starch dextrinmaltoseglucose

Video experiment “Acid hydrolysis of cellulose”

Esterification reactions

Cellulose is a polyhydric alcohol; there are three hydroxyl groups per unit cell of the polymer. In this regard, cellulose is characterized by esterification reactions (formation of esters). Reactions with nitric acid and acetic anhydride are of greatest practical importance. Cellulose does not produce a “silver mirror” reaction.

1. Nitration:

(C 6 H 7 O 2 (OH ) 3) n + 3 nHNO 3 H 2 SO4(conc.)→(C 6 H 7 O 2 (ONO 2 ) 3) n + 3 nH 2 O

pyroxylin

Video experiment “Preparation and properties of nitrocellulose”

Fully esterified fiber is known as gunpowder, which, after proper processing, turns into smokeless gunpowder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which in technology is called colloxylin. It is also used in the manufacture of gunpowder and solid rocket propellants. In addition, celluloid is made from colloxylin.

2. Interaction with acetic acid:

(C 6 H 7 O 2 (OH) 3) n + 3nCH 3 COOH H2SO4( conc. .)→ (C 6 H 7 O 2 (OCOCH 3) 3) n + 3nH 2 O

When cellulose reacts with acetic anhydride in the presence of acetic and sulfuric acids, triacetylcellulose is formed.

Triacetyl cellulose (or cellulose acetate) is a valuable product for the manufacture of flame retardant film andacetate silk. To do this, cellulose acetate is dissolved in a mixture of dichloromethane and ethanol, and this solution is forced through dies into a stream of warm air.

And the die itself schematically looks like this:

1 - spinning solution,
2 - die,
3 - fibers.

The solvent evaporates and the streams of solution turn into the finest threads of acetate silk.

Speaking about the use of cellulose, one cannot help but say that a large amount of cellulose is consumed for the production of various papers. Paper- This is a thin layer of fiber fibers, glued and pressed on a special paper-making machine.

Polysaccharides. Starch and cellulose Philon M.V. chemistry teacher MBOU secondary school No. 266

Comparative characteristics of starch and cellulose

Signs of comparison

Starch

Formula

Cellulose

Structural link

Molecule structure

Physical properties

Chemical properties

Application

Structural formula of starch

α-Glucose residues

Structural formula of cellulose

β-Glucose residues

Physical properties

starch

cellulose

• hard, fibrous white substance

• white amorphous powder

• does not dissolve in cold water

• does not dissolve in water

• swells in hot water

• does not have a sweet taste

• does not have a sweet taste

Chemical properties of starch

• Qualitative reaction

(C 6 H 10 O 5) n + I 2 → blue color

2. Hydrolysis

Starch → dextrins → maltose → glucose

Chemical properties of cellulose

1. Hydrolysis

(C 6 H 10 O 5) n + nH 2 O → nC 6 H 12 O 6

2. Formation of esters

Let's check ourselves

1. The starch macromolecule consists of molecular residues...

α - glucose

fructose

β - glucose

Let's check ourselves

2. Qualitative reaction to starch - interaction with...

copper(II) hydroxide

ammonia solution of silver oxide

Let's check ourselves

3. The hydrolysis of cellulose produces...

Let's check ourselves

4. Cellulose trinitrate is used as...

medicine

explosive

for extinguishing fires

Polysaccharides: starch, cellulose

Polysaccharides are high molecular weight compounds containing hundreds and thousands of monosaccharide residues. What is common to the structure of polysaccharides is that monosaccharide residues are linked by the hemiacetal hydroxyl of one molecule and the alcohol hydroxyl of another, etc. Each monosaccharide residue is linked to adjacent residues by glycosidic bonds.

Polyglycosides can contain branched and unbranched chains. The monosaccharide residues that make up the molecule can be the same or different. The most important of the higher polysaccharides are starch, glycogen (animal starch), fiber (or cellulose). All three of these polysaccharides are made up of glucose molecules linked together in different ways. The composition of all three compounds can be expressed by the general formula: (C 6 H 10 O 5) n

Starch

Starch belongs to the polysaccharides. The molecular mass of this substance has not been precisely established, but it is known that it is very large (about 100,000) and may vary for different samples. Therefore, the formula of starch, like other polysaccharides, is depicted as (C 6 H 10 O 5) n. For each polysaccharide n has different meanings.

Physical properties

Starch is a tasteless powder, insoluble in cold water. It swells in hot water, forming a paste.

