CARBON OXIDE (CARBON MONOXIDE). Carbon (II) oxide (carbon monoxide) CO, non-salt-forming carbon monoxide. This means that there is no acid corresponding to this oxide. Carbon monoxide (II) is a colorless and odorless gas that liquefies at atmospheric pressure at a temperature of -191.5 ° C and solidifies at -205 ° C. The CO molecule is similar in structure to the N2 molecule: both contain an equal number of electrons (such molecules are called isoelectronic) , the atoms in them are connected by a triple bond (two bonds in the CO molecule are formed due to the 2p electrons of carbon and oxygen atoms, and the third - by the donor-acceptor mechanism with the participation of the oxygen lone electron pair and the free 2p orbital of carbon). As a result, the physical properties of CO and N2 (melting and boiling points, water solubility, etc.) are very close.
Carbon monoxide (II) is formed during the combustion of carbon-containing compounds with insufficient oxygen access, as well as when hot coal comes into contact with the product of complete combustion - carbon dioxide: С + СО2 → 2СО. In the laboratory, SS is obtained by dehydration of formic acid by the action of concentrated sulfuric acid on liquid formic acid when heated, or by passing formic acid vapors over P2O5: HCOOH → CO + H2O. CO is obtained by the decomposition of oxalic acid: Н2С2О4 → СО + СО2 + Н2О. CO can be easily separated from other gases by passing it through an alkali solution.
Under normal conditions, CO, like nitrogen, is chemically quite inert. Only at elevated temperatures does CO exhibit a tendency towards oxidation, addition, and reduction reactions. So, at elevated temperatures, it reacts with alkalis: CO + NaOH → HCOONa, CO + Ca (OH) 2 → CaCO3 + H2. These reactions are used to remove CO from industrial gases.
Carbon monoxide (II) is a high-calorie fuel: combustion is accompanied by the release of a significant amount of heat (283 kJ per 1 mol of CO). Mixtures of CO with air explode when its content is from 12 to 74%; fortunately, such mixtures are extremely rare in practice. In industry, to obtain CO, gasification of solid fuel is carried out. For example, blowing water vapor through a layer of coal heated to 1000oC leads to the formation of water gas: C + H2O → CO + H2, which has a very high calorific value. However, incineration is far from the most profitable use of water gas. From it, for example, it is possible to obtain (in the presence of various catalysts under pressure) a mixture of solid, liquid and gaseous hydrocarbons - a valuable raw material for the chemical industry (Fischer-Tropsch reaction). From the same mixture, enriching it with hydrogen and applying the necessary catalysts, one can obtain alcohols, aldehydes, acids. The synthesis of methanol is of particular importance: CO + 2H2 → CH3OH - the most important raw material for organic synthesis, therefore this reaction is carried out in industry on a large scale.
Reactions in which CO is a reducing agent can be demonstrated by the example of iron reduction from ore in the course of a blast furnace process: Fe3O4 + 4CO → 3Fe + 4CO2. The reduction of metal oxides with carbon monoxide (II) is of great importance in metallurgical processes.
CO molecules are characterized by addition reactions to transition metals and their compounds with the formation of complex compounds - carbonyls. Examples are liquid or solid metal carbonyls Fe (CO) 4, Fe (CO) 5, Fe2 (CO) 9, Ni (CO) 4, Cr (CO) 6, etc. These are very poisonous substances that, when heated, decompose again into metal and CO. In this way, powdered metals of high purity can be obtained. Sometimes metal "smudges" are visible on the burner of a gas stove, this is a consequence of the formation and decay of iron carbonyl. Currently, thousands of various metal carbonyls have been synthesized containing, in addition to CO, inorganic and organic ligands, for example, PtCl2 (CO), K3, Cr (C6H5Cl) (CO) 3.
CO is also characterized by the reaction of a compound with chlorine, which proceeds in the light even at room temperature with the formation of an extremely poisonous phosgene: CO + Cl2 → COCl2. This is a chain reaction, it goes by a radical mechanism with the participation of chlorine atoms and free radicals COCl. Despite its toxicity, phosgene is widely used for the synthesis of many organic compounds.
Carbon monoxide (II) is a strong poison, as it forms strong complexes with metal-containing biologically active molecules; at the same time tissue respiration is disturbed. The cells of the central nervous system are especially affected. The binding of CO with Fe (II) atoms in the hemoglobin of the blood prevents the formation of oxyhemoglobin, which carries oxygen from the lungs to the tissues. Already with a content of 0.1% CO in the air, this gas displaces half of the oxygen from oxyhemoglobin. In the presence of CO, death from suffocation can occur even in the presence of a large amount of oxygen. Therefore, CO was called carbon monoxide. In a "burnt" person, the brain and nervous system are the first to suffer. For salvation, first of all, clean air that does not contain CO (or, even better, pure oxygen) is needed, while the CO associated with hemoglobin is gradually replaced by O2 molecules and the suffocation passes. The maximum permissible average daily concentration of CO in the ambient air is 3 mg / m3 (about 3.10–5%), in the air of the working area - 20 mg / m3.
Usually, the CO content in the atmosphere does not exceed 10–5%. This gas enters the air as part of volcanic and swamp gases, with the release of plankton and other microorganisms. So, from the surface layers of the ocean, 220 million tons of CO are released into the atmosphere annually. The concentration of CO is high in coal mines. A lot of carbon monoxide is generated by forest fires. Smelting of each million tons of steel is accompanied by the formation of 300 - 400 tons of CO. In total, the technogenic release of CO into the air reaches 600 million tons per year, of which more than half is accounted for by motor vehicles. With an unregulated carburetor, the exhaust gases can contain up to 12% CO! Therefore, in most countries, strict standards for the content of CO in the exhaust of cars have been introduced.
