acetylene


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acetylene

(əsĕt`əlēn') or

ethyne

(ĕth`īn), HC≡CH, a colorless gas. It melts at −80.8°C; and boils at −84.0°C;. Offensive odors often noted in commercial acetylene are due to impurities. Acetylene forms explosive mixtures with oxygen or air. It is soluble in acetone, ethanol, and water. When dissolved in acetone it is nonexplosive and so is stored dissolved in acetone under pressure in steel cylinders for commercial use. Since it is explosive in the liquid state, it is not generally stored in this form. Acetylene is easily prepared commercially by the reaction of calcium carbidecarbide,
any one of a group of compounds that contain carbon and one other element that is either a metal, boron, or silicon. Generally, a carbide is prepared by heating a metal, metal oxide, or metal hydride with carbon or a carbon compound.
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 with water, but is prepared commercially by the pyrolysis of hydrocarbons. It is used for cutting and welding metals (see oxyacetylene torchoxyacetylene torch
, tool that mixes and burns oxygen and acetylene to produce an extremely hot flame. This torch can be used for cutting steel and for welding iron and various other metals. The temperature of the flame can reach as high as 6,300°F; (3,480°C;).
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) and is sometimes used as an illuminant gas. When subjected to high temperatures, it undergoes polymerization; benzene may also be formed. It is used in the production of many organic compounds, e.g., neoprene rubber, plastics, and resins. Acetylene is the simplest alkynealkyne
, any of a group of aliphatic hydrocarbons whose molecules contain one or more carbon-carbon triple bonds (see chemical bond). Alkynes with one triple bond have the general formula CnH2n−2.
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.

Acetylene

 

an unsaturated hydrocarbon, CH ≡ CH; a colorless gas. Its melting point is -81.8°C. It bypasses the liquid state in solidifying. Its density is 1.171 kg/m3 (at ρ = 101.3 kilonewtons per sq m [kN/m2] or 760 mm of mercury and t = 0°C); it is only slightly soluble in water and very soluble in acetone (at 15°C, 25 parts of acetylene to 1 part of acetone). A mixture of acetylene with air (2.3–80.7 percent acetylene by volume) is explosive. Acetylene has narcotic properties.

Acetylene was discovered in 1836 by the English chemist H. Davy and synthesized in 1862 by the French chemist M. Berthelot from carbon and hydrogen; it was first obtained from calcium carbide by the German chemist F. Wöhler by the reaction CaC2 + 2H2O = C2H2 + Ca(OH)2; even today this method retains its significance as one of the industrial means of obtaining acetylene. An important modern industrial method is thermal oxidation cracking of natural gases, mainly methane, based on the decomposition of methane caused by the heat of its partial combustion: 6CH4 + 4O2 = C2H2 + 8H2O + 3CO + CO2 + 3H2O. Acetylene can also be obtained by electrocracking by passing methane through an electrical arc (temperature, 1600°C): 2 CH4 → C2H2 + 3H2.

Acetylene is a highly reactive compound; it serves as raw material for synthesis of a great number of valuable industrial products. The combination of acetylene with hydrogen chloride gives vinyl chloride, CH2 = CHC1, the starting material for the production of plastics; combination with hydrocyanic acid gives acrylonitrile, CH2 = CHCN, which is used for deriving several types of synthetic rubber and fibers. The hydration of acetylene results in acetaldehyde, CH3CHO, the starting material for production of acetic and other acids. The chlorination of acetylene is the basis for obtaining trichloroethylene, tetrachloroethane, and other compounds containing chlorine. Vinyl acetylene, vinyl esters, polyvinyl acetate, and polyvinyl alcohol are among the substances derived from acetylene.

Upon combustion, acetylene liberates a huge quantity of heat (14,000 kilocalories per cu m [kcal/m3]); here the oxygen-acetylene flame (maximum temperature, 3150°C) is successfully used for welding and cutting nonferrous and ferrous metals. Acetylene is stored and transported in steel cylinders under a pressure of 1.9 MN/m2 (19 kilograms-force per sq cm [kgf/cm2]) in the form of an acetone solution absorbed by a porous material such as charcoal.

The acetylene output in the industrially developed countries reaches hundreds of thousands of tons; in the USA it exceeds a million tons.

REFERENCE

Iukel son, I. I. Tekhnologiia osnovnogo organicheskogo sinteza. Moscow, 1968.

V. N. FROSIN

acetylene

[ə′sed·əl‚ēn]
(organic chemistry)
C2H2 A colorless, highly flammable gas that is explosive when compressed; the simplest compound containing a triple bond; used in organic synthesis and as a welding fuel. Also known as ethyne.

acetylene

A colorless gas, when mixed with oxygen, burns at a temperature of about 3500°C; used in welding.

acetylene

1. a colourless flammable gas used in the manufacture of organic chemicals and in cutting and welding metals. Formula: C2H2
2. 
a. another name for alkyne
b. (as modifier): acetylene series
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