Selective condensation

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

The product gases are first cooled below 200°C to selectively condense so-called zirconium tetrachloride snow in a large space condenser. The sihcon tetrachloride subsequendy is condensed in a quench condenser wherein the warm gases are countercurrendy scmbbed with Hquid siUcon tetrachloride at —20° C. The siUcon tetrachloride is purified by stripping and distillation. 

Cell-free translation system, used for the identification of cloned genes and gene expression, has been investigated extensively as a preparative production system of commercially interesting proteins after the development of continuous-flow cell-free translation system. Many efforts have been devoted to improve the productivity of cell-free system [1], but the relatively low productivity of cell-free translation system still limits its potential as an alternative to the protein production using recombinant cells. One approach to enhance the translational efficiency is to use a condensed cell-free translation extract. However, simple addition of a condensed extract to a continuous-flow cell-free system equipped with an ultrafiltration membrane can cause fouling. Therefore, it needs to be developed a selective condensation of cell-free extract for the improvement of translational efficiency without fouling problem. 

Selective Condensation of Vaporized Organophosphorus Ligand. Certain phosphorus ligands have sufficient volatility that portions may be volatilized when aldehyde and higher boiling aldehyde condensation byproducts are separated from the catalyst solution in, for example, a liquid recycle vaporizer. The phosphorus ligand may be condensed, recovered and returned to the catalyst solution [35] according to the procedure disclosed in US 5,110,990. 

An additional entirely selective condensation synthesis for asymmetric TTF molecules is based on strategy S6, which consists in the reaction of an organotin dichalcogenolate with an ester in the presence of a Lewis acid such as MesAl (Yamada et al, 2004). A scheme of the reaction is given in Fig. 2.7. The method applies to the preparation of varied asymmetric IT Fs and can also be extended to the synthesis of selenium-containing analogues. 

Efficient purification is achieved by selective evaporation and condensation. This technique is applicable to actinides of medium volatility i.e. Am or Cm The volatile impurities are eUminated by selective condensation of the actinide metal, less volatile impurities are left in the crucible. The efficiency of this refining method is determined by the relative evaporation ratio, which for two elements A and B equals the ratio of their activities at a given temperature. 

Enantioselective condensation of aldehydes and enol silyl ethers is promoted by addition of chiral Lewis acids. Through coordination of aldehyde oxygen to the Lewis acids containing an Al, Eu, or Rh atom (286), the prochiral substrates are endowed with high electrophilicity and chiral environments. Although the optical yields in the early works remained poor to moderate, the use of a chiral (acyloxy)borane complex as catalyst allowed the erythro-selective condensation with high enan-tioselectivity (Scheme 119) (287). This aldol-type reaction may proceed via an extended acyclic transition state rather than a six-membered pericyclic structure (288). Not only ketone enolates but ester enolates... 

In die chloride process, the feedstock must be high in titanium and low m iron. Mineral rutile (95% TiO ) is best suited, but leucoxene (65% Ti02) can be used. See also Brookite, An economical conversion of ilmenite for use as a chloride process feedstock has not been developed to date. The ore is mixed with coke and chlorinated at about 900°C in a fluidized bed. The principal product is titanium tetrachloride, but other impurities including iron also are chlorinated and thus must be removed by selective condensation and distillation. Up to this point, the process is... 

According to Scheme 28, hexanoylmethylene-triphenylphosphorane 145 was used as the olefinating agent for the introduction of the C-12 side chain of a series of PG-analogs 130 -133>. The fifth example in this scheme shows the ( )-selective condensation of 159 with formylmethylene-triphenylphosphorane 47, The resulting E)-a, P-unsaturated aldehyde 160 is a further Starting compound for the synthesis of PG-derivatives with a hydroxy group at C-15 l34) (Scheme 28). 

Figure 11 (A) An optical micrograph of water selectively condensed on a SAM-pattemed...

Figure 15.6 Process flow for commercial pyrolysis plant (Thermofuel ) for converting waste plastics into diesel fuel. The plastic is heated to 375-425°C and the pyrolysis vapours are catalytically cracked and then selectively condensed. Note that the pyrolysis vessel is purged with nitrogen gas and that the hot pyrolytic vapours pass from the pyrolysis vessel to the catalytic reaction tower where they are cracked and reformed to give a high-purity diesel stream. (Reproduced by permission of Ozmotech Pty Ltd)...

P. T. Williams and A. J. Brindle, Temperature selective condensation of tyre pyrolysis oils to maximise the recovery of single ring aromatic compounds. Fuel, 82, 1023-1031 (2003). 

Aminopyrazoles 189 were readily converted into 4,5-diaminopyrazoles 190, via nitrosation and reduction, which were selectively condensed with isocyanates to yield 5-amino-4-pyrazolyl ureas 191 (Scheme 10) <2003TL3009>. 

SCHEME 13.2 Selective condensations of glycolaldehyde phosphate alone (a) or in the presence of formaldehyde (b). 

A) Selective condensation of glycolaldehyde phosphate alon (B) in the presence of fomialdehyde... 

A system for separating ozone from oxygen being recycled through the ozonator is shown in Figure 1 (I). It consists of selective condensation of the ozone, separation of the condensate from the recycle gas, and then revaporization of the condensate. 

Adsorption is analogous to selective condensation of gas molecules or to selective crystallization or fusion from a liquid. It is based upon inter-molecular attractive forces of the van der Waals type between a solute and the solid surface. These attractive forces will be most effective and most selective in a region adjacent to the surface and only one solute molecule thick (the monomolecular layer, or monolayer). Although multilayer deposition may develop as the concentration of solute increases toward a condition of normal condensation or precipitation, in general only monolayer adsorption will be involved and the available surface will not even be covered completely. 

Alkali-exchanged zeolites can be used for selective condensation reactions [32-37], double bond isomerization, alkylation of toluene by methanol, mono-methylation of phenylacetonitrile with methanol and dimethyl carbonate (DMC) [38], and selective N-alkylation with methanol, ethanol, and 2-propanol as alkylating agents [39-44]. However, the basicity of alkaline exchanged zeolites is rather low. 

Aldols derived from propargylic aldehydes are also versatile synthetic intermediates. The anti-selective condensation is changed to a yn-selective when the hexacar-bonyldicobalt-complexed acceptors are used. ... 

In 1968, Rowlands et al. (27A102) published an extension of their previous work in which the reaction of cigarette smoke condensate (CSC) with hemoglobin was studied in more detail. In addition, the electron transfer properties of the smoke condensate were studied. The involvement of the oxides of nitrogen in the free radical properties of the smoke was suggested by a selective condensation experiment in which the smoke was fractionated at various temperatures and the various condensates reacted with hemoglobin. 

A different approach to a-methylenebutyrolactones is a further development of the chemistry of 2-silyloxycyclopropane carboxylates (393), which, when treated with the trifluoromethanesulphonate analogue of Eschenmoser s salt and a Lewis acid (TMSOTf), are converted into 8-amino-esters (394) and thence lactones (395) following borohydride reduction and elimination.33 Overall yields are reasonable for this multi-step approach. A carbanion based approach to monosubstituted lactones. (390) begins by metallation and regio-selective condensation of ketene dithioacetal (396) with an aldehyde. 

Noble gases collected from air or water (see Section 3.6.1) may be separated from each other in the carrier gas by selective condensation on sorption media, followed by selective volatilization at temperatures near their boiling points of the separated gases (see Section 15.4.2). Radon can be sorbed from air or water and... 

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