§5. Determination of one or more substances based on qualitative reactions. Experimental procedure
Problem 10
The analytical laboratory of a pharmaceutical enterprise received ampoules and vials with a solution of a medicinal substance having the following chemical structure and not meeting the requirements of the ND in the “Description” section - yellowing of the solution was observed.
Give justification for possible changes in the drug substance during the preparation of the dosage form.
Give the Russian, Latin and rational name of the drug. Describe the physical and chemical properties ( appearance, solubility, spectral and optical characteristics) and their use for quality assessment.
According to the chemical properties, suggest identification reactions and quantification methods. Write the reaction equations.
Carbohydrates
Carbohydrates constitute a large group of natural substances that perform various functions in plant and animal organisms. Carbohydrates are obtained primarily from plant sources.
The most significant drug in this group is glucose. Slightly less sucrose and starch.
Properties of medicinal substances from the carbohydrate group. 
The ND requirements for the quality of glucose as a medicinal product correspond to the requirements for chemically pure substances. The characteristic physical properties of glucose are optical activity with a pronounced rotation of the plane of polarization (specific rotation of a 10% glucose solution +52.3°), T pl of anhydrous glucose.
For glucose, which is obtained in the form of monohydrate, the amount of water of crystallization is an indicator of the quality of the drug. The content of water of crystallization should be 10% by weight of glucose monohydrate.
In freshly prepared glucose solutions, mutarotation occurs (a change in the rotation angle over time).
Mutarotation can be accelerated by adding ammonia solution (no more than 0.1%) to the glucose solution.
For α-D-glucose, the rotation angle is +109.6°, and for β-D-glucose +20.5°.
CHEMICAL PROPERTIES
Glucose is a monosaccharide, sucrose is an oligosaccharide, starch is a polysaccharide. Monosaccharides, being substances with dual functions, alcohols and aldehydes. Oligosaccharides and polysaccharides undergo hydrolysis to monosaccharides.
Reactions to alcohol hydroxyls
As polyhydric alcohols, glucose, sucrose (like ethylene glycol and glycerol) are able to react with copper (II.) hydroxide to form blue complex compounds
Drugs from the carbohydrate group are also capable of esterification reactions.
Reactions to aldehyde group
Oxidation.
Depending on the oxidation conditions, monosaccharides are converted into different products. In an alkaline environment, monosaccharides are oxidized under the influence of such mild oxidizing agents as Tollens and Fehling reagents). Tollens' reagent undergoes a “silver mirror” reaction, which is characteristic of aldehydes. Consequently, monosaccharides enter into this reaction in their open (aldehyde) form
When using these reactions in pharmaceutical analysis, their sensitivity must be taken into account. Yes, for confirmationauthenticity of the drug with an aldehyde group in a molecule, a reaction with silver nitrate and Fe reagent linga , and for aldehyde detection as impurities should be used in medicinal preparations more sensitivereaction (with Nessler's solution).
Glycosides and other carbohydrate derivatives that do not contain hemiacetal hydroxyl cannot transform into the aldehyde form and therefore do not have reducing ability and do not react with these reagents.
Authenticity G lucose ( As a test of authenticity, the FS uses the reaction of glucose oxidation with Fehling's reagent).
There are other sensitive and specific reactions to glucose that are not included in the ND. Thus, under the action of concentrated sulfuric acid, furfural is formed, which, with any phenol (resorcinol, thymol, a-naphthol) or aromatic amine, forms colored reaction products (red):
With copper (II) sulfate, glucose, when alkalized (without heating!), forms a soluble violet-blue complex. Thus, the presence of both aldehyde and alcohol functional groups is simultaneously proven.
The definition of specific rotation is also regulated.
Purity. The Global Fund article on glucose includes standard tests: transparency and color of the solution, acidity, presence of chlorides, sulfates, calcium, barium, dextrin, arsenic. Injection solutions are additionally tested for pyrogenicity.
quantitation .
The Global Fund does not regulate quantitative new definition of substance. In glucose preparations, in particular in solutions for injections, glucose is determined polarimetrically.
Quantitative determination of glucose preparation is based on analogy with formaldehyde. Iodine, hydrogen peroxide, and Nessler's reagent can be used as an oxidizing agent.
The formation of hypoiodite creates the possibility of formaldehyde oxidation.
After formaldehyde has oxidized, sulfuric acid is added, which displaces iodine from the remaining salts (NaOI, NaOI 3) and an equivalent amount of sodium iodide.
The released iodine is titrated with sodium thiosulfate. The difference between the amount of iodine and sodium thiosulfate used for titrating iodine is equal to the amount of iodine used for the oxidation of formaldehyde.
Target: developing skills in recognizing organic substances using characteristic (qualitative) reactions, consolidating skills in drawing up reaction equations for the properties and production of substances, solving experimental problems.
lead time: 2 hours
Theoretical material
Almost every organic substance can be determined using characteristic reactions. These reactions are called qualitative.
Affiliation organic matter to certain classes of compounds, their structure and degree of purity are established using elemental and functional analysis. Qualitative elemental analysis allows one to determine the qualitative composition of the molecules of an organic compound; Quantitative elemental analysis establishes the elemental composition of a compound and its simplest formula.
The structure of an organic compound can be considered conclusively proven if a counter synthesis is carried out; systematic chemical analysis, including: preliminary tests, qualitative reactions to functional and non-functional groups, various derivatives were obtained; spectral analysis methods were carried out.
As a result, before performing the main identification task, which consists in determining the structure of a polyfunctional organic substance or identifying the components of a binary mixture, it is advisable to develop methods for detecting functional groups (qualitative reactions, characteristic absorption frequencies in IR spectra, UV and NMR spectra), obtaining and purifying functional derivatives of each of the five most important classes of organic compounds (alcohols, phenols, aldehydes or ketones, carboxylic acids and amines).
Functional analysis and identification of organic substances begin with preliminary tests, including: determination of physical constants, combustion test, solubility in water and organic solvents, qualitative analysis. Belonging to classes of organic substances can be determined by their relationship to reagents
Experience No. 1. Glucose is an aldehyde alcohol
Obtain a small amount of copper hydroxide. Add 2-3 ml to the resulting sediment. glucose solution. Shake the test tube until the precipitate dissolves and a bright blue solution is obtained. This is proof of what? Carefully heat the top of the liquid in the flame of a spirit lamp until it begins to boil. Observe the transition of the blue color to green, yellow, the appearance of a red, then brown precipitate. What does his appearance mean? Draw a conclusion about the recognition of glucose and what it is. Write the reaction equation.
Experience No. 2."Silver Mirror" reaction
Pour 2 ml into a clean test tube. ammonia solution of silver nitrate, add 5-10 drops of glucose solution. Gently heat the mixture. Write down observations, reaction equation. Draw a conclusion about glucose recognition. Why is this reaction called the “silver mirror” reaction?
Experience No. 3. Sucrose
a) Obtain a copper hydroxide precipitate in a test tube. Pour the sugar solution into it and shake. What happened to the sediment? Why? What is the structure of sucrose? Heat. Is brown sediment forming? Draw a conclusion.
b) Pour a little sugar solution into a test tube, add a drop of sulfuric acid and boil.
Write the equation for the reaction of an aqueous solution of sucrose with sulfuric acid. What is this reaction called?
c) Prove experimentally the formation of glucose from sucrose. To do this, add 2-3 drops of copper sulfate and sodium hydroxide to the solution until a precipitate forms. Heat. Pay attention to the color change. Draw a conclusion. What substance is formed during the hydrolysis of sucrose?
Experience No. 4. Starch
Pour a little starch into the bottom of the test tube, add a little cold water, shake and pour into another test tube with hot water. Boil until a starch paste forms.
Add a little alcohol solution of iodine to the test tube. What is being observed? Draw a conclusion about the recognition of starch.
Experience No. 5. Starch hydrolysis
Add 1-3 drops of sulfuric acid to the blue starch paste solution. Boil the solution until the blue color disappears. Why did the blue color disappear? What happened to starch? What substance was formed as a result of the reaction? Write the reaction equation. Draw a conclusion.
experimental part
Recognize substances using characteristic reactions, write reaction equations, and indicate conditions.
1 option
1. Using one reagent, determine glucose and glycerol. Write down the reaction equations
Option 2
1. In test tubes there is sucrose and glucose. Determine each substance using one reagent and write the reaction equations.
Option 3
1. Prove experimentally that glucose is an aldehyde alcohol. Write the reaction equations.
Option 4
1. Using one reagent, determine glycerol and aldehyde. Write the reaction equations.
Option 5
1. Identify the solutions provided: ethyl alcohol and glycerin. Write the reaction equations.
1. What reactions are called qualitative?
2. What is a functional group?
3. What are the functional groups of alcohols, aldehydes, acids?
Laboratory lesson No. 4
1. We need to identify three substances: glycerol (polyhydric alcohol), aldehyde, glucose (carbohydrate).
One of the characteristic reactions for these substances is interaction with Cu(OH) 2.
First we get copper(II) hydroxide. To do this, add a little NaOH solution to the copper sulfate.
CuSO 4 + 2NaOH<----->Cu(OH) 2 ↓ + Na 2 SO 4
A blue precipitate of Cu(OH) 2 falls out.
1) Add a little aldehyde to the formed precipitate and heat the mixture.
As a result, a red precipitate Cu 2 O↓ is formed.
2) Now add glycerin drop by drop to Cu(OH) 2 and shake the mixture. The precipitate dissolves, resulting in a bright blue solution. A stable complex of glycerol and copper is formed. 
3) Glucose, in its chemical properties, is an aldehyde alcohol, i.e. it exhibits the properties of both aldehydes and polyhydric alcohols. As an aldehyde, it enters into reactions characteristic of this class of substances; in particular, when heated, it reacts with Cu(OH) 2 to form a red-brown precipitate Cu 2 O. As a polyhydric alcohol, glucose gives a bright blue solution when added to it fresh precipitate Cu(OH) 2. 
A red precipitate of Cu 2 O precipitates.
4) to determine these three substances from each test tube, add a little Cu(OH) 2. A bright blue solution (glucose and glycerol) is formed in two test tubes. Now let’s heat all three mixtures: a red precipitate (aldehyde and glucose) will form in two test tubes. Thus, we find out which test tube contains which substance.
2. Machine oil consists mainly of saturated hydrocarbons, and vegetable oil consists of fats formed by unsaturated acids. Vegetable oil discolors bromine water, but machine oil does not.
3. a) to receive ether Let's carry out the dehydration reaction of ethyl alcohol.
The forming ester is called diethyl. this reaction occurs only under certain conditions: heating, in the presence of H 2 SO 4, and in excess of alcohol.
b) to obtain aldehyde from alcohol, you need to use a weak oxidizing agent, for example, Cu 2+. 
Formed acetic acid.
4. Sugar is a complex organic substance containing a fairly large amount of carbon. To prove this, take some sugar and add H 2 SO 4 (conc.) to it.
Sugar, under the influence of concentrated sulfuric acid, will give up water and turn into carbon.
Concentrated H 2 SO 4 takes water from the sugar, resulting in free carbon (black substance).
5. a) for the determination of starch there is a good qualitative reaction with iodine. A stable complex of bright blue color is formed.
Drop a few drops of iodine solution onto potatoes and white bread. If a blue spot forms on foods, they contain starch.
b) to test an apple for glucose content, prepare a few drops of apple juice and add a little blue precipitate Cu(OH) 2. If the solution under study contains glucose, then first we will obtain a blue soluble glucose complex, which, when heated, will decompose to red Cu 2 O.
6. a) First, let's determine starch by adding iodine solution to each of the three substances. A blue complex is formed in a test tube with starch. Glucose and sucrose can be distinguished by their aldehyde properties. Both substances have the properties of a polyhydric alcohol, but only glucose also has the properties of an aldehyde. add Cu(OH) 2 to both test tubes, a blue solution is formed. But only when heated with glucose does a red precipitate of Cu 2 O precipitate (i.e., oxidation of the aldehyde group occurs).
b) First, let's determine starch using iodine. A blue complex is formed.
Now let’s check the acidity of the soap and glycerin solutions. Glycerin is slightly acidic, while soap is alkaline.
Glycerol also forms a blue solution with Cu(OH) 2 (property of polyhydric alcohols).
7. Heat the resulting solutions. A white precipitate will form in one of the test tubes - protein denaturation occurs. Nothing happens to glycerin when heated.
Class 891, 1ov No. 11665!
I. V. Lebedev, B. O. Lyubin and A. A. Bannikova
METHOD FOR ISOLATING CRYSTAL GLUCOSE
FROM ITS WATER SOLUTIONS
Declared on November 18, 1957 under No. 586359 in the 1st Office for Inventions and Disruptions under the Council il;.;:ps.por; USSR
Studies have shown that in the presence of 16 – 30/vol of sodium chloride by weight of glucose, the latter easily crystallizes from its supersaturated solutions in the form of a double compound compound (SvH120b) in NaCI. HBO, which forms well-shaped and easily fusible crystals.
On the other hand, as a result of studying the equipoise state of the three-component system glucose - sodium chloride - water, it was found that the specified double compound has the following two temperature ranges of decomposition. At temperatures below 28.5, the double compound (when mixed with water in certain proportions) breaks down into its component components, releasing solid phase hydrated glucose crystals; in this case, all sodium chloride and some glucose remain in solution. At temperatures above 95.5, the double compound (when mixed with water in certain proportions) decomposes into its constituent components with the release of sodium chloride crystals into the solid phase; in this case, all glucose and some sodium chloride remain in solution.
Taking into account the described properties of the double compound of glucose with sodium chloride, the following method is proposed for isolating crystalline glucose from its aqueous solutions through the double compound: the latter is decomposed with water at temperatures below 28.5, the released glucose crystals are separated from the intercrystalline liquid, which is then pressed at 92.5 and higher until sodium chloride crystallizes, after which the latter is separated from the intercrystalline solution, which is returned to the cycle.
In practice, the proposed method can be implemented approximately as follows.
The required amount of sodium chloride is introduced into the initial glucose solution, for example, by neutralizing the hydrochloric acid present in solution No. 116651 with sodium base or adding table salt, and the resulting solution is evaporated to a concentration that ensures crystallization of the double compound. Crystals of the latter are separated from the intercrystalline solution and decomposed with water at temperatures below
28.5 and the released crystalline glucose is separated from the intercrystalline solution. The latter contains an excess amount of sodium chloride compared to the composition of the double compound, which is released by evaporating the intercrystalline solution to a certain concentration and bringing its temperature to 92.5 and above.
In this case, only table salt crystals are released from the solution, which are separated from the solution. The resulting filtrate is sent for crystallization of the double compound or directly for decomposition with the release of crystalline glucose by cooling to a temperature below 28.5 and adding the required amount of water.
In the case when it is necessary to add ready-made table salt to the initial glucose solution, the drainage from the decomposition of the double compound is mixed in the required proportion with the glucose solution supplied for evaporation. and crystallization of the double compound.
Compared to direct crystallization of glucose from its solutions, the proposed method has the following advantages. The high crystallization capacity of the double compound allows the extraction of glucose from solutions of very low quality, from which it cannot be isolated by direct crystallization, thereby reducing the cost of purifying the original solutions. In addition, the process of releasing glucose through a double connection proceeds many times faster than with direct crystallization and does not require strict temperature conditions, which allows reducing the number of pieces of equipment.
Example. Isolation of crystalline glucose from solutions obtained by hydrolysis of wood with concentrated hydrochloric acid.
According to known methods of glucose production using this method of wood hydrolysis, preliminary hydrolysis of the latter is required in order to remove non-glucose sugars (xylose, mannose, galactose) that interfere with the crystallization of glucose. In addition, it uses deep ion exchange purification of solutions to remove residual amounts of HC1 and other impurities and obtain high-quality glucose solutions.
According to the proposed method, the process of isolating crystalline glucose is carried out according to the following schematic diagram, according to which both preliminary hydrolysis of cellulose and ion-exchange purification of solutions are excluded. No.ll665i
INVERTED HYDROLYZATE
eleven. (NaOH solution)
NATEALIVATION
FILTRATION
LIGHTENING
FILTRATION
VACUUM EVAPORATOR OF NEUTRALIZATE h
CRYSTALLIZATION OF DOUBLE COMPOUND (DC)
MANUAL MANUAL LS
OUTFLOW (hydrol)
CRYSTALS DS,1, DECOMPOSITION DS (water)
MANUAL MANUAL
— “CRYSTALLINE GLUCOSE (activated carbon) OTTEK I.
EVAPORATION at temperatures above 92.5
SEPARATION OF EXCESS NaC1 IN THE FORM OF CRYSTALS
OUTTEK N! (Otden of C! returns to the vacuum evaporation of the neutralizer) Subject of the invention
A method for isolating crystalline glucose from its aqueous solutions through a double compound with sodium chloride, characterized in that said double compound is decomposed with water at temperatures below 28.5, the released glucose crystals are separated from the intercrystalline liquid, which is then evaporated at 92.5 and above until crystalline ".àöèè sodium chloride separated from the intercrystalline solution, which is returned to the cycle.
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“Truth is not born in the head of an individual, it is born between people searching together, in the process of their dialogical thinking.”
MM. Bakhtin
Lesson objectives:
- educational: conduct research to study the structure, physical and chemical properties of glucose, its qualitative determination in vegetables, fruits, honey, sawdust;
- developing: develop the ability to compare, generalize, draw conclusions based on experiment, develop cognitive interest, resolve contradictions, experimental verification hypotheses;
- educational: nurturing collectivism, kindness, focus, control and mutual control skills, and a dialectical-materialistic worldview.
