Barium in Organic Synthesis

Homo- and cross-coupling reactions of allyhc halides and reactions of conjugated dienes with dichloroalkanes using reactive barium are reviewed in Section 5.2. The next section covers methods of generating allylic barium reagents and reactions of these carbanions with a variety of electrophiles. The last section describes examples of other carbon-carbon bond forming reactions promoted by barium compounds. 

Reactive Barium-promoted Carbon-Carbon Bond-forming Reactions 

Main Group Metals in Organic Synthesis. Edited by H. Yamamoto, K. Oshima Copyright WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

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Barium acetate is used as a mordant for printing textile fabrics for drying paints and varnishes in lubricating oil in the preparation of other acetates and as a catalyst in organic synthesis. 

Barium manganate (BaMn04) was a little known oxidant in organic synthesis till Firouzabadi et al. published in 1978 83 two foundational papers76 showing that it behaves against alcohols in a similar way as active MnC>2. 

Barium hydroxide [33, 34] is a strong base which has been employed not only in organic synthesis but also for other purposes. The commercially available octahydrate, l a(OI 1)2 8 11,/) is often used after transformation to the anhydrous form at 200-500 °C. Dehydrated Ba(OH)2 activated at 200°C is denoted C-200. It is known to be a heterogeneous basic catalyst in the Horner-Wadsworth-Emmons (HWE) reaction of triethyl phosphonoacetate (69) with aldehydes 70 to give the 3-substituted ethyl acrylates 71 (Scheme 5.13) [35]. The HWE reaction proceeds at 70 °C in 1,4-dioxane with a small amount of water. The yields of products 71 are usually better than those provided by typical basic catalysts such as NaOH or... 

Garcia-Raso, A Sinisterra, JV Marinas. JM. Activated barium hydroxide as a catalyst in organic synthesis. Polish Journal of Chemistry. 1982 56, 1435-1445. 

The aldol condensation and related reactions are among the most important, and ubiquitous, construction reactions in organic synthesis. In these condensations, the carbonyl compound acts as both nucleophile and electrophile—the enol or enolate is the nucleophile, and the keto form is the electrophile. The reaction works with enolizable aldehydes (Figure 17.24) or ketones (Figure 17.25) and may be catalyzed by either acid or base. Almost all of the steps we write are equilibria—how can we persuade the reaction to go to completion In the base-catalyzed reaction, a catalyst such as barium hydroxide is placed inside a Soxhlet thimble, as in Figure 17.26. The reaction mixture is heated so that the acetone refluxes, but the product does not. Thus only the SM, and not the product, comes into contact with the catalyst, ensuring that the reverse reaction does not occur. Note that in the acid-catalyzed processes, it is common for the product to be dehydrated under the reaction conditions—this usually pulls the equilibrium over to the product. The mechanism of the elimination reaction may be El or E2 depending on the... 

Indeed, many metals other than magnesium have been activated and used in the synthesis of many organic compounds [55]. Most notably, copper, zinc, calcium, indium, cadmium, nickel, aluminum, and barium have been activated and used in the synthesis of many complex molecules [56]. 

Sinisterra, J.V., Mouloungui, Z., Delmas, M., and Gaset, A., Barium hydroxide as catalyst in organic reactions. Part 5. Application in the Homer reaction under solid-liquid phase-transfer conditions. Synthesis, 1097, 1985. 

Decomposition of the organics leads then to the separation of all elements into Cu and Y oxides and barium carbonate. This brings the synthesis parameters back to the problems encountered in the conventional solid state approach except that the heterogeneity may be over a submicron scale. Thus, reaction temperature may be slightly lowered (850°C instead of 900°C). 

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