If your Joseph Rintel was born in Hamburg, then I would run, not just walk, to post a query at the German SIG Mailing List at http://JewishGen.org
That is an incredibly friendly, helpful list, and may well lead you to a lot more helpful information and connections.
I also do not recall if I mentioned the JewishGen FamilyFinder before, but even if I did, let me suggest you add more information about other locations for Rintel to your entries there. That networking database is only as good as the information we add to it as researchers.
JewishGen FamilyFinder for people seeking fellow researchers of same Jewish ancestral lines: