Reaction mechanism for the conversion of acyl hydrazide to acyl azide How is an an acyl hydrazide converted into an acyl azide in the presence of $\ce{HNO2}$? According to me, the $\ce{-NH2}$ group of hydrazide will get converted into $\ce{-N2+}$ through $\ce{HNO2}$. However, I am unable to proceed after that.
You are correct acyl hydrazide can be converted into acyl azide by adding $\ce{HNO2}$ also you wrote that the $\ce{NH2}$ group of hydrazide will be diazotisated making a $\ce{N2+}$ group hence I am assuming that you know the mechanism, after diazotisation the adjacent $\ce{N}$ donate the lone pair to the $\ce{N2+}$ group making the final product as acyl azide.

The mechanism scheme is in the following picture :