What is the correct name of tranquilizing medication, that sounds like Clopasin
and has beeb called the Valium of the 21st century?

Hello,  the drugs that would seem to fit your description are:

Generic name  -   Brand names                     - category of drug
------------------------------------------------------------------------------
clonazepam      Klonopin, Clonapam, Rivotril    benzodiazepine(same as
Valium)
chlorazepate    Tranxene                        benzodiazepine
chlorpromazine  Thorazine                       anti-psychotic
(tranquilizer)
clozapine       Clozaril                        anti-psychotic 

I would guess that clozapine would be the drug to which you are
referring.  Clozapine was the protypical atypical anti-psychotic,
that, even though it was introduced in the 1960's, did not receive
much attention until the 1980's.
http://www.cpa-apc.org/Publications/Archives/PDF/1997/Mar/lehmann.pdf

Brief descriptions of the drugs can be found at the links below:

clonazepam: http://www.druginfonet.com/index.php?pageID=klonopin.htm
chlorazepate: www.clorazepate.com/
chlorpromazine: http://www.mentalhealth.com/drug/p30-c01.html
clozapine: http://www.mentalhealth.com/drug/p30-c02.html
http://www.clozapine.com/


Please let me know if you need further information.

synarchy

Google search for references:
clonazepam
chlorazepate
chlorpromazine
clozapine

My guess would be clonazepam. Like valium, it is a benzodiazapine drug
that is increasingly subject to abuse.