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* [[Hofmann rearrangement]], a reaction in which a primary [[amide]] is treated with a [[Oxidizing agent|strong oxidizer]] such as sodium [[hypobromite]][http://alpha.chem.umb.edu/chemistry/orgchem/CH20Handout.pdf {{Webarchive|url=https://web.archive.org/web/20060911031125/http://alpha.chem.umb.edu/chemistry/orgchem/CH20Handout.pdf |date=2006-09-11 }}, Ch20Handout, University of Massachusetts Boston][{{cite book|last1= Mann |first1= F. G. |last2= Saunders |first2= B. C.|title=Practical Organic Chemistry, 4th Ed.|year=1960|publisher=Longman|location=London|isbn=978-0-582-44407-2|page=128|url=https://www.scribd.com/doc/46973684/Practical-Organic-Chemistry-Frederick-George-Mann}}][{{cite book|last=Cohen|first=Julius|title=Practical Organic Chemistry 2nd Ed.|year=1900|publisher=Macmillan and Co., Limited|location=London|page=[https://archive.org/details/practicalorgani00cohegoog/page/n90 72]|url=https://archive.org/details/practicalorgani00cohegoog|quote=Practical Organic Chemistry Cohen Julius.}}] or [[lead tetraacetate]][{{cite journal|author1=Baumgarten, Henry |author2=Smith, Howard |author3=Staklis, Andris |title=Reactions of amines. XVIII. Oxidative rearrangement of amides with lead tetraacetate|journal=The Journal of Organic Chemistry|year=1975|volume=40|issue=24|pages=3554–3561|doi=10.1021/jo00912a019}}] to form an isocyanate intermediate. |
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* [[Hofmann rearrangement]], a reaction in which a primary [[amide]] is treated with a [[Oxidizing agent|strong oxidizer]] such as sodium [[hypobromite]][http://alpha.chem.umb.edu/chemistry/orgchem/CH20Handout.pdf {{Webarchive|url=https://web.archive.org/web/20060911031125/http://alpha.chem.umb.edu/chemistry/orgchem/CH20Handout.pdf |date=2006-09-11 }}, Ch20Handout, University of Massachusetts Boston][{{cite book|last1= Mann |first1= F. G. |last2= Saunders |first2= B. C.|title=Practical Organic Chemistry, 4th Ed.|year=1960|publisher=Longman|location=London|isbn=978-0-582-44407-2|page=128|url=https://www.scribd.com/doc/46973684/Practical-Organic-Chemistry-Frederick-George-Mann}}][{{cite book|last=Cohen|first=Julius|title=Practical Organic Chemistry 2nd Ed.|year=1900|publisher=Macmillan and Co., Limited|location=London|page=[https://archive.org/details/practicalorgani00cohegoog/page/n90 72]|url=https://archive.org/details/practicalorgani00cohegoog|quote=Practical Organic Chemistry Cohen Julius.}}] or [[lead tetraacetate]][{{cite journal|author1=Baumgarten, Henry |author2=Smith, Howard |author3=Staklis, Andris |title=Reactions of amines. XVIII. Oxidative rearrangement of amides with lead tetraacetate|journal=The Journal of Organic Chemistry|year=1975|volume=40|issue=24|pages=3554–3561|doi=10.1021/jo00912a019}}] to form an isocyanate intermediate. |
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In the production of polyurethane prepolymers, a certain amount of unreacted monomeric diisocyanates such as TDI, MDI, or HDI typically remains after the reaction between polyols and isocyanates.[{{cite book |last1=Brereton |first1=George |last2=Emanuel |first2=Ronald M. |last3=Lomax |first3=Robert |last4=Pennington |first4=Keith |last5=Ryan |first5=Tyler |last6=Tebbe |first6=Heiko |last7=Timm |first7=Michael |last8=Ware |first8=Polina |last9=Winkler |first9=Karen |last10=Yuan |first10=Tingting |last11=Zhu |first11=Zhenya |last12=Adam |first12=Norbert |last13=Avar |first13=Geza |last14=Blankenheim |first14=Herbert |last15=Friederichs |first15=Wolfgang |last16=Giersig |first16=Manfred |last17=Weigand |first17=Eckehard |last18=Halfmann |first18=Michael |last19=Wittbecker |first19=Friedrich-Wilhelm |last20=Larimer |first20=Donald-Richard |last21=Maier |first21=Udo |last22=Meyer-Ahrens |first22=Sven |last23=Noble |first23=Karl-Ludwig |last24=Wussow |first24=Hans-Georg |title=Ullmann's Encyclopedia of Industrial Chemistry |chapter=Polyurethanes |date=2019 |pages=1–76 |doi=10.1002/14356007.a21_665.pub3 |isbn=978-3-527-30673-2 }}][{{Cite web |title=Reducing free monomer content in MDI-based prepolymers |url=https://pdf.benchchem.com/179/Reducing_free_monomer_content_in_MDI_based_prepolymers.pdf |archive-date=2026-03-16}}][{{Cite patent|number=CA2257214C|title=Removal of unreacted diisocyanate monomer from polyurethane prepolymers|gdate=2006-11-21|invent1=Rosenberg|invent2=Singh|invent3=Maupin|invent4=Lombardo|inventor1-first=Ronald Owen|inventor2-first=Ajaib|inventor3-first=Christopher James|inventor4-first=Brian Scott|url=https://patents.google.com/patent/CA2257214C/en}}] Because many monomeric isocyanates are classified as hazardous substances, numerous regulations (e.g. GHS, EU restriction 2020/1149[{{Cite web |title=Low Free Technology |url=https://www.ube.co.jp/ube/ |access-date=2026-03-16 |website=UBE Corporation |language=en}}], OSHA[{{Cite web |title=Isocyanates - Overview {{!}} Occupational Safety and Health Administration |url=https://www.osha.gov/isocyanates |access-date=2026-03-16 |website=www.osha.gov}}], or California Proposition 65) set strict limits for the maximum allowable content of free isocyanates in commercial products. |
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