Salts of Picric Acid

Picric acid is used on a large scale as a high explosive, but for this purpose requires a detonator. If a few small crystals of the pure acid are heated on a crucible lid, they first melt, and ultimately burn harmlessly with a smoky flame. Metallic salts of picric acid are much less stable than the free acid,... 

Trinitrophenol (4), commonly known as picric acid (VOD 7350 m/s, d = 1.71 g/cm ), was once used as a military explosive although its highly acidic nature enables it to readily corrode metals. This kind of reaction has led to many fatal accidents, a consequence of some metal picrates being very sensitive primary explosives. The lead salt of picric acid is a dangerous explosive and should be avoided at all cost. In contrast, the ammonium (Explosive D, VOD 7050 m/s, d = 1.60 g/cm ) and guanidine salts of picric acid are unusually insensitive to impact and have been used in armour piercing munitions. 

Trinitrochlorobenzene (picryl chloride) (87) can be prepared from the nitration of 2,4-dinitrochlorobenzene with nitronium tetrafluoroborate or mixed acid composed of fuming nitric acid and oleum. Picryl chloride is also synthesized from the reaction of phosphorous oxychloride with the pyridinium salt of picric acid. ... 

Originally, salts of picric acid (10.4) were used. 

A number of salts of picric acid have been described already (Vol. I). Some salts of polynitrophenols and of heavy metals have initiating properties. One of the earliest known substances of this kind is lead picrate. Its high sensitiveness to the action of mechanical impact, however, raised difficulties in its practical utilization. 

Unfortunately, salts of picric acid are also called picrates. Similar complexes are formed between phenols and quinones (quinhydrones).53 Olefins that contain electron-withdrawing substituents also act as acceptor molecules as do carbon tetrahalidesS4 and certain anhydrides.55 A particularly strong olefin acceptor is tetracyanoethylene.56... 

The heavy metal salts of picric acid are dangerously sensitive, and its major use is for the manufacture of ammonium picrate (Explosive D). 

Metal salts of picric acid may be formed by the action of picric acid on metals, their oxides or carbonates and in certain cases also on their other salts. They are crystalline substances, mostly more sensitive to friction, impact and heat, than picric acid itself. Due to their high sensitivity to stimuli, the explosive properties of picrates were known long before those of picric acid. 

Negative substituents enhance the acidic properties of phenols, an effect opposite to that produced with aromatic amines. o and p-Chloro-phenols are considerably stronger acids than phenol itself, and o- and p-nitrophenols are still stronger. Trinitrophenol, picric acid, is a strong acid whose salts are neutral and not decomposed by carbonic acid or by ammonium salts. These salts of picric acid can be salted out of neutral solutions by sodium or potassium chloride. With negatively substituted phenols, it may be possible to separate the phenolate from solutions which are neutral or weakly alkaline to litmus. In doubtful cases, just as with the amines, the precipitated material must be studied to determine whether it is the free phenol or one of its salts. The color of the precipitate gives an indication in the case of the nitrophenols, since the free phenols have only a weak yellow color, whereas the alkali salts are deep yellow. Solubility tests with indififerent solvents may be used in the case of uncolored compounds. Only the free phenol can be separated from acidic solutions. 

Picrate Explosives.—A most important property of the salts of picric acid, especially ammonimn picrate, is their explosive character. They are used in the manufacture of certain smokeless powders, e.g. melinite and liddite. Picric acid itself is not explosive but the salts are exploded either by percussion or ignition. Picric acid is used as an antiseptic and alleviator in the case of burns. It precipitates organic bases and proteins and is used in this way as a test for proteins. 

Environmental problems of TNT manufacture Other nitroaromatics Nitro derivatives of hydrocarbons Nitro derivatives of halogcnohydrocarbons Nitrophcnols Picric acid Salts of picric acid 2,4-Dinitrorcsorcinol Purification Slyphnic acid Tetranitrodian Picric acid ethers Hexanitrodiphenylaminc (hexyl)... 

EXPLOSION and FIRE CONCERNS flammable solid NFPA rating Health 3, Flammability 4, Reactivity 4 very unstable severe explosion hazard when shocked or exposed to heat can form salts of picric acid that are initiators and shock-sensitive forms unstable salts with concrete, ammonia, bases, and metals (e.g., lead, mercury, copper, and zinc) can form extremely explosive mixtures with uranium perchlorate mixtures with aluminum and water ignite after a delay period incompatible with all oxidizable substances, albumin, gelatin, and alkaloids toxic gases and vapors, such as carbon monoxide and oxides of nitrogen, may be released in a fire use flooding quantities of water for firefighting purposes. 

Generally, the drier or more desiccated a compound with potential explosive properties becomes, the greater the risk for an explosion. Picric acid, aka trinitrophenol, is related very closely to TNT (trinitrotoluene) and it is used in some laboratory operations. Normally, picric acid comes in a moist state from the supplier, and in this state it is safe to handle and store. However, when picric acid reaches a dry state it has the same potential as TNT to be explosive. Metal salts of picric acid are also known to be shock-sensitive. Picric acid needs to be on a timed disposal protocol to ensure that it is discarded before it can dry out and become hazardous. 

The pH-dependence of the effect of TFB and other uncouplers on the electrical conductivity of the BLM described above has been studied in detail by Sotnikov and Melnik i. They were interested in establishing the relationship between the pKa value of the modifier (e.g., DNP) and the conductivity of the BLM and found that the effectiveness of these compounds in lowering the conductivity follows their pK values. The conductivity for picric acid-modified BLM was about 10 Q cm. More recently, Wardak has investigated the effect of picric acid on the transport of and K+ and found that the salt of picric acid is highly permeable in the BLM. 

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