The formation of CO always occurs during the combustion of carbon-containing compounds, including wood, with insufficient access to oxygen, as well as when hot coal comes into contact with carbon dioxide: C + CO2 → 2CO. Such processes also occur in the village ovens. Therefore, prematurely closing the chimney of the stove to conserve heat often leads to carbon monoxide poisoning. One should not think that the townspeople who do not heat the stoves are insured against CO poisoning; for example, it is easy for them to get poisoned in a poorly ventilated garage where there is a car with a running engine. CO is also contained in the combustion products of natural gas in the kitchen. Many aircraft accidents in the past occurred due to engine wear or poor adjustment: CO entered the cockpit and poisoned the crew. The danger is compounded by the fact that CO cannot be detected by smell; in this respect carbon monoxide is more dangerous than chlorine!
Carbon monoxide (II) is practically not absorbed by active carbon and therefore a regular gas mask does not save you from this gas; to absorb it, an additional hopcalite cartridge is needed, containing a catalyst that “burns” CO to CO2 with the help of atmospheric oxygen. An increasing number of passenger cars are now being supplied with post-combustion catalysts, despite the high cost of these catalysts based on platinum metals.
Carbon oxides
In recent years, in pedagogical science, preference has been given to student-centered learning. The formation of individual personality traits occurs in the process of activity: study, play, work. Therefore, an important factor in learning is the organization of the learning process, the nature of the teacher's relationship with students and students among themselves. Based on these ideas, I am trying to build the educational process in a special way. At the same time, each student chooses his own pace of studying the material, has the opportunity to work at a level accessible to him, in a situation of success. In the lesson, it is possible to master and improve not only subject, but also such general educational skills and abilities as setting an educational goal, choosing the means and ways to achieve it, exercising control over one's achievements, and correcting errors. Students learn to work with literature, make notes, diagrams, drawings, work in a group, in pairs, individually, conduct a constructive exchange of views, reason logically and draw conclusions.
It is not easy to do such lessons, but if you are lucky, you can feel satisfaction. Here's a script for one of my lessons. It was attended by colleagues, administration and a psychologist.
Lesson type. Learning new material.
Goals. On the basis of motivation and actualization of the basic knowledge and skills of students, consider the structure, physical and chemical properties, the production and use of carbon monoxide and carbon dioxide.
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Equipment and reagents. Cards "Programmed interrogation", poster-scheme, devices for obtaining gases, glasses, test tubes, fire extinguisher, matches; lime water, sodium oxide, chalk, hydrochloric acid, indicator solutions, H 2 SO 4 (conc.), HCOOH, Fe 2 O 3.
Poster diagram
"The structure of the carbon monoxide (carbon monoxide (II)) CO molecule"
DURING THE CLASSES
Tables for students in the study are arranged in a circle. The teacher and students have the opportunity to freely move to laboratory tables (1, 2, 3). For the lesson, children sit at study tables (4, 5, 6, 7, ...) with each other at will (free groups of 4 people).
Teacher. Wise Chinese proverb(written beautifully on the board) reads:
“I hear - I forget
I see - I remember
I do - I understand. "
Do you agree with the conclusions of the Chinese sages?
What Russian proverbs reflect Chinese wisdom?
Children give examples.
Teacher. Indeed, only by creating, by creating, you can get a valuable product: new substances, devices, machines, as well as intangible values - conclusions, generalizations, inferences. Today I suggest you take part in the study of the properties of two substances. It is known that when passing a technical inspection of a car, the driver provides a certificate of the state of the car's exhaust gases. What gas concentration is indicated in the certificate?
(Answer CO.)
Student. This gas is poisonous. Once in the bloodstream, it causes poisoning of the body ("burnout", hence the name of the oxide - carbon monoxide). It is found in life-threatening quantities in car exhaust fumes(reads out a message from the newspaper that the driver who fell asleep while the engine was running in the garage got mad to death). The antidote for carbon monoxide poisoning is the inhalation of fresh air and pure oxygen. Another carbon monoxide is carbon dioxide.
Teacher. There is a programmed survey card on your tables. Familiarize yourself with its content and on a blank piece of paper, mark the numbers of those assignments, the answers to which you know on the basis of your life experience. Next to the statement number, write the formula for the carbon monoxide to which the statement applies.
Pupils-consultants (2 people) collect answer sheets and, based on the results of the answers, form new groups for further work.
Programmed polling "Carbon oxides"
1. The molecule of this oxide consists of one carbon atom and one oxygen atom.
2. The bond between atoms in a molecule is covalent polar.
3. A gas practically insoluble in water.
4. The molecule of this oxide has one carbon atom and two oxygen atoms.
5. Has no smell and color.
6. Water soluble gas.
7. Does not liquefy even at -190 ° С ( t bale = -191.5 ° C).
8. Acidic oxide.
9. Easily compressed, at 20 ° C under a pressure of 58.5 atm becomes liquid, solidifies into "dry ice".
10. Not poisonous.
11. Non-salt-forming.
12. Combustible.
13. Interacts with water.
14. Interacts with basic oxides.
15. Reacts with metal oxides, reducing free metals from them.
16. Obtained by the interaction of acids with carbonic acid salts.
17. I.
18. Interacts with alkalis.
19. The carbon source for plants to use in greenhouses and greenhouses results in higher yields.
20. Used when carbonating water and drinks.
Teacher. Review the contents of the card again. Group the information into 4 blocks:
structure,
physical properties,
Chemical properties,
receiving.
