is much less soluble. 

---