Equation for the reaction of glucose with carboxylic acids. What is glucose? Definition, chemical and physical properties

Glucose C 6 H 12 O 6- a monosaccharide that is not hydrolyzed to form simpler carbohydrates.

As can be seen from the structural formula, glucose is both a polyhydric alcohol and an aldehyde, that is aldehyde alcohol. In aqueous solutions, glucose can take a cyclic form.

Physical properties

Glucose is a colorless crystalline substance with a sweet taste, highly soluble in water. Less sweet than beet sugar.

1) it is found in almost all plant organs: in fruits, roots, leaves, flowers;
2) especially a lot of glucose in grape juice and ripe fruits, berries;
3) glucose is found in animal organisms;
4) it contains approximately 0.1% in human blood.

Features of the structure of glucose:

1. The composition of glucose is expressed by the formula: C6H12O6, it belongs to polyhydric alcohols.
2. If a solution of this substance is added to freshly precipitated copper (II) hydroxide, a bright blue solution is formed, as in the case of glycerin.
Experience confirms that glucose belongs to polyhydric alcohols.
3. There is an ester of glucose, in the molecule of which there are five residues of acetic acid. From this it follows that there are five hydroxyl groups in the carbohydrate molecule. This fact explains why glucose dissolves well in water and tastes sweet.
If a glucose solution is heated with an ammonia solution of silver oxide (I), then a characteristic "silver mirror" will be obtained.
The sixth oxygen atom in the molecule of the substance is part of the aldehyde group.
4. To get a complete picture of the structure of glucose, you need to know how the skeleton of the molecule is built. Since all six oxygen atoms are part of the functional groups, therefore, the carbon atoms that form the skeleton are directly connected to each other.
5. The chain of carbon atoms is straight, not branched.
6. An aldehyde group can only be at the end of an unbranched carbon chain, and hydroxyl groups can be stable only at different carbon atoms.

Chemical properties

Glucose has chemical properties characteristic of alcohols and aldehydes. In addition, it also has some specific properties.

1. Glucose is a polyhydric alcohol.

Glucose with Cu (OH) 2 gives a blue solution (copper gluconate)

2. Glucose - aldehyde.

a) Reacts with an ammonia solution of silver oxide to form a silver mirror:

CH 2 OH-(CHOH) 4 -CHO + Ag 2 O → CH 2 OH-(CHOH) 4 -COOH + 2Ag

gluconic acid

b) With copper hydroxide gives a red precipitate Cu 2 O

CH 2 OH-(CHOH) 4 -CHO + 2Cu(OH) 2 → CH 2 OH-(CHOH) 4 -COOH + Cu 2 O↓ + 2H 2 O

gluconic acid

c) It is reduced by hydrogen to form a six-hydric alcohol (sorbitol)

CH 2 OH-(CHOH) 4 -CHO + H 2 → CH 2 OH-(CHOH) 4 -CH 2 OH

3. Fermentation

a) Alcoholic fermentation (to obtain alcoholic beverages)

C 6 H 12 O 6 → 2CH 3 -CH 2 OH + 2CO 2

ethanol

b) Lactic acid fermentation (souring of milk, fermentation of vegetables)

C 6 H 12 O 6 → 2CH 3 -CHOH-COOH

lactic acid

Application, meaning

Glucose is produced in plants during photosynthesis. Animals get it from food. Glucose is the main source of energy in living organisms. Glucose is a valuable nutritious product. It is used in confectionery, in medicine as a tonic, for the production of alcohol, vitamin C, etc.

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Glucose has chemical properties characteristic of alcohols and aldehydes. In addition, it also has some specific properties:

D-glucose gives general reactions to aldoses, it is a reducing sugar, forms a number of derivatives due to the aldehyde group (phenylhydrazone, n- bromophenylhydrazone, etc.). Glucose ozazone is identical to mannose ozonose, which is an epimer of glucose, and fructose ozazone. When glucose is reduced, the six-hydric alcohol sorbitol is formed; during the oxidation of the aldehyde group of glucose - monobasic D-gluconic acid, with further oxidation - dibasic D-sugar acid. When only the secondary alcohol group of glucose is oxidized (provided that the aldehyde group is protected), D-glucuronic acid is formed. The formation of D-glucuronic acid from D-glucose can occur under the action of glucose oxidase or dehydrogenase enzymes. During the pyrolysis of D-glucose, glycosans are formed: a-glycosan and levoglucosan (b-glucosan).

