158  Blue  Hydrocarbon  in  Essential  Oils.  {AT°i^ 
Jour.  Pharm. 
1915. 
In  a  few  instances  where  intensely  colored  fractions  have  been 
obtained,  the  investigators  have  thought  themselves  in  the  possession 
of  a  pure  substance.2  In  most  cases,  however,  they  have  recognized 
that  the  color  is  due  to  the  presence  of  some  colored  substance  other 
than  the  bodies  making  up  the  bulk  of  the  oil,  and  the  usually  accepted 
view  has  been,  that  this  is  an  oxygenated  substance  related  to  the 
sesquiterpene  alcohols.3 
Semmler  4  has  summarized  the  literature  covering  these  oils,  and 
remarks  that  there  are  two  views  possible  in  regard  to  the  blue 
fractions :  either  the  greater  part  is  colorless,  and  appears  colored 
owing  to  the  presence  of  a  small  amount  of  ah  intensely  blue  sub- 
stance, or  the  sections  boiling  between  275°  and  3000  are  actually 
composed  principally  of  a  blue  compound.  That  the  latter  is  not  the 
case,  however,  is  evident  from  a  survey  of  the  literature,  since  the  only 
purification  method  resorted  to  is  a  fractionation  out  of  oils  which 
contain  large  amounts  of  sesquiterpenes  and  sesquiterpene  alcohols, 
with  boiling-points  also  ranging  from  2500  to  3000.  For  the  same 
reason  no  importance  can  be  assigned  to  the  various  analyses  of  the 
blue  fractions. 
Blue  products  have  also  been  obtained  in  the  laboratory  by  various 
reactions,  usually  from  oils  composed  principally  of  sesquiterpenes 
and  sesquiterpene  alcohols.  In  such  cases,  there  seems  always  to 
have  taken  place  a  dehydration  and  subsequent  oxidation  of  a  sesqui- 
terpene alcohol,  or  a  direct  oxidation  of  a  sesquiterpene.  For  ex- 
ample, Wallach  and  Tuttle,5  by  the  action  of  phosphoric  anhydride, 
or  zinc  chloride  on  guaiol,  the  alcohol  of  guaiac-wood  oil,  obtained  a 
blue  sesquiterpene.  They  considered  the  color  to  be  due  to  the 
presence  of  a  small  amount  of  an  oxidation  product.  On  the  other 
hand,  Gadamer  and  Amenomija  6  obtained  a  guaiene  without  blue 
color,  by  dehydrating  guaiol  with  potassium  acid  sulfate. 
An  interesting  observation  was  made  by  Hentschel  and  Wis- 
licenus,7  who  found,  on  rectifying  the  products  of  the  dry  distillation 
of  calcium  adipate,  that  the  fraction  boiling  between  1350  and  145 0 
at  30  mm.  had  a  blue  color  resembling  that  of  Roman  chamomile. 
2  Piesse,  "  Art  of  Perfumery,"  1879,  p.  57. 
3  Bartelt,  "  Die  Terpene  und  Campherarten,"  1908,  p.  4. 
4 Die  Aetherischen  Ole,  3,  p.  260. 
5  Ann.,  279,  379  (1894). 
6  Archiv.  der  pharm.,  241,  33  (1903). 
"Ann.,  275,  312  (1893). 
