378 C. H. Maryott — Halogens in Benzol Derivatives. 



Art. XL. — The Use of Metallic Potassium in Determining 

 Halogens in Benzol Derivatives ; by C. H. Maryott. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxvi.] 



A METHOD for the estimation of halogens in organic com- 

 pounds by reduction with sodium and alcoliol was described a 

 few years ago by Stephanoff.* The writer recently attempted 

 to use tliis method in determining chlorbenzol, but the results 

 obtained were very irregular and unsatisfactory. Before 

 enough sodium had been added to effect complete reduction, 

 the liquid became pasty owing to the separation of sodium 

 ethylate, and this localized and greatly hindered the action of 

 the sodium. By increasing the amount of alcohol above bhat 

 recommended by Stephanoff, the sodium ethylate could be 

 kept in solution, but the large volume of liquid retarded the 

 reduction, and thus increased both the time and the amount of 

 sodinm required. In all cases the results of the analyses were 

 low. 



A failure to obtain satisfactory results with Stephanoff 's 

 method has likewise been i-eported by Bacon,f who, however, 

 devised a moditication of the method, in which accurate results 

 were obtained by heating the mixture for an hour after the 

 solution of the sodium, thus utilizing the action of the sodium 

 ethylate upon the halogens. Bacon's method was not tried by 

 the writer, as the article cited came to his attention after the 

 completion of the experiments described below. The long 

 time required, about two hours, would seem to be a disadvan- 

 tage, and the fact that certain of the benzol halogen derivatives 

 such as monochlor- and monobrombenzol are attacked but 

 little, if at all,:}: by boiling with sodium ethylate, a possible 

 source of error in the method. 



The use of potassium instead of sodium as a means of 

 obtaining a more rapid reduction was suggested to the writer 

 by Professor E,. G. Van Name, and upon trial proved to be a 

 great improvement. As the action of potassium upon alcohol 

 is very energetic, a mixture of one volume of 98 per cent 

 alcohol with two of thiophene-free benzol was employed. The 

 presence of thiophene had to be avoided to prevent the forma- 

 tion of potassium sulphide, which would interfere in the 

 subsequent estimation of the halogen. The reduction was 



*Ber., xxxix, 4056, 1906. f Jour. Am. Chem. Soc, xxxi, 49, 1909. 



X The writer boiled monochlor- and monobrombenzol in a concentrated 

 BolutioQ of sodium ethylate for three hours, but failed to get any test for 

 halogens upon acidifying and adding silver nitrate. Bacon states in his 

 article that he was unable to convert monobrombenzol into phenetol by 

 heating with sodinm ethylate, although 25 per cent of the chlorine was 

 removed from hexachlorbenzol by the same treatment. 



