acetylene

[y ǐ qu ē]

Organic compound

Collection

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Acetylene is an organic compound with chemical formula C two H two , commonly known as wind coal or calcium carbide gas, is the smallest of alkyne compounds. It is a colorless gas at normal temperature and pressure, slightly soluble in water, ethanol, acetone, chloroform, benzene, and ether. It is one of the important raw materials for organic synthesis, as well as a monomer for synthetic rubber, synthetic fiber, and plastic, and can also be used for oxyacetylene welding and cutting.

Chinese name: acetylene^[3]
Foreign name: acetylene^[3]
Alias: Carbide gas^[3] 、 Wind coal
chemical formula: C two H two^[3]
molecular weight: twenty-six point zero three seven^[3]
CAS login number: 74-86-2^[3]
EINECS login number: 200-816-9^[3]
Melting point: -81.8 ℃ (198K, sublimation)

Boiling point: -84 ℃
Water solubility: Slightly soluble
Density: 0.62 kg/m ³ （-82℃）
Appearance: Colourless gas
Security description: S9； S16； S33
Hazard symbol: F+
Hazard description: R5
Pinyin: qu ē

catalog

A brief history of discovery

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In 1836, Davy, Edmund 1785-1857, a cousin of the famous British chemist David Humphry (1778-1829) and a professor of chemistry at the Royal College in Cork, an Irish port city, heated charcoal and Potassium carbonate To make Metallic potassium During the process, the residue (potassium carbide) is put into water to produce a gas that explodes. The chemical composition of this gas is determined by analysis to be C, H (calculated by using the atomic weight of carbon equal to 6 at that time), which is called "a new hydrogen bicarbide". This is because as early as 1825, his fellow chemists Faraday (Faraday, MIChael 1791-1867) A compound of carbon and hydrogen was also obtained from the gas obtained by pressurized distillation of whale oil (used for European lighting at that time). Its chemical composition was determined to be C and H by analysis, and it was named "hydrogen bicarbide". In fact, Faraday discovered benzene, and David Edmond discovered acetylene.^[1]

physical property

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Simple structural formula of acetylene

Pure acetylene is a colorless and odorless flammable gas. However, acetylene made of calcium carbide is mixed with hydrogen sulfide H two S. Phosphine PH three Hydrogen arsenide is toxic and has a special odor. Melting point - 81.8 ° C (198K, sublimation), boiling point - 84 ° C, relative density 0.6208 (- 82/4 ℃), flash point (open cup) - 17.78 ℃, self ignition point 305 ℃. Explosion limit in air is 2.3% - 72.3% (vol). There is a danger of violent explosion in the liquid and solid state or in the gaseous state and under a certain pressure. Heating, vibration, electric spark and other factors can cause explosion, so it cannot be stored or transported after pressurized liquefaction. Slightly soluble in water, soluble in ethanol, benzene and acetone. At 15 ℃ and 1.5MPa, the solubility of acetylene in acetone is 237g/L, and the solution is stable.

Acetylene molecular model

Therefore, in industry, it is in steel cylinders filled with porous materials such as asbestos that the porous materials absorb acetone and then press acetylene for storage and transportation. In order to distinguish from other gases, the color of acetylene cylinder is generally milky white, the rubber gas pipe is generally black, and the thread of acetylene pipe is generally left-handed (there is a radial gap on the nut).

When the partial pressure of acetylene gas is equal to 101.325 kPa, the volume of the gas absorbed by the integral water (converted into standard conditions)

