United  States  Patent  Office  3,382,228  Patented  May  7,  1968  1  2  3,382,228  PROCESS  FOR  PREPARING  AZOMALONANILIDE  PIGMENTS  John  E.  Ferrari,  Scarsdale,  and  Arthur  P.  Kurtz,  Staten  Island,  N.Y.,  assignors  to  Interchemical  Corporation,  New  York,  N.Y.,  a  corporation  of  Ohio  No  Drawing.  Filed  May  3,  1965,  Ser.  No.  452,863  6  Claims.  (CI.  260-158)  Preparation  of $_{azomalonanilide }$ pigments  by  coupling  a  diazonium  salt  with  a  malonanilide  derivative  in  an  or› ganic  solvent  containing  a  substantial  amount  of  an  acid  having  a  pKa  value  less  than  about  5.  The  organic  solvent  is  inert  towards  the  reactants  and  has  substantial  solvent  action  on  them  under  the  reaction  ,conditions.  ABSTRACT  OF  THE  DISCLOSURE  This  invention  relates  to  an  improved  process  for  manu› facturing  azomalonanilide  pigments  wherein  the  coupling  step  is  carried  out  in  a  strongly  acidic  medium.  Application  Ser.  No.  267,791,  filed  Mar.  25,  1963,  and  now  U.S.  Patent  No.  3,252,968,  disclosed  azomalonanilide  pigments  made  by  coupling  in  alkaline  media.  While  it  is  true  that  alkaline  media  favors  proton  removal  from  malonanilides,  they  also  promote  decomposition  of  the  diazo  components,  impairing  the  purity  of  the  product  and  reducing  the  yield.  The  therein  disclosed  pigments  were  made  with  yields  of  28,  34,  35,  44,  66,  67,  and  82%.  It  has  now  been  found  that  coupling  in  strongly  acidic  media  yields  "crude"  products  as  pure  as  the  recrystallized  products  disclosed  in  the  above  mentioned  application,  while  the  yields  are  improved,  usually  to  a  striking  degree.  It  is  believed  the  herein  disclosed  coupling  in  strongly  acidic  media  is  new  in  the  art.  In  this  method  the  diazo› tization  is  carried  out  in  a  suitable  organic  solvent  such  as  $^{dimethylformamide }$with  an  acid  such  as  sulfuric  acid  or  acetic  acid  and  a  nitrite  such  as  lower  alkyl  nitrites  or  alkali  metal  nitrites.  The  diazonium  salt  remains  stable  and  substantially  in  solution  throughout  the  coupling  pe› riod.  The  malonanilide  is  dissolved  in  the  solvent  and  added  to  the  diazo  solution.  Coupling  is  usually  com› plete  in  1 to  3  hours.  The  "crude"  products  are  of  excel› lent  purity  compared  to  those  obtained  by  the  pyridine- base  catalyst  process,  which  was  used  in  the  aforemen› tioned  filed  application.  The  essential  features  of  the  in› stant  invention  comprise  a  medium  ,containing  an  organic  solvent  and  a  substantial  amount  of  an  acid  catalyst  system  for  enolization  of  malonanilides,  and  the  conse- quent  enhanced  stability  of  the  diazo  solution,  the  acid  having  a  pKa  value  of  less  than  about  5.  Malonanilide  can  be  prepared  according  to  the  pre- viously  mentioned  patent  application,  yielding  a  product  with  a  melting  point  of  229-30°  C.  A  commercially  avail› able,  "label  3829"  malonanilide,  having  a  M.P.  of  229- 300  C.,  however,  was  used  in  all  the  instantly  disclosed  malonanilide  reactions.  2,2’  -dimethoxymalonanilide,  re- crystallized  from  isopropanol  and  with  a  M.P.  of  165- 1670  C.;  2,2’-dimethylanilide,  recrystallized  twice  from  isopropanol  and  with  a  M.P.  of  195-197°  C.;  and  2,2’› dichloromalonanilide,  recrystallized  from  isopropanol  and  with  a  M.P.  of  174.5-176.5°  C.  were  all  prepared  by  the  method  of  the  aforesaid  patent  application.  2,2’,4,4’-tetra› methoxymalonanilide  was  prepared  by  heating  at  reflux  temperature,  under  a  blanket  of  nitrogen,  a  mixture  of  1000  ml.  xylene,  268  g.  (1.75  mole)  of  2,4-dimethoxy› aniline,  131  g.  (0.82  mole)  of $_{diethylmalonate, }$ and  5  g.  of  the  acid  form  of  sulfonated  polystyrene,  sold  under  the  name  "Permutit  Q,"  for  24  hours  while  101  ml.  ethanol  distilled  off.  