Hexanitrohexaazaisowurtzitane, also called HNIW and CL-20, is a polycyclic nitroamine explosive with the formula C₆H₆N₁₂O₁₂. In the 1980s, CL-20 was developed by the

China Lake Naval Air Weapons Station China Lake is a United States military facility in California. China Lake may also refer to: Places in the United States * China Lake, Kern County, California, an unincorporated community named for a nearby dry lake *Ch ...

facility, primarily to be used in

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...

s. It has a better

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...

-to-

fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...

ratio than conventional

HMX HMX, also called octogen, is a powerful and relatively insensitive nitroamine high explosive, chemically related to RDX. Like RDX, the compound's name is the subject of much speculation, having been variously listed as High Melting Explosive, Her ...

or RDX. It releases 20% more energy than traditional HMX-based propellants, and is widely superior to conventional high-energy propellants and explosives. While most development of CL-20 has been fielded by the Thiokol Corporation, the

US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

(through ONR) has also been interested in CL-20 for use in

rocket propellant Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemic ...

s, such as for

missiles In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...

, as it has lower observability characteristics such as less visible smoke. CL-20 has not yet been fielded in any production weapons system, but is undergoing testing for stability, production capabilities, and other weapons characteristics.

Synthesis

First, benzylamine (1) is condensed with

glyoxal Glyoxal is an organic compound with the chemical formula OCHCHO. It is the smallest dialdehyde (a compound with two aldehyde groups). It is a crystalline solid, white at low temperatures and yellow near the melting point (15 °C). The li ...

(2) under acidic and dehydrating conditions to yield the first intermediate compound.(3). Four benzyl groups selectively undergo hydrogenolysis using

palladium on carbon Palladium on carbon, often referred to as Pd/C, is a form of palladium used as a catalyst. The metal is supported on activated carbon to maximize its surface area and activity. Uses Hydrogenation Palladium on carbon is used for catalytic hydrog ...

and hydrogen. The amino groups are then acetylated during the same step using

acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a co ...

as the solvent. (4). Finally, compound 4 is reacted with nitronium tetrafluoroborate and

nitrosonium tetrafluoroborate Nitrosonium tetrafluoroborate, also called nitrosyl tetrafluoroborate, is a chemical compound with the chemical formula NOBF4. This colourless solid is used in organic synthesis as a nitrosating agent. NOBF4 is the nitrosonium salt of fluorob ...

, resulting in HNIW.

Cocrystal product with HMX

In August 2012, Onas Bolton et al. published results showing that a cocrystal of 2 parts CL-20 and 1 part

had similar safety properties to HMX, but with a greater firing power closer to CL-20.

Cocrystal product with TNT

In August 2011,

Adam Matzger Adam J. Matzger, a researcher in polymers and crystals, is the Charles G. Overberger Collegiate Professor of Chemistry at the University of Michigan, and an associate editor for the American Chemical Society's journal '' Crystal Growth & Design'' ...

and Onas Bolton published results showing that a cocrystal of CL-20 and TNT had twice the stability of CL-20—safe enough to transport, but when heated to the cocrystal may separate into liquid TNT and a crystal form of CL-20 with structural defects that is somewhat less stable than CL-20.

CL-20 covalent chains and networks

In 2017, K.P. Katin and M.M. Maslov designed one-dimensional covalent chains based on the CL-20 molecules. Such chains were constructed using CH₂ molecular bridges for the covalent bonding between the isolated CL-20 fragments. It was theoretically predicted that their stability increased with efficient length growth. A year later, M.A. Gimaldinova and colleagues demonstrated the versatility of CH₂ molecular bridges. It is shown that the use of CH₂ bridges is the universal technique to connect both CL-20 fragments in the chain and the chains together to make a network (linear or zigzag). It is confirmed that the increase of the effective sizes and dimensionality of the CL-20 covalent systems leads to their thermodynamic stability growth. Therefore, the formation of CL-20 crystalline covalent solids seems to be energetically favorable, and CL-20 molecules are capable of forming not only molecular crystals but bulk covalent structures as well. Numerical calculations of CL-20 chains and networks' electronic characteristics revealed that they were wide-bandgap semiconductors.

Synthesis

Cocrystal product with HMX

Cocrystal product with TNT

CL-20 covalent chains and networks

See also

References

Further reading