chapter8-amide-131023012231-phpapp02.pptx

Amide

1. NURU L ’ A I N B INT I J A MION ORGANIC CHEMISTRY II CHM 3 01 AMIDES

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 -NH 2 group.

3. □ Primary amides are named by changing the name of the acid by dropping the -oic acid or -ic acid endings and adding -amide . Nomenclature of amides

4. 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. Nomenclature of amides

5. Nomenclature of amides

6. Preparation of Amides □ Carboxylic acids □ Acid chlorides

7. Preparation of Amides □ C arb oxyl i c ac i ds  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 □ Ac id chlorid es  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 Hydrolysis With nitrous acid Reduction Hoffmann degradation Dehydration

10. Reactions of amides Hydrolysis Acidic Used: concentrated acid (HCl/H 2 SO 4 ). Products: a mm o n i u m o r a m m o n i u m s a l t a n d carboxylic acid Example:

11. Hydrolysis Acidic General equation: Reactions of amides C O R NH 2 H 3 O + + HCl reflux C O R O H Cl - + NH 4 + N R ' H C O R N + H 3 O + reflux C O R O H + H R' ' R' ' R '

12. Reactions of amides Hydrolysis Alkaline U s ed : c o n c e n t r a t e d s o d i u m h y d r o x i d e solution . P r o d u c ts: a mm o n i a o r a n a m i n e a n d carboxylate salt Example:

13. Reactions of amides Hydrolysis Alkaline ➢ General equation: C O R NH 2 + OH - reflux C O R O - + NH 3 C O R + OH - reflux C O R O - + NH N R ' R '' R ' R ' '

14. Reactions of amides ➢ ➢ 2. With nitrous acid Amides reacts with nitrous acid (HNO 2 ) to give carboxylic acid and N 2 gas. Nitrous acid (HNO 2 ) is unstable and is prepared in situ by the reaction of dilute HCl or dilute H 2 SO 4 with sodium nitrite in the absence of heat. NaNO 2 (s) + HCl (aq) → NaCl (aq) + O=N-OH (aq) nitrous acid R-CONH 2 + HNO 2  R-COOH + N 2 (evolved)+H 2 O

15. 2. With nitrous acid O R C NH 2 N 2 O R C OH HNO 2 EXAMPLE O CH 3 C NH 2 ethanamide 2 3 O C H C OH N HNO 2 a mi d e carboxylic acid ethanoic acid Reactions of amides

16. Reactions of amides  3. Reduction Amides , RCONR' 2 , can be reduced to the amine , R C H 2 N R ' 2 b y conve rs io n o f t h e C = O to - C H 2 -  A m ide s c a n b e r e d u c e d b y L i A l H 4 b u t N O T t he less reactive NaBH 4

17. Reactions of amides ➢ 3. Reduction Look at the N substituent in the following examples (those bonds don't change!)

18. Reactions of amides    4. Hoffmann degradation 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 -CO- part of the amide group. You get a primary amine with one less carbon atom than the original amide had. The general equation: ∆

19.  Hoffmann degradation Example: Ethanamide  methylamine full equation for the reaction is: The Hofmann degradation is used as a way of cutting a single carbon atom out of a chain . Reactions of amides

20. Reactions of amides    5. Dehydration Amides are dehydrated by heating a solid mixture of the amide and phosphorus(V) oxide, P 4 O 10 / phosphorus oxychloride, POCl 3 . 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 A C Y L C H L O R I D E E S T E R A M I D E W a t e r Vigorous. White fumes (HCl) liberated. No reaction No reaction Acid hydrolysis Vigorous, R C OO H f o r m e d Reversible, produces RCOOH and alcohol F o r m R C OO H a n d a mm o n i u m salt Base hydrolysis Vigorous, salt of R C O O H f o r m N o n r e v e r s i b l e , forms carboxylate salt and alcohol A mm o n i a g a s liberated A m m o n i a Forms amide F o r m a m id e No reaction Reduction No reaction Forms two alcohols Forms amine Hoffman d e g r a d a t i o n No reaction No reaction Forms amine