Acetylene solubility in water
Temperature (℃)	solubility	Temperature (℃)	solubility	Temperature (℃)	solubility
zero	one point seven three	twenty-five	zero point nine three	seventy	zero point two five
five	one point four nine	thirty	zero point eight four	eighty	zero point one five
ten	one point three one	forty	zero point six five	ninety	zero point zero five
fifteen	one point one five	fifty	zero point five zero
twenty	one point zero three	sixty	zero point three seven

chemical property

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Acetylene, the simplest alkyne, is also called calcium carbide. Structural formula H-C ∨ C-H, structural simple formula CH ∨ CH, simplest formula (also called experimental formula) CH, molecular formula C two H two The central C atom of acetylene is sp hybridized. Electronic formula H: C 9479┇ C: H Acetylene molecular weight 26.04, gas specific gravity 0.91 (kg/m three ）, flame temperature 3150 ℃, calorific value 12800 (kcal/m three ）The combustion speed in oxygen is 7.5, pure acetylene burns about 2100 degrees in air, and can burn up to 3600 degrees in oxygen. Its chemical properties are very active, and it can react with addition, oxidation, polymerization and metal substitution.

oxidation reaction

Combustion of acetylene

a. Flammability:

Phenomenon: the flame is bright, with thick smoke, and the flame temperature is very high (>3000 ℃) when burning. It is used for gas welding and cutting. The flame is called Oxyacetylene flame 。

b. By KMnO four Oxidation: It can fade the purple acid potassium permanganate solution.

C two H two + 2KMnO four + 3H two SO four = 2CO two + K two SO four + 2MnSO four + 4H two O

Addition reaction

You can talk to Br two 、H two , HX, etc. For example:

And Br two Bonus of:

Phenomenon: Bromine fading or Br two CCl of four Solution fading

Therefore, acidic KMnO solution or bromine water can be used to distinguish alkynes and alkanes.

And H two Bonus of:

Addition with HX:

Vinyl chloride used to produce polyvinyl chloride

"Polymerization" reaction

Three acetylene molecules combine to form a benzene molecule:

As acetylene and ethylene are unsaturated hydrocarbons, their chemical properties are basically similar. Under suitable conditions, three molecules of acetylene can polymerize into one molecule of benzene. However, the yield of benzene is not high and there are many by-products. If palladium and other transition metal compounds are used as catalysts, acetylene and other alkynes can successfully generate benzene and its derivatives.

Under certain conditions, acetylene can also be polymerized into polymers like olefins—— Polyacetylene 。

In Ni (CN) two Under the condition of 80~120 ℃ and 1.5MPa, the polymerization of 4-molecule acetylene mainly produces cyclooctetraene.

Metal substitution reaction (can be used for qualitative identification of acetylene)

Hydrogen will be released when acetylene is introduced into liquid ammonia dissolved with metal sodium. Acetylene reacts with silver ammonia solution to produce white Silver acetylene Sedimentation.

Acetylene has weak acidity, because the hydrocarbon bond in acetylene molecule is overlapped by SP-S. The carbon atom in the hydrocarbon is more attractive to the electron, which makes the density of the electron cloud between the hydrocarbons much higher near the carbon side, and makes the polarity of the hydrocarbon bond + It shows certain acidity. （p K a =25）

Put it into silver nitrate or cuprous chloride ammonia solution, and immediately generate white silver acetylene (AgC ∨ CAg) and brown red Cuprous acetylene (CuC ∨ CCu) precipitation can be used for qualitative identification of acetylene. When these two kinds of metal alkynides are dry, they are easy to explode when heated or impacted. If they are treated with hydrochloric acid or nitric acid after reaction, they can be decomposed to avoid danger. be careful : Acetylene shall not contact with copper during use, storage and transportation.

Acid-base reaction

C of C ∨ C in alkynes is sp hybrid, which makes Csp-H σ The electron cloud of the bond is closer to the carbon atom, which enhances the polarity of the C-H bond and makes the hydrogen atom easy to dissociate, showing "acidity". The hydrogen atom connected to the carbon atom of C ∨ C is quite active and easy to be replaced by metals. The alkyne metal derivatives are called Acetylide 。

CH≡CH + Na → CH≡CNa + 1/2H two (Conditional liquid ammonia)

CH≡CH + 2Na → CNa≡CNa + H two (Condition liquid ammonia, 190 ℃~220 ℃)

CH≡CH + NaNH two → CH≡CNa + NH three

CH≡CH + Cu2Cl two (2AgCl)+2NH four OH → CCu≡CCu（CAg≡CAg）↓ + 2NH four Cl +2H two O (Note: it only occurs when there is a hydrogen atom on the triple bond, which is used to identify the terminal alkyne RH ∨ CH).