The teacher provides an opportunity to speak to each group of students, summarizes the speeches. Then students from different groups choose their work plan - the order of studying oxides. For this purpose, they number blocks of information and justify their choice. The order of study can be as written above, or with any other combination of the four blocks marked.
The teacher draws the students' attention to the key points of the topic. As carbon oxides are gaseous, they must be handled with care (safety regulations). The teacher approves the plan for each group and assigns counselors (pre-trained students).
Demonstration experiments
1. Pouring carbon dioxide from glass to glass.
2. Extinguishing candles in a glass as CO 2 accumulates.
3. Put a few small pieces of "dry ice" in a glass of water. The water will gurgle, and thick white smoke will pour out of it.
CO2 gas liquefies already at room temperature under a pressure of 6 MPa. In a liquid state, it is stored and transported in steel cylinders. If you open the valve of such a cylinder, the liquid CO 2 will begin to evaporate, due to which strong cooling occurs and part of the gas turns into a snow-like mass - "dry ice", which is pressed and used to store ice cream.
4. Demonstration of a chemical foam fire extinguisher (CFS) and an explanation of the principle of its operation using a model - a test tube with a stopper and a gas outlet pipe.
Information on structure at table number 1 (instruction cards 1 and 2, the structure of CO and CO 2 molecules).
Information about physical properties- at table number 2 (work with the textbook - Gabrielyan O.S. Chemistry-9. M .: Bustard, 2002, p. 134-135).
Data on the receipt and chemical properties- on tables 3 and 4 (instruction cards 3 and 4, instructions for practical work, pp. 149–150 of the textbook).
Practical work Add a few pieces of chalk or marble to a test tube and add a little diluted hydrochloric acid. Close the tube quickly with a stopper with a vent tube. Dip the end of the tube into another tube containing 2-3 ml of lime water. Watch gas bubbles pass through the lime water for a few minutes. Then take the end of the flue tube out of the solution and rinse it in distilled water. Place the tube in another tube with 2-3 ml of distilled water and pass the gas through it. After a few minutes, remove the tube from the solution, add a few drops of blue litmus to the resulting solution. Pour 2-3 ml of diluted sodium hydroxide solution into a test tube and add a few drops of phenolphthalein to it. Then pass the gas through the solution. Answer the questions. Questions 1. What happens if chalk or marble is attacked with hydrochloric acid? 2. Why, when carbon dioxide is passed through lime water, the solution first becomes cloudy, and then lime dissolves? 3. What happens when you pass carbon monoxide (IV) through distilled water? Write the equations of the corresponding reactions in molecular, ionic and ionic forms. Recognition of carbonates The four test tubes given to you contain crystalline substances: sodium sulfate, zinc chloride, potassium carbonate, sodium silicate. Determine what substance is in each tube. Write the reaction equations in molecular, ionic and abbreviated ionic forms. |
Homework
The teacher suggests taking the “Programmable Survey” card home and, in preparation for the next lesson, think over ways of obtaining information. (How did you know that the gas under study liquefies, interacts with acid, is poisonous, etc.?)
Independent work of students
Groups of children perform practical work at different speeds. Therefore, games are offered to those who complete their work faster.
Fifth extra
Four substances can be found to have something in common, and the fifth substance is out of the ordinary, superfluous.
1. Carbon, diamond, graphite, carbide, carbyne. (Carbide.)
2. Anthracite, peat, coke, oil, glass. (Glass.)
3. Limestone, chalk, marble, malachite, calcite. (Malachite.)
4. Crystalline soda, marble, potash, caustic, malachite. (Caustic.)
5. Phosgene, phosphine, hydrocyanic acid, potassium cyanide, carbon disulfide. (Phosphine.)
6. Sea water, mineral water, distilled water, ground water, hard water. (Distilled water.)
7. Lime milk, fluff, slaked lime, limestone, lime water. (Limestone.)
8. Li 2 CO 3; (NH 4) 2 CO 3; CaCO 3; K 2 CO 3, Na 2 CO 3. (CaCO 3.)
Synonyms
Write the chemical formulas of the substances or their names.
1. Halogen - ... (Chlorine or bromine.)
2. Magnesite - ... (MgCO 3.)
3. Urea - ... ( Urea H 2 NC (O) NH 2.)
4. Potash - ... (K 2 CO 3.)
5. Dry ice -… (CO 2.)
6. Hydrogen oxide - ... ( Water.)
7. Ammonia - ... ( 10% aqueous ammonia solution.)
8. Salts of nitric acid - ... ( Nitrates- KNO 3, Ca (NO 3) 2, NaNO 3.)
9. Natural gas - ... ( Methane CH 4.)
Antonyms
Write chemical terms that are opposite in meaning to those suggested.
1. Oxidant - ... ( Reducing agent.)
2. Electron donor - ... ( Electron acceptor.)
3. Acidic properties - ... ( Basic properties.)
4. Dissociation - ... ( Association.)
5. Adsorption - ... ( Desorption.)
6. Anode - ... ( Cathode.)
7. Anion - ... ( Cation.)
8. Metal - ... ( Non-metal.)
9. Initial substances - ... ( Reaction products.)
Search for patterns
Establish a sign that unites the indicated substances and phenomena.
1. Diamond, carbyne, graphite - ... ( Allotropic modifications of carbon.)
2. Glass, cement, brick - ... ( Construction Materials.)
3. Breathing, decay, volcanic eruption - ... ( Processes accompanied by the release of carbon dioxide.)
4. CO, CO 2, CH 4, SiH 4 - ... ( Compounds of IV group elements.)
5. NaHCO 3, CaCO 3, CO 2, H 2 CO 3 - ... ( Oxygen compounds of carbon.)
Carbon monoxide, or carbon monoxide (CO), is a colorless, odorless and tasteless gas. Burns with a blue flame like hydrogen. Because of this, in 1776, chemists confused it with hydrogen when they first produced carbon monoxide by heating zinc oxide with carbon. The molecule of this gas has a strong triple bond, like the nitrogen molecule. That is why there is some similarity between them: the melting and boiling points are practically the same. The carbon monoxide molecule has a high ionization potential.
