amines reactions (1)

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Slide 1: 

Amines, reactions Amines are similar to ammonia in their reactions. Like ammonia, amines are basic . Like ammonia, amines are nucleophilic and react with alkyl halides, acid chlorides, and carbonyl compounds. The aromatic amines are highly reactive in electrophilic aromatic substitution.

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Amine, reactions: As bases Alkylation Reductive amination Conversion into amides EAS Hofmann elimination from quarternary ammonium salts Reactions with nitrous acid

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As bases a) with acids b) relative base strength c) Kb d) effect of groups on base strength

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with acids

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relative base strength RNH 2 > NH 3 > ArNH 2 K b ionization of the base in water :Base + H 2 O H:Base + + OH - K b = [ H:Base + ] [ OH - ] / [ :Base ] K b aliphatic amines 10 -3 – 10 -4 ammonia 1.8 x 10 -5 anilines 10 -9 or less

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Why are aliphatic amines more basic than ammonia? NH 3 + H 2 O  NH 4 + + OH - R-NH 2 + H 2 O  R-NH 3 + + OH - The alkyl group, -R, is an electron donating group. The donation of electrons helps to stabilize the ammonium ion by decreasing the positive charge, lowering the ΔH, shifting the ionization farther to the right and increasing the basicity.

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Why are aromatic amines less basic than aliphatic amines? R-NH 2 + H 2 O  R-NH 3 + + OH - resonance stabilization of the free base, increases the ΔH, shifts the ionization to the left, decreasing base strength.

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Effect of substituent groups on base strength : Electron donating groups will stabilize the anilinium ion, decreasing the ΔH, shifting the ionization farther to the right and making the compound a stronger base . Electron withdrawing groups destabilize the anilinium ion, increasing the ΔH, shifting the ionization towards the reactants, making the compound a weaker base .

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Common substituent groups: -NH 2 , -NHR, -NR 2 -OH -OR -NHCOCH 3 electron donating -C 6 H 5 groups -R -H -X -CHO, -COR -SO 3 H electron withdrawing -COOH, -COOR groups -CN -NR 3 + -NO 2

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Number the following in decreasing order of base strength (let #1 = most basic, etc. 4 1 5 3 2

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2. Alkylation (ammonolysis of alkyl halides)

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3. Reductive amination

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Conversion into amides R-NH 2 + RCOCl  RCONHR + HCl 1 o N -subst. amide R 2 NH + RCOCl  RCONR 2 + HCl 2 o N,N -disubst. amide R 3 N + RCOCl  NR 3 o

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Conversion into sulfonamides R-NH 2 + ArSO 2 Cl  ArSO2NHR + HCl 1 o N -subst.sulfonamide R 2 NH + ArSO 2 Cl  ArSO 2 NR 2 + HCl 2 o N,N -disubst.sufonamide R 3 N + ArSO 2 Cl  NR

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Schotten-Baumann technique: reactions of aromatic acid chlorides are sped up by the addition of base. R-NH 2 + ArSO 2 Cl + KOH  ArSO2N H R 1 o acidic ArSO 2 NR water soluble salt R 2 NH + ArSO 2 Cl + KOH  ArSO 2 NR 2 + HCl 2 o N,N -disubst.sufonamide water insoluble

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Hinsberg Test: unknown amine + benzenesulfonyl chloride, KOH (aq) Reacts to produce a clear solution and then gives a ppt upon acidification  primary amine . Reacts to produce a ppt  secondary amine . Doesn’t react  tertiary amine .

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sulfanilamide “magic bullet” antibiotic

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EAS -NH 2 , -NHR, -NR 2 are powerful activating groups and ortho/para directors a) nitration b) sulfonation c) halogenation d) Friedel-Crafts alkylation e) Friedel-Crafts acylation f) coupling with diazonium salts g) nitrosation

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a) nitration

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b) sulfonation

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c) halogenation

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Swimming pool test kit for chlorine:

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Friedel-Crafts alkylation NR with –NH 2 , -NHR, -NR 2

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Friedel-Crafts acylation NR with –NH 2 , -NHR, -NR 2

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g) nitrosation

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h) coupling with diazonium salts  azo dyes

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Hofmann elimination from quarternary hydroxides step 1, exhaustive methylation  4 o salt step 2, reaction with Ag 2 O  4 o hydroxide + AgX step 3, heat to eliminate  alkene(s) + R 3 N

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7. Reactions with nitrous acid

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note: 90% of all tested nitrosamines are carcinogenic in man. Many nitrosamine cancers are organ specific. For example, dimethylnitrosamine causes liver cancer while the nitrosamines in tobacco smoke cause lung cancer. Sodium nitrite (“cure”) is used as a preservative in meats such as bacon, bologna, hot dogs, etc. to kill the organism responsible for botulism poisoning. In the stomach, the nitrous acid produced from sodium nitrite can react with secondary and tertiary amines to form nitrosamines. To reduce the formation of nitrosamines, ascorbic acid (Vitamin C) is now added to foods cured with sodium nitrite. Nitrosamines are also found in beer!

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Amines, reactions Amines are similar to ammonia in their reactions. Like ammonia, amines are basic . Like ammonia, amines are nucleophilic and react with alkyl halides, acid chlorides, and carbonyl compounds. The aromatic amines are highly reactive in electrophilic aromatic substitution.

Slide 37: 

Amine, reactions: As bases Alkylation Reductive amination Conversion into amides EAS Hofmann elimination from quarternary ammonium salts Reactions with nitrous acid