TLDR;
Alright, folks! This video is a crash course on amines, covering everything from their preparation to their properties, with a special focus on aniline and diazonium compounds. It's like a cheat sheet for your Class 12 exams, NEET, and JEE Mains.
- Methods of preparation and properties of amines
- Preparation and properties of aniline
- Diazonium compounds
Introduction to Amines [0:00]
The video starts with a quick intro to amines, contrasting them with other organic functional groups like alcohols, phenols, and ketones. The instructor emphasizes that amines are vital, pointing to the word "vitamine" (vital + amine) as an example. The lecture will cover methods to prepare amines, properties of amines and modifications of aniline, specifically diazonium compounds.
Preparation of Amines from Nitro Compounds and Alkyl Azides [2:08]
The first method discussed is reducing nitro compounds (RNO2) to amines (RNH2). This involves adding nascent hydrogen, which can be achieved by reacting a metal (like tin or zinc) with an acid (like HCl). The video also explains the degree of amines: primary (one carbon attached to NH2), secondary (two carbons), and tertiary (three carbons), all of which act as nitrogenous bases due to the lone pair of electrons on the nitrogen atom. Then, alkyl azides (RN3) can also be reduced to primary amines using reagents like metal-hydrogen based catalysts or lithium aluminum hydride, followed by the addition of H+ or water.
Reduction of Cyanides and Isocyanides [7:52]
Next up is the reduction of cyanides (RCN) to primary amines. The process involves adding hydride (from lithium aluminum hydride or sodium borohydride) to the carbon, followed by water or mild acid. The presenter asks the audience to comment on the source of two hydrogen atoms in the final product. Cyanides can also be reduced using sodium and ethanol (Mendius reaction), which generates nascent hydrogen for the reduction. Isocyanides can be reduced to secondary amines using lithium aluminum hydride.
Preparation of Amines from Aldehydes and Ketones [14:48]
Aldehydes and ketones can be reacted with amine derivatives to form carbon-nitrogen double bonds, also known as Schiff bases, imines, or aldimines. These compounds are water-sensitive. Hydroxyamine reacts with carbonyl compounds to form oximes, which can be reduced to primary amines using zinc and HCl. The video also explains how to synthesize different degrees of amines (primary, secondary, tertiary) using ketones as starting materials and reacting them with different amine derivatives. The instructor shares a cautionary note that prolonged use of nitrogenous bases can be bad for men.
Gabriel Synthesis and Hofmann Bromide Degradation [24:20]
The video then covers two important reactions: the Gabriel synthesis and the Hofmann bromide degradation. Gabriel synthesis is an excellent method for preparing primary amines from phthalimide. Hofmann bromide degradation involves treating an amide with X2 and NaOH (or NaOX) to degrade the amide and yield a primary amine. The carbonyl group is lost in this process, turning into sodium carbonate.
Reactions with Acyl Chlorides and Exhaustive Alkylation [30:25]
Primary amines can react with acyl chlorides via SN2 attack to form secondary amides. These amides can then be reduced using lithium aluminum hydride to obtain amines. The video also explains how to prepare tertiary amines through a similar process. The concept of Hofmann exhaustive alkylation is introduced, where a nitrogen atom is completely exhausted by reacting it with alkyl halides to form a quaternary ammonium salt.
Reactions and Tests for Amines [42:48]
The lecture moves on to discuss various reactions and tests for amines. Primary amines can react with chloroform in the presence of KOH (carbylamine test) to produce isocyanides, which have a very bad smell. This test is specific to primary amines. Amines can also undergo oxidation to form aldimines or ketimines, depending on the starting material. Secondary amines can be oxidized to form tetra-alkyl hydrazines. The video also touches upon the Caro's acid reaction, where secondary amines react with H2SO5 to form dialkyl hydroxylamines.
Hinsberg's Test and Reactions with Nitrous Acid [51:47]
Hinsberg's test is discussed as a method to distinguish between primary, secondary, and tertiary amines. Primary amines react with Hinsberg reagent (phenylsulfonyl chloride) to form a product soluble in NaOH, secondary amines form a product insoluble in NaOH, and tertiary amines do not react. Amines can also react with nitrous acid (HNO2) to form diazonium salts. The video also covers the Hofmann mustard oil reaction, which is specific to primary amines and produces a mustard oil-type smell.
Preparation of Aniline [59:04]
The lecture transitions to aniline, explaining how it can be prepared by reducing nitrobenzene using various methods like metal with HCl, lithium aluminum hydride, or catalytic hydrogenation. Other methods include reacting chlorobenzene with ammonia under harsh conditions, or through Hofmann bromide degradation.
Reactions of Aniline [1:05:52]
Aniline, being a base, reacts with acids to form salts. It also undergoes reactions with methyl iodide (Hofmann exhaustive alkylation) and acyl chlorides to form amides. The video explains the concept of protecting the amino group in aniline by reacting it with acetyl chloride, which reduces the electron-donating ability of the nitrogen and allows for selective nitration.
Diazonium Salts and Azo Dyes [1:16:27]
Diazonium salts can be treated with copper salts (Sandmeyer reaction) to prepare haloarenes. They can also react with phenol to form azo dyes, which are colorful compounds due to extended conjugation. The video concludes by discussing various reactions of diazonium salts, including their conversion to benzene using H3PO2.