Oxidizing, carbon monoxide forms carbon dioxide. In this reaction, a large amount of heat energy is released. This is why carbon monoxide is used in heating systems.
Carbon monoxide at low temperatures hardly reacts with other substances; in the case of high temperatures, the situation is different. The reactions of addition of various organic substances pass very quickly. A mixture of CO and oxygen in certain proportions is very dangerous due to the possibility of its explosion.
Obtaining carbon monoxide
Under laboratory conditions, carbon monoxide is produced by decomposition. It occurs under the influence of hot concentrated sulfuric acid, or when passing it through phosphorus oxide. Another method is that the mixture of formic and oxalic acids is heated to a certain temperature. The evolved CO can be removed from this mixture by passing it through barite water (saturated solution).
Danger of carbon monoxide
Carbon monoxide is extremely dangerous to humans. It causes severe poisoning, and can often cause death. The thing is that carbon monoxide has the ability to react with blood hemoglobin, which carries out the transfer of oxygen to all cells of the body. As a result of this reaction, carbohemoglobin is formed. Due to the lack of oxygen, cells starve.
The following symptoms of poisoning can be distinguished: nausea, vomiting, headache, loss of color perception, respiratory distress and others. A person who has been poisoned by carbon monoxide should be given first aid as soon as possible. First, you need to take it out into fresh air and put a cotton swab dipped in ammonia to your nose. Then rub the victim's chest and apply heating pads to his legs. A plentiful warm drink is recommended. It is necessary to call a doctor immediately after detecting symptoms.
Carbon monoxide, carbon monoxide (CO) is a colorless, odorless and tasteless gas that is slightly less dense than air. It is toxic to hemoglobin animals (including humans) if concentrations are higher than about 35 ppm, although it is also produced in normal animal metabolism in small amounts and is believed to have some normal biological function. In the atmosphere, it is spatially variable and rapidly decaying, and has a role in the formation of ozone at ground level. Carbon monoxide is made up of one carbon atom and one oxygen atom linked by a triple bond, which is made up of two covalent bonds as well as one dative covalent bond. It is the simplest carbon monoxide. It is an isoelectron with cyanide anion, nitrosonium cation and molecular nitrogen. In coordination complexes, the carbon monoxide ligand is called a carbonyl.
History
Aristotle (384-322 BC) was the first to describe the process of burning coal, which leads to the formation of toxic fumes. In ancient times, there was a method of execution - to close a criminal in a bathroom with embers. However, at that time, the mechanism of death was not clear. The Greek physician Galen (AD 129-199) suggested that there was a change in the composition of the air that caused harm to humans when inhaled. In 1776, the French chemist de Lasson produced CO by heating zinc oxide with coke, but the scientist erroneously concluded that the gaseous product was hydrogen because it burned with a blue flame. The gas was identified as a compound containing carbon and oxygen by Scottish chemist William Cumberland Cruickshank in 1800. Its toxicity in dogs was extensively investigated by Claude Bernard around 1846. During World War II, a gas mixture containing carbon monoxide was used to support motor vehicles operating in parts of the world where gasoline and diesel were scarce. External (with some exceptions) charcoal or wood-derived gas generators were installed and a mixture of atmospheric nitrogen, carbon monoxide and small amounts of other gases from gasification was fed to the gas mixer. The gas mixture resulting from this process is known as wood gas. Carbon monoxide was also used on a large scale during the Holocaust in some German Nazi death camps, most notably in gas vans in Chelmno and in the T4 killing program "euthanasia".
Sources of
Carbon monoxide is formed during the partial oxidation of carbon-containing compounds; it is formed when there is not enough oxygen to form carbon dioxide (CO2), for example when working with a stove or an internal combustion engine in an enclosed space. In the presence of oxygen, including its concentration in the atmosphere, carbon monoxide burns with a blue flame, producing carbon dioxide. Coal gas, which was widely used until the 1960s for indoor lighting, cooking, and heating, contained carbon monoxide as a significant fuel constituent. Some processes in modern technology, such as iron smelting, still produce carbon monoxide as a by-product. Worldwide, the largest sources of carbon monoxide are natural sources, due to photochemical reactions in the troposphere, which generate about 5 × 1012 kg of carbon monoxide per year. Other natural sources of CO include volcanoes, forest fires, and other forms of combustion. In biology, carbon monoxide is naturally produced by the action of heme oxygenase 1 and 2 on heme from the breakdown of hemoglobin. This process produces a certain amount of carboxyhemoglobin in normal people, even if they do not inhale carbon monoxide. After the first report that carbon monoxide is a normal neurotransmitter in 1993, as well as one of three gases that naturally modulate inflammatory responses in the body (the other two are nitric oxide and hydrogen sulfide), carbon monoxide has received a lot of scientific attention as a biological regulator. In many tissues, all three gases act as anti-inflammatory agents, vasodilators, and promoters of neovascular growth. Clinical trials are ongoing with small amounts of carbon monoxide as a drug. However, excessive amounts of carbon monoxide cause carbon monoxide poisoning.