For the quantitative determination of glucose, calorimetric, iodometric and other methods are used.

Good day, dear tenth graders!

We are beginning to get acquainted with a new group of organic compounds - carbohydrates.
Carbohydrates ... And these are the very sweets that you love so much (fruits, cakes, sweets, jam, chocolate, etc., especially grapes contain a lot of carbohydrates). Carbohydrates are vital substances that every body needs. These substances are consumed, and a person must constantly replenish their reserves. It is clear that the substances that make up the tissues of the body are not similar to those that it eats. The human body processes food and in the course of its life constantly consumes energy, which, as we know, is released during oxidation in body tissues, carbohydrates are part of nucleic acids that carry out protein biosynthesis and the transmission of hereditary traits.
Animals and humans do not synthesize carbohydrates. In green plants, with the participation of chlorophyll and sunlight, a number of processes are carried out to convert carbon dioxide absorbed from the air and water absorbed from the soil. The end product of this process, photosynthesis, is a complex carbohydrate molecule.

Carbohydrates are an important source of energy for the body, they are involved in metabolism. The main sources of carbohydrates are plant foods.

Physiologists have found that physical activity, which is 10 times higher than usual, a person who follows a fat diet loses strength in half an hour. But a carbohydrate diet allows you to withstand the same load for four hours. It turns out that getting the body of energy from fat is a long process. This is due to the low reactivity of fats, especially their hydrocarbon chains. Carbohydrates, although they provide less energy than fats, however, release it much faster. Therefore, if a thorough load is ahead, it is preferable to eat sweet rather than fatty.

Classification of carbohydrates.

Qualitative composition carbohydrates.

The structure of the glucose molecule. Isomerism.

Conclusion: thus, glucose is an aldehyde alcohol, more precisely, a polyhydric aldehyde alcohol. It has been established that not only its aldehyde form is found in a glucose solution; but also molecules of a cyclic structure.
It has been established that at the third carbon atom the group - OH is located differently than at other carbon atoms, the common structure of glucose looks like this:

The transformation of a linear molecule into a cyclic molecule is understandable if we remember that carbon atoms can rotate around sigma bonds. The aldehyde group can approach the hydroxyl group of the 5th carbon atom, since the oxygen atom of the carbonyl group carries a partial - charge, and the hydrogen atom of the hydroxyl group carries a partial + charge.

A peculiar chemical process: there is a rupture of the -bond of the carbonyl group, a hydrogen atom is attached to the oxygen atom, and the oxygen atom of the hydroxyl group closes the chain with the carbon atom. Cyclic forms are in balance, turning into alpha and beta form. Thus, in an aqueous solution of glucose are three isomeric forms. The crystalline glucose molecule has an alpha form, when dissolved in water, an open form, and then again a cyclic beta form. Such isomerism called dynamic (tautomerism).

Chemical properties glucose.
Monosaccharides enter into chemical reactions characteristic of carbonyl and hydroxyl groups.

1) Silver mirror reaction
You can prove the presence of an aldehyde group in glucose using an ammonia solution of silver oxide. This reaction is called the silver mirror reaction. It is used as quality for opening aldehydes . The aldehyde group of glucose is oxidized to a carboxyl group. Glucose is converted to gluconic acid.
CH 2 OH - (CHOH) 4 - COOH + Ag 2 O \u003d CH 2 OH - (CHOH) 4 - COOH + 2Ag
(The reaction of a silver mirror is used in industry for silvering mirrors, making flasks for thermoses, Christmas tree decorations).


2) Interaction of glucose with copper (II) hydroxide

4) Specific properties. Of great importance are the processes of glucose fermentation occurring under the action of organic enzyme catalysts (they are produced by microorganisms).

a) alcoholic fermentation (by the action of yeast)

C 6 H 12 O 6 = 2C 2 H 5 OH + 2CO 2

• in baking, glucose improves fermentation conditions, gives porosity and good taste to products, slows down hardening;

• in the production of ice cream, it lowers the freezing point, increases its hardness;

• in the production of fruit preserves, juices, liqueurs, wines, soft drinks, since glucose does not mask the aroma and taste;

• in the dairy industry, in the manufacture of dairy products and baby food, it is recommended to use glucose in a certain proportion with sucrose to give these products a higher nutritional value;

• in veterinary medicine;

• in poultry farming;

• in the pharmaceutical industry.

