Class: 10
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1. Purpose of the lesson: to acquaint students with the general and specific properties of methanoic acid while completing the crossword puzzle “Chemistry of formic acid”, including when solving problems to derive the formula of an organic substance (see. Annex 1 ) (slides 1-2).
2. Lesson type: lesson of learning new material.
3. Equipment: computer, projector, screen, videos of a chemical experiment (oxidation of formic acid with potassium permanganate and decomposition of formic acid under the influence of concentrated sulfuric acid), presentation for the lesson, sheets for students (see. Appendix 2 ).
4. Lesson progress
When studying the structure of formic acid, the teacher reports that this acid is different from the other members of the homologous series of saturated monocarboxylic acids, because the carboxyl group is not connected to the hydrocarbon radical –R, but to the H atom ( slide 3). Students come to the conclusion that formic acid exhibits the properties of both carboxylic acids and aldehydes, i.e. is aldehyde acid (slide 4).
The study of nomenclature is carried out in the process of solving a problem ( slide 5): « Salts of a saturated monobasic carboxylic acid are called formates. Establish the name of this acid (according to IUPAC nomenclature) if it is known that it contains 69.5% oxygen" The solution to the problem is written down by one of the students in the class on the board. The answer is ant or methane acid ( slide 6).
Next, the teacher tells the students ( slide 7), that formic acid is found in the acrid secretions of stinging caterpillars and bees, in stinging nettles, pine needles, some fruits, in the sweat and urine of animals and in acidic secretions ants, where it was discovered in 1794 by the German chemist Margraf Andreas-Sigismund ( slide 8).
When studying the physical properties of formic acid, the teacher reports that it is a colorless, caustic liquid with a pungent odor and pungent taste, having boiling and melting points close to water (tboiling = 100.7 o C, tmelting = 8.4 o C ). Like water, it forms hydrogen bonds, therefore, in liquid and solid states it forms linear and cyclic associates ( slide 9), mixes with water in any proportion (“like dissolves in like”). Next, one of the students is asked to solve the problem at the board: “ It is known that the nitrogen vapor density of formic acid is 3.29. Therefore, it can be argued that in the gaseous state, formic acid exists in the form...» While solving the problem, students come to the conclusion that in the gaseous state formic acid exists in the form dimers– cyclic associates ( slide 10).
Preparation of formic acid ( slide 11-12) we study using the following examples:
1. Oxidation of methane on a catalyst:
2. Hydrolysis of hydrocyanic acid (here students should be reminded that a carbon atom cannot simultaneously have more than two hydroxyl groups - dehydration occurs with the formation of a carboxyl group):
3. The interaction of potassium hydride with carbon monoxide (IV):
4. Thermal decomposition of oxalic acid in the presence of glycerol:
5. Interaction of carbon monoxide with alkali:
6. The most profitable way (from the point of view of economic costs - a waste-free process) for producing formic acid is to obtain an ester of formic acid (followed by acid hydrolysis) from carbon monoxide and saturated monohydric alcohol:
Since the latter method of obtaining formic acid is the most promising, students are then asked to solve the following problem at the board ( slide 12): “Establish the formula of an alcohol that is repeatedly used (returning to the cycle) to react with carbon monoxide (II), if it is known that the combustion of 30 g of ether produces 22.4 liters of carbon dioxide and 18 g of water. Determine the name of this alcohol." In the course of solving the problem, students come to the conclusion that for the synthesis of formic acid it is used methyl alcohol ( slide 13).
When studying the effect of formic acid on the human body ( slide 14) the teacher informs students that formic acid vapors irritate the upper respiratory tract and mucous membranes of the eyes, exhibit an irritating effect or a corrosive effect - cause chemical burns (slide 15). Next, schoolchildren are asked to find in the media or reference books ways to eliminate the burning sensation caused by nettles and ant bites (checked in the next lesson).
We begin to study the chemical properties of formic acid ( slide 16) from reactions with cleavage of the O-H bond (substitution of the H atom):
To consolidate the material, it is proposed to solve the following problem ( slide 18): « When 4.6 g of formic acid interacted with an unknown saturated monohydric alcohol, 5.92 g of ester was formed (used as a solvent and additive to some types of rum to give it a characteristic aroma, used in the production of vitamins B1, A, E). Determine the formula of the ester if it is known that the reaction yield is 80%. Name the ester using IUPAC nomenclature.” While solving the problem, tenth graders come to the conclusion that the resulting ester is - ethyl formate (slide 19).
The teacher reports ( slide 20), that reactions with the cleavage of the C-H bond (at the α-C atom) for formic acid not typical, because R=H. And the reaction with the cleavage of the C-C bond (decarboxylation of salts of carboxylic acids leads to the formation of alkanes!) leads to the production of hydrogen:
As examples of acid reduction reactions, we give the interaction with hydrogen and a strong reducing agent - hydroiodic acid:
Introduction to oxidation reactions that proceed according to the scheme ( slide 21):
it is advisable to carry out during the task ( slide 22):
« Correlate the formulas of the reagents, reaction conditions with the reaction products"(the teacher can show the first equation as an example, and offer the rest to students as homework):
| UNDC + | Reagent, reaction conditions | Product 1 |
Product 2 |
|||
| 1) | Ag 2 O, NH 3, t o C | 1) | CO | 1) | – | |
| 2) | Br 2 (solution) | 2) | CO, H2O | 2) | K2SO4, MnSO4 | |
| 3) | KMnO4, H 2 SO 4, t o C | 3) | H2O | 3) | Cu2Ov | |
| 4) | Cl 2 (solution) | 4) | CO2 | 4) | HCl | |
| 5) | Cu(OH) 2 (fresh), t o C | 5) | CO 2 , H 2 O | 5) | Agv | |
| 6) | Ir or Rh | 6) | CO 2 , H 2 | 6) | HBr | |
| 7) | H2O2 | 7) | CO, H2 | 7) | H-C(O)OOH | |
Answers should be written down as a sequence of numbers.
Answers:
| 1) 2) 3) 4) 5) 6) 7) |
5 4 5 4 5 6 3 |
5 6 2 4 3 1 7 |
When composing equations, students come to the conclusion that in all these reactions what happens is oxidation formic acid, because it is a strong reducing agent ( slide 23).
Studying the issue “Use of formic acid” is carried out by familiarizing yourself with the diagram ( slide 24).
Students clarify the use of “formic alcohol” in medicine (you can go online) and name the disease - rheumatism(slide 25).
If there is free time, the teacher informs the students ( slide 26) that earlier “ant alcohol” was prepared by infusing ants in alcohol.
Reports that the total world production of formic acid has begun to increase in recent years, as... In all countries of the world, the death of bees from mites (Varroa) is observed: gnawing through the chitinous cover of bees, they suck out the hemolymph, and the bees die (formic acid is an effective remedy against these mites).