Molecular properties
Carbon monoxide has a molecular weight of 28.0, making it slightly lighter than air, which has an average molecular weight of 28.8. According to the ideal gas law, CO therefore has a lower density than air. The bond length between a carbon atom and an oxygen atom is 112.8 pm. This bond length is consistent with a triple bond as in molecular nitrogen (N2), which has a similar bond length and almost the same molecular weight. The carbon-oxygen double bonds are much longer, for example, 120.8 m for formaldehyde. The boiling point (82 K) and melting point (68 K) are very similar to N2 (77 K and 63 K, respectively). The bond dissociation energy of 1072 kJ / mol is stronger than that of N2 (942 kJ / mol) and represents the strongest known chemical bond. The ground state of the carbon monoxide electron is singlet, since there are no unpaired electrons.
Coupling and dipole moment
Carbon and oxygen together have a total of 10 electrons in the valence shell. Following the octet rule for carbon and oxygen, the two atoms form a triple bond, with six electrons shared in three bonding molecular orbitals, rather than the usual double bond as with organic carbonyl compounds. Since four of the shared electrons come from oxygen and only two from carbon, one bonding orbital is occupied by two electrons from oxygen atoms, forming a dative or dipole bond. This results in a C ← O polarization of the molecule, with a small negative charge on carbon and a small positive charge on oxygen. The other two bonding orbitals each occupy one electron from carbon and one from oxygen, forming (polar) covalent bonds with reverse C → O polarization, since oxygen is more electronegative than carbon. In free carbon monoxide, the net negative charge δ- remains at the end of the carbon, and the molecule has a small dipole moment of 0.122 D. Thus, the molecule is asymmetric: oxygen has more electron density than carbon, and also a small positive charge compared to carbon. which is negative. In contrast, the isoelectronic dinitrogen molecule has no dipole moment. If carbon monoxide acts as a ligand, the polarity of the dipole can change with a net negative charge at the oxygen end, depending on the structure of the coordination complex.
Bond polarity and oxidation state
Theoretical and experimental studies show that, despite the large electronegativity of oxygen, the dipole moment comes from the more negative end of carbon to the more positive end of oxygen. These three bonds are actually polar covalent bonds that are highly polarized. The calculated polarization to oxygen is 71% for the σ bond and 77% for both π bonds. The oxidation state of carbon to carbon monoxide in each of these structures is +2. It is calculated as follows: all bonding electrons are considered to belong to the more electronegative oxygen atoms. Only two non-bonding electrons on carbon are carbon. With this calculation, carbon has only two valence electrons in a molecule, compared to four in a free atom.
Biological and physiological properties
Toxicity
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is a colorless, odorless and tasteless substance that is highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which usurps a site in hemoglobin that normally carries oxygen but is ineffective in delivering oxygen to body tissues. Concentrations as low as 667 ppm can cause up to 50% of the body's hemoglobin to be converted to carboxyhemoglobin. 50% carboxyhemoglobin levels can lead to seizures, coma, and death. In the United States, the Department of Labor limits long-term levels of workplace carbon monoxide exposure to 50 ppm. Over a short period of time, the absorption of carbon monoxide is cumulative, since its half-life is about 5 hours in the open air. The most common symptoms of carbon monoxide poisoning can be similar to other types of poisoning and infections, and include symptoms such as headache, nausea, vomiting, dizziness, tiredness, and feeling weak. Affected families often believe they are victims of food poisoning. Babies can be irritable and eat poorly. Neurological symptoms include confusion, disorientation, blurred vision, fainting (loss of consciousness), and seizures. Some descriptions of carbon monoxide poisoning include retinal hemorrhages, as well as an abnormal cherry-red tinge of the blood. In most clinical diagnoses, these signs are rare. One of the difficulties associated with the usefulness of this "cherry" effect is related to the fact that it corrects, or masks, otherwise unhealthy appearance, since the main effect of removing venous hemoglobin is associated with the fact that the strangled person appears more normal, or a dead person appears to be alive, similar to the effect of red dyes in an embalming compound. This dyeing effect in oxygen-free CO-poisoned tissue is associated with the commercial use of carbon monoxide in dyeing meat. Carbon monoxide also binds to other molecules such as myoglobin and mitochondrial cytochrome oxidase. Exposure to carbon monoxide can cause significant damage to the heart and central nervous system, especially in globus pallidus, often associated with long-term chronic conditions. Carbon monoxide can have serious adverse effects on the fetus of a pregnant woman.
Normal human physiology
Carbon monoxide is produced naturally in the human body as a signaling molecule. Thus, carbon monoxide may have a physiological role in the body as a neurotransmitter or blood vessel relaxant. Because of the role of carbon monoxide in the body, disturbances in its metabolism are associated with various diseases, including neurodegeneration, hypertension, heart failure, and inflammation.
CO functions as an endogenous signaling molecule.
CO modulates the functions of the cardiovascular system
CO inhibits platelet aggregation and adhesion
CO may play a role as a potential therapeutic agent
Microbiology
Carbon monoxide is a breeding ground for methanogenic archaea, a building block for acetyl coenzyme A. This is a topic for a new field of bioorganic chemistry. Extremophilic microorganisms can thus metabolize carbon monoxide in places such as the thermal vents of volcanoes. In bacteria, carbon monoxide is produced by reducing carbon dioxide by the enzyme carbon monoxide dehydrogenase, a Fe-Ni-S-containing protein. CooA is a carbon monoxide receptor protein. The scope of its biological activity is still unknown. It may be part of a signaling pathway in bacteria and archaea. Its prevalence in mammals has not been established.
Prevalence
Carbon monoxide is found in a variety of natural and artificial environments.
