598  Test  for  Caffeine  and  Theobromine.    { Am-  J°putn  ^rm" 
A  CHEMICAL  TEST  TO  DISTINGUISH  BETWEEN 
CAFFEINE  AND  THEOBROMINE.1 
By  Freeman  P.  Stroup,  Ph.M. 
Careful  study  of  the  properties  of  caffeine  and  theobromine  has 
shown  that  structurally  they  are,  doubtless,  very  much  alike,  the 
chief  difference  being  that  in  the  former  a  methyl  group  replaces  a 
hydrogen  atom  of  the  latter,  resulting  in  the  molecule  of  the  former 
containing  one  carbon  atom  and  two  hydrogen  atoms  more  than  the 
latter.  Otherwise  the  arrangement  of  the  atoms  in  the  molecule  ap- 
pears to  be  the  same  in  both.  This  being  the  case,  the  pursuit  of  any 
logical  plan  of  testing  offered  no  inducements,  and  it  was  decided  to 
go  at  the  task  in  a  purely  empirical  manner. 
Recalling  the  fact  that  potassium  dichromate  and  concentrated 
sulphuric  acid  properly  used  produce  some  striking  color  effects  with 
certain  alkaloids,  strychnine  in  particular,  it  was  decided  to  try  this 
combination  first.  The  results  were  both  surprising  and  gratifying. 
Various  proportions  of  the  salt  and  acid,  and  various  techniques 
were  tried,  but  the  best  results  were  obtained  by  carrying  out  the 
test  as  follows : 
The  Reagent. — A  solution  of  potassium  dichromate  approxi- 
mately one  part  by  weight  in  concentrated  sulphuric  acid  twenty 
parts  by  volume.  It  may  be  made  by  dissolving  50  milligrams  of  the 
salt  in  1  mil  of  the  acid,  or  3  grains  of  the  salt  in  1  fluidrachm  of 
the  acid. 
The  Test:  Technique  A. — Place  on  a  white  porcelain  surface  a 
small  quantity  of  the  alkaloid  to  be  tested  (what  would  lie  on  the 
tip  of  a  small  knife  blade  will  be  sufficient),  spread  it  out  to  cover  a 
space  about  1  centimeter  (}i  inch)  in  diameter,  and  put  two  drops 
of  the  reagent  in  the  center  of  the  mass.  With  caffeine  the  yellow 
color  of  the  reagent  is  almost  immediately  changed  to  a  bright 
bluish-green.  With  theobromine  the  yellow  color  is  first  changed  to 
a  dark  purplish,  which  gradually  changes  to  a  purplish-green,  later 
an  olive-green,  and  finally  to  the  same  bluish-green  that  is  given  by 
caffeine. 
Technique  B. — Transfer  5  or  6  drops  of  the  reagent  to  a  white 
porcelain  surface,  spreading  the  liquid  to  form  a  spot  about  2  cen- 
1  Presented  at  the  annual  meeting  of  the  Pennsylvania  Pharmaceutical 
Association,  Buena  Vista,  Pa.,  June,  1919. 