5. Lesson summary
At the end of the lesson, students sum up: evaluate the work of their classmates at the blackboard, explain what new educational material (general and specific properties of formic acid) they have become acquainted with.
6. Literature
1. Deryabina N.E. Organic chemistry. Book 1. Hydrocarbons and their monofunctional derivatives. Textbook-notebook. – M.: IPO “At the Nikitsky Gates”, 2012. – P. 154-165.
2. Kazennova N.B. Student's Guide to Organic Chemistry/For high school. – M.: Aquarium, 1997. – P. 155-156.
3. Levitina T.P. Handbook of Organic Chemistry: Textbook. – St. Petersburg: “Paritet”, 2002. – P. 283-284.
4. Chemistry tutor/Ed. A.S. Egorova. 14th ed. – Rostov n/d: Phoenix, 2005. – P. 633-635.
5. Rutzitis G.E., Feldman F.G. Chemistry 10. Organic chemistry: Textbook for 10th grade. high school. – M., 1992. – P. 110.
6. Chernobelskaya G.M. Chemistry: textbook. allowance for medical education Institutions/ G.M. Chernobelskaya, I.N. Chertkov.– M.: Bustard, 2005. – P.561-562.
7. Atkins P. Molecules: Transl. from English – M.: Mir, 1991. – P. 61-62.
Interaction of formic acid with ammonia solutionsilver hydroxide(silver mirror reaction). The formic acid molecule HCOOH contains an aldehyde group, so it can be opened in solution by reactions characteristic of aldehydes, for example, the silver mirror reaction.
An ammonia solution of argentum (I) hydroxide is prepared in a test tube. To do this, add 1-2 drops of a 10% solution of sodium hydroxide to 1 - 2 ml of a 1% solution of argentum (I) nitrate, the resulting precipitate of argentum (I) oxide is dissolved by adding dropwise a 5% solution of ammonia. 0.5 ml of formic acid is added to the resulting clear solution. The test tube with the reaction mixture is heated for several minutes in a water bath (water temperature in the bath is 60 0 -70 0 C). Metallic silver is released in the form of a mirror coating on the walls of the test tube or in the form of a dark precipitate.
HCOOH+2Ag[(NH 3) 2 ]OH → CO 2 + H 2 O+2Ag+ 4NH 3
b) Oxidation of formic acid with potassium permanganate. Approximately 0.5 g of formic acid or its salt, 0.5 ml of a 10% solution of sulfate acid and 1 ml of a 5% solution of potassium permanganate are placed in a test tube. The test tube is closed with a stopper with a gas outlet tube, the end of which is lowered into another test tube with 2 ml of lime (or barite) water, and the reaction mixture is heated.
5HCOOH+2KMnO 4 +3H 2 SO 4 → 5CO 2 +8H 2 O+K 2 SO 4 +2MnSO 4
V) Decomposition of formic acid when heated withconcentrated sulfuric acid. (Craft!) Add 1 ml of formic acid or 1 g of its salt and 1 ml of concentrated sulfate acid to a dry test tube. The test tube is closed with a stopper with a gas outlet tube and carefully heated. Formic acid decomposes to form carbon (II) oxide and water. Carbon (II) oxide is ignited at the opening of the gas outlet tube. Pay attention to the nature of the flame.
After finishing work, the test tube with the reaction mixture must be cooled to stop the release of poisonous carbon monoxide.
Experience 12. Interaction of stearic and oleic acids with alkali.
In a dry test tube, dissolve approximately 0.5 g of stearin in diethyl ether (without heating) and add 2 drops of a 1% alcohol solution of phenolphthalein. Then a 10% sodium hydroxide solution is added drop by drop. The crimson color that appears initially disappears when shaken.
Write the equation for the reaction of stearic acid with sodium hydroxide. (Stearin is a mixture of stearic and palmitic acids.)
C 17 H 35 COOH+NaOH→ C 17 H 35 COONa+H 2 O
sodium stearate
Repeat the experiment using 0.5 ml of oleic acid
C 17 H 33 COOH+NaOH→C 17 H 33 COONa+H 2 O
sodium oleate
Experience13. The ratio of oleic acid to bromine water and potassium permanganate solution.
A) Reaction of oleic acid with bromine water 2 ml of water is poured into a test tube and about 0.5 g of oleic acid is added. The mixture is shaken vigorously.
b) Oxidation of oleic acid with potassium permanganate. 1 ml of a 5% solution of potassium permanganate, 1 ml of a 10% solution of sodium carbonate and 0.5 ml of oleic acid are placed in a test tube. The mixture is stirred vigorously. Note the changes occurring in the reaction mixture.
Experience 14. Sublimation of benzoic acid.
The sublimation of small quantities of benzoic acid is carried out in a porcelain cup, closed with the wide end of a conical funnel (see Fig. 1), the diameter of which is slightly smaller than the diameter of the cup.
The spout of the funnel is secured in the leg of the tripod and tightly covered with cotton wool, and in order to prevent the sublimate from falling back into the cup, it is covered with a round piece of filter paper with several holes in it. A porcelain cup with small crystals of benzoic acid (t pl = 122.4 0 C; sublimes below t pl) is carefully slowly heated on a small flame-gas burner (on an asbestos mesh). You can cool the top funnel by applying a piece of filter paper moistened with cold water. After sublimation stops (after 15 - 20 minutes), the sublimate is carefully transferred with a spatula into a bottle.
Note. To carry out the work, benzoic acid can be contaminated with sand.
The test tube in which the emulsion has formed is sealed with a reflux stopper, heated in a water bath until it begins to boil and shaken. Does oil solubility increase with heating?
The experiment is repeated, but instead of sunflower oil, a small amount of animal fat (pork, beef or lamb fat) is added to test tubes with organic solvents.
b) Determination of the degree of unsaturation of fat by reaction with brominewater. (Craft!) 0.5 ml of sunflower oil and 3 ml of bromine water are poured into a test tube. The contents of the tube are shaken vigorously. What happens to bromine water?
V) Interaction of vegetable oil with an aqueous solution of potassiumpermanganate (E.E. Wagner reaction). Approximately 0.5 ml of sunflower oil, 1 ml of a 10% sodium carbonate solution and 1 ml of a 2% potassium permanganate solution are poured into a test tube. Shake the contents of the test tube vigorously. The purple color of potassium permanganate disappears.
Discoloration of bromine water and reaction with an aqueous solution of potassium permanganate are qualitative reactions to the presence of a multiple bond (unsaturation) in a molecule of an organic substance.
G) Saponification of fat with an alcoholic solution of sodium hydroxide 1.5 - 2 g of solid fat is placed in a conical flask with a capacity of 50 - 100 ml and 6 ml of a 15% alcohol solution of sodium hydroxide is added. The flask is closed with a stopper with an air cooler, the reaction mixture is stirred and the flask is heated in a water bath with shaking for 10 - 12 minutes (water temperature in the bath is about 80 0 C). To determine the end of the reaction, a few drops of hydrolyzate are poured into 2-3 ml of hot distilled water: if the hydrolyzate dissolves completely, without releasing drops of fat, then the reaction can be considered complete. After saponification is completed, the soap is salted out from the hydrolyzate by adding 6 - 7 ml of a hot saturated sodium chloride solution. The released soap floats to the surface, forming a layer on the surface of the solution. After settling, the mixture is cooled with cold water, and the hardened soap is separated.
