Reagents recycling

Figure 12. Main production sequence, present Pu residue recycle, proposed Pu residue recycle, and proposed reagent recycle.

A recent report9 described the use of scandium triflate in conjunction with tributyltin cyanide, a more water stable cyanide source compared to TMSCN. These reaction conditions could be carried out in both organic and aqueous solutions. It was observed that rare earth triflates are stable Lewis acids in water. Thus, a variety of aldehydes 1 and amine 12 were converted to a-aminonitriles 13 in excellent yield. The spent reagent could be completely recovered and, along with the scandium reagent, recycled for subsequent use. 

REACTIVE POLYMERS. See Polymer-supported Reagents. RECYCLING, PLASTICS. See Volume 7. 

Chiral 2-oxazolidones are useful recyclable auxiliaries for carboxylic acids in highly enantioselective aldol type reactions via the boron enolates derived from N-propionyl-2-oxazolidones (D.A. Evans, 1981). Two reagents exhibiting opposite enantioselectivity ate prepared from (S)-valinol and from (lS,2R)-norephedrine by cyclization with COClj or diethyl carbonate and subsequent lithiation and acylation with propionyl chloride at — 78°C. En-olization with dibutylboryl triflate forms the (Z)-enolates (>99% Z) which react with aldehydes at low temperature. The pure (2S,3R) and (2R,3S) acids or methyl esters are isolated in a 70% yield after mild solvolysis. 

Oxidation and reduction reactions can be carried out usiag reformer hydrogen and oxygen from the air. To decide when electroorganic synthesis is likely to be a viable option for a desired product, some opportunity factors are use of cheaper feedstock elimination of process step(s) or a difficult reaction avoidance of waste disposal, toxic materials, and/or abiUty to recycle reagent and abiUty to obtain products from anode and cathode. 

The economics seem to be better for systems where dry powdered fresh hme plus ground recycled hme is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [Hs EC Res., 28(1) 20 (1989)]. Witnum et al. [9th Ann. Pitt. Coal Prep. Util. Euv. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet hme-stone scrubbing for >90 percent flue gas desirffurization. 

Of the removal processes that have attained commercial status, the current favorite employs a shiny of lime or limestone. The activity of the reagent is promoted by the addition of small amounts of carboxylic acids such as adipic acid. The gas and the shiny are contacted in a spray tower. The calcium salt is discarded. A process that employs aqueous sodium citrate, however, is suited for the recoveiy of elemental sulfur. The citrate solution is regenerated and recycled. (Kohl and Riesenfeld, Gas Purification, Gulf, 1985, p. 356.)... 

By using various trapping reagents, it has been deduced that the transannular fragmentation is rapidly reversible. The cyclization of the fragmented radical C is less favorable, and it is trapped at rates which exceed that for recyclization under most circumstances. " Radicals derived from ethers and acetals by hydrogen abstraction are subject to fragmentation, with formation of a ketone or ester, respectively. 

The recovered dg-dimethyl sulfoxide may be recycled to prepare additional deuteriomethyl iodide or purified for use as a reagent by gentle warming with a little solid sodium thiosulfate followed by distillation from barium oxide. Both products show 99% deuteration. ... 

The iron, now in a reduced ferrous form, is not consumed instead, it is continuously regenerated by bubbling air through the solution. The sulfur precipitates out of the solution and is removed from the reactor with a portion of the reagent. The sulfur slurry is pumped to a melter requiring a small amount of heat and then to a sulfur separator where the reagent in the vapor phase is recovered, condensed, and recycled back to the reactor. 

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