Starch is widely distributed in nature. It is a reserve nutrient material for various plants and is contained in them in the form of starch grains. The richest grains in starch are cereals: rice (up to 86%), wheat (up to 75%), corn (up to 72%), and potato tubers (up to 24%). In potato tubers, starch grains float in cell sap, and in cereals they are tightly glued together with a protein substance called gluten. Starch is one of the products of photosynthesis.

Receipt

Starch is extracted from plants by destroying the cells and washing it with water. On an industrial scale, it is obtained mainly from potato tubers (in the form of potato flour), as well as from corn.

Chemical properties

1) Under the action of enzymes or when heated with acids (hydrogen ions serve as a catalyst), starch, like all complex carbohydrates, undergoes hydrolysis. In this case, soluble starch is formed first, then less complex substances - dextrins. The final product of hydrolysis is glucose. The overall reaction equation can be expressed as follows:

There is a gradual breakdown of macromolecules. Hydrolysis of starch is its important chemical property.

2) Starch does not give the “silver mirror” reaction, but the products of its hydrolysis do. Starch macromolecules consist of many molecules of cyclic a-glucose. The process of starch formation can be expressed as follows (polycondensation reaction):

3) A characteristic reaction is the interaction of starch with iodine solutions. If an iodine solution is added to a cooled starch paste, a blue color appears. When the paste is heated, it disappears, and when cooled, it appears again. This property is used in determining starch in food products. For example, if a drop of iodine is applied to a cut potato or a slice of white bread, a blue color appears.

Application

Starch is the main carbohydrate in human food; it is found in large quantities in bread, cereals, potatoes, and vegetables. Significant quantities of starch are processed into dextrins, molasses, and glucose, which are used in the confectionery industry. Starch is used as an adhesive, used for finishing fabrics and starching linen. In medicine, ointments, powders, etc. are prepared based on starch.

Cellulose or fiber

Cellulose is an even more common carbohydrate than starch. It consists mainly of the walls of plant cells. Wood contains up to 60%, cotton wool and filter paper - up to 90% cellulose.

Physical properties

Pure cellulose is a white solid, insoluble in water and in common organic solvents, highly soluble in concentrated ammonia solution of copper (II) hydroxide (Schweitzer reagent). From this acid solution, cellulose is precipitated in the form of fibers (hydrated cellulose). Fiber has quite high mechanical strength.

Composition and structure

The composition of cellulose, as well as starch, is expressed by the formula (C 6 H 10 O 5) n. The n value in some types of cellulose reaches 10-12 thousand, and the molecular weight reaches several million. Its molecules have a linear (unbranched) structure, as a result of which cellulose easily forms fibers. Starch molecules have both linear and branched structures. This is the main difference between starch and cellulose.

There are differences in the structure of these substances: starch macromolecules consist of residues of a-glucose molecules, and cellulose macromolecules consist of residues of b-glucose. The process of formation of a fragment of a cellulose macromolecule can be represented by the diagram:

Chemical properties. Applications of cellulose Small differences in the structure of molecules cause significant differences in the properties of polymers: starch is a food product, cellulose is unsuitable for this purpose.

1) Cellulose does not give a “silver mirror” reaction (no aldehyde group). This allows us to consider each C 6 H 10 O 5 unit as a glucose residue containing three hydroxyl groups. The latter in the cellulose formula are often distinguished:

Due to hydroxyl groups, cellulose can form ethers and esters.

For example, the reaction to form an ester with acetic acid is:

[C 6 H 7 O 2 (OH) 3 ] n +3nCH 3 COOH® [C 6 H 7 O 2 (OSOCH 3) 3 ] n +3nH 2 O

When cellulose reacts with concentrated nitric acid in the presence of concentrated sulfuric acid as a water-removing agent, an ester is formed - cellulose trinitrate:

This is an explosive substance used to make gunpowder.

Thus, at ordinary temperatures, cellulose reacts only with concentrated acids.

2) Like starch, when heated with dilute acids, cellulose undergoes hydrolysis to form glucose:

(С 6 Н 10 0 6) n +nН 2 O®nС b Н 12 O 6

Hydrolysis of cellulose, otherwise called saccharification, is a very important property of cellulose; it makes it possible to obtain cellulose from sawdust and shavings, and by fermenting the latter, ethyl alcohol. Ethyl alcohol obtained from wood is called hydrolytic.

At hydrolysis plants, up to 200 liters of ethyl alcohol are obtained from 1 ton of wood, which can replace 1.5 tons of potatoes or 0.7 tons of grain.

Crude glucose obtained from wood can be used as livestock feed.

