Test for Amide Group

Theoretical Background / Context

• Amides are organic compounds that are considered acid amides. Although the main dominant class of amides is the carboxyamide, phosphamides and sulphamides are also abundant.
• Carboxyamindes possess at least one amide group in organic compound (-CONH-). The functional group a carbonyl group (C=O) and amino group (-NH2) linked together. 
• Amides (R – CON – R2’) are characterized by the possibility of having their R groups as a terminal H in their structure. 
• In other words, the N can be linked with one or two H atoms instead of R groups.
• The role that amides play in our real life is controlled by their properties. 
• Amides are used in various applications in different fields such as the food industry, pharmaceutics, etc. 

First: Preparation of Amides

• The simplest form of amide is prepared from ammonia, where a hydrogen atom is replaced by an acyl group. 
• The product is described as a primary amide where its general formula is represented as R – CO – NH2. 
• In the same way, secondary and tertiary amides can be prepared from primary and secondary amines, respectively.

Second: General Properties of Amides

• Amides are considered very weak bases compared to their corresponding amines.
• This is noticed from their pKa which is around -0.5, while that of the corresponding amines exceeds 9.5. Amides are less soluble than their corresponding carboxylic acid and amines. 
• This is attributed to the ability of the later compounds to both accept and donate hydrogen bonds. 
• The solubility of amides can be  comparable to their corresponding esters.

Principle of Work

• In this experiment, amides are tested by detecting their carboxyamide groups using chemical tests for amide qualitative analysis.
• In addition, these tests can be used to differentiate between amides and other organic classes, especially those containing carbonyl groups. 
• This is done by using specific reagents.

Sodium hydroxide and Hydrochloric acid Test

• In this test, sodium hydroxide is added to a sample containing an amide compound, where the sodium oxide replaces the amino group leading to the evolution of ammonia gas. 
• Ammonia gas then can be detected using hydrochloric acid as they react together forming white fumes of ammonium chloride as shown in the following chemical reactions.

R – CO – NH2 + NaOH   →  R – COO – Na + NH3 ↑

NH3 + HCl → NH4Cl ↑