Question

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

Answer 1

	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 carbylamine	No reaction with $CH{Cl}_3$ and $KOH$	No reaction with $CH{Cl}_3$ and $KOH$
	3. With ${CS}_2$ and $HgCl$ it forms alkyl isothiocyanate (mustard oil)	No reaction with ${CS}_2$ and $Hg{Cl}_2$	No reaction with ${CS}_2$ and $Hg{Cl}_2$
	4. With diethyl oxalate, it forms solid dialkyl oxamide at room temperature	With diethyl oxalate, it forms liquid N,N dialkyl oxamic ester	No reaction with diethyl oxalate
	5. With acetyl chloride it forms N-alkyl acetamide.	With acetyl chloride it forms N,N-dialkyl acetamide	No 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 formed	With 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 $C_6{H}_{12}{O}_6$.
(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.
$Fructose\underset{Reduction}{\overset{HI/P}{\to }}\underset{n-hexane}{{CH}_3-{CH}_2-{CH}_2-{CH}_2-{CH}_2-{CH}_3}$
(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.