Allylbenzene isolation with H2SO4

[El_Zorro]

So I've been reading TSII again, and I read the section on purifying safrole for the first time.  The thing that really caught my eye was the bit about using conc. H₂SO₄ to isolate an allylbenzene, which is then hydrolyzed to the alcohol on the alpha carbon, which can be processed with a bisulfate to give the propenylbenzene as the final product.  The example given was even for elemicin from elemi oil, and ended up with isoelemicin, which was what I was looking for anyway!   So is this true?  Could it be?  Please tell me this will work!

And another thing, I've read some discussions here about trying to get MDP2Pol via a markovnikov reaction using cold sulfuric, but it seems do want to do what Strike describes in TSII, and let the -OH stabilize on the alpha carbon.  So what?  Couldn't the sassy oil be thrown in a pot with some ice cold conc.  sulfuric, then the acid drawn off, and water thrown in, and it heated, and then left out for a day or two to make sure all of the -OH has migrated to the alpha pos?  Well, I guess it could be washed first, to get rid of all that sulfuric, which would be hell on the MD ring.  But then it could be processed with a bisulfate to isosafrole, very quick and easy, and very pure!  Is this feasable?  Or does conc. sulfuric polymerize safrole, even at low temps?  Should 70% be used?
It is seductive, way too seductive.             -Eleusis

[Rhodium]

In theory all this works just fine, but a lot of people have had practical problems, as you can see in the archives.

[El_Zorro]

So what about the issues with the sulfuric and the MD ring?  Does anyone have any thoughts on how the ice cold sulfuric would affect the ring?
It is seductive, way too seductive.             -Eleusis

[ChemisTris]

Well, here are some examples of MD ring in the presence of sulfuric acid.

Patent EP1229031

A flat bottom separable flask with an internal volume of 500 mL as shown in fig 1 was charged with 50.0 g (0.409 mol) of 1,2 methylenedioxybenzene and 25 mL of 4-methyl-2-pentanone...in a nitrogen atmosphere, and the mixture was cooled to -5° with stirring.
Then a mixture of  83.4 g (0.450 mol) of a 40% by weight aqueous glycoxylic acid solution and 85.8 g (0.839 mol) of 96% by weight sulfuric acid was added dropwise thereto, and the mixture was stirred at -5° for 21 hours.
Thereafter, the reaction solution was neutralized by adding 102.0 g (1.67 mol) of 28% by weight aqueous ammonia little by little...

Preparation of piperonal.
Harada, Katsumasa; Aoi, Motojiro; Shirai,
Masashi; Furuya, Toshio.  (Ube Industries, Japan).
CA 124:317136 

Abstract
Piperonal (I), useful as an intermediate for pharmaceuticals and agrochems., is prepd. by oxidn. of 3,4-methylenedioxymandelic acid (II) by a nitrate or nitrite salt in the presence of sulfuric acid.  Thus, a soln. of sodium nitrate 15.3 g in 16 mL water was added during 2 h to a mixt. of II 45.6 g and 97 wt.% sulfuric acid 55 g in toluene 75 mL at 50°; after the addn. of said soln. is completed and gas generation ceased, the reaction mixt. was stirred for a further 30 min to give, after workup, 96% I.  The title method is highly
economical.



Method for producing piperonal.
CA 124:117294

Abstract
Piperonal (heliotropin) (I), which is a heliotrope fragrant base, widely used in cosmetic fragrants, and also useful a synthetic raw material for drugs and agrochems., and as a brightener for metal plating, is prepd. by oxidn. of 3,4-methylenedioxymandelic acid (II) with HNO3 in the presence of H2SO4.  Thus, 15.8 g 61 wt.% HNO3 was added dropwise over 2 h to a stirred mixt. of H2O 123.4, 97 wt.% H2SO4 55, II 45.6 g, and 75 mL PhMe at 50-54° and the resulting
mixt. was allowed to react at 54° for 30 min, cooled to room temp., and extd. with toluene to give 96% I.

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