Self-reduction

Using terminal propargylic formates, allenes were prepared much more cleanly by Pd-catalyzed intramolecular reduction [46, 47]. The reduction process can be seen as a kind of decomposition reaction and therefore no additional reductant (ammonium formate) is required. In the Pd-catalyzed self-reduction of 28, the terminal allene 29 was formed in 86% yield with 99% selectivity and only a trace amount of alkyne 30 was detected (Scheme 3.15). 

However, it can undergo self-reductive dissolution (loss of active material) accompanied by oxygen evolution [349]. The active material of the positive electrode (in pocket plate cells) consists of nickel hydroxide mixed with small additions of cobalt and barium hydroxides to improve the capacity and charging/discharging performance and graphite to improve conductivity [348]. 

Gold(iu).—Group VII Donors. The intermediate in the reduction of [AuC14] by NIV -diphenylthiourea has been isolated as [AuC12(DPT)2]C1.229 The self-reduction of this complex was followed kinetically (equation 51). A new improved preparation of AuC13 has also been reported.230 HAuC14 has been shown to oxidize (S)-methionine... 

History—Occurrence—Formation—Preparation—Concentration of Solutions— Physical Properties — Chemical Properties — Catalytic Decomposition — Decomposition with Self-reduction—Oxidation Processes—Applications. 

Table 1 demonstrates that NaBH4 may be used in the presence of heterocyclic rings (entries 8-10, 13-17), esters (entries 8-10, 17), amides (entries 1, 9), conjugated double bonds (entry 7), alkynes (entry 5) and acetals (entry 4). The process can also be used to methylate an amine with formaldehyde as the carbonyl (entry 13). With certain structures, further reactions may occur subsequent to reduction (e.g. entry 6). Entry 15 illustrates a synthetically useful amine alkylation reaction which may occur in acetic acid. This remarkable reaction is attributed to self-reduction of an acyloxyborohydride to an aldehyde... 

Results of an i.r. study of the thermal decomposition of ammonium uranate have been interpreted in terms of the final self-reduction of the amide as represented by the equation... 

This is the only important oxidation state for Th, and is one of the two for which U is stable in aqueous solution it is moderately stable for Pa and Np also. In water Pu, like Pu, dispropor-tionates into a mixture of oxidation states III, IV, V and VI, while Am not only disproportionates into Am -I- Am 02" " but also (like the strongly oxidizing Cm ) undergoes rapid self-reduction due to its a-radioactivity. As a result, aqueous Am and Cm require stabilization with high concentrations of F ion. Berkelium(IV), though easily reduced, clearly has an enhanced stability, presumably due to its f configuration, and the only other -1-4 ion is Cf, found in the solids CfFq and Cf02. 

Aqueous solutions of Pu, Amv, Amvi and especially Amiv undergo rapid self-reduction due to their a-radiation. 

Nevertheless, this reaction mechanism carmot take into account the effect of oxygen addition to the feed which has been observed in Fig.2. In order to model these further experimental evidences, another reaction step has been considered and added to mechanism Ml. This step, which was also reported in [9], describes the catalyst self-reduction by O2 desorption, which is known to occur at high temperature on the Cu-ZSM5 catalyst. It is expressed by the following reaction step ... 

Figure 4.7. Volume distribution functions of the Pt nanoparticles in PODS. Curves 1-3 correspond to the samples based on K2PtCl4 after self-reduction and H2PtCl6 x 6H2O after H2 and NaBH4 reduction, respectively. (Reprinted with permission from reference 26. Copyright 2000, American Chemical Society.)...

It has been demonstrated that, at elevated temperature, Cu(II) in ZSM-5 can be auto-reduced to Cu(I) in an inert gas flow or in vacuo. For example, Li and Hall showed the formation of Cu(I) from Cu(II) in He flow by ESR spectroscopy and demonstrated that the self-reduction results from the desorption of oxygen(7). By activating underexchanged Cu-ZSM-5 in ultra-high purity He flow at 773 K, we observed the growth of a narrow, intense peak at 5.3 eV above the Cu° K-edge... 

Power self-reduction during emergencies owing to the negative void reactivity effect in beyond design accidents. 

Power self-reduction during any emergencies due to the negative reactivity coefficients. RESIDUAL HEAT REMOVAL... 

Yu X, Xu X, Yang P et al (2012) Photoluminescence properties and the self-reduction process of CaAl2Si20g Eu phosphor. Res Bull 47 117-120 Zaitsev A (2005) Optical properties of diamond. Springer, Berlin, 502 p... 

All other starting materials trace their origins to this commercial source of the element. Ammonium pertechentate from the supplier is black in color rather than the expected pure white. This is due to self-reduction to TcO over long periods of time. Fortunately, the TcOj coating represents only a small fraction of the total mass and is easily converted back to pertechnetate by the recrystallization of the salt from a warm basic aqueous peroxide solution. 

In 13 M NH4F, Am(iv) autoreduces at a rate of about 4% per hour [140], increasing to 10% per hour in 3 m fluoride solution [261]. Self-reduction of Am(iv) to Am(iii) in phosphoric acid solution follows first-order reaction kinetics [261-263]. 

---