The reactions of carbohydrates

BIOCHEMISTRY - CARBOHYDRATES

1. The reactions of carbohydrates

2. Reactions of monosaccharide's Reactions of disaccharides Reactions of polysaccharides Colour reactions NAVEENA GIRISH MSc PLANT SCIENCE CENTRAL UNIVERSITY OF KERALA

3. OXIDA TION SPECIFIC FOR ALDOSE MILD STRONG

4. 1 2 3 4 5 5 reactions Reduction

5. Reduction of Monosaccharide C=O of aldoses or ketoses can be reduced to C-OH by NaBH4 or Name the sugar alcohol by adding – itol to the root name of the sugar; commonly known as an alditol . Reduction of D-glucose produces D- glucitol , commonly called D- sorbitol . Reduction of D-fructose produces a mixture of D- glucitol and D- mannitol .

6. Examples Glucose + sodium amalgam = sorbitol Fructose + sodium amalgam = sorbitol and mannitol Glucose/fructose + HI/ Red phosphorus = n – hexane (prolonger heating with con. Hydroic acid and red phosphorus )

7. Glucose /fructose + hydrogen cyanide = glucose cyanohydrid / fructose cyanohydrin Glucose/ fructose + hydroxyl amine = glucose amine / fructose amine +water

8. Reducing action Oxidation by TollensReagent Sugars that reduce Tollensreagent are called Reducing sugars Tollens reagent – ammoniacal silvar nitrate solution Silvar mirror test Metallic silver formation Glucose gives gluconic acid + metallic silver Fructose gives glycollic acid + trihydroxy butyric acid+glycollic acid + metallic silver

9. Acetylation glucose / fructose + acetic anhydride glucose /fructose pentaacetate + acetic acid Methylation Glucose / fructose + penta methyl glucose (In presence of DRY HCl ) Methyl fructoside /methyl glucoside + H2O

10. Glucose / fructose Dimethyl sulphate In presence of alkali

11. pentamethyl fructose pentamethyl glucose

12. Enediol Rearrangement In base, the position of the C=O can shift Aldose ketose Chemists use acidic or neutral solutions of sugars to preserve their identity.

13. Epimerization

14. Proton alpha to carbonyl group (in aldehyde or ketone ) is reversibly removed; form an enolate-C2 no longer chiral . Reprotonation can occur on either side of the enolate to give configuration products

15. Ester Formation

16. Aldoses & ketoses are converted to acetals by treatment with alcohol in the presence of acid Aldose / ketose +ammonia = glycosylamine Aldose ketose Acid Base Forms Acetals

17. Ether Formation • Convert all -OH groups to -OR, using a Williamson synthesis, after converting sugar to acetal

18. Ruff Degradation Aldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation

19. Kiliani -Fischer Synthesis • This process lengthens the aldose chain

20. Sucrose

21. Inversion of cane sugar hydrolysis Sucrose invertase glucose + fructose

22. Sucrosate formation Sucrose + Ca hydroxide Ba hydroxide Sr hydroxide Respective sucrosate formation with water

23. oxidation Acetylation

24. Dehydration Sucrose con. H2SO4 CO2 C H2O SO2

25. METHYLATION SUCROSE + DIMETHYL SULPHATE = OCTAMETHYL SUCROSE +SULPHURIC ACID IN PRESENCE OF ALKALI FERMENTATION SUCROSE+ H2O GLUCOSE + FRUCTOSE ETHANOL+ CO2

26. NO REACTION WITH Tollens reagent Fehlings Benedicts Phenyl hydrazine Hydroxyl amine Non reducing sugar

27. Starch Action of heat 200- 250 Cleavage of polymer Dextrin (a polysccharide of lower molecular weight ) Iodine test shows a deep blue colour with starch

28. Hydrolysis On boiling with dil. Acid , starch become dextrin then ultimately yield glucose Starch hydrolysed by enzyme diastase , yield maltose

29. Cellulose Hydrolysed with acid to yield glucose

30. Nitration CON H2SO4, CON HNO3, CELLULOSE MONO NITRATE DI NITRITE TRI NITRITE MANUFACTURE PLASTICS , PHOTOGRAPHIC FILM GUN COTTON ,EXPLOSIVE

31. ACETYLATION ACETIC ANHYDRIDE , GLACIAL ACETIC ACID ,SULPHURIC ACID DI AND TRI ACETATES SYNTHETIC FIBRES PAINTS AND VARNISHES

32. Colour reactions

33. Molischs test It is indicative of carbohydrate Furfural / hydroxy furfural formed by the action H2SO4 Condenses to form violet ring with alpha naphthanol

34. Barfoeds test Acetic acid + cupric acetate – barfoeds solution Monosaccharides test Cuprous oxide makes red ppt.

35. Benedicts test Benedicts solution – CuSO4 + sodium carbonate + sodium citrate +H2O Reducing sugar Red ppt of cuprous oxide , depending on con.

36. Fehling's Test Fehling's solution –( CuSO4 +CON. H2SO4+H20)+ SODIUM POTASSIUM TARTARATE + NaOH ) For reducing testing Red ppt of cuprous oxide Glucose gives gluconic acid +cuprous oxide Fructose gives trihydroxy butyric acid+ glycollic acid +cuprous oxide

37. Bials test Bials reagent – ferric chloride hexahydrate +con. HCl + orcinol Distinguish b/w pentose and hexose Furfural formation Furfural + orcinol + ferric iron = coloured product Pentose – green Hexose - muddy brown

38. Seliwanoff test For ketoses Reagent – HCl + resorcinol Ketose + HCl =furfural derivative + recorcinol = deep red colour

39. Diphenylamine test Reagent – H2SO4 , DIPHENYL AMINE,GLACIAL ACETIC ACID ADD TO TEST SOLUTION BOIL 10’ 2 DEOXY SUGAR BLUE / GREEN COLOUR

40. Schiff test ALDOSE + SCHIFFS = MAGENTA COLOUR

41. Anthrone method Furfural formation by H2SO4 Naphthanol form blue colour show prescence of carbohydrate

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