Amines

what is an amine

structure of amine

what is a simple amine and mixed amine

Nomenclature of common names of amines

Nomenclature of IUPAC of amines

IUPAC name of the structure

ethane-1,2-diamine

note: when more that 1 amine grp is present- you have the e in ethane

structure of aniline

this is the simplest aryl amine

Preparation of amines

prep of amines by reduction of Nitro compounds

2 ways

why is TIN+HCl preferred to make amines?

• cus they give a product FeCl₂ which hydolyses and gives HCl back again which can again take part in the reaction and supports forward reaction

• giving HCl in beginning is sufficient as it gets made over and over again in the reaction

prep of amines by Ammonolysis of alkyl halides

Disadvantage:

• you get a mixture of 1^o,2^o,3^o amines

• so if you want just primary amine then you can take excess of ammonia

the X in R—X can be chloride, bromide or iodide

their reactivity is as follows:

• RI>RBr>RCl

Amines prep from Nitrile(CN) reduction

(Ascent of amines)

prep of amines from reduction of Amide

Prep of amines by Gabriel Phthalimide synthesis

note:

• only 1^o amines can be formed

• aryl amines cannot be prepared as the aromatic halide has resonance and partial double bond chr because of which the bond wont break easily

Prep of amines by Hoffmann Bromomide Degradation

• the no of C in amine is one less than that it amide

• only primary amines can be made

Physical properties of Amines

1 or 2 carbon amines- gasses

more than 3 - liquids

many more carbons- solid

aromatic amine- are colorless generally but when stored they look colord because of atmospheric oxidation

Sollubility of amines

(alkyl grps are hydrophobic)

BP

Amines form intermolecular hydrogen bonding, therefore boiling point is high

• BP of alcohols more than amines

• BP directly propotional to molecular mass

Odour of amines

lower aliphatic amines are gasses with fishy odour

higher amines dont have strong odour

character of amines

• basic

• behave as nucleophiles due to unshared pair of electron

• tertiary amine- most basic as it has 3 alky groups(alkyl groups are electron donating shows casic chr) holds true only in gseous state

• in acqueous state solvation energy matters (solute and solvent interactions )(solvation energy ensures that the solute in solution is stabilised)

• in acqueous amine 2^o amine is most basic

• in methyl substituted acqueous amine—> most basic 2^o,1^o,3^o

• in ethyl substituted acqueous amine—>most basic 2^o, 3^o,1^o

Basic character comparison between alkanamine and ammonia

ammonia< alkanamine

• alkanamine has alkyl grp which donates more electron to N

• upon adding H⁺ ammonium ion formed from alkanamine is more stable than ammoniam ion

Basic character comparison between arylamine and ammonia

In Ammonia the lone pair is easily available for donation whereas in aniline lone pair of electrons are involved in resonance therefore aryl amines are less basic than Ammonia

aniline less basic than ammonia

• aniline when acceps H⁺ becomes annilinium ion which is less stable than aniline

• becuz aniline has more resonance stabilization( has 5 reonating structures, but annillinium has got 2) therefore it would not want to become a less stable structure by gaining H+ (gaining H+ shows basic chr)

• but ammonia on the other hand will gain H+ (showing basic chr)

• when electron releasing grps are added to aniline - basic chr increases

• when electron withdrawing grps are added - become less basic

chemical reactions of amines

• Reaction with strong acids

• Reaction with aldehyde

• Reaction with nitrous acid

• Alkylation

• Acylation

• Oxidation

• Electrophilic substitution

Reaction with strong acids

• when reacted with acids they form salts

• and when these salts are reacted with a strong base you get the amine back

Alkylation

when you keep adding R—X you get primary, sec, tertiary amines followed by a diazonium salt

Acylation (RCO)

Compounds with acyl group:

• Acid chlorids

• Acid anhydricdes

• esters

primary and secondary show this reaction. tertiary does not because it does not have any H in N to be substituted

Benzoylation

Carbylamine reaction

aka isocyanide test

Reaction of 1^o amines with Nitrous acid (HNO₂)

gives diazonium salt (N₂⁺Cl) —> unstable (but benzenediazonium salts are stable)

HNO₂—>NaNO₂+ HCl

Reaction of 2^o , 3^o amines with Nitrous acid (HNO₂)

Aromatic amines reaction with nitrous acid

they also make diazonium salts (they are stable)

Reaction of 1^o amines with Aryl Suphonyl Chloride

soluble in alkali

Reaction of 2^o amines with Aryl Suphonyl Chloride

insoluble in alkali

Reaction of 3^o amines with Aryl Suphonyl Chloride

reaction does not happen

use of Hinsberg reagent

Position in which electrophillic substituition takes place

Electrophillic substituition- Bromination

Electrophillic substituition- Suphonation (SO₃H)

Electrophillic substituition- Nitration (NO₂)

Diazonium salts

Nomenclature of Diazonium salts

Diazonium salts stability

• Primary aliphatic amines form highly unstable alkyldiazonium salts

• Primary aromatic amines form arenediazonium salts which are stable for a short time in solution at low temperatures (273–278 K) due to resonance

• arenediazonium salts made from aromatic amine(aniline )

preparation of diazonium salt

The conversion of primary aromatic amines into diazonium salts is known as diazotisation

cannot be stored for long hence used

Physical properties of benzene diazonium salts

• exception for solubility in water - Benzenediazonium fluoroborate

Chemical reaction of diazonium salts

mainly:

reactions involving displacement of nitrogen

Reactions involving retention of diazo group coupling reactions

what can N be replaced in chemical reactions of diazonium salts

• N₂⁺ is a LEAVING GROUP (leaves in gaseous form)

Diazonium Salts: Replacement by halide or cyanide

SANDMEYER REACTION (Cl^-,Br^-, CN^-)

Reaction always takes place in presence of Cu ion

GATTERMAN REACTION:

Copper powder and halogen acid

same product in both

SANDMEYERS RXN has better yeild than GATTERMANN

seperate raction for replacemnet with Iodide

Diazonium Salts: Replacement by Iodide

Diazonium Salts: Replacement by Fluoride

Diazonium Salts: Replacement by H

2 methods:

• with alcohol

• hypophosphourous acid (phosphinic acid)

Diazonium Salts: Replacement by Hydroxy grp (OH)

Diazonium Salts: Retention of Diazo group

we get colored products so used as dyes

Retention of Diazo group

orange dye

Retention of Diazo group

yellow dye

Diazonium saltts importance