You may have to stir the solutions for long time (about 2 hr) after mixing acetophenone and aldehyde group (make sure they are equimolar). The reaction mixture should be dissolved very well in alcoholic solution before mixing them. Don't add too much NaOH. If you are not getting precipitation then try with different concentrations.

Good luck.

If you are using NaOH so 2- hydroxy naphthaldehyde react with NaOH to given sodium salt of naphthaldehyde so please try these reaction with basic condition (Not used NaOH).

Good luck

Thanks shivraj and jitesh.  I will try as per your suggestion. 

Take acetic acid as solvent and catalyst.

Thank you Hosseinsir

You might want to use acid catalysis in this case, and if it wont work - protect OH group with  MOM and use base catalysis afterwards.This article might be useful for you:  http://www.pharmainfo.in/jpsr/Documents/Volumes/Vol1Issue3/pdf/jpsr01030902.pdf

Thank you Alexeysir

I am trying the same work but it is difficult have you done it?

Riki P Tailor