Chemical properties of cellulose. The chemical structure of cellulose What physical bodies are made up of cellulose
A complex carbohydrate from the group of polysaccharides, which is part of the cell wall of plants, is called cellulose or fiber. The substance was discovered in 1838 by the French chemist Anselm Payen. Cellulose formula - (C 6 H 10 O 5) n.
Structure
Despite the common features, cellulose differs from another plant polysaccharide - starch. The cellulose molecule is a long, extremely unbranched chain of saccharides. Unlike starch, which consists of α-glucose residues, it includes many β-glucose residues linked together.
Due to the dense linear structure, the molecules form fibers.
Rice. 1. The structure of the cellulose molecule.
Cellulose has a higher degree of polymerization than starch.
Receipt
Cellulose in industrial conditions is boiled out from wood (chips). For this, acidic or alkaline reagents are used. For example, sodium hydrosulfite, sodium hydroxide, lye.
As a result of cooking, cellulose is formed with an admixture of organic compounds. To clean it, use an alkali solution.
Physical properties
Cellulose is a tasteless white solid fibrous substance. Cellulose is poorly soluble in water and organic solvents. It dissolves in Schweitzer's reagent - an ammonia solution of copper (II) hydroxide.
Main physical properties:
- collapses at 200°C;
- burns at 275°C;
- spontaneously ignites at 420°C;
- melts at 467°C.
In nature, cellulose is found in plants. It is formed during photosynthesis and performs a structural function in plants. It is a food additive E460.
Rice. 2. Plant cell wall.
Chemical properties
Due to the presence of three hydroxyl groups in one saccharide, fiber exhibits the properties of polyhydric alcohols and is able to enter into esterification reactions with the formation of esters. When decomposed without access to oxygen, it decomposes into charcoal, water and volatile organic substances.
The main chemical properties of fiber are presented in the table.
|
Reaction |
Description |
The equation |
|
Hydrolysis |
Occurs when heated in an acidic environment with the formation of glucose |
(C 6 H 10 O 5) n + nH 2 O (t °, H 2 SO 4) → nC 6 H 12 O 6 |
|
With acetic anhydride |
Formation of triacetylcellulose in the presence of sulfuric and acetic acids |
(C 6 H 10 O 5) n + 3nCH 3 COOH (H 2 SO 4) → (C 6 H 7 O 2 (OCOCH 3) 3) n + 3nH 2 O |
|
Nitration |
It reacts with concentrated nitric acid at ordinary temperature. An ester is formed - cellulose trinitrate or pyroxylin, used to make smokeless powder |
(C 6 H 10 O 5) n + nHNO 3 (H 2 SO 4) → n |
|
Complete oxidation to carbon dioxide and water |
(C 6 H 10 O 5) n + 6nO 2 (t °) → 6nCO 2 + 5nH 2 O |
Rice. 3. Pyroxylin.
Cellulose is mainly used for making paper, as well as for the production of esters, alcohols, glucose.
What have we learned?
Cellulose or fiber is a polymer from the class of carbohydrates, consisting of β-glucose residues. It is part of plant cell walls. It is a white, tasteless substance that forms fibers that are poorly soluble in water and organic solvents. Cellulose is isolated from wood by pulping. The compound enters into esterification and hydrolysis reactions, and can decompose in the absence of air. When completely decomposed, it forms water and carbon dioxide.
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Cellulose (fiber) is a plant polysaccharide, which is the most common organic substance on Earth. Cellulose is a natural polymer-polysaccharide. This substance is white, tasteless and odorless, insoluble in water, having a fibrous structure.
Cellulose is used to make various semi-synthetic fibers. They are called viscose fiber. The cellulose needed to make viscose fiber is usually obtained from wood.
