Safrole separation with Mercuric Acetate

Contributed by Hunter S. Thompson

DISCLAIMER: I'm a writer, plaguerizing the works of Japanese Chemists who are probably already dead from over-exposure to mercury salts or the radioactive particulates spreading from Hiroshima and Nagasaki. I'll leave the real chemistry to the likes of Rhodium, Drone et al. Of course, should I happen to hear some experimentals, I'll pass them along...

Here are the first three references from TSII that deal with the purification of safrole from essential oils using another mercury salt, mercuric acetate [Mg(AcO)2]. Note than in TSII, Strike says this procedure should only be applied to eugenol-free sassy since eugenol also contains a terminal double-bonded carbon [Strike, Total Synthesis II, p. 34] - so do that 28% acetic wash first [my suggestion]. This procedure seems an attractive way to get high-purity safrole without careful and/or repeated distillation, and the mercuric acetate can be used over and over again. Be aware that it utilizes yet another toxic mercury salt that is hazardous both to the chemist and the environment.

Mercuric derivatives of safrole. T. Tsukamoto. J. Pharm. Soc. Japan 50, 7-19 (1930) - Asahina and T. (cf. CA 20, 2845) reported the sepn. of sesquiterpene alc. from other oils be means of (AcO)2Hg (cf. T and Ishibashi, CA 22, 3405; Balbiano, Ber. 42, 1502). B. reported some intermediates compds., RC3H5(OH)HgOAc and RC3H5(OH)2. T. obtained a compd. corresponding to R(OH)HgOAc and with either NaOH or NaCl it gave the stable compds. it gave the stable compds. R(OH)HgOH and R(OH)HgCl, R(OH)HgCl. Safrole (15g) (I) on treating with (AcO)2Hg (30g) in 100-cc of water and NaCl (7g) gave hydroxychloro mercurisafrole (II), C10H10O2(OH)HgCl (yield 29g), m. 135o. II is decompd. by concd. HCl to safrole, Hg(OAc)2 and NaCl, and by Na2S and Zn in KOH. I (16.g) on treating with HgCl2 (2.7g) and KOH (1g in 10cc water) gave a compd. (III) that did not depress the mp of II. By substituting KI for NaCl in prepg. II, T. obtained hydroxyiodomercurisafrole (IV), m. 155o. IV (5g) in Et20 (20cc) on treating with I (2.5g) in KI gave 1-iodo-2-hydroxy-3- [3,4-methylenedioxyphenyl]propane (V), m.. 76o. II on treating as above gave a similar cmpd. V (5g) in 5% KOH on boiling for 0.5-1hr gave a compd. (VI) m. 76o, the mp of V and VI being close to 80o. VI does not depress the mp of the compd. obtained by treating I (4g) with KMnO4 (3g). V (5g) in abs. alc. on treating with alc. NHMe2 (33%) and KOH gave 1-dimethylamino-2-hydroxy-2-hydroxy-3-[3,4-methylene-dioxyphenyl]propane (VII), picrate, m. 161o. VII on treating MeI in excess gave the methiodide of VII, m. 150. II on treating with d-tartaric acid gave (after fractional crystn. in MeOH) a compd., decomp 128o, 135o, 145o, and 155o. Each constituent was further fractionated in MeOH into 2 constituents, most sol. and insol. portions. The detn. of optical activity indicates there is no difference between the two.

[CA v.24 (1930), pp. 1853-1854]

A method for the determination of safrole. Tessaku Ikeda and Shosaburo Takeda. J. Chem. Soc. Japan 57, 565-73(1936) - Estn. of safrole in red camphor oil and in crude safrole: Weigh a 4g sample into a 300-cc weighing flask, add 40cc. acetone, 44cc. (AcO)2Hg soln. (contg. 53g in 200cc water) and 32cc NaCl soln. (30g in150cc) in the order named and stir for 5 hrs, at 0o, transfer the contents into a short-necked distg. flask and distil in vacuo at 20o to remove all acetone. Pour the ppt. of safrole-HgClOH on a Gooch crucible with double filter, and wash crystals with 150cc water using 15cc at each washing, then with 100cc ether in 8 portions. Dry in dessicator in vacuo for 5 hrs. [(Wt. crystals + 0.3140)*39.041]/wt. sample = percentage safrole, where 0.3140 is a const. for correction. Estn. of safrole in "pure" safrole: The method is the same as in preceding estn., except that half quantities of (AcO)2Hg and NaCl soln. are used and the washing are made with petroleum ether. The use of 0.3140 in the calcn. of percentage is unnecessary. Caution must be taken the remove all the acetone, and glass is unsatisfactory for filtration.

[CA c.24 (1936), pp. 7497]

Determination of safrole in essential oils. Yasuzi Huzita and Kimio Nakahara. J. Chem Soc. Japan 62, 5-9 (1941). - To det. safrol weigh 0.5g of sample in a 50-cc test tube, slowly add 6 cc. of 33% Hg(C2H3O2)2 soln., and then 4 cc. of 35% NaCl soln., and finally 7 cc. of acetone, shaking the tube constantly. After the reaction had been completed, head the tube, adding H2O repeatedly, and wash the contents into a 250-cc beaker as thoroughly as possible. Heat the beaker to boiling, filter the contents while hot, and wash the filtrate with hot water. From the filtrate safrol mercuriochloride seps. in brilliant needles. Collect these with a Gooch glass filter overnight, dry in vacuo and weigh. The percentage of safrol (w/s) 46.5, where w = wt. of crystals and s = wt. of sample. When the yield is 85% or more, repeat the above process without the addn of acetone; the percentage of safrole is given by (ws)*44.1. When the yield is 30% or less, add 0.3-0.4g of this sample to 0.1-0.2g of pure safrol and repeat the above detn. without change; safrol = [(w*0.465-w')/s]*100, where w' = wt. of pure safrol. The max. error is +/- 1.5% in general and +/- 0.5% when the yield is 85% or more.

[CA v.37 (1943) , pp.3882]