4NO

4NO refers to the chemical compound dinitrogen tetroxide, with the chemical formula N2O4. It is a colorless, highly toxic gas that is a dimer of nitrogen dioxide (NO2). At room temperature, dinitrogen tetroxide exists in equilibrium with nitrogen dioxide, with the ratio of the two gases depending on temperature and pressure. The reddish-brown color associated with nitrogen dioxide is absent in pure dinitrogen tetroxide.

Dinitrogen tetroxide is a powerful oxidizing agent and is used as a propellant in rockets, often in combination with hydrazine or monomethylhydrazine. Its high energy density and stability make it a reliable choice for space applications. The compound is also employed in the synthesis of other chemicals, including nitric acid and organic nitrates.

The production of dinitrogen tetroxide typically involves the oxidation of ammonia. Environmental concerns arise from its potential release into the atmosphere, as it can contribute to acid rain and stratospheric ozone depletion. Due to its toxicity, handling dinitrogen tetroxide requires strict safety protocols.