The Collaborative International Dictionary of English v.0.48:

Diazotize \Di*az"o*tize\, v. t. (Chem.)
   To subject to such reactions or processes that diazo
   compounds, or their derivatives, shall be produced by
   chemical exchange or substitution.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diazotize
    v 1: convert (an amine) into a diazo compound