amines Flashcards
what are amines
Amines constitute organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl group(s)
what are the uses of amines in nature and humans
they occur among proteins, vitamins, alkaloids and hormones. Synthetic examples include polymers,
dyestuffs and drugs Two biologically active compounds, namely adrenaline and ephedrine both containing
secondary amino group, are used to increase blood
pressure
what is Benadryl,
Benadryl, a well known antihistaminic drug also contains tertiary amino group.
what is Novocain
Novocain, a synthetic amino compound, is
used as an anaesthetic in dentistry
what are the uses of Quaternary ammonium
Quaternary ammonium salts are used as
surfactants
what are Diazonium salts
Diazonium salts are intermediates in the
preparation of a variety of aromatic compounds including dyes
explain Structure of Amines
nitrogen atom of amines is trivalent and
carries an unshared pair of electrons. Nitrogen orbitals in amines are therefore, sp3 hybridized and the geometry
of amines is pyramidal. Each of the three sp3 hybridised orbitals of nitrogen overlap with orbitals of hydrogen or carbon depending upon the composition of the amines. The fourth orbital of nitrogen in all amines contains an unshared pair of electrons. Due to the presence of
unshared pair of electrons, the angle C–N–E
is less than 109.5°
__________ is the simplest example of arylamine.
C6H5NH2 or aniline
what is the bond angle in trimethylamine
108
Amines are said to be
_______ when all the alkyl or aryl groups are the same, and ______
when they are different.
simple and mixed
Preparation of Amines
Reduction of nitro compounds
Ammonolysis of alkyl halides
Reduction of nitriles
Reduction of amides
Gabriel phthalimide synthesis
Hoffmann bromamide degradation reaction
Preparation of Amines by Reduction of nitriles
Nitriles on reduction with lithium aluminum hydride (LiAlH4) or catalytic hydrogenation produce primary amines. This reaction is
used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine
Preparation of Amines by Reduction of nitro compounds
Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum and also by reduction with metals in acidic medium. Nitroalkanes can
also be similarly reduced to the corresponding alkanamines.
Reduction with iron scrap and hydrochloric acid is preferred because FeCl2 formed gets hydrolyzed to release hydrochloric acid during the reaction. Thus, only a small amount of hydrochloric acid is required
to initiate the reaction
Preparation of Amines by Ammonolysis of alkyl halides
the carbon - halogen bond in alkyl or benzyl halides can be easily cleaved by a nucleophile. Hence, an alkyl or benzyl halide on reaction with an ethanolic solution of ammonia undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (–NH2) group. This process of cleavage of the C–X bond by ammonia molecule is known as ammonolysis. The reaction is carried out in a sealed tube at 373 K. The primary amine thus obtained behaves as a nucleophile and can further react with alkyl halide to form secondary and tertiary amines, and finally quaternary ammonium salt.
Preparation of Amines by Reduction of amides
The amides on reduction with lithium aluminium hydride yield amines.
Preparation of Amines by Hoffmann bromamide degradation reaction
Hoffmann developed a method for preparation of primary amines by
treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.
Preparation of Amines by Gabriel phthalimide synthesis
Gabriel synthesis is used for the preparation of primary amines. Phthalimide on treatment with ethanolic potassium hydroxide forms potassium salt of phthalimide which on heating with alkyl halide followed by alkaline hydrolysis produces the corresponding primary amine. Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide
Physical Properties of amines
The lower aliphatic amines are gases with fishy odour. Primary amines with three or more carbon atoms are liquid and still higher ones are solid. Aniline and other arylamines are usually colorless but get
coloured on storage due to atmospheric oxidation.
why are Lower aliphatic amines are soluble in water?
Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules