CAS Registry Number

CAS registry numbers^[1] are unique numerical identifiers for chemical elements, compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS #s.

Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers to every chemical that has been described in the literature. The intention is to make database searches more convenient, as chemicals often have many names. Almost all molecule databases today allow searching by CAS number.

As of December 2008, there were more than 40 million organic and inorganic substances and more than 60 million sequences in the CAS registry.^[2] Around 50,000 new numbers are added each week.

CAS also maintains and sells a database of these chemicals, known as the CAS registry.

Format

A CAS registry number is separated by hyphens into three parts, the first consisting of up to 7 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit. The numbers are assigned in increasing order and do not have any inherent meaning.

The check digit is calculated by taking the last digit times 1, the next digit times 2, the next 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.

Isomers, enzymes, and mixtures

Different stereoisomers of a molecule receive different CAS numbers: D-glucose has 50-99-7, L-glucose has 921-60-8, α-D-glucose has 26655-34-5, etc. Occasionally, whole classes of molecules receive a single CAS number: the group of alcohol dehydrogenases has 9031-72-5. An example of a mixture with a CAS number is mustard oil (8007-40-7).

Ownership Issues

CAS information is copyrighted by the American Chemical Society. Users who wish to incorporate CAS numbers into their own databases should see the details of the CAS usage policy:^[3]

A User or Organization may include, without a license and without paying a fee, up to 10,000 CAS Registry Numbers or CASRNs in a catalog, website, or other product for which there is no charge

CAS number search engine

Search Tool of Australian Inventory of Chemical Substances ^[4]
Common Chemistry ^TM ^[5] via Australian Inventory of Chemical Substances ^[6]
European chemical Substances Information System ^[7] via the website of Royal Society of Chemistry ^[8]

Notes

^ CAS registry description, by the Chemical Abstracts Service
^ CAS Registry Number and Substance Counts
^ http://www.cas.org/legal/infopolicy.html#authorized
^ National Industrial Chemicals Notification and Assessment Scheme. "AICS Search Tool". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ American Chemical Society. "Substance Search". Retrieved 8 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ National Industrial Chemicals Notification and Assessment Scheme. "AICS Detailed Help / Guidance Notes". Retrieved 8 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ European Commission Joint research Centre. "ESIS : European chemical Substances Information System". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ Library & Information Centre. "Finding a CAS Registry Number". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

External links

CAS registry description, by the Chemical Abstracts Service

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

[1] CAS registry description, by the Chemical Abstracts Service

[2] CAS Registry Number and Substance Counts

[3] ttp://www.cas.org/legal/infopolicy.html#authorized

[ast-4] National Industrial Chemicals Notification and Assessment Scheme. "AICS Search Tool". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[ss-5] American Chemical Society. "Substance Search". Retrieved 8 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[adhg-6] National Industrial Chemicals Notification and Assessment Scheme. "AICS Detailed Help / Guidance Notes". Retrieved 8 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[eecs-7] European Commission Joint research Centre. "ESIS : European chemical Substances Information System". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[fcrn-8] Library & Information Centre. "Finding a CAS Registry Number". Retrieved 11 July. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |coauthors= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

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