These are just some examples of the use of cellulose. Cellulose in the form of cotton, flax or hemp is used to make fabrics - cotton and linen. Large quantities of it are spent on paper production. Cheap grades of paper are made from coniferous wood, the best grades are made from linen and cotton waste paper. By subjecting cellulose to chemical processing, several types of artificial silk, plastics, film, smokeless powder, varnishes and much more are obtained.

High molecular weight organic structures that contain a large number of monosaccharide residues are called polysaccharides.

The structure of all polysaccharides is the same in that the monosaccharide residues are connected by the hemiacetate hydroxyl of a given molecule and the alcohol hydroxyl of another molecule. Monosaccharide residues can be identical or different. The most significant of the polysaccharides are starch and cellulose. The molecular weight of these substances is quite large. They have a structure made of glucose, but its molecules are connected differently. These two polysaccharides are designated by the same chemical formula (C6H10O5)n.

Starch

Starch is a complex carbohydrate that is a granular, crunchy white powder that has no taste. It does not dissolve in cold water, but in water at high temperatures it swells and forms a paste.

This polysaccharide is very common in the natural environment. It became a reserve material and food material for the plant. Found in them as starch grain. Cereal grains contain the largest amount of starch: eighty-six percent in rice, seventy-five percent in wheat, seventy-two percent in corn kernels. Potatoes contain the most starch. Here, starch grains are found in cell juice, and in cereal grains they are glued together with plant protein (gluten). This polymer is the result of the process of photosynthesis.

Starch is obtained from destroyed plant cells by washing it out with liquid. Industrially, it is extracted mainly from potatoes (potato flour) and corn cobs.

Starch is extracted from vegetables in the following way:

1. Preparation of plant raw materials (washing and cleaning).
2. Chopping vegetables, obtaining starch liquid, washing.
3. Settling the resulting mass and washing it again (removing impurities).
4. The resulting gray powder is dried, cooled and sifted.

Under the influence of enzymes or during heating together with acids (the catalyst is hydrogen ions), starch is hydrolyzed. In the process of this chemical reaction, starch first appears, which is soluble, and then dextrins (simple substances) are formed. Ultimately, glucose is formed.

Starch does not produce the “silver mirror” reaction (it results in the appearance of silver deposited on the surface), but the products that are formed as a result of its hydrolysis do produce this reaction.

Starch reacts with iodine solution. When an iodine solution is added to a cold paste made by brewing starch with hot water, the paste turns blue. When such a paste is heated, this color is lost, and when the paste becomes cold again, the color returns. This feature of starch is used when it is necessary to determine the presence of starch in food products. For example, a small drop of iodine applied to a piece of potato tuber or a piece of wheat bread turns the product blue.

In human food, starch has become the main carbohydrate; it acts as an energy source. An insufficient amount of starch in the human body leads to weakness; rapid fatigue; to reduce resistance to infections; to brittle nail plates; and also to the fact that the hair splits. Food products with a high content of this substance can replenish its amount in the human body. There is a lot of starch in wheat bread, various cereals, potatoes, and vegetables. It is processed into glucose, dextrins, molasses and used in the manufacture of confectionery products. Moreover, different types of starch provide different densities in the same volume of water. The greatest density is obtained when using rice starch, a slightly more liquid substance is formed from potato starch, and the most delicate consistency is obtained from corn starch.

In food products, starch reduces the taste of the product; a bland, soggy, uninteresting taste is felt, so adding starch leads to an increase in the amount of other ingredients so that the food tastes normal. For example, in thick jelly you need to put more sugar and lemon.

Starch is also used as glue. It is also necessary in finishing textile fabrics and starching clothes. It is used to make ointments and powders in the medical industry.

Cellulose

Cellulose is also a carbohydrate. It is more widespread than starch itself and is an integral part of the cell wall of plants. Cellulose is also called fiber. Raw wood contains sixty percent cellulose, and paper that has been filtered contains approximately ninety percent cellulose.

Cellulose is an odorless, white solid that is insoluble in aqueous solutions and other organic solvents. It dissolves well in a concentrated solution of ammonia with copper hydroxide (called Schweitzer's reagent). From this acidic solution, cellulose fibers called hydrated cellulose are obtained. The substance fiber (cellulose) has significant mechanical strength and elasticity.

Cellulose molecules are built unbranched (nonlinear), so it is the fibers of this substance that are formed. And starch molecules are built both branched and linear. This is the difference between starch and cellulose.

