Alkenes - is unsaturated acyclic hydrocarbons, which include only one double bond carbon atoms.They form a single homology complex of (series), which is displayed by the equation formula of substance CnH2n.For example, the formula in this initial series of substances - ethylene - C2H4, the fifth in the series formula pentene - C5H10, decene tenth - C10H20.
carbon atoms in these substances in the presence of a double bond in a state sp² hybridization, thus, the valence angle of the molecular structure is 120 °.The simplest alkene is ethylene compound with the formula C2H4.Homologous series of alkenes and reflect their names, which are formed by addition of corresponding prefix.
It should be noted that the preparation of alkenes is entirely determined by its chemical properties and characteristics.For example, those which have more than two carbon atoms incorporating create isomers.Thus there is a pattern consisting in the fact that the greater the number of carbon atoms contained in a specific alkene, the more he is able to form isomers.
Physical properties of these compounds also depends on the position in the homologous series.For example, melting point, boiling point and density for ethylene are respectively -169.1, -103.7 and 0.5700.The same parameters of the eighth in a series of alkene - octene - equal, respectively, -101.7, -121.3 and 0.7140.
first obtaining alkenes took place in 1669 when a German chemist Becher singled him out in the impact of sulfuric acid in ethyl alcohol.At this time, the scientist could not accurately determine the gas emitted, and therefore did not give him the name, and is simply called "air."Later, "the air Becher" in exactly the same method was Dutch Deyman Potts and Van Troostvik in 1795.This time, the scientists describe in detail their methods of preparation of alkenes, and give them a unique name - "maslorodny gas."This name was born because, during the reaction with chlorine to form an oily liquid, only later identified as dichloroethane from France chemist Antoine Fourcroy.
Then, at the beginning of the last century by J. Gay-Lussac found that ethanol includes, besides the actual "maslorodnogo" gas, and water molecules.
J. Dumas and P. Bull in 1928 opened obtain alkenes from ethyl chloride.Interestingly, a very long time, chemists could not correctly write the formula of this compound.Only in 1848, mowing brought it to ethylene and recorded as a S4N4.In nature
alkenes practically not present.Ethylene is the most simple representative of the homologous series is in the form of the hormone in some plants.
Lower alkenes are toxic and can in high concentrations cause a narcotic effect.In case of ingestion of higher alkenes can be observed convulsions, and edema of the respiratory tract.
the molecular weight determines the boiling point and the melting of these compounds and their physical state.Alkene from first to fourth in the series - the gases of the fifth to seventeenth have the form of liquid and subsequent - solids.Without exception alkenes are insoluble in water, but well soluble in organic solvents.
Under current conditions, there are many different ways to produce alkenes.Thus, methods for preparing alkenes include the following industrial methods.
main method is catalytic cracking of high temperature, which involves natural gas and hydrocarbon compounds contained in crude oil.With regard to the lower ones, can be applied a method of dehydration of alcohols.
The laboratories also use this method, but here the reaction is conducted in the presence of strong acids are used as methods of synthesizing and Hoffmann Chugaeva.For other methods of synthesizing reaction include Burda, which is the elimination of bromine.
alkenes are an indispensable raw material for the chemical industry, which are used for a huge number of chemical compounds.So getting alkenes is an important direction of development of chemical promyschlennosti in all industrialized countries.
