(Stranger)
05-22-02 00:43
No 312146
(Rated as: excellent)
From:J.O.C.,40,3577(1975)
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The oxidation of terminal olefins by Jones reagent in the presence of a catalytic quantity of mercury(II) affords good yields (>70%) of the corresponding methyl ketones. Similar oxidations of 1,2–disubstituted olefins gives fair. (20–70%) yields; in the case of unsymmetrically substituted olefins, mixtures of ketones are produced.
Introduction
Wacker oxidation is an extremely useful and general reaction. It is, nonetheless, worthwhile to try to develop procedures for oxidizing olefins that use as catalysts metals less expensive than palladium, and which involve reactions (and possibly generate products) different from those of the Wacker oxidation. Mercury(II) is an obvious candidate for the catalyst for new oxidation reactions: it resembles palladium(II) in its ability to activate olefins for nucleophilic attack,4 but differs in that decomposition of the oxymercuration products normally generates cations by loss of mercury(0) rather than olefins by loss of mercury hydride.5 Unfortunately, neither we nor others6 have been able to discover a satisfactory solution to the principal problem in developing a mercury(II)–catalyzed analog of the Wacker oxidation: viz., an efficient regeneration of mercury(II) from mercury(0). In the absence of a solution to this problem, there are, however, ways of involving mercury(II) in catalytic oxidation of olefins other than in a direct analog of a Wacker oxidation.
One, explored in this paper, utilizes mercury(II) in oxymercuration of an olefin, oxidizes the hydroxyl moiety of the resulting 2–hydroxyalkylmercury(II) compound to an acid–labile 2–ketoalkylmercury(II) derivative, and regenerates mercury(II) by proteolysis of the carbon–mercury bond of this substance (eq 1). Thus, the mercury(II) performs the essential function of olefin activation, but is regenerated without leaving the mercury(II) oxidation level. This cycle is, in a sense, one in which mercury(II) catalyzes the hydration of the double bond, and in which the reaction is driven in the direction of the thermodynamically less stable hydrated form by trapping this form by oxidation to ketone.
Discussion
When Jones reagent is added to an acetone solution of an olefin at 20°, a slow, nonselective oxidation takes place. Addition of mercuric acetate or mercuric propionate (20 mol % based on olefin) to the solution results in a rapid consumption of the oxidant. Terminal olefins are converted to methyl ketones in yields of 80–90% (Table 1); 1,2–disubstituted olefins react readily, but give low yields of ketones under these conditions. The yield of methyl ketones resulting from the catalyzed Jones oxidation of terminal olefins is relatively insensitive to the amount of mercuric salt added.
Several metal ions other than mercury(II) were explored briefly, and found to be unsatisfactory as catalysts. No reaction took place on treating 2–octene with sodium dichromate–trifluoroacetic acid solution in the presence of thallium(I), suggesting that olefin activation was slow. Similar treatment of 2–octene in the presence of gold(III), palladium(II), and rhodium(III) afforded mixtures of 2– and 3–octanone in yields of 30, 10, and 2%, respectively. Gold(0) and palladium(0) deposited on the walls of the reaction vessel in substantial amounts during the oxidation.
Experimental Section
Mercuric Propionate. Red mercuric oxide (108 g) was added in 10 g portions to 100 ml of hot propionic acid. The oxide dissolved, giving a slightly yellowish solution which was filtered and allowed to cool to room temperature. The resulting crystals were recrystallized from propionic acid, washed with cold, dry acetone, and dried under vacuum (0.04 mm) at room temperature for 24 hr. The yield of product was 168.7 g (97%) as white needles having mp 114–116°.
General Procedure for the Mercury(II)–Catalyzed Oxidation of Olefins.
Method A. To a 500 ml erlenmeyer flask was added 22.0 g (74 mmol) of sodium dichromate dihydrate, 50 ml of water, and 300 ml of dioxane. With stirring, 6.8 g (20 mmol) of mercuric propionate and 35 ml of trifluoroacetic acid were added. The dark orange–red solution was stirred until the salts had dissolved (ca 10 min), and the flask was placed in a water bath. With continued stirring, 100 mmol of olefin was added. The solution became dark and warm; ice was added as necessary to maintain the temperature at 25 ± 5°. The solution was stirred for 18 hr, poured into water (300 ml), and extracted with hexane (3 x 75 ml). The combined extracts were washed with water (3 x 50 ml), saturated sodium chloride solution (1 x 50 ml), and water (1 x 50 ml) and dried (MgSO4).
General Procedure for the Mercury(II)–Catalyzed Oxidation of Olefins.
Method B. To a 500 ml erlenmeyer flask was added 200 ml of acetone, 5 ml of water, and 6.8 g (20 mmol) of mercuric propionate. The flask was placed in a water bath and, with stirring, 100 mmol of olefin was added to the bright yellow solution. Jones reagent7 (2M, 75 ml) was added dropwise during 4 hr.
Ice was added as necessary to maintain the temperature at 25 ± 5°. The dark greenish–brown solution was stirred for an additional 4 hr and then poured into water (200 ml) and extracted with diethyl ether (3 x 75 ml). The combined extracts were washed with water (3 x 50 ml), saturated sodium chloride solution (1 x 50 ml), and water (1 x 50 ml) and dried (MgSO4).
Table 1
Olefin______________________Product_____
1–Octene_________________2–Octanone_____
Undecylenic acid_________10–Oxoundecanoic acid____________83
3,3–Dimethyl–l–butene____3,3–Dimethyl–2–
2–Allylcyclododecanone___B–Oxo–2–propylc
Styrene__________________Acetophenoneb________________26
1,3–Hexadiene__________Polymer
a In addition, a 7% yield of 2–allyl–2–hydroxycyclododecanone was obtained.
b Benzoic acid (16%) was also isolated, together with polymer.
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Question:
could we apply (or modify) this method to allylbenzenes w/o oxydizing the lateral chain?
L.S.Dog!
(Pioneer Researcher)
05-22-02 00:51
No 312152
6.8 gr of propionate for 100 mmol of oleofin, say 16.2 gr of safrol for example... It is far from being an ecological procedure.