Am.  jour,  pharm.  \     Manufacture  of  Anthraquinone. 
January,  1918.    J  J  J  J- 
41 
Anthraquinone  forms  yellow  crystals.  In  a  finely  divided  state 
it  is  almost  white.  The  fusing  point  is  284.60  C,  the  boiling  point 
382 0  C.  It  sublimes  very  easily.  It  is  completely  insoluble  in 
water,  slightly  soluble  in  alcohol,  ether,  and  benzene  in  the  cold, 
rather  more  soluble  with  heat  in  benzene  and  in  glacial  acetic  acid. 
It  is  not  a  commercial  product.  Apart  from  a  limited  use  as 
catalyzer  in  certain  sulphoxylate  discharges,  it  is  employed  solely  in 
the  color  works. 
It  is  interesting  to  note  that  it  may  be  synthesized  without  using 
anthracene  as  the  point  of  departure.  Phthalic  acid  is  condensed 
with  benzene  in  the  presence  of  chloride  of  aluminum.  This  gives 
orthobenzoyl-benzoic  acid.  By  anhydrization  with  hot  concentrated 
sulphuric  acid  this  gives  anthraquinone.  The  reaction  is  so  simple 
that  its  industrial  application  has  been  considered.  As  a  matter 
of  fact,  although  it  has  not  been  used  for  anthraquinone  itself,  it  is 
employed  in  the  synthesis  of  different  derivatives  of  anthraquinone. 
A  very  important  factor  in  the  economy  of  anthraquinone 
manufacture  is  the  regeneration  of  the  chrome,  which,  after  oxida- 
tion, is  in  the  state  of  chromic  sulphate.  This  can  be  crystallized 
and  recovered  in  the  form  of  chrome  alum,  after  the  addition  of 
the  necessary  quantity  of  sulphate  of  potassium  or  of  sulphate  of 
ammonium,  as  the  ammonia  alum  crystallizes  as  well  as  the  potash 
salt. 
The  high  price  of  chrome  alum,  which  is  very  largely  used  at  the 
tanneries,  makes  the  recovery  of  importance.  An  annual  produc- 
tion of  300  tons  of  anthraquinone  nearly  corresponds  with  the 
French  consumption,  and  in  the  manufacture  1,500  tons  of  chrome 
alum  are  obtained. 
Another  way  is  to  precipitate  the  chromic  sulphate  with  soda, 
which  gives  chromium  hydroxide  used  in  the  preparation  of  chro- 
mium acetate,  chromium  fluoride,  and  other  salts  used  in  the  textile 
industries.  In  the  German  works  the  chromic  acid  is  recovered  by 
electrolysis,  which  is  by  far  the  most  economical  way  where  the 
electric  current  is  cheap. 
Uses. 
Except  for  certain  special  purposes,  anthraquinone  serves  almost 
solely  as  the  raw  material  for  the  anthraquinone  colors,  of  which 
alizarin  is  the  most  important.    By  sulphonation,  nitration,  chlori- 
