6o  Resins  and  Relations  to  Ter penes.     { AFebraa?y Pi9iym' 
Some  time  previous  to  this  work,  Kondakow  c  in  his  work  on 
angelic  and  tiglic  acids  obtained  from  them  a  hydrocarbon  which 
proved  to  be  a  methyl  derivative  of  crotonylene.  It  had  the 
general  formula  for  the  hemiterpenes.  From  the  description  it 
seems  quite  likely  that  this  hydrocarbon  is  related  to  the  terpenes, 
for  it  has  the  formula  CH3==C(CH3) — CH  —  CH2,  which  is 
identical  with  the  hemiterpene,  isoprene.7  Now,  angelic  and  tiglic 
acids  are  comparatively  common  in  the  plant  world  and  if,  as 
Kondakow  states,  these  hydrocarbons  are  readily  obtained  from 
the  acids,  then  it  is  possible  that  the  hemiterpenes  are  formed 
in  this  way  and  by  the  condensation  of  two  molecules  of  the  hemi- 
terpenes, a  terpene  in  this  particular  case,  camphene,  is  formed 
according  to  the  following  simple  equation : 
2C5H8  =  C10H16. 
In  pursuing  the  work  of  the  terpene  polymerization,  prac- 
tically all  of  the  methods  in  the  terpene  literature  were  tried. 
All  of  them,  however,  were  unsatisfactory.  It  was  noticed  in 
previous  work  on  the  chlorhydrochlorides 8  of  terpenes,  that  in 
the  preparation  of  the  hydrochloride  on  a  large  scale  there  was 
always  left  a  considerable  portion  of  material  of  thick  oil  con- 
sistency after  the  chloride  had  been  removed.  Examination  showed 
that  this  oil  contained  a  small  quantity  of  resinous  matter.  After 
unsatisfactory  attempts  to  isolate  the  resin,  other  agents  were 
tried.  Bromine  and  iodine  were  tried  and  each  was  found  to 
produce  resins  more  readily  than  chlorine.  As  iodine  gave  best 
results,  it  was  used  in  the  experimental  work  which  follows.  It 
was  found,  first  of  all,  that  iodides  somewhat  similar  to  the  chlor- 
hydrochlorides could  be  formed,  especially  if  the  reaction  took 
place  in  sunlight.  These  iodides  were  first  isolated  and  studied. 
The  di-iodide  proved  to  be  of  special  interest.  When  pure  it  is  a 
heavy  colorless  oil  with  a  slight  camphoraceous  odor.  When  ex- 
posed to  sunlight  it  readily  decomposes,  liberating  iodine  and 
resins,  notwithstanding  the  fact  that  sunlight  seems  to  play  an 
important  part  in  its  formation.    If  exposed  to  sunlight  for  some 
8  Jour,  of  the  Russ.  Phys.  Chem.  Soc,  1891,  I.,  178. 
7  It  may  be  interesting-  to  the  reader  to  note  that  isoprene  has  very 
recently  been  polymerized  to  India  rubber. 
*Jour.  Am.  Chem.  Soc.,  28,  p.  1461. 