Chemistry of the process using tristearin as an example:
Experience 17. Comparison of the properties of soap and synthetic detergents
A) Relation to phenolphthalein. Pour 2-3 ml of a 1% solution of laundry soap into one test tube, and into the other - the same amount of a 1% solution of synthetic washing powder. Add 2-3 drops of phenolphthalein solution to both test tubes. Can these detergents be used to wash alkali-sensitive fabrics?
b) Relation to acids. To the soap and washing powder solutions in test tubes, add a few drops of a 10% acid solution (chloride or sulfate). Does foam form when shaken? Are the cleaning properties of the tested products maintained in an acidic environment?
C 17 H 35 COONa+HCl→C 17 H 35 COOH↓+NaCl
V) AttitudeTocalcium chloride. To solutions of soap and washing powder in test tubes, add 0.5 ml of a 10% solution of calcium chloride. Shake the contents of the test tubes. Does this create foam? Can these detergents be used in hard water?
C 17 H 35 COONa+CaCl 2 →Ca(C 17 H 35 COO) 2 ↓+2NaCl
Experience 18 . Interaction of glucose with an ammonia solution of argentum (I) oxide (silver mirror reaction).
0.5 ml of a 1% solution of argentum(I) nitrate, 1 ml of a 10% solution of sodium hydroxide are poured into a test tube and a 5% solution of ammonia is added dropwise until the resulting precipitate of argentum(I) hydroxide dissolves. Then add 1 ml of a 1% glucose solution and heat the contents of the test tube for 5 - 10 minutes in a water bath at 70 0 - 80 0 C. Metallic silver is released on the walls of the test tube in the form of a mirror coating. During heating, the test tubes must not be shaken, otherwise metallic silver will not be released on the walls of the test tubes, but in the form of a dark precipitate. To get a good mirror, a 10% solution of sodium hydroxide is first boiled in test tubes, then they are rinsed with distilled water.
3 ml of a 1% sucrose solution is poured into a test tube and 1 ml of a 10% sulfuric acid solution is added. The resulting solution is boiled for 5 minutes, then cooled and neutralized with dry sodium bicarbonate, adding it in small portions while stirring (be careful, the liquid foams from the released carbon monoxide (IY)). After neutralization (when the evolution of CO 2 stops), an equal volume of Fehling’s reagent is added and the upper part of the liquid is heated until it begins to boil.
Does the color of the reaction mixture change?
In another test tube, a mixture of 1.5 ml of a 1% sucrose solution with an equal volume of Fehling’s reagent is heated. The results of the experiment are compared - the reaction of sucrose with Fehling's reagent before hydrolysis and after hydrolysis.
C 12 H 22 O 11 + H 2 O C 6 H 12 O 6 + C 6 H 12 O 6
glucose fructose
Note. In a school laboratory, Fehling's reagent can be replaced with cuprum (ΙΙ)hydroxide.
Experiment 20. Hydrolysis of cellulose.
Place some very finely chopped pieces of filter paper (cellulose) into a dry conical flask with a capacity of 50–100 ml and moisten them with concentrated sulfate acid. Thoroughly mix the contents of the flask with a glass rod until the paper is completely destroyed and a colorless viscous solution is formed. After this, 15–20 ml of water are added to it in small portions with stirring (carefully!), the flask is connected to an air reflux condenser and the reaction mixture is boiled for 20–30 minutes, stirring it periodically. After hydrolysis is completed, 2–3 ml of liquid is poured, it is neutralized with dry sodium carbonate, adding it in small portions (the liquid foams), and the presence of reducing sugars is detected by reaction with Fehling’s reagent or cuprum (ΙΙ) hydroxide.
(C 6 H 10 O 5)n+nH 2 O→nC 6 H 12 O 6
Cellulose glucose
Experiment 21. Interaction of glucose with cuprum (ΙΙ) hydroxide.
a) 2 ml of a 1% glucose solution and 1 ml of 10% sodium hydroxide are placed in a test tube. Add 1 - 2 drops of a 5% solution of cuprum (ΙΙ) sulfate to the resulting mixture and shake the contents of the test tube. The initially formed bluish precipitate of cuprum (II) hydroxide instantly dissolves, resulting in a blue transparent solution of cuprum (II) saccharate. Chemistry of the process (simplified): - 
b) The contents of the test tube are heated over a burner flame, holding the test tube inclined so that only the upper part of the solution is heated, and the lower part remains unheated (for control). When gently heated to boiling, the heated portion of the blue solution turns orange-yellow due to the formation of cuprum (I) hydroxide. With longer heating, a precipitate of cuprum(I)oxide may form.
Experience 22. Interaction of sucrose with metal hydroxides. A) Reaction with cuprum (ΙΙ) hydroxide) in an alkaline medium. In a test tube, mix 1.5 ml of a 1% sucrose solution and 1.5 ml of a 10% sodium hydroxide solution. Then a 5% solution of cuprum (ΙΙ) sulfate is added dropwise. The initially formed pale blue precipitate of cuprum (ΙΙ) hydroxide dissolves when shaken, and the solution acquires a blue-violet color due to the formation of complex cuprum (ΙΙ) saccharate.
b) Obtaining calcium saccharate. In a small glass (25 - 50 ml), pour 5 - 7 ml of a 20% sucrose solution and add freshly prepared lime milk drop by drop with stirring. Calcium hydroxide dissolves in sucrose solution. The ability of sucrose to produce soluble calcium saccharates is used in industry to purify sugar when isolating it from sugar beets. V) Specific color reactions. 2-5 ml of a 10% sucrose solution and 1 ml of a 5% sodium hydroxide solution are poured into two test tubes. Then add a few drops to one test tube 5- percent solution of cobalt (ΙΙ) sulfate, in another - a few drops 5- percentage solution of nickel (ΙΙ) sulfate. In a test tube with cobalt salt a violet color appears, and in a test tube with nickel salt a green color appears, Experiment 23. Interaction of starch with iodine. 1 ml of a 1% solution of starch paste is poured into a test tube and then a few drops of iodine in potassium iodide very diluted with water are added. The contents of the test tube turn blue. The resulting dark blue liquid is heated to a boil. The color disappears, but appears again upon cooling. Starch is a heterogeneous compound. It is a mixture of two polysaccharides - amylose (20%) and amylopectin (80%). Amylose is soluble in warm water and gives a blue color with iodine. Amylose consists of almost unbranched chains of glucose residues with a screw or helix structure (approximately 6 glucose residues per screw). A free channel with a diameter of about 5 μm remains inside the helix, into which iodine molecules are embedded, forming colored complexes. When heated, these complexes are destroyed. Amylopectin is insoluble in warm water and swells in it, forming a starch paste. It consists of branched chains of glucose residues. Amylopectin with iodine gives a reddish-violet color due to the adsorption of iodine molecules on the surface of the side chains. Experience 24. Hydrolysis of starch. A) Acid hydrolysis of starch. 20 - 25 ml of 1% starch paste and 3 - 5 ml of 10% sulfate acid solution are poured into a 50 ml conical flask. 1 ml of a very dilute solution of iodine in potassium iodide (light yellow) is poured into 7 - 8 test tubes, the test tubes are placed in a stand. Add 1–3 drops of starch solution prepared for the experiment into the first test tube. The resulting color is noted. The flask is then heated on an asbestos grid with a small burner flame. 30 seconds after the start of boiling, a second sample of the solution is taken with a pipette, which is added to a second test tube with an iodine solution, and after shaking, the color of the solution is noted. Subsequently, samples of the solution are taken every 30 seconds and added to subsequent test tubes with iodine solution. Note a gradual change in the color of the solutions upon reaction with iodine. The color change occurs in the following order, see table.
