264 
Determination  of  Urea. 
{  Am.  Jour.  Pharm. 
I     April,  1921. 
THE  DETERMINATION  OF  UREA  BY  XANTHYDROL  * 
By  M.  Frenkel. 
In  1828  Wohler  made  urea  according  to  the  following  reaction : 
2CNO.K  +  (NH4)2S04  =  K2S04  +  2CO<^2 
-\-n2 
This  great  triumph  of  the  materialists  demonstrated  urea  as  a 
product  of  the  laboratory  obtained  from  materials  in  part  mineral. 
Of  the  different  methods  of  preparation,  the  most  important  in- 
dustrially consists  in  the  hydrolosis  of  cyanamide : 
CN.NH2  +  H20  =  CO(NH2)2 
The  industrial  uses  of  urea  are  diverse.  When  impure,  it  is 
added  to  fattening  food  for  poultry.  Pure  urea  is  essential  for  the 
preparation  of  certain  medicinal  products  such  as  the  urethanes, 
veronal  or  diethylbarbituric  acid. 
A  good  analytical  method  for  determining  urea  in  a  mixture 
with  the  different  substances  that  accompany  it  in  the  course  of  its 
manufacture,  is  important.  In  the  process  of  hydrolysis  of  cyana- 
mide, the  impurities  obtained  are  ammonia,  the  cyanamide,  the  dicy- 
anamide  and  dicyandiamide.  In  the  method  wherein  sodium  hypo- 
bromite  is  used,  not  only  urea  but  also  the  ammonium  salts,  which 
the  urine  contains  as  well  as  creatinine  are  determined.  Therefore 
a  precise  and  expeditious  method  for  the  determination  of  urea  in 
urine  is  desired.  Heretofore,  all  the  nitrogen  liberated  in  the  hypo- 
bromite  reaction  has  been  attributed  to  urea.  In  reality,  this  nitrogen 
is  due,  not  only  to  urea,  but  also  to  ammonium  salts,  the  acid  amines, 
creatinine,  the  oxyproteic  acids,  etc.  Again,  all  the  nitrogen  of  the 
urea  is  not  set  free  by  the  sodium  hypobromite.  All  the  methods  for 
determining  urea  in  mixtures  with  nitrogen  compounds,  based  on 
the  employment  of  sodium  hypobromite,  have  no  value. 
The  xanthydrol  method,  brought  forth  by  M.  Fosse,  for  the 
determination  of  urea  gives  excellent  results.    If  phenyl  salicylate 
is  distilled,  an  anhydride  of  o-dioxybenzophenone  is  formed : 
C«H4<COOC6H5  =C6H4<Co>C6H4  +  H20 
This  product  is  also  called  xanthone.  By  reduction  with  sodium 
*  Annates  de  Chemie  Analytique  et  de  Chemie  Appliquee,  August,  1920, 
page  234.    Abstract  prepared  by  V.  O.  Homerberg. 