Wood is approximately 50% cellulose and 30% lignin. Lignin is also a natural polymer, but it is not a carbohydrate. The skeletal structure of the monomeric unit of lignin is as follows:
To obtain cellulose, soft wood is used, for example, pine or fir. Lignin is removed by heating the wood chips in a calcium hydrosulfite solution containing excess sulfur dioxide. In this solution, the lignin dissolves, after which the cellulose fiber is separated by filtration. The product is subjected to milling to obtain wood pulp. Pure cellulose is obtained by treating wood pulp with the Schweitzer reagent, which is an ammonia solution of copper (II) hydroxide. After the addition of dilute mineral acid, pure cellulose precipitates.
Physical properties: it is a white substance, tasteless and odorless, insoluble in water, having a fibrous structure. It dissolves in an ammonia solution of copper (II) hydroxide - Schweitzer's reagent.
This biopolymer has high mechanical strength and acts as a supporting material for plants, forming the wall of plant cells. A large amount of cellulose is found in wood tissues (40-55%), in flax fibers (60-85%) and cotton (95-98%). The main component of the plant cell membrane. Formed in plants during photosynthesis.
Wood consists of 50% cellulose, and cotton and linen, hemp are almost pure cellulose. Chitin (an analogue of cellulose) is the main component of the external skeleton of arthropods and other invertebrates, as well as in the cell walls of fungi and bacteria.
Structure: consists of residues in - glucose
Obtained from wood.
Application: cellulose is used in the production of paper, artificial fibers, films, plastics, paints and varnishes, smokeless powder, explosives, solid rocket fuel, to obtain hydrolytic alcohol, etc. Production of acetate silk - artificial fiber, plexiglass, non-combustible film from cellulose acetate. Obtaining smokeless powder from triacetylcellulose (pyroxylin). Obtaining collodion (dense film for medicine) and celluloid (manufacturing of films, toys) from diacetylcellulose. Production of threads, ropes, paper. Obtaining glucose, ethyl alcohol (for rubber production)
The most important cellulose derivatives are:
methylcellulose (cellulose methyl ethers) of the general formula
n (x = 1, 2 or 3);
cellulose acetate (cellulose triacetate) - an ester of cellulose and acetic acid n
nitrocellulose (cellulose nitrates) - cellulose nitrate esters:
n (x = 1, 2 or 3).
Chemical properties
Hydrolysis of (C6H10O5)n + nH2O t,H2SO4 > nC6H12O6
Hydrolysis proceeds in steps:
(C6H10O5)n > (C6H10O5)m > xC12H22O11 > n C6H12O6 (Note, m starch dextrins maltose glucose 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 (the formation of esters). Of greatest practical importance are reactions with nitric acid and acetic anhydride. Cellulose does not give a "silver mirror" reaction. derivative experimental industrial Nitration: (C6H7O2(OH)3)n + 3nHNO3 H2SO4(conc.)> (C6H7O2(ONO2)3)n + 3nH2O pyroxylin cellulose cellulose trinitrate Fully esterified fiber is known as pyroxylin, which, after appropriate processing, turns into smokeless powder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which is called colloxylin in the technique. It is also used in the manufacture of gunpowder and solid propellants. In addition, celluloid is made on the basis of colloxylin. Interaction with acetic acid: (C6H7O2(OH)3)n + 3nCH3COOH H2SO4(conc.)> (C6H7O2(OCOCH3)3)n + 3nH2O When cellulose reacts with acetic anhydride in the presence of acetic and sulfuric acids, triacetylcellulose is formed. Triacetylcellulose Triacetylcellulose (or cellulose acetate) is a valuable product for the manufacture of non-combustible film and acetate silk. The solvent evaporates and the streams of the solution turn into the thinnest threads of acetate silk. Celluloid, which was previously used to make photographic and film films, is obtained by treating cellulose with dilute nitric acid and mixing the resulting product with camphor. Celluloid is extremely flammable because it burns very violently. This caused serious fires in movie theaters and hospital radiology rooms. Currently, celluloid has been replaced by cellulose acetate for the manufacture of photographic and film. Cellulose (fiber) is a plant polysaccharide, which is the most common organic substance on Earth. 1. Physical properties
This substance is white, tasteless and odorless, insoluble in water, having a fibrous structure. It dissolves in an ammonia solution of copper (II) hydroxide - Schweitzer's reagent. Video experiment "Dissolution of cellulose in an ammonia solution of copper (II) hydroxide"