After the reaction mixture ceases to give color with iodine, the mixture is boiled for another 2 - 3 minutes, after which it is cooled and neutralized with a 10 percent solution of sodium hydroxide, adding it drop by drop until the medium is alkaline (the appearance of a pink color on phenolphthalein indicator paper). Part of the alkaline solution is poured into a test tube, mixed with an equal volume of Fehling’s reagent or a freshly prepared suspension of cuprum (ΙΙ) hydroxide and the upper part of the liquid is heated until it begins to boil.
(
Soluble
Dextrins
C 6 H 10 O 5)n (C 6 H 10 O 5)x (C 6 H 10 O 5)y
maltose
n/2 C 12 H 22 O 11 nC 6 H 12 O 6
b) Enzymatic hydrolysis of starch.
Chew a small piece of black bread well and place it in a test tube. Add a few drops of a 5 percent solution of cuprum (ΙΙ) sulfate and 05 - 1 ml of a 10 percent solution of sodium hydroxide into it. The test tube with its contents is heated. 3. Technique and methodology for demonstration experiments on the production and study of the properties of nitrogen-containing organic substances.
Equipment: beakers, glass rod, test tubes, Wurtz flask, dropping funnel, beaker, glass gas outlet tubes, connecting rubber tubes, splinter.
Reagents: aniline, methylamine, litmus and phenolphthalein solutions, concentrated chloride acid, sodium hydroxide solution (10%), bleach solution, concentrated sulfate acid, concentrated nitrate acid, egg white, copper sulfate solution, plumbum (ΙΙ) acetate, phenol solution , formalin.
Experience 1. Preparation of methylamine. Add 5-7 g of methylamine chloride to a Wurtz flask with a volume of 100-150 ml and close it with a stopper with a dropping funnel inserted into it. Connect the gas outlet tube with a rubber tube to a glass tip and lower it into a glass of water. Add potassium hydroxide solution (50%) dropwise from the funnel. Heat the mixture in the flask carefully. The salt decomposes and methylamine is released, which is easily recognized by its characteristic odor, which resembles the smell of ammonia. Methylamine collects at the bottom of the glass under a layer of water: + Cl - +KOH → H 3 C – NH 2 +KCl+H 2 O
Experience 2. Combustion of methylamine. Methylamine burns with a colorless flame in air. Apply a burning splinter to the hole in the gas outlet tube of the device described in the previous experiment and observe the combustion of methylamine: 4H 3 C – NH 2 +9O 2 → 4CO 2 +10 H 2 O+2N 2
Experience 3. Relation of methylamine to indicators. Pass the resulting methylamine into a test tube filled with water and one of the indicators. Litmus turns blue, and phenolphthalein turns crimson: H 3 C – NH 2 + H – OH → OH This indicates the basic properties of methylamine.
Experience 4. Formation of salts by methylamine. a) A glass rod moistened with concentrated chloride acid is brought to the opening of the test tube from which methylamine gas is released. The wand is shrouded in fog.
H 3 C – NH 2 +HCl → + Cl -
b) 1 - 2 ml are poured into two test tubes: into one - a 3% solution of ferum (III) chloride, into the other - a 5% solution of cuprum (ΙΙ) sulfate. Methylamine gas is passed into each test tube. In a test tube with a solution of ferum (III) chloride, a brown precipitate precipitates, and in a test tube with a solution of cuprum (III) sulfate, the blue precipitate that initially forms dissolves to form a complex salt, colored bright blue. Chemistry of processes:
3 + OH - +FeCl 3 → Fe(OH)↓+3 + Cl -
2 + OH - +CuSO 4 →Cu(OH) 2 ↓+ + SO 4 -
4 + OH - + Cu(OH) 2 →(OH) 2 +4H 2 O
Experience 5. Reaction of aniline with chloride acid. In a test tube with 5 Add the same amount of concentrated chloride acid to ml of aniline. Cool the test tube in cold water. A precipitate of aniline hydrogen chloride appears. Add some water to a test tube with solid hydrogen chloride aniline. After stirring, aniline hydrogen chloride dissolves in water.
C 6 H 5 – NH 2 + HCl → Cl - Experiment 6. Interaction of aniline with bromine water. Add 2-3 drops of aniline to 5 ml of water and shake the mixture vigorously. Add bromine water drop by drop to the resulting emulsion. The mixture becomes discolored and a white precipitate of tribromoaniline precipitates.
Experience 7. Dyeing fabric with aniline dye. Wool dyeing And silk with acid dyes. Dissolve 0.1 g of methyl orange in 50 ml of water. The solution is poured into 2 glasses. 5 ml of 4N sulfate acid solution is added to one of them. Then pieces of white wool (or silk) fabric are dipped into both glasses. Solutions with tissue are boiled for 5 minutes. Then the fabric is taken out, washed with water, squeezed out and dried in air, hanging on glass rods. Pay attention to the difference in color intensity of the pieces of fabric. How does the acidity of the medium affect the dyeing process of fabric?
Experience 8. Evidence of the presence of functional groups in amino acid solutions. a) Detection of the carboxyl group. To 1 ml of a 0.2 percent solution of sodium hydroxide, colored pink with phenolphthalein, add dropwise a 1 percent solution of aminoacetate acid (glycine) until the mixture becomes discolored: HOOC – CH 2 – NH 2 + NaOH → NaOOC – CH 2 – NH 2 + H 2 O b) Detection of the amino group. To 1 ml of a 0.2 percent chloride acid solution, colored blue with Congo indicator (acidic medium), add a 1 percent glycine solution drop by drop until the color of the mixture changes to pink (neutral medium):
HOOC – CH 2 – NH 2 +HCl → Cl -
Experience 9. The effect of amino acids on indicators. Add 0.3 g of glycine to the test tube and add 3 ml of water. Pour the solution into three test tubes. Add 1-2 drops of methyl orange to the first test tube, the same amount of phenolphthalein solution to the second, and litmus solution to the third. The color of the indicators does not change, which is explained by the presence in the glycine molecule of acidic (-COOH) and basic (-NH 2) groups, which are mutually neutralized.
