Carbohydrates sem 3 bsc

carbohydrates ,carbohydrates chemistry ,bsc ,bsc chemistry ,classification of carbohydrates ,monosaccharides ,disaccharide ,glucose ,fructose ,starch ,reactions of monosaccharides ,reactions of disaccharides ,reactions of glucose ,reactions of fructose

1. Introduction: The carbohydrates are the most important naturally occurring organic substances. These classes of natural products are important biologically and essential to sustain life. They are wide spread in animals and plants. The dry weight of plants is typically composed of 55% to 80% of polymetric carbohydrate cellulose along with relatd structural materials. These along with fats, proteins, forms the basis of animal nutrition. Sugars, starches, cellulose are best known members of this group. BY- Ms MAYURI R SOMPURA 2

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4. Introduction: Carbohydrate moieties also occur in a number of complex materials such as: glycosides Mucoproteins Nucleicacids Carbohydrates are only composed of carbon, hydrogen and oxygen. General formula - C X (H 2 O) Y C 6 H 12 O 6 Or C 6 (H 2 O) 6 / C 12 H 2 2 O 11 Or C 12 (H 2 O) 11 They appear to be hydrates of carbon. BY- Ms MAYURI R SOMPURA 5

5. Introduction: Carbohydrates are formed in plants by photosynthesis from carbon dioxide and water. This fundamental principle in life is catalyzed by the green plant pigment- chlorophyll , Enzyme systems & oxygen. nCO 2 + nH 2 O → ( CH 2 O) n + nO 2 6 CO 2 + 6H 2 O → (CH 2 O) 6 + 6O 2 BY- Ms MAYURI R SOMPURA 6

6. Introduction: We come across carbohydrates at almost every turn in our daily lives. The paper is largely composed of cellulose. The flour from which we prepare bread is largely composed of starch. Starch is also a major constituent of many other food stuffs such as potatoes, rice, beans, corn, peas. BY- Ms MAYURI R SOMPURA 7

7. Introduction: Carbohydrates are white solids, sparingly soluble in organic liquids except for some polysaccharides, soluble in water. Many carbohydrates of low molecular weight have sweet taste. BY- Ms MAYURI R SOMPURA 8

8. Classification of carbohydrates: Carbohydrates are classified into 4 major classes depending upon whether or not they undergo hydrolysis. If they do undergo hydrolysis, what are the number of products formed. BY- Ms MAYURI R SOMPURA 9

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10. (a) monosaccharides: These are the simplest from of Carbohydrates. They are also called as ‘simple sugars’. They cannot be further hydrolyzed. The most important of them are pentoses (CH 2 O) 5 and hexoses (CH 2 O) 6. General formula - (CH 2 O) n BY- Ms MAYURI R SOMPURA 11

11. (a) monosaccharides: The monosaccharaides are further sub-divided in terms of number of carbons and nature of carbonyl group present in the molecule. Aldehyde group – aldose Ketone group – ketose A three carbon chain is called – aldotriose or ketotriose . A four carbon chain is called – aldotetrose and ketotetrose And so on.. BY- Ms MAYURI R SOMPURA 12

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13. (b) oligosaccharides: The carbohydrates that hydrolyze to yield 2-10 molecules of a monosaccharaide is known as oligosaccharide . General formula – Cn(H 2 O) n-1 Carbohydrates that undergo hydrolysis to produce only two molecules of monosaccharide is known as a disaccharide . Eg , sucrose & maltose – same molecular formula - C 12 (H 2 O) 11 But raffinose is hydrolyzed to give three moles of a monosaccharide and hence is called a trisaccharide . BY- Ms MAYURI R SOMPURA 14

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15. (c) polysaccharides: These are composed of several monosaccharide units are polymers on hydrolysis. They yield a large number i.e. > 10 of monosaccharides. Eg , starch and cellulose (glucose polymer) These are non-sugars, insoluble in water and are most abundant form of carbohydrates. BY- Ms MAYURI R SOMPURA 16

16. Nomenclature: Aldehyde group present in carbohydrates :- Aldo triose Having 3 carbons Aldo tetrose Having 4 carbons Aldo pentose Having 5 carbons Aldo hexose Having 6 carbons Ketone group present in carbohydrates :- Aldo triose Having 3 carbons Aldo tetrose Having 4 carbons Aldo pentose Having 5 carbons Aldo hexose Having 6 carbons BY- Ms MAYURI R SOMPURA 17

17. General reactions of monosaccharides: Monosaccharides are aldehyde and ketone derivative of higher polyhydric alcohols, they give most, but not all, of the characteristic reaction of arbonyl group as well as the alcoholic group. In addition to these relationships they also gove rise to some special reactions due to the presence of a carbonyl and alcoholic group in the same molecule.. Osazone formation :- Glucose and fructose react with phenylhydrazine to form same osazones . 3 moles of phenylhydrazines are consumed in aldoses as well as in ketoses to form osazones , aniline and ammonia. BY- Ms MAYURI R SOMPURA 18