Lesson objectives:
- study the composition, structure and properties of glucose,
- prove experimentally that glucose is an aldehyde alcohol,
- continue to develop students’ skills and abilities to work with laboratory equipment and reagents,
- continue to develop students’ skills in working with video materials and multimedia presentations,
- develop logical thinking students, establish cause-and-effect relationships, systematize, draw conclusions.
Form: lesson-research.
Object of study: freshly prepared juices of grapes, cucumbers, honey, sawdust.
Subject of study: glucose.
Hypotheses:
- glucose contains carbon, hydrogen, and oxygen atoms;
- glucose belongs to carbohydrates and is a polyhydric aldehyde alcohol;
- glucose is included in the juice of grapes and cucumbers;
- glucose is contained in honey;
- Glucose is formed during the hydrolysis of sawdust.
Forms of work: group, individual.
Equipment:
Group 1: glucose, alcohol lamp, matches, test tube, test tube holder;
Group 2: glucose, water, magnifying glass, beaker, glass rod;
Group 3: glucose, water, universal indicator, blue litmus, copper (II) sulfate, sodium hydroxide, ammonia solution of silver (I) oxide, heating devices;
Group 4: grapes, water, wide test tube, copper (II) sulfate, sodium hydroxide, heating devices;
Group 5: fresh cucumber, grater, copper (II) sulfate, sodium hydroxide, glass, heating devices;
Group 6: four test tubes with natural honey, artificial honey, sugar solution, water, beaker, copper (II) sulfate, sodium hydroxide, heating devices;
Group 7: porcelain cup, sawdust, sand bath, sulfuric acid, water, heating devices, calcium hydroxide;
Interactive whiteboard, laptop, safety instructions on the rules of working with solutions of acids and alkalis, heating devices on each table.
Methods: research, project method.
During the classes
It is advisable to conduct the lesson in a class with in-depth study of chemistry. To conduct the lesson, the class is divided into groups. Each group prepares only one experiment to conduct it in class and explain the results of the experiment, the result of which should be a presentation in Microsoft Power Point. Lesson duration 90 minutes.
Lesson timing:
- Organizational moment – 5 minutes
- Small group work – 20 minutes
- Reports on the work of each group – 5 minutes (35 minutes)
- Reflection (viewing a lesson presentation) – 5 minutes
- Verification testing – 20 minutes
- Summing up the lesson (grading with commentary) – 5 minutes
Group 1.
Exercise:
Determine the elemental composition of glucose.
To determine the elemental composition of glucose, perform the following experiment.
Place some glucose in a dry test tube and heat it in the flame of an alcohol lamp. As heating progresses, you will observe the stages of glucose decomposition. What elements are included in this substance?
Answer:
When glucose is heated in the flame of an alcohol lamp, an amorphous state is first formed - caramel, and then a black substance - coal and droplets of water vapor - appears on the walls of the test tube. Thus, the substance under study consists of the elements: C, H and O.
Task:
Determine the molecular formula of glucose if it is known that it has the following qualitative composition (in%): carbon - 40, hydrogen - 6.7, oxygen - 53.3. The molar mass of glucose is 2 times greater molar mass lactic acid.
Solution:
CH 3 CH(OH)COOH – lactic acid
M(CH 3 CH(OH)COOH) = 90 g/mol
M(glucose) = 90 * 2 = 180 g/mol
n(C) = 40 * 180/ 12 * 100 = 6
n(H) = 6.7 * 180/ 1 * 100 = 12
n(O) = 53.3 * 180/ 16 * 100 = 6
therefore, the molecular formula of glucose is C 6 H 12 O 6
Group 2.
Exercise:
Explore physical properties glucose.
Experimental procedure:
Determine the state of aggregation, color, taste and solubility of glucose in water. To do this, look at the glucose sample through a magnifying glass. Place a small amount of glucose in a test tube and add some water to it, mix the solution. What properties does glucose exhibit when dissolved in water?
Answer:
Glucose is a white crystalline solid, highly soluble in water, and has a sweet taste.
The discovery of glucose is associated with the name of the London physician William Prout (1802). The first synthesis of glucose from formaldehyde in the presence of calcium hydroxide was carried out by A. M. Butlerov in 1861.
Question:
A 20% glucose solution is used in medicine for intravenous infusion to improve the body's nutrition. The same glucose solution is used in ophthalmic practice to relieve swelling of the cornea. Explain the different effects of the same solution on different tissues of the body. Is it possible to replace the glucose solution with a 20% sucrose solution in both cases?