Experience 10. Protein precipitation. a) Add dropwise solutions of copper sulfate and plumbum (ΙΙ) acetate into two test tubes with a protein solution. Flocculate precipitates are formed that dissolve in excess salt solutions.
b) Add equal volumes of phenol and formalin solutions to two test tubes with a protein solution. Observe protein precipitation. c) Heat the protein solution in the burner flame. Observe the turbidity of the solution, which is due to the destruction of hydration shells near the protein particles and their increase.
Experience 11. Color reactions of proteins. a) Xanthoprotein reaction. Add 5-6 drops of concentrated nitrate acid to 1 ml of protein. When heated, the solution and precipitate turn bright yellow. b) Biuret reaction. To 1 - 2 ml of protein solution add the same amount of diluted copper sulfate solution. The liquid turns red-violet. The biuret reaction makes it possible to identify a peptide bond in a protein molecule. The xanthoprotein reaction occurs only if the protein molecules contain aromatic amino acid residues (phenylalanine, tyrosine, tryptophan).
Experience 12. Reactions with urea. A) Solubility of urea in water. Place in a test tube 0,5 g of crystalline urea and gradually add water until the urea is completely dissolved. A drop of the resulting solution is applied to red and blue litmus paper. What reaction (acidic, neutral or alkaline) does an aqueous solution of urea have? In aqueous solution, urea occurs in two tautomeric forms:
b) Hydrolysis of urea. Like all acid amides, urea is easily hydrolyzed in acidic and alkaline environments. Pour 1 ml of a 20% urea solution into a test tube and add 2 ml of clear barite water. The solution is boiled until a precipitate of barium carbonate appears in the test tube. Ammonia released from a test tube is detected by the blueness of wet litmus paper.
H 2 N – C – NH 2 +2H 2 O→2NH 3 +[HO – C – OH]→CO 2
→H 2 O 
Ba(OH) 2 + CO 2 →BaCO 3 ↓+ H 2 O
c) Formation of biuret. Heated in a dry test tube 0,2 g urea. First, urea melts (at 133 C), then with further heating it decomposes, releasing ammonia. Ammonia can be detected by smell (carefully!) and by the blueness of wet red litmus paper brought to the opening of the test tube. After some time, the melt in the test tube solidifies, despite continued heating:
Cool the test tube and add 1-2 ml of water and dissolve the biuret under low heat. The melt, in addition to biuret, contains a certain amount of cyanuric acid, which is sparingly soluble in water, so the solution turns out cloudy. When the sediment has settled, pour the biuret solution into another test tube, add a few drops of a 10% solution of sodium hydroxide (the solution becomes clear) and 1-2 drops of a 1% solution of cuprum (ΙΙ) sulfate. The solution turns pink-violet. Excess cuprum (ΙΙ) sulfate masks the characteristic coloration, causing the solution to turn blue, and should therefore be avoided.
Experience 13. Functional analysis of organic substances. 1. Qualitative elemental analysis of organic compounds. The most common elements in organic compounds, besides Carbon, are Hydrogen, Oxygen, Nitrogen, halogens, Sulfur, Phosphorus. Conventional qualitative analytical methods are not applicable to the analysis of organic compounds. To detect Carbon, Nitrogen, Sulfur and other elements, organic matter is destroyed by fusion with sodium, and the elements under study are converted into inorganic compounds. For example, Carbon turns into carbon (IU) oxide, Hydrogen into water, Nitrogen into sodium cyanide, Sulfur into sodium sulfide, halogens into sodium halides. Next, the elements are discovered using conventional methods of analytical chemistry.
1. Detection of Carbon and Hydrogen by oxidation of the substance cuprum(II) oxide.
Device for simultaneous detection of Carbon and Hydrogen in organic matter:
1 – dry test tube with a mixture of sucrose and cuprum (II) oxide;
2 – test tube with lime water;
4 – anhydrous cuprum (ΙΙ) sulfate.
The most common, universal method of detection in organic matter. carbon and at the same time hydrogen is the oxidation of cuprum (II) oxide. In this case, Carbon is converted into carbon (IU) oxide, and Hydrogen into water. Place 0.2 in a dry test tube with a gas outlet tube (Fig. 2). - 0.3 g of sucrose and 1 - 2 g of cuprum (II) oxide powder. The contents of the test tube are thoroughly mixed, the mixture is covered with a layer of cuprum (II) oxide on top - approximately 1 g. A small piece of cotton wool is placed in the upper part of the test tube (under the stopper), which is poured with a little anhydrous copper (II) sulfate. The test tube is closed with a stopper with a gas outlet tube and secured in the tripod leg with a slight inclination towards the stopper. I lower the free end of the gas outlet tube into a test tube with lime (or barite) water so that the tube almost touches the surface of the liquid. First, the entire test tube is heated, then the part containing the reaction mixture is heated strongly. Notice what happens to lime water. Why does cuprum (ΙΙ) sulfate change color?
Chemistry of processes: C 12 H 22 O 11 +24CuO→12CO 2 +11H 2 O+24Cu
Ca(OH) 2 +CO 2 →CaCO 3 ↓+H 2 O
CuSO 4 +5H 2 O→CuSO 4 ∙ 5H 2 O
2. Beilstei sample on on halogens. When an organic substance is calcined with cuprum (II) oxide, its oxidation occurs. Carbon is converted into carbon(ІУ) oxide, Hydrogen - into water, and halogens (except fluor) form volatile halides with Cuprum, which color the flame bright green. The reaction is very sensitive. However, it should be borne in mind that some other cuprum salts, for example cyanides formed during the calcination of nitrogen-containing organic compounds (urea, pyridine derivatives, quinoline, etc.), also color the flame. The copper wire is held by the plug and the other end (loop) is calcined in the burner flame until the flame stops coloring and a black coating of cuprum(II) oxide forms on the surface. The cooled loop is moistened with chloroform poured into a test tube and reintroduced into the burner flame. First, the flame becomes luminous (Carbon burns), then an intense green color appears. 2Cu+O 2 →2CuO
2CH – Cl 3 +5CuO→CuCl 2 +4CuCl+2CO 2 +H 2 O
A control experiment should be done using a halogen-free substance (benzene, water, alcohol) instead of chloroform. To clean, the wire is moistened with chloride acid and calcined.
II. Opening of functional groups. Based on preliminary analysis (physical properties, elemental analysis), it is possible to approximately determine the class to which the given substance under study belongs. These assumptions are confirmed by qualitative responses to functional groups.
