Amines Part-One power point presentation
- 1. AMINES By Dr.M.Prashanthi Assistant Professor Department of Chemistry Government Degree College for Women Karimnagar
- 2. Classification Nomenclature Preparations of Amines Physical properties Basic character of amines AMINES
- 3. The Compounds formed when one or two or three hydrogen's of ammonia molecule are substituted by alkyl or aryl groups are called amines. AMINES NH3 ---->CH3NH2---->(CH3)2-NH---->(CH3)3-N
- 4. Classification of Amines depends up on the number of Alkyl or Aryl groups present on Nitrogen atom in Ammonia. Amines are classified into four types Primary amines Secondary amines Tertiary amines Quaternary ammonium salt or amines. CLASSIFICATION
- 5. If one hydrogen atom in Ammonia is replaced by one alkyl group or aryl group the amine is called primary amine. The general formula is R-NH2 or Ar-NH2. Ex:CH3-NH2 Methyl amine , C6H5-NH2 Aniline. PRIMARY AMINE
- 6. If two hydrogen atoms in ammonia are replaced by two alkyl groups the amine is called secondary amine. The general formula is R2-NH or Ar2NH or R-NH-Ar SECONDARY AMINE
- 7. If three hydrogen atoms in ammonia are replaced by three alkyl groups the amine is called Tertiary amine. The general formula is R3N. TERTIARY AMINE
- 8. In these compounds the nitrogen is attached to four alkyl groups and exists as tetra alkyl ammonium cation. To neutralize the positive charge it combines with halide ion and forms ammonium salt. The general formula is R4N+ X- . QUATERNARY SALTS
- 9. The Amino functional group is indicated by the suffix amine in IUPAC nomenclature this means that the last letter ‘e’ of Alkane is removed and amine term is added in place of it. Methane + Amine= Methanamine H2N-CH3 Aliphatic amines : These are named both by common and IUPAC System. Common system: According to this system the amines are named by prefixing the names of the nitrogen attached to alkyl groups to the word amine. If the substituent's are identical the prefixes di or tri employed. NOMENCLATURE
- 10. CH3-NH2 Methyl amine/Methanamine CH3-CH2-NH2 Ethyl amine/Ethanamine CH3-NH-CH3 Dimethyl amine/ N-methyl methanamine (CH3)3-N Trimethyl amine/ N,N Dimethyl methanamine (CH3)2-CH-NH2 Isopropyl amine/ 1-methyl ethanamine Examples
- 11. The simplest aromatic amines is called aniline. Its methyl homologues are named as Ortho ,Meta and Para Toludines. AROMATIC AMINES
- 12. Amines are prepared by the following methods- 1.Ammonolysis of alkyl halides 2.Gabriel synthesis 3.Hoffman bromamide reaction 4.Reduction of amides 5.Schmidt reaction PREPARATION OF AMINES
- 13. When an alkyl halide is heated with an aqueous or alkali solution of ammonia in a sealed tube at 100*C, then a mixture of primary, secondary, and tertiary amines along with quaternary ammonium salt is formed. It is Nucleophilic substitution reaction. Ammonolysis of Alkyl halides
- 14. REACTIONS NH3 + R-X------->R-NH2 + HX PRIMARY AMINE R-NH2 + R-X-----> R2-NH + HX SECONDARY AMINE R2-NH + R-X------> R3-N + HX TERTIARY AMINE R3-N + R-X --------> R4-N+ X- QUARTERNARY AMINE
- 15. Aryl halide do not react with ammonia easily, this is because partial double bond is present between halogen and benzene ring. If electron with drawing groups are present on the benzene ring , then halogen can be easily replaced by amino group. Ammonolysis of alkyl halides
- 16. In this reaction Pthalimide is treated with ethanolic solution of KOH to form Potassium pthalimide.This reacts with alkyl halide to give N-alkyl pthalimide. Hydrolysis of this alkyl pthalimide with NaOH gives primary amines. GABRIEL’S SYNTHESIS
- 17. When an amide (Aliphatic / Aromatic) is treated with bromine and, alkali, primary amines are formed. HOFFMANN’S BROMAMIDE REACTION R-CO-NH2 + X2 + 4 NaOH----------->R-NH2 + 2NaX + Na2CO3 + 2 H2O 1*amine
- 18. Amides on reduction with Lithium aluminium hydride/Na-ethylalcohol gives amines. REDUCTION OF AMIDES
