EXPERIMENT 8 Organic Chemistry II Pahlavan Cherif Carboxylic Acids Reactions and Derivatives Materials Beakers 50 150 400 mL Graduated cylinders 10 25 mL Medium test tubes 6 Test tube rack Ice Hot plate Chemicals Benzoic acid 10 NaOH Sodium acetate Methanol conc H2SO4 Acetamide Butanol Acetyl chloride Red Blue litmus papers 10 H2SO4 pH papers Salicylic acid Purpose Study the Carboxylic acids and their derivatives with one or more carbonyl groups Reactions such as formation and hydrolysis of carboxylic salts and esterification This experiment will illustrate some of the more important reactions of carboxylic acids and their derivatives Introduction Carboxylic acids contain one or more carboxyl functional groups COOH The IUPAC nomenclature drops the e of the suffix of the Alkane name and adds oic acid review the names of the first ten alkanes and convert these names to the corresponding carboxylic acid The carboxyl functional group is polar both at the carbonyl part and at the hydroxyl part because of the difference in electronegativity value of carbon oxygen and oxygen hydrogen Thus carboxylic acids form hydrogen bond with themselves and any other appropriate polar molecule and this structure will influence their physical properties and their chemical properties as we have seen in other cases Note that if the number of total carbons is more than one for example six then five of the carbons are hydrocarbons and non polar The resulting molecule then has a hydrophilic part the carboxyl group and a hydrophobic part the other five carbons with their associated hydrogen atoms One area will be soluble in water and the other not soluble in water Note also that the hydrocarbon part has much reduced carbon The carboxyl group differs from a hydroxyl group in having a delocalized negative charge and this results in resonance stability Note this means that either oxygen carbonyl or hydroxyl can double bond when proton is removed from hydroxyl Carboxylic acids are an important class of organic compounds Other important classes of compounds called acid derivatives are related to acids but differ from them in that the hydroxyl portion of the carboxyl function is replaced by other groups Among these acid derivatives are the acyl halides anhydrides esters and amides O R C X acyl halide O O R C O C R acid anhydride 1 O O R C O R ester R C NH2 amide Review carboxylic acid derivatives nomenclature Acyl Halides The acyl group is named first followed by the halogen name as a separate word CH3CH2COCl is propanoyl chloride or propionyl chloride Acid anhydrides The name of the related acid s is used first followed by the separate word anhydride CH3 CH2 2CO 2O is butanoic anhydride CH3COOCOCH2CH3 is ethanoic propanoic anhydride or acetic propionic anhydride Esters The alkyl group is named first followed by a derived name for the acyl group the oic or ic suffix in the acid name is replaced by ate CH3 CH2 2CO2C2H5 is ethyl butanoate or ethyl butyrate ethylpropyl ester Cyclic esters are called lactones A Greek letter identifies the location of the alkyl oxygen relative to the carboxyl carbonyl group O C O 4 butanolide butanolactone Amides The name of the related acid is used first and the oic acid or ic acid suffix is replaced by amide only for 1 amides CH3CONH2 is ethanamide or acetamide 1o amide 2 3 amides have alkyl substituents on the nitrogen atom These are designated by N alkyl term s at the beginning of the name CH3 CH2 2CONHC2H5 is N ethylbutanamide 2o aminde HCON CH3 2 is N N dimethylmethanamide or N N dimethylformamide 3o amide Cyclic amides are called lactams A Greek letter identifies the location of the nitrogen on the alkyl chain relative to the carboxyl carbonyl group O C N H butanolactam 2 PART A Carboxylic Acid Salts I Salt Formation Carboxylic acids may be neutralized by strong base to give salts Because salts are ionic and usually water soluble acids that are only slightly soluble in water can extracted by aqueous base from a solution in an organic solvent O O NaOH R C OH R C O Na H2O sodium salt water soluble Example O O CH3 CH2 CH2 C OH NaOH CH3 CH2 CH2 C O Na H2O sodium butanoate salt Butanoic acid II Salt Hydrolysis Because carboxylic acids are weak acids partially dissociated in aqueous solution their salt solutions are alkaline In water a carboxylic acid salt hydrolyzes to the undissociated acid and hydroxide ion O R C O O Na H2O R C OH NaOH sodium salt water soluble Example O CH3 CH2 CH2 C O Na O H2O CH3 CH2 CH2 C OH NaOH sodium butanoate salt Butanoic acid 3 PART B Esters Esters can be prepared by the reaction of alcohols with carboxylic acids or their derivatives The acid catalyzed reaction of an alcohol with a carboxylic acid is most commonly used for such preparations The acyl halide ion is a good leaving group making acyl halides very reactive toward nucleophilic acyl substitution Acid halides or acyl halides are highly reactive that they are not found in nature since they even react with water For small scale preparations however the reaction of an acyl halide with an alcohol is often faster and simpler Example PART C Amides Hydrolysis of an Amide Three classes of amides are known Primary 1o amide Benzamide secondary 2o amide N methylbenzamide 4 tertiary 3o amide N ethyl N methylbenzamide Of the various acid derivatives studied here amides are the least reactive toward nucleophilic attack because the unshared electron pair on the nitrogen is delocalized to the carbonyl carbon through resonance Thus unlike most acyl halides or anhydrides amides must be heated to boiling with aqueous acid or base in order to hydrolyze them For a primary amide the product will be ammonium ion and the acid for acidic hydrolysis or ammonia and carboxylate ion for alkaline hydrolysis The reaction mechanisms are similar to those for the hydrolysis of other acid derivatives In this experiment you will hydrolyze acetamide under alkaline and acidic conditions O R C N O H R C H N H H In basic solution In acidic solution Ammonium carboxylate ion Example 5 Safety Note Caution 1 Acetic anhydride is irritating in the liquid or vapor state Avoid contact with skin and eyes 2 When handling concentrated sulfuric or phosphoric acid be careful to avoid contact with skin and clothing Wear disposable gloves Procedure Part A Carboxylic Acid Salts I Salt Formation In each of two test tubes place 0 1 g of benzoic acid To one tube add 3 ml of cold water to the other add 3 ml of 10 sodium hydroxide solution Shake both