i  m.  Jour.  Pharm.  \ 
December,  1895.  J 
The  Chemistry  of  Rhubarb. 
621 
to  possess  any  purgative  property.  The  composition  of  rhein  is 
represented  by  the  formula  C15H10O6 
Calculated.  Found. 
Carbon   62*93  62*95 
Hydrogen   .         3  49  3-54 
By  treatment  with  hydriodic  acid  (17  sp.  gr.),  rhein  does  not 
yield  any  alkyl  iodide,  but  it  appears  to  undergo  alteration  in  the 
same  manner  as  chrysophanic  acid  and  emodin.  The  immediate 
product  thus  obtained  was  very  probably  chrysophan-dioxy-hydro- 
anthron ;  it  was  a  pale  yellow  crystalline  product,  but  I  was  unable 
to  obtain  it  in  a  condition  fit  for  analysis  by  recrystallization  from 
glacial  acetic  acid,  as  the  solution  gradually  became  dark-colored, 
and  deposited  an  unpromising  semi-crystalline  powder. 
When  rhein  is  heated  to  85 0  C.  with  a  large  excess  of  acetic  anhy- 
dride for  several  days,  it  is  gradually  converted  into  a  pale  yellow 
crystalline  powder  consisting  of  minute  scales,  which  melt  between 
2620  and  265 0  C,  after  previously  softening.  This  derivative  of 
rhein  is  very  sparingly  soluble  in  hot  glacial  acetic  acid  or  in  hot 
alcohol,  but  it  dissolves  readily  in  water  solutions  of  potassium  car- 
bonate or  caustic  potash.  These  solutions  have  an  intense  purple 
color.  When  the  potash  solution  is  heated  for  some  time,  the  pro- 
duct of  acetylation  is  reconverted  into  rhein  and  acetic  acid  accord- 
ing to  the  equation — 
C,H9(CH30)06  ,     _     j  CJ5H10O6 
H20  [     -     1  C2H,02 
A  determination  of  the  acetic  acid  so  produced  gave  the  following 
results  : 
Found.  Calculated. 
Acetic  acid  14*1  p.  c.  13*1  p.  c. 
Analysis  of  the  acetylated  substance  gave  : 
Calculated  for 
Found.  C1SH9(.C2H30)06. 
Carbon    61 -88  6219 
Hydrogen   3-94  3-65 
When  this  product  or  rhein  is  heated  to  190°  C.  for  five  hours 
with  acetic  anhydride  in  a  sealed  tube,  further  acetylation  takes 
place,  and  diacetyl  rhein,  Cj-H^CoH.O^O^  is  produced.  This  com- 
pound was  obtained  in  the  form  of  small  greenish-yellow  needles;  it 
dissolved  more  readily  in  glacial  acetic  acid  or  in  acetic  anhydride 
