Isomerization exchange reaction

Solvent for Base-Catalyzed Reactions. The abihty of hydroxide or alkoxide ions to remove protons is enhanced by DMSO instead of water or alcohols (91). The equiUbrium change is also accompanied by a rate increase of 10 or more (92). Thus, reactions in which proton removal is rate-determining are favorably accompHshed in DMSO. These include olefin isomerizations, elimination reactions to produce olefins, racemizations, and H—D exchange reactions. 

Monoalkylthallium(III) compounds are unstable (73, 79), and very few examples of this class have been isolated. A number of alkylthallium diacetates have been obtained either from oxythallation of olefins with thallium-(III) acetate (see below) or from exchange reactions such as that shown in Eq. (11) (74, 75). Only four alkylthallium dihalides have been isolated so far, namely a neopentylthallium dihalide (60) [Eq. (12)] and the isomeric 2-, 3-, and 4-pyridiomethylthallium dichlorides (20) [Eq. (13)]. Monoaryl-and monovinylthallium(III) derivatives are considerably more stable than... 

Detailed examination of the results of isomerization, hydrogenation, and related exchange reactions reveals defects in the above scheme (6, 7), but despite its shortcomings, it remains the best simple approximation to the truth. 

Even under the most inert atmosphere conditions, the 31CP/MAS spectrum of the immobilized ligand showed a major signal at 6 = 42 ppm (wrt 85% H3POO characteristic of phosphine oxide rather than phosphine. This could be quantitatively reduced by HSiCl3 and this surface reaction monitored by NMR but the subsequent exchange reaction (equation [5]) generated substantial quantities of phosphine oxide and a number of different isomeric complexes were f ormed. 

The unsaturated retro-Michael product easily isomerizes to a dicarbonyl when the Cy also carries a hydroxyl group (X = OH in Fig. 2.3). Such components are notoriously unstable. They undergo decarbonylation to a shorter aldehyde and CO. The retro-Michael product can also be converted into a carboxylic acid via hydration of the aldehyde function (Fig. 2.3). Notably, the formation of the carboxylic acid is accompanied by the saturation of the Cp it in fact represents an exchange reaction between the OH, and the aldehydic H. 

Elimination Reactions, Cleavage and Rearrangement Reactions, Isomerism and H/D Exchange Reactions... 

These two isomeric forms of R2 are physically different because of the pairing of the nuclear spins on the hydrogen nnclei in the molecule. They can be physically separated by chromatography at very low temperatures. Generally to convert one isomer to the other requires a cleavage of the R-R bond. As with the hydrogen-isotope-exchange reactions, no external acceptor or donor is required. 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

Vinyl ethers are important raw materials in the production of glutaraldehyde, as well as of vinyl polymer materials which contain oxygen and are expected to degrade easily in Nature. The [IrCl(cod)]2 catalyzes an efficient exchange reaction between vinyl acetate 57 and alcohols or phenols 58, leading to the corresponding vinyl ethers 59 (Equation 10.11) [27]. Usually, the acid-catalyzed exchange reaction between alcohols and vinyl acetate results in alkyl acetates 60, and also to vinyl alcohol 61 which is readily isomerized to acetaldehyde 62. 

Exchange reactions of neopentane have already lead to the conclusion (755, 158, 162) that 3C complexes, bound to the surface by the ay carbon atoms, may be formed on some metals (e.g., Rh or Pt). However, it was evident from those experiments that 3Cay complexes are formed by metals much more reluctantly than the 2Ca(1 or the aa-bound complexes. It means that their formation can only be studied at (much) higher temperatures than those suited for the study of the HC/D2 exchange reactions. In this case one can advantageously use the skeletal reactions of neopentane themselves as evidence for the formation of 3C complexes. When neopentane is being isomerized or split into Q and C3 fragments, 3C complexes are certainly... 

---