Acid+anyhdrides

=__Acid anhydrides__=

"Anhydride" simply means "without water" so an acid anhydride is simply a dehydrated form of the original acid

An acid anhydride is an organic compound that has two acyl groups bound to the same oxygen atom. Most commonly, the acyl groups are from the same carboxylic acid, the formula of the anhydride is (RC(O))2O.

[] look on here for a 3d model!!! =) Symmetrical acid anhydrides are named by replacing the word acid by the word anhydride

Inorganic acid anhydrides are called [|acidic oxide]

__**making an acid anhydride**__ starting with two molecules of ethanoic acid with the structure:

Removing a molecule of water between them leaves you with the acid anhydride, ethanoic anhydride.

__**Naming acid anhydrides**__ You take the name of the parent acid, and replace the word "acid" by "anhydride".

for example: __**Reactivity of acid anhydrides**__
 * ethanoic acid || ethanoic anhydride ||
 * propanoic acid || propanoic anhydride ||

Compare the structure of an acid anhydride with that of an acyl chloride - looking carefully at the way it is colour-coded in the diagram.

In the reactions of ethanoic anhydride, the red group at the bottom always stays intact. It is behaving in many ways as if it was a single atom - just like the chlorine atom in the acyl chloride. The usual reaction of an acyl chloride is replacement of the chlorine by something else. Taking ethanoyl chloride as typical, the initial reaction is of this kind: Hydrogen chloride gas is given off, although that might go on to react with other components of the mixture. With an acid anhydride, the reaction is slower, but the only essential difference is that instead of hydrogen chloride being produced as the other product, you get ethanoic acid instead. Just like the hydrogen chloride, this might afterwards go on to react with other things present.

**ethanoic anhydride** ||< CH3C(=O)OC(=O)CH3 ||<  || **butanoic propanoic anhydride** ||< ||<   || **pentandioic anhydride** ||< ||
 * < * Functional group is an acid anhydride therefore suffix = - **oic anhydride**
 * Hydrocarbon structure is an alkane therefore **-an-**
 * The longest continuous chain is C2 therefore root = **eth**
 * < * Functional group is an acid anhydride therefore suffix = - **oic anhydride**
 * Hydrocarbon structure is an alkane therefore **-an-**
 * The longest continuous chain is C4 therefore root = **but**
 * The other group is C3 = **prop**
 * < * Functional group is a cyclic acid anhydride therefore suffix = - **dioic anhydride**
 * Hydrocarbon structure is an alkane therefore **-an-**
 * The longest continuous chain is C5 therefore root = **pent**