- 19. In presence of Conc.H2SO4, carboxylic acids reacts with hydrazoic acid, and form primary amine. This reaction is called Schmidt reaction. In this reaction sulphuric acid or any Lewis acid is used as catalyst The amine formed in this reaction has one carbon atom less than the taken carboxylic acid.(Curtius Degradation). CH3COOH+N3H CH3NH2+CO2+N2 SCHMIDT REACTION
- 20. Amines of low molecular weights are colorless liquids. Amines containing 4 carbons or more carbons are liquids and are volatile Amines of high molecular weights are colorless solids. Aromatic amines are colorless liquids or solids but on exposure to air they change their color to brown due to oxidation of Nitrogen. Low molecular weight amines are lighter than water. Primary ,Secondary amines contain hydrogens on nitrogen there will be hydrogen bonds formation. Hence primary secondary amines posses higher melting points and boiling points compared to the tertiary amines. Physical Properties
- 21. The M.P and B.P of amines are less than alcohols due to the less electro negativity of nitrogen than that of oxygen. Aliphatic amines forms hydrogen bonds with water molecules and these are soluble in water. Aromatic amines cannot form hydrogen bonds with water and these are insoluble in water.
- 23. The basic character is due to the presence of unshared electron pair on nitrogen atom. The readiness which the lone pair electrons is available for co- ordination with a proton determines the relative basic strength of amines. BASIC NATURE OF AMINES
- 24. Due to positive inductive effect of alkyl groups the nitrogen atom becomes strongly electro negative due to this the lone pair of electrons on nitrogen atoms is more readily available than in ammonia. Hence amines are stronger bases than ammonia. The basicity of amines should increase with the increase in number of alkyl groups. The basicity of different amines should be in the following order. Tertiary > Secondary > Primary COMPARATIVE BASIC STRENGTH OF AMMONIA METHYLAMINE,DIMETHYLAMINE,TRIMETHYLAMINE
- 25. But the actual decreasing order of basic strength is Secondary > Primary > Tertiary > NH3 Because the alkyl groups around nitrogen atom cause crowding and decrease the availability of lone pair. This is called Steric effect. This results in the fall of basic strength.
- 26. In aqueous solutions, basic strength also depends on the steric effect and hydration effect Steric effect: with the nature of the alkyl groups the basic nature of various amines also varies. (CH3)2-NH > CH3-NH2 > (CH3)3-N > NH3 2 1 3 (C2H5)2-NH > (C2H5)3-N > C2H5-NH2 > NH3 2 3 1
- 27. Hydration effect :It refers to the stabilization of the protonated amine by water molecules. The water molecules form H-bonding with the protonated amine and releases energy,called as hydration energy. Based on this the basic strength of amines in aqueous solution shows the following order- R-NH2 > R2-NH > R3-N 1 2 3
- 28. Finally it is based on the combination of electron releasing factor,steric effects and hydration effects, the basic strength of aliphatic amines is as follows- Secondary amines > tertiary amines > primary amines
- 29. Aniline is less basic than ammonia. The phenyl group exerts –IE.It withdraws electrons. Therefore the electrons on nitrogen atom are less available for protonation. Electron withdrawing groups decreases electron density on nitrogen atom which in turn decreases the basicity. :NH3 > C6H5-NH2 Comparison between Aryl amines and Alkyl amines
- 30. Aryl amines are weaker bases than alkyl amines. Alkyl groups increases the basicity of aromatic amines. N-alkyl anilines are stronger bases than aniline. R----->---:NH2 Ar----<----:NH2 The aryl alkyl amines are stronger bases than aryl amines but weaker than alkyl amines. R-NH2 > Ar-CH2-NH2 > Ar-NH2 continued in part-2