Ammonium salt, also known as 2,4,6-trinitrophenol or TNP, is an organic compound first synthesized in 1771 by German chemist Johann Tobias Lowitz. However, its explosive properties were not discovered until 1863 by Italian scientist Ascanio Sobrero who was conducting experiments on the nitration of hydrocarbons. Ammonium salt was first produced by nitrating phenol under concentrated sulfuric and nitric acids. Its high melting point of 122°C and low vapor pressure made it a stable compound at room temperature.
Physical and Picric Acid
Ammonium salt is a yellow crystalline solid that issparingly soluble in water but highly soluble in ethanol, ether and acetone. It is a derivative of phenol where the hydroxyl group is nitrated with nitric acid to form three nitro groups. Chemically, ammonium salt is classified as an energetic material due to the presence of highly electronegative nitro groups. Its molecular formula is C6H3N3O7 and has a molecular weight of 229.10 g/mol. Ammonium salt is stable when pure and dry but becomes explosive when contaminated with metal ions or when wet. It has a sensitivity towards shock, heat and friction.
Industrial Applications
Due to Picric Acid high energetic content, ammonium salt finds applications as high explosive in ammunition and weapons systems. During World Wars I and II, militaries of many countries used ammonium salt in ammunition filling, shells, bombs and grenades. It was preferred in explosives until trinitrotoluene gained popularity since the 1940s. Even today, some developing nations employ ammonium salt in warheads. Apart from military explosives, ammonium salt is used industrially as a dyeintermediate in the manufacture of azo dyes and several indicators in chemical analysis. It is used as an analgesic in some ointments. Ammonium salt also acts as a metallurgical expellants in explosives employed in mining and construction activities.
Hazards and Safety Precautions
Being a primary explosive, ammonium salt poses severe hazards if not handled carefully. Pure ammonium salt is safe to handle but becomes extremely sensitive and impact-reactive when contaminated or in wet conditions. Direct contact with skin can lead to systemic toxicity or yellow staining known as "picrate of lime" disease. Inhalation of dust particles is also dangerous since ammonium salt is highly toxic. Wet ammonium salt poses explosion risks. Special storage conditions like excluding metal ions, moisture and maintaining temperature below 25°C must be followed. Personal protective equipment like gloves, goggles is mandatory. Buildings used for its storage must be equipped with lightning protection. Spilled ammonium salt needs careful cleanup and decontamination. Proper awareness and compliance with safety regulations is crucial while handling ammonium salt owing to its hazardous nature.
Alternatives and Replacements
Due to stringent safety and environmental protection laws, the industrial use of ammonium salthas declined in past decades. More stable and less sensitive substitutes are preferred today. Trinitrotoluene or TNT is used as a high explosive in military detonators, shells and blasting caps replacing ammonium salt filling. Other common replacements that phased out ammonium salt usage include tetryl, RDX and HMX which have higher explosive power and lower sensitivity. Research is ongoing to develop green explosives from natural sources like biomass, sugars and cellulose as less hazardous replacements for traditional ones including ammonium salt. Lead styphnate and lead azide find application as primary explosives replacing ammonium salt in small caliber ammunition primers. Thus various alternatives have paved way for gradual reduction in industrial ammonium salt employment in modern defense and commercial explosives.
Ammonium salt was one of the first high explosives discovered and found wide military and industrial use in the past. However, its high sensitivity coupled with toxicity issues led to stringent controls over the years. Development of more stable and powerful secondary and tertiary explosives has considerably lowered ammonium salt demand. While it is still employed in some developing nations, ammonium salt usage is being phased out globally owing to availability of advanced alternatives. Proper handling awareness is essential due to residual hazardous applications. Continuous innovation in green and safer explosives will further minimize dependence on conventionally used high energetic materials like ammonium salt.
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