Carbon monoxide is present in small amounts in the atmosphere, mainly as a product of volcanic activity, but is also a product of natural and man-made fires (eg forest fires, burning of plant residues, and burning of sugar cane). Burning fossil fuels also contributes to the formation of carbon monoxide. Carbon monoxide occurs in dissolved form in molten volcanic rocks at high pressures in the Earth's mantle. Because natural sources of carbon monoxide are variable, it is extremely difficult to accurately measure natural gas emissions. Carbon monoxide is a rapidly decaying greenhouse gas, and it also exerts an indirect radiative forcing by increasing the concentration of methane and tropospheric ozone as a result of chemical reactions with other components of the atmosphere (for example, hydroxyl radical, OH), which would otherwise destroy them. As a result of natural processes in the atmosphere, it eventually oxidizes to carbon dioxide. Carbon monoxide is simultaneously short-lived in the atmosphere (it remains on average for about two months) and has a spatially variable concentration. In the atmosphere of Venus, carbon monoxide is created by photodissociation of carbon dioxide by electromagnetic radiation with wavelengths shorter than 169 nm. Because of its long life in the middle troposphere, carbon monoxide is also used as a transport tracer for jets of pollutants.
Pollution of cities
Carbon monoxide is a temporary air pollutant in some urban areas, mainly from the exhaust pipes of internal combustion engines (including vehicles, portable and standby generators, lawn mowers, washing machines, etc.) and from incomplete combustion various other fuels (including firewood, coal, charcoal, oil, paraffin, propane, natural gas and garbage). Large CO pollution can be observed from space over cities.
Role in the formation of ground-level ozone
Carbon monoxide, along with aldehydes, is part of a series of chemical reaction cycles that form photochemical smog. It reacts with a hydroxyl radical (OH) to form the radical intermediate HOCO, which rapidly transfers the radical hydrogen to O2 to form a peroxide radical (HO2) and carbon dioxide (CO2). The peroxide radical then reacts with nitrogen oxide (NO) to form nitrogen dioxide (NO2) and a hydroxyl radical. NO 2 gives O (3P) through photolysis, thereby forming O3 after reaction with O2. Since the hydroxyl radical is formed during the formation of NO2, the balance of the sequence of chemical reactions, starting with carbon monoxide, leads to the formation of ozone: CO + 2O2 + hν → CO2 + O3 (where hν refers to the photon of light absorbed by the NO2 molecule in the sequence) Although the creation NO2 is an important step in producing low level ozone, it also increases ozone in a different, somewhat mutually exclusive way by reducing the amount of NO that is available to react with ozone.
Indoor air pollution
In closed environments, the concentration of carbon monoxide can easily increase to lethal levels. On average, 170 people die each year from non-automotive consumer products that produce carbon monoxide in the United States. However, according to the Florida Department of Health, "More than 500 Americans die each year from accidental exposure to carbon monoxide and thousands more in the United States require emergency medical attention for non-fatal carbon monoxide poisoning." These products include faulty fuel combustion appliances such as stoves, stoves, water heaters, and gas and kerosene room heaters; mechanically driven equipment such as portable generators; fireplaces; and charcoal, which is burned in homes and other enclosed spaces. The American Association of Poison Control Centers (AAPCC) reported 15,769 cases of carbon monoxide poisoning, which resulted in 39 deaths in 2007. In 2005, the CPSC reported 94 deaths associated with generator carbon monoxide poisoning. Forty-seven of these deaths occurred during power outages due to severe weather, including Hurricane Katrina. However, people die from carbon monoxide poisoning from non-food items such as cars left behind by workers in garages adjacent to their homes. The Centers for Disease Control and Prevention reports that several thousand people visit an emergency hospital each year for carbon monoxide poisoning.
Presence in blood
Carbon monoxide is absorbed through respiration and enters the bloodstream through gas exchange in the lungs. It is also produced during the metabolism of hemoglobin and enters the bloodstream from tissues, and thus is present in all normal tissues, even if it does not enter the body through respiration. Normal levels of carbon monoxide circulating in the blood are between 0% and 3%, and are higher in smokers. Carbon monoxide levels cannot be assessed by physical examination. Laboratory testing requires a blood sample (arterial or venous) and laboratory analysis with a CO-oximeter. In addition, non-invasive carboxyhemoglobin (SPCO) with pulsed CO-oximetry is more effective than invasive methods.
Astrophysics
Outside of Earth, carbon monoxide is the second most abundant molecule in the interstellar medium, after molecular hydrogen. Because of its asymmetry, the carbon monoxide molecule produces much brighter spectral lines than the hydrogen molecule, making CO much easier to detect. Interstellar CO was first detected with radio telescopes in 1970. It is currently the most commonly used indicator of molecular gas in the interstellar medium of galaxies, and molecular hydrogen can only be detected using ultraviolet light, which requires space telescopes. Observations of carbon monoxide provide most of the information about the molecular clouds in which most stars form. Beta Pictoris, the second brightest star in the constellation Pictor, exhibits an excess of infrared radiation compared to normal stars of its type, due to the large amount of dust and gas (including carbon monoxide) near the star.
Production
Many methods have been developed for the production of carbon monoxide.
Industrial production
The main industrial source of CO is generator gas, a mixture of mainly carbon monoxide and nitrogen formed when carbon is burned in high temperature air when there is excess carbon. In an oven, air is passed through a layer of coke. The original CO2 produced is equilibrated with the remaining hot coal to produce CO. The reaction of CO2 with carbon to produce CO is described as the Boudouard reaction. At temperatures above 800 ° C, CO is the predominant product:
CO2 + C → 2 CO (ΔH = 170 kJ / mol)
Another source is "water gas", a mixture of hydrogen and carbon monoxide produced by the endothermic reaction of steam and carbon:
H2O + C → H2 + CO (ΔH = +131 kJ / mol)
Other similar "syngas" can be obtained from natural gas and other fuels. Carbon monoxide is also a by-product of the reduction of metal oxide ores with carbon:
MO + C → M + CO
Carbon monoxide is also produced by direct oxidation of carbon in a limited amount of oxygen or air.