Answer:
The different effects of the same glucose solution are associated with different concentrations of intracellular fluid substances in different tissues of the body and are determined by osmotic pressure. If two solutions of different concentrations are separated by a semi-permeable partition (cell membrane), then due to the difference in osmotic pressure on both sides of the membrane, absorption occurs from a solution with a lower concentration into a solution of higher concentration, which leads to a decrease in the difference in concentrations. In this case, the transfer of low molecular weight nutrients occurs.
The osmotic pressure of blood plasma approximately corresponds to an isotonic solution (0.85-0.9% NaCl solution or 4.5-5% glucose solution). With intravenous infusion of a 20% glucose solution, it is greatly diluted with blood fluid and it becomes possible to transfer glucose into cell tissue. On the mucous membrane of the cornea of the eye, in contact with a 20% glucose solution, fluid is transferred from the edematous cornea to the outer surface. This process resembles the drying out of plants on saline soils.
Glucose solution can be replaced with sucrose solution when removing edema. This solution is not suitable for improving tissue nutrition, since human blood does not contain enzymes that break down sucrose into monosaccharides that provide intracellular nutrition.
Group 3.
Exercise.
Study the structure and Chemical properties glucose.
Experimental procedure:
How theory teaches chemical structure A.M. Butlerov: “Knowing the structure of a substance, we can talk about its properties and, conversely, knowing the properties, we can guess the structure.”
In order to find out the structure of glucose, check experimentally which groups it contains. On your tables there is a glucose solution and reagents: paper indicators, solutions of copper sulfate, alkali, an ammonia solution of silver (I) oxide. Based on experimental data, compose the structural formula of glucose if it is known that 1 mole of glucose reacts with 5 moles of acetic acid and it has been experimentally proven that all carbon atoms are linked together in a straight chain.
Answer:
- Let's check whether glucose is an acid. To do this, we examine the glucose solution with indicators. Glucose does not change the color of indicators, therefore, it does not contain a carboxyl group and is not an acid.
- Let's check whether glucose contains an aldehyde group. To do this, we will carry out a qualitative reaction to aldehydes - the “silver mirror” reaction. Glucose gives characteristic feature, therefore, it contains an aldehyde group.
CH 2 OH-(CHOH) 4 -COH + Ag 2 O = CH 2 OH-(CHOH) 4 -COOH + 2Ag - Let's check whether glucose is a polyhydric alcohol. To do this, we will carry out a qualitative reaction on polyhydric alcohols with a freshly prepared solution of copper (II) hydroxide. Glucose gives the characteristic blue color of the solution.
Thus, we found out that glucose is a polyhydric aldehyde alcohol, its structural formula: CH 2 OH-(CHOH) 4 -COH
Question.
The “black box” contains a substance that was first isolated from grape juice by the French chemist Joseph Louis Proust in 1802. When dissolved in water, it forms three non-isomeric forms. What substance is in the “black box”? Give a reasoned answer.
Answer:
This substance is glucose. There are three forms of glucose (α-, β- and aldehyde), which differ in their structure. Solid glucose consists of the α-form, and its solution contains all three forms in mobile equilibrium. In this equilibrium, the β-form predominates; it is energetically more stable, since the hydroxo groups C 1 and C 2 are located on opposite sides of the ring plane. In the α-form, the hydroxo groups at the same carbon atoms are located on one side of the plane, so it is energetically less stable than the β-form. The phenomenon of the simultaneous existence of several forms of one substance that are in equilibrium is called tautomerism. Tautomeric forms are not isomers, since they cannot be isolated individually, but are always present together.
Group 4.
Exercise:
Determine experimentally the presence of glucose in berries and fruits.
Experimental procedure:
Squeeze the juice from grapes (raspberries or apples) into a wide test tube. Dilute the juice by half with water. Pour 5 ml of the resulting solution into another test tube and add to the solution equal volume alkali and a few drops of copper (II) sulfate. Heat the test tube with the mixture in the flame of an alcohol lamp. What are you observing? Write down the reaction equations.
Answer:
When grape juice is heated with a freshly prepared solution of copper (II) hydroxide, first a yellow and then a red precipitate is formed. This reaction proves the presence of glucose in the juice.
CHOH-(CHOH) 4 -COH + 2Cu(OH) 2 = CHOH-(CHOH) 4 -COOH + Cu 2 O + 2H 2 O
In Russian, the word “glucose” was first mentioned in Tol’s dictionary (1863). It came from French: glucose - “grape sugar” - goes back to the ancient Greek glyukos, glyukeros - “sweet”.
Question.
The grape juice, prepared by the housewife for future use, suddenly fermented; there was a smell of alcohol. What caused the juice to ferment? Who discovered this process, and what is its essence?
