Primary amines can be prepared by the reaction of halogenoalkanes with ammonia or by the reduction of nitriles.
Justify the statement that it is better to prepare primary amines from nitriles rather than from halogenoalkanes
With halogenoalkane:
further reaction
With nitriles
No further reaction
Draw the structure of a primary amine with four carbon atoms that cannot be formed from a nitrile.
(CH3)3CNH2
A student dissolves a few drops of propylamine in 1 cm3 of water in a test tube.
Give an equation for the reaction that occurs.
Describe what is observed when Universal Indicator is added to this solution.
CH3CH2CH2NH2 + H2O ⇌ CH3CH2CH2NH3+ + OH
turns blue
Phenylamine can be prepared by a process involving the reduction of nitrobenzene using tin and an excess of hydrochloric acid.
Give an equation for the reduction of nitrobenzene to form phenylamine. Use [H] to represent the reducing agent.
Explain why an aqueous solution is obtained in this reduction even though phenylamine is insoluble in water.
C6H5NO2 + 6[H] → C6H5NH2 + 2H2O
C6H5NH2 present as ionic salt
Name the compound (CH3)2NH
dimethylamine
(CH3)2NH can be formed by the reaction of an excess of CH3NH2 with CH3Br. Name and outline a mechanism for this reaction.
nucleophilic substitution
Name the type of compound produced when a large excess of CH3Br reacts with CH3NH2 Give a use for this type of compound.
quaternary ammonium salt
detergent
Haloalkanes such as CH3Cl are used in organic synthesis.
Outline a three-step synthesis of CH3CH2NH2 starting from methane. Your first step should involve the formation of CH3Cl
In your answer, identify the product of the second step and give the reagents and conditions for each step.
ethanonitrile
step 1: Cl2 UV light
step2 :KCN aq and alcoholic
step 3: LiAlH4
Amines E, F and G are weak bases.
Explain the difference in base strength of the three amines and give the order of increasing base strength.
Strength depends on availability of lone pair on N
E - N (next to ring): (lp) delocalised into ring
F or G: N (next to alkyl): electrons pushed to
(lp) more available (to donate to a H+)
E<G<F
Use Table 1 on the Data Sheet to explain how you could use infrared spectra in the range outside the fingerprint region to distinguish between the secondary amine and the tertiary amine
Absorption at 3300−3500 (cm−1) in spectrum
N–H (bond) (only) present in secondary amine
Compound K (C6H5CH2NH2) is a structural isomer of J.
Explain why J is a weaker base than K.
electron pair on N
in J less available
N.m.r. spectra are recorded using samples in solution. The 1H n.m.r. spectrum was recorded using a solution of atenolol in CDCl3
Suggest why CDCl3 and not CHCl3 was used as the solvent.
Solvent must be proton-free
Suggest why CDCl3 is a more effective solvent than CCl4 for polar molecules such as atenolol
CDCl3 is polar
Suggest a reducing agent that could reduce a ketone to form atenolol
NaBH4
Suggest how you could show that the atenolol produced by reduction of a ketone was a racemate and not a single enantiomer.
(plane) polarised light
Suggest one advantage and one disadvantage of using a racemate rather than a single enantiomer in medicines.
cheaper medicine due to cost
only half the product works
Lidocaine is used medically as the salt lidocaine hydrochloride.
Suggest which one of the nitrogen atoms labelled a or b is protonated in lidocaine hydrochloride. Explain your answer.
lp on N
alkyl groups donate electron density
(lp on Nb) more available or protonated amine stabilised or better lp donor/H+ acceptor
suggest why lidocaine hydrochloride is used medically in preference to lidocaine.
Explain your answer.
salt is ionic
The medicine is usually supplied as a salt. The salt is formed when one mole of imipramine reacts with one mole of hydrochloric acid.
Suggest why the nitrogen atom labelled b is more likely to be protonated than the nitrogen atom labelled a when the salt is formed.
Lone pair on N labelled b more available
electrons delocalized into ring
alkyl groups push electrons