2. Being in nature
This biopolymer has high mechanical strength and acts as a supporting material for plants, forming the wall of plant cells. A large amount of cellulose is found in wood tissues (40-55%), in flax fibers (60-85%) and cotton (95-98%). The main component of the plant cell membrane. Formed in plants during photosynthesis. Wood consists of 50% cellulose, and cotton and linen, hemp are almost pure cellulose. Chitin (an analogue of cellulose) is the main component of the external skeleton of arthropods and other invertebrates, as well as in the cell walls of fungi and bacteria. 3. Structure
Consists of β-glucose residues 4. Receipt
Obtained from wood 5. Application
Cellulose is used in the production of paper, artificial fibers, films, plastics, paints and varnishes, smokeless powder, explosives, solid rocket fuel, to produce hydrolytic alcohol, etc. · Obtaining acetate silk - artificial fiber, plexiglass, non-combustible film from cellulose acetate. Obtaining smokeless powder from triacetylcellulose (pyroxylin). · Obtaining collodion (dense film for medicine) and celluloid (manufacturing of films, toys) from diacetylcellulose. · Manufacture of threads, ropes, paper. Obtaining glucose, ethyl alcohol (for rubber production) The most important cellulose derivatives are: N( X= 1, 2 or 3); - cellulose acetate(cellulose triacetate) - an ester of cellulose and acetic acid - nitrocellulose(cellulose nitrates) - cellulose nitrate esters: N( X= 1, 2 or 3). 6. Chemical properties
Hydrolysis
(C 6 H 10 O 5) n + nH 2 O t,H2SO4→ nC 6 H 12 O 6
glucose
Hydrolysis proceeds in steps: (C 6 H 10 O 5) n → (C 6 H 10 O 5) m → xC 12 H 22 O 11 → n C 6 H 12 O 6 (
Note, m starch dextrinymaltoseglucose
Video experience "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 (the formation of esters). Of greatest practical importance are reactions with nitric acid and acetic anhydride. Cellulose does not give 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 experience "Obtaining and properties of nitrocellulose"
Fully esterified fiber is known as pyroxylin, which, after appropriate processing, turns into smokeless powder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which is called colloxylin in the technique. It is also used in the manufacture of gunpowder and solid propellants. In addition, celluloid is made on the basis of 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. Triacetylcellulose (or cellulose acetate) is a valuable product for the manufacture of incombustible film andacetate silk. To do this, cellulose acetate is dissolved in a mixture of dichloromethane and ethanol, and this solution is forced through spinnerets into a stream of warm air. And the die itself schematically looks like this:
1 - spinning solution, The solvent evaporates and the streams of the solution turn into the thinnest threads of acetate silk. Speaking about the use of cellulose, one cannot but say that a large amount of cellulose is consumed for the manufacture of various papers. Paper- This is a thin layer of fiber fibers, glued and pressed on a special paper machine. Which consists of the remains of a glucose molecule and is a necessary element for the formation of the shell of all plant cells. Molecules have it and contain three hydroxyl groups. Due to this, it exhibits properties. Cellulose is a white solid that can reach temperatures of 200°C without breaking down. But when the temperature rises to 275 ° C, it begins to ignite, which indicates that it belongs to combustible substances. If we look at cellulose under a microscope, we can see that its structure is formed by fibers having a length of no more than 20 mm. Cellulose fibers are connected by many hydrogen bonds, but they do not have branches. This gives the cellulose the greatest strength and ability to maintain elasticity. Remains of glucose molecules that make up cellulose are formed at. Sulfuric acid and iodine in the process of hydrolysis stain cellulose blue, and just iodine brown. There are many reactions with cellulose in which new molecules are formed. Cellulose reacts with nitric acid to form nitrocellulose. And in the process with acetic acid, cellulose triacetate is formed. Cellulose does not dissolve in water. Its most effective solvent is an ionic liquid. Wood consists of 50% cellulose. By long-term cooking of wood chips in a solution of reagents, and then cleaning the resulting solution, you can get it in its pure form. Methods for pulping differ in the type of reagents. They can be acidic or alkaline. Acidic reagents contain sulfurous acid and are used to