CBSE Class 12 Chemistry Notes: Biomolecules – Reactions of Glucose

(a)  With HI/P: It undergoes reduction to form n-hexane while with sodium amalgam it forms s orbitol.

n-hexane

sorbitol

(b)  With H₂O: It forms neutral solution

(c)  With Hydroxylamine (NH₂OH)

(d)  With HCN: It forms addition product cyanohydrin

(e)  Oxidation: Glucose on oxidation with Br₂ gives gluconic acid which on further oxidation with HNO₃ gives glucaric acid

(f)   With Tollen reagent and Fehling solution. Glucose forms silver mirror and red ppt. of Cu₂O respectively.

(g)  With acetic anhydride. In presence of pyridine glucose forms pentaacetate.

(h)  With phenylhydrazine: it forms glucosazone

(i)   With conc. HCl acid: Glucose gives laevulinic acid

(j)   Glycoside formation: When a small amount of gaseous HCl is passed into a solution of  D (+) glucose in methanol , a reaction takes place that results in the formation of anomeric methyl acetals.

Carbohydrate acetals, generally are called glycosides and an acetal of glucose is called glucoside.

Illustration1      Glucose and fructose give the same osazone. One may therefore conclude that

 (A)  glucose and fructose have identical structures

(B)  glucose and fructose are anomers

(C)  the structures of glucose and fructose have mirror – image relationship

 (D)  the structure of glucose and fructose differ only in those carbon atoms which take part in asazone formation.

Solution: (D) Glucose and fructose give the same osazone, but differ from each other only in configuration at C₁ and C₂.

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