HALOGEN DERIVATIVES OF HYDROCARBONS 59 



and changes into ethylene bromide which may have a straw-yellow colour. 

 The heavy liquid product is shaken in a separating funnel with dilute caustic 

 soda solution and then with water. It is dried with calcium chloride and 

 purified by distillation (b.p. 130-132). About 60 gm. should be obtained. 



. Properties of the Monohalogen and Dihalogen Derivatives. 



The monohalogen derivatives are liquids heavier than water in 

 which they are insoluble or only slightly soluble. They have a 

 peculiar smell and do not burn readily. Their properties are in 

 general like those of chloroform (p. 60). 



Chemically the monohalogen derivatives or alkylhalides are very 

 reactive substances and readily exchange the atom of halogen with 

 other atoms or groups. They are thus largely used for introducing 

 alkyl radicles into other compounds, thus : 



1. CH 3 I + 2 H = CH 4 + HI (p. 53). 



2. CH 3 I + Zn + CH 3 I = C 2 H 6 + ZnI 2 (p. 53). 



3. CH 3 I + 2 Zn + CH 3 I = CH 3 . Zn . CH 3 + ZnL. 



4. CH 3 I + KOH = CH 3 OH + KI (p. 63). 



aqueous 



5. C 2 H 5 I + KOH = C 2 H 4 +KI + H 2 (p. 54). 



alcoholic 



6. C H 5 I + NH 3 = C 2 H 5 NH 2 + HI (p. 124). 



7. C;H 5 I + KCN = C 9 H 5 CN + KI (p. 158). 



8. C 2 H 5 I + KN0 2 = C 2 H 5 N0 2 + KI. 



9. C 2 H 5 I + KHS = C 2 H 5 HS + KI (p. 78). 



The dihalogen derivatives are very similar to the monohalogen de- 

 rivatives in both their physical and chemical properties. Both the 

 halogen atoms can be replaced by OH, NH 2 , etc. 



TRIHALOGEN DERIVATIVES. 

 CHLOROFORM. 



Preparation. 



100 gm. of fresh bleaching powder are rubbed up in a mortar with 

 200 c.c. of water so as to form a paste, the paste is rinsed into a large 

 flask of about 1000 c.c. capacity with another 200 c.c. of water ; 25 

 c.c. of acetone or alcohol are added and the mixture shaken up thor- 

 oughly. The flask is connected by means of a bent tube to a con- 

 denser and receiver and gently heated through a wire gauze. As soon 

 as the reaction commences, which is shown by the frothing, the flame 

 is removed. When the frothing has subsided and the reaction has 

 moderated, the contents of the flask are boiled until no more chloro- 

 form distils over with the water. The chloroform consists of heavy 

 oily drops which sink in water, and it forms the lower layer of the 

 distillate. 



The distillate is transferred to a separating funnel and shaken 

 with a little dilute caustic soda solution ; the lower layer of chloroform 



