Deselenation

On the other hand, wet chlorination of refinery slimes has proven to be a rapid and simple method of obtaining high extractions of selenium from slimes. A simple wet chlorination flow sheet is shown in Figure 3. Slimes chlorination per se is not a simple deselenization operation, but rather a process wherein virtually all the constituents of slimes which form soluble chlorides report as a complex solution of mixed chlorides. Thus the use of wet chlorination requires a complete change in the process to recover the metal values in slimes. The first plant to use wet chlorination of slimes was started by Kennecott (Salt Lake City, Utah) in 1995. 

Disubstituted 1,2,3-selenadiazoles react with [(i/ -Cp)Mo(CO)2]2 to form a series of ring-opened and finally deselenated products (92JA5467). 

The Group VI organometallic chemistry is mainly characterized by the occurrence of N- and C-coordination and carbene complex-formation, as well as by some unique cases of Se- (Te-) coordination, ring opening and deselenation. The Group VII organometallic chemistry is known for the carbene and chelate structures of the derivatized thiazoles. 

The first examples of a diarylgermanethione21 or -germaneselone22 not stabilized by interaction with a Lewis base were synthesized by the desulfurization or deselenization of the corresponding 1,2,3,4,5-tetrathia- or -selenagermolanes using triphenylphosphine. 

Since the chemistry of the C-Se bond is very similar to the chemistry of the C-S bond, the deselenation procedures are also very similar to the desulfurization methods. Thus, Ra-Ni is an efficient reagent in hydrogenolytic desel-enations, but the outcome of the reaction depends on the preparation of the catalyst.426 28... 

By contrast, deselenation of the bulkier precursor Tbt(Tip)GeSe4 72b with 3 molar amounts of triphenylphosphine in refluxing hexane under argon resulted in the quantitative isolation of the first stable germaneselone Tbt(Tip)Ge=Se 75 as red... 

In addition to the successful isolation of the stable stannaneselone 127, it should be noted that deselenation of 126 with two equivalent molar amounts of triph-enylphosphine resulted in the isolation of a novel tin-containing cyclic diselenide, diselenastannirane 128, as a stable crystalline compound.60... 

The (RME) heterocycles can be used as sources for the unstable six-electron RM species. Deselenation of (RSbSe)3 in the presence of 1,3-butadienes results in the formation of cycloadducts of the stibinidene RSb,... 

The deselenization of t-butyl phenylphosphinoselenoic acid by Raney nickel is highly stereoselective, allowing a stereochemical correlation between the selenoate and the analogous phosphorothioic acid through a common intermediate.125... 

Abstract This presentation is a brief review on the resnlts of our work on iodine interaction with thioamides, selenoamides and amides. The thioamides, benzothia-zole-2-thione (BZT) (1), 6-n-propyl-2-thiouracil (PTU) (2), 5-chloro-2-mercap-tobenzothiazole (CMBZT) (3), N-methyl-benzothiazole-2-thione (NMBZT) (4), benzimidazole-2-thione (BZIM) (5), thiazolidine-2-thione (TZD) (6), 2-mercapto-pyridine (PYSH) (7), 2-mercapto-nicotinic acid (MNA) (8), 2-mercapto-benzoic acid (MBA) (9) and 2-mercapto-pyrimidine (PMT) (10) react with producing three type of complexes of formulae [(HL)IJ(l2) (HL= thioamide and n= 0, 1), [(HL) [I3 ] and [(HL-L)]+[l3 ]. The interaction of seleno-amides, derived from, 6-n-propyl-2-thiouracil (RSelJ) (R= Me- (11), Et- (12), n-Pr- (13) and i-Pr- (14)) with I, have also been studied and produced the complexes [(RSeU)IJ of spoke structure. These complexes are stable in non-polar solvents, but they decompose in polar solvents, producing dimeric diselenide compounds or undertake deselenation. 

The diselenides [A -(6-Et-4-pyrimidone)(6-Et-SeU)J (31) and [7V-(6-n-Pr-4-pyrimidone)(6-n-Pr-SeU)j] (32) were produced upon re-ciystallization of [( -PrSeU)IJ (30) and [(n-EtSeU) ] (33) from acetone, as oxidation products. On the other hand deselenation with the formation of 6-n-propyl-2-uracil (n-Pr-U) (34) was observed when (30) was re-crystallized from methanol/acetonitrile solutions [7]. 

The combination of the electrogenerated chloro cation [Cl] with diphenyldise-lenide is a typical example of the functionalization of an olefin. The electrochemical oxyselenation-deselenation of (1) to (2) proceeds in an MeOH-NaCl-(Pt) system (Scheme 1) [32]. The bromide salt-promoted oxyselenation of olefins is discussed in Sect. 15.2.2. Penicillin (3) can be converted into the oxazoline-azetidinone (4) by a chloride salt-promoted paired reaction in an MeOH-t-BuOH(5 l)-MgCl2-(Pt) system at —40°C in 74 93% yield (Scheme 2) [33, 34]. This conversion probably involves an initial attack of an... 

Scheme 12 Oxyselenation-deselenation of alkenes to allyl alcohols.

Silylated 1,4-cyclohexadienes were introduced as reducing agents in radical chain reactions such as dehalogenation, deoxygenation via thionocarbonate ester and deselenization [120]. Two examples are given in Reactions (4.75)... 

The advantage of this synthetic approach over the total synthesis of selenocysteine peptides is the reduced number of synthetic steps to which the Se-protected selenocysteine is exposed, thus, largely preventing deselenation as an undesired side reaction. It also allows access to larger peptides and even proteins containing selenocysteine to exploit the Se atom for X-ray crystallography, 13 or as 77Se nucleus for NMR spectroscopy. 60 ... 

Tellurium and many other impurities remain undissolved. The solution is filtered and cooled to reverse the reaction and to deposit solid selenium. Deselenized liquor is recycled to the dissolution step. 

A novel synthesis of an oxetane from a 1,4-diene by means of the new reagent PhSeOH has been reported. From 2,4-dimethyl-1,4-pe ntadiene there was obtained 2,4-dimethyl-2,4-bis(phenylselenomethyl)oxetane (65) in 34% yield. This compound can be deselenated with Raney nickel to 2,2,4,4-tetramethyloxetane (79JOC1742). 

In many cases even the oxyselenation-deselenation sequence can be performed electrochemically in one step (Eq. (49), Table 4, No. 27-31)... 

This allyloxylation was used to produce d,l-rose oxide from citronellol (Eq. 50) 1 -Similarly d, 1-dihydroactinidiolide was formed in one step by the intramolecular oxyselenation-deselenation sequence (Eq. (51))... 

G. Janrand, J.-M. Beau, and P. Sinay, Glycosyloxyselenation-deselenation of glycals A new approach to 2 -deoxy-disaccharide, J. Chem. Soc. Chem. Commurt. p. 572 (1981). 

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