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Nitro Compounds DR. TANUJA NAUTIYAL DEPT OF CHEMISTRY NORTHERN INDIA ENGINEERING COLLEGE

Nitro compounds

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Page 1: Nitro compounds

Nitro Compounds

DR. TANUJA NAUTIYALDEPT OF CHEMISTRY

NORTHERN INDIA ENGINEERING COLLEGE

Page 2: Nitro compounds

• Organic compounds containing nitrogen can be broadly classified into two groups.

• Compounds containing nitro functional group -NO2

• Compounds containing amine functional group -NH2 and their derivatives.

• In this nitro compounds are primary source of organic compounds with functional group -NO2 to start the synthesis of many other important compounds

Nitro Compound

Page 3: Nitro compounds

• The NO2 group attached with organic chain is called as nitro functional group.

• All the compounds containing the nitro functional group are called as organic nitro compounds.

They are classified as

• Aliphatic nitro compounds

• Aromatic nitro compounds

Nitro Compound

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Aliphatic Nitro Compounds

• If the nitro functional group is attached withaliphatic carbon chain it is called as aliphatic nitrocompound.

• They are weakly acidic due to their azinitro formand they are soluble in alkalies and can undergocondensation reaction with aldehydes.

CH3-NO2 - Nitro methane.

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Aromatic Nitro Compounds

• If the nitro functional group is attached with benzene ring it is called as aromatic nitro compound.

• All aromatic nitro compounds are yellow colored liquids which may change to dark brown color due to oxidation.

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• The NO2 group is called as nitro group.

• It is electron withdrawing group due to its -Inductive effect as well as -Resonance effect.

Nitro Compound

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Nomenclature of Nitro Compounds

• Organic compounds containing nitro -NO2 functional group are called as nitro compounds.

• They are obtained by replacing one or more hydrogen in the hydrocarbon with nitro group. Here, the nitrogen is directly attached to the carbon atom in the organic chain.

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Nomenclature of Nitro Compounds

• The general formula of nitro compounds is

• Nitro compounds are named by prefixing thenitro with the root alkane name with thelocant.

• CH3NO2 is amino methane

• CH3-CH(NO2)-CH3 is 2-nitropropane

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General method of preparation

1. Nitration of alkanes

2. From alkyl halides

3. From salts of α-halogeno carboxylic acid

4. From primary amines

5. From a-nitroalkenes

6. From oximes

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By direct nitration of alkanes

Alkanes are treated with nitrating mixture(fuming nitric acid) with concentrated sulfuricacid to give nitro compounds. This method willnot give good yield in case of aliphatic nitrocompounds, but will give best yield for aromaticnitro compounds like nitro benzene.

Ethane on nitration gives nitro ethane.

CH3-CH3 + HNO3/H2SO4 → CH3-CH2-NO2

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From alkyl halides

• By treating iodoalkanes with silver nitrite

• Iodo alkanes on reacting with silver nitrite give nitro compounds. This method will not give good yield for nitro benzene. But all the aliphatic nitro compounds can be prepared by this method.

For example iodoethane on treating with silver nitrite gives nitroethane.

CH3-CH2-I + AgNO2 → CH3-CH2-NO2 + AgI

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By treating amines with alkaline KMnO4

• Tertiary amines on treating with alkaline KMnO4 gives tertiary nitro compounds. This method works only with tertiary amines.

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Physical Properties of Nitro Compounds

• Aliphatic nitro compounds are mostly gaseousin nature and higher members are liquids.

• Aromatic nitro compounds are yellow colorliquids which intensified to brown color bytime.

• They are polar due to the presence of nitrogroup.

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Isomerism in Nitro Compounds

• The isomerism exhibited by organic nitro compounds can be classified into the following types.

1. Chain isomerism

•Compounds having same molecular formula and difference in the nature of carbon chain is called as chain isomers. For example 1-nitro butane and 2-methyl 1-nitro propane.

CH3-CH2-CH2-CH2-NO2 CH3-CH(CH3)-CH2-NO2

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• 2. Position isomerism

• Compounds having same molecular formula and difference in the position of attachment of functional group is called as position isomers. For example 1-nitro propane and 2-nitro propane.

• CH3-CH2-CH2-NO2

• CH3-CH(NO2)-CH3

Isomerism in Nitro Compounds

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• 3. Functional group isomers

• Nitro compounds are functional group isomers for nitrite compounds in which the oxygen is bonded with the carbon chain. The following diagram explains the difference between nitro methane and methyl nitrite.

Isomerism in Nitro Compounds

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• 4. Tautamerism

• In solution the nitro form is in equilibrium with azinitro form. The azinitro form is acidic in nature and hence nitro methane is soluble in alkalis.

Isomerism in Nitro Compounds

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Nitro compounds undergo tautomerism in

solution to azinitro form, which is acidic in

nature.

Hence, all the nitro compounds are weakly

acidic in nature.

Chemical Properties of Nitro Compounds

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• They dissolve in bases to give salts and can be regenerated by adding a stronger acid like HCl.

• Similarly they can be reduced to aminocompounds in acidic or basic medium.

Chemical Properties of Nitro Compounds

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Reaction of nitroalkane

1. Reduction

2. Hydrolysis

3. Halogenation

4. Reaction with nitrous acid

5. Condensation with aldehydes and ketones

Chemical Properties of Nitro Compounds

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1. Reduction of aliphatic nitro compounds

Aliphatic nitro compounds can be reduced to amines by treating with Sn/HCl. This is the effect way to convert nitro compounds to amines.

CH3NO2 →→ CH3NH2

Chemical Properties of Nitro Compounds

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Aliphatic nitro compound can be reduced to hydroxyl amines by treating with diborane.

CH3NO2 →→ CH3NHOH

Aliphatic nitro compounds are reduced to oximesusing stannous chloride.

CH3NO2 →→ CH3-N = OH

Chemical Properties of Nitro Compounds

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Reduction of aromatic nitro compounds

• Nitro benzene can be reduced to aniline by Sn/HCl.

On treating with Raney Nickle, nitro benzene is reduced to phenyl hydroxylamine.

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Uses of nitro compounds

• They are useful intermediates in the preparation of amino compounds and diazonium salts which are synthetic important materials to prepare almost all organic compounds.

• Nitro benzene is used in shoe and floor polishes.• It is also used in paint and solvents and to mask

unpleasant odor in chemicals.• They are used to prepare the azo-dyes and in soil

sterility.• It is used in the manufacture of Paracetamol (a

popular analgesic)

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THANK YOU

DR. TANUJA NAUTIYALDEPT OF CHEMISTRY

NORTHERN INDIA ENGINEERING COLLEGE