bottleneck (Hive Bee)
03-17-03 21:19
No 418138
      Etherification by cat. amounts of a tosylate?  Bookmark   

I checked out and stumbled on what might be of interest for the reasonably safe and OTC methods of methylating phenols. :

"3. Discussion

Anisole can be prepared from phenol or its salts by the use of the following methylating agents:

sodium methyl sulfate (2)
methyl alcohol and β-naphthalenesulfonic acid (4)
or potassium hydrogen sulfate (5)

2. Nollau and Daniels, J. Am. Chem. Soc. 36, 1890 (1914).
4. Krafft and Roos, Patent DE76574 (Frdl. 4, 17 (1894–97))
4. Rodionow, Bull. soc. chim. (4) 45, 118 (1929)
4. Terlinck, Ing. chim. 8, 233 (1924) (C. A. 21, 1978 (1927)).
5. Aktien-Gesellschaft für Anilin-Fabrikation, Patent DE23775
 (Frdl. 1, 43 (1877–87))"

The first reference seems to substantiate that phenols can be methylated by sodium methyl sulfate, eliminating the need for the dimethylsulfate, as also claimed in Patent GB646736, although I haven't read the article yet.

In the patent on using methanol and naphtalenesulfonic acid (reference marked 4 above), the mechanism seems to be in situ etherification of the sulfonic acid, and subsequent methylation of the phenol.

Like I say, my german is not at all useful, but the following formulas from the patent seems to mean there are needed only catalytic amounts of the sulfonic acid, in this case naphtalenesulfonic acid, since the sulfonic acid is contiuously reformed.

(Ethylating acetic acid):

"C10H7.SO2.OH + C2H5.OH  =  C10H7.SO2.OC2H5 + HOH
C10H7.SO2.OC2H5 + CH3.CO.OH  =  C10H7.SO2.OH + CH3.CO.OC2H5"

It is also supposed to work fine with dihydric phenols like resorcinol using a 6-8 fold weight of methanol.

According to Patent DE69115, some of the methanol itself is also methylated to form dimethyl ether.

As far as I understand, they carry out the etherification at about 140 degrees C, so I guess the methanol is constantly being added to the hot mixture by dropping, with excess methanol and water distilling off, a bit like how you methylate with dimethyl carbonate. Seems simple enough.

Any help from speakers of German would be great.

Finally, in the reference on using potassium hydrogen sulfate, methanol, potassium hydrogen sulfate and the phenol are heated in an autoclave at 150 degrees C. Though I wonder if this drastic heating is actually required, since they appear to use this autoclave-thing for every reaction in the patent, even aldol condensations.