Am.  Jour.  Pharm.  \ 
August,  19 19. 
Oxymethylanthraquinones. 
541 
QUANTITATIVE  DETERMINATION  OF 
OXYMETHYLANTHRAQUINONES.1 
Four  methods  for  the  determination  of  the  oxymethylanthra- 
quinones in  such  drugs  as  rhubarb,  senna,  etc.,  have  been  suggested. 
They  are:  (1)  Spectroscopical,  (2)  colorimetric  without  colorimeter, 
(3)  colorimetric  with  colorimeter,  and  (4)  gravimetrical  by  precipi- 
tation by  azonitroaniline.  The  method  now  proposed  depends  upon 
the  hydrolysis  of  the  glucosides  of  the  oxymethylanthraquinones 
and  the  separation  of  the  latter  in  such  a  state  of  purity  that  they 
can  be  weighed.  As  the  glucosides  are  sensitive  to  heat,  hydrolysis 
is  effected  at  the  boiling  point  of  chloroform.  The  determination  is 
effected  as  follows :  A  weighed  quantity  of  the  finely  powdered  drug 
(about  2  Gm.  of  rhubarb,  5  Gm.  of  senna),  dried  at  6o°-jo°,  is 
introduced  into  a  short-necked  flat-bottomed  flask  and  200  Cc.  of 
dry  chloroform  added;  the  whole  is  weighed  and  boiled  under  a 
reflux  condenser  for  fifteen  minutes.  When  quite  cold  the  chloro- 
formic  solution  is  filtered  off  and  the  residual  drug  washed.  The 
solution  is  shaken  with  a  5  per  cent,  solution  of  caustic  soda,  which 
is  separated,  washed  with  chloroform,  acidified  with  hydrochloric 
acid,  again  shaken  with  chloroform,  and  the  chloroformic  solution 
separated,  filtered,  evaporated  to  dryness,  and  the  residue  weighed. 
This  is  the  weight  of  the  free  oxymethylanthraquinones.  The  resid- 
ual drug  (after  boiling  with  chloroform)  is  carefully  returned  to 
the  flask  and  make  up  to  the  original  weight  with  chloroform. 
Fifty  Cc.  of  25  per  cent,  sulphuric  acid  are  added,  and  the  whole 
weighed.  The  mixture  is  then  boiled  on  a  water-bath  for  2J/2  hours, 
shaking  from  time  to  time.  After  cooling,  the  weight  is  made  up 
with  chloroform,  the  whole  transferred  to  a  separating  funnel,  and 
about  150  Cc.  of  the  chloroformic  solution  separated.  This  is 
shaken  first  with  50  Cc.  of  a  10  per  cent,  solution  of  sodium  bi- 
sulphite, separated,  and  filtered  through  kieselguhr  and  shaken  with 
IOO  Cc.  of  1  per  cent,  hydrochloric  acid.  One  hundred  Cc.  of  the 
chloroformic  solution  are  then  evaporated  to  dryness,  and  the  resi- 
due weighed,  from  which  the  percentage  of  the  combined  oxymethyl- 
anthraquinones can  be  calculated.  Rhapontic  rhubarb  was  found 
to  contain  3.18  to  3.95  per  cent,  combined  and  0.24  to  0.28  free 
oxymethylanthraquinones,  senna  1.98  to  2.12,  total  and  cascara 
1.32  to  1.47  total  oxymethylanthraquinones. 
1Journ.  de  Belgique,  1,  200.  Reprinted  from  The  Pharm.  Jour,  and 
Pharmacist,  April  26,  1919. 
