Acid Amides

Acid amides are derivatives of a carboxylic acid in which the -OH portion of the carboxyl group has been replaced by -NH2, general formula R-CO-NH2. The book focuses its worked examples specifically on acetamide, CH3-CO-NH2, as the repres …

(1) Ammonolysis of acid derivatives: amides are prepared by the action of ammonia on either an acid chloride or an acid anhydride (both reactions already introduced, Sections 12.14.2.3 and 12.14.3.2) -- acetyl chloride + NH3 gives acetamide + HCl; acetic anhydride + NH3 gives acetamide + acetic acid. (2) Heating ammonium carboxylates: an ammonium salt of a carboxylic acid, on heating, loses a molecule of water to form the corresponding amide -- ammonium acetate, heated, gives acetamide + H2O (the same transformation already met, from the acid's own point of view, in Section 12.12.C.4). (3) Partial hydrolysis of alkyl cyanides (nitriles): treating a nitrile with COLD concentrated HCl (a deliberately mild, PARTIAL hydrolysis, stopping short of the FULL hydrolysis t …

(1) AMPHOTERIC CHARACTER: amides behave as both a weak base AND a weak acid. As a base, acetamide reacts with hydrochloric acid to form a salt: acetamide + HCl gives acetamide hydrochloride. As an acid, acetamide reacts with sodium metal, liberating hydrogen gas: 2 acetamide + 2 Na gives 2 sodium acetamide + H2. (2) HYDROLYSIS: amides are hydrolysed, on prolonged heating, in EITHER acidic or alkaline solution. Acidic hydrolysis: acetamide + H2O (dilute HCl) gives acetic acid + NH4Cl. Alkaline hydrolysis: acetamide + NaOH gives sodium acetate + NH3. (3) DEHYDRATION: amides, heated with a strong dehydrating agent such as P2O5, lose water and are converted BACK to the corresponding nitrile -- the exact reverse of nitrile hydration/partial hydrolysis (Section 12.14.5.1, method 3). Example: acetamide + P2O5 gives methyl cyanide (acetonitrile) + H2O. (4) HOFMANN'S BROMAMIDE DEGRADATION: amides react with bromine in the presence of caustic alkali (NaOH/KOH) to give a primary amine carrying ONE CARBON FEWER than the parent amide -- a carbon-degrading rearrangement, not a simple substitution. Example: acetamide + Br2 (4 KOH) gives methylamine + K2CO3 + 2 KBr + 2 H2O -- this is exactly the route used in Question 9's benzoic-acid-to-aniline sequence (benzamide, via Hofmann degradation, gives aniline, a phenyl amine with one fewer carbon than benzamide's own acyl-plus-ring count implies at the nitrogen-bearing carbon). (5) REDUCTION: amides, reduced with LiAlH4 (or with sodium and ethyl alcohol), give the corresponding AMINE. Example: acetamide + 4[H] (LiAlH4) gives ethylamin …