Acetic anhydride

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Acetic anhydride
Acetic anhydride.png
Acetic anhydride structure
Names
IUPAC name
Acetic anhydride
Preferred IUPAC name
Acetic anhydride
Systematic IUPAC name
Ethanoic anhydride
Other names
Ethanoyl ethanoate
Acetic acid anhydride
Acetyl acetate
Acetyl oxide
Acetic oxide
Properties
C4H6O3
Molar mass 102.09 g/mol
Appearance Colorless liquid
Odor Acetic
Density 1.082 g/cm3
Melting point −73.1 °C (−99.6 °F; 200.1 K)
Boiling point 139.8 °C (283.6 °F; 412.9 K)
Slowly hydrolyzes
Solubility Miscible with acetic acid, diethyl ether, ethanol, ethyl acetate
Vapor pressure 4 mmHg (20 °C)
Hazards
Safety data sheet Sigma-Aldrich
Flash point 49 °C (120 °F; 322 K)
Lethal dose or concentration (LD, LC):
1,000 ppm (rat, 4 hr)
Related compounds
Related compounds
Acetic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Acetic anhydride is a colorless organic liquid with the formula (CH3CO)2O and the simplest example of a carboxylic acid anhydride (the simpler formic anhydride is too unstable to exist as pure substance). It is a very useful reagent in organic synthesis.

Properties

Chemical

Acetic anhydride is most widely used as an agent for acetylation, the addition of an acetyl group to a compound, such as its reaction with ethanol to form ethyl acetate. Being a carboxylic acid anhydride, acetic anhydride will slowly decay in contact with water into acetic acid. This process, however, is slow enough for aqueous solutions to be made and used immediately.

Physical

Acetic anhydride is a colorless liquid with a density almost identical to that of water. It is moderately flammable and, due to its volatility, smells strongly of acetic acid from reaction with water in the air.

Availability

Elemental Scientific sells acetic anhydride in 125ml and 500ml sizes. They, however, are one of the only reliable sellers who are selling this chemical in the US due to its status as DEA List II.

Restrictions

Acetic anhydride is used illicitly in the drug trade to acetylate morphine to heroin. Because it is used for this purpose, it is classified in the US as a DEA List II chemical and as such is significantly harder to obtain. In Russia, it's a FSKN List I chemical and is impossible to obtain legally. This is also true for most countries.

Preparation

Many amateurs have attempted to make acetic anhydride at home due to its tremendous usefulness. Only a few have succeeded, though a write-up of the preparation of acetic anhydride from sulfur, bromine, and anhydrous sodium acetate was reported by Magpie.

Another more accessible method involves the reaction of acetyl chloride and anhydrous sodium acetate.[1]

A readily accessible route, but very dangerous, involves the reaction of ethenone with glacial acetic acid. Ethenone can be easily produced by pyrolyzing acetone at high temperatures in an oxygen-free atmosphere, which is not very difficult to do, all you need is a reflux setup and an electric heating element. However, ethenone is an extremely toxic gas, with an LD50 close to that of hydrogen cyanide and phosgene and working with it carries the risk of severe injury or even death.

A preparation that is as of yet not well-researched involves the dry vacuum distillation of anhydrous zinc acetate, which gives off acetic anhydride and converts to basic zinc acetate. If achievable, this would mean a route to acetic anhydride that only requires glacial acetic acid and cheap zinc metal.

Projects

Handling

Safety

Acetic anhydride, similar to glacial acetic acid, is highly acidic and corrosive, so proper protection must be worn when handling the compound. When mixed with hydrogen peroxide with the acetic anhydride in excess, a shock sensitive explosive, diacetyl peroxide, is formed.

Storage

Acetic anhydride should be stored in sealed bottles as it is sensitive to water. In addition, it should be stored away from any heat or flame source due to it's flammability .

Disposal

Acetic anhydride can be neutralized with sodium bicarbonate or any other base which is then safe to pour down the drain.

References

  1. https://www.erowid.org/archive/rhodium/chemistry/anhydrides.html

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