Lowest CAS Registry Number on record

I've been looking for a while and I still can't get a straight answer. I just need to know the lowest CAS Registry Number on record and the corresponding chemical. 




I work at CAS and recently answered a similar question on Twitter (@CASChemistry). In fact, there are 8 pre-50-00-0 CAS Registry Numbers in our database:


* 35-66-5
* 35-67-6
* 36-51-1
* 36-88-4
* 37-71-8
* 37-82-1
* 37-87-6
* 38-26-6


So, the lowest CAS Registry Number on record is **35-66-5** for "Benzacridine, 7,​9-​dimethyl- (9CI)".


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"Carotenes" has a CAS Registry Number of 36-88-4.


If that chemical is "too vague", [Naphthol AS-BI $\beta$-D-glucuronide](http://www.sigmaaldrich.com/catalog/product/sigma/n1875?lang=en&region=US) has a CAS Registry Number of 37-87-6


According to semi-independent source [Organic Chemist's Desk Reference 2nd ed. (2010) pg 6 sec 1.1.1.5](http://books.google.com/books?id=ahbUc5M0I5AC&pg=PA6#v=onepage&q&f=false), CAS 35-66-5 DOES seem to be the lowest, but how do we know "Benzacridine, 7,​9-​dimethyl- (9CI)" exist? Cl- and methyl- are occupying the same position at the aromatic ring. 


Also "Carotenes" (CAS 36-88-4) by the name itself does not seem to exist as a single compound but a set of compounds.


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