Preferential removal

Formate is an excellent hydride source for the hydrogenolysis of aryl halides[682]. Ammonium or triethylammonium formate[683] and sodium formate are mostly used[684,685]. Dechlorination of the chloroarene 806 is carried out with ammonium formate using Pd charcoal as a catalyst[686]. By the treatment of 2,4,6-trichloroamline with formate, the chlorine atom at the /iiara-position is preferentially removed[687]. The dehalogenation of 2,4-diha-loestrogene is achieved with formic acid, KI, and ascorbic acid[688]. 

Effusion separator (or effusion enricher). An interface in which carrier gas is preferentially removed from the gas entering the mass spectrometer by effusive flow (e.g., through a porous tube or through a slit). This flow is usually molecular flow, such that the mean free path is much greater than the largest dimension of a traverse section of the channel. The flow characteristics are determined by collisions of the gas molecules with surfaces flow effects from molecular collisions are insignificant. 

Jet separator. An interface in which carrier gas is preferentially removed by diffusion out of a gas jet flowing from a nozzle. Jet separator, jet-orifice separator, jet enricher, and jet orifice are synonymous terms. 

Adsorption Processes. Adsorption represents the second and newer method for separating and producing high purity PX. In this process, adsorbents such as molecular sieves are used to produce high purity PX by preferentially removing PX from mixed xylene streams. Separation is accomphshed by exploiting the differences in affinity of the adsorbent for PX, relative to the other Cg isomers. The adsorbed PX is subsequendy removed... 

Preferential Removal of Crystals. Crystal size distributions produced ia a perfectiy mixed continuous crystallizer are highly constraiaed the form of the CSD ia such systems is determined entirely by the residence time distribution of a perfectly mixed crystallizer. Greater flexibiUty can be obtained through iatroduction of selective removal devices that alter the residence time distribution of materials flowing from the crystallizer. The... 

The model of the ciystallizei and selective removal devices that led to equations 64—66 is referred to as the R-Z crystallizer. It is an obvious idealization of actual crystallizers because of the perfect cuts assumed at and However, it is a useful approximation to many systems and it allows quahtative analyses of complex operations. The R-Z model may also be representative of inadvertant classification, ie, fines or course crystals may be preferentially removed from a crystallizer without installation of specific hardware to accomphsh such an objective. 

A number of excellent studies have used a variety of radiolabeled sods to iavestigate the removal of small amounts of colorless sods such as ods (102—104). By proper use of different radiolabels (such as and " C), the preferential removal of various components ia a sod mixture can be followed. In these cases ia particular, detergency can also be calculated from measurements of the amount of radioactivity that is removed from the fabric and is found ia the wash Hquor. 

In the thiophene and selenophene series, a-halogens are preferentially removed by reduction with zinc and acetic acid, as is illustrated by the preparation of 3-bromothiophene... 

For manganese which has a vapour pressure of 4.57 x 10 atmos at 1873 K, this depletion amounts to about one half of the bulk concentration, thus lowering the rate of manganese evaporation by half. These equations may be used to derive tire condition for the preferential removal of a solute. A, from liquid iron... 

The direction of elimination is also affected by steric effects, and if both the base and die reactant are highly branched, steric factors may lead to preferential removal of the less hindered hydrogen. Thus, when 4-methyl-2-pentyl iodide reacts with very hindered bases such as potassium tricyclohexylmethoxide, there is preferential formation of the... 

One feature of this process is that at low pressures DIPA will preferentially remove H2S. As pressure increases the selectivity of the proee s decreases. The DIPA removes increasing amounts of COt as well as the HiS. Therefore, this system can be used either selectively to remove ff-S or to remove both COt and H S. 

In a similar vein, acylation of the corticoid 50 with furoyl chloride gives the diacyl derivative 51. Reduction with sodium borohydride serves to convert the 11-ketone to the alcohol 52. Hydrolysis under mild acid conditions preferentially removes the acyl group at the less hindered 21 position. The hydroxyl group in that derivative (53) is then converted to the mesylate 54. Replacement by chlorine affords mometasone (55) [12]. 

In contrast chemical and electrolytic polishing enables a smooth level surface to be produced without any residual stress being developed in the surface because the surface is removed by dissolution at relatively low chemical potential and at relatively low rates is such a way that metallic surface asperities are preferentially removed. For this to be most effective the solution properties must be optimised and the pretreatment must leave an essentially bare metal surface for attack by the electrolyte. 

The electronegative O atoms of the carboxylic acid group withdraw electrons from the whole ring, thereby reducing its overall electron density. Moreover, resonance preferentially removes electrons from the ortho and para positions. To focus on the essentials, only the lone pairs of electrons involved in resonance are shown ... 

It now appears that both the extreme magnitude and geographic limitations of the Antarctic ozone depletion are due to meteorologic patterns peculiar to the South Polar regions. The large decrease beyond the small reduction in the rest of the stratosphere apparently involves the circulation of the polar vortex, a complex interaction of Cl with oxides of nitrogen, their physical trapping in extremely cold (T < — 80°C) clouds and preferential removal of some species by precipitation. 

C to 800°C), the decrease of nitrogen content is frequently accompanied with the degradation of the film. In this process, nitrogen atoms bonded to sp hybridized carbon are preferentially removed and those bonded to sp hybridized carbon are relatively stable, resulting in the graphi-tization of the film [64-67]. 

Ra. Exceptions to this are environments where Rn is lost from the system by degassing (e.g., see Condomines et al. 2003), or aqueous systems where the insoluble nature of °Pb leads to its preferential removal. The speciation of Pb in natural waters is rather complex and heavily depends on the availability of organic complexing agents for which Pb has the highest affinity. In the oceans, Pb has a very short residence (30-150 yrs) and is rapidly scavenged by particles. 

Scheme 9.28). Despite the modest enantioselectivity, we knew from our previous work that upgrade of enantiomeric purity was possible via preferential removal of the less soluble racemic material by crystallization. In this manner, after a carbon treatment to achieve acceptable levels of residual rhodium, racemic 1 was removed by partial crystallization, followed by subsequent isolation of 1 as a crystalline solid in 72% yield from 22, and in 98.5% ee. 

A close examination of the data in Figure 1 and Table I leads to two interesting observations. First, as the amount of chlorine (Cl) removed was increased, the ratio of racemic (r) to meso (m) W diads increased, and second the disappearance of W diads was greater than anticipated for the random removal of Cl s. Consequently, we concluded from the (n-Bu)3SnH reduction of PVC to E-V copolymers and eventually to PE, that Cl s belonging to W diads are preferentially removed relative to isolated Cl s (EVE) and that m-W diads are reduced faster than r-W diads. 

---