MODULE – IV

 

Contents:

1. Aromatic Chemistry

 

2. Carbonyl Compounds 

 

3. Carboxylic Acids and Derivatives 

 

4. Amines 

 

5. Preparation and Properties of some Important Inorganic Compounds 

 

 

 

 

P L A N N I N G

1. In aromatic chemistry we are going to take up some important reactions like halogenation, oxidation of alkylbenzene, nitrocompounds  and aromatic amines.

 

2. Here we shall mainly focus on different methods of preparation of carboxyls and their reactions with special emphasis to condensation (Aldol, Claisen), oxidation  and reduction (Cannizzaro) and other reduction (MPV, LAH) and oxidation reactions (Bayer Villiger oxidation) we shall also focus on the point of difference of aldehydes and ketones (in terms of reaction.) 

 

3. In carboxylic acid our focus should be on methods of preparation of acid , the relative order of reactivity of derivatives with special emphasis in esters.

 

4. In amines our point focus is on the sythesis and reaction of amines (1°,2° and 3°) 

 

5. In this chapter we have mainly given emphasis to preparation and properties of certain important inorganic compounds 

 

AROMATIC CHEMISTRY

 

Aromatic Compounds 

Alkylbenzene (Toluene) ⎯⎯→ Halogenation

 

Halogenation  of toluene can be carried out in 2 ways 

(i) side chain chlorination when the hydrogen of the side chain are replaced by chlorine 

(ii) Nucleus chlorination where the hydrogens of the ring are replaced giving o & p products 

The products of nucleus chlorination are resistant towards hydrolysis while the side chain products can be hydrolysed.

Side chain or benzylic halogenation taken place when the reaction is carried out in absence of Lewis acid and under conditions that favour formation of radical.

 

The greater stability of bezylic radicals accounts for the fact that when ethylbenzene  is halogenated the major product is 1-halo-1-phenylethane.

Addition to double bond of Alkenyl benzenes 

In absence of peroxides  HBr adds to the double bond of 1-Phenyl propene to give 2- bromo 1 phenylpropane as the major product .

Strong oxidising agents oxidises toluene to benzoic acid eg. hot Alk. KMnO4. Alkyl benzenes with alkyl groups longer than methyl are ultimately degraded to benzoic acids.

 

Nitro compounds: Nitrobenzene can be reduced in different media to give different products.

   

In dilute acid solution phenyl hydroxylamine rearranges to p – aminophenol.

 

Aniline  

In aniline direct nitration cannot be carried out as NH2 being an activating group activates the ring ; so that any oxidising atmosphere will result in the charring of ring.

 

Illustration 1 : Aniline ⎯⎯→ O – Bromo Aniline 

 

Solution:

Mono and dialkylanilines ( and quaternary compounds) as their hydrochlorides undergo rearrangement on strong heating an alkyl group migrating from nitrogen atom and entering preferentially the p – position.

ALDEHYDE AND KETONES 

Carbonyl compounds include both aldehydes and ketones having the formula where R and R′ may be different or same 

 

Methods of Preparation

 

1. oxidation

(a) A primary alcohol an oxidation gives an aldehyde and this on further oxidation gives an acid. Both aldehyde and acid contains the same number of carbon atoms as the original alcohol.

RCH2OH RCHO ⎯⎯→ RCOOH 

It is better to use pyridinium chlorochromate (PCC) which does not oxidise the aldehyde further.

Secondary alcohols on oxidation gives ketones 

R2CHOH  R2C = O 

Ketone 

 

There is however specific reagent for oxidising secondary alcohols to ketones by using aluminum t – butoxide [(CH3)3CO]3Al in acetone medium t – butyl alkoxide is used since t – butyl alcohol produced is not further oxidised under these condition.

 

By pyrolysis of Ca, Ba salts of fattyacids 

Formic acid salts will always produce aldehydes.

The reaction first leads to the formation of β – keto acids which then eliminate CO2 to give the desired ketone. 

 

 

Intramolecular chelation by hydrogen bonding through a 6 membered cyclic TS.

Rosenmund Reaction  (From Acyl chloride) 

RCHO

quinoline

 

Aldehydes are more easily reduced than acid chlorides and therefore we should expect to obtain the alcohol as the final product. It is BaSO4 that by acting as a poison to the palladium catalyst in this reaction prevents reduction of aldehydes further 

 

Stephen’s Reduction:

RC ≡ N

↓ H2O 

RCHO

 

From Alkynes 

R – C ≡ C – H + H2O

↓ 

     

From 1,2  diols 

Pb(OH)4

 

 

illustration-1 : One mole of each of the following is treated with HIO4. What product will be formed and how many moles HIO4 will  be consumed.

(a) CH3CHOHCH2OH

(b)

(c) cis – 1,2 cyclopentandiol 

 

Solution: (a)  CH3CHO and HCHO 1 mole HIO4 

(b) HCHO and OHC CH2OCH3 1 mole  HIO4

(c) 1 mole HIO4

 

Reactions:

As far reactivity is  concerned ketones are less reactive than aldehydes because of (I) less electrophilicity of the carboxyl carbon and (ii) steric effect of R groups 

 

1. Addition of HCN 

⎯⎯→ α – hydroxy acid 

 

2. Addition of NH2 – Z types of substances 

The reaction is acid catalysed and fully reversible