amines and amides

Why amine group which reacts with sulfuric acid and potassium hydroxide having a different main results? (With 95% potassium hydroxide, sulfuric acid 88-90%)

Because sulfuric acid is less reactive than potassium hydroxide, and the first reaction of the electron arrangement changes that bind to the N atom of the anion or cation entry.

Why is the reaction H + H2O and H3O + can be formed?

This is due to ionized water is perfect, and the O atom atom merupaka very conducive to the formation of coordinate covalent bond to the O atom H3O + as rich in free electron pair.

The structure of acid anhydrides

A carboxylic acid such as ethanoic acid has the structure:

If you took two ethanoic acid molecules and removed a molecule of water between them you would get the acid anhydride, ethanoic anhydride (old name: acetic anhydride).

You can actually make ethanoic anhydride by dehydrating ethanoic acid, but it is normally made in a more efficient, round-about way. (Making ethanoic anhydride is beyond the scope of UK A level.)

Naming acid anhydrides

This is really easy. You just take the name of the parent acid, and replace the word "acid" by "anhydride". "Anhydride" simply means "without water".

So . . . ethanoic acid forms ethanoic anhydride; propanoic acid forms propanoic anhydride, and so on.

For UK A level purposes, the only one you are at all likely to come across is ethanoic anhydride.

Physical properties of acid anhydrides

We will take ethanoic anhydride as typical.

Appearance

Ethanoic anhydride is a colourless liquid, smelling strongly of vinegar (ethanoic acid).

The smell is because ethanoic anhydride reacts with water vapour in the air (and moisture in your nose) to produce ethanoic acid again. This reaction with water is given in detail on another page. (Find it from the acid anhydrides menu - link at the bottom of this page.)

Solubility in water

Ethanoic anhydride can't be said to dissolve in water because it reacts with it to give ethanoic acid. There is no such thing as an aqueous solution of ethanoic anhydride.

Boiling point

Ethanoic anhydride boils at 140°C. This is because it is a fairly big polar molecule and so has both van der Waals dispersion forces and dipole-dipole attractions.

It doesn't, however, form hydrogen bonds. That means that its boiling point isn't as high as a carboxylic acid of similar size. For example, pentanoic acid (the most similarly sized acid) boils at 186°C.

Reactivity of acid anhydrides

Comparing acid anhydrides with acyl chlorides (acid chlorides)

You have almost certainly come across acid anhydrides for the first time just after looking at acyl chlorides, or you may be studying them at the same time as acyl chlorides.

It is much, much easier to think of acid anhydrides as if they were a sort of modified acyl chloride than to try to learn about them from scratch. That is the line I intend to take throughout all this section.

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.

The reactions (of both acyl chlorides and acid anhydrides) involve things like water, alcohols and phenols, or ammonia and amines. All of these particular cases contain a very electronegative element with an active lone pair of electrons - either oxygen or nitrogen.

 

Why is the reaction of acyl ammonium chloride and experience the difference in the formation of acid anhydride reaction products?

Reaction with acyl chloride
We will take the example of chloride as an acyl chloride ethanoyl simple.
The general reaction of chloride with a compound XNH2 ethanoyl (wherein X is hydrogen or an alkyl group or a benzene ring) involves two stages of the reaction:
First:
  
Each reaction will initially produce hydrogen chloride gas - hydrogen coming from the-NH2, and chlorine from hydrochloric ethanoyl. The remaining components are all joined into one structure.
However, ammonia and amines are acidic, and reacts with hydrogen chloride produces a salt. So the second stage of the reaction is:
  
Reaction with acid anhydride
We take the example ethanoic anhydride as an acid anhydride of the most commonly encountered in the discussion of the basic level.
The reaction also occurs in two stages. In the first stage:
  
If you compare the above equation with the equation for the reaction of acyl chloride, you can see that the only difference is that the second product is generated as ethanoic acid instead of hydrogen chloride as the reaction of acyl chloride.
Furthermore ethanoic acid reacts with ammonia or amines which produces an excess of salt - this time it is ethanoate.
  
It seems more difficult than in the acyl chloride as a way of writing the structure of the salt formed. On this structure there ethanoate ion and a positive ion:

• In the first phase, ethanoic acid is formed as a second product gas instead of hydrogen chloride.
• The second phase of the reaction involves the formation of ethanoic instead of chloride.
• The reactions are slower. Not very reactive acid anhydride as acyl chloride, and the reactions usually require heating.