itunes 11.4 under Snow Leopard doesnot recognize itunes 12 library

It doesn't matter about OS change, it all has to do with the version of iTunes used.

Older versions of iTunes will not open a library once opened with a newer version. The best you can do (in the absence of a backup) is to rebuild the library using the .xml version of the library file. This will entail losing some data (play count, ratings, date added).

"If you don't see your content after updating iTunes" - https://support.apple.com/en-us/HT203225 - These instructions use a trimmed-down version of your library file to rebuild your primary library file. You lose some metadata (ratings, play count, date added) but the listing should be fairly up to date.

If it isn't working you have to say why it isn't working. It is the standard resolution to this issue given in every downgrade article I have ever read. It works in many other situations where the .itl file is not a viable solution. If it isn't working for you there must be something specific in your case and you will need to tell us what that is if we are to solve this problem. As I already said, iTunes 11.4 will not open an iTunes library file after iTunes 12 has opened it. You will have to rebuild the main (.itl) library file using the .xml which should be importable to old iTunes.