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19. (a) Osazone formation : According to Fisher’s mechanism, glucose reacts first with phenyl hydrazine molecule with the carbonyl group of aldehyde of aldose to form phenylhydrazone . The second ,molecule of phenylhydrazine oxidises the C-2 hydroxyl group of phenylhydrazone to carbonyl group and is itself reduced to aniline and ammonia. Finally the newly deve;loped carbonyl group reacts with the third molecule of phenylhydrazine to form phenylosazone . These three steps summarized in case of glucose molecule. BY- Ms MAYURI R SOMPURA 20

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21. (a) Osazone formation : A phenylhydrazine molecule reacts with carbonyl group at C-2 to from phenylhydrazone . Then second molecule of phenylhydrazine oxides the C-1 hydroxyl group of phenylhydrazone to a carbonyl group and is itself reduced to aniline and ammonia. Finally the newly formed carbonyl group reacts with the third molecule of phenylhydrazine to form osazone . BY- Ms MAYURI R SOMPURA 22

22. (b)oxidation: Oxidation with bromine water. Oxidation with nitric acid Oxidation with periodic acid Oxidation with Fehling solution/ tollens reagent/ Benedict reagent BY- Ms MAYURI R SOMPURA 23

23. (1)Oxidation with bromine water: Bromine water is mildly acidic solution (PH=6.0) . When they react with glucose, glucose oxidises the –CHO group to –COOH group. Aldose → Aldonic acid ( gluconic acid) Bromine water donot react with fructose as it doesnot have an aldehyde group. BY- Ms MAYURI R SOMPURA 24

24. (2)Oxidation with nitric acid: When glucose is oxidised with nitric acid to yield dicarboxylic acids kown as aldaric acid ( saccharic acid). Primary alcoholic group at C-6 position and –CHO at C-1 position will be oxidized to yield –COOH group. Fructose can be oxidized with nitric acid. Fructose is converted into mixture of three acids. Hence this gives the evidence of the presence of C=O group in fructose molecule. BY- Ms MAYURI R SOMPURA 25

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26. (3)Oxidation with periodic acid: Oxidation of periodic acid shows that 5 moles of HIO 4 is used. After the oxidation reaction 5 moles of formic acid and one mole of formaldehyde are obtained. Fructose is oxidized with periodic acid to obtain: 2 moles – formaldehyde 1 mole - glycolic acid 3 moles – formic acid BY- Ms MAYURI R SOMPURA 27

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28. (4)Oxidation with reagents: Sr.no Reagent name Chemical formation of reagent 1 Fehling’s reagent Fehling’s reagent A – Copper sulphate solution Fehling’s reagent B – Sodium hydroxide + Sodium Potassium Tartrate 2 Benedict’s reagent Copper sulphate + Sodium carbonate + Sodium citrate 3 Tollen’s reagent Silver nitrate + Sodium hydroxide + Ammonium hydroxide BY- Ms MAYURI R SOMPURA 29

29. (4)Oxidation with reagents: Gluocse and fructose react with Fehling’s or Benedict’s reagent to produce the precipitate of Cu 2 O. Glucose is oxidized and converted into gluconic acid. Fructose id oxidized and converted into glycolid and tartaric acid. With tollen’s – glucose and fructose give the same reaction and produces silver. Glucose is converted to gluconic acid that means it has –CHO group. Fructose is oxidized and fragmented. Glycolic acid and tartaric acid are produced that means fructose has C=O group. BY- Ms MAYURI R SOMPURA 30

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32. (b) Reduction : Gluocse reacts with Na-Hg amalgam in aqueous solution, the glucose is reduced and converted to hexahydroxy alcohol (sorbitol). Fructose is reduced by electric reduction method in presence of acidic medium and alkali medium converted into sorbitol and mannitol. Epimers - are optical isomers which differ only in the configuration of one asymmetric center. Sorbitol and mannitol are epimers . BY- Ms MAYURI R SOMPURA 33

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34. (b) Reduction : On reduction with red phosphorous and hydroiodic acid at 100℃ temperatire yield sorbitol ( + mannitol for fructose ) which again reacts with same to form 2-iodohexane . 2-iodohexane is further heated for a long time to get n-hexane. Which means glucose and fructose molecule structure is in a single chain. BY- Ms MAYURI R SOMPURA 35

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36. (C) ACETYLATION : On acetylation, glucose and fructose yield ester derivatives. Acetylated penta acetyl derivatives are formed. Which means they both hsve 5 –OH groups present in their structure. BY- Ms MAYURI R SOMPURA 37