Acetic anhydride

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Acetic anhydride

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 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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