1 8  Constitution  of  the  Alkaloids.  {^aiuaryfiS.112' 
Hyoscine,  which  is  identical  with  scopolamine,  however,  is  differ- 
ent from  the  other  two,  atropine  and  hyoscyamine,  as  it  melts  at 
59°,  and  when  split  up  analogously  to  atropine,  yields  scopoline  and 
tropic  acid,  while  atropine,  as  we  saw,  yields  tropine  and  tropic  acid. 
That  scopoline  is  different  from  tropine  their  melting  points  show, 
tropine  melting  at  620  and  scopoline  at  1  io°. 
The  first  alkaloid  made  synthetically  was,  however,  coniine,  because 
it  is  such  a  simple  derivative  of  pyridine,  being  a  propyl-piperidine, 
i.  e.y  a-propyl-hexahydropyridine.  This  synthesis  was  also  made  by 
Ladenburg  in  1885.  Before  this  synthesis,  however,  the  consti- 
tution of  the  alkaloid  had  been  definitely  established  by  Hofmann 
in  1884.  Oil  heating  some  coniine  with  some  zinc  dust,  he 
observed  a  great  evolution  of  hydrogen,  and  obtained  as  a  residue 
the  alkaloid  conyrine — C8H17N  =  C8HnN  -f  6H.  This  indicated 
that  it  was  a  pyridine  derivative,  and  Hofmann  confirmed 
this  by  oxidizing  conyrine  when  he  obtained  picolinic  acid — a 
monocarbonic  acid  of  pyridine  then  fully  known.  The  difference  in 
composition  by  atoms  left  only  the  possibility  of  the  side  chain 
being  propyl  or  isopropyl.  But  isopropyl-pyridine  had  been  made 
synthetically  by  Ladenburg,  and  was  not  identical  with  conyrine, 
hence  conyrine  is  by  exclusion  propyl-pyridine.  Hofmann  con- 
firmed this  also  by 'reducing  coniine  by  hydriodic  acid  when  he 
obtained  normal  octane,  which  would  have  been  impossible  if  the 
coniine  had  contained  an  isopropyl  group.  As  coniine  was  shown 
to  yield  conyrine  and  six  hydrogen  atoms  by  reduction  with  zinc 
dust,  it  follows  that  coniine  is  propyl-hexahydro-pyridine,  i.  e.,  pro- 
pyl-piperidine. Ladenburg  tried  to  make  the  synthesis  of  coniine  by 
heating  pyridine  with  propyl  iodide.  By  this  heating  the  propyl 
group  is  changed  to  the  isopropyl  group,  and  he  actually  obtained 
isopropyl-piperidine.  He  then  started  from  a  different  source  by 
heating  picoline,  i.  e.,  a-methylpyridine  with  acetic  aldehyde,  which 
yielded  him,  as  expected,  allyl-pyridine : 
H 
C  CH 
/N  /\  . 
HC       CH  O  HC  CH 
II  II  II 
HC       C.CH3  +  CH3.C  —  H=HC       CCH  =  CH— CH3  -f-  H20. 
N  N 
Picoline.         Acetic  Aldehyde. 
Allyl-pyridiue. 
