Properties of amines

Amines are compounds based on an ammonia molecule (NH 3 ), where one or more of the hydrogen atoms is replaced by a carbon chain. Thus R—NH 2 is a primary amine, while R—NH—R’ is a secondary amine, and R—N(R’)—R’’ is a tertiary amine. You will only be asked to name primary amines. Note that 2-aminopropane, CH 3 —CH(NH 2 )—CH 3, is a primary amine, yet the haloalkane from which it was made, CH 3 —CHCl—CH 3, is a secondary haloalkane. Hydrogen bonding occurs in amines, but it is not as strong as the hydrogen bonding occurring in alcohols because the N—H bond is not as polar as the O—H bond. So amines have lower boiling points than the corresponding alcohols.

Low-mass amines are miscible in water.

Like ammonia itself, amines are bases. Amines turn litmus paper blue. Amines are the only class of organic compounds you will meet this year which turn litmus blue. C 3 H 7 —NH 2 + H 2 O C 3 H 7 —NH OH – Learn this equation.

The low-mass amines are gases or volatile liquids with a noticeably fishy smell. (Actually, it is dead fish which smell of amines as the proteins in their flesh break down.) Like ammonia itself, amines react with inorganic acids to form ionic salts which are soluble in water and have no odour. C 3 H 7 —NH 2 + HCl → C 3 H 7 —NH 3 + Cl – propyl aminepropyl ammonium chloride

A few drops of universal indicator solution are added to dilute hydrochloric acid.

Ethylamine is a gas, so this bottle contains a solution of ethylamine in alcohol.

Ethylamine is added dropwise until no further colour change takes place. C 2 H 5 —NH 2 + HCl → C 2 H 5 —NH 3 + Cl – ethylamine ethyl ammonium chloride Learn this equation and the product name.

We added acid dropwise until the mixture was exactly neutral. Amines are bases which react with acids to form salts, just like inorganic bases do.

Also like ammonia, amines react with copper sulfate solution to form a royal blue complex. Cu C 3 H 7 NH 2 → [Cu(C 3 H 7 NH 2 ) 4 ] 2+ This pale blue ppt is copper hydroxide