Editing CAS Registry Number

{{Short description|Chemical identifier}}
{{Use dmy dates|date=May 2018}}
[[File:Cascommonchemistry2022.png|thumb|Screenshot of the CAS Common Chemistry database with information about [[caffeine]] ([https://commonchemistry.cas.org/detail?cas_rn=58-08-2 58-08-2]).]]
 
A '''CAS Registry Number'''<ref>[http://www.cas.org/expertise/cascontent/registry/regsys.html CAS registry description] {{Webarchive |url=https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html# |date=2008-07-25 }}, by Chemical Abstracts Service</ref> (also referred to as '''CAS RN'''<ref>{{cite web|url=https://www.cas.org/support/documentation/chemical-substances/cas-rn-verified-partner-program|title=CAS Registry Number Verified Partner Program|access-date=2021-08-04|publisher=CAS}}</ref> or informally '''CAS Number''') is a [[unique identifier|unique identification number]], assigned by the [[Chemical Abstracts Service]] (CAS) in the US to every [[chemical substance]] described in the open scientific literature, in order to index the substance in the '''CAS Registry'''. This registry includes all substances described since 1957, plus some substances from as far back as the early 1800s.<ref name=CAScontent/> It is a [[chemical database]] that includes [[Organic compounds|organic]] and [[inorganic compounds|inorganic]] compounds, [[mineral]]s, [[isotope]]s, [[alloys]], mixtures, and nonstructurable materials (UVCBs - substances of '''u'''nknown or '''v'''ariable composition, '''c'''omplex reaction products, or '''b'''iological origin).<ref name=crc>{{cite web |author=American Chemical Society |author-link=American Chemical Society |title=CAS Registry and CASRNs |url=http://www.cas.org/expertise/cascontent/registry/regsys.html#q2 |access-date=2009-07-25 |archive-url=https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html#q2#q2 |archive-date=2008-07-25 |url-status=dead |df=dmy-all}}</ref> CAS RNs are generally [[serial number]]s (with a [[check digit]]), so they do not contain any information about the structures themselves the way [[Simplified molecular-input line-entry system|SMILES]] and [[International Chemical Identifier|InChI]] strings do.

The CAS Registry is an authoritative collection of disclosed chemical substance information. It identifies more than 204 million unique organic and inorganic substances and 69 million protein and DNA sequences,<ref name=CAScontent>{{cite web |title=CAS Content: Substances |url=https://www.cas.org/about/cas-content |website=www.cas.org|access-date=2020-08-10 |language=en}}</ref> plus additional information about each substance. It is updated with around 15,000 additional new substances daily.<ref>{{Cite web|url=https://www.cas.org/cas-data/cas-registry|title=CAS REGISTRY|website=www.cas.org}}</ref> A collection of almost 500 thousand CAS registry numbers is made available under a [[CC BY-NC]] license at ACS Commons Chemistry.<ref>{{cite news |title=CAS Common Chemistry expands collection of publicly available chemical information |url=https://www.cas.org/resources/press-releases/common-chemistry |access-date=17 March 2021 |work=CAS |language=en}}</ref>

== History and use ==
Historically, chemicals have been identified by a wide variety of synonyms and propeties. One of the biggest challenges in the early development of substance indexing, a task undertaken by the Chemical Abstracts Service, was in identifying if a substance in literature was new or if it had been previously discovered. Well-known chemicals may be known via multiple generic, historical, commercial, and/or [[Black market|(black)-market]] names, and even [[Chemical nomenclature|systematic nomenclature]] based on structure alone was not universally useful. An algorithm was developed to translate the [[structural formula]] of a chemical into a computer-searchable table, which provided a basis for the service that listed each chemical with its CAS Registry Number, the CAS Chemical Registry System, which became operational in 1965.<ref>{{Cite web |last=Shively |first=Eric |date=June 11, 2007 |title=CAS Surveys Its First 100 Years |url=https://cen.acs.org/articles/85/i24/CAS-Surveys-First-100-Years.html |access-date=2024-04-16 |website=Chemical & Engineering News |language=en}}</ref>

