[unknown_analysis]

We are doing some diazo synthesis (Alizarin Yellow R) in our basic chemistry lab with acetanilide as the starting compound. I know that acetanilide is first nitrated then hydrolyzed to form para-nitroaniline then diazotisized and coupled with salicyclic acid to form the Alizarin Yellow R. Nitration of acetanilide was done with concentrated HNO3 and H2SO4. The crystallized product was refluxed with HCl, 20mL H2O, and heat, to hydrolyze the product, then reacted with NH3 in ice bath. In the diazotization, p-nitroaniline reacted first with HCl then with NaNO2.

I somehow need the reaction mechanism (yes, with those arrow-pushing diagrams) to fully understand the experiment.
* Nitration of acetanilide forms the para-nitroacetanilide, but why not the ortho-product form at low temperature (i.e, the reactants were reacted while in an ice bath)?
* I am bothered at the mechanism of hydrolysis of p-nitroacetanilide. It did form an amide cation which was neutralized by NH3, but how? 
* In all the books I have read, NaNO2 was acidified first, then reacted with p-nitroaniline... but not in our experiment. Why does HCl needed to react first with the p-nitroaniline? Why not first acidify the NaNO2? Is the diazotization mechanism different in the experiment from the books or just the same?

I seem to hit my rock bottom now, and no books help answer my questions, so I am turning to all of you Thank you!  

[opsomath]

Hi,

Ok, there are several questions here. I am going to tackle them in what I see as the order of importance:

In all the books I have read, NaNO2 was acidified first, then reacted with p-nitroaniline... but not in our experiment. Why does HCl needed to react first with the p-nitroaniline? Why not first acidify the NaNO2? Is the diazotization mechanism different in the experiment from the books or just the same?

I'm guessing this is to ensure that the starting material is completely dissolved, and not any big mechanistic difference. The only oddity here is that you have a very electron deficient starting material; sometimes you see H2SO4 used here instead to absorb water and drive the reaction forward, but that doesn't appear to be necessary with your stuff.

I am bothered at the mechanism of hydrolysis of p-nitroacetanilide. It did form an amide cation which was neutralized by NH3, but how?

You're overthinking this: the mechanism is just the acid-catalyzed hydrolysis of an amide. The NH3 is just to neutralize the solution afterward, getting rid of excess HCl and yielding the free aniline rather than the  HCl salt.

http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch20reactionsamides.html

 

Nitration of acetanilide forms the para-nitroacetanilide, but why not the ortho-product form at low temperature (i.e, the reactants were reacted while in an ice bath)?

I honestly don't know for sure but this is consistent with other electrophilic reactions I have done with aniline and acetanilide; mostly the para product is formed. I am guessing it is due to the p-position being more sterically available.

[unknown_analysis]

So the p-nitroaniline did not react with HCl but only to dissolve? 
What would happen if p-nitoaniline reacted first with NaNO2, then with HCl, will a different mechanism occur?

Thanks for the link, opsomath.
Really helpful! I think I'm just overthinking.