Chapter 8 amide
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1. Amides are derived from carboxylic acids by replacing the -OH group of the carboxylic acid with an -NH2 group. Primary amides are named by changing the acid name to the acid name amide. Secondary and tertiary amides use uppercase N to designate the alkyl group on nitrogen. 2. Amides can be prepared from carboxylic acids or acid chlorides. From acids, an ammonium salt is formed which dehydrates to the amide upon heating. From acid chlorides, the acid chloride reacts with ammonia. 3. Amides undergo hydrolysis to form carboxylic acids and ammonia/ammonium salts. They also react with nitro
Chapter 8 amide
- 1. ORGANIC CHEMISTRY II CHM301 AMIDES NURUL’ AIN BINTI JAMION
- 2. INTRODUCTION The functional group: Amides are derived from carboxylic acids. A carboxylic acid contains the -COOH group, and in an amide the -OH part of that group is replaced by an -NH2 group.
- 3. Nomenclature of amides Primary amides are named by changing the name of the acid by dropping the -oic acid or -ic acid endings and adding -amide.
- 4. Nomenclature of amides Secondary amides are named by using an upper case N to designate that the alkyl group is on the nitrogen atom. Tertiary amides are named in the same way.
- 6. Preparation of Amides Carboxylic acids Acid chlorides
- 7. Preparation of Amides Carboxylic acids The carboxylic acid is first converted into an ammonium salt which then produces an amide on heating. The ammonium salt is formed by adding solid ammonium carbonate to an excess of the acid. For example, ammonium ethanoate is made by adding ammonium carbonate to an excess of ethanoic acid. When the reaction is complete, the mixture is heated and the ammonium salt dehydrates producing ethanamide.
- 8. Preparation of Amides Acid chlorides In the first stage, the ammonia reacts with the ethanoyl chloride to give ethanamide and hydrogen chloride gas. Then the hydrogen chloride produced reacts with excess ammonia to give ammonium chloride. …and you can combine both equation to give one overall equation:
- 9. Reactions of amides 1. 2. 3. 4. 5. Hydrolysis With nitrous acid Reduction Hoffmann degradation Dehydration
- 10. Reactions of amides 1. Hydrolysis Acidic Used: concentrated acid (HCl/ 2SO4). H Products: ammonium or ammonium salt and carboxylic acid Example:
- 11. Reactions of amides 1. Hydrolysis Acidic General equation: O H3O+ + HCl C R O NH2 R O + R C N R' R'' C O H3 O+ Cl- reflux + reflux R C OH + NH4+ OH R' N R'' H H
- 12. Reactions of amides 1. Hydrolysis Alkaline Used: concentrated sodium hydroxide solution. Products: ammonia or an amine and carboxylate salt Example:
- 13. Reactions of amides Hydrolysis 1. Alkaline General equation: O + C R NH2 O OH- + OH- R'' + reflux R N R' R' O C C NH3 O- C R O R + reflux O- NH R''
- 14. Reactions of amides With nitrous acid 2. Amides reacts with nitrous acid (HNO2) to give carboxylic acid and N2 gas. Nitrous acid (HNO2) is unstable and is prepared in situ by the reaction of dilute HCl or dilute H2SO4 with sodium nitrite in the absence of heat. NaNO2 (s) + HCl (aq) → NaCl (aq) + O=N-OH (aq) nitrous acid R-CONH2 + HNO2 R-COOH + N2(evolved)+H2O
- 15. Reactions of amides 2. With nitrous acid O R C NH2 HNO2 amide O R C OH N2 carboxylic acid EXAMPLE O CH3 C NH2 ethanamide HNO2 O CH3 C OH ethanoic acid N2
- 16. Reactions of amides Reduction 3. Amides, RCONR'2, can be reduced to the amine, RCH2NR'2 by conversion of the C=O to -CH2Amides can be reduced by LiAlH4 but NOT the less reactive NaBH4
- 17. Reactions of amides Reduction 3. Look at the N substituent in the following examples (those bonds don't change!)
- 18. Reactions of amides Hoffmann degradation 4. Hofmann degradation is a reaction between an amide and a mixture of bromine and sodium hydroxide solution. Heat is needed. The net effect of the reaction is a loss of the -COpart of the amide group. You get a primary amine with one less carbon atom than the original amide had. The general equation: ∆
- 19. Reactions of amides Hoffmann degradation 4. Example: Ethanamide methylamine full The equation for the reaction is: Hofmann degradation is used as a way of cutting a single carbon atom out of a chain.
- 20. Reactions of amides Dehydration 5. Amides are dehydrated by heating a solid mixture of the amide and phosphorus(V) oxide, P4O10 / phosphorus oxychloride, POCl3 . Water is removed from the amide group to leave a nitrile group, -CN. The liquid nitrile is collected by simple distillation. For example, with ethanamide, you will get ethanenitrile.
- 21. CHEMICAL TESTS TO DIFFERENTIATE BETWEEN CARBOXYLIC ACID DERIVATIVES ACYL CHLORIDE ESTER AMIDE W ater Vigorous. W hite fumes (HCl) liberated. No reaction No reaction Acid hydrolysis Vigorous, RCOOH formed Reversible, produces RCOOH and alcohol Form RCOOH and ammonium salt Base hydrolysis Vigorous, salt of RCOOH form Non reversible, forms carboxylate salt and alcohol Ammonia gas liberated Ammonia Forms amide Form amide No reaction Reduction No reaction Forms two alcohols Forms amine Hoffman degradation No reaction No reaction Forms amine