Substitutions, for unavailable

The peroxide was substituted for (unavailable) potassium permanganate in a process for purifying the crude anhydride in an open vessel. After several operations, when only minor explosions occurred, a violent explosion and fire occurred. Acetyl peroxide would be produced. 

The dialkene 1,3-butadiene is widely used in the manufacture of polymers, particularly synthetic rubber. The first synthetic rubber to be manufactured on a large scale and used as a substitute for unavailable natural rubber during World War II was a styrene-butadiene polymer ... 

Ytterbium metal has possible use in improving the grain refinement, strength, and other mechanical properties of stainless steel. One isotope is reported to have been used as a radiation source substitute for a portable X-ray machine where electricity is unavailable. Few other uses have been found. 

RCHO to a ketone RCOR (for other methods, see 10-71, 16-82, and 18-9). In this procedure the normal mode of reaction of a carbonyl carbon is reversed. The C atom of an aldehyde molecule is normally electrophilic and is attacked by nucleophiles (Chapter 16), but by conversion to the protected cyanohydrin this carbon atom has been induced to perform as a nucleophile. The German word Umpolung is used to describe this kind of reversal (another example is found in 10-71). Since the ion 166 serves as a substitute for the unavailable R— C=0 anion, it is often called a masked R( C=0) ion. This method fads for formaldehyde (R = H), but other masked formaldehydes have proved successful. In an interesting variation of nitrile alkylation, a quaternary bromide [PhC(Br)(Me)CN] reacted with allyl bromide, in the presence of a Grignard reagent, to give the alkylated product [PhC(CN)(Me)CH2CH=CH2]. ... 

Chromium in soils potentially occurs in the +3 (chromic) oxidation state as the Cr " cation, and in the -f 6 oxidation state as chromate, Cr04 . However, soil conditions generally favor the Cr form, a very immobile cation that complexes strongly with organic matter and chemisorbs on oxides and silicate clays, even at quite low pH. Furthermore, Cr readily substitutes for Fe in mineral structures, and precipitates as insoluble Cr(OH)3 at higher pH. The chromic form is, therefore, very immobile in most soils and generally unavailable to plants, at least if the soil is not exceedingly acid. 

There is a pending rulemaking to require certain classes of polymers with perfluorinated units—polymers in which fluorine atoms are substituted for the hydrogen atoms that are present in many polymers—to go through the PMN process. The proposed rule would make the polymer exemption unavailable for these polymers because, as the EPA explained in its proposed rule, the EPA could not assume that all such polymers are risk-free. The EPA cited liver, developmental, and reproductive toxicity at very low exposure levels as well as data that indicates that some perfluorinated polymers maybe carcinogens. These generalizations have been criticized by the chemical industry. ... 

Several clay minerals, above all vermiculite and illite, have crystal lattices whose individual sheets are expandable. When NH4 is substituted for Ca and Mg, the two dominant interlayer cations, it becomes mineral-bound, resists both inorganic hydrolysis and bacterial attack, and becomes unavailable for rapid recycling. Little binding takes place where kaolinite is dominant, but in nonkaolinite soils the unavailable NH4+ accounts for up to 8% of all N in the near-surface layer, and to 45 % of subsoil N. Actual amount of mineral-bound N thus ranges from just a few kilograms to more than 1 t/ha see Stevenson, F. J. 1986. Cycles of Soil. New York Wiley-Interscience, pp. 199-202. 

The house drink, the Belladonna, which was named for Ms. Arpaia, was unavailable because the kitchen had not sent out the ginger-orange puree required. And the Blue Moon, based on a fresh blueberry puree, which is another of the chef s touches meant to distinguish the cocktails, was being served with a commercial substitute and garnished with a raspberry. 

The mechanism of substitution on an electron-rich benzene ring is electrophilic substitution, electrophilic attack on an atom and the replacement of one atom by another or by a group of atoms. The fact that substitution occurs rather than addition to the double bonds can be traced to the stability of the delocalized 7T-electrons in the ring. Delocalization gives the electrons such low energy—that is, they are bound so tightly—that they are unavailable for forming new cr-bonds (see Sections 2.7 and 3.12). 

In view of these potentials for major reductions in preservative efficacy, considerable effort has gone into attempts to devise equations in which one might substitute variously derived system parameters such as partition coefficients, surfactant and polymer binding constants and oil water ratios in order to obtain estimates of residual preservative levels in aqueous phases. Although some modestly successful predictions have been obtained for very simple laboratory systems, they have proved of limited practical value as data for many of the required parameters are unavailable for technical grade ingredients or for the more complex commercial systems. 

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