United  States  Patent  Office  3,496,212  Patented  Feb.  17,  1970  1  2  3,496,212  Purification  of  adiponitrile  by  treatment  with  an  alde› hyde  in  presence  of  water  and  a  strong  acid  anion,  prefer› ably  at pH  1 to  3, to  convert  impurities  either  to  water› soluble  derivatives  or  high  boilers.  ABSTRACT  OF  THE  DISCLOSURE  This  invention  relates  to a  process  for  purifying  crude  adiponitrile.  Adiponitrile  is  manufactured  in  large  quantity  as an  in› termediate  in the  production  of  nylon  66  (polyhexamethyl› eneadipamide).  It  is  required  in a  high  state  of  purity  for  reduction  to  pure  hexamethylene  diamine,  one  of the  in› termediates  from  which  the  polymer  is  directly  made.  Even  very  small  amounts  of  impurity  in the  hexamethyl› ene  diamine  have  large  effects  upon  the  properties  of the  nylon  polymer  produced  therefrom.  Whether  manufac› tured  by  dehydration  of  ammonium  adipate  (adipic  acid  and  ammonia)  or  from  1,4-dichlorobutene  and  sodium  cyanide,  or by  reductive  dime’risation  of  acrylonitrile  or  by any  other  method,  crude  adiponitrile  is  difficult  to pur- ify  sufficiently  to  make  it  acceptable  as a  nylon  interme- diate.  Crude  adiponitrile  obtained  by  dehydration  of  am› moniam  adipate  contains  impurities  which  may  be  classi› fied  as  (a)  Incomplete  conversion  products,  for  example  cyano› valeramide  and  cyanovaleric  acid  (b)  Degradation  products,  for  example  1-cyano-cyclo› pentylidineimine  and  pyrimidine  derivatives.  The  boiling  points  of  some  of  these  impurities  are  so  close  to  that  of  adiponitrile  that  efficient  purification  by  fractional  distil› lation  requires  either  multi-stage  distillation  or  columns  with  very  large  numbers  of  plates  and  high  reflux  ratios.  As  alternatives  to  fractional  distillation  it  has  been  proposed  to  purify  crude  adiponitrile  by  fractional  crystal› lisation,  and  by  passage  over  exchange  resins.  It  has  also  been  proposed  to  hydrolyse  the  imine  im› purity  in  crude  adiponitrile  to  ketone  before  distilling.  In  a  further  proposal  which  has  been  made  crude  adiponi› trile  is  treated  with  aqueous  formaldehyde  at  high  tem› peratures  e.g.  100  °  C.  to  convert  certain  impurities  into  water-soluble  methylol  compounds.  According  to the  present  invention  a  process  for  purify› ing  adiponitrile  comprises  treating  impure  adiponitrile  with  an  aldehyde  in the  presence  of  water,  strong  acid  anions  and  cations  comprising  hydrogen  ions,  ammonium  ions  as  hereinafter  defined,  or a  combination  thereof  and  thereafter  separating  adiponitrile  from  the  mixture.  The  term  "ammonium  ions"  include  ammonium  itself  and  ions  of  organic  primary  or  secondary  amines  particu› larly  primary  or  secondary  alkylamines  and  especially  methylamine  or  dimethylamine.  The  aldehyde  used  in the  process  of the  invention  is  conveniently  a  water-soluble  aldehyde,  preferably  form› aldehyde,  but  if  desired  insoluble  aldehydes  can  -be  used,  for  example  immobilised  in  resin-bed  form.  The  amount  of  aldehyde  should  be  sufficient  to  react  with  all  the  im- purity  which  it  is  desired  to  separate.  Using  formaldehyde  amounts  of  about  1-2%  on the  weight  of the  impure  adi› ponitrile  are  usually  satisfactory.  Examples  of  strong  acid  anions  which  may  be  present  are  sulphate,  nitrate,  chloride,  phosphate  and  p-toluene› sulphonate.  Of  these,  sulphate  and  nitrate  are  the  pre› ferred  ions  because  of  their  cheapness  and  because  they  are  less  corrosive  than  chloride  ions.  For  operation  above  a  pH  of  about  3  strong  carboxylic  acid  anions,  e.g.  for› mate  ions  •can  be  present.  For  operation  below  a  pH  of  about  3  the  presence  of  strong  inorganic  acid  anions  is  necessary.  