obtain cellulose from low-resinous trees. There are two types of alkaline reagents: soda and sulfate. Thanks to soda reagents, cellulose can be obtained from deciduous trees and annual plants. But using this reagent, cellulose is very expensive, so sodium reagents are rarely used or not used at all. The most common method for producing cellulose is the method based on sulfate reagents. Sodium sulfate is the basis for white liquor, which is used as a reagent and is suitable for obtaining cellulose from any plant material. Cellulose and its esters are used to create artificial fibers, viscose and acetate. Wood pulp is used to create a variety of things: paper, plastics, explosive devices, varnishes, etc. The everyday objects that have become familiar to us, which are ubiquitous in our daily life, could not be imagined without the use of organic chemistry products. Long before Anselm Payat, as a result of which he was able to discover and describe in 1838 the polysaccharide that received "cellulose" (a derivative of the French cellulose and the Latin cellula, which means "cell, cell"), the property of this substance was actively used in the production of the most irreplaceable things. The expansion of knowledge about cellulose has led to the emergence of a wide variety of things made on its basis. Paper of various grades, cardboard, parts made of plastic and artificial viscose, copper-ammonia), polymer films, enamels and varnishes, detergents, food additives (E460) and even smokeless powder are products of the production and processing of cellulose. In its pure form, cellulose is a white solid with rather attractive properties, showing high resistance to various chemical and physical influences. Nature has chosen cellulose (fiber) as its main building material. In the plant world, it forms the basis for trees and other higher plants. Cellulose is found in its purest form in nature in the hairs of cotton seeds. The unique properties of this substance are determined by its original structure. The cellulose formula has a common record (C6 H10 O5) n from which we see a pronounced polymer structure. The β-glucose residue repeating a huge number of times, having a more expanded form as -[C6 H7 O2 (OH) 3]-, combines into a long linear molecule. The molecular formula of cellulose determines its unique chemical properties to withstand the effects of aggressive environments. Also, cellulose has a high resistance to heat, even at 200 degrees Celsius, the substance retains its structure and does not collapse. Self-ignition occurs at a temperature of 420°C. Cellulose is no less attractive for its physical properties. cellulose in the form of long filaments containing from 300 to 10,000 glucose residues without side branches, largely determines the high stability of this substance. The glucose formula shows how many give cellulose fibers not only great mechanical strength, but also high elasticity. The result of the analytical processing of many chemical experiments and studies was the creation of a model of the cellulose macromolecule. It is a rigid helix with a step of 2-3 elementary links, which is stabilized by intramolecular hydrogen bonds. Not the formula of cellulose, but the degree of its polymerization is the main characteristic for many substances. So in untreated cotton, the number of glucoside residues reaches 2500-3000, in purified cotton - from 900 to 1000, purified wood pulp has an indicator of 800-1000, in regenerative cellulose their number is reduced to 200-400, and in industrial cellulose acetate it ranges from 150 up to 270 "links" in a molecule. The main product for the production of cellulose is wood. The main technological process of production involves cooking wood chips with various chemicals, followed by cleaning, drying and cutting the finished product. The subsequent processing of cellulose makes it possible to obtain a variety of materials with desired physical and chemical properties, which make it possible to produce a wide variety of products, without which the life of a modern person is difficult to imagine. The unique formula of cellulose, corrected by chemical and physical processing, became the basis for obtaining materials that have no analogues in nature, which allowed them to be widely used in the chemical industry, medicine and other branches of human activity.
- methylcellulose(cellulose methyl ethers) of the general formula
2 - die,
3 - fibers.
Physical properties of cellulose
Chemical properties of cellulose
How is cellulose obtained?
Cellulose application
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