Answer:
The reasons causing juice fermentation could be the following: lack of heat treatment (pasteurization or sterilization), insufficient tightness of containers. Heat treatment kills the yeast cells in the juice, so the juice does not ferment; The tightness of the containers prevents the entry of microorganisms.
The biological nature of fermentation was studied by the French chemist and microbiologist L. Pasteur. Fermentation associated with glucose under the action of yeast was defined by L. Pasteur as life without oxygen. Fermentation slows down the respiration of yeast, and alcohol helps it survive in the fight against other microorganisms that cannot tolerate the presence of alcohol.
C 6 H 12 O 6 = 2C 2 H 5 OH + 2CO 2
Group 5.
Exercise:
Determine experimentally the presence of glucose in vegetables.
Experimental procedure:
Grate a fresh cucumber and squeeze the juice out of it. Prepare copper(II) hydroxide in a test tube by adding 3 drops of copper(II) sulfate solution to 1 ml of sodium hydroxide solution. Add the same volume of cucumber juice to this test tube and shake. What are you observing? Heat the test tube containing the resulting solution to a boil. What happens when this happens? Does cucumber juice contain glucose?
Answer:
When freshly prepared copper(II) hydroxide is added to a cucumber juice solution, the precipitate dissolves and a blue solution is formed. This reaction is typical for polyhydric alcohols. When the resulting solution is heated, the following happens: first it turns yellow, then turns orange, and after cooling, a red precipitate of copper (I) oxide precipitates. This reaction is typical for aldehydes. Consequently, cucumber juice contains a substance that is both a polyhydric alcohol and an aldehyde. This is glucose.
CHOH-(CHOH) 24 -COH + 2Cu(OH) 2 = CHOH-(CHOH) 4 -COOH + Cu 2 O + 2H 2 O
Question.
The following episode is described in Agatha Christie’s drafts: “A certain businessman, having decided to do away with his competitors, invited them to visit and prepared a poisonous mixture, calcining the dry residue of bull’s blood with coal. One of the guests liked dry wine, while the other preferred sweet wine. The businessman quietly mixed poison into the wine and, having declared a toast, began to watch his guests. Having finished his glass, the first guest grabbed his throat, staggered and fell; his lips turned blue and he died a few minutes later. The second guest felt slightly unwell and hurried to leave the “hospitable” house. What was the active principle of the poison used? What kind of wine did the surviving guest drink?
Answer:
When dry blood residue is calcined with charcoal, pyrolysis of all organic substances contained in the blood occurs, water vapor is released, and the nitrogen contained in the blood is converted into the CN- anion, which forms potassium and sodium salts (sodium is contained in the blood plasma, and potassium in charcoal). Extracting this melt with alcohol allows one to obtain an alcohol solution of KCN and NaCN. Dry wine contains ethyl alcohol, water, odorous substances, tartaric acids and their salts. Therefore, one of the guests who preferred dry wine received a lethal dose of cyanide with the first sips and died immediately.
It is known that monosaccharides add HCN in a neutral environment. Hydrogen cyanide is formed by the action of potassium and sodium cyanides on the acids contained in wine. In sweet wine, HCN reacted with glucose to form cyanohydrin, which is not poisonous:
CH 2 OH-(CHOH) 4 -COH + HCN = CH 2 OH – (CHOH) 4 – CH(OH) – CN
Therefore, the guest who drank sweet wine survived.
Group 6.
Exercise:
Determine the glucose content in different types of honey.
Experimental procedure:
Prepare 4 test tubes containing: 1 test tube – 5 drops of natural honey in 5 ml of water, 2 test tube – 5 drops of artificial honey in 5 ml of water, 3 test tube – sugar solution, 4 test tube – 5 ml of water. Pour 10 ml of copper (II) sulfate solution into a 100 ml glass while stirring and 20 ml of sodium hydroxide solution. Then pour the resulting alkaline suspension of copper (II) hydroxide in equal portions (7.5 ml each) into four test tubes at room temperature. Determine the time at which signs of the reaction appear in each test tube.
Answer:
Natural honey contains the most glucose, and the reaction will begin within 2-3 minutes; sugar can enter into this reaction only after alkaline hydrolysis of the disaccharide.
Question.
Which enzyme causes isomerization of glucose? What uses does this process have and why?
Answer:
Glucose isomerase isomerizes glucose into fructose. Fructose is 60-70% sweeter than sugar. Due to its greater sweetness, it can be used in smaller quantities, which leads to a reduction in calorie content of products. Fructose, unlike glucose and sucrose, can be consumed by patients with diabetes, since the pathways for converting fructose in the human body are completely different from those of glucose and are not related to the presence of insulin. Glucose isomerase makes it possible to obtain fructose from starch for the preparation of fruit syrups, which are used to produce soft drinks.