A  convenient  method  of  carrying  out  the  aldehyde  treatment  consists  in  dissolving  the  impure  adiponitrile  in a  substantially  water-insoluble  solvent  of low  polarity,  for  example  an  aromatic  hydrocarbon,  e.g.,  benzene  or  toluene,  and  washing  the  solution  with  an  aqueous  solu› tion  containing  a  water-soluble  aldehyde  and  cations  as  aforesaid.  The  aldehyde  treatment  may  be  carried  out  at  any  desired  temperature  between  the  freezing  and  boiling  points  of the  liquids  which  are  present,  preferred  operat› ing  temperatures  being  from  ambient  to  about  50°  C.  In the  higher  pH  regions  reaction  of the  aldehyde  with  impurities  in the  adiponitrile  is  somewhat  slow,  particu- larly  below  20 °  C.  In  a  preferred  form  therefore  the  process  of the  inven› tion  comprises  treating  impure  adiponitrile  with  an  alde› hyde  in  presence  of an  aqueous  liquor  of pH  from  1 to  6  especially  pH  1 to  3,  containing  strong  acid  anions  and  cations  as  aforesaid  and  thereafter  separating  adiponi› trile  from  the  mixture.  In the  process  of the  invention,  particularly  when  op› ~rated  at pH  1-6,  especially  pH  1-3,  the  aldehyde  wash› mg  step  has  the  following  effects:  (I)  Neutral  heterocyclic  impurities  (e.g.  pyrroles)  react  with  the  aldehyde  to  give  products  which  can  be re› moved  by  water-washing,  filtration  or as  high  boiling  still  residues.  When  ammonium  cations  are  present  the  prod› ~cts  are  usually  water-soluble;  when  hydrogen  ion  only  rs  used  the  products  are  usually  solids  or  tars  of  high  molecular  weight.  (2)  2-cyanocyclopentylidineimine  is  hydrolysed  to 2- cyanocyclopentanone  which  can  more  readily  be  separated  from  adiponitrile  by  distillation,  or  mriy  preferably  be re- db  b  move  y a  su  sequent  alkaline  extraction  followed  by  a  water  wash.  (3)  Heterocyclic  and  other  bases  are  removed  from  the  adiponitrile  by  solution  in the  aqueous  liquor.  A  preferred  feature  of  our  invention  therefore  com- prises  purifying  impure  adiponitrile  by  treating  a  solution  thereof  in a  water-insoluble  solvent  of low  polarity  with  a  water-soluble  aldehyde  in  presence  0£ an  aqueous  liquor  of pH  from  1 to  3  containing  strong  acid  anions  and  ca- tions  comprising  hydrogen  ions,  ammonium  ions  as  here› inbefore  defined  or a  combination  thereof,  separating  the  non-aqueous  phase  and  extracting  it  with  aqueous  alkali  subsequently  washing  the  non-aqueous  phase  with  wate;  if  desired,  removing  the  solvent  by  distillation  and  dis- till)ng  the  adiponitrile  to  separate  it  from  high  boiling  residues.  In this  process  the  aldehyde-treatment  may  convenient› ly be  O  carrie_d  out  at  _ambient  temperatures,  for  example,  at 20  C.  with  no  deliberate  heating  or  cooling,  but  higher  or  lower  temperatures  can  be  used  if  desired.  Contact  times  of  10-15  minutes  have  been  found  adequate  at am› bient  temperatures  and  this  makes  the  process  especially  well  suited  to  continuous  operation.  As  aqueous  alkali  a  solution  of  sodium  hydroxide  or  ammonium  hydroxide  may  conveniently  be  used.  A  sub› sequent  water  wash  is  beneficial  in  order  to  avoid  the  presence  of  alkali  in the  distillation  stage,  but  is  not  es- PROCESS  FOR  PURIFYING  ADIPONITRILE  John  Derrick  Davison,  John  Milton  Dossor,  and  Charles  Henry  Vasey,  Manchester,  England,  assignors  to  Im› perial  Chemical  Industries  Limited,  London,  England,  a  corporation  of  Great  Britain  No  Drawing.  Filed  Jnne  26,  1967,  Ser.  No.  648,949  Claims  priority,  application  Great  Britain,  July  1,  1966,  29,609/66;  Feb.  9,  1967,  6,174/67  Int.  CI.  C07c  121176;  B0ld  3/34  U.S.  CI.  260-465.2  5  Claims 