CAS Registry Numbers (CAS RN) are simple and regular, convenient for database searches. They offer a reliable, common and international link to every specific substance across the various nomenclatures and disciplines used by branches of science, industry, and regulatory bodies. Almost all molecule databases today allow searching by CAS Registry Number, and it is used as a global standard.<ref>{{Cite journal |last=Jacobs |first=Andrea |last2=Williams |first2=Dustin |last3=Hickey |first3=Katherine |last4=Patrick |first4=Nathan |last5=Williams |first5=Antony J. |last6=Chalk |first6=Stuart |last7=McEwen |first7=Leah |last8=Willighagen |first8=Egon |last9=Walker |first9=Martin |last10=Bolton |first10=Evan |last11=Sinclair |first11=Gabriel |last12=Sanford |first12=Adam |date=2022-06-13 |title=CAS Common Chemistry in 2021: Expanding Access to Trusted Chemical Information for the Scientific Community |url=https://pubs.acs.org/doi/10.1021/acs.jcim.2c00268 |journal=Journal of Chemical Information and Modeling |language=en |volume=62 |issue=11 |pages=2737–2743 |doi=10.1021/acs.jcim.2c00268 |issn=1549-9596 |pmc=9199008 |pmid=35559614}}</ref>

== Format ==
A CAS Registry Number has no inherent meaning, but is assigned in sequential, increasing order when the substance is identified by CAS scientists for inclusion in  the CAS Registry database.

A CAS RN is separated by hyphens into three parts, the first consisting from two up to seven digits,<ref>2014-06-18, https://www.cas.org/content/chemical-substances/faqs</ref> the second consisting of two digits, and the third consisting of a single digit serving as a [[check digit]]. This format gives CAS a maximum capacity of 1,000,000,000 unique numbers.

The check digit is found by taking the last digit times 1, the preceding digit times 2, the preceding digit times 3 etc., adding all these up and computing the sum [[modular arithmetic|modulo]] 10. For example, the CAS number of [[water]] is 7732-18-5: the checksum 5 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.

== Granularity ==
* [[Stereoisomer]]s and [[racemic mixture]]s are assigned discrete CAS Registry Numbers: {{sc|L}}-[[epinephrine]] has 51-43-4, {{sc|D}}-epinephrine has 150-05-0, and racemic {{sc|DL}}-epinephrine has 329-65-7
* Different [[phase (matter)|phase]]s do not receive different CAS RNs (liquid water and ice both have 7732-18-5), but different crystal structures do ([[carbon]] in general is 7440-44-0, [[graphite]] is 7782-42-5 and [[diamond]] is 7782-40-3)
* Commonly encountered mixtures of known or unknown composition may receive a CAS RN; examples are [[Leishman stain]] (12627-53-1) and [[mustard oil]] (8007-40-7).
* Some [[chemical elements]] are discerned by their oxidation state, e.g. the element [[chromium]] has 7440-47-3, the trivalent Cr(III) has 16065-83-1 and the [[Hexavalent chromium|hexavalent Cr(VI) species]] have 18540-29-9.
* Occasionally whole classes of molecules receive a single CAS RN: the class of enzymes known as [[alcohol dehydrogenase]]s has 9031-72-5.

