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Question

(a) Distinguish between primary, secondary and tertiary amines.
(b) Explain the structure of fructose.

Solution
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Primary
amine
Secondary
amine
Tertiary
amine

1. With nitrous acid it forms
primary alcohol
With nitrous acid,it forms
yellow oily N-nitroso amine.
With nitrous acid
it forms salt.

2. With chloroform and KOH it forms carbylamineNo reaction with CHCl3 and KOHNo reaction with CHCl3 and KOH

3. With CS2 and HgCl it forms alkyl isothiocyanate (mustard oil)No reaction with CS2 and HgCl2No reaction with CS2 and HgCl2

4. With diethyl oxalate, it forms solid dialkyl oxamide at room temperatureWith diethyl oxalate, it forms liquid N,N dialkyl oxamic esterNo reaction with diethyl oxalate

5. With acetyl chloride it forms N-alkyl acetamide.With acetyl chloride it forms N,N-dialkyl acetamideNo reaction

6. With three molar proportion of alkyl halide, quaternary ammonium salt-a crystalline compound is formed
With two molar proprtion of alkyl halide, quaternary ammonium salt is formedWith only one molar proportion of alkyl halide quaternary ammonium salt is formed.
(b) Structure elucidation of fructose:
(i) Elemental analysis and molecular weight determination show that the molecular formula of fructose is C6H12O6.
(ii) Complete reduction of fructose with concentrated hydroiodic acid in the presence of red phosphorus gives n-hexane as the major product. This indicates that six carbon atoms in the fructose molecule form a consecutive unbranched chain.
FructoseHI/P−−−−−ReductionCH3CH2CH2CH2CH2CH3nhexane
(iii) It dissolves in water to give a neutral solution. This indicates that the fructose molecule does not contain a carboxyl group.
(iv) It reacts with acetic anhydride in the presence of pyridine to form a penta acetate. This reaction indicates the presence of five hydroxyl groups in a fructose molecule.
(v) It reacts with hydroxylamine to form a monooxime or adds only one mole of HCN to give a cyanohydrin. This reaction indicates the presence of either an aldehyde
(vi) It is not oxidised by bromine water indicating the absence of aldehyde group.
(vii) Oxidation of fructose with concentrated nitric tartaric acid. Since this oxidation occurs with the rupture of the carbon chain, the carbonyl group must be present as ketone group.
(viii) When it treated with HCN, it forms an addition product which upon hydrolysis and subsequent reduction with HI and Red P gives 2-methyl hexanoic acid. This indicates that the ketone group is adjacent to one of the terminal carbon atoms.
(ix) From the above evidences we conclude that fructose is a pentahydroxy hexanone (a ketohexose) and can be represented by the given structure.

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