Other chemical characteristics

When acetylene is in contact with copper, silver, mercury and other metals or their salts for a long time, it will generate copper acetylene (Cu two C two ）And silver acetylene (Ag two C two ）Such explosive mixture will explode when subjected to friction and impact. Therefore, all equipment used for acetylene cannot be made of silver or copper alloy with more than 70% copper content.

Preparation method

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Carbide method

It is made of calcium carbide (calcium carbide) and water.^[2]

Calcium carbide is often used to react with water to produce acetylene in the laboratory. The reaction with water is quite intense, and the amount of water can be controlled by the separating funnel to adjust the gas outlet speed. It can also be used saturated Salt water 。

Principle: calcium carbide undergoes hydrolysis reaction to generate acetylene. Device: Flask and separating funnel (Kip generator cannot be used). Cotton should be placed at the mouth of the flask to prevent foam overflow.

Reagent: calcium carbide (CaC ₂) and water.

Reaction equation: CaC ₂+2H-OH → Ca (OH) ₂+CH ∨ CH ↑

Collection method: Drainage and gas gathering method Or downward exhaust gas gathering method (not commonly used)

Tail gas treatment: ignition

The preparation device is similar to hydrogen and other gases.^[2]

natural gas law

natural gas Acetylene production process

The feed natural gas and oxygen preheated to 600-650 ℃ enter the multi tube burner plate acetylene furnace. At 1500 ℃, methane is cracked to produce about 8% dilute acetylene, and then N-Methylpyrrolidone 99% of the finished acetylene is obtained by concentration.^[2]

purpose

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Acetylene can be used for lighting, welding and cutting off metal (oxyacetylene flame), and is also the basic raw material for manufacturing acetaldehyde, acetic acid, benzene, synthetic rubber, synthetic fiber, etc.

When acetylene burns, it can produce high temperature, and the temperature of oxyacetylene flame can reach about 3200 ℃, which is used for cutting and welding metal. With proper air supply, it can completely burn and emit bright white light. It can be used as a light source in places where electric lights are not popular or there is no power. Acetylene is chemically active and can occur with many reagents Addition reaction 。 Before the 1960s, acetylene was the most important raw material for organic synthesis, and it is still one of the important raw materials. As with Hydrogen chloride 、 Hydrocyanic acid 、 acetic acid Addition can generate raw materials for polymer production.

Acetylene can undergo different polymerization under different conditions and generate Vinyl acetylene Or divinylacetylene, the former can be added with hydrogen chloride to obtain the raw material for neoprene 2-Chloro-1,3-butadiene 。 Acetylene can undergo cyclic tripolymerization to form benzene at 400~500 ℃; with Nickel cyanide Ni(CN) two As a catalyst, it can generate Cyclooctetraene 。

Acetylene is decomposed into carbon and hydrogen at high temperature, which can be prepared Acetylene black 。 Acetylene polymerization under certain conditions benzene ， toluene ， xylene ， naphthalene ， anthracene ， styrene ， Indene etc. aromatic hydrocarbon 。 Through substitution reaction and addition reaction, a series of valuable products can be produced. E.g. acetylene dimerization Vinyl acetylene , and then Hydrogen chloride Obtained by addition reaction Chloroprene ； Direct hydration of acetylene acetaldehyde ； Acetylene is prepared by addition reaction with hydrogen chloride vinyl chloride ； Acetylene and acetic acid Vinyl acetate ； Acetylene and Hydrogen cyanide Reaction preparation acrylonitrile ； Acetylene reacts with ammonia to form Picoline and 2-Methyl-5-ethylpyridine ； Acetylene reacts with toluene to produce xylenylethylene, and further catalytic cracking produces three isomers of methylstyrene: acetylene and a molecule formaldehyde Condensed as Propargyl alcohol , condensed with bimolecular formaldehyde to Butynediol ； Methylethynol can be prepared by addition reaction of acetylene and acetone, and then reacted to form isoprene ； Acetylene and carbon monoxide And other compounds (such as water, alcohol, mercaptan) Acrylic acid And its derivatives.

