Chemistry Lecture Notes: Amines and Diazonium Salts

A comprehensive set of flashcards covering the properties, classification, preparation, and reactions of amines and diazonium salts as described in the provided textbook transcript.

How are amines derived from the ammonia molecule?

By replacing one or more hydrogen atoms of the ammonia molecule with alkyl or aryl group(s).

Which two biologically active compounds containing secondary amino groups are used to increase blood pressure?

Adrenaline and ephedrine.

What is the medical use of the synthetic amino compound Novocain?

It is used as an anaesthetic in dentistry.

What is the hybridization and geometry of the nitrogen atom in amines?

The nitrogen atom is $sp^3$ hybridised and the geometry is pyramidal.

Why is the $C–N–E$ angle in amines (where $E$ is $C$ or $H$) less than $109.5^\text{o}$?

Due to the presence of an unshared pair of electrons.

What is the specifically measured bond angle in trimethylamine?

$$108^\text{o}$$

How are amines classified based on the number of hydrogen atoms replaced in ammonia?

Primary ($1^\text{o}$), secondary ($2^\text{o}$), and tertiary ($3^\text{o}$).

What is the difference between 'simple' and 'mixed' amines?

'Simple' amines have identical alkyl or aryl groups, while 'mixed' amines have different groups.

According to the IUPAC system, how are primary amines named?

They are named as alkanamines, derived by replacing the 'e' of the alkane with 'amine'.

What is the IUPAC name for hexamethylenediamine?

$$Hexane-1,6-diamine$$

What is the simplest example of an arylamine and its accepted IUPAC name?

$C_6H_5NH_2$, commonly known as aniline and IUPAC named as benzenamine.

Why is reduction with iron scrap and hydrochloric acid preferred for making amines from nitro compounds?

Because the $FeCl_2$ formed gets hydrolysed to release hydrochloric acid, requiring only a small amount of $HCl$ to initiate the reaction.

What is the process of cleavage of the $C–X$ bond by an ammonia molecule called?

Ammonolysis.

What is the order of reactivity of halides with amines in ammonolysis?

$$RI > RBr > RCl$$

Which reagent is used for the 'ascent of amine series' by reducing nitriles?

Lithium aluminium hydride ($LiAlH_4$) or catalytic hydrogenation.

What specific class of amines is prepared using the Gabriel phthalimide synthesis?

Primary aliphatic amines.

Why can aromatic primary amines NOT be prepared by the Gabriel phthalimide synthesis?

Because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.

Define the Hoffmann bromamide degradation reaction.

A method for preparing primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide.

How does the carbon count change in the Hoffmann bromamide degradation reaction?

The resulting amine contains one carbon less than the starting amide.

What is the characteristic odour of lower aliphatic amines?

A fishy odour.

Why does the solubility of amines in water decrease with increasing molar mass?

Due to the increase in the size of the hydrophobic alkyl part.

What is the order of boiling points for isomeric amines?

Primary > Secondary > Tertiary.

Why do tertiary amines lack intermolecular association via hydrogen bonding?

Because they lack a hydrogen atom attached to the nitrogen atom.

What is the relationship between the $pKb$ value and the basic strength of an amine?

A smaller $pKb$ value indicates a stronger base.

What is the $pKb$ value of ammonia?

$$4.75$$

Why are aliphatic amines stronger bases than ammonia?

Due to the $+I$ effect of alkyl groups, which leads to high electron density on the nitrogen atom.

What is the order of basicity of amines in the gaseous phase?

Tertiary amine > secondary amine > primary amine > $NH_3$

What is the aqueous basicity order for methyl-substituted amines?

$$(CH_3)_2NH > CH_3NH_2 > (CH_3)_3N > NH_3$$

What is the aqueous basicity order for ethyl-substituted amines?

$$(C_2H_5)_2NH > (C_2H_5)_3N > C2H5NH2 > NH_3$$

Why is aniline a weaker base than ammonia?

The unshared electron pair on nitrogen is in conjugation with the benzene ring, making it less available for protonation.

How do electron-withdrawing groups (like $-NO_2$) affect the basic strength of substituted aniline?

They decrease the basic strength.

What is the product of the reaction between an amine and an acid chloride?

An amide.

What is 'benzoylation' in the context of amine reactions?

The reaction of amines with benzoyl chloride ($C_6H_5COCl$).

What is the Carbylamine reaction used to test for?

Primary amines (both aliphatic and aromatic).

What are the reagents used in the Carbylamine reaction?

Chloroform ($CHCl_3$) and ethanolic potassium hydroxide ($KOH$).

What is the stable temperature range for forming arenediazonium salts?

$$273-278 K$$

What is Hinsberg’s reagent?

Benzenesulphonyl chloride ($C_6H_5SO_2Cl$).

How does a tertiary amine react with Hinsberg’s reagent?

Tertiary amines do not react with benzenesulphonyl chloride.

Why is the sulphonamide formed from a primary amine soluble in alkali?

Because the hydrogen attached to the nitrogen is strongly acidic due to the electron-withdrawing sulphonyl group.

What product is formed when aniline reacts with bromine water at room temperature?

A white precipitate of $2,4,6-tribromoaniline$.

How can the activating effect of the $-NH_2$ group in aniline be controlled during electrophilic substitution?

By protecting the $-NH_2$ group through acetylation with acetic anhydride.

Why does the direct nitration of aniline produce a significant amount of meta-derivative?

In strongly acidic medium, aniline is protonated to the anilinium ion, which is meta-directing.

What is the common name for $p-aminobenzene$ sulphonic acid?

Sulphanilic acid.

Why doesn't aniline undergo Friedel-Crafts reactions?

Because it forms a salt with the Lewis acid catalyst ($AlCl_3$), making the nitrogen positively charged and strongly deactivating.

What is the general formula for diazonium salts?

$$R N_2^+ X^-$$

What is the process of converting primary aromatic amines into diazonium salts called?

Diazotisation.

What happens in the Sandmeyer reaction?

Diazonium group is replaced by $Cl^-$, $Br^-$, or $CN^-$ nucleophiles in the presence of $Cu(I)$ ions.

What reagent is used to replace the diazonium group with an iodine atom?

Potassium iodide ($KI$).

What is the product of a coupling reaction between benzenediazonium chloride and phenol?

$p-hydroxyazobenzene$ (an orange dye).

Which compound is used as an insect attractant?

Trimethylamine.