Amines, amino acids and proteins
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If some text books its suggests that amides are weak bases and in other text books it suggets that amides are weak acids. Are they acidic or basic? Is there a chemical test to identify whether a chemical is an amine and amide?
Corrie writes ...
Amides certainly have the potential to act both as bases, by the -NH2 group accepting a proton, or as acids, by it donating a proton. However, both these properties are very weak, as evidenced by the fact that amides do not affect the pH of an aqueous solution to any significant extent.
To get an amide to react as an acid or base you would have to react it with a very strong base or a very strong acid. Thus they are known to form unstable salts, RCONH3+Cl-, with HCl, and the sodium salt, R-CONH-Na+ can be formed by reacting an amide with sodium or sodamide, Na+NH2-.
To tell the difference between an amine and amide depends rather on the amine involved. Amides are
are solids which are usually water soluble. If boiled with NaOH solution (Care!), amides evolve ammonia.
Amines can be gases, liquids or solids and will usually have an unpleasant smell. Most aliphatic (i.e. not aromatic) amines are water soluble and will generally turn the solution alkaline. Amines that are not very water soluble will dissolve in hydrochloric acid and re-appear as a separate layer or a precipitate if excess NaOH(aq) is added.
There are also specialised tests for amines that are rather beyond A-level now, and for aromatic amines. Come back to me via Re:act (not via e-mail) if you want more information.
Do not rely on what is said here. Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 28 November 2007