Fixing:

Alkylation. The result of the interaction depends on the nature of the alkylating agent and the reaction conditions. Methanol in the presence of dry HCl methylates only hemiacetal or semiketal hydroxyl, forming a mixture of b- and c-methylglucopyranosides. Alkylation of the remaining hydroxyl groups can only be carried out by the action of strong alkylating agents, for example, dimethyl sulfate (CH 3) 2 SO 4 and alkali.

b-D-glucopyranose methyl-b-D-glucopyranoside methyl-b-D-glucopyranoside

methyl-2,3,4,5-tetramethyl-b-D-glucopyranoside

Acylation. Glucose is readily esterified to form esters. Acylation is usually carried out with an excess of acetic anhydride in the presence of acidic (H 2 SO 4 , ZnCl 2 ) or basic (CH 3 COONa) catalysts. The ratio between b- and b-anomeric pentaacetates can be controlled by changing the reaction conditions.

At elevated temperatures, as a result of interconversions of b- and b-acetates, a mixture is formed, consisting of 90% of b- and 10% of b-anomers. At 0 °C, mainly the β-anomer is formed.

Reactions at the carbonyl group

As a result of the interaction of D-glucose with an excess of phenylhydrazine, phenylhydrazone is first formed, which is dehydrated by the second phenylhydrazine molecule, which in this case turns into ammonia and aniline with the formation of the second carbonyl group. The subsequent reaction of the third phenylhydrazine molecule leads to bis-phenylhydrazone, or ozone.

Reactions of glucose with hydroxylamine. Glucose oximes in solutions form tautomeric cyclic b- and c-forms.

One of the ways to shorten the glucose chain is based on this reaction:

The dehydration of the oxime under the action of acetic anhydride is accompanied by the simultaneous acylation of all hydroxyl groups. As a result of the subsequent transesterification with the formation of methyl acetate and the simultaneous elimination of HCN, an aldose is formed with a carbon chain shortened by one carbon atom compared to the original one, D-arabinose.

Glucose dehydration

Occurs under the action of mineral acids and leads to a derivative of furan - 4-hydroxymethylfurfural, which, losing a formic acid molecule, turns into levulinic (4-oxopentanoic) acid.

Oxidation reactions

Glucose oxidation can be carried out with oxidizing agents of various strengths, which, accordingly, give different oxidation products.

Glucose is oxidized to glyconic acid in mild conditions such weak oxidizing agents as:

Bromine water Br 2 / H 2 O

Tollens' reagent ("silver mirror" reaction):

Fehling's solution: CuSO 4 + NaOH + KOOC-CHOHCHOHCOONа.

As a result of the reaction, a red precipitate of copper oxide precipitates.

Strong oxidizing agents, such as concentrated HNO3, oxidize both terminal carbons of glucose to form sugar (glycar) dibasic acids:

In an alkaline environment, oxidation usually proceeds with gap C-C bonds and the formation of oxidation products with a shorter carbon chain length.

Cleavage of glucose is also carried out by the action of the periodate ion IO - 4 or lead tetraacetate (CH3COO) 4 Rb - specific reagents for the b-glycol group.

Analysis of the oxidation products allows you to establish the structure of monosaccharides.

As a result of the breakdown of D-glucose, other reaction products are formed:

Recovery reactions

The reduction of glucose with sodium amalgam in dilute H 2 SO 4 , NaBH 4 in water or catalytically with hydrogen over Ni, Pt, Pd is easy, with the formation of polyhydric alcohols. Glucose, when reduced, gives D-sorbitol.

Fermentation of monosaccharides

A distinctive property of monosaccharides is their ability to enter into anaerobic (without oxygen access) cleavage under the influence of microorganisms or enzymes isolated from them. Such processes are called fermentation.

The nature of fermentation products depends on the type of microorganism, the conditions under which it is carried out (pH, the presence or absence of oxygen, the nature of the substrate, etc.).

Alcoholic fermentation is the breakdown of glucose under anaerobic conditions by a mixture of enzymes - zymase, which is secreted by yeast fungi.

