ALKYL IODIDES HAROLD S. KING 91 



When all the iodine has reacted, allow the flask to cool. 

 Then, instead of the special apparatus, attach a condenser 

 arranged for downward distillation. The condenser previously 

 used for refluxing is suitable for this purpose. The lower end 

 is attached to an adapter dipping under a slush of ice and water. 

 After the methyl iodide has all distilled over, wash once with 

 water containing a little sodium hydroxide and separate. Care 

 should be taken in disposing of the residues left in the flask 

 after this distillation because they contain yellow phosphorus. 

 Dry the crude product with anhydrous calcium chloride, sep- 

 arate and distill a second time. Unless special precautions are 

 taken a loss of yield will result in this second distillation because 

 of the high vapor pressure of methyl iodide. Very little material 

 will escape if the following device is used. One end of a coil 

 of glass tubing 2 mm. in diameter is attached to the end of 

 the condenser. The coil is cooled in a freezing mixture. 

 The other end of the coil is connected with a tube leading 

 through a stopper into the collecting vessel also cooled in a 

 freezing mixture. A Bunsen valve is inserted into the stopper 

 of the collecting vessel to prevent the entrance of moisture 

 from the air. One should obtain over 90 per cent of the 

 theoretical yield based on the iodine used. In one run u^ing 

 all precaution against volatilization the yield was found to be 

 95 per cent. 



