SEIDELL: BROMINE METHOD FOR PHENOLS 



197 



aqueous solutions, or to its loss by volatilization during the deter- 

 mination. After many experiments these difficulties were sur- 

 mounted and the following new method devised. 



Briefly the principal involved is the conversion of the thymol 

 to the dibrom compound, with formation of two molecules of 

 hydrobromic acid, by addition of an excess of bromine vapor to 

 an aqueous solution of the thymol in contact with a small amount 

 of carbon bisulphide. After allowing to stand at ordinary tem- 

 perature a short time, the excess of bromine is removed by means 

 of potassium iodide and thiosulphate, and the free hydrobromir 

 acid is then titrated after addition of excess of potassium iodate, 

 by means of standard thiosulphate solution. 



In practice the determination of thymol is made as follows. 

 The weighed sample of 0.1 to 0.5 grams is placed in a 200 cc. glass 

 stoppered bottle with 5 cc. CS 2 and about 100 cc. H 2 0. Bromine 

 vapor is then poured into the mixture until the color after 

 thorough shaking shows that a considerable excess of Br is pres- 

 ent. After one-half hour an excess of 10 per cent KI solution 

 is added and the liberated iodine corresponding to the free bromine 

 is titrated with 0.1 n thiosulphate, an excess of about 5 per cent 

 KI0 3 solution is then added, the liberated iodine equivalent to 

 the free HBr is titrated with 0.1 n thiosulphate. The difference 

 between the two readings of thiosulphate gives the amount of 

 HBr formed during the reaction, and calculating two molecules 

 of HBr for each molecule of thymol the amount of the latter is 

 directly obtained. A number of determinations gave the fol- 

 lowing results: 



(Factors for standard thiosulphate, Readings x 1.086 = 0.1 N exactly). 



