{{Short description|Industrial and food chemical}} {{Use dmy dates|date=August 2023}} {{chembox | Watchedfields = changed | verifiedrevid = 408554140 | ImageFile = Azodicarbonamide.png | ImageAlt = Skeletal formula of azodicarbonamide | ImageFile1 = Azodicarbonamide 3D spacefill.png | ImageAlt1 = Space-filling model of azodicarbonamide | IUPACName = Carbamoyliminourea | OtherNames = {{Unbulleted list|Azodicarboxamide|Azobisformamide|C,C'-Azodi(formamide)|Diazenedicarboxamide|Ayngaroxamide}} |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 4575589 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 56Z28B9C8O | InChI = 1/C2H4N4O2/c3-1(7)5-6-2(4)8/h(H2,3,7)(H2,4,8)/b6-5+ | InChIKey = XOZUGNYVDXMRKW-AATRIKPKBW | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 28517 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C2H4N4O2/c3-1(7)5-6-2(4)8/h(H2,3,7)(H2,4,8)/b6-5+ | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = XOZUGNYVDXMRKW-AATRIKPKSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 123-77-3 | EC_number = 204-650-8 | PubChem = 31269 | SMILES = O=C(/N=N/C(=O)N)N }} |Section2={{Chembox Properties | C=2 | H=4 | O=2 | N=4 | Appearance = Yellow to orange/red crystalline powder | Density = | MeltingPtC = 225 | MeltingPt_notes = (decomposes) | BoilingPt = | Solubility = }} |Section3={{Chembox Hazards | MainHazards = oxidizer | FlashPt = | AutoignitionPt = | NFPA-H = 1 | NFPA-F = 1 | NFPA-R = 0 | GHSPictograms = {{GHS08}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|242|331|334|}} | PPhrases = {{P-phrases|}} | ExternalSDS = [http://www.sciencelab.com/msds.php?msdsId=9922989] }} }}
'''Azodicarbonamide''', '''ADCA''', '''ACA''',<ref>{{Cite news |last=Farah |first=Troy |date=2019-05-28 |title=Banned bread: why does the US allow additives that Europe says are unsafe? |url=https://www.theguardian.com/us-news/2019/may/28/bread-additives-chemicals-us-toxic-america |access-date=2024-06-07 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref> '''ADA,''' or '''azo(''bis'')formamide''', is a chemical compound with the molecular formula {{chem2|C2H4O2N4}}.<ref>{{Cite web|url=http://www.inchem.org/documents/cicads/cicads/cicad16.htm#PartNumber:2|title=Azodicarbonamide (CICADS)|publisher=International Programme on Chemical Safety|work=Inchem|access-date=2010-08-14| archive-url= https://web.archive.org/web/20100824055553/http://www.inchem.org/documents/cicads/cicads/cicad16.htm| archive-date= 24 August 2010 | url-status= live}} Also published by World Health Organization, Geneva, 1999.</ref> It is a yellow to orange-red, odorless, crystalline powder. It is sometimes called "the yoga mat chemical" because of widespread use in foamed plastics.<ref>{{cite journal |last1=Arts |first1=Josje |last2=Kimber |first2=Ian |title=Azodicarbonamide (ADCA): A reconsideration of classification as a respiratory sensitiser |journal=Regulatory Toxicology and Pharmacology |date=October 2017 |volume=89 |pages=268–278 |doi=10.1016/j.yrtph.2017.07.018 |pmid=28734852 |doi-access=free }}</ref><ref>{{Cite web | url=https://www.npr.org/sections/thesalt/2014/03/06/286886095/almost-500-foods-contain-the-yoga-mat-compound-should-we-care-keep |title = Almost 500 Foods Contain the 'Yoga Mat' Compound. Should We Care?| website=NPR }}</ref> It was first described by John Bryden in 1959.<ref>{{cite journal |last1=Bryden |first1=J. H. |title=The crystal structure of azodicarbonamide |journal=Acta Crystallographica |date=10 January 1961 |volume=14 |issue=1 |pages=61–63 |doi=10.1107/S0365110X61000139 |doi-access= |bibcode=1961AcCry..14...61B }}</ref>
==Synthesis== It is prepared in two steps via treatment of urea with hydrazine to form biurea, as described in this idealized equation: :{{chem2|2 O\dC(NH2)2 + H2N\sNH2 → H2N\sC(\dO)\sNH\sNH\sC(\dO)\sNH2 + 2 NH3}}
