Organic chemistry / by Frank C. Whitmore.

  • Frank C. Whitmore
Date:
1937
Catalogue details

Licence: In copyright

Credit: Organic chemistry / by Frank C. Whitmore. Source: Wellcome Collection.

    48/1104 page 32
    1. Hydrogen adds under the influence of catalysts such as platinum black or colloidal palladium in water or alcohol suspen- sion or, best, finely divided nickel at temperatures around 300° (Sabatier, Senderens 1905). The discovery of this process laid the basis for the countless hydrogenations of theoretical and practical importance which are now conducted in nearly every field of organic chemistry. A copper catalyst can be used in place of nickel. The combination of ethylene and hydrogen is a homogeneous second-order reaction (Pease 1932). Ethylene may be activated by the action of alpha particles (Lind 1926) and by excited Hg atoms (Taylor 1929). A mechanism has been suggested for the hydrogenation in- volving the steps: (1) Addition of a proton to an activated ethylene molecule, (2) addition of two electrons (from the metal catalyst), and (3) addition of a second proton (Ingold 1929). Hydrogenation of ethylene with a Pt catalyst is used as an accurate method of determination in presence of ethane and methane (Meulen 1931). The volume of hydrogen consumed equals the volume of ethylene present. 2. Halogens add to ethylene, chlorine most readily and iodine least. Besides ethylene dichloride, chlorine gives higher chlorides such as 1,1,2-trichloroethane (Stewart 1929). This is ascribed to activation of the molecules during the reaction. This activation may well take the form of the addition of a positive Cl and the loss of a proton followed by the further addition of CL. Similar changes are common with olefins having the grouping RR'C = C (p. 41). Ethylene with a mixture of chlorine and bromine (bromine chloride) gives ethylene chlorobromide (l-chloro-2-bromoethane). No ethylene chloride is obtained. The reaction of ethylene with bromine has been studied ex- tensively (Ingold 1932). In the gaseous state there is no reaction (Stewart 1923). Glass, moisture and light favor the reaction. A lining of paraffin in the reaction vessel practically stops the reaction between ethylene and gaseous bromine while a lining of stearic acid catalyzes it better than glass. (Norrish 1923). Ethylene acts very slowly in the dark with a solution of bromine in dry CC14. Strangely it acts more rapidly at 0° than at 25°.
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