HYDROCARBONS 55 



Properties. 



The lower members with 2, 3 and 4 atoms of carbon are gases. 

 The higher members are liquids and solids. They are lighter than 

 water in which they are only slightly soluble. They are soluble in 

 alcohol, ether and other organic liquids. They are inflammable and 

 burn with a luminous, smoky flame. 



Addition Reactions. 



(1) Hydrogen. When mixed with hydrogen and passed through 

 a hot tube over platinum black, or finely divided nickel, they are con- 

 verted into saturated hydrocarbons : 



L/XT-o - v-/Alo -J- ^~*o ^ JtiQ" 1 "" \-/Xjl 



The catalyst can be suspended in an inert solvent and a mixture of 

 ethylene and hydrogen bubbled through the liquid. 



(2) Halogens. The olefines combine with the halogens, chlorine 

 and bromine, but less readily with iodine, to form halogen compounds 

 containing two atoms of halogen (see p. 57): 



CH 2 =rCH 2 + Br.. = CH 2 Br . CH 2 Br. 



(3) Halogen Acids. The following reaction occurs : 



CH 2 =: CH 2 + HI = CH 3 . CH 2 I. 



(4) Sulphuric Acid. The alkyl hydrogen sulphate (p. 71) is 

 formed by addition : 



CH 2 =CH 2 + H 2 SO 4 = CH 3 . CH 2 . HSO 4 . 



This reaction serves for the separation of saturated and unsaturated 

 hydrocarbons. 



(5) Hypochlorous Acid. Chlorhydrins are formed : 



CH 2 =CH 2 + HOCl = CH 2 OH . CH 2 C1 



Ethylene chlorhydrin. 



(6) Potassium Permanganate. The olefines are oxidised by dilute 

 permanganate : 



CH 2 =CH 2 + H 2 + O = CH 2 OH . CH 2 OH 

 Ethylene glycol. 



This reaction may be used for detecting unsaturated compounds in 

 a mixture of hydrocarbons. 



