Ning: The H2O2 sounds good!
The yields are extremely high to phenylacetic acid, well in the patent that ning translated in the other post it is reported as such. Ill paste it here to help with organisation.
In a reaction vessel was placed:
Styrene 21.7 g
Sulfur 37.6 g
Ammonia 50 ml
Ethanol 30 ml
'Under stirring and heated at 93-95 C for 3-4 hours. Fluids were evaporated from the mixture, it was allowed to cool, and extracted 3 times with 500 ml hot water. The decolorized solution after standing yielded
26.7 g (97%) white sheets having MP of 157-158 C and BP of 280-290. (Phenylacetamide C8H9NO)
100 g of the above phenylacetonitrile and 80 ml HCl were added to 150 ml water and refluxed for 2-3 hours. After cooling to room temp, a precipitate formed and was filtered and recrystallized from 1:2 ethanol/water to yield
84 g (84%) of shining white crystals. (Phenylacetic acid C8H8O2)'
So it works out to about 90% from styrene monomer to phenylacetic acid. That's fucken good for 2 steps and OTC ingredients.
Knock a big fat 30% off that, and we're really in the realistic (pesimistic) zone, and it's still very nice.
Ac2O (acetic anhydride) or AcOH (acetic acid) seem to be the hardest, and the most fiddle to setup an apparatus.
Dangerous too, ketene is deadly and flammable, but won't explode if O2 is absent (same with acetone)
Also although acetone is cheap, it isn't expendable IMO, and it wouldn't surprize me if it disappeared at some point. I hop not, but you have to plan for the worst.
So having an implementation in your aparatus to save acetone that isn't successfully decomposed is almost essential.
Dripping acetone on a glowing toaster wire inside a copper tube should do the trick. Bubble the ketene produced through a hot flask or jar of vinegar, fitted with a two-hole teflon-coated cork.
The 2nd hole leads to a jar sitting in ice to condense the acetone that distills off the first jar.
Still I've never done it, but that's where my thoughts start.
Oh, boys! I've got a phat surprICE for ya! If you can't acquire methylamine, or just don't want it around, you can have plain amphetamine from the Al/Hg, in high yields (96-98%), using only 25% ammonia water.
See for glee: https://www.thevespiary.org/rhodium/Rhodium/chemistry/amph.alhg.html
Actually the yield at the introduction of this page is totally different to the experimental, at 30%. I'd trust the 30% as more realistic
The yields of P2P from PAA and AA, with NaOAc aren't very good, and a large excess of AA is used (to avoid useless dibenzyl ketone formation, it states) , but even then, 50% is optimistic.
Read for yourself here:
https://www.thevespiary.org/rhodium/Rhodium/chemistry/phenylacetone.html#phenylacetic
A longer reaction seems important for yields too.
ORG:
There isn't much info on methods that use acetic acid instead of acetic anhydride. Sure there's that Mastermind post, but what is that worth? What guidance is it? Ill try find more but I think it'll turn out to be more wise to put the effort in to acetic anhydride, don't you think?