China banned production of the meph pre cursor 4-methylpropiophen one which contains up to 10% 3-methylpropiophen one (technical grade reagent). Separation of 3-methylmethcathin one from 4-methylmethcathin one is difficult. On large scale, multiple recrystallizations are required which I doubt most RC manufacturers would do because of lost material and thus lost profit - hence the impurity. Thats why Chinese meph was different as it contained 3-mmc as a by product which happened to give you a better buzz, although bad for your health. They were losing too much product in washing it out. China was main world producer of 4-methylpropiophen one so when it dried up i presume that's when India started producing meph but were unable to get the banned pre cursors so used probably one of these methods, both produce mephedrone but none of them contain 3-mmc in the final product; Cleaner yes but the buzz is not as intense as the 3-mmc was helping the Chinese gears potency
India synth option It can also be produced by oxidising the ephedrine analogue (4-methylephedrine ) using potassium permanganate dissolved in sulfuric acid. Because 4-methylephedrine can be obtained in a specific enantiomeric form it is possible to produce mephedrone consisting of only one enantiomer. There is a danger associated with this method as it may cause manganese poisoning if the product is not correctly purified.
India synth option A stereo-specific form of (S)-mephedrone could be prepared via Friedel–Crafts acylation. The first step in the synthesis would react toluene and (S)-N-trifluoroace tylalanoyl chloride in the presence of aluminium chloride, then deprotect the intermediate with hydrochloric acid-propyl alcohol . This would produce (S)-4-methylcathin one, which could then be methylated to produce mephedrone There are loads more synth recipes about but none contain 3-mmc in the final product unless 4-methylpropiophen one was used as the pre cursor.
Only now has India sussed out a better pre cursor and you can now find very good indian meph but still not as evil as Chinese but getting close