Stobbe studies

The connection between synthesis and photochemistry is vital. As long as photochemistry is felt as a sanctuary of the small group of professional photochemists, many synthetic perspectives will be ignored, and this is a negative impact also on mechanistic photochemistry that loses part of its interest. As a matter of fact, this remark is not new. In a talk in Leipzig in 1908, Hans Stobbe, a pioneer of photochemistry (well known for his innovative studies on the photochromism of... 

Stobbe s wish has been only partially fulfilled in the century which has elapsed in the meantime. Whilst many photochemical reactions have been discovered, certainly many more wait to be uncovered, and it still holds true that more photochemistry carried out by synthetic chemists would contribute to the growth of photochemistry as a whole. This Handbook represents a modest attempt to contribute towards this aim and to foster the synthetic use of photochemistry. The presentation is referred to the small-scale laboratory synthesis of fine chemicals. In this aspect, the photochemical literature does not differ from the large majority of published synthetic work, most of which is carried out on the 100 mg scale for exploratory studies. However, there is no reason to think that a photochemical reaction is unfit for scaling up. As will shown below, an increase up to the 100 g scale can be obtained in the laboratory by simple arrangements. Furthermore, while the presently running industrial applications are limited in number, they are nonetheless rather important [3]. Some of these are well established, an example being the synthesis of vitamin D3 which has been produced at the several tons level each year for several decades, and for which dedicated plants continue to be built. This indeed demonstrates that photochemical syntheses are commercially viable. 

P. A. Davidse, J. L. M. Dillen, A. M. Heyns, T. A. Modro, and P. H. van Rooyen, Photochromic systems. Part 1. Structural and spectroscopic study of photochemically active products of Stobbe condensation. 2,3-dibenzylidene-succinic acid and its anhydride, Can. J. Chem., 68, 741-746 (1990). 

Jabbar, S., Gupta, G. Study of dissociation constants of Stobbe condensation and cyclization products. J. Indian Chem. Soc. 1991,68, GOBI. 

Let us now assign numerical values to the parameters g (lattice constant), a (Madelung s constant), s (permittivity), and 2,(fugacity) (other parameters are elementary charge e, dielectric constant o, and the temperature T, which can be set at 300 K). For liquid water we can set g = 0.281 nm for the estimation let a be 1.3 and let s be 4 (though s = 81 for bulk water). Stobbe and Peschel [405], based on literature data [417—419] and their own studies, have concluded that the dielectric constant s varies from 5 to 10 for the absorbed water layer with thickness from 1 nm to 12 nm. A cluster of water molecules with the radius on the order of lOg just falls under the aforementioned water layer thickness. 

Hernandin (15) is a new compound which belongs to the category of phenyl-tetralin-type lignans. Many studies have been reported on the syntheses of this type lignans (ref. 2, 47), and some of them were carried out in connection with the syntheses of steganacin (ref. 48) and deoxyschizandrin (ref. 49). A route via an itaconic acid derivative, obtained by Stobbe condensation of a benzophenone derivative with diethyl succinate, followed by cyclization (ref. 41a, 50) was first undertaken through the scheme outlined in Chart 10. 

The oxalylfulgides (129) have been prepared and studied. These photochromic yellow dyes undergo ring closure in the conventional manner. The quantum yields for the process and the solvent dependency results are shown below the struetures. " A double Stobbe condensation of 3,5-dimethoxybenzaldehyde with succinic anhydride affords the fulgide (130). This is photochemically reactive and undergoes cyclization to afford a pink cyclic form on irradiation at 366 nm. ... 

Solid-phase Extraction of Atrazine from Soil. This procedure was modified firom the method described by Hill and Stobbe (g). For studies involving spiked samples, atrazine standards in methanol were added to give the desired ng of atrazine per gram of dry soil, and the samples were dried again before extraction. Samples of 5 grams of U.S. Army Standard Soil were suspended in 10 ml of acetonitrile water 9 1, and the slurry was sonicated (30 min. 

The fulgide material studied here is 3-indoly-benzylfulgimide, which was synthesized by the Stobbe condensation routine l l. The target compoimd of 3mg was dissolved in a 0.1ml 10% (by weight) PMMA-cyclohexanone solution. Then the solution was coated on a 1-mm thick K9 glass plane (0 25 mm x 1.5 mm) with a span coater and dried in air. The thickness of the film is determined to be about lOjim by microscopy of the cross section. The photochromic or photo-induced anisotropic paoperties of fulgides are due to a reversible photochromic (photoisomerization) reaction that occurs between one of the colorless E-form (bleached state) and the C-form (colored state). These are the two spectrally separated... 

The Stobbe condensation between 5-methylthiophen-2-aldehyde and dimethyl succinate has been studied. Through reduction of a mixture of thiophen-2-aldehyde and acrolein the vinylthienyl glycol (160) was obtained... 

Botton, G.A., Appel, C.C., HorseweU, A., and Stobbs, W.M. Quantification of the EELS near-edge structures to study Mn doping in oxides. J. Microsc. 1995, 180, 211-216. 

An alternative method for the classical Knoevenagel-type preparation of cinnamic acids has been reported this came to light during a study of the bromine-induced decarboxylation of substituted cinnamic acids. Cinnamic acid derivatives can also be prepared by the palladium-catalysed coupling of methyl acrylate with electron-rich aryl iodidessimilarly 5-arylpenta-2,4-dienoic acids (29) can be synthesized from penta-2,4-dienoic acid and bromo-aryls. A Stobbe-type condensation between aromatic aldehydes and methyl propylidenemalonate leads to the , -unsaturated acids (30), probably via a 5-lactone intermediate. ... 

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