These substances are also different in their structure, namely: starch molecules consist of alpha-glucose residues, and fiber molecules consist of beta-glucose residues.

These minor differences in the structure of these substances lead to large differences in their properties. Starch is a food product, but cellulose is not used in food.

When interacting with iodine and sulfuric acid, cellulose turns blue. And when interacting only with iodine, it turns brown.

Cellulose does not produce a “silver mirror” reaction. Each glucose residue in it contains three hydroxyl groups, due to which esters can be formed. At standard temperatures, cellulose reacts only with acid concentrates. Like starch, it is subject to hydrolysis with the appearance of glucose when it is heated with non-concentrated acids.

Cellulose hydrolysis is also called saccharification. This is an important property that helps to obtain cellulose from wood sawdust and wood shavings. When it is fermented, it produces ethyl, which is called hydrolytic alcohol. At hydrolysis enterprises, approximately two hundred liters of ethyl come out of one ton of wood raw material, which makes it possible to replace one and a half tons of potatoes or zero point seven tons of grain crops.

Glucose in its raw state, which was obtained from wood raw materials, is used as feed for livestock. And cotton, flax and hemp (all of this is also cellulose) are used to produce cotton and linen fabrics.

A lot of cellulose is used to make paper products. Paper is a thin layer of cellulose fibers that are pressed and sized to prevent ink and paint from bleeding. Initially, paper was made from rice stalks, cotton fiber and old fabrics. Then this raw material became scarce. They began to use wood raw materials. In industry, cellulose can be obtained by cooking wood chips. A lot of paper is needed to produce newspapers, but its quality (white color, strength, wear resistance) does not matter. Cheap paper is made from coniferous wood raw materials, and expensive high-quality paper is made from cotton and linen waste paper. Cellulose is chemically processed to produce artificial fabric fiber (viscose, silk, wool), plastic, varnish, film for films and photographs, and smokeless gunpowder.

Thus, a comparative characterization of starch and cellulose showed that starch and cellulose are similar polymeric substances (complex carbohydrates). Both of these polymers are white in color. They do not dissolve in water. They are built from glucose molecules. They are designated by one chemical formula, are capable of hydrolysis and do not produce a “silver mirror” reaction. They differ in their structure (for cellulose it is linear, and for starch it is both linear and branched). Their structure is also different, although glucose is present in their composition (starch is built from alpha-glucose residues, and cellulose is made from beta-glucose residues). They also differ in their area of ​​use (starch is used as a food product, but cellulose is not; cellulose is used for the production of paper and textile products, for the manufacture of various items, but starch is not). Glucose differs from starch in its strength; it can be used to make fiber. It also takes longer to decompose than starch.

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Slide captions:

Polysaccharides. Starch Cellulose

WHO ARE CARBOHYDRATES Carbohydrates are multifunctional compounds, organic substances whose molecules consist of carbon, hydrogen and oxygen atoms, and hydrogen and oxygen are found in them, as a rule, in the same ratio as in a water molecule (2:1). General formula of carbohydrates C n (H 2 O) m

FUNCTIONS OF CARBOHYDRATES 1.. They supply energy for biological processes. 2. They are the starting material for the synthesis of other intermediate or final metabolites in the body. 3.Carbohydrates account for about 80% of the dry matter of plants and about 20% of animals. 4. Human food consists of approximately 70% carbohydrates.

HISTORICAL BACKGROUND Carbohydrates have been used since ancient times - the very first carbohydrate (more precisely, a mixture of carbohydrates) that man became acquainted with was honey. Sugarcane is native to northwestern India-Bengal. Europeans became familiar with cane sugar thanks to the campaigns of Alexander the Great in 327 BC. Starch was known to the ancient Greeks.

1. Beet sugar in its pure form was discovered only in 1747 by the German chemist A. Marggraf 2. In 1811, the Russian chemist Kirchhoff first obtained glucose by hydrolysis of starch 3. For the first time, the correct empirical formula for glucose was proposed by the Swedish chemist J. Bercellius in 1837. C 6 H 12 O 6 4. The synthesis of carbohydrates from formaldehyde in the presence of Ca(OH) 2 was carried out by A.M. Butlerov in 1861

Carbohydrates Monosaccharides Oligosaccharides Polysaccharides Glucose, fructose, ribose Sucrose Starch, cellulose