1. Qualitative reactions to multiple carbon - carbon bonds. a) addition of bromine. Hydrocarbons containing double and triple bonds easily add bromine:
To a solution of 0.1 g (or 0.1 ml) of the substance in 2-3 ml of carbon tetrachloride or chloroform, add dropwise with shaking a 5% solution of bromine in the same solvent. The instantaneous disappearance of the color of bromine indicates the presence of a multiple bond in the substance. But bromine solution is also discolored by compounds containing mobile Hydrogen (phenols, aromatic amines, tertiary hydrocarbons). However, a substitution reaction occurs with the release of hydrogen bromide, the presence of which can be easily detected using wet blue litmus or Congo paper. b) Test with potassium permanganate. In a weakly alkaline environment, under the influence of potassium permanganate, the substance is oxidized with the cleavage of the multiple bond, the solution becomes discolored, and a flocculent precipitate of MnO 2 is formed - manganese (IU) oxide. To 0.1 g (or 0.1 ml) of a substance dissolved in water or acetone, add a 1% solution of potassium permanganate dropwise with shaking. The crimson-violet color quickly disappears, and a brown precipitate of MnO 2 appears. However, potassium permanganate oxidizes substances of other classes: aldehydes, polyhydric alcohols, aromatic amines. In this case, the solutions also become discolored, but oxidation generally proceeds much more slowly.
2. Detection of aromatic systems. Aromatic compounds, unlike aliphatic compounds, can easily undergo substitution reactions, often forming colored compounds. Typically, nitration and alkylation reactions are used for this. Nitration of aromatic compounds. (‘Caution! Traction!,) Nitration is carried out with nitric acid or a nitrating mixture:
R – H + HNO 3 → RNO 2 + H 2 O
0.1 g (or 0.1 ml) of the substance is placed in a test tube and, with continuous shaking, 3 ml of a nitrating mixture (1 part concentrated nitrate acid and 1 part concentrated sulfate acid) is gradually added. The test tube is closed with a stopper with a long glass tube, which serves as a reflux condenser, and heated in a water bath 5 min at 50 0 C. The mixture is poured into a glass with 10 g of crushed ice. If this results in the precipitation of a solid product or oil that is insoluble in water and differs from the original substance, then the presence of an aromatic system can be assumed. 3. Qualitative reactions of alcohols. When analyzing alcohols, substitution reactions of both the mobile hydrogen in the hydroxyl group and the entire hydroxyl group are used. a) Reaction with sodium metal. Alcohols easily react with sodium, forming alcoholates that are soluble in alcohol:
2 R – OH + 2 Na → 2 RONa + H 2
0.2 - 0.3 ml of anhydrous test substance is placed in a test tube and a small piece of metallic sodium the size of a millet grain is carefully added. The release of gas when sodium dissolves indicates the presence of active hydrogen. (However, this reaction can also be given by acids and CH-acids.) b) Reaction with cuprum (II) hydroxide. In di-, tri- and polyhydric alcohols, unlike monohydric alcohols, freshly prepared cuprum (II) hydroxide dissolves to form a dark blue solution of complex salts of the corresponding derivatives (glycolates, glycerates). A few drops are poured into a test tube (0.3 - 0.5 ml) of a 3% solution of cuprum (ΙΙ) sulfate, and then 1 ml of a 10% solution of sodium hydroxide. A gelatinous blue precipitate of cuprum (ΙΙ) hydroxide precipitates. Dissolution of the precipitate upon addition of 0.1 g of the test substance and a change in the color of the solution to dark blue confirm the presence of a polyhydric alcohol with hydroxyl groups located at adjacent carbon atoms.
4. Qualitative reactions of phenols. a) Reaction with ferum (III) chloride. Phenols give intensely colored complex salts with ferum (III) chloride. A deep blue or purple coloration usually appears. Some phenols give a green or red color, which is more pronounced in water and chloroform and worse in alcohol. Several crystals (or 1 - 2 drops) of the test substance are placed in 2 ml of water or chloroform in a test tube, then 1 - 2 drops of a 3 percent solution of ferum (III) chloride are added with shaking. In the presence of phenol, an intense violet or blue color appears. Aliphatic phenols with ferum (ΙΙΙ) chloride in alcohol give a brighter color than in water, and phenols are characterized by a blood-red color. b) Reaction with bromine water. Phenols with free ortho- And pair-positions in the benzene ring easily decolorize bromine water, resulting in a precipitate of 2,4,6-tribromophenol 
A small amount of the test substance is shaken with 1 ml of water, then bromine water is added dropwise. The solution becomes discolored And precipitation of a white precipitate.
5. Qualitative reactions of aldehydes. Unlike ketones, all aldehydes are easily oxidized. The discovery of aldehydes, but not ketones, is based on this property. a) Reaction of the silver mirror. All aldehydes are easily reduced by an ammonia solution of argentum (I) oxide. Ketones do not give this reaction:
In a well-washed test tube, mix 1 ml of silver nitrate solution with 1 ml of dilute sodium hydroxide solution. The precipitate of argentum (I) hydroxide is dissolved by adding a 25% ammonia solution. A few drops of an alcohol solution of the analyzed substance are added to the resulting solution. The test tube is placed in a water bath and heated to 50 0 - 60 0 C. If a shiny coating of metallic silver is released on the walls of the test tube, this indicates the presence of an aldehyde group in the sample. It should be noted that this reaction can also be given by other easily oxidized compounds: polyhydric phenols, diketones, some aromatic amines. b) Reaction with feling liquid. Fatty aldehydes are capable of reducing divalent cuprum to monovalent:
A test tube with 0.05 g of the substance and 3 ml of feling liquid is heated for 3 - 5 minutes in a boiling water bath. The appearance of a yellow or red precipitate of cuprum(I) oxide confirms the presence of an aldehyde group. b. Qualitative reactions of acids. a) Determination of acidity. Aqueous-alcoholic solutions of carboxylic acids show an acidic reaction to litmus, Congo or a universal indicator. A drop of an aqueous-alcohol solution of the test substance is applied to blue wet litmus, Congo, or universal indicator paper. In the presence of acid, the indicator changes its color: litmus becomes pink, Congo blue, and the universal indicator, depending on the acidity, from yellow to orange. It should be borne in mind that sulfonic acids, nitrophenols and
some other compounds with mobile “acidic” hydrogen that do not contain a carboxyl group can also give a change in the color of the indicator. b) Reaction with sodium bicarbonate. When carboxylic acids interact with sodium bicarbonate, carbon(IY) oxide is released: 1 - 1.5 ml of a saturated solution of sodium bicarbonate is poured into a test tube and 0.1 - 0.2 ml of an aqueous-alcohol solution of the test substance is added. The release of carbon(IY) oxide bubbles indicates the presence of acid.