The  charge  was  cooled  to  80°  C.  and  then  1000  ml.  isopropanol  and  20  g.  activated  charcoal,  sold  under  the  name  "Darco  60,"  were  added.  The  batch  was  digested  ‰  hour  at  84  °  C.,  reflux  temperature,  filtered,  and  allowed  to  cool  slowly.  The  light  pink  crystals  were  filtered  and  washed  with  1000  ml.  isopropanol  before  being  dried  in  a  60-65  °  C.  oven.  The  product  did  not  show  any  change  in  melting  point  when  recrystallized  from  isopropanol.  $^{2,2’,5,5’-tetrachloromalonanilide }$was  prepared  by  heating  24  hours  at  reflux  a  mixture  of  500  g.  ( 3  .09  mole)  of $_{2,5-dichloroaniline, }$ 242  g.  (  1.51  mole)  of  diethylmalonate,  and  3000  ml.  of  xylene.  During  this  period  150  ml.  ethanol  and  500  ml.  xylene  distilled  off.  There  were  added  10  g.  "Darco  60"  and  30  g.  "Celite  545"  and  then  the  batch  was  digested  ‰  hour  at  reflux  before  filtering.  A  product  having  a  M.P.  of  237-238.5  °  C.  was  obtained  by  filtration,  washing  with  1000  ml.  of  iso› propanol,  and  drying  at  50-55  °  C.  The  bases  used  were  all  commercially,  available  prod- ucts.  All  the  pigments  were  prepared  by  adding  0.1  mole  of  the  base  to  the  organic  solvent,  such  as  dimethylform› amide  and  cooled  to  0-5°  C.  To  this  solution  or  slurry  was  added  dropwise  0.2  mole  of  concentrated  sulfuric  acid  and  the  temperature  was  again  brought  to  0-5  °  C.  0.1  mole  of  isoamyl  nitrite,  in  the  form  of  a  32%  solu› tion  in  dimethylformamide  was  added  over  a  period  of  time  sufficient  to  attain  the  maximum  rate  of  addition  possible  without  raising  the  temperature  of  the  batch.  The  cold  mixture  was  stirred  one  hour.  A  concentrated  solution  of  0.1  mole  malonanilide  in  the  same  organic  solvent,  such  as  $^{dimethylformamide }$was  added  dropwise  to  the  diazo  solution,  again  at  the  maximum  rate  possible  without  rise  in  temperature.  The  batch  was  stirred  at  0-5°  C.  for  5  hours,  followed  by  16  hours  at  room  temperature.  The  product  was  filtered  and  the  solids  slurried  in  water  and  again  filtered.  The  malonanilides  were  thus  coupled  to  the  following  bases.  In  this  application  percentages  and  parts  are  on  the  weight  basis.  azomalonamilide  5.5  g.  of $_{ortho-nitroaniline }$ were  dissolved  in  20  ml.  of $_{dimethylformamide }$ and  the  solution  was  cooled  to  5°  C.  7.84  g.  (0.08  mole)  of  sulfuric  add  were  added  slowly,  keeping  the  temperature  below  15°  C.  The  solution  was  brought  to  0°  C.  and  16  ml.  of  a  2.5  N  solution  in  di› methylformamide  of  amyl  nitrite  were  added  dropwise  over  a  period  of  30  minutes,  keeping  temperature  at  -5°  to  +5°  C.  and  stirring  continued  for  1  hour  afterwards.  While  this  temperature  was  still  maintained,  there  was  then  added  dropwise  over  a  period  of  15  minutes  a  solution  of  10.2  g.  of  malonanilide  in  50  ml.  of  dimethyl› formamide.  The  cold  mixture  was  stirred  4  hours  more  and  then  50  ml.  of $_{dimethylformamide }$ were  added.  The  batch  was  then  stirred  14  hours  at  about  20°  C.  200  ml.  water  added,  and  the  solid  was  filtered  off.  The  filter  cake  $^{PiEPARATION }$OF  THE $_{MALONANILIDES }$ Example  !.-Preparation  of  ortho-nitrophenyl› (  1)  Ortho-nitroaniline  ("ONA")  (2)  Alpha-aminoanthraquinone  ("Scarlet  AL")  (3)  $^{2-amino-4-diethylsulfonamide }$anisole  ("Red  ITR")  (  4)  $^{2-methyl-5-nitroaniline }$("Scarlet  6")  (5)  2,4-dinitroaniline  ("2,4-DNA")  (6)  1-amino-5-benzoylamino  anthraquinone  (Vat  base)  (7)  p-Phenylazoaniline  ("p-PAA")  (8)  o-Chloroaniline  (’"Yellow  6G")  (9)  2-hydroxy-5-nitroaniline  ("2-H-5-N-A-")  (10)  $^{4’-nitro-4-aminophenyazobenzene }$("4N-pPAA")  (  11)  $^{2-amino-4,5-dinitrobenzothiazole }$(Heterocyclic  base). 