Carbohydrates = saccharides Simple (CH 2 O) n, where n = 3-9 monosaccharides Complex Disaccharides C 12 H 22 O 11 Polysaccharides C x (H 2 O) y glucose fructose galactose C 6 - hexoses ribose deoxyribose C 5 - pentoses sucrose lactose maltose 2 hexoses starch glycogen cellulose chitin polyhexose The higher the molecular weight of carbohydrates, the less soluble the substance is and the less sweet it tastes. Classification of carbohydrates

Monosaccharides - pentoses ribose deoxyribose

Glucose Fructose Galactose Monosaccharides - hexoses

1) alcoholic fermentation C 6 H 12 O 6 → 2CH 3 -CH 2 OH + 2CO 2 Ethyl alcohol 2) lactic fermentation C 6 H 12 O 6 → 2CH 3 -CHOH -COOH Lactic acid 3) butyric fermentation C 6 H 12 O 6 → C 3 H 7 COOH + 2H 2 + 2CO 2 4) Complete oxidation of C 6 H 12 O 6 +6O 2 → 6H 2O + 6CO 2 Specific properties of glucose

Sucrose is a disaccharide formed by glucose and fructose.

Evidence for the presence of hydroxyl groups in sucrose

Charring of sucrose

Maltose Maltose (malt sugar) Maltose can be obtained by hydrolysis of starch under the action of enzymes contained in malt.

REVIEW RESULTS: In a balanced diet, carbohydrates make up 60% of the daily diet. Carbohydrates A lack of carbohydrates in food is harmful and leads to the body beginning to increase the use of the energy capabilities of proteins and fats. In this case, the amount of their breakdown products, which are harmful to humans, sharply increases. According to their composition, they can be classified into Complex starch (C 6 H 10 O 5) n simple glucose C 6 H 12 O 6 They contain two functional groups: 1) a hydroxo group, the structural formula of which is -OH 2) a carbonyl group, the structural formula of which is -HC = O Excess carbohydrates in food are harmful and lead to obesity. Excessive consumption of sugar negatively affects the function of intestinal microflora, leads to disruption of cholesterol metabolism and an increase in its level in the blood serum. Carbohydrates can be stored in the human body! glucose C 6 H 1 2 O 6 oxidation to carbon dioxide CO 2 and water H 2 O with the release of energy (1 g of carbohydrates - 4.1 kcal.)

Topic: "Polysaccharides: starch and cellulose" Starch Cellulose Glycogen (C6H10O5) n (hydrolyzed into a large number of monosaccharide molecules)

Starch is a reserve polysaccharide of many plants. Industrially, it is obtained from potatoes. This is a white powder. Polysaccharides

Cellulose (lettuce) is widespread in nature: plant tissues are built from it. Cotton wool and filter paper are the purest forms of cellulose (up to 96%). A component of wood is cellulose. Polysaccharides

Glycogen is animal starch, which is deposited in the liver and is a reserve substance in the body of humans and animals. Polysaccharides

Comparison of starch and cellulose Starch Cellulose Composition Structure Physical properties Chemical properties Occurrence in nature Biological role Application

Structural formula of starch Residues α - glucose

The structure of starch.

Structural formula of cellulose β - glucose residues

Physical properties white amorphous powder does not dissolve in cold water does not swell in hot water does not have a sweet taste solid fibrous white substance does not dissolve in water does not have a sweet taste cellulose starch

Video experience

Chemical properties of starch Qualitative reaction (C 6 H 10 O 5) n + I 2 → blue color 2. Hydrolysis (C 6 H 10 O 5) n + (n -1) H 2 O → nC 6 H 12 O 6 Starch → dextrins → maltose → glucose

Starch hydrolysis

Chemical properties of cellulose 1. Hydrolysis (C 6 H 10 O 5) n + (n -1) H 2 O → nC 6 H 12 O 6

Chemical properties of cellulose 2. Formation of esters

Preparation and properties of trinitrocellulose

Obtaining acetate fiber

Cellulose dissolution

Starch in nature

Cellulose in nature

Application of starch and cellulose

Let's test ourselves 1. The starch macromolecule consists of remnants of molecules... α - glucose β - fructose glucose

Let's test ourselves 2. Qualitative reaction to starch - interaction with ... copper (II) hydroxide, iodine, ammonia solution of silver oxide

Let's test ourselves 3. The hydrolysis of cellulose produces... starch glucose ethanol

Let's test ourselves 4. Cellulose trinitrate is used as ... a medicine, an explosive, a fire extinguishing agent

Let's test ourselves 5. To make acetate fiber, we use... cellulose salts, cellulose oxides, cellulose esters

Congratulations! You have successfully completed all tasks!

Homework Paragraph 24. exercises 3.5 after paragraph