Органическая химия = Organic Chemistry. Лабораторный практикум

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In a disaccharide, the two monosaccharides are joined together by acetal or glycoside formation. The hemiacetal OH of one monosaccharide and an OH group of the second one dehydrate to establish the bond (called glycosidic bond) between the two monosaccharides.Disaccharides can be reducing or non-reducing.

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Reducing sugars are like glucose, because the second component has the hemiacetal grouping readily converting into the aldehyde form, they can be oxidized by Ferling’s solution. Due to a free hemiacetal group, reducing sugars also have chain-ring tautomerism.

In non-reducing sugars two monosaccharides are joined together by two hemiacetal OH groups forming disaccharide without hemiacetal hydroxyl group which is necessary for the ring-chain tautomerism. Thus, being dissolved these disaccharides do not give rise to the oxo-form which provides “silver” and “copper mirrors”.

HO

H H O H

OH H

sucrose

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Not shaking the test tube, put it accurately into a steam bath for 5 minutes.

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Place about 2 ml of amylum solution into a test tube.

Into the test tube add 2 drops of iodine solution. Pay attention to the color of your solution.

Put the test tube into a steam bath for 2 minutes until the color disappears.

Cool the mixture, the color appears again.

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