unit 13 - NCERT

1 Amines constitute an important class of organiccompounds derived by replacing one or more hydrogenatoms of ammonia molecule by alkyl/aryl group(s). Innature, they occur among proteins, vitamins, alkaloidsand hormones. Synthetic examples include polymers,dye stuffs and drugs. Two biologically activecompounds, namely adrenaline and ephedrine, bothcontaining secondary amino group, are used to increaseblood pressure. Novocain, a synthetic amino compound,is used as an anaesthetic in dentistry. Benadryl, a wellknown antihistaminic drug also contains tertiary aminogroup. Quaternary ammonium salts are used assurfactants. Diazonium salts are intermediates in thepreparation of a variety of aromatic compoundsincluding dyes. In this Unit, you will learn about aminesand diazonium AMINESA mines can be considered as derivatives of ammonia,obtained by replacement of one, two or all the threehydrogen atoms by alkyl and/or aryl example:Like ammonia, nitrogen atom of amines is trivalent andcarries an unshared pair of electrons.

2 Nitrogen orbitalsin amines are therefore, sp3 hybridised and the geometryof amines is pyramidal. Each of the three sp3 hybridisedorbitals of nitrogen overlap with orbitals of hydrogen orcarbon depending upon the composition of the fourth orbital of nitrogen in all amines contains anunshared pair of electrons. Due to the presence ofunshared pair of electrons, the angle C N E, (where E isAfter studying this Unit, you will beable to describe amines as derivatives ofammonia having a pyramidalstructure; classify amines as primary,secondary and tertiary; name amines by common namesand IUPAC system; describe some of the importantmethods of preparation of amines; explain the properties of amines; distinguish between primary,secondary and tertiary amines; describe the method of prepara-tion of diazonium salts and theirimportance in the synthesis of aseries of aromatic compoundsincluding azo The chief commercial use of amines is as intermediates in thesynthesis of medicines and fibres.)

3 Structure of Structure of Structure of Structure of Structure of Amines2022-23390 ChemistryC or H) is less than ; for instance, it is 108o in case oftrimethylamine as shown in Fig. are classified as primary (1o), secondary (2o) and tertiary (3o)depending upon the number of hydrogen atoms replaced by alkyl oraryl groups in ammonia molecule. If one hydrogen atom of ammoniais replaced by R or Ar , we get RNH2 or ArNH2, a primary amine (1o).If two hydrogen atoms of ammonia or one hydrogen atom of R-NH2 arereplaced by another alkyl/aryl(R ) group, what would you get? Youget R-NHR , secondary amine. The second alkyl/aryl group may besame or different. Replacement of another hydrogen atom by alkyl/arylgroup leads to the formation of tertiary amine. Amines are said to be simple when all the alkyl or aryl groups are the same, and mixed when they are common system, an aliphatic amine is named by prefixing alkylgroup to amine, , alkylamine as one word ( , methylamine).

4 Insecondary and tertiary amines, when two or more groups are the same,the prefix di or tri is appended before the name of alkyl group. InIUPAC system, primary amines are named as alkanamines. The nameis derived by replacement of e of alkane by the word amine. Forexample, CH3NH2 is named as methanamine. In case, more than oneamino group is present at different positions in the parent chain, theirpositions are specified by giving numbers to the carbon atoms bearing NH2 groups and suitable prefix such as di, tri, etc. is attached to theamine. The letter e of the suffix of the hydrocarbon part is retained. Forexample, H2N CH2 CH2 NH2 is named as ethane-1, name secondary and tertiary amines, we use locant N to designatesubstituent attached to a nitrogen atom. For example, CH3 NHCH2CH3 Pyramidal shape of as N-methylethanamine and (CH3CH2)3N is named as N, N-diethylethanamine.

5 More examples are given in Table arylamines, NH2 group is directly attached to the benzene is the simplest example of arylamine. In common system, itis known as aniline. It is also an accepted IUPAC name. While namingarylamines according to IUPAC system, suffix e of arene is replaced by amine . Thus in IUPAC system, C6H5 NH2 is named as and IUPAC names of some alkylamines and arylamines aregiven in Table nameIUPAC nameCH3- CH2 NH2 EthylamineEthanamineCH3 CH2 CH2 NH2n-PropylaminePropan-1-amineIsopropyla minePropan-2-amineEthylmethylamineN-Meth ylethanamineTrimethylamineN,N-Dimethylme thanamineN,N-DiethylbutylamineN,N-Diethy lbutan-1-amineAllylamineProp-2-en-1-amin eHexamethylenediamineHexane-1,6-diamineA nilineAniline or Benzenamineo-Toluidine2-Methylanilinep-B romoaniline4-Bromobenzenamineor4-Bromoan ilineN,N-DimethylanilineN,N-Dimethylbenz enamineTable : Nomenclature of Some Alkylamines and Arylamines2022-23392 ChemistryAmines are prepared by the following of nitro compoundsNitro compounds are reduced to amines by passing hydrogen gasin the presence of finely divided nickel, palladium or platinum andalso by reduction with metals in acidic medium.

6 Nitroalkanes canalso be similarly reduced to the corresponding with iron scrap and hydrochloric acid is preferred becauseFeCl2 formed gets hydrolysed to release hydrochloric acid during thereaction. Thus, only a small amount of hydrochloric acid is requiredto initiate the of alkyl halidesYou have read (Unit 10, Class XII) that the carbon - halogen bondin alkyl or benzyl halides can be easily cleaved by a , an alkyl or benzyl halide on reaction with an ethanolicsolution of ammonia undergoes nucleophilic substitution reactionin which the halogen atom is replaced by an amino ( NH2) process of cleavage of the C X bond by ammonia molecule isknown as ammonolysis. The reaction is carried out in a sealedtube at 373 K. The primary amine thus obtained behaves as anucleophile and can further react with alkyl halide to form secondaryand tertiary amines, and finally quaternary ammonium Aminesof Aminesof Aminesof Aminesof the following amines as primary, secondary or (i)Write structures of different isomeric amines corresponding to the molecularformula, C4H11N.

7 (ii)Write IUPAC names of all the isomers.(iii)What type of isomerism is exhibited by different pairs of amines?Intext QuestionsIntext QuestionsIntext QuestionsIntext QuestionsIntext Questions2022-23393 AminesThe free amine can be obtained from the ammonium salt by treatmentwith a strong base:Ammonolysis has the disadvantage of yielding a mixture of primary,secondary and tertiary amines and also a quaternary ammonium , primary amine is obtained as a major product by takinglarge excess of order of reactivity of halides with amines is RI > RBr > of nitrilesNitriles on reduction with lithium aluminium hydride (LiAlH4) orcatalytic hydrogenation produce primary amines. This reaction isused for ascent of amine series, , for preparation of aminescontaining one carbon atom more than the starting of amidesThe amides on reduction with lithium aluminium hydride chemical equations for the following reactions:(i)Reaction of ethanolic NH3 with C2H5Cl.

8 (ii)Ammonolysis of benzyl chloride and reaction of amine so formedwith two moles of phthalimide synthesisGabriel synthesis is used for the preparation of primary on treatment with ethanolic potassium hydroxide formspotassium salt of phthalimide which on heating with alkyl halidefollowed by alkaline hydrolysis produces the corresponding primaryamine. aromatic primary amines cannot be prepared by this methodbecause aryl halides do not undergo nucleophilic substitution withthe anion formed by bromamide degradation reactionHoffmann developed a method for preparation of primary amines bytreating an amide with bromine in an aqueous or ethanolic solutionof sodium hydroxide. In this degradation reaction, migration of analkyl or aryl group takes place from carbonyl carbon of the amideto the nitrogen atom. The amine so formed contains one carbon lessthan that present in the chemical equations for the following conversions:(i)CH3 CH2 Cl into CH3 CH2 CH2 NH2(ii)C6H5 CH2 Cl into C6H5 CH2 CH2 NH2 Example lower aliphatic amines are gases with fishy odour.

9 Primary amineswith three or more carbon atoms are liquid and still higher ones aresolid. Aniline and other arylamines are usually colourless but getcoloured on storage due to atmospheric aliphatic amines are soluble in water because they can formhydrogen bonds with water molecules. However, solubility decreaseswith increase in molar mass of amines due to increase in size of thehydrophobic alkyl part. Higher amines are essentially insoluble in the electronegativity of nitrogen of amine and oxygen ofalcohol as and respectively, you can predict the pattern ofsolubility of amines and alcohols in water. Out of butan-1-ol andbutan-1-amine, which will be more soluble in water and why? Aminesare soluble in organic solvents like alcohol, ether and benzene. Youmay remember that alcohols are more polar than amines and formstronger intermolecular hydrogen bonds than and secondary amines are engaged in intermolecularassociation due to hydrogen bonding between nitrogen of one andhydrogen of another molecule.

10 This intermolecular association is morein primary amines than in secondary amines as there are two hydrogenatoms available for hydrogen bond formation in it. Tertiary amines donot have intermolecular association due to the absence of hydrogenatom available for hydrogen bond formation. Therefore, the order ofboiling points of isomeric amines is as will you convert(i)Benzene into aniline (ii) Benzene into N, N-dimethylaniline(iii)Cl (CH2)4 Cl into hexan-1,6-diamine?Intext QuestionIntext QuestionIntext QuestionIntext QuestionIntext QuestionWrite structures and IUPAC names of(i)the amide which gives propanamine by Hoffmann bromamidereaction.(ii)the amine produced by the Hoffmann degradation of benzamide.(i)Propanamine contains three carbons. Hence, the amide molecule mustcontain four carbon atoms. Structure and IUPAC name of the startingamide with four carbon atoms are given below:Butanamide(ii)Benzamide is an aromatic amide containing seven carbon , the amine formed from benzamide is aromatic primary aminecontaining six carbon or benzenamineExample > Secondary > TertiaryIntermolecular hydrogen bonding in primary amines is shown inFig.