# CAS number

The CAS number (also CAS registry number and CAS registry number , Engl. CAS Registry Number , CAS = C hemical A bstracts S ervice is) an international standard designation for chemical substances. There is a unique CAS number for every chemical substance (including bio-sequences, alloys , polymers ) registered in the CAS database . In many cases, however, a clear assignment is not possible with polymers because, for example, different molar masses of the polymer still only have one CAS number.

Sum formulas are rarely unambiguous, trivial names (in different languages) only exist partially and are not always unambiguous, IUPAC names are often very complicated, so that confusion can arise. In fact, it is not the substance itself that is referenced, but the relevant literature. Accordingly, different isomers (e.g. enantiomers or diastereomers ) of a molecule can be recorded under individual CAS numbers. In contrast, some entries refer to groups of substances (e.g. fatty alcohol ethoxylates ). There are also separate entries for some technically important substance mixtures (e.g. isomer mixtures such as racemates or reaction mixtures typical for production), although their individual components may already be referenced under other CAS numbers .

## construction

CAS numbers consist of three numbers separated by two hyphens. The first number can contain up to seven digits and the second number can contain two digits. The numbers are coded with a checksum - this is the third number - and therefore relatively easy to check for plausibility . CAS numbers are assigned in ascending order and do not contain any internal order. On September 8, 2009, the 50 millionth substance was registered. Together with over 61 million sequences, over 111 million numbers were assigned. Around 12,000 new substances are registered every day. In June 2015 the 100 million mark was exceeded.

CAS numbers have been assigned since 1965 by the Chemical Abstracts Service , an institution administered by the American Chemical Society based in Columbus , Ohio , USA . Use of the CAS registry database, in which each chemical structure is referenced using the CAS number, is subject to a charge.

## Checking CAS numbers

A CAS register number is a sequence of n decimal digits in the general form:

${\ displaystyle Z_ {n} \, \ ldots \, Z_ {4} \, Z_ {3} \, - \, Z_ {2} \, Z_ {1} \, - \, R}$

where a check digit and each represent a decimal digit. ${\ displaystyle R}$${\ displaystyle Z_ {n} \, Z_ {n-1} \, \ ldots \, Z_ {1}}$

A CAS number is correct if

${\ displaystyle \ left (\ sum _ {i = 1} ^ {n} i \ cdot Z_ {i} \ right) {\ bmod {10}} = R}$

So the sum of the digits up to 10 weighted with the digit position leaves the remainder R.${\ displaystyle i}$ ${\ displaystyle Z_ {1}}$${\ displaystyle Z_ {n}}$

“Mod 10” does not mean the Modulo 10 test procedure ( Luhn algorithm ), but the mathematical definition . This is to be understood as the last decimal digit of the total result, i.e.:

10 · {Total result: 10 - ([Total result: 10])} = check number R.

The sum result means the term " weighted sum of digits to  " listed above . ${\ displaystyle Z_ {1}}$${\ displaystyle Z_ {n}}$

### Sample calculation

CAS number for ethanol is 64-17-5.

 Digit 6th 4th 1 7th position 4th 3 2 1 Contribution 6 4 = 24 4 x 3 = 12 1 x 2 = 2 7 · 1 = 7 Sum = 45

With the condition is fulfilled. ${\ displaystyle R = 45 {\ bmod {10}} = 5}$

## Examples

• L- methionine - CAS No. 63-68-3
• D- methionine - CAS No. 348-67-4

## Legal

In contrast to the EC number, the CAS number is not used to identify a substance under chemical law , but merely provides information. The substances described in the research may differ from those on the market due to impurities typical of production or the above-mentioned problems of demarcation with regard to hazardousness.

The indication of the CAS number in the safety data sheet is mandatory for hazardous substances and voluntary for substances not classified in the GHS .