2C (s) + O 2 → 2CO (g)
Since CO is a gas, the reduction process can be controlled by heating using the positive (favorable) entropy of the reaction. The Ellingham diagram shows that the formation of CO is preferred over CO2 at high temperatures.
Laboratory preparation
Carbon monoxide is conveniently obtained in the laboratory by dehydration of formic acid or oxalic acid, for example, using concentrated sulfuric acid. Another method is to heat a homogeneous mixture of powdered zinc metal and calcium carbonate, which releases CO and leaves zinc oxide and calcium oxide:
Zn + CaCO3 → ZnO + CaO + CO
Silver nitrate and iodoform also give carbon monoxide:
CHI3 + 3AgNO3 + H2O → 3HNO3 + CO + 3AgI
Coordination chemistry
Most metals form coordination complexes containing covalently attached carbon monoxide. Only metals in the lowest oxidation states will bond with carbon monoxide ligands. This is because sufficient electron density is needed to facilitate the reverse donation from the metal DXZ orbital to the π * molecular orbital from CO. The lone pair on the carbon atom in CO also donates the electron density in dx²-y² on the metal to form a sigma bond. This electron donation also manifests itself as a cis effect, or labilization of CO ligands in the cis position. Nickel carbonyl, for example, is formed by the direct combination of carbon monoxide and metallic nickel:
Ni + 4 CO → Ni (CO) 4 (1 bar, 55 ° C)
For this reason, the nickel in the tube or part of it should not come into prolonged contact with carbon monoxide. Nickel carbonyl readily decomposes back to Ni and CO on contact with hot surfaces, and this method is used for industrial purification of nickel in the Mond process. In nickel carbonyl and other carbonyls, an electron pair on carbon interacts with a metal; carbon monoxide donates an electron pair to metal. In these situations, carbon monoxide is called a carbonyl ligand. One of the most important metal carbonyls is iron pentacarbonyl, Fe (CO) 5. Many metal-CO complexes are produced by decarbonylation of organic solvents rather than CO. For example, iridium trichloride and triphenylphosphine react in boiling 2-methoxyethanol or DMF to give IrCl (CO) (PPh3) 2. Metal carbonyls in coordination chemistry are usually studied by infrared spectroscopy.
Organic chemistry and chemistry of the main groups of elements
In the presence of strong acids and water, carbon monoxide reacts with alkenes to form carboxylic acids in a process known as the Koch-Haaf reaction. In the Guttermann-Koch reaction, arenes are converted to benzaldehyde derivatives in the presence of AlCl3 and HCl. Organolithium compounds (for example, butyllithium) react with carbon monoxide, but these reactions have little scientific application. Although CO reacts with carbocations and carbanions, it is relatively unreactive to organic compounds without the intervention of metal catalysts. With reagents from the main group, CO undergoes several remarkable reactions. Chlorination of CO is an industrial process that leads to the formation of the important compound phosgene. With borane, CO forms an adduct, H3BCO, which is isoelectronic with acylium + cation. CO reacts with sodium to create products derived from the C-C bond. The compounds cyclohexagehexone or trivinoyl (C6O6) and cyclopentanepentone or leuconic acid (C5O5), which have so far been obtained only in trace amounts, can be regarded as polymers of carbon monoxide. At pressures over 5 GPa, carbon monoxide is converted into a solid polymer of carbon and oxygen. It is a metastable substance at atmospheric pressure, but it is a powerful explosive.
Usage
Chemical industry
Carbon monoxide is an industrial gas that has many uses in the production of bulk chemicals. Large amounts of aldehydes are obtained by the hydroformylation reaction of alkenes, carbon monoxide and H2. Hydroformylation in the Shell process makes it possible to create detergent precursors. Phosgene, suitable for the production of isocyanates, polycarbonates and polyurethanes, is produced by passing purified carbon monoxide and chlorine gas through a bed of porous activated carbon that serves as a catalyst. World production of this compound in 1989 was estimated at 2.74 million tons.
CO + Cl2 → COCl2
Methanol is produced by hydrogenation of carbon monoxide. In a related reaction, hydrogenation of carbon monoxide is associated with the formation of a C-C bond, as in the Fischer-Tropsch process, where carbon monoxide is hydrogenated to liquid hydrocarbon fuels. This technology converts coal or biomass into diesel fuel. In the Monsanto process, carbon monoxide and methanol react in the presence of a rhodium-based catalyst and homogeneous hydroiodic acid to form acetic acid. This process is responsible for most of the industrial production of acetic acid. On an industrial scale, pure carbon monoxide is used to refine nickel in the Mond process.
Meat coloring
Carbon monoxide is used in modified atmospheric packaging systems in the United States, primarily in the packaging of fresh meat products such as beef, pork and fish to maintain their fresh appearance. Carbon monoxide combines with myoglobin to form carboxymyoglobin, a bright cherry red pigment. Carboxymyoglobin is more stable than the oxidized form of myoglobin, oxymyoglobin, which can be oxidized to the brown pigment metmyoglobin. This stable red color can last much longer than regular packaged meat. Typical levels of carbon monoxide used in plants using this process are between 0.4% and 0.5%. This technology was first recognized as "Generally Safe" (GRAS) by the US Food and Drug Administration (FDA) in 2002 for use as a secondary packaging system, and does not require labeling. In 2004, the FDA approved CO as its primary packaging method, stating that CO does not hide the odor of spoilage. Despite this ruling, it remains controversial whether this method masks food spoilage. In 2007, a bill was proposed in the US House of Representatives calling the modified carbon monoxide packaging process a color additive, but the bill was not passed. This packaging process is banned in many other countries, including Japan, Singapore, and the European Union.
