add organic base ( TEA or pyridine or..) is very important, since acetylation will form HCl(using acetyl chloride) or acetic acid (using acetic anhydride), HCl or acetic acid will form salt with your SM, the salt will not react.
Use as starting material 4-nitroaniline.After acetylation by acetic anhydride with trace of sulfuric acid hydrogenate the resulting product. You should get high purity p-phenylenediamine monoacetate.