Ii6  Ur ethanes  of  Thymol  and  Carvacrol.  |^bJuaryPi92im' 
The  phenyl  derivative  of  thymol  was  prepared  by  Leuckart 11 
by  the  action  of  phenyl  isocyanate  on  thymol  in  the  presence  of 
aluminum  chloride.  Hoffman  12  had  first  obtained  these  products  by 
heating  the  isocyanate  and  phenol  at  ioo°  for  long  periods  of  time 
in  sealed  tubes.  The  yields  varied  from  16  to  64  per  cent.  The  use 
of  aluminum  chloride  was  an  improvement.  Goldschmidt 13  first 
mentions  the  preparation  of  the  phenyl  derivative  of  carvacrol  by 
the  use  of  aluminum  chloride  and  suggests  its  usefulness  as  a 
method  of  identification.  Weehuizen  14  simply  heats  the  constituents 
with  the  isocyanate  in  slight  excess,  together  in  a  petroleum  hydro- 
carbon boiling  about  170-2000.  The  urethane  crystallizes  out; 
while  the  components  not  reacting  remain  dissolved.  This  modifica- 
tion of  the  method  requires  no  condensing  agent,  and  heating  at  the 
boiling  point  for  one-half  hour  is  all  that  is  necessary  to  cause  the 
reaction  to  take  place.  The  phenol  is  dissolved  in  10  parts  of  sol- 
vent; the  isocyanate  added  in  slight  excess,  and  the  mixture  re- 
fluxed  for  one-half  to  one  hour.  The  urethane  crystallizes  out  on 
cooling  and  after  filtering  and  washing  with  two  small  portions  of 
the  hydrocarbon  it  may  be  purified  in  the  usual  manner. 
Application  to  Thymol. — An  attempt  was  made  to  adapt  the 
method  to  a  somewhat  larger  scale  of  production  than  1  gram. 
Accordingly,  5.28  g.  of  thymol  with  4.6  g.  phenyl  isocyanate,  repre- 
senting a  10  per  cent,  excess,  were  introduced  into  an  acetylation 
flask.  The  mixture  became  cold.  To  this  were  added  20  cc.  petro- 
leum (boiling  170-2000)  and  the  mixture  heated  one  hour.  The 
cooled  reaction  mixture  deposited  crystals  which  were  washed  with 
two  5  cc.  portions  of  petroleum  and  weighed.  The  yield  was  6.75  g. 
or  71  per  cent.,  with  a  melting  point  of  1030.  Weehuizen  14  reports 
1 06- 1 07 0 ;  while  the  literature  gives  either  1040  or  1070  as  the  melting 
point.  Crystallized  once  from  alcohol  (95  per  cent.)  it  melts  at  1060, 
a  second  crystallization  raises  tins  to  106.5-1070.  It  does  not  crystal- 
lize well  from  benzene  on  cooling,  and  does  not  precipitate  on  addi- 
tion of  heptane. 
The  determination  of  nitrogen  by  the  Kjeldahl  method  pre- 
11  Leuckart,  J.,  pr.  Chemie,  II,  p.  320. 
12  Hoffmann,  Ber.i,  4  (1871),  p.  249. 
13  Goldschmidt,  Ber.,  26  (1893),  p.  2086. 
"Weehuizen,  Rec.  trav.  Chim.,  87  (1918),  p.<  266. 
