Experiment 6: Classification Tests for Carboxylic Acids and Derivative Compounds

Carboxylic acids (RCOOH)

• is a class of organic compound with the -COOH (carboxyl) functional group.

• many are found in natural sources and possess medicinal and industrial application.

• together with its derivative compounds occupy the highest priority positions in terms of functional groups

Generally, carboxylic acids structurally contains

an acyl group and a leaving group.

Derivatives are synthesized via different reaction by

replacing the -OH (leaving group of RCOOH) with different other Nü

• The best leaving groups are

the anions of strong acids (e.g -X > -NH2).

Acid halides (RCOX), Acid anhydride (RCOOCOR’), Esters (RCOOR’), and Amides (RCONH2)

are all derivatives of RCOOH

Acid halides (RCOX), Acid anhydride (RCOOCOR’), Esters (RCOOR’), and Amides (RCONH2)

were synthesized via SN acyl mechanism using different Nü sources

RCOOH

are completely water soluble (especially those with C1-C4).

Water solubility decreases as the size

of the acid increases

Boiling points of RCOOH

increases as the size of the molecule increases

RCOOH, RCOX, and RCOOCOR’

commonly have acrid piercing odors.

RCOOR’

has volatile fragrant odors.

RCONH2

has biological importance (e.g., proteins) and are mostly odorless and colorless.

Hydrolysis of acid derivatives

uses water as the source of Nü and leads to the synthesis of its parent RCOOH.

Alcoholysis

is the reaction for synthesizing ester derivatives from carboxylic acids and more reactive derivatives like acid halide and acid anhydride.

Aminolysis

is the reaction for synthesizing amide derivatives from carboxylic acids and more reactive derivatives like acid halide and acid anhydride

Hydroxamic acid test

classically is a test to detect the presence of esters but will also give a positive result with acid halides, acid anhydrides, and amides

Hydrolysis of Acid Derivatives

The Cl- of acetyl chloride as it leaves it reacts with AgNO3 resulting to AgCl — a white precipitate.

Basic hydrolysis of ethyl acetate

Ethyl acetate + NaOH → Na acetate + EtOH + HCl → Acetic acid •

Basic hydrolysis of ethyl acetate

NaOH (base) hydrolyzes the ester creating a salt. Upon acidification, Na acetate become acetic acid (with NaCl as by-product).

Basic hydrolysis of benzamide

Benzamide + NaOH → Na benzoate + NH3 ↑ (gas)

Basic hydrolysis of benzamide

Ammonia (NH3) is a gas with a very strong foul odor and has basic properties, hence the litmus test confirms the evolution of gas:

• Red litmus → blue

• Blue litmus → blue

Both acetic chloride and acetic anhydride will test positive for alcoholysis

• formation of 2 layers.

• fruity, plastic balloon odor.

• Both acetic chloride and acetic anhydride upon reacting with aniline (an amine) will test positive for aminolysis

— formation of white ppt.

Aminolysis:

The product formed is known as acetanilide (phenyl amide derivative) has a large benzene ring exhibiting non-polar properties hence the white ppt. In water solution.

Hydroxamic acid test

test common for ester but will also give positive results for acid halide, acid anhydrides, and amides.

Hydroxamic acid test

preliminary test is performed

to check if sufficient enol was formed which is needed to form the colored complex with FeCl3 (+ result).

Hydroxamic acid test

Amides will give a bluish red complex.

Hydroxamic acid test

Other derivatives will give burgundy or magenta complex.