190  Estimation  of  Menthol.  {^a^S*?111, 
The  value  of  acetic  anhydride  as  a  chemical  reagent  has  long 
been  known  to  organic  chemists.  But  it  was  left  for  the  genius  of 
the  late  Dr.  R.  Benedikt1  to  formulate  a  qualitative  method  embody- 
ing the  well-known  property  of  acetic  anhydride. 
The  method  is  based  on  the  principle  that  alcohols  and  hydroxy 
acids  on  being  heated  with  acetic  anhydride,  have  the  hydrogen 
atom  of  the  hydroxyl  group  replaced  by  the  acetyl  group,  thus  form- 
ing compound  ethers. 
The  process,  according  to  Benedikt  and  to  Benedikt2  and  Ulzer, 
is  briefly  as  follows :  from  20  to  50  grammes  of  the  fatty  acids  are 
boiled  with  an  equal  weight  of  the  acetic  anhydride  for  two  hours 
in  a  flask  provided  with  an  inverted  condenser.  The  mixture  is 
then  transferred  to  a  suitable  vessel,  about  600  c.c.  of  hot  water 
added  and  boiled  for  half  an  hour.  The  mixture  is  then  allowed  to 
separate  into  two  layers,  the  aqueous  portion  withdrawn  and  the  oily 
layer  treated  thrice  more  in  the  same  manner.  The  acetylized  pro- 
ducts are  then  filtered  in  a  drying  oven  to  eliminate  all  moisture. 
From  3  to  5  grammes  are  carefully  weighed  off  and  dissolved  in  pure 
alcohol.  In  this  alcoholic  solution  the  acid  and  the  ether  values 
are  determined  as  usual.  The  former  is  called  the  acetyl  acid  value, 
the  latter  the  acetyl  value  and  the  sum  of  both  is  termed  the  acetyl 
saponification  value. 
The  theory  of  the  process  can  readily  be  seen  from  the  following 
equations  : 
C16H330H  -j-  (C2H30)20  =  C16H330.C2H30  -j-  HC2H302. 
Cetyl  Acetic  Cetyl  Acetic 
Alcohol.  Anlu-dride.  Acetate.  Acid. 
Q6H330.C2H30  +  KOH  =  C16H33OH  +  KC2H302 
Cetyl  Potassium  Cetyl  Potassium 
Acetate.  Hydroxide.  Alcohol.  Acetate. 
C17H32(OH)C02H^(C2H30)20  =  C17H32O.C2H3O.C02H  -f  HC2H302 
Ricinoleic  Acetic  Acetyl  Acetic 
Acid.  Anhydride.  Ricinoleic  Acid.  Acid. 
C17H32O.C2H3O.C02H  +    KOH    =  C17H32O.C2H3O.C02K  4-  H20 
Acetyl  Potassium  Acetyl 
Ricinoleic  Acid.  Hydroxide.  Ricinoleate  of  Potassium. 
1i887,  Ztschr.  f.  d.  Chem.  Bid.,  1,  149,  communicated  Feb.  26,  1886. 
2 1887,  Monatshefte  fiir  Chemie,  8,  47  ;  1892,  Die  Analyse  der  Fette  und 
Wachsarten,  zweite  Auf  ,  p.  113  ;  1895,  Chemical  Analysis  of  Oils,  Fats, 
Waxes,  etc.,  by  Benedikt  and  Lewkowitsch,  p.  127. 