Group 7.
Exercise:
Determine experimentally the presence of glucose in sawdust.
Experimental procedure:(home experiment)
Pour sawdust into a porcelain cup and moisten it with water. Add sulfuric acid solution until you obtain a liquid slurry. Add the same amount of water and heat the cup, covered with a lid, in a sand bath for a long time (for an hour). Add water and neutralize the acid with calcium hydroxide solution until the emission of carbon dioxide bubbles stops. Pour the contents of the cup into the flask and let it settle. Calcium sulfate will settle to the bottom, and a glucose solution will remain on top. Pour it into a flask and filter, pour into a cup and evaporate the water in a water bath. Glucose crystals will remain at the bottom. Compare the glucose obtained with the sample provided.
In 1819, Henri Braconneau obtained glucose from sawdust by the action of dilute sulfuric acid.
(C 6 H 10 O 5)n + nH 2 O = nC 6 H 12 O 6
Question.
Why is it preferable to drink grape juice to quench thirst that arises during intense physical work?
Answer:
The lack of glucose during intense physical work is replenished due to the hydrolysis of glycogen deposited in the muscles and liver. Thirst occurs not only due to the loss of water through sweat, but also due to its partial consumption for the hydrolysis of glycogen. Grape juice quenches thirst and replenishes glycogen consumption.
Question.
Why does a lack of glucose in the body cause loss of consciousness?
Answer:
Glucose serves as the main substrate for tissue respiration and must enter the cells continuously. Brain cells, which cannot use other metabolites as an energy source, are especially sensitive to a lack of glucose. Lack of glucose causes loss of consciousness.
After completing the experiment and answering the questions asked, representatives from each group present a report on the work done. While listening to the report, the rest of the students make appropriate notes in their notebooks. At the reflection stage, the whole class views the prepared presentation, and the information received is comprehended. Students develop their own attitude towards the material studied.
To check the studied material, the teacher conducts a final test control.
Test questions(shown on the interactive whiteboard):
- In what hybrid states are the carbon atoms in glucose (open aldehyde form):
A) in sp 2;
B) in sp and sp 3;
B) in sp 2 and sp 3;
D) in sp 3. - Which substances exhibit dual functions:
A) glucose and acetic acid;
B) glucose and glycerol;
B) glucose and oleic acid;
D) glucose and methanoic acid. - Which groups of substances give the silver mirror reaction:
A) glucose, glycerin, ethylene glycol;
B) glucose, glycerin, ethyl alcohol;
B) glucose, formaldehyde, formic acid;
D) glucose, fructose, lactic acid. - With the help of chlorophyll, a green plant produces:
A) nitrogen;
B) water;
B) glucose;
G) carbon dioxide. - You can distinguish a glycerol solution from a glucose solution using:
A) litmus;
B) copper (II) sulfate;
B) sodium carbonate;
D) ammonia solution of silver (I) oxide. - One of the products of sucrose hydrolysis is:
A) cellulose;
B) starch;
B) ribose;
D) glucose. - Match the name of the connection with the class to which it belongs:
- Carry out transformations according to the scheme:
CH 4 → CH 3 Cl → CH 3 OH → HCOH → C 6 H 12 O 6 → CO 2 - When burning an organic substance weighing 0.9 g, carbon dioxide weighing 1.32 g (n.s.) and water weighing 0.54 g were obtained. The relative vapor density of this substance with respect to hydrogen is 90. Determine the formula of the substance.
- An excess of an ammonia solution of silver (I) oxide was added to the glucose obtained from 16.2 g of starch. As a result of the reaction, 20 g of metal precipitate was obtained. Determine the yield of glucose if the yield in the second reaction is 100%.
The test is mutually checked (using an interactive whiteboard).
The teacher sums up the lesson and comments on the grades for the lesson.
Literature:
- O.S. Arshanskaya, I.V. Buraya " Project activities schoolchildren in the process of learning chemistry." Moscow, "Ventana-Graf", 2007.
- V.N. Aleksinsky "Entertaining experiments in chemistry." Moscow, “Enlightenment”, 1980.
- SOUTH. Orlik "Chemical Kaleidoscope". Minsk, “People's Asveta”, 1988.
- E.N. Dmitrov “Cognitive tasks in organic chemistry and their decisions." Tula, "Arktous", 1996.
- V Soros Olympiad for schoolchildren 1998-1999, publishing house MCNMO, 1999.