Oxidation of biurea with gaseous chlorine yields azodicarbonamide: :{{chem2|H2N\sC(\dO)\sNH\sNH\sC(\dO)\sNH2 + Cl2 → H2N\sC(\dO)\sN\dN\sC(\dO)\sNH2 + 2 HCl}}
== Applications == ===Blowing agent=== The principal use of azodicarbonamide is in the production of foamed plastics as a blowing agent. The thermal decomposition of azodicarbonamide produces nitrogen, carbon monoxide, carbon dioxide, and ammonia gases, which are trapped in the polymer as bubbles to form a foamed article.<ref name=Ull>{{cite encyclopedia|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |author=Heinz Weber |author2=Isidoor De Grave |author3=Eckhard Röhrl |author4=Volker Altstädt |year=2016|pages= 1–54|doi=10.1002/14356007.a11_435.pub2|publisher=Wiley-VCH|chapter=Foamed Plastics|isbn= 978-3-527-30673-2}}</ref>
Azodicarbonamide is used in plastics, synthetic leather, and other industries and can be pure or modified. Modification affects the reaction temperatures. Pure azodicarbonamide generally reacts around 200 °C. In the plastic, leather, and other industries, modified azodicarbonamide (average decomposition temperature 170 °C) contains additives that accelerate the reaction or react at lower temperatures.<ref name=Ull/>
An example of the use of azodicarbonamide as a blowing agent is found in the manufacture of vinyl (PVC) and EVA-PE foams, where it forms bubbles upon breaking down into gas at high temperature. Vinyl foam is springy and does not slip on smooth surfaces. It is useful for carpet underlay and floor mats. Commercial yoga mats made of vinyl foam have been available since the 1980s; the first mats were cut from carpet underlay.<ref>{{cite book | first=John | last=Friend | author-link=John Friend (yogi) | year=2009 | title=History of Yoga Mat - Looking back with Friends }}</ref>
===Food additive=== As a food additive, azodicarbonamide is used as a flour bleaching agent and a dough conditioner in some countries such as the US and Canada (up to 45 ppm), but not in the European Union.<ref name="FDA">{{Cite journal |author=Human Foods Program |date=2025-02-05 |title=Azodicarbonamide (ADA) Frequently Asked Questions |url=https://www.fda.gov/food/food-additives-petitions/azodicarbonamide-ada-frequently-asked-questions |journal=FDA |language=en}}</ref> It reacts with moist flour as an oxidizing agent. The main reaction product is biurea, which is stable during baking.<ref name="WHOFAO">{{Cite web |title=054. Azodicarbonamide (FAO Nutrition Meetings Report Series 40abc) |url=https://www.inchem.org:443/documents/jecfa/jecmono/40abcj28.htm |access-date=2025-05-12 |website=www.inchem.org}}</ref> Secondary reaction products include semicarbazide (aminourea) and ethyl carbamate (urethane).<ref name="FDA" /> It is known by the E number '''E927'''. Many restaurants in the US fast food industry removed '''E927''' from foodstuffs in response to negative publicity.<ref name="bloomberg">{{Cite news|url=https://www.bloomberg.com/news/articles/2016-08-08/the-yoga-mat-chemical-s-quiet-fast-food-exit|title= The Yoga-Mat Chemical's Quiet Fast-Food Exit|access-date=2016-08-08|newspaper=Bloomberg|date= 8 August 2016}}</ref>
==Safety and regulation==
=== Occupational (inhalation) === In a 1999 report, the World Health Organization has linked exposure to azodicarbonamide at workplaces where it is manufactured or handled in raw form to "respiratory issues, allergies and asthma". The available data are restricted to these occupational environments. Exposure of the general public to azodicarbonamide could not be evaluated because of the lack of available data.<ref>{{Cite web|url=https://www.who.int/ipcs/publications/cicad/en/cicad16.pdf|title=Concise International Chemical Assessment Document 16: Azodicarbonamide|publisher=World Health Organization|access-date=2014-02-05}}</ref> The WHO concluded, "The level of risk is uncertain; hence, exposure levels should be reduced as much as possible".
