Carboxylic acids

• The most important chemical property of carboxylic acids is their acidic behavior. The hydrogen attached to oxygen of the carboxyl group gives carboxylic acids their acidic a

  character. In water, this proton may leave the acid, converting it into a carboxylate ion.
• This reaction involves the replacement of the -OH group of the acid by the -OR group of the alcohol leading to the formation of an ester, which can be detected by the onset of a pleasant odor.
•  A very important reaction occurs when carboxylic acids are heated with alcohols or phenols in the presence of an acid catalyst.
• Although carboxylic acids are generally resistant to oxidation, some carboxylic acids like a- hydroxy acids and other multifunctional acids can be oxidized to carbon dioxide by reagents such as KMnO4, K2Cr2O7 and Tollen's reagent.
• Acid derivatives undergo nucleophilic subsitution
• Hydrolysis to the parent acid

  All acid derivatives react

  with water to give carboxylic acids. Low

  molecular weight acid chlorides and acid anhydrides react rapidly with water.

  Esters are much less reactive with water and hydrolyze only in the presence of an acid or base catalyst and the rate of reaction varies with the structure of the ester. Amides undergo hydrolysis only when boiled in acidic or basic solution.
• Alcoholysis: Schotten-Baumann Reaction

  Nucleophilic substitution reactions of acid chlorides and acid anhydrides with alcohols give esters. The reactive hydrogen of the alcohol is

  Alcoholysis: Schotten-Baumann Reaction

  Nucleophilic substitution reactions of acid chlorides and acid anhydrides with alcohols give esters. The reactive hydrogen of the alcohol is replaced by the acyl group of the acid chloride or anhydride yielding the corresponding ester.

  .
• The Schotten-Baumann reaction is a method of converting an alcohol into its ester with benzoyl chloride
• Ammonolysis

  Amides are produced by the reaction of ammonia or amines with esters, acid chlorides and acid anhydrides. The acyl group of the carboxylic acid derivative replaces the reactive hydrogen of the ammonia or amine.
• Hydroxamic acid test

  Acid derivatives can be made to react with hydroxylamine to form hydroxamic acid which forms red or violet ferric hydroxamate complex with FeCls.
• Should contact with an acid occur, wash it off with plenty of water and then with dilute sodium bicarbonate solution
• In case of contact with a base, flood the affected area with water and then thoroughly rinse the area with dilute acetic acid.
• Test for AcidityADissolve 3 drops of formic acid in 20 drops of water.

  b. Determine the pH of the solution with the use of a pH paper.

  c. Repeat the test using the following test compounds: acetic acid and benzoic acid. For benzoic acid, use a mixture of 95% ethanol and water(1:1) as solvent in place of water.
• Test for acidity

  a.Dissolve 3 drops of formic acid in 20 drops of water.

  b. Determine the pH of the solution with the use of a pH paper.

  c. Repeat the test using the following test compounds: acetic acid and benzoic acid. For benzoic acid, use a mixture of 95% ethanol and water(1:1) as solvent in place of water.
• Ester formation

  a.Place 10 drops of ethanol and 5 drops of glacial acetic acid in a test tube.

  b. Add 1 to 2 drops of conc. H2SO4. Shake the tube.

  c. Warm in a water bath for 5 minutes. Note the resulting odor.
• Oxidation

  a.Place 5 drops of formic acid in a test tube.

  b. Add 5 drops of 10% aqueous K2Cr207 and 5 drops of 6M H2O4.

  Shake the tube and observe any color change

  c. Repeat the test using acetic acid, oxalic acid and citric acid in place of formic acid.
• Reactions of acid derivatives

  1.1 Hydrolysis of Acid Chlorides

  1. In a test tube, place 20 drops of water and a piece of red and blue litmus papers.

  b. Cautiously add 5 drops of acetyl chloride. Shake and feel the test tube. Note any temperature change. Note also the change in the color of the litmus and the change in the color of the mixture
• 1.2 Hydrolysis of an Ester

  1. Place 20 drops of ethyl acetate and 5 drops of 25% NaOH solution in a test tube.

  b. Cover the tube loosely with a cork and heat in a water bath for 15 minutes.

  c. Add 1M HCI drop by drop until the solution is neutral to litmus.

  Note any change in the odor of the mixture.
• 1.3 Hydrolysis of an Amide

  1. Place a few crystals of acetamide in a test tube and add 20 drops of 3M NaOH.

  b. Warm gently. Note the odor of the gas evolved.

  C.Hold a piece of red litmus paper at the mouth of the test tube.

  Note any change in the color of the litmus paper.
• 2. Alcoholysis: Schotten-Baumann Reaction

  1. Place 10 drops of ethyl alcohol and 20 drops of water in a test tube

  b. Cautiously add 5 drops of benzoyl chloride.

  c. Cover the tube with a cork and shake the mixture.

  d. Add 20 drops of 10% NaOH with mixing. Note the odor.
• 3.Ammonolysis

  1. Place 10 drops of acetyl chloride and 10 drops of acetic anhydride in two separate test tubes.

  b. Add 10 drops of aniline into each test tube. Add 2 mL of cold water and observe.