RCOOH + NaHCO 3 → RCOONa + CO 2 + H 2 O
7. Qualitative reactions of amines. Amines dissolve in acids. Many amines (especially the aliphatic series) have a characteristic odor (herring, ammonia, etc.). Basicity of amines. Aliphatic amines, as strong bases, can change the color of indicators such as red litmus, phenolphthalein, and universal indicator paper. A drop of an aqueous solution of the test substance is applied to indicator paper (litmus, phenolphthalein, universal indicator paper). A change in the color of the indicator indicates the presence of amines. Depending on the structure of the amine, its basicity varies over a wide range. Therefore, it is better to use universal indicator paper. 8. Qualitative reactions of polyfunctional compounds. For high-quality detection of bifunctional compounds (carbohydrates, amino acids), use the complex of reactions described above.
This substance can be considered not only as an acid, but also as an aldehyde. The aldehyde group is outlined in brown.
Therefore, formic acid exhibits reducing properties typical of aldehydes:
1. Silver mirror reaction:
2Ag (NH3)2OH ® NH4HCO3 + 3NH3 + 2Ag + H2O.
2. Reaction with copper hydroxide when heated:
HCOONa + 2Cu (OH)2 + NaOH ® Na2CO3 + Cu2O¯ + 3H2O.
3. Oxidation with chlorine to carbon dioxide:
HCOOH + Cl2 ® CO2 + 2HCl.
Concentrated sulfuric acid takes away water from formic acid. This produces carbon monoxide:
The acetic acid molecule contains a methyl group, the remainder of a saturated hydrocarbon - methane.
Therefore, acetic acid (and other saturated acids) will undergo radical substitution reactions characteristic of alkanes, for example:
CH3COOH + Cl2 + HCl
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In redox reactions organic substances more often they exhibit the properties of reducing agents, and themselves are oxidized. The ease of oxidation of organic compounds depends on the availability of electrons when interacting with the oxidizing agent. All known factors that cause an increase in electron density in molecules of organic compounds (for example, positive inductive and mesomeric effects) will increase their ability to oxidize and vice versa.
The tendency of organic compounds to oxidize increases with their nucleophilicity, which corresponds to the following rows:
Increase in nucleophilicity in the series
Let's consider redox reactions representatives of the most important classes organic matter with some inorganic oxidizing agents.
Oxidation of alkenes
During mild oxidation, alkenes are converted to glycols (dihydric alcohols). The reducing atoms in these reactions are carbon atoms linked by a double bond.
The reaction with a solution of potassium permanganate occurs in a neutral or slightly alkaline medium as follows:
3C 2 H 4 + 2KMnO 4 + 4H 2 O → 3CH 2 OH–CH 2 OH + 2MnO 2 + 2KOH
Under more severe conditions, oxidation leads to the rupture of the carbon chain at the double bond and the formation of two acids (in a strongly alkaline environment - two salts) or an acid and carbon dioxide (in a strongly alkaline environment - a salt and a carbonate):
1) 5CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5C 2 H 5 COOH + 8MnSO 4 + 4K 2 SO 4 + 17H 2 O
2) 5CH 3 CH=CH 2 + 10KMnO 4 + 15H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 10MnSO 4 + 5K 2 SO 4 + 20H 2 O
3) CH 3 CH=CHCH 2 CH 3 + 8KMnO 4 + 10KOH → CH 3 COOK + C 2 H 5 COOK + 6H 2 O + 8K 2 MnO 4
4) CH 3 CH=CH 2 + 10KMnO 4 + 13KOH → CH 3 COOK + K 2 CO 3 + 8H 2 O + 10K 2 MnO 4
Potassium dichromate in a sulfuric acid medium oxidizes alkenes similarly to reactions 1 and 2.
During the oxidation of alkenes, in which the carbon atoms at the double bond contain two carbon radicals, two ketones are formed:
Alkyne oxidation
Alkynes oxidize under slightly more severe conditions than alkenes, so they usually oxidize by breaking the carbon chain at the triple bond. As in the case of alkenes, the reducing atoms here are carbon atoms connected by a multiple bond. As a result of the reactions, acids and carbon dioxide are formed. Oxidation can be carried out with potassium permanganate or dichromate in an acidic environment, for example:
5CH 3 C≡CH + 8KMnO 4 + 12H 2 SO 4 → 5CH 3 COOH + 5CO 2 + 8MnSO 4 + 4K 2 SO 4 + 12H 2 O
Acetylene can be oxidized with potassium permanganate in a neutral environment to potassium oxalate:
3CH≡CH +8KMnO 4 → 3KOOC –COOK +8MnO 2 +2KOH +2H 2 O
In an acidic environment, oxidation proceeds to oxalic acid or carbon dioxide:
5CH≡CH +8KMnO 4 +12H 2 SO 4 → 5HOOC –COOH +8MnSO 4 +4K 2 SO 4 +12H 2 O
CH≡CH + 2KMnO 4 +3H 2 SO 4 → 2CO 2 + 2MnSO 4 + 4H 2 O + K 2 SO 4
Oxidation of benzene homologues
Benzene does not oxidize even under fairly harsh conditions. Benzene homologues can be oxidized with a solution of potassium permanganate in a neutral environment to potassium benzoate:
C 6 H 5 CH 3 + 2KMnO 4 → C 6 H 5 COOK + 2MnO 2 + KOH + H 2 O
C 6 H 5 CH 2 CH 3 + 4KMnO 4 → C 6 H 5 COOK + K 2 CO 3 + 2H 2 O + 4MnO 2 + KOH
Oxidation of benzene homologues with potassium dichromate or permanganate in an acidic environment leads to the formation of benzoic acid.
5C 6 H 5 CH 3 +6KMnO 4 +9 H 2 SO 4 → 5C 6 H 5 COOH+6MnSO 4 +3K 2 SO 4 + 14H 2 O
5C 6 H 5 –C 2 H 5 + 12KMnO 4 + 18H 2 SO 4 → 5C 6 H 5 COOH + 5CO 2 + 12MnSO 4 + 6K 2 SO 4 + 28H 2 O
Oxidation of alcohols
The direct oxidation product of primary alcohols is aldehydes, and the oxidation products of secondary alcohols are ketones.
Aldehydes formed during the oxidation of alcohols are easily oxidized to acids, therefore aldehydes from primary alcohols are obtained by oxidation with potassium dichromate in an acidic medium at the boiling point of the aldehyde. When aldehydes evaporate, they do not have time to oxidize.
3C 2 H 5 OH + K 2 Cr 2 O 7 + 4H 2 SO 4 → 3CH 3 CHO + K 2 SO 4 + Cr 2 (SO 4) 3 + 7H 2 O
With an excess of oxidizing agent (KMnO 4, K 2 Cr 2 O 7) in any environment, primary alcohols are oxidized to carboxylic acids or their salts, and secondary alcohols are oxidized to ketones.
5C 2 H 5 OH + 4KMnO 4 + 6H 2 SO 4 → 5CH 3 COOH + 4MnSO 4 + 2K 2 SO 4 + 11H 2 O
3CH 3 –CH 2 OH + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 3CH 3 –COOH + 2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O
Tertiary alcohols do not oxidize under these conditions, but methyl alcohol is oxidized to carbon dioxide.
