Acetone peroxide

Acetone peroxide
IUPAC name	3,3,6,6-Tetramethyl-1,2,4,5-tetraoxane (dimer) 3,3,6,6,9,9-Hexamethyl-1,2,4, 5,7,8-hexaoxacyclononane (trimer)
Identifiers
CAS number	17088-37-8
PubChem	536100
SMILES	CC1(C)OOC(C)(C)OO1 (dimer) CC1(C)OOC(C)(C)OOC(C)(C)OO1 (trimer)
Properties
Molecular formula	C6H12O4 (dimer) C9H18O6 (trimer)
Molar mass	148.157 g/mol (dimer) 222.24 g/mol (trimer)
Appearance	White crystalline solid
Melting point	91 °C, 364 K, 196 °F
Boiling point	97-160 °C
Explosive data
Shock sensitivity	Very high / moderate when wet
Friction sensitivity	Very high / moderate when wet
Explosive velocity	5300 m/s 17,384 ft/s 3.29 Miles per second
RE factor	.83
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Acetone peroxide (triacetone triperoxide, peroxyacetone, TATP, TCAP) is an organic peroxide and a primary high explosive. It takes the form of a white crystalline powder with a distinctive acrid odor.

It is highly susceptible to heat, friction, and shock. However the instability is greatly altered by impurities. It is normally stable when pure, but it dissolves quickly. It is one of the few explosives which remain explosive when wet or kept underwater.

Acetone peroxide was discovered in 1895 by Richard Wolffenstein.^[1] He was the first chemist to use inorganic acids as catalysts. He was also the first researcher to receive a patent for using the peroxide as an explosive compound. In 1900 Bayer and Villiger described in the same journal the first synthesis of the dimer and also described use of acids for the synthesis of both peroxides. Information about these procedures including the relative proportions of monomer, dimer, and trimer is also available in an article by Milas and Golubović.^[2] Other sources include crystal structure and 3d analysis in "The Chemistry of Peroxides" edited by Saul Patai (pp. 396–7), as well as the "Textbook of Practical Organic Chemistry" by Vogel.

Acetone peroxide has been used in various crimes and terrorist acts. It has also been the cause of accidental injuries.

Chemistry

"Acetone peroxide" most commonly refers to the cyclic trimer TCAP (tri-cyclic acetone peroxide, or tri-cyclo, C₉H₁₈O₆) obtained by a reaction between hydrogen peroxide and acetone in an acid-catalyzed nucleophilic addition.^[3] The dimer (C₆H₁₂O₄) and open monomer are also formed, but under proper conditions the cyclic trimer is the primary product. A tetrameric form was also described.^[4] In mildly acidic or neutral conditions, the reaction is much slower and produces more monomeric organic peroxide than the reaction with a strong acid catalyst. Due to significant strain of the chemical bonds in the dimer and especially the monomer, they are even more unstable than the trimer.^[5]

At room temperature, the trimeric form slowly sublimes, reforming as larger crystals of the same peroxide.

Acetone peroxide is notable as a high explosive not containing nitrogen. This is one reason why it has become popular with terrorists,^[6] as it can pass through scanners designed to detect nitrogenous explosives.^[7]

TCAP generally burns when ignited, unconfined, in quantities less than about 2 grams. More than 2 grams will usually detonate when ignited; smaller quantities might detonate when even slightly confined. Completely dry TCAP is much more prone to detonation than the fresh product still wetted with water or acetone. The oxidation that occurs when burning is:

2 C₉H₁₈O₆ + 21 O₂ → 18 H₂O + 18 CO₂

Theoretical examination of the explosive decomposition of TCAP, in contrast, predicts in "formation of acetone and ozone as the main decomposition products and not the intuitively expected oxidation products."^[8] But even in 1943 German researcher(s) described in the case of detonation of the trimer the formation of formaldehyde which is clearly a result of a fragmentation of primary formed oxyradicals^{[citation needed]}. This result is in good agreement with the results of 60 years of the study of controlled decompositions in various organic peroxides. It is the rapid creation of gas from a solid that creates the explosion. Very little heat is created by the explosive decomposition of TCAP. Recent research describes TCAP decomposition as an entropic explosion.^[8]

The extreme shock, heat, and friction sensitivity are due to the instability of the molecule. Big crystals, found in older mixtures, are more dangerous, as they are easier to shatter — and initiate — than small ones.

Due to the cost and ease with which the precursors can be obtained, acetone peroxide can be manufactured by those without the resources needed to manufacture or buy more sophisticated explosives.^{[citation needed]} When the reaction is carried out without proper equipment the risk of an accident is significant. Simply mixing sulfuric acid, hydrogen peroxide, and acetone can create the substance. The mixture starts as a liquid that quickly crystallizes into a powder. However when mixed it immediately detonates.

