# Centralite

Ethyl centralite is an organic compound. Its chemical name is 1,3-diethyl-1,3-diphenylurea. The molecular formula of ethyl centralite is C$_{17}$H$_{20}$N$_2$O. This compound has important uses in industry and forensics. The structure of ethyl centralite includes two phenyl groups (aromatic rings) attached to a central urea group. There are also ethyl groups (–C₂H₅) bound to the nitrogen atoms of the urea. This structure gives ethyl centralite its special chemical properties. Ethyl centralite is an important part of gunshot residue (GSR). When a gun is fired, the chemical reactions from the burning of the propellant leave behind tiny particles called gunshot residue. Ethyl centralite is one of the compounds found in GSR. It serves as an indicator in forensic investigations. Ethyl centralite helps determine if a firearm was recently fired. Ethyl centralite is widely used in various industries. Its main use is in the production of smokeless powder. In this use, it acts as a burning rate moderator and stabilizer. These functions are important for the controlled and consistent ignition of propellants. This is essential for the safety and effectiveness of ammunition. Ethyl centralite is also used as a plasticizer in the manufacturing of celluloid and enhances the flexibility and durability of the material.

## History

In the 19th century chemists identified that nitrocellulose can destroy itself with the help of nitrogen oxides separating from it at storage, and tried to find bases which might capture those oxides. Urea has been used for stabilizing celluloid in the 19th century (and even in early American military powders), but like other water-soluble bases, it also attacks nitrocellulose, so German chemists substituted hydrogen atoms with nonpolar organic radicals to diminish this effect.

## Naming

The term "Centralite" was originally applied to dimethyldiphenylurea developed about 1906 at the German private military-industrial laboratory Zentralstelle für wissenschaftlich-technische Untersuchungen [de] (Center for Scientific-Technical Research) in Neubabelsberg as a deterrent coating for smokeless powder in military rifle cartridges. Thereafter, all hydrocarbon-substituted symmetrical diphenyl urea compounds used as smokeless powder deterrents (or moderants) were called centralites after the laboratory. The preferred ethyl centralite became known as Centralite No. 1 and the original methyl centralite was identified as Centralite No. 2. Butyl centralite was also used as a celluloid plasticizer.

## Comparison with analogs

Compared to diphenylurea, it has a far more convoluted reaction history. Finally, nitrated anilines are produced. Centralite-2, also known as sym-dimethyldiphenylurea, is a methyl analog that is moderately utilized overseas. Though they are likewise excellent plasticizers, centralites are thought to be a little less effective stabilizer than 2-nitrodiphenylamine. To benefit from their plasticizing qualities, they are commonly employed in propellants at higher fractions than diphenylamines.

## Synthesis

Ethyl centralite is also known as 1,3-diethyl-1,3-diphenylurea. It is synthesized through a chemical reaction. This reaction involves the condensation of aniline (C₆H₅NH₂) with ethyl isocyanate (C₂H₅NCO). The reaction typically occurs under controlled conditions. In this reaction, aniline reacts with ethyl isocyanate. This forms ethyl centralite through the formation of urea linkages.
The general reaction can be represented as follows:
    2 C$_6$H$_5$NH$_2$ + 2 C$_2$H$_5$NCO → C$_6$H$_5$NHCONHC$_6$H$_5$(C$_2$H$_5$)$_2$ + 2 CO$_2$
In this reaction, aniline (C$_6$H$_5$NH$_2$) serves as the aromatic amine and ethyl isocyanate (C$_2$H$_5$NCO) is the isocyanate compound that reacts with the amine groups.
The reaction produces ethyl centralite. It also produces carbon dioxide (CO₂) as a byproduct. The process is usually done in a solvent, such as an alcohol. The solvent helps dissolve the reactants. It also helps control the reaction temperature. After the reaction is finished, the ethyl centralite is purified. This is done through recrystallization or other purification methods. The goal is to obtain a pure product.

## Applications
### Smokeless powder

* Burning rate moderator: Smokeless powder is a type of propellant used in firearms and ammunition. It burns in a more controlled and steady way. It produces less smoke and residue than traditional black powder. The burning rate of this powder is crucial for a firearm to work properly. If it burns too fast, it can create too much pressure. This can damage the weapon and cause injury. If it burns too slow, it may not generate enough pressure to shoot the bullet effectively. Ethyl centralite helps regulate the burning rate of smokeless powder. It controls the chemical reactions that happen during the ignition of the powder. The presence of ethyl centralite in the powder formulation ensures a steady and predictable energy release during combustion. This controlled burn is important for maintaining the balance between pressure and velocity. This balance enhances the accuracy, safety, and performance of firearms. By moderating the burn rate, ethyl centralite contributes to the reliability of the ammunition. It is a vital component in the manufacturing of smokeless powder.
* Stabilizer: It also acts as a stabilizer in smokeless powder. The chemical compounds in smokeless powder can decompose over time. This is especially true when exposed to heat, moisture, and age. The decomposition can create acidic byproducts. These byproducts can speed up the breakdown of the powder. This can compromise the powder's stability. Ethyl centralite acts as a stabilizer. It inhibits the degradation processes. It neutralizes the acidic byproducts that form over time. This slows down the overall decomposition of the powder. This stabilization is important. It extends the shelf life of the smokeless powder. This ensures that the powder remains effective and safe to use even after long periods of storage. Smokeless powder can become unstable without ethyl centralite. This can lead to inconsistent performance. In extreme cases, it can even lead to spontaneous ignition or explosion. Ethyl centralite prevents the powder from degrading prematurely. This helps maintain the integrity and safety of ammunition. Ethyl centralite is an indispensable additive in the production of smokeless powder.

### Forensic science

* Gunshot Residue (GSR) Analysis: Ethyl centralite is important in forensic science. It is used to analyze gunshot residue (GSR). GSR is tiny particles that come out of a gun when it is fired. These particles can be found on the hands, clothes, or around the person who fired the gun. Analyzing GSR can give important evidence in criminal cases. It can help determine if a suspect recently fired a gun.
* Detection of Ethyl Centralite in GSR: Ethyl centralite is an important organic compound found in GSR analysis. When a gun is fired, the smokeless powder used as fuel burns. This creates a mixture of gases and particles. Ethyl centralite is a part of this smokeless powder. It is released along with other residues. Forensic scientists use advanced techniques like gas chromatography-mass spectrometry (GC-MS) to detect ethyl centralite in the residue collected from a suspect or crime scene.Some other compounds may be present in the environment, but ethyl centralite is strongly linked to the firing of a gun. Its presence in GSR can be strong evidence connecting a suspect to the use of a firearm.