As a result of anaerobic enzymatic cleavage, glucose is converted to pyruvic acid, which is decarboxylated by pyruvate decarboxylase. The resulting acetaldehyde is reduced to ethanol by reduced nicotinamide adenine dinucleotide (NADH), which is part of the alcohol dehydrogenase enzyme.

Acetic fermentation. If fermentation is carried out in the presence of oxygen, then as the main product, acetic acid. In the atmosphere of air, the alcohol arising during the fermentation process is oxidized by oxygen during catalysis by alcohol oxidase, secreted by acetic acid bacteria (Acetobacter).

CH 3 CH 2 OH > CH 3 COOH + H 2 O 2

Lactic acid fermentation. In enzymatic fermentation, under the action of Lactobacillus delbruckii, pyruvic acid is reduced to lactic acid with the help of NADH.

d) Citric acid fermentation of glucose can be carried out under the action of Aspergillusniger, Citromycespfefferianus, Citromycesgraber.

Glucomza (from other Greek glkhket sweet) (C 6 H 12 O 6), or grape sugar, or dextrose, is found in the juice of many fruits and berries, including grapes, from which the name of this type of sugar comes from. It is a monosaccharide and a six-atomic sugar (hexose). The glucose link is part of polysaccharides (cellulose, starch, glycogen) and a number of disaccharides (maltose, lactose and sucrose), which, for example, are quickly broken down in the digestive tract into glucose and fructose.

Glucose belongs to the group of hexoses, it can exist in the form of β-glucose or β-glucose. The difference between these spatial isomers lies in the fact that at the first carbon atom in β-glucose the hydroxyl group is located under the plane of the ring, and in β-glucose it is above the plane.

Glucose is a bifunctional compound, because. contains functional groups - one aldehyde and 5 hydroxyl. Thus, glucose is a polyhydric aldehyde alcohol.

The structural formula of glucose is:

Short formula

Chemical properties and structure of glucose

It has been experimentally established that aldehyde and hydroxyl groups are present in the glucose molecule. As a result of the interaction of the carbonyl group with one of the hydroxyl groups, glucose can exist in two forms: open chain and cyclic.

In glucose solution, these forms are in equilibrium with each other.

For example, in an aqueous solution of glucose, the following structures exist:

Cyclic b- and c-forms of glucose are spatial isomers that differ in the position of the hemiacetal hydroxyl relative to the plane of the ring. In β-glucose, this hydroxyl is in the trans position to the hydroxymethyl group -CH 2 OH, in β-glucose - in the cis position. Taking into account the spatial structure of the six-membered ring, the formulas of these isomers have the form:

In the solid state, glucose has a cyclic structure. Ordinary crystalline glucose is the b form. In solution, the s-form is more stable (at equilibrium, it accounts for more than 60% of the molecules). The proportion of the aldehyde form in equilibrium is insignificant. This explains the lack of interaction with fuchsine sulphurous acid ( qualitative reaction aldehydes).

For glucose, in addition to the phenomenon of tautomerism, structural isomerism with ketones is characteristic (glucose and fructose are structural interclass isomers)

Chemical properties of glucose:

Glucose has chemical properties characteristic of alcohols and aldehydes. In addition, it also has some specific properties.

1. Glucose is a polyhydric alcohol.

Glucose with Cu (OH) 2 gives a blue solution (copper gluconate)

• 2. Glucose - aldehyde.
• a) Reacts with an ammonia solution of silver oxide to form a silver mirror:

CH 2 OH-(CHOH) 4 -CHO + Ag 2 O> CH 2 OH-(CHOH) 4 -COOH + 2Ag

gluconic acid

b) With copper hydroxide gives a red precipitate Cu 2 O

CH 2 OH-(CHOH) 4 -CHO + 2Cu(OH) 2 > CH 2 OH-(CHOH) 4 -COOH + Cu 2 Ov + 2H 2 O

gluconic acid

c) It is reduced by hydrogen to form a six-hydric alcohol (sorbitol)

CH 2 OH-(CHOH) 4 -CHO + H 2 > CH 2 OH-(CHOH) 4 -CH 2 OH

• 3. Fermentation
• a) Alcoholic fermentation (to obtain alcoholic beverages)

C 6 H 12 O 6 > 2CH 3 -CH 2 OH + 2CO 2 ^

ethanol

b) Lactic acid fermentation (souring of milk, fermentation of vegetables)

C 6 H 12 O 6 > 2CH 3 -CHOH-COOH

lactic acid