There is a common myth that the only "safe" acetone peroxide is the trimer, made at low temperatures:

"The mixture must be kept below 10 degrees Celsius. If the crystals form at this temperature, it forms the isomer called tricycloacetone peroxide, which is relatively stable and safe to handle. If the crystals form above this temperature, the dimerric form, called dicycloacetone peroxide. This isomer is much more unstable, and could go off at the touch, making it not safe enough to be considered a practical explosive. As long as the temperature is kept below 10 degrees Celsius, then there is little to worry about."^[9]

In reality, the acid-catalyzed peroxidation of acetone always produces a mixture of dimeric and trimeric forms.^{[citation needed]}

The trimer is the more stable form, but not much more so than the dimer. All forms of acetone peroxide are very sensitive to initiation. Organic peroxides are sensitive, dangerous explosives; due to their sensitivity they are rarely used by well funded militaries. Even for those who synthesize explosives as a hobby there are far safer explosives with syntheses nearly as simple as that of acetone peroxide. It is commonly combined with nitrocellulose by dissolving the nitrocellulose in acetone and then mixing in the acetone peroxide and letting it dry, this results in a mixture that is both more stable and somewhat more powerful than acetone peroxide by itself. This mixture is commonly referred to as APNC.

Tetrameric acetone peroxide is more chemically stable (heating to 120°C for 4 hours), but despite this, it is still a very dangerous primary explosive. It can be prepared using tin(IV) chloride (without acid present) as a catalyst with up to 40% yield if radical inhibitor such as hydroquinone, or a chelator such as EDTA is added.^[4]

Industrial occurrence

Acetone peroxides are common and unwanted by-products of oxidation reactions, eg. those used in phenol syntheses. Due to their explosivity, they are hazardous. Numerous methods are used to reduce their production - shifting the pH to more alkaline, adjusting the reaction temperature, or adding a soluble copper(II) compound.^[10]

Acetone peroxide and benzoyl peroxide are used as flour bleaching agents to bleach and "mature" flour.

Ketone peroxides, including acetone peroxide, methyl ethyl ketone peroxide, and benzoyl peroxide, find applications as initiators for polymerization reactions of eg. silicone or polyester resins, often encountered when making fiberglass-reinforced composites. For these uses, the peroxides are typically in the form of a dilute solution in an organic solvent, however, even commercial products with higher concentrations of organic peroxides can form crystals around the lid when older, making the can shock-sensitive. Methyl ethyl ketone is more common for this purpose, however, as it is stable in storage.

Accidental byproduct

Acetone peroxide can also occur accidentally, when suitable chemicals are mixed together. For example, when methyl ethyl ketone peroxide is mixed with acetone when making fiberglass composites, and left to stand for some time, or when a mixture of peroxide and hydrochloric acid from printed circuit board etching is mixed with waste acetone from cleaning the finished board and allowed to stand. While amounts obtained this way are typically much smaller than from intentional production, they are also less pure and prepared without cooling, and hence very unstable.

It is also a hazardous by-product of isosafrole oxidation in acetone, a step in the synthesis of MDMA.

Notable terrorist incidents

TATP is relatively easy to make and has been used in various terrorist acts.^[11]

• Richard Reid, targeted American Airlines Flight 63 with a bomb concealed in his shoe with a TATP trigger.
• It is also believed that acetone peroxide was used as the explosive in the 7 July 2005 London bombings.^[12]
• On September 5, 2006, homemade TATP was found during the arrest of seven suspected terrorists in Vollsmose, a neighborhood in the Danish city Odense,^[13]
• On September 4, 2007, homemade TATP was found during the arrest of eight suspected Al-Qaeda collaborators in Copenhagen, Denmark.^[14]
• The 2006 transatlantic aircraft plot was a terrorist plot to detonate liquid explosives carried on board at least 10 airliners travelling from the United Kingdom to the United States and Canada.
• TATP was the explosive used to manufacture the suicide bombs that were to be used by Palestinian terrorists Gazi Ibrahim Abu Mezer and Lafi Khalil for their 1997 suicide bombing plot on the New York City Subway.
• A member of the French anti-speed camera group, Front national anti-radars (FNAR), was hospitalised after losing both hands to an accidental explosion of his bomb based on TATP. ^[15]
• On September 24, 2009, Najibullah Zazi was officially indicted on charges of conspiracy to use weapons of mass destruction against persons or property in the United States. U.S. officials expressed concern that Zazi and several yet unnamed accomplices planned to use peroxide-based explosives against targets in the New York City area.^[16]

Notable accidents and incidents involving amateur chemists and hobbyists

A 13-year-old student in Hong Kong was injured on March 28, 2009 when he tried to light some TATP powder, which was provided by another 14-year-old boy and Police found six bottles of TATP from his apartment. Police believe those bottles of TATP were homemade by the 14-year-old boy for curiosity's sake. Including the injured boy, 3 teenagers were later arrested on explosives possession charges. ^[17][18]

References