Nitric acid

Nitric acid known as aqua fortis and spirit of niter, is a corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68% in water; when the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%. Nitric acid is the primary reagent used for nitration – the addition of a nitro group to an organic molecule. While some resulting nitro compounds are shock- and thermally-sensitive explosives, a few are stable enough to be used in munitions and demolition, while others are still more stable and used as pigments in inks and dyes. Nitric acid is commonly used as a strong oxidizing agent. Commercially available nitric acid is an azeotrope with water at a concentration of 68% HNO3.

This solution has a boiling temperature of 120.5 °C at 1 atm. It is known as "concentrated nitric acid". Pure concentrated. Two solid hydrates are known. An older density scale is seen, with concentrated nitric acid specified as 42° Baumé. Nitric acid is subject to thermal or light decomposition and for this reason it was stored in brown glass bottles: 4 HNO3 → 2 H2O + 4 NO2 + O2This reaction may give rise to some non-negligible variations in the vapor pressure above the liquid because the nitrogen oxides produced dissolve or in the acid; the nitrogen dioxide remains dissolved in the nitric acid coloring it yellow or red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors, leading to the common names "red fuming nitric acid" and "white fuming nitric acid". Nitrogen oxides are soluble in nitric acid. A commercial grade of fuming nitric acid contains 98% HNO3 and has a density of 1.50 g/cm3.

This grade is used in the explosives industry. It is not as volatile nor as corrosive as the anhydrous acid and has the approximate concentration of 21.4 M. Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide leaving the solution with a reddish-brown color. Due to the dissolved nitrogen dioxide, the density of red fuming nitric acid is lower at 1.490 g/cm3. An inhibited fuming nitric acid can be made by the addition of 0.6 to 0.7% hydrogen fluoride. This fluoride is added for corrosion resistance in metal tanks; the fluoride creates a metal fluoride layer. White fuming nitric acid, pure nitric acid or WFNA, is close to anhydrous nitric acid, it is available as 99.9% nitric acid by assay. One specification for white fuming nitric acid is that it has a maximum of 2% water and a maximum of 0.5% dissolved NO2. Anhydrous nitric acid has a density of 1.513 g/cm3 and has the approximate concentration of 24 molar. Anhydrous nitric acid is a colorless mobile liquid with a density of 1.512 g/cm3 that solidifies at −42 °C to form white crystals.

As it decomposes to NO2 and water, it obtains a yellow tint. It boils at 83 °C, it is stored in a glass shatterproof amber bottle with twice the volume of head space to allow for pressure build up, but with those precautions the bottle must be vented monthly to release pressure. Two of the N–O bonds are equivalent and short, the third N–O bond is elongated because the O atom is attached to a proton. Nitric acid is considered to be a strong acid at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the pKa value is reported as less than −1; this means that the nitric acid in diluted solution is dissociated except in acidic solutions. The pKa value rises to 1 at a temperature of 250 °C. Nitric acid can act as a base with respect to an acid such as sulfuric acid: HNO3 + 2 H2SO4 ⇌ NO+2 + H3O+ + 2 HSO−4. Since nitric acid has both acidic and basic properties, it can undergo an autoprotolysis reaction, similar to the self-ionization of water: 2 HNO3 ⇌ NO+2 + NO−3 + H2O Nitric acid reacts with most metals, but the details depend on the concentration of the acid and the nature of the metal.

Dilute nitric acid behaves as a typical acid in its reaction with most metals. Magnesium and zinc liberate H2: Mg + 2 HNO3 → Mg2 + H2 Mn + 2 HNO3 → Mn2 + H2 Nitric acid can oxidize non-active metals such as copper and silver. With these non-active or less electropositive metals the products depend on temperature and the acid concentration. For example, copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry: 3 Cu + 8 HNO3 → 3 Cu2+ + 2 NO + 4 H2O + 6 NO−3The nitric oxide produced may react with atmospheric oxygen to give nitrogen dioxide. With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry: Cu + 4 H+ + 2 NO−3 → Cu2+ + 2 NO2 + 2 H2OUpon reaction with nitric acid, most metals give the corresponding nitrates; some metalloids and metals give the oxides.

Nagpur level crossing disaster

The Nagpur level crossing disaster was an accident that occurred on 3 February 2005, when a crowded trailer being towed by a tractor was hit by a train near the village of Kanan, 20 km from Nagpur in Maharashtra, causing 58 fatalities. The accident happened on an isolated, unmanned level crossing, when a wedding party of 70 people was being transported to the ceremony on a trailer being towed by a tractor; the crossing had barriers. The locomotive struck the trailer and stopped just after the crossing, the crumpled trailer still underneath it, passengers provided what assistance they could until emergency services arrived. 58 people died in the crash or in the days following, the surviving members of the party were all critically injured. The dead included 18 children. No train passengers suffered more than minor injuries or shock; the tragedy was one of a series of multiple-casualty accidents on India's overcrowded and under-maintained railway system, resulted in demands that Transport Minister Laloo Prasad Yadav resign.

The director of the South East Central Railway commented that no gate was installed at the rail crossing due to the low frequency of trains on the route, while assuring to look into the matter. List of level crossing accidents List of rail accidents List of road accidents BBC News Report


1,5-Cyclooctadiene is the organic compound with the chemical formula C8H12. Abbreviated COD, this diene is a useful precursor to other organic compounds and serves as a ligand in organometallic chemistry, it is a colorless liquid with a strong odor. 1,5-Cyclooctadiene can be prepared by dimerization of butadiene in the presence of a nickel catalyst, a coproduct being vinylcyclohexene. 10,000 tons were produced in 2005. COD reacts with borane to give 9-borabicyclononane known as 9-BBN, a reagent in organic chemistry used in hydroborations: COD adds SCl2 to give 2,6-dichloro-9-thiabicyclononane: The resulting dichloride can be further modified as the diazide or dicyano derivative in a nucleophilic substitution aided by anchimeric assistance. Selected metal 1,5-COD complexes. 1,5-COD binds to low-valent metals via both alkene groups. Metal-COD complexes are attractive because they are sufficiently stable to be isolated being more robust than related ethylene complexes; the stability of COD complexes is attributable to the chelate effect.

The COD ligands are displaced by other ligands, such as phosphines. Ni2 is prepared by reduction of anhydrous nickel acetylacetonate in the presence of the ligand, using triethylaluminium ​1⁄3 3 + 2 COD + 2 Al3 → Ni2 + 2 Al2 + C2H4 + C2H6The related Pt2 is prepared by a more circuitous route involving the dilithium cyclooctatetraene: Li2C8H8 + PtCl2 + 3 C7H10 → + 2 LiCl + C8H8 + C8H12 Pt3 + 2 COD → Pt2 + 3 C7H10Extensive work has been reported on complexes of COD, much of, described in volumes 25, 26, 28 of Inorganic Syntheses; the platinum complex is a precursor to a 16-electron complex of ethylene: Pt2 + 3 C2H4 → Pt3 + 2 CODCOD complexes are useful as starting materials. Other low-valent metal complexes of COD include cyclooctadiene rhodium chloride dimer, cyclooctadiene iridium chloride dimer, Fe3, Crabtree's catalyst; the M2 complexes with nickel and platinum have tetrahedral geometry, whereas + complexes of rhodium and iridium are square planar. The strained trans,trans isomer of 1,5-cyclooctadiene is a known compound.

-COD was first synthesized by Whitesides and Cope in 1969 by photoisomerization of the cis,cis compound. Another synthesis was reported by Huisgen in 1987; the molecular conformation of -COD is twisted rather than chair-like. The compound has been investigated as a click chemistry mediator