In the UK, the Health and Safety Executive has identified azodicarbonamide as a respiratory sensitizer (a possible cause of asthma) in workplace settings and determined that containers of it should be labeled with "May cause sensitisation by inhalation."<ref>{{Cite web|url=http://www.ohsrep.org.au/index.cfm?section=10&Category=69&viewmode=content&contentid=62 |title=Substances causing/worsening asthma |work=UK Occupational Health and Safety |publisher=WorkSafe Victoria |access-date=2010-08-14 |archive-url=https://web.archive.org/web/20130531062959/http://www.ohsrep.org.au/index.cfm?section=10&Category=69&viewmode=content&contentid=62 |archive-date=May 31, 2013 }}</ref> Azodicarbonamide was added to the REACH Regulation candidate Substances of Very High Concern list in 2012, for its respiratory sensitizing properties.<ref>{{Cite web|url=https://echa.europa.eu/candidate-list-table?p_p_id=disslists_WAR_disslistsportlet&p_p_lifecycle=0&p_p_state=normal&p_p_mode=view&p_p_col_id=column-1&p_p_col_pos=2&p_p_col_count=3&_disslists_WAR_disslistsportlet_keywords=&_disslists_WAR_disslistsportlet_orderByCol=dte_inclusion&_disslists_WAR_disslistsportlet_advancedSearch=false&_disslists_WAR_disslistsportlet_casNumber=&_disslists_WAR_disslistsportlet_deltaParamValue=50&_disslists_WAR_disslistsportlet_andOperator=true&_disslists_WAR_disslistsportlet_haz_detailed_concern=&_disslists_WAR_disslistsportlet_name=&_disslists_WAR_disslistsportlet_orderByType=desc&_disslists_WAR_disslistsportlet_ecNumber=&_disslists_WAR_disslistsportlet_dte_inclusionFrom=&_disslists_WAR_disslistsportlet_dte_inclusionTo=&_disslists_WAR_disslistsportlet_doSearch=&_disslists_WAR_disslistsportlet_resetCur=false&_disslists_WAR_disslistsportlet_delta=200|title=Candidate List of substances of very high concern for Authorisation|website=ECHA|language=en-GB|access-date=2018-10-30 |quote=Diazene-1,2-dicarboxamide (C,C'-azodi(formamide)) (ADCA)... respiratory sensitising properties (Article 57(f) - human health)}}</ref>
=== Food (ingestion) === In jurisdictions such as Australia and the European Union, azodicarbonamide as a food additive is banned.<ref name="FADB">{{cite book|title=Food additives data book|last1=Smith|first1=Jim|last2=Hong-Shum|first2=Lily|publisher=Wiley-Blackwell|year=2011|isbn=978-1-4051-9543-0|edition=2nd|location=Chichester, West Sussex|page=548}}</ref><ref name="EU">{{cite web|title=European Union: Authorisation of Additives|url=https://webgate.ec.europa.eu/sanco_foods/main/|author=European Commission|access-date=2014-12-31|archive-url=https://web.archive.org/web/20141231123803/https://webgate.ec.europa.eu/sanco_foods/main/|archive-date=2014-12-31|author-link=European Commission}}</ref> Azodicarbonamide as a blowing agent in plastics was banned in the EU in August 2005 in plastic articles that are intended to come into direct contact with food.<ref name=EU05>{{Cite web|url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2004:007:0045:0046:EN:PDF|title=COMMISSION DIRECTIVE 2004/1/EC of 6 January 2004 amending Directive 2002/72/EC as regards the suspension of the use of azodicarbonamide as blowing agent|date=2004-01-13|access-date=2011-03-10|publisher=Official Journal of the European Union}}</ref> In the United States, azodicarbonamide is generally recognized as safe (GRAS) and is allowed to be added to flour at levels up to 45 ppm.<ref>{{cite journal|date=April 1, 2012|title=21CFR172.806|url=http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=172.806|archive-url=https://web.archive.org/web/20030915174345/http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=172.806|url-status=dead|archive-date=15 September 2003|journal=Code of Federal Regulations}}</ref><ref name="FADB" /> However, use in products intended for human consumption is in decline under pressure of the public opinion.<ref name="bloomberg"/> In 2014, amid public discomfort with the dual uses of azodicarbonamide, Subway and Wendy's announced that they would no longer use it as a dough conditioner.<ref name="CNN">{{cite news|url=http://www.cnn.com/2014/02/06/health/subway-bread-chemical/|title=Subway to remove 'dough conditioner' chemical from bread|date=February 17, 2014|agency=CNN|last1=Landau|first1=Elizabeth|access-date=3 November 2015}}</ref> As of February 2014, the Center for Science in the Public Interest stated azodicarbonamide "has been poorly tested" and advocated for reducing the amount of azodicarbonamide used in food.<ref name="CNN" />
Banning ADA in food is motivated by studies of semicarbazide (aminourea) - a breakdown product of ADA that shows "weak carcinogenic activity in laboratory animals", but data is inconclusive in humans.<ref name=EU05/> The EU banned ADA in food containers despite an EFSA report considering such exposure "not a concern" due to low levels produced. The FDA considers ADA to be safe in permissible concentrations.<ref name="FDA" />
==References== {{Reflist|30em}}
==External links== *[https://www.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0380&p_version=2 International Chemical Safety Card]
{{E number infobox 920-929}}
Category:Food additives Category:Azo compounds Category:Bleaches Category:Food safety