alkyl halides: (Laboratory method) a) Alkyl bromides (or) iodides on heating with ethanolic solution of potassium nitrite gives nitroethane. CH3CH2 -Br + K ethanol/ SN CH3CH2- NO2 NO Ethyl bromide D + KBr Nitroethane The reaction follows SN2 mechanism. This method is not suitable for preparing nitrobenzene because the bromine directly attached to the benzene ring cannot be cleaved easily. ) Vapour phase nitration of alkanes: (Industrial method) Gaseous mixture of methane and nitric acid passed through a red hot metal tube to give nitromethane.
nitro methane Methane K CH + H CH - +H O Red hot Si tube (g NO NO2 (g ) Except methane, other alkanes (upto n – hexane) give a mixture of nitroalkanes due to C-C cleavage. The individual nitro alkanes can be separated by fractional distillation. CH3-CH3 Ethane +H K CH3CH2- Nitroethane( %) CH3N NO3 NO2 O2 Nitromethane ( %) ) From a- halocarboxylic acid α - choloroacetic acid when boiled with aqueous solution of sodium nitrite gives nitromethane. Cl - CH2-COOH - chloro acetic acid +Na H2O/Heat SN NO2 α CH3- Nitromethane +CO2+NaCl NO2 XII U13-Organic Nitrogen XII U13-Organic Nitrogen - - - - Evaluate yourself ) Find out the product of the following reactions.
i) CH CH(Cl)COOH i) NaNO ii) H O/ ?[X] D ii) CH CH -Br+NaNO alcohol / [Y] D ) Oxidation of tert – alkyl amines tert – butyl amine is oxidised with aqueous KMnO to give tert – nitro alkanes. NH [O] NO + H O KMnO tert-butylamine - methyl - - nitro propane ) Oxidation of Oximes Oxidation of acetaldoxime and acetoneoxime with trifluoroperoxy acetic acid gives nitroethane ( ) and – nitropropane ( ) respectively. Nitroethane Acetaldoxime CF COOOH CH -CH=N-OH CH CH -NO [O] . .
Preparation of Nitroarenes ) By Direct nitration When benzene is heated at 330K with a nitrating mixture (Con.HNO + Con.H SO ) , electrophilic substitution takes place to form nitro benzene. (Oil of