== Search engines ==
* CHEMINDEX Search via [[Canadian Centre for Occupational Health and Safety]]<ref name="cis">{{cite web|author=Canadian Centre for Occupational Health and Safety|author-link=Canadian Centre for Occupational Health and Safety|title=CHEMINDEX Search|url=http://ccinfoweb.ccohs.ca/chemindex/search.html|access-date=13 July 2009}}</ref>
* ChemIDplus Advanced via [[United States National Library of Medicine]]<ref name="adv">{{cite web|author=United States National Library of Medicine|author-link=United States National Library of Medicine|title=ChemIDplus Advanced|url=https://chem.nlm.nih.gov/chemidplus/|access-date=28 June 2021}}</ref>
* Common Chemistry<ref name="ss">{{cite web|author=American Chemical Society |author-link=American Chemical Society|title=Substance Search|url=http://www.commonchemistry.org/|access-date=8 July 2009}}</ref><ref>{{cite journal |last1=Jacobs |first1=Andrea |last2=Williams |first2=Dustin |last3=Hickey |first3=Katherine |last4=Patrick |first4=Nathan |last5=Williams |first5=Antony J. |last6=Chalk |first6=Stuart |last7=McEwen |first7=Leah |last8=Willighagen |first8=Egon |last9=Walker |first9=Martin |last10=Bolton |first10=Evan |last11=Sinclair |first11=Gabriel |last12=Sanford |first12=Adam |title=CAS Common Chemistry in 2021: Expanding Access to Trusted Chemical Information for the Scientific Community |journal=Journal of Chemical Information and Modeling |date=13 May 2022 |volume=62 |issue=11 |pages=2737–2743 |doi=10.1021/acs.jcim.2c00268 |pmid=35559614 |pmc=9199008 |s2cid=248778162 }}</ref> via Australian Inventory of Chemical Substances<ref name="adhg">{{cite web|author=National Industrial Chemicals Notification and Assessment Scheme|title=AICS Detailed Help / Guidance Notes|url=http://www.nicnas.gov.au/Industry/AICS/Search/AICS_Detailed_Help.asp#CAS_Number_Search|access-date=8 July 2009|url-status=dead|archive-url=https://web.archive.org/web/20090709011639/http://www.nicnas.gov.au/industry/AICS/Search/AICS_Detailed_Help.asp|archive-date=9 July 2009}}</ref>
* [[European chemical Substances Information System]]<ref name="eecs">{{cite web|author=European Commission Joint research Centre|title=ESIS : European chemical Substances Information System|url=http://esis.jrc.ec.europa.eu/|access-date=11 July 2009|url-status=dead|archive-url=https://web.archive.org/web/20140101220543/http://esis.jrc.ec.europa.eu/|archive-date=1 January 2014}}</ref> via the website of [[Royal Society of Chemistry]]<ref name="fcrn">{{cite web|author=Library & Information Centre|title=Finding a CAS Registry Number|url=http://www.rsc.org/Library/Features/Tips/CASNumbers.asp|access-date=11 July 2009}}</ref>
* HSNO Chemical Classification Information Database via [[Environmental Risk Management Authority]]<ref name="hcci">{{cite web|author=Environmental Risk Management Authority |author-link=Environmental Risk Management Authority|title=HSNO Chemical Classification Information Database|url=http://www.ermanz.govt.nz/Chemicals/ChemicalSearch.aspx|access-date=14 July 2009|url-status=dead |archive-url=https://web.archive.org/web/20090711220034/http://www.ermanz.govt.nz/Chemicals/ChemicalSearch.aspx |archive-date=11 July 2009}}</ref>
* Search Tool of Australian Inventory of Chemical Substances<ref name="ast">{{cite web|author=National Induscctrial Chemicals Notification and Assessment Scheme|title=AICS Search Tool|url=http://www.nicnas.gov.au/Industry/AICS/Search.asp|access-date=11 July 2009|url-status=dead|archive-url=https://web.archive.org/web/20090514095645/http://www.nicnas.gov.au/Industry/AICS/Search.asp|archive-date=14 May 2009}}</ref>
*USEPA CompTox Chemicals Dashboard<ref>{{Cite web|title=CompTox Chemicals Dashboard {{!}} Home|url=https://comptox.epa.gov/dashboard|access-date=2021-10-14|website=comptox.epa.gov}}</ref>

== See also ==
* [[Academic publishing]]
* [[Beilstein Registry Number]]
* [[Chemical file format]]
* [[Dictionary of chemical formulas]]
* [[European Community number|EC#]] (EINECS and ELINCS, European Community)
* [[Enzyme Commission number|EC number]] (Enzyme Commission)
* [[International Union of Pure and Applied Chemistry]]
* [[List of CAS numbers by chemical compound]]
* [[Chemical file format#MDL number|MDL number]]
* [[PubChem]]
* [[Registration authority]]
* [[UN number]]

== References ==
{{reflist}}

== External links ==
{{Wikidata property|P231}}

* [https://web.archive.org/web/20080725010848/http://www.cas.org/expertise/cascontent/registry/regsys.html CAS registry description], by Chemical Abstracts Service

To find the CAS number of a compound given its name, [[chemical formula|formula]] or structure, the following free resources can be used:
* [https://commonchemistry.cas.org/ CAS Common Chemistry]
* [http://webbook.nist.gov/chemistry/ NIST Chemistry WebBook]
* [https://cactus.nci.nih.gov/chemical/structure NCI/CADD Chemical Identifier Resolver]
* [http://chemsub.online.fr/ ChemSub Online (Multilingual chemical names)]
* [https://www.cdc.gov/niosh/npg/npgdcas.html NIOSH Pocket Guide to Chemical Hazards, index of CAS numbers]


{{DEFAULTSORT:Cas Registry Number}}
[[Category:Chemical numbering schemes]]
[[Category:American Chemical Society]]
[[Category:Unique identifiers]]