Hexanitrohexaazaisowurtzitane, also called HNIW and CL-20, is a polycyclic nitroamine explosive with the formula . 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 ''electron donor''). In ot ...

-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 (physics), work. The concept was originally applied solely to those materials capable of releasing chem ...

ratio than conventional HMX or

RDX RDX (Research Department Explosive or Royal Demolition Explosive) or hexogen, among other names, is an organic compound with the formula (CH2N2O2)3. It is white, odorless, and tasteless, widely used as an explosive. Chemically, it is classified ...

. It releases 20% more energy than traditional HMX-based propellants.

History and use

In the 1980s, CL-20 was developed by the China Lake 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 another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicle ...

s. While most development of CL-20 has been fielded by the Thiokol Corporation, the

US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

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

rocket propellant Rocket propellant is used as reaction mass ejected from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines. Overvi ...

s, such as for missiles, as it has lower observability characteristics such as less visible smoke. Thus far, CL-20 has only been used in the AeroVironment Switchblade 300 “kamikaze” drone, but is undergoing testing for use in the Lockheed Martin MT AGM-158C Long Range Anti-Ship Missile (LRASM) and AGM-158B Joint Air-to-Surface Standoff Missile-Extended Range (JASSM-ER). The

Indian Armed Forces The Indian Armed Forces are the armed forces, military forces of the India, Republic of India. It consists of three professional uniformed services: the Indian Army, the Indian Navy, and the Indian Air Force.—— Additionally, the Indian Ar ...

have also looked into CL-20. The Taiwanese National Chung-Shan Institute of Science and Technology innaugerated a CL-20 production facility in 2022 with reported integration into the HF-2 and HF-3 product lines.

Synthesis

First,

benzylamine Benzylamine, also known as phenylmethylamine, is an Organic chemistry, organic chemical compound with the Structural formula#Condensed formulas, condensed structural formula C6H5CH2NH2 (sometimes abbreviated as Phenyl group#Nomenclature, PhCH2NH2 ...

(1) is condensed with glyoxal (2) under acidic and dehydrating conditions to yield the first intermediate compound (3). Four benzyl groups selectively undergo hydrogenolysis using palladium on carbon 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 chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of c ...

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

nitronium tetrafluoroborate Nitronium tetrafluoroborate is an inorganic compound with formula NO2BF4. It is a salt of nitronium cation and tetrafluoroborate anion. It is a colorless crystalline solid, which reacts with water to form the corrosive acids HF and HNO3. As su ...

and nitrosonium tetrafluoroborate, resulting in HNIW.

Cocrystals

In August 2011, Adam Matzger 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. In August 2012, Onas Bolton et al. published results showing that a cocrystal of 2 parts CL-20 and 1 part HMX had similar safety properties to HMX, but with a greater firing power closer to CL-20.

Polymeric derivatives

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 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 molecular bridges. It is shown that the use of 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.

History and use

Synthesis

Cocrystals

Polymeric derivatives

See also

References

Further reading