Co source

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

The calibration procedure is sufficiently accurate for Doppler velocities in the regime 0 to 10 mm s beyond this range, laser calibration is more suitable. Calibration with ot-iron, as described, can also be used for Mossbauer measurements with other isotopes, e.g., Ni, Au, and Ir, for which suitable standard absorbers are not available (provided that the Doppler velocity range of interest is not significantly greater than 10 mm s ). This, of course, requires that the spectrometer is temporarily equipped with a Co source and an a-iron absorber. 

The effective shielding of the detector system from direct and cascade radiation from the Co/Rh source is also very important. A graded shield consisting of concentric tubes of brass, tantalum, and lead was selected. The thickness and the shape of different parts of the shielding were optimized so that nearly zero direct 122 and 136 keV radiation (emitted by the Co source) was in a direct line with the detectors (see Fig. 3.16). 

Fig. 7.8 Ni Mossbauer spectra of NiFc204 without (top) and with (bottom) an external magnetic field of 5 T. The source was Co in Nio.8sCro.i5, enriched to 98% and activated in a 300 MeV electron accelerator at Mainz University making use of the reaction Ni(y, p) Co. Source and absorber were kept at 4.2 K (from [19])...

Figure 21. Electrochemical production of formic acid (HCOOH) and CO. Source third Carbon Dioxide Utilisation Summit. DNV GL.

Morimoto, Kakiuchi, and co-workers were the first to show that aldehydes are a useful source of CO in the catalytic PKR [68]. Based on 13C-labeling experiments, it was proposed that after decarbonylation of the aldehyde, an active metal catalyst is formed. This was proven by the absence of free carbon monoxide. As a consequence CO, which is directly generated by previous aldehyde decarbonylation, is incorporated in situ into the carbonylative coupling. The best results were obtained using C5F5CHO and cinnamaldehyde as CO source in combination with [RhCl(cod)]2/dppp as the catalyst system. In the presence of an excess of aldehyde the corresponding products were isolated in the range of 52-97%. 

The hydroformylation of alkenes to aldehydes or directly to alcohols by using CO2 as CO source (Eq. 4) was reported by Tominaga and Sasaki [214,215]. 

Except for death and possibly damage to the heart, these effects are reversible when the CO source is removed, because COHb eventually... 

Subsequently, it was found that aldehydes could be used as a CO source rather than the toxic CO gas. However, the choice of aldehydes proved to be very important for example, when Shibata used cinnamaldehyde and Chan used decanal, highly enantioselective Ir-catalyzed Pauson-Khand-type reactions were achieved independently [30b, 32] (Scheme 11.20). Whilst Shibata realized at an early stage that the Rh-tolBlNAP complex-catalyzed enantioselective Pauson-Khand-type reaction served as a CO source [33], it was apparent that the Ir-catalysts could induce a greater enantioselectivity. 

Asymmetric catalytic reactions under solvent-free conditions have also been reported. Contrary to the previous result, a neutral rhodium(I) complex provided comparable enantioselectivity with high chemical yield [24c], Eor certain cases, benzaldehyde gave improved enantioselectivity over cirmamaldehyde (Tab. 11.6), although the rationale behind choosing this particular CO source is not entirely clear. Additionally it should be noted that when the reaction was carried out using a stoichiometric amount of an aldehyde as the CO source in xylene, the reaction takes much longer and the enantioselectivity decreases substantially. 

Area Name/chemical class/structure Trade name/Co Source ... 

Sample Preparation. PBS-MP20, obtained in powder form from Mead Chemical Co., was the primary source of the samples used in this study. A portion of the MP20 powder was dissolved in 2-methoxyethyl acetate (Mead Chemical) and films were spin-coated on silicon wafers. Films were baked at 120 C for 1 hour prior to irradiation. MP20 samples, both in powder and film form, were irradiated under vacuum at 30 C in a Co source. Films were spun from methoxyethyl acetate solutions of the irradiated powders. These films were also baked at 120 C for 1 hour. The above procedure created two types of degraded MP20 samples (1) those irradiated in film form and (2) those irradiated in powder form. The first type of films were designated as IF-type films. Films spun from solutions of the irradiated powders were designated as IP-type films. 

Shibata and co-workers used an excess of cinnamaldehyde, which was employed as a CO source without solvent to furnish the corresponding PKR product in almost quantitative yield. ... 

Table 4 The catalytic Pauson-Khand reaction using aldehydes as CO source...

An example of the use of DMF as CO source in the Pd-catalyzed aminocarbonylation with microwave irradiation is shown in Scheme 28. Thus, n-bromotoluene was reacted with benzylamine (4 equiv.) in the presence of Pd-dppf catalyst, imidazole, KOBu, and DMF (17equiv.) with microwave irradiation for 20min to give amide 196 in 94% yield (Scheme 28). A proposed mechanism (Scheme 28) has a close similarity to that of the aminocarbonylation of aryl bromide with formamide (see Scheme 22). However, in this process, a large excess (4 equiv.) of benzylamine was used to suppress a possible reaction involving dimethylamine generated in situ from DMF under reaction conditions. 

The Pd-catalyzed carbonylation of o-vinylaryl bromides using Mo(CO)6 as CO source with microwave irradiation gave indanone 338 and 3-acylaminoindanone 340, which are key intermediates for the synthesis of inhibitors of human immunodeficiency virus type 1 (HIV-1) protease and Plasmepsin I and II (Scheme 46). These polycyclic compounds were obtained in less than 30 min in high yields. The results clearly indicate the power and advantage of this protocol, especially for the combinatorial parallel synthesis of a library of compounds. 

Most of the kinetic measurements were made at 77 K. In these experiments at 77 K, the trapped electrons and the O anion radicals were generated by irradiation at 77 K of vitreous 10 M solutions of NaOH in H20 either with electrons with an energy of 4.5 MeV or with y-quanta from a60 Co source. In the EPR measurements, the ampoules in which the vitreous solutions were irradiated had been preliminarily covered with a thin layer of Indian ink to prevent photobleaching of the et . These ampoules were also used as EPR cells. In the optical experiments, the irradiated ampoules were stored in dark containers between measurements. Special tests have shown that, for both the optical and the EPR measurements, no decrease in concentration of et , takes place during transfer of samples from the containers to the cells of the spectrometers. Also, no bleaching of ety by the analyzing light of the spectrophotometer is observed. 

Palladium-catalysed coupling reactions under carbon monoxide have been extensively used in traditional medicinal chemistry72. Despite this, these crucial transformations have hardly been employed in combinatorial chemistry. These shortcomings have recently been recognised and a series of microwave-heated carbonylative transformations with solid or liquid CO-sources have been reported. 

Note A- = (C4H90)2P0- -B- = (C4H90)P0-. Conditions Gamma irradiation with Co source at 0.6 MGy in the EDIT test loop that simulated the nuclear fuel reprocessing, room temperature. 

Irradiation with Co source (2.5 kGy h )—vigorous stirring with a magnetic bar at 50°C of equal ... 

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