CAS Registry Number

A CAS Registry Number,[1] also referred to as CASRN or CAS Number, is a unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every chemical substance described in the open scientific literature (currently including all substances described from 1957 through the present, plus some substances from the early or mid 1900s), including organic and inorganic compounds, minerals, isotopes, alloys and nonstructurable materials (UVCBs, substances of unknown or variable composition, complex reaction products, or biological origin).[2]

The registry maintained by CAS is an authoritative collection of disclosed chemical substance information. It currently identifies more than 144 million unique organic and inorganic substances and 67 million protein and DNA sequences,[3] plus additional information about each substance. It is updated with around 15,000 additional new substances daily.[4]


Historically, chemicals have been identified by a wide variety of synonyms. Frequently these are arcane and constructed according to regional naming conventions relating to chemical formulae, structures or origins. Well-known chemicals may additionally be known via multiple generic, historical, commercial, and/or (black)-market names.

CAS Registry Numbers (CASRN) 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.

On the other hand, CASRNs are not related to chemistry, are proprietary and unrelated to any previous systems, and do not readily form phonetic analogs or synonyms.


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 CASRN is separated by hyphens into three parts, the first consisting from two up to seven digits,[5] the second consisting of two digits, and the third consisting of a single digit serving as a check digit. This current format gives CAS a maximum capacity of 1,000,000,000 unique identifiers.

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 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.


  • Stereoisomers and racemic mixtures are assigned discrete CAS Registry Numbers: L-epinephrine has 51-43-4, D-epinephrine has 150-05-0, and racemic DL-epinephrine has 329-65-7
  • Different phases do not receive different CASRNs (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 CASRN; examples are Leishman stain (12627-53-1) and mustard oil (8007-40-7).
  • Some metals 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 Cr(VI) ion has 18540-29-9.
  • Occasionally whole classes of molecules receive a single CASRN: the class of enzymes known as alcohol dehydrogenases has 9031-72-5.

Search engines

See also


  1. ^ CAS registry description Archived 25 July 2008 at the Wayback Machine, by Chemical Abstracts Service
  2. ^ American Chemical Society. "CAS Registry and CASRNs". Archived from the original on 25 July 2008. Retrieved 25 July 2009.
  3. ^ "CAS database counter (updated daily)". Retrieved 12 September 2018.
  4. ^ Chemical Substances - CAS REGISTRY
  5. ^ 2014-06-18,
  6. ^ Canadian Centre for Occupational Health and Safety. "CHEMINDEX Search". Retrieved 13 July 2009.
  7. ^ United States National Library of Medicine. "Advanced". Retrieved 1 December 2009.
  8. ^ American Chemical Society. "Substance Search". Retrieved 8 July 2009.
  9. ^ National Industrial Chemicals Notification and Assessment Scheme. "AICS Detailed Help / Guidance Notes". Archived from the original on 9 July 2009. Retrieved 8 July 2009.
  10. ^ European Commission Joint research Centre. "ESIS : European chemical Substances Information System". Archived from the original on 1 January 2014. Retrieved 11 July 2009.
  11. ^ Library & Information Centre. "Finding a CAS Registry Number". Retrieved 11 July 2009.
  12. ^ Environmental Risk Management Authority. "HSNO Chemical Classification Information Database". Archived from the original on 11 July 2009. Retrieved 14 July 2009.
  13. ^ National Industrial Chemicals Notification and Assessment Scheme. "AICS Search Tool". Archived from the original on 14 May 2009. Retrieved 11 July 2009.

External links

To find the CAS number of a compound given its name, formula or structure, the following free resources can be used:


(–)-18-Methylaminocoronaridine (18-MAC) is a second generation synthetic derivative of ibogaine developed by the research team led by the pharmacologist Stanley D. Glick from the Albany Medical College and the chemist Martin E. Kuehne from the University of Vermont. In animal studies it has shown around twice the efficacy of the related compound 18-methoxycoronaridine (18-MC) at reducing self-administration of morphine when administered in an equivalent dose, although it is less effective than 18-MC at reducing methamphetamine administration. Similarly to 18-MC itself, 18-MAC acts primarily as a selective α3β4 nicotinic acetylcholine antagonist, and is even more selective than 18-MC with very little activity as an NMDA antagonist and only slight affinity for the delta opioid receptor.


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It is reported to possess opioid antagonist properties in mice.


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F-2 (drug)

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Metazosin is an antihypertensive alpha-adrenergic antagonist.


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Piperacetazine (Quide) is an antipsychotic prodrug, most notably used for schizophrenia.


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RB-3007 is an orally active analogue of RB-101. It acts as an enkephalinase inhibitor, which is used in scientific research.


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