Reactions of amine

reaction of amine and basicity of amine

1. Reactions of Amine

2. Basicity salt formation

3. Aniline react with HCl gives anilinium chloride

4. Basicity of amine Like ammonia, amines are converted into their salts by aqueous mineral acids and are liberated from their salts by aqueous hydroxides . Like ammonia, therefore, amines are more basic than water and less basic than hydroxide ion : RNH2 + H3O+ ---  R-NH3+ + H2O Stronger base weak base R-NH3+ + OH- --- RNH2 + H2O Strong base weak base

5. T o compare acidities of carboxylic acids by measuring the extent to which they give up hydrogen ion to water; the equilibrium constant for this reaction was called the acidity constant, Ka . In the same way, it is convenient to compare basicities of amines by measuring the extent to which they accept hydrogen ion from water; the equilibrium constant for this reaction is called a basicity constant, Kb .

6. R-NH2 + H2O ----> RNH3+ + OH- <---- Kb = [ RNH3+] [OH-] [RNH2] Concentration of solvent water is omitted. Kb is larger value than it will be stronger base. aliphatic amines of all three classes are thus somewhat stronger bases than ammonia. Aromatic amines, on the other hand, are considerably weaker bases than ammonia.

7. Substituents on the ring have a marked effect on the basicity of aromatic amines, p-nitro aniline, for example, being only 1/4000 as basic as aniline

8. Structure and basicity The more stable the ion relative to the amine from which it is formed, the more basic the am Amines are more basic than alcohols, ethers, esters, etc :, for the same reason that ammonia is more basic than water: N itrogen is less electronegative than oxygen, and can better accommodate the positive charge of the ion.

9. An aliphatic amine is more basic than ammonia because the electron-releasing alkyl groups tend to disperse the positive charge of the substituted ammonium ion and therefore stabilize it in a way that is not possible for the unsubstituted ammonium ion. An alkyl group pushes electrons toward nitrogen, and thus makes the fourth pair more available for sharing with an acid.

10. AMMONIA

11. Aniline and anilinium ion contain the benzene ring and therefore are hybrids of the Kekule structures I and II, and III and IV. This resonance presumably stabilizes both amine and ion to the same extent . It lowers the energy content of each by the same number of kcal/mole, and hence does not affect indifference in their energy contents , that is, does not affect Delta G of ionization.

12. If there were no other factors involved , then, we might expect the basicity of aniline to be about the same as the basicity of ammonia . To account for the powerful activating effect of the NH2 group on electrophilic aromatic substitution, we considered that the intermediate carbonium ion is stabilized by structures in which there is a double bond between nitrogen and the ring ; contribution from these structures is simply a way of indicating the tendency for nitrogen to share its fourth pair of electrons and to accept a positive charge.

13. It is generally believed that the -NH 2 group tends to share electrons with the ring, not only in the carbonium ion which is the intermediate in electrophilic aromatic substitution , but also in the aniline molecule itself . Thus aniline is a hybrid not only of structures I and II but also of structures V , VI, and VII. We cannot draw comparable structures for the anilinium ion.

14. Resonance lowers the energy content of aniline more than it lowers the energy content of aniline more than it lowers the energy content of anilinium ion. The low basicity of aromatic amines is thus due to the fact that the amine is stabilized by resonance to a greater extent than the ion. Aniline is a weaker base than ammonia because it share its fouth pair of electron with the ring and less available for sharing with a hydrogen ion.

15. The tentency of amino group NH2 to release electrons to the aromatic ring makes the ring more reactive towards the electrophillic attack; at the same time this tendency necessarily makes the amine less basic . Similar considerations apply to other aromatic amines.

16. Effect of substituent on basicity of aromatic amines Electron donating group like CH3 increases basicity of aniline and an electron withdrawing substituents like –X and –NO2 decreases the basicity. These effects are understandable. Electron release tends to disperse the positive charge of the anilinium ion and thus destabilizes the ion relative to the amine. Electron withdrawl tends to intensify the positive charge of the anilinium ion, and thus destabilizes the ion relative to the amine.

17. Base strengthening substituents are the ones that activate an aromatic ring toward electrophillic substitution. Base weakening substituents are the ones that deactivates an aromatic ring toward electrophillic substitution. Basicity depends on the position of equilibrium. Reactivity in electrophillic aromatic substitution depends upon rate, relative stabilities of reactant and transition state. Controlling factor is accomodation of a positive charge.

18. Comparison of substituent in amine and carboxylic acid Substituents affect the basicity of an amine and the acidity of a carboxylic acid in opposite ways. Basicity depends upon ability to accommodate a positive charge and acidity depends upon ability to accommodate a negative charge.

19. Ortho effect Electron releasing substituents weaken basicity when they are ortho to amino group. Electron withdrawing substituents do so to a much greater extent from the ortho position than from the meta or para position.

20. Another point of view Electron releasing group pushes electrons toward nitrogen and makes the fourth pair more available for sharing with an acid. An electron withdrawing substituents helps to pull electrons from nitrogen and thus makes the fourth pair less available for sharing.

21. Reaction of amine

22. Salt formation- amines are bases react with mineral acid to form salt

23. Reaction with alkyl halide

24. Reaction with alkyl halide

25. Reaction amine with acid chloride

26. Reaction with nitrous acid

27. Reaction of primary amine with nitrous acid

28. Reaction of Secondary amine with nitrous acid

29. It is the basic test to differentiate between primary, secondary and tertiary amine. this test is known as Nitrous acid test. Primary amine react with nitrous acid to produce nitrogen gas [ seen as bubbles] Secondary amine react with nitrous acid to produce a yellow oily layer. Tertiary amine react with nitrous acid to form soluble nitrite salts . there is no visible sign of reaction.

30. Reaction with benzene sulfonyl chloride- tertiary wont produce the reaction due to lack of active hydrogen

31. The sulfonamide from primary amines still have a replacable hydrogen on the nitrogen. This hydrogen is acidic . Thus sulfonamide from primary amines dissolve in base to form salts. The sulfonamide from secondary amine do not have replaceable hydrogen and so do not dissolve in bases. T his reaction is used as the basis of a test to distinguish from primary, secondary and tertiary amine. This test is known as Hinsberg Test

32. Primary amine react with benzenesulfonyl chloride to form a precipitate that is soluble in NaOH solution. Secondary amine react with benzenesulfonyl chloride to give a precipitate that is insoluble in NaOH . Tertiary amine do not react with benzenesulfonyl chloride.

33. Carbylamine reaction-primary amine give isonitrile where as secondary and tertiary amine wont react. The carbylamine are evil smelling and can be easily detected. This reaction is used to distinguish primary from secondary and tertiary amine

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