Medicine
In biology, carbon monoxide is naturally produced by the action of heme oxygenase 1 and 2 on heme from the breakdown of hemoglobin. This process produces a certain amount of carboxyhemoglobin in normal people, even if they do not inhale carbon monoxide. After first reporting that carbon monoxide is a normal neurotransmitter in 1993 and one of three gases that naturally modulate inflammatory responses in the body (the other two are nitric oxide and hydrogen sulfide), carbon monoxide has received a lot of clinical attention as a biological regulator. ... In many tissues, all three gases are known to act as anti-inflammatory agents, vasodilators, and neovascular growth enhancers. However, these questions are complex as neovascular growth is not always beneficial, as it plays a role in tumor growth as well as in the development of wet macular degeneration, a disease whose risk increases 4 to 6 times when smoking (the main source of carbon monoxide in blood, several times more than natural production). There is a theory that at some nerve cell synapses, when long-term memories are deposited, the receiving cell produces carbon monoxide, which is transferred back to the transmitting chamber, causing it to be transmitted more easily in the future. Some of these nerve cells have been shown to contain guanylate cyclase, an enzyme that is activated by carbon monoxide. In many laboratories around the world, studies have been carried out with carbon monoxide regarding its anti-inflammatory and cytoprotective properties. These properties can be used to prevent the development of a number of pathological conditions, including ischemic reperfusion injury, graft rejection, atherosclerosis, severe sepsis, severe malaria, or autoimmune diseases. Human clinical trials have been conducted, but the results have not yet been released.
Carbon monoxide (II ), or carbon monoxide, CO was discovered by the English chemist Joseph Priestley in 1799. It is a colorless gas, tasteless and odorless, it is poorly soluble in water (3.5 ml in 100 ml of water at 0 ° C), has low melting temperature (-205 ° C) and boiling point (-192 ° C).
Carbon monoxide enters the Earth's atmosphere during incomplete combustion of organic substances, during volcanic eruptions, as well as as a result of the vital activity of some lower plants (algae). The natural level of CO in the air is 0.01-0.9 mg / m 3. Carbon monoxide is highly toxic. In the human body and higher animals, it actively reacts with
The flame of burning carbon monoxide is a beautiful blue-violet color. It is easy to observe it yourself. To do this, you need to light a match. The lower part of the flame is glowing - this color is given to it by incandescent carbon particles (a product of incomplete combustion of wood). Above, the flame is surrounded by a blue-violet border. This burns carbon monoxide formed during the oxidation of wood.
a complex compound of iron - blood heme (associated with the protein globin), disrupting the functions of transport and consumption of oxygen by tissues. In addition, it enters into irreversible interaction with some enzymes involved in the energy metabolism of the cell. At a concentration of carbon monoxide in a room of 880 mg / m 3, death occurs in a few hours, and at 10 g / m 3 - almost instantly. The maximum permissible content of carbon monoxide in the air is 20 mg / m 3. The first signs of CO poisoning (at a concentration of 6-30 mg / m 3) are decreased sensitivity of vision and hearing, headache, changes in heart rate. If a person is poisoned by carbon monoxide, he must be taken out into fresh air, artificial respiration should be given to him, in light cases of poisoning - strong tea or coffee should be given.
Large amounts of carbon monoxide ( II ) enter the atmosphere as a result of human activity. For example, a car emits about 530 kg of CO into the air on average per year. When 1 liter of gasoline is burned in an internal combustion engine, carbon monoxide emissions fluctuate from 1 50 to 800 g. On highways in Russia, the average concentration of CO is 6-57 mg / m 3, that is, it exceeds the poisoning threshold ... Carbon monoxide accumulates in poorly ventilated courtyards in front of houses located near highways, in basements and garages. In recent years, special points have been organized on the highways to control the content of carbon monoxide and other products of incomplete combustion of fuel (CO-CH-control).
At room temperature, carbon monoxide is fairly inert. It does not interact with water and alkali solutions, that is, it is a non-salt-forming oxide, however, when heated, it reacts with solid alkalis: CO + KOH = NSOOK (potassium formate, salt of formic acid); CO + Ca (OH) 2 = CaCO 3 + H 2. These reactions are used to evolve hydrogen from synthesis gas (CO + 3H 2) formed by the interaction of methane with superheated steam.
An interesting property of carbon monoxide is its ability to form compounds with transition metals - carbonyls, for example: Ni + 4CO ® 70 ° C Ni (CO) 4.
Carbon monoxide (II ) Is an excellent reducing agent. When heated, it is oxidized by atmospheric oxygen: 2CO + O 2 = 2CO 2. This reaction can be carried out at room temperature using a catalyst - platinum or palladium. These catalysts are installed in automobiles to reduce CO emissions into the atmosphere.
When CO reacts with chlorine, a very poisonous gas phosgene is formed (t bale = 7.6 ° C): CO + Cl 2 = COCl 2 ... Previously, it was used as a chemical warfare agent, and now it is used in the production of synthetic polymers of polyurethanes.
Carbon monoxide is used in the smelting of iron and steel for the reduction of iron from oxides; it is also widely used in organic synthesis. When a mixture of carbon monoxide interacts ( II ) with hydrogen, depending on the conditions (temperature, pressure), various products are formed - alcohols, carbonyl compounds, carboxylic acids. The reaction of methanol synthesis is of particular importance: CO + 2H 2 = CH 3 OH , which is one of the main products of organic synthesis. Carbon monoxide is used for the synthesis of phos-gene, formic acid, as a high-calorie fuel.
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