Expense in preparation

The expense in preparation derives from the need for high purity products. The cost in fabricating three-dimensional shapes of SiC, SijN or BN arises from the need to sinter powders of these materials at high temperatures (>1500°C) and often under high pressure. Coatings of these materials are at present produced by chemical or... 

If the organization pleaded guilty before the prosecution was put to substantial effort or expense in preparing for trial and cooperated with the prosecution in all relevant respects except by failing to disclose the names and... 

Although Pd is cheaper than Rh and Pt, it is still expensive. In Pd(0)- or Pd(ll)-catalyzed reactions, particularly in commercial processes, repeated use of Pd catalysts is required. When the products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example. For less volatile products, there are several approaches to the economical uses of Pd catalysts. As one method, an alkyldi-phenylphosphine 9, in which the alkyl group is a polyethylene chain, is prepared as shown. The Pd complex of this phosphine has low solubility in some organic solvents such as toluene at room temperature, and is soluble at higher temperature[28]. Pd(0)-catalyzed reactions such as an allylation reaction of nucleophiles using this complex as a catalyst proceed smoothly at higher temperatures. After the reaction, the Pd complex precipitates and is recovered when the reaction mixture is cooled. 

Cellulose esters of aromatic acids, aUphatic acids containing more than four carbon atoms and aUphatic diacids are difficult and expensive to prepare because of the poor reactivity of the corresponding anhydrides with cellulose Httle commercial interest has been shown in these esters. Of notable exception, however, is the recent interest in the mixed esters of cellulose succinates, prepared by the sodium acetate catalyzed reaction of cellulose with succinic anhydride. The additional expense incurred in manufacturing succinate esters is compensated by the improved film properties observed in waterborne coatings (5). 

To prepare for teaching, Carothers was ordered to enroll at his own expense in summer school at the University of Chicago. The experience was an eye-opener and contributed to Carothers disenchantment with Tarkio. 

In our case, the prime robbery was a national program of aggrandizement at the expense of the peoples of other nations. As for the defendants part, was it necessary to show that they knew with absolute certainty that the weapon would be fired If it was proved that they had participated substantially in preparing the weapon, and that they knew it would be used in the holdup as a threat, was that not enough to prove their guilt as participants in the resulting crimes ... 

Reduction is an important method for polymer modification resulting in a variety of useful elastomers and thermoplastics with unique structures and properties. Reduction also offers a convenient synthetic route to polymers with special monomer sequences, which are inaccessible, difficult or too expensive to prepare by conventional polymerization... 

We have seen that isotope effects on the properties of atoms and molecules are usually small, and this is true for all except the lightest elements. Consequently separation of single isotopes from mixtures of isotopes or isotopomers is tedious and difficult. The difficulty is compounded by the fact that the desired isotope is often present at low or very low concentration in the starting material (normally a naturally occurring fluid, ore, or mineral). Even so, the nuclear properties of certain separated isotopes are enough different from their sisters to justify the (usually enormous) expense of preparing isotopically pure or nearly pure materials. Three important examples follow ... 

The so-called Weinreb amides (or Af-methoxy-A-methylamides) are versatile building blocks in organic synthesis . Their preparation can be accomplished by coupling carboxylic acids and Af,0-dimethylhydroxylamme. The majority of the methods reported use peptide coupling reagents such as chloroformates , BOP , DCC and others "" or phosphonic derivatives ". These reactive reagents are expensive in some cases, and the removal of their excess (and/or the removal of byproducts) from the reaction mixtures may be difficult. Additional purification of the reaction product is often required. 

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