Dihydric alcohol, ethylene glycol HOCH 2 –CH 2 OH, when heated in an acidic environment with a solution of KMnO 4 or K 2 Cr 2 O 7, is easily oxidized to oxalic acid, and in a neutral environment to potassium oxalate.
5CH 2 (OH) – CH 2 (OH) + 8КMnO 4 +12H 2 SO 4 → 5HOOC –COOH +8MnSO 4 +4К 2 SO 4 +22Н 2 О
3CH 2 (OH) – CH 2 (OH) + 8KMnO 4 → 3KOOC –COOK +8MnO 2 +2KOH +8H 2 O
Oxidation of aldehydes and ketones
Aldehydes are quite strong reducing agents, and therefore are easily oxidized by various oxidizing agents, for example: KMnO 4, K 2 Cr 2 O 7, OH, Cu(OH) 2. All reactions occur when heated:
3CH 3 CHO + 2KMnO 4 → CH 3 COOH + 2CH 3 COOK + 2MnO 2 + H 2 O
3CH 3 CHO + K 2 Cr 2 O 7 + 4H 2 SO 4 → 3CH 3 COOH + Cr 2 (SO 4) 3 + 7H 2 O
CH 3 CHO + 2KMnO 4 + 3KOH → CH 3 COOK + 2K 2 MnO 4 + 2H 2 O
5CH 3 CHO + 2KMnO 4 + 3H 2 SO 4 → 5CH 3 COOH + 2MnSO 4 + K 2 SO 4 + 3H 2 O
CH 3 CHO + Br 2 + 3NaOH → CH 3 COONa + 2NaBr + 2H 2 O
"silver mirror" reaction
With an ammonia solution of silver oxide, aldehydes are oxidized to carboxylic acids, which in an ammonia solution give ammonium salts (the “silver mirror” reaction):
CH 3 CH=O + 2OH → CH 3 COONH 4 + 2Ag + H 2 O + 3NH 3
CH 3 –CH=O + 2Cu(OH) 2 → CH 3 COOH + Cu 2 O + 2H 2 O
Formic aldehyde (formaldehyde) is usually oxidized to carbon dioxide:
5HCOH + 4KMnO4 (hut) + 6H 2 SO 4 → 4MnSO 4 + 2K 2 SO 4 + 5CO 2 + 11H 2 O
3CH 2 O + 2K 2 Cr 2 O 7 + 8H 2 SO 4 → 3CO 2 +2K 2 SO 4 + 2Cr 2 (SO 4) 3 + 11H 2 O
HCHO + 4OH → (NH 4) 2 CO 3 + 4Ag↓ + 2H 2 O + 6NH 3
HCOH + 4Cu(OH) 2 → CO 2 + 2Cu 2 O↓+ 5H 2 O
Ketones are oxidized under harsh conditions by strong oxidizing agents with the rupture of C-C bonds and give mixtures of acids:
Carboxylic acids. Among the acids, formic and oxalic acids have strong reducing properties, which oxidize to carbon dioxide.
HCOOH + HgCl 2 =CO 2 + Hg + 2HCl
HCOOH+ Cl 2 = CO 2 +2HCl
HOOC-COOH+ Cl 2 =2CO 2 +2HCl
Formic acid, in addition to acidic properties, also exhibits some properties of aldehydes, in particular, reducing ones. At the same time, it is oxidized to carbon dioxide. For example:
2KMnO4 + 5HCOOH + 3H2SO4 → K2SO4 + 2MnSO4 + 5CO2 + 8H2O
When heated with strong dewatering agents (H2SO4 (conc.) or P4O10) it decomposes:
HCOOH →(t)CO + H2O
Catalytic oxidation of alkanes:
Catalytic oxidation of alkenes:
Oxidation of phenols:
C 6 H 5 -CHO + O 2 ® C 6 H 5 -CO-O-OH
The resulting perbenzoic acid oxidizes the second molecule of benzoaldehyde to benzoic acid:
C 6 H 5 -CHO + C 6 H 5 -CO-O-OH ® 2C 6 H 5 -COOH
Experiment No. 34. Oxidation of benzoaldehyde with potassium permanganate
Reagents:
Benzoaldehyde
Potassium permanganate solution
Ethanol
Progress:
Place ~3 drops of benzaldehyde in a test tube, add ~2 ml of potassium permanganate solution and heat in a water bath with shaking until the odor of aldehyde disappears. If the solution does not discolor, then the color is destroyed with a few drops of alcohol. The solution is cooled. Benzoic acid crystals fall out:
C 6 H 5 -CHO + [O] ® C 6 H 5 -COOH
Experiment No. 35. Oxidation-reduction reaction of benzaldehyde (Cannizzaro reaction)
Reagents:
Benzoaldehyde
Alcohol solution of potassium hydroxide
Progress:
Add ~5 ml of a 10% alcohol solution of potassium hydroxide to ~1 ml of benzoaldehyde in a test tube and shake vigorously. This generates heat and solidifies the liquid.
The redox reaction of benzoaldehyde in the presence of alkali proceeds according to the following scheme:
2C 6 H 5 -CHO + KOH ® C 6 H 5 -COOK + C 6 H 5 -CH 2 -OH
The potassium salt of benzoic acid (the oxidation product of benzoaldehyde) and benzyl alcohol (the reduction product of benzoaldehyde) are formed.
The resulting crystals are filtered and dissolved in a minimal amount of water. When ~1 ml of 10% hydrochloric acid solution is added to the solution, free benzoic acid precipitates:
C 6 H 5 -COOK + HCl ® C 6 H 5 -COOH¯ + KCl
Benzyl alcohol is in the solution remaining after separating the crystals of the potassium salt of benzoic acid (the solution has the smell of benzyl alcohol).
VII. CARBOXYLIC ACIDS AND THEIR DERIVATIVES
Experiment No. 36. Oxidation of formic acid
Reagents:
Formic acid
10% sulfuric acid solution
Potassium permanganate solution
Barite or lime water
Progress:
~0.5-1 ml of formic acid, ~1 ml of a 10% sulfuric acid solution and ~4-5 ml of potassium permanganate solution are poured into a test tube with a gas outlet tube. The gas outlet tube is immersed in a test tube with a solution of lime or barite water. The reaction mixture is carefully heated by placing boiling stones in the test tube to ensure uniform boiling. The solution first turns brown, then becomes discolored, and carbon dioxide is released:
5H-COOH + 2KMnO4 + 3H2SO4 ® 5HO-CO-OH + K2SO4 + 2MnSO4 + 3H2O
HO-CO-OH ® CO 2 + H 2 O
Experiment No. 37. Reduction of an ammonia solution of silver hydroxide with formic acid
Reagents:
Ammonia solution of silver hydroxide (Tollens reagent)
Formic acid
