amines

Question 1

what are amines

Answer 1

Amines constitute organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl group(s)

Question 2

what are the uses of amines in nature and humans

Answer 2

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

Question 3

what is Benadryl,

Answer 3

Benadryl, a well known antihistaminic drug also contains tertiary amino group.

Question 3

what is Novocain

Answer 3

Novocain, a synthetic amino compound, is
used as an anaesthetic in dentistry

Question 4

what are the uses of Quaternary ammonium

Answer 4

Quaternary ammonium salts are used as
surfactants

Question 5

what are Diazonium salts

Answer 5

Diazonium salts are intermediates in the
preparation of a variety of aromatic compounds including dyes

Question 5

explain Structure of Amines

Answer 5

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°

Question 6

__________ is the simplest example of arylamine.

Answer 6

C6H5NH2 or aniline

Question 6

what is the bond angle in trimethylamine

Answer 6

108

Question 6

Amines are said to be
_______ when all the alkyl or aryl groups are the same, and ______
when they are different.

Answer 6

simple and mixed

Question 7

Preparation of Amines

Answer 7

Reduction of nitro compounds
Ammonolysis of alkyl halides
Reduction of nitriles
Reduction of amides
Gabriel phthalimide synthesis
Hoffmann bromamide degradation reaction

Question 7

Preparation of Amines by Reduction of nitriles

Answer 7

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

Question 7

Preparation of Amines by Reduction of nitro compounds

Answer 7

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

Question 8

Preparation of Amines by Ammonolysis of alkyl halides

Answer 8

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.

Question 9

Preparation of Amines by Reduction of amides

Answer 9

The amides on reduction with lithium aluminium hydride yield amines.

Question 10

Preparation of Amines by Hoffmann bromamide degradation reaction

Answer 10

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.

Question 10

Preparation of Amines by Gabriel phthalimide synthesis

Answer 10

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

Question 11

Physical Properties of amines

Answer 11

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.

Question 11

why are Lower aliphatic amines are soluble in water?

Answer 11

Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules

Question 12

solubility in amines

Answer 12

solubility decreases with increase in molar mass of amines due to increase in size of the hydrophobic alkyl part. Higher amines are essentially insoluble in water.

Question 13

the order of boiling points of isomeric amines is

Answer 13

Primary > Secondary > Tertiary

Question 13

what makes amines reactive

Answer 13

Difference in electronegativity between nitrogen and hydrogen atoms and the presence of unshared pair of electrons over the nitrogen atom makes amines reactive

Question 14

what decides the course of reaction of amines

Answer 14

The number of hydrogen atoms attached to nitrogen atom also decides the course of reaction of amines

Question 15

why amines behave as nucleophiles

Answer 15

amines behave as nucleophiles due to the presence of unshared electron pair

Question 15

Alkylation of amines

Answer 15

Amines undergo alkylation on reaction with alkyl halides

Question 15

Acylation of amines

Answer 15

Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. This reaction is known as acylation The products obtained by acylation reaction are known as amides The reaction is carried out in the presence of a base stronger than the amine, like pyridine, which removes HCl so formed and shifts the equilibrium to the right hand side

Question 16

what is benzoylation

Answer 16

Amines also react with benzoyl chloride (C6H5COCl). This reaction is known as benzoylation

Question 16

Carbylamine reaction

Answer 16

Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines which are foul smelling substances. Secondary and tertiary amines do not show this reaction. This reaction is known as carbylamine reaction or isocyanide test and is used as a test for primary amines.

Question 16

amines Reaction with nitrous acid

Answer 16

(a) Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts which being unstable, liberate nitrogen gas quantitatively and alcohols. Quantitative evolution of nitrogen is used in estimation of amino acids and proteins. (b) Aromatic amines react with nitrous acid at low temperatures(273-278 K) to form diazonium salts, a very important class of compounds used for synthesis of a variety of aromatic compounds

Question 17

amines Reaction with Benzenesulphonyl chloride

Answer 17

Benzenesulphonyl chloride (C6H5SO2Cl), which is also known as Hinsberg’s reagent, reacts with primary and secondary amines to form sulphonamides. (a) The reaction of benzenesulphonyl chloride with primary amine yields N-ethylbenzenesulphonyl amide The hydrogen attached to nitrogen in sulphonamide is strongly acidic due to the presence of strong electron withdrawing sulphonyl group. Hence, it is soluble in alkali.

Question 17

secondary amines Reaction with Benzenesulphonyl chloride

Answer 17

In the reaction with secondary amine, N,N-diethylbenzenesulphonamide is formed Since N, N-diethylbenzene sulphonamide does not contain any hydrogen atom attached to nitrogen atom, it is not acidic and hence insoluble in alkali.

