Carboxylic Acids and Derivatives (Formal Report)

Name: Group No: II Experiment No: XIV

ACID AND ACID DERIVATIVES

Objective: To investigate the physical and chemical properties of Carboxylic Acids and the Acid Derivatives. Procedure: [Esterification] Obtain 1mL CH3CH2OH add 10 drops CH3COOH and 5 drops conc. H2SO4

Warmed

In as watch glass: Mix 0.1g Benzoic acid 5drop methanol and 5 drops conc. H2SO4 and observe [Reaction with FeCl3] Acidify 3mL of 10% NaOH with HOAc. Add Few drops of FeCl3 sol’n and note formation of Fe(OAc)3

Divide sol’n to three

Heat the first portion

Add few drops of dilute HCl to 2nd portion

Untreat 3rd portion (standard) Dissolve 0.2g Benzoic acid in 2mL H2O and heat

Add 10% NH3 to basicity; boil off excess ammonia and 2 drops FeCl3 sol’n [Reactions of Acid derivatives] Add 2mL water in test tube and 1mL Acetic Anhydride

Agitate and test with litmus In another test tube Mix 0.1g benzamide and NaOH; heat [Reactions with dicarboxylic acids] Stain white cloth with iron soak in warm K2C2O4 for 10-15mins

Observe

[Reactions of substituted acids] (Test for tartaric and citric acid) Place 5mL tartaric acid in test tube Add Dilute NaOH sol’n Add KMnO4 to purple and boil Repeat Wth citric acid sol’n Treat with CaCl2 Purple solutions of tartaric and citric Acid and note the behavior. Data and Results: TABLE 14.1 BEHAVIOR OF CARBOXYLIC ACIDS AND ITS DERIVATIVES

TEST

ESTERIFICATION

TREATMENT 1mL ethanol + 10 drops HOAc + 5 drops conc. H2SO4; warmed 0.1 g benzoic acid plus 5 drops methanol + 5 drops conc. H2SO4

REACTION WITH FERRIC CHLORIDE

3mL of 10% NaOH and dilute HOAc and few drops of FeCl3 divided into 3 equal amounts. Test tube 1 – heat to boiling Test tube 2 – added few drops of dilute HCl

OBSERVATION Smells like plastic balloon The solution formed crystal on the watch glass and it smells like a rotten rat. The solution turns brown and produced orange precipitates Solution turns slightly cloudy

Test tube 3 – untreated

The solution is actually color orange.

Dissolved 0.2g benzoic acid in 2mL hot water and 10% NH4OH. Boiled and added 2 drops ferric chloride

After addition of Ferric chloride reddish brown precipitate was formed

REACTIONS OF ACID DERIVATIVES

REACTIONS OF DICARBOXYLIC ACIDS

2mL water and 1mL acetic anhydride – agitated and tested with litmus: 0.1 g benzamine and 5mL of 10% NaOH.

The litmus paper turns red indicating that solution is acidic and the solution appears to have two immiscible liquids: Smells like ammonia (strong odor)

0.1g benzamide + NaOH; heated

Ammoniacal odor

Iron stain on white cloth soaked in a warm solution of K2C2O4; heated for 10-15mins

The stain was slightly removed (tartaric)

REACTIONS OF SUBSTITUTED ACIDS

Add 5mL tartaric acid solution/citric acid solution and rendered alkaline with NaOH and KMnO4

The solution was golden and yellow and brown precipitate formed.

(citric) Brown precipitate was formed and solution has two layers Upper – dark green Lower – light green

Discussion: Carboxylic acids are acidic, indicated by the change of litmus paper to red. The acidity of the hydrogen in the carboxyl group accounts for this case. The carboxyl group with the attached acidic hydrogen is the active site for the reaction of carboxylic acids, whether it’s esterification, or other reactions. Esterification of carboxylic acids is possible in reaction with alcohol. Here, esterification takes place in addition with ethanol. The attack of the nucleophilic species, in this case, CH3CH2OH, would lead to cleavage of carbon-oxygen bond, which is usually known as acyl-oxygen type of cleavage, indicated by the onset of pleasant odor. After reaction of carboxylic acids to form salts, the salts form precipitates with Ferric Chloride because of double displacement reaction, replacing chloride ions with a carboxylate ion forming sparingly soluble compound. Acid derivatives containing amino groups attached to the carboxyl groups cab react with strong bases, causing the removal of –NH2 group as NH3 and replacing it with –OH attached to the carboxyl group. The indication for this reaction is the odor of ammonia upon addition of NaOH to benzamide.

Dicarboxylic acids such as oxalic acid not only undergo thermal decarboxylation but also forms various metallic salts which has unique properties. In this case, oxalic acid in its salt form can remove rust. Oxalic acids can dissolve rust like stain rust in a cloth, depending upon the solubility of heavy metal oxalates in solutions of alkali oxalates. Alpha hydroxy polycarboxylic acids such as tartaric and citric acid form soluble colored complex salts with Ferric Chloride. Though the two acids are both alpha hydroxy polycarboxylic acids, tartaric acid in the experiment hydrated manganese in KMnO4 producing brown precipitate, while citric acid turned KMnO4 to K2MnO4 by adding 1e- to MnO4-.

Answers to Questions:

1. Why it is that carboxylic acid is an acid? Carboxylic acids are Brønsted-Lowry acids because they are electron pair acceptors in their –COOH groups. The acidity of hydrogen in the –COOH group accounts for the acid-base case of reactions. Acetic acid, the simplest of all carboxylic acid has pKa = 1.75x10-5, making it relatively strong acid. 2. Write the chemical reaction involve in the following: Esterification of acetic acid H2SO4

CH3COOH + CH3CH2OH

(CH3COO)SO4 + H3O+

Hydrolysis of acetic anhydride CH3COOCOCH3 + H2O

2CH3COOH

Hydrolysis of benzamide C6H5COONH2 + OH-

C6H5COO- + NH3

3. Differentiate citric acid and tartaric acid by reaction with potassium permanganate. Though the two acids are both alpha hydroxy polycarboxylic acids, tartaric acid in the experiment hydrated manganese in KMnO4 producing brown precipitate, while citric acid turned KMnO4 to K2MnO4 by adding 1e- to MnO4-.