I have been recently doing bromomethylation on 1,3,5-triethylbenzene and I experience a problem. Here are the detials:
1. All the literature use the key reagent which is 33% HBr in HOAc. But because my lab (even the whole department) does not have this and I do not want to wait for shipping, I try the following recipe, after considering the mechanism of the reaction (which should be very simple): paraformaldehyde, KBr, HOAc as solvent and H2SO4 as acid catalyst and reagent. Heat at 90oC for overnight.
2. The result is that I did obtain products but it is always contaminated by another thing which has 7.00ppm, 4.67ppm (same as ArCH2-Br) and a slight lower ppm of CH2CH3 compared with my desired product. This impurity cannot be removed by recrystallization and column chromatography (one spot)
This makes me even wonder I obtained a single product or mixture. But it is too hard to explain if it is a single pure substance.