Borole

Economic Aspects. U.S. capacity for production of merchant sodium dithionite (soHds basis) was estimated at 93,000 metric tons in 1994. There are three North American producers of sodium dithionite. Hoechst Celanese is the largest producer (68,000 tons capacity) with two formate production locations and one zinc process location. Olin (25,000 t capacity) produces solution product only at two locations using both the amalgam and electrochemical processes. In 1994, Vulcan started a small solution plant in Wisconsin using the Olin electrochemical process. In addition, it is estimated that 13,000 t/yr is produced at U.S. pulp mills using the Borol process from sulfur dioxide and sodium borohydride. Growth is estimated at 2—3%/yr. The... 

A particularly interesting reaction (and one of considerable commercial value in the BOROL process for the in situ bleaching of wood pulp) is the production of dithionite, S204 , from SO2 ... 

Reaction of l-(dimethylamino)-2,5-dihydro-2,5-diphenyl-l//-borole with diisopropylaminolithium and then TMEDA gives 293 [90AG(E)317 95JOM (502)67]. 

The most satisfactory route to the synthesis of the ri -borole complexes is the reaction of dihydroboroles (2-borolenes and 3-borolenes) with metal carbonyls. An alternative method of synthesis includes formation of the borole adducts with ammonia, 320 (R = Me, Ph) [87JOM(336)29]. Thermal reaction of 320 (R = Me, Ph) with M(C0)6 (M = Cr, Mo, W) gives 321 (M = Cr, R = Me, Ph M = Mo, W, R = Ph). There are data in favor of the Tr-electron delocalization over the borole... 

Boroles are the ri -complex-forming ligands. However, in the presence of the TT-donor substituents at the heteroatom, they tend to give V or species, especially for the low-valent early transition metals. 

The fourth chapter of this volume comprises the second part of an ongoing series by Professor A. P. Sadimenko (Fort Hare University, South Africa) dealing with organometallic compounds of pyrrole, indole, carbazole, phospholes, siloles, and boroles. This follows the review in Volume 78 of Advances covering organometallic compounds of thiophene and furan. The enormous recent advances in this area are summarized and classified according to the nature of the heterocycle and of the metals. 

In the complexes of 1,3-boroles containing the unsaturated substituents (89CB633, 90CB2273, 94CB2393), the coordination mode is in the case of iron tricarbonyl complexes 10 and 11 (R = H, Me). 

Pyrroles, indoles, carbazoles, phospholes, siloles and boroles in... 

Pentaphenylborol-tricarbonyliron, e.g., is prepared from Fc2(CO)9 and the borole in toluene at 45-50°C. Chromatography on AI2O3 yields the complex as yellow light-and air-sensitive crystals . ... 

The triple-decked Tj -CpFe(PhBC4H3Et)FeCp-T7 complex is formed from 1-phenyl-4,5-dihydroborepine and [T) -CpFe(CO)2l2 by thermal reaction the boraben-zene derivative 77 -CpFe(PhBC5H4Me) also forms. With Mn2(CO), l-phenyl-4,5-dihydroborepine yields the triple-decker complex (CO)3Mn(PhBC4H3Et)Mn(CO)3. The borole complexes described so far are available using stable boroles as reactants. But borole molecules can also be generated from precursers in the course of complexation. 

The reaction of 2- and 3-borolenes C4H6BR (R = Ph, Me, C H, OMe) with Co, Fe and Mn carbonyls leads, under dehydrogenation of the borolenes, to i7 -borole complexes. 2-Borolene and 3-borolene also react with Mn2(CO), at 160°C to a red-brown triple-decked complex ... 

Dihydro-lH-l,5,2-azasilaboroles derive from the 2,5-dihydro-lH-l,2-aza-boroles ( 6.5.3.3) by substitution of the carbon neighboring N by a silicon atom. They may act as four-electron donors using electron density from the C=C double bond and the N atom. The B atom behaves as an acceptor center. Two pathways are known for complex synthesis reaction with a generated transition-metal complex fragment and reaction with metal atoms by the metal-vapor synthesis method. 

Dihydro-l,2,5-azaadiboroles are comparable to the 2,5-dihydro-l,2,5-thia-diboroles, but compared with boroles and thiadiboroles they are weaker ligands . Their transition-metal complexes are accessible photochemically or thermally in... 

One Rh complex with a 2,3-dihydro-l,3-diborolyl ligand is prepared by dehalo-genation of [(Et2C2B2Et2CMe)RhCl]2 with K in the presence of free 2,3-dihydro-1,3-diborole (Et2C2B2Et2CHMe)Rh(Et2C2B2Et2CMe) possesses one borole and one borolyl ring ligand. ... 

Borole complexes ( 6.5.3), normally prepared from dihydroboroles by loss of hydrogen during the complexation process, are also available using a borole dianion via lithiation of dihydroboroles . ... 

The studies of U in river waters has enabled to assess the mean activity ratio of the dissolved U flux carried by rivers to ocean. The value of 1.17, based on 50% of the global exported U flux (Table 1), is in the lower range of older estimates based on smaller data sets (e.g., Mangini et al. 1979 Borole et al. 1982). Such an estimate is too low compared to the ratios of seawater. The point has been already raised by... 

Borole DV, Krishnaswami S, Somayulu BLK (1982) Uranium isotopes in rivers, estuaries and adjacent coastal sediments of western India Their weathering, transport and oceanic budget. Geochim Cosmochim Acta 46 125-137... 

India (Borole et al. 1982) and the Forth estuary in the UK (Toole et al. 1987), nonconservative behavior of uranium was also demonstrated. In the Amazon estuary, uranium showed elevated concentrations compared to simple mixing (McKee et al. 1987). Release of uranium from bottom sediments on the shelf was suggested to be a source of dissolved (<0.4 im) uranium. However, subsequent studies in the Amazon also demonstrated that U removal (Fig. 3) occurred at salinities <12 (Swarzenski et al. 1995, Swarzenski et al. 2003). Overall, it was established that the behavior of U is highly variable examples have been found of conservative behavior as well as both additions and removal of U by interaction with sediments. 

The first authenticated borole (94) was made by the exchange reaction of phenylboron dichloride with l,l-dimethyl-2,3,4,5-tetraphenylstannole (93) (Eq. 29)w in toluene. 

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