Hydrocarbons of the Ethylene Series

Ethylene was originally called olefiant (meaning oil forming) gas, on account of the fact that it formed an oil when it reacted with chlorine. For this reason homologues of ethylene are often called olefines. 

Ethylene is frequently formed when non-volatile organic compounds are subjected to destructive distillation, or when hydrocarbons are heated to such a temperature that they undergo decomposition. The ethylene found in coal gas and in carbureted water gas is produced in this way. Natural gas also contains a small percentage of this hydrocarbon. The luminosity of illuminating gas is due in part to the presence of ethylene, which is present in the gas to the extent of from four to five per cent. 

Ethylene is a colorless gas which possesses a peculiar, sweetish odor. One volume of water dissolves one-fourth volume of the gas, and one volume of alcohol about three and one-half volumes. It is much less stable toward heat than methane. At about 400° it decomposes methane, acetylene, benzene, 

A second method of preparing the hydrocarbon illustrates another principle which is important, as it can be applied to the preparation of many compounds which show the behavior of ethylene. When an alkyl halide, ethyl bromide for example, is heated with an alcoholic solution of potassium hydroxide, the base removes one hydrogen and one halogen atom. In this way ethylene can be prepared from ethyl bromide — 

If the potassium hydroxide is dissolved in water the halogen atom is replaced by the hydroxyl group, and alcohol is formed. 

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BlaC33 Blair, C. M., Henze, H. R. The number of structurally isomeric hydrocarbons of the ethylene series. J. Amer. Chem. Soc. 55 (1933) 680-686. 

A hydrocarbon of the ethylene series, containing two double bonds in the molecule. Dipentamethylene Thiuram Tetrasulphide DPTT, accelerator. 

Geraniol.— Alcohols derived from higher hydrocarbons of the ethylene series are known. The most important one is derived from a di-ene containing ten carbons and belongs to a class of compounds known as terpenes which will be considered later (Pt. II). It is called geraniol and has the following constitution. 

The aldehyde derived from the next higher hydrocarbon of the ethylene series, viz., the four carbon hydrocarbon, butene, is known as crotonic aldehyde because on oxidation it yields an acid known as crotonic acid. As there are two isomeric butenes due to the position of the double bond there will likewise be possible two isomeric aldehydes or butenals. 

Further, the halogen alkyls serve for the preparation of the unsaturated hydrocarbons of the ethylene series. 

The hydrocarbons of the ethylene series may be prepared, in general, by abstracting water from the corresponding alcohol, e.g. ... 

In these cases it Is much more convenient to prepare an ester from the alcohol by the action of the chloride of a higher fatty add, and subjecting this to distillation by which it is decomposed into an hydrocarbon of the ethylene series and the free fatty add, e.g. r... 

In this reaction the tertiary chloride is formed as an intermediate product. The method is of importance for the preparation of di-add alcohols (glycols), especially for the a-glycols, in which the hydroxyl groups are dombined with the two adjacent carbon atoms. The dibromides corresponding to these alcohols are easily obtained by the addition of bromine to the hydrocarbons of the ethylene series. In this way glycol was first prepared by Wurtz.1... 

Heat of Combustion and Heat of Formation of the Hydrocarbons of the Ethylene Series.—The significance of the heat of combustion and heat of formation of the members of the ethylene series can best be seen by comparing the values of the constants of these hydrocarbons with those of the paraffins. 

A number of hydrocarbons are known which are isomeric with members of the acetylene series, but do not contain a triple bond. They contain four less hydrogen atoms than the saturated hydrocarbon with the same number of carbon atoms. A study of the reactions of these hydrocarbons has shown that the property of unsaturation which they possess is produced as the result of the presence of two double bonds. Allene, which is isomeric with allylene, has the structure represented by the formula H2C = C = CH2. The hydrocarbons of this series are called diolefines on account of the fact that they contain two double bonds. Allene is sometimes called propadiene. The first two syllables indicate that the compound contains three carbon atoms (from propane CaHs) the termination diene indicates the presence of two double bonds in the compound. Other compounds are named in a similar way. The methods of preparation and reactions of the members of this series are analogous to those of the hydrocarbons of the ethylene series. 

If alcohol is heated to 160°-180° with concentrated sulphuric acid, the ethyl sulphuric acid first formed is decomposed and ethylene is produced. It will be remembered that the unsaturated hydrocarbons of the ethylene series can be prepared in a similar way from other alcohols. 

Unsaturated Compounds.—Read the section on the identification of hydrocarbons of the ethylene series (38), and of compounds containing a triple bond (46). If a substance of unknown structure forms a compound by the direct addition of two halogen atoms, the conclusion can be drawn that it is an unsaturated compound. In most cases it can be assumed that the substance contains a double bond between two carbon atoms. Thus, if a substance of the composition CaHeO is converted by bromine into one of the composition C3H60Br2, it is probable that it contains a double bond. If four atoms of halogen are added. 

Dihydrobenzene and similar compounds are prepared by a method which is analogous to that used to prepare unsaturated hydrocarbons of the ethylene series, namely, the elimination of halogen hydride from halogen derivatives of hexahydrobenzene ... 

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