(Guardian)
11-20-03 05:53
No 471882
(Rated as: excellent)
I could not seem to find this reference on the hive, however it sounds vaguely familiar, I think this journal came up quite a bit in microwave isomerization methods. None the less quite interesting, (from a Green perspective). I apologize if this post has been posted previously.
Isomerization of eugenol and safrole over MgAl hydrotalcite, a solid base catalyst
D. Kishore and S. Kannan
Green Chemistry 4, 607–610 (2000) (../rhodium/pdf /safrole.isom
DOI:10.1039/b207865a
Abstract
Isomerization of olefins, in particular eugenol and safrole, is an important reaction as the products, namely isoeugenol and isosafrole, find application in pharmaceuticals and fragrances. The catalyst employed to carry out this reaction is either a strong alkaline solution (KOH or KOtBu) or precious metal catalysts under homogenous conditions, which pose severe environmental problems such as handling and effluent disposal as well as cost. The present paper discloses a new alternative route wherein hydrotalcite is used as a solid base catalyst, which is environmentally friendly as well as economical in obtaining good yields of the isomerized products.
Unipolar Mania, It's good for life...
(Chief Bee)
11-20-03 13:48
No 471958
(Rated as: excellent)
Rhodium-catalysed Isomerisation of Some Unsaturated Organic Substrates
Jean Andrieux. Derek H. R. Barton. and Henri Patin
J. Chem. Soc. Perkin Trans. 1, 359-363 (1977)
The versatile rhodium trichloride trihydrate has been employed in catalytic amounts to promote double-bond migration. This method allows good yields in otherwise difficult, or impossible, exocyclic-endocyclic isomerisations.
Migration of a double bond may be difficult to bring about when the molecule concerned is fragile. The classical methods usually require drastic conditions, i. e. strong bases or acids or high temperature heterogeneous catalysis1. The recent discovery that several transition metal complexes, used as homogeneous catalysts, can isomerise double bonds in simple olefinic systems2,3 has been applied to a few more sophisticated molecules4,5,6. The potential interest of these reagents in organic chemistry lies in their selectivity and ability to bring about reaction under mild conditions.
Isomerisation occurs readily when the migrating double bond moves into conjugation with an aromatic nucleus. In contrast to the fact that allyl groupings are isomerised by strong bases with formation of significant amounts of cis-isomer1, eugenol (7a) and safrole (7b) gave predominantly the trans-isomers (8a) and (8b). The 1:9 cis-trans ratio in isoeugenol was altered neither by the amount of catalyst nor by the reaction time, but was slightly sensitive to an increase of the reaction temperature, as recently noted18.
The commercially available isoeugenol contains approximately 40% of cis-isomer. The cis-trans ratio remained unchanged even after a long period of contact with the rhodium catalyst. It has been reported that the ratio of cis- to trans-isosafrole was 4:6 when tris(triphenylphosphine)rhodium chloride was used as catalyst5.
Isomerisation of Eugenol
To eugenol (20 g) in ethanol (5 ml) was added RhCl3·3 H20 (0.1 g). The temperature was maintained at 20°C by cooling and after 2 h the mixture was poured into water and extracted with ether. The usual work-up was followed by distillation; the yield of the fraction bp 140-142°C at 15 mmHg was 92%. The minimum amount of catalyst for 20 g of eugenol is 5 mg; complete transformation requires 24 h in this case. The amount of the trans-isomer of eugenol was always at least 90%.
Isomerisation of Safrole
Under the same conditions safrole (20 g) was converted into isosafrole, bp 130-132°C at 15 mmHg (93%). The amount of trans-isomer was about 80%.
References
[1] A. J. Hubert and H. Reimlinger, "The Isomerization of Olefins Part I. Base-Catalysed Isomerization of Olefins", Synthesis 97 (1969);
"The Isomerization of Olefins Part II. Thermal and Catalytic Isomerization of Olefins using Acids, Metals, Metal Complexes, or Boron Compounds as Catalysts", Synthesis 405 (1970) Post 473104 (Rhodium: "Review: The Isomerization of Olefins, Part I & II", Novel Discourse)
[2] G. C. Bond, Ann. Reports, 63, 27 (1966)
[3] R. Cramer, "Transition metal catalysis exemplified by some rhodium-promoted reactions of olefins", Acc. Chem. Res., 1, 186 (1968)
[4] J. F. Biellmann and M. J. Jung, "The mechanism of isomerization of an olefin and its possible relation to the mechanism of the catalytic hydrogenation with tris(triphenylphosphine)rhodium chloride", J. Amer. Chem. Soc., 90, 1673-74 (1958)
[5] A. J. Birch and G. S. R. Subba Rao, "Olefin isomerisations using tristriphenylphosphinerhodium chloride", Tetrahedron Letters 3797 (1968)
[6] E. J. Corey and J. W. Suggs, "Selective cleavage of allyl ethers under mild conditions by transition metal reagents", J. Org. Chem. 38, 3224 (1973); "A new method for protection of carbonyl compounds as 5-methylene-1,3-dioxanes", Tetrahedron Letters 3775 (1975)
[18] Patent DE2508347
(One Remarkable HyperLab Bee)
11-25-03 16:45
No 473093
(Rated as: excellent)
Isomerization of Eugenol to Isoeugenol
L. Cerveny, A. Krejcikova, A. Marhoul and V. Ruzicka
Reaction Kinetics and Catalysis Letters, 33(2), 471-476 (1987) (http://hyperlab.0catch.com/Eugenol_Isom
Abstract
The isomerization of eugenol to isoeugenol was investigated by employing catalysis by KOH in amyl alcohol or glycerol, or by RhCl3. A number of factors which affect the reaction (solvent, temperature, molar ratios, presence of water) were examined.
