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REACTIONS OF CARBOHYDRATES

NAVEENA GIRISH MSc PLANT SCIENCE CENTRAL UNIVERSITY OF KERALA KASARAGOD

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REACTIONS OF CARBOHYDRATES

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  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. OXIDATION SPECIFIC FOR ALDOSE MILD STRONG

  4. Reduction 1 3 5 2 4 5 reactions

  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 – ammoniacalsilvar 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. Acetylationglucose / fructose + acetic anhydrideglucose /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 Aldoseketose 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 treatmentwith alcohol in the presence of acid • Aldose /ketose +ammonia = glycosylamine Forms ketose Acetals Aldose Acid Base

  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 sugarhydrolysis Sucrose invertase glucose + fructose

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

  23. oxidation Acetylation

  24. Dehydration • Sucrose con. H2SO4 H2O CO2 C 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'sTest • 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

  42. Thank u

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