Unit 5- Topic 19

Nitrogen containing compounds where the nitrogen is has 3 bonds to one or more alkyl groups. There are primary, secondary and tertiary amine. CH3NH2 (1), CH3NHCH3 (2), CH3N(CH3)CH3 (3)

From nucleophilic substitution of halogenoalkanes or reduction by hydrogenation of nitriles

Heating a halogenoalkane with ammonia, (under pressure and in a sealed container since ammonia is a gas) or with concentrated aqueous ammonia. It creates a primary amine and hydrogen chloride. This reaction is done by the nucleophilic attack of the lone pair of electrons to the C of halogeno… Amine creates also has lone pair which exults in the reaction going further (previous halogeno + product) to produce a secondary amine and HCl.

Excess used to prevent unwanted side-reaction (a further reaction between halogeno and primary amine). In excess so that it out-numbers the molecules of the primary amine formed. However the excess ammonia may react with the acidic hydrogen chloride formed so: CH3Cl + 2NH3 -> CH3NH2 + NH4Cl. the products can be separated from the reactants by fractional distillation which will also prevent unwanted reactions.

Nitriles (RCN) (are reduced) + LiAlH4 in dry ether -> primary aliphatic amines Eg: CH3CN + 4[H+] -> CH3CH2NH2

C6H5NO2+ 6[H+] -> C6H5NH2 +. H2O Nitrobenzene (is reduced) Reagent: Tin mixed with concentrated hydrochloric acid Conditions: heated under reflux

the phenylamine produced will react with the acid needed for the preparation to occur to form phenylammonium: that by adding sodium hydroxide is easily converted into a phenylamine

Manufacture of polymers and pharmaceuticals.

aliphatic amines + water -> produces a hydroxide ion and a aliphatic amine with a positive charge. the hydroxide ions makes the solution alkaline.

aliphatic amines are completely miscible. As size of molecule increases, solubility decreases. they dissolve in water due to hydrogen bonding with water molecules. phenylamine is only slightly soluble therefore only slighlty alkaline when reacting with water

methylamine ammonia water phenylamine

because the methyl group is electron-releasing, and so has an increased electron density on nitrogen compared with ammonia.

because the lone-pair of electrons on nitrogen is incorporated into the delocalised electrons in the benzene ring, making nitrogen less electron-rich therefore the lone pair of electrons less available for donating to the hydrogen of a water molecule.

all react with strong acids to form ionic salts C6H5NH2 + HCl -> C6H5NH3+Cl- phenylamine+ HCl -> phenylammonium chloride

mechanism: addition- elimination products: amide (RCONH2) or N-substituted amide (RCONHR’) and hydrogen chloride normally, phenylamine: amide. butylamine: N- substituted amide

halogenoalkanes contain an electron-deficient carbon atom and amines contain an electron-rich nitrogen atom. it is a substitution reaction. however since the product also conatins a electron-rich nitrogen, it can further react to form a tertiary and quaternary ammonium salt. RNH2 + R’X -> RNHR’ + HX -> product a secondary amine. R= alkyl in amine and R’= alkyl group in halogenoalkane

HCl is not formed since tertiary amines do not have a hydrogen bonded to the nitrogen atom. therefore there is only one product which causes the nitrogen to become positive and chloride negative eg: CH3CH2CH2CH2N+(CH2CH3)3Cl-

copper ions react with water to form a copper aqua ion: [Cu(H2O)6]2+ the amine then accepts protons to give a pale blue precipitate and ammonium salt. so: [Cu(H2O)6]2+ +2CH3CH2CH2CH2NH2 -> [Cu(H2O)4(OH)2] + 2CH3CH2CH2CH2NH3+ it can further react to give a deep blue solution so: [Cu(H2O)4(OH)2] + 4CH3CH2CH2CH2NH2 -> [Cu(CH3CH2CH2CH2NH2)4(H2O)2]2+ +2H2O + 2OH-

overall reaction of phenylamine with copper solution: [Cu(H2O)6]2+ + 4C6H5NH2 -> [Cu(C6H5NH2)4(H2O)2]2+ + 4H2O

because it is a very unstable compound. it exists only in a very aqueous solution and decomposes at room temperature.

due to the acid decomposing at room temperature, any reactions involving nitrous acid have to be carried out in under very carefully controlled conditions. Can be prepared by: mixing ice-cold solutions of sodium nitrite and dilute hydrochloric acid. NaNO2(aq) + HCl(aq) -> NaCl(aq) + HNO2(aq)

by adding an aromatic amine (phenylamine) to the reaction mixture to create nitrous acid in situ giving this chemical formula: (phenylamine) + HNO2(aq) + HCl (aq) -> (benzenediazonium ion) + Cl- + 2H2O (l) conditions: reaction vessel must be ice-cold or 5ºC or below since if the temperature rises phenol is formed. (forming with it N2 gas and water)

diazonium ions act as strong electrophiles. they react with alikaline solutions of phenol to produce (after acidificaton with dilute HCl), a (4-hydroxyphenyl)azobenzene. Reaction: coupling Formed: coumpound formed creates a energetically stable, yellow azo dye System of product: conjugated system

the stability comes from extensive delocalisation of electrons ia the nitrogen-to-nitrogen double bond.