Bismuth catalyst

Several bismuth compounds that can be used in aqueous media have been introduced. Due to increasing demand of water as a solvent in organic synthesis, catalysts that can be used in aqueous media are becoming more and more important. Although bismuth Lewis acids are not very stable in water, it has been shown that they can be stabilized by basic ligands. Chiral amine and related basic ligands combined with bismuth Lewis acids are particularly useful in asymmetric catalysis in aqueous media. On the other hand, Bi(OH)3 is stable in water and works as an efficient catalyst in water. Because of the unique characteristics of bismuth compounds, other chiral and achiral bismuth catalysts will be focused on and developed rapidly in the field of synthetic organic chemistry. 

Keywords Bismuth Catalyst C-N bond formation Hydroamination Substitution reaction... 

Moreover, the use of bismuth catalysts has definitively contributed to the area of environmentally benign catalysts, known as green catalysts. These are fascinating... 

DABCO 33 LV is also known as triethylene diamine. It is a cage-like compound with no steric hindrance (Figure 2.39), which helps make it a very effective catalyst. It is reactive at close to ambient temperatures. The application range is in the range of 0.3 to 0.6 parts per 100 of prepolymer. To obtain the desired rate, a mixture of an acid (such as oleic) with a bismuth catalyst can be used. Bismuth catalysts include bismuth neodecanoate and bismuth ocotate. 

Bismuth catalysts promote the isocyanate and OH reaction from the isocyanate side. This has the effect of reducing the water reaction and hence reduces the liberation of carbon dioxide gas. They are particularly useful in controlling the reactions when used in one-shot systems. 

Depending on the temperature at which the material is processed, various amounts of a metallic catalyst are added. Tin-based catalysts, such as Air Products T12, catalyze the OH-NCO reactions. The metallic catalyst increases the total reaction speed but also equals out the reaction rates of the high molecular polyols and the low molecular polyols. Bismuth catalysts are now preferred to the previously used mercury catalysts. Polyether polyols are slow in reaction, and both a tin and an amine catalyst may be needed to obtain the best speed and properties. 

As an example, platinum-bismuth catalysts with different atomic ratios have been prepared by the water-in-oil method and tested for the ethylene glycol electro-oxidation in alkaline medium [59],... 

Kimura H, Tsuto K, Wakisaka T, Kazumi Y, Inaya Y. Selective oxidation of glycerol on a platinum-bismuth catalyst. Appl Catal A Gen. 1993 96 217-28. 

The Reppe process is used to make 1,4-1 butanediol from acetylene. In this process, acetylene and formaldehyde are reacted in the presence of a copper-bismuth catalyst. The resulting intermediate, 2-butyne-l,4-diol is hydrogenated over a Raney nickel catalyst ... 

Decen-l-ol is oxidized by air to 9-decenoic acid in aqueous media in the presence of a supported platinum catalyst with bismuth atoms deposited on the surface of the platinum particles [221]. Metal-supported bismuth catalysts have been studied extensively for selective oxidation of hydrocarbons and alcohols for industrial use [222]. 

By using close-to-neutral conditions for the catalytic oxidation of glyceric and tartronic acids on platinum-bismuth catalysts to their respective keto derivatives, deactivation of the catalyst by adsorbed acids may be reduced, leading to higher degrees of conversion and improved yields. In addition, higher loadings of bismuth promoter may also serve to reduce deactivation by adsorbed acids. 

Glucose can be oxidized to gluconic acid by oxygen (4.38) in the presence of palladium on alumina, a palladium-bismuth catalyst, or a platinum-bismuth catalyst in 99-100% yield.186... 

Dihydroxyacetone (DHA), the oxidation product of the secondary hydroxy group of glycerol, is an artificial tanning agent in cosmetics and a pharmaceutical intermediate. Glycerol oxidation in acidic medium on a platinum-bismuth catalyst (Bi/ Pt atomic ratio = 3) prepared by coprecipitation of Pt and Bi salts, yielded 20 % DHA at 30 % conversion [70]. The deposition of bismuth on platinum particles by oxido-reduction (Bi/Pt = 0.13) yielded 37 % DHA at 70% conversion... 

According to the reactivity scale proposed by Heyns et al. [2-4], oxidation at the anomeric position at C] is easier than for primary or secondary alcohol functions. Selectivity higher than 95 % for aldonic acids were indeed observed in the catalytic oxidation of o-glucose, and of reducing disaccharides such as lactose and maltose. Palladium catalysts or palladium-bismuth catalysts are more selective than platinum because they are less active in the oxidation of primary or secondary alcohol functions. 

The selective oxidation of lactose to lactobionate with air on palladium-bismuth catalysts was first reported in patents [47]. Hendriks et al. [16] studied the oxidation of a 0.5 mol solution of lactose as a function of pH, temperature and Pd/Bi ratios of promoted Pd/C catalysts. Sodium lactobionate was obtained with 100% selectivity up to 95% conversion on Pd-Bi/C catalysts (Bi/Pd = 0.5) at 333 K and pH 9. Oxygen mass-transfer limited the maximum initial reaction rate (0.47 mol kg s ). The catalyst was recycled 15 times without any significant loss of activity and selectivity. 

Variations in the selectivity of propene oxidation as a function of the catalyst composition are shown in Fig. 19a and b. If the suggested electronic mechanism of the action of mixed catalysts is true, the electron work function () of mixtures should be higher than that of pure molybdenum and bismuth oxides. The dependence of A on the composition of a molybdenum-bismuth catalyst is shown in Fig. 19b. The maximum change in the electron work function corresponds to highest selectivity. Such a proportional change in catalytic and electronic properties seems to provide evidence for the electronic mechanism of the effect of these mixed catalysts. 

Tungsten yields compounds displaying chemical properties approaching those of molybdenum. Like molybdenum, W03 is a mild catalyst for low conversion of hydrocarbons. Variations in electron work functions of mixed tungsten-bismuth catalysts of various composition are shown in Fig. 19, also. A relationship was observed between selectivity and the electronic properties of these catalysts. ... 

Organometallic complexes of Sn, Bi, Hg, Zn, Fe, and Co are all potent urethane catalysts, with Sn carboxylates being the most common. Hg catalysts have long induction periods that allow long open times. Hg catalysts also promote the isocyanate hydroxyl reaction much more strongly than the isocyanate water reaction. This allows their use in casting applications where pot life and bubble-free parts are critical. Bismuth catalysts are replacing mercury salts in numerous applications as the mercury complexes have come under environmental pressure. 

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