A\tTiwT'}       Acids  with  0il  °f  Peppermint  363 
THE  REACTIONS  OF  ACIDS  WITH  OIL  OF  PEPPERMINT,  AND 
THEIR  BEARING  ON  THE  FORMATION  OF  CHLOROPHYLL.* 
By  M.  A.  Frebault. 
With  the  object  of  combining  the  hydrocarbon  of  oil  of  peppermint 
with  picric  acid,  the  author  heated  gently  together  an  alcoholic  solu- 
tion of  that  acid  with  some  of  the  essential  oil ;  water  was  added  to 
dissolve  the  excess  of  acid,  and  the  mixture  left  to  stand.  Twenty- 
four  hours  afterwards  the  oil,  which  had  collected  at  the  surface  of 
the  liquid,  presented  a  magnificent  green  color.  This  formed  the 
starting  point  for  the  author's  investigation. 
Action  of  Picric  Acid  upon  Oil  of  Peppermint. — If  oil  of  pepper- 
mint be  agitated  with  picric  acid,  nothing  is  observed  at  first  further 
than  that  the  picric  acid  partially  dissolves,  and  communicates  its 
yellow  color  to  the  oil ;  but  in  half  an  hour  the  mixture  is  colored 
manifestly  green,  and  in  twenty-four  hours  this  coloration  acquires  a 
great  intensity.  If  a  slight  heat  be  applied  to  the  mixture  the  green 
color  appears  more  rapidly. 
This  green  product,  exposed  to  the  air  upon  water  during  four  or 
five  days,  acquires  the  reddish-yellow  color  of  dead  leaves.  Intro- 
duced floating  on  water  into  a  test-tube  containing  nitrogen,  the  color 
is  retained  for  some  time ;  but  in  oxygen  it  disappears  more  quickly. 
Treated  several  times  with  cold  water,  the  washings  remove  each  time 
some  of  the  picric  acid  together  with  a  red  coloring  matter,  and  finally 
the  essential  oil  remains  of  a  reddish-yellow  color. 
The  green  product  has  a  strong  red  fluorescence,  and  in  an  alco- 
holic or  ethereal  solution,  this  phenomenon  is  still  more  marked. 
Treated  with  solution  of  caustic  potash  or  ammonia,  a  picrate  of  the 
base  employed  is  formed,  and  the  essential  oil  remains  of  a  reddish- 
yellow  color.  When  the  green  product  is  distilled  from  caustic  potash, 
a  colorless  liquid  passes  over  into  the  receiver,  and  there  remains  in 
the  retort  a  black  mass  analogous  to  that  obtained  by  treating  oil  of 
peppermint  with  chromate  of  potash.  The  distillate  no  longer  yields 
the  green  reaction  with  picric  acid.  Nascent  hydrogen  reduces  the 
green  product,  and  transforms  it  into  a  brown  substance.  If,  instead 
of  operating  in  the  cold  or  with  a  gentle  heat,  the  solution  of  picric 
acid  in  oil  of  peppermint  is  boiled  for  a  few  moments,  it  passes  from 
the  green  state  to  yellow-brown,  and  then  reddish-brown.    Upon  the 
*  Abstract  of  a  paper  in  the  Repertoire  de  Pharmacie,  vol.  ii,  p.  199. 