I apologize for misspelling the names. I merely couldn't find the correct entity names for certain letters. - azole
Edit: Article now also available at ../rhodium /eugenol
(Chief Bee)
11-25-03 17:32
No 473104
(Rated as: excellent)
The Isomerization of Olefins Part I.
Base-Catalysed Isomerization of Olefins
A. J. Hubert and H. Reimlinger
Synthesis (3), 97-112 (1969) (../rhodium/pdf /isomerizatio
Abstract
Isomerization of olefinic and acetylenic compounds have received much attention during the last few years both in their theoretical and in practical aspects. The methods used in isomerization of olefins (migration of the olefinic double bond) and related reactions are the subject of this review; isomerization involving rearrangement of the carbon skeleton are not considered. Part I deals with base-catalysed isomerizations. Part II is concerned with isomerizations catalysed by acids, metal complexes, radicals, etc. The knowledge of the conditions under which isomerization of olefins occurs, is not only valuable for the conversion of olefins to their isomers, but is an important consideration when olefins are to be prepared by any other mean. Under such conditions as here described an unwanted reaction product may be formed as a result of isomerization.
____ ___ __ _
The Isomerization of Olefins Part II.
Thermal and Catalytic Isomerization of Olefins using Acids, Metals, Metal Complexes, or Boron Compounds as Catalysts
A. J. Hubert and H. Reimlinger
Synthesis (8), 405-430 (1970) (../rhodium/pdf /isomerizatio
Abstract
Part I of this review was devoted to the base-catalyzed isomerization of olefins. All other methods used to isomerize olefins are treated in Part II. As in Part I, isomerizations involving rearrangement of the carbon skeleton are not considered.
(Chief Bee)
12-11-03 20:22
No 476204
(Rated as: excellent)
Isomerization of Safrole to Isosafrole in Solventless System Promoted by Microwave Irradiation
Le Ngoc Thach, Tran Huu Anh, Nguyen Anh Kiet, Tran Kim Phuong
Top chi Hoa hoc, 37(1), 92-94 (1999) (../rhodium /isomer
Excellent article describing the isomerization of safrole to isosafrole without solvent, using either conventional heating or microwave irradiation. Basic catalysts tested (with or without PTC) under a variety of temperatures and reaction times are KOH, KOt-Bu and KF-Al2O3. Yields are close to quantitative and the reaction times very short.
The Hive - Clandestine Chemists Without Borders
(Chief Bee)
04-01-04 22:37
No 498514
Quantitative safrole isomerization at room temp from J. Pharm. Sci. 81(12), 1219-1222 (1992)
As part of a research program to synthesize bioactive compounds from abundant Brazilian natural products, we have previously described8 the synthesis of an indomethacin analogue from natural safrole9. [...] previous results from our laboratory21 indicated that [safrole] could be isomerized in almost quantitative yield to [isosafrole].
Experimental
Isomerization of [safrole] to [isosafrole]10
To 80.0 grams of [safrole] was added 100 ml of a 3 M solution of potassium hydroxide in n-butyl alcohol and the reaction mixture was stirred at room temperature for 3h. The mixture was poured into a solution of 12 mL concentrated HCl and 52 mL of ice cater. After neutralization with additional concentrated HCl, the organic layer was extracted with 3x35 mL ethyl acetate. After usual workup, a white oily residue was obtained and distilled to furnish 78.4 grams (96-98%) of [isosafrole] as a colorless oil. An analytical sample showed spectroscopic data in agreement with the literature27.
References
[8] J. Med. Chem. 24, 1197-1202 (1981)
[9] J. Chem. Res. 1142-1165 (1982) Post 459320 (Lego: "From Safrole to anywhere", Methods Discourse)
[10] An. Acad. Brasil Cienc. 53, 65-67 (1981)
[21] Quim. Nova 10, 154-155 (1987)
[27] J. Chem. Res. 2301-2332 (1985)
A caveat is that an illustration says "3N KOH, nBuOH, reflux, 3h (98%)", but even if that is the truth (and the experimental part wrong), it still constitutes a great procedure.
The Hive - Clandestine Chemists Without Borders
(Chief Bee)
04-19-04 03:20
No 501529
(Rated as: good read)
Isomerization of Olefins Catalyzed by the Hexaaquaruthenium(II) Ion
Thomas Karlen and Andreas Ludi
Helv. Chim. Acta 75, 1604-1605 (1992) (../rhodium /isomer
Abstract
Isomerization of olefins, in particular the useful transformation of allyl to vinyl ethers is catalyzed by the hexaaquaruthenium(II) ion, producing the (E)-isomers under mild conditions.
The Hive - Clandestine Chemists Without Borders
(Chief Bee)
06-09-04 12:44
No 512359
(Rated as: good read)
Isomerization of Some Allylbenzenes in a Microwave Batch Reactor
Le Ngoc Thach and Christopher R. Strauss
Journal of Chemistry, 38(1), 76-79 (2000) (../rhodium /isomer
Abstract
In this paper we would like to present our study of the isomerization of some allylbenzenes as: allylbenzene, eugenol, methylchavicol and safrole. It is the first time this reaction take place in the microwave batch reactor under aqueous acidic condition. The high yields of 1-propenylbenzene, was obtained in a short reaction times.
The Hive - Clandestine Chemists Without Borders