Q.(a) Distinguish between primary, secondary and tertiary amines.

(a) 1°, 2° and 3° amines are distinguished mainly by Hinsberg's test (based on the acidity/solubility of the benzenesulfonamide formed) and the carbylamine test (positive only for 1° amines). (b) Polysaccharides are polymeric carbohydrates of repeating monosaccharide units joined by glycosidic linkages; starch and glycogen are storage polysaccharides while cellulose is structural.

(a) Distinguishing primary, secondary and tertiary amines

1. Hinsberg's test (using benzenesulfonyl chloride, $C_6H_5SO_2Cl$, "Hinsberg's reagent", with aqueous KOH):

• Primary amine ($1^{\circ}$, $RNH_2$): reacts to form an N-alkylbenzenesulfonamide, $C_6H_5SO_2NHR$. The remaining N–H hydrogen is rendered acidic by the strongly electron-withdrawing $-SO_2-$ group, so this product dissolves in excess KOH (forming the soluble potassium salt $C_6H_5SO_2NR\,K^+$). Acidifying this alkaline solution (e.g. with dilute HCl) reprecipitates the free sulfonamide.

$RNH_2 + C_6H_5SO_2Cl \xrightarrow{KOH} C_6H_5SO_2NHR \; (\text{soluble in excess KOH})$

• Secondary amine ($2^{\circ}$, $R_2NH$): reacts to form an N,N-dialkylbenzenesulfonamide, $C_6H_5SO_2NR_2$. Since there is no remaining N–H hydrogen, this product has no acidic proton and is insoluble in KOH; it separates out directly as a solid/oily precipitate that does not dissolve on adding excess alkali.

$R_2NH + C_6H_5SO_2Cl \xrightarrow{KOH} C_6H_5SO_2NR_2 \; (\text{insoluble in KOH})$

• Tertiary amine ($3^{\circ}$, $R_3N$): has no N–H hydrogen to be substituted at all, so it simply does not react with benzenesulfonyl chloride under these conditions; the amine is recovered largely unchanged, typically observed as an oily layer that does not dissolve, and no sulfonamide is formed.

2. Carbylamine (isocyanide) test: a primary amine, when warmed with chloroform and alcoholic potassium hydroxide, gives the foul-smelling alkyl/aryl isocyanide (carbylamine):

$RNH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} RNC + 3KCl + 3H_2O$

Secondary and tertiary amines give no reaction (no foul-smelling product) under these conditions, so this test is specific for and diagnostic of primary amines.

(Reaction with nitrous acid, $HNO_2$, is another classical distinguishing test: 1° amines liberate $N_2$ gas with formation of the alcohol/diazonium salt; 2° amines give a yellow oily N-nitrosamine; 3° aliphatic amines merely form an unstable, water-soluble salt with no visible change.)

(b) Polysaccharides

Polysaccharides are naturally occurring macromolecular carbohydrates built from a very large number of monosaccharide units (usually glucose) joined together by glycosidic linkages, with the general formula $(C_6H_{10}O_5)_n$.

General characteristics:

• High molecular mass polymers of monosaccharides.
• Not sweet in taste (unlike mono- and disaccharides).
• Essentially non-reducing in behaviour (the vast majority of potential reducing ends are buried within the enormous polymer, so the bulk sugar does not give a positive Fehling's/Tollens' test in the way a simple sugar does).
• Generally insoluble in water, or form only colloidal (not true) solutions.

Important examples:

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