Monitoring methods

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1. On site emergency monitoring method

(1) Gas detection tube method.

(2) Gas quick measuring tube.

2. Laboratory monitoring methods

Monitoring methods	category	source
Gas chromatography	atmosphere	Monitoring Methods for Hazardous Substances in the Workplace	Edited by Xu Bohong and Yan Huifang
Gas chromatography	atmosphere	Determination Method of Harmful Substances in Air (Second Edition)	Edited by Hang Shiping
Acetylene cuprous colorimetry	atmosphere	Determination Method of Harmful Substances in the Air of Chemical Enterprises	Chemical Industry Press

3. On site monitoring method

(1) 2M004 Acetylene gas sensor detection micro sensor.

(2) K204 acetylene module detects acetylene leakage.

Protective measures

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Protective parts	Protective measures
respiratory system protection	Generally, no special protection is required, but it is recommended to wear a suitable self-priming filtering gas mask in special circumstances (when the oxygen content is the same or close to that in the air).
Eye protection	Generally, no special protection is required, and chemical safety goggles can be worn in case of high concentration contact.
Body protection	Wear anti-static work clothes.
Hand protection	Wear general operation protective gloves.
Other protection	Smoking is strictly prohibited at the work site. Avoid long-term repeated contact. When working in tanks, confined spaces or other high concentration areas, someone must supervise.

Leakage emergency treatment

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Evacuate the personnel in the leakage contaminated area to the windward place quickly, isolate them, and strictly restrict access. Cut off the ignition source. It is recommended that emergency personnel wear self-contained positive pressure respirators and anti-static work clothes. Cut off the leakage source as much as possible. Reasonable ventilation to accelerate diffusion. Dilute and dissolve with spray water. Build a dike or dig a pit to contain a large amount of wastewater generated. If possible, use an exhaust fan to send the leaked gas to an open place or install an appropriate nozzle to burn it. Leaking containers shall be properly treated, repaired and inspected before reuse.

Emergency medical treatment

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Diagnostic points

(1) Slight headache and dizziness after inhalation of certain concentration.

(2) When inhaled at high concentration, the patient is excited, talkative, and uneasy in crying and laughing, and then has headache, dizziness, nausea, vomiting, unstable gait, and drowsiness.

(3) In serious cases, the patient is unconscious.

(4) The acute toxicity of acetylene is mainly due to the replacement of oxygen in the air at high concentrations, resulting in simple asphyxia, and hypoxia is the main cause of death.

preventive measure

Stop inhaling, and the symptoms disappear rapidly. In fact, the symptoms of acetylene poisoning are partly caused by the mixed phosphine, hydrogen sulfide and other gases. Attention should be paid to whether there is mixed gas poisoning, especially the possibility of phosphine poisoning, so as to rescue in time.

Toxicological data

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acute toxicity

Pure acetylene is slightly toxic and has the effect of weak anesthesia and preventing cell oxidation. At high concentrations, oxygen in the air is squeezed out, causing simple asphyxia. Acetylene is often mixed with phosphine, hydrogen sulfide and other gases, so it is often accompanied by the toxic effect of such poisons. Human exposure 100 mg/m three It can withstand 30~60 min, 20% will cause obvious hypoxia, 30% will cause ataxia, 35% will cause loss of consciousness for 5 min, and there will be mild toxic reaction in the air containing 10% acetylene for 5 h.

Subacute and chronic toxicity

Long term inhalation of non lethal concentration of the product by animals resulted in increased hemoglobin, reticulocyte, lymphocyte and neutropenia. At autopsy, there were bronchitis, pneumonia, pulmonary edema, liver congestion and fat infiltration.

Safety and protection

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Emergency disposal

Inhalation: quickly leave the site to a place with fresh air. Keep the respiratory tract unobstructed. If breathing is difficult, give oxygen. If breathing stops, perform artificial respiration immediately and seek medical advice.