Question 18

tertiary amines Reaction with Benzenesulphonyl chloride

Answer 18

Tertiary amines do not react with benzenesulphonyl chloride. This property of amines reacting with benzenesulphonyl chloride in a different manner is used for the distinction of primary, secondary and tertiary amines and also for the separation of a mixture of amines. However, these days benzenesulphonyl chloride is replaced by p-toluenesulphonyl chloride

Question 18

amine on Bromination

Answer 18

Aniline reacts with bromine water at room temperature to give a white precipitate of 2,4,6-tribromoaniline

Question 19

what is the problem with amine on Bromination

Answer 19

The main problem encountered during electrophilic substitution reactions of aromatic amines is that of their very high reactivity. Substitution tends to occur at ortho- and para-positions in order to control activating effect of –NH2 group This can be done by protecting the -NH2 group by acetylation with acetic anhydride, then carrying out the desired substitution followed by hydrolysis of the substituted amide to the substituted amine.

Question 19

Nitration on amines

Answer 19

Direct nitration of aniline yields tarry oxidation products in addition to the nitro derivatives. Moreover, in the strongly acidic medium, aniline is protonated to form the anilinium ion which is meta directing However, by protecting the –NH2 group by acetylation reaction with acetic anhydride, the nitration reaction can be controlled and the p-nitro derivative can be obtained as the major product.

Question 20

Sulphonation on amines

Answer 20

Aniline reacts with concentrated sulphuric acid to form anilinium hydrogensulphate which on heating with sulphuric acid at 453-473K produces p-aminobenzene sulphonic acid, commonly known as sulphanilic acid, as the major product.Aniline does not undergo Friedel-Crafts reaction (alkylation andacetylation) due to salt formation with aluminium chloride, the Lewis acid, which is used as a catalyst. Due to this, nitrogen of aniline acquires positive charge and hence acts as a strong deactivating group for further reaction.

Question 20

what are DIAZONIUM SALT

Answer 20

The diazonium salts have the general formula –R N X2+where R stands for an aryl group and –X ion The N2+group is called diazonium group.

Question 20

Method Preparation of Diazonium Salts

Answer 20

Benzenediazonium chloride is prepared by the reaction of aniline with nitrous acid at 273-278K. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The conversion of primary aromatic amines into diazonium salts is known as diazotisation. Due to its instability, the diazonium salt is not generally stored and is used immediately after its preparation.

Question 20

Physical Properties of Diazonium Salts

Answer 20

Benzenediazonium chloride is a colourless crystalline solid. It is readily soluble in water and is stable in cold but reacts with water when warmed. It decomposes easily in the dry state. Benzenediazonium fluoroborate is water insoluble and stable at room temperature

Question 21

Chemical Reactions Of Diazonium Salts

Answer 21

Diazonium group being a very good leaving group, is substituted by other groups such as Cl –, Br–, I–, CN–and OH– which displace nitrogen from the aromatic ring. The nitrogen formed escapes from the reaction mixture as a gas

Question 22

Diazonium Salts Replacement by halide or cyanide ion

Answer 22

nucleophiles can easily be introduced in the benzene ring in the presence of Cu(I) ion. This reaction is called Sandmeyer reaction. chlorine or bromine can also be introduced in the benzene ring by treating the diazonium salt solution with corresponding halogen acid in the presence of copper powder. This is referred as Gatterman reaction The yield in Sandmeyer reaction is found to be better than Gattermann reaction

Question 22

Diazonium Salts Replacement by iodide ion

Answer 22

Iodine is not easily introduced into the benzene ring directly, but, when the diazonium salt solution is treated with potassium iodide, iodobenzene is formed

Question 23

Diazonium Salts Replacement by fluoride ion

Answer 23

When arenediazonium chloride is treated with fluoroboric acid, arene diazonium fluoroborate is precipitated which on heating decomposes to yield aryl fluoride.

Question 24

Diazonium Salts Replacement by H:

Answer 24

Certain mild reducing agents like hypophosphorous acid (phosphinic acid) or ethanol reduce diazonium salts to arenes and themselves get oxidised to phosphorous acid and ethanal, respectively

Question 25

Diazonium Salts Replacement by –NO2 group:

Answer 25

When diazonium fluoroborate is heated with aqueous sodium nitrite solution in the presence of copper, the diazonium group is replaced by –NO2 group.

Question 25

Diazonium Salts Replacement by hydroxyl group:

Answer 25

If the temperature of the diazonium salt solution is allowed to rise upto 283 K, the salt gets hydrolysed to phenol