Emergency treatment for leakage: quickly evacuate the personnel in the leakage contaminated area to the windward place, isolate them, and strictly restrict access. Cut off the ignition source. It is recommended that emergency personnel wear self-contained positive pressure respirators and anti-static work clothes. Cut off the leakage source as much as possible. Reasonable ventilation to accelerate diffusion. Dilute and dissolve with spray water. Build a dike or dig a pit to contain a large amount of wastewater generated. If possible, use an exhaust fan to send the leaked gas to an open place or install an appropriate nozzle to burn it. Leaking containers shall be properly treated, repaired and inspected before reuse.

Hazardous combustion products: carbon monoxide, carbon dioxide.

Extinguishing method: cut off the gas source. If the air source cannot be cut off, it is not allowed to extinguish the flame at the leakage. Spray water to cool the container, and move the container from the fire site to an open place if possible.

Extinguishing agent: spray water, foam, carbon dioxide, dry powder.

Emergency medical treatment

Diagnostic points:

(1) Slight headache and dizziness after inhalation of certain concentration.

(2) When inhaled at high concentration, the patient is excited, talkative, and uneasy in crying and laughing, and then has headache, dizziness, nausea, vomiting, unstable gait, and drowsiness.

(3) In serious cases, the patient is unconscious.

(4) The acute toxicity of acetylene is mainly due to the replacement of oxygen in the air at high concentrations, resulting in simple asphyxia, and hypoxia is the main cause of death.

Precautions:

Toxicological data

Acute toxicity:

Subacute and chronic toxicity:

Handling and storage

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Precautions for operation: closed operation, full ventilation. Operators must be specially trained and strictly abide by the operating procedures. It is recommended that operators wear anti-static work clothes. Keep away from kindling and heat sources, and smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent gas leakage into the air of the workplace. Avoid contact with oxidants, acids and halogens. During transmission, the cylinder and container must be grounded and bridged to prevent static electricity. The cylinder and accessories shall be handled with care to prevent damage. Fire fighting equipment and leakage emergency treatment equipment of corresponding types and quantities shall be provided.

Precautions for storage: Acetylene is usually dissolved in solvent and porous materials and put into steel cylinders. Store in a cool and ventilated warehouse. Keep away from kindling and heat sources. The warehouse temperature should not exceed 30 ℃. It shall be stored separately from oxidants, acids and halogens, and mixed storage is strictly prohibited. Explosion proof lighting and ventilation facilities shall be adopted. It is prohibited to use mechanical equipment and tools that are easy to generate sparks. The storage area shall be equipped with leakage emergency treatment equipment.

Precautions for transportation: the safety helmet on the cylinder must be worn when the cylinder is used for transportation. Cylinders are generally placed horizontally, and the mouth of the cylinder should be in the same direction, not crossed; The height shall not exceed the protective fence of the vehicle, and shall be firmly clamped with triangular wood pad to prevent rolling. The transport vehicles shall be equipped with corresponding types and quantities of fire-fighting equipment. The exhaust pipe of the vehicle transporting this article must be equipped with a fire retardant device. It is prohibited to use mechanical equipment and tools that are easy to generate sparks for loading and unloading. It is strictly prohibited to mix with oxidants, acids, halogens, etc. Transport in the morning and evening in summer to prevent sunlight exposure. Keep away from kindling and heat sources during stopover. Road transportation shall be carried out according to the specified route, and do not stay in residential areas and densely populated areas. It is forbidden to slip during railway transportation.

Related terms

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Safety terminology	S9：Keep container in a well-ventilated place. Keep the container in a well ventilated place.
	S16：Keep away from sources of ignition - No smoking. Keep away from ignition sources and no smoking.
	S33：Take precautionary measures against static discharges. Take precautions against static electricity.
Risk terminology	R5：Heating may cause an explosion. Heating may cause explosion.

security information

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Hazard category: 2.1
Customs code: 2901292000
Dangerous goods transportation code: UN 1001
Hazard category code: R5
Safety instructions: S9-S16-S33
Dangerous goods sign: F+: Highlyflammable

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