Alternative methods important considerations

An alternative to the rotating disk method in a quiescent fluid is a stationary disk placed in a rotating fluid. This method, like the rotating disk, is based on fluid mechanics principles and has been studied using benzoic acid dissolving into water [30], Khoury et al. [31] applied the stationary disk method to the study of the mass transport of steroids into dilute polymer solutions. Since this method assumes that the rotating fluid near the disk obeys solid body rotation, the stirring device and the distance of the stirrer from the disk become important considerations when it is used. A similar device was developed by Braun and Parrott [32], who used stationary spherical tablets in a stirred liquid to study the effect of various parameters on the mass transport of benzoic acid. 

See Section IV.1 for alternative methods of chiral resolution. Partial chemical hydrolysis of proteins and peptides with hot 6 M HC1, followed by enzymatic hydrolysis with pronase, leucine aminopeptidase and peptidyl D-amino acid hydrolase, avoids racemiza-tion of the amino acids281. The problems arising from optical rotation measurements of chiral purity were reviewed. Important considerations are the nonideal dependence of optical rotation on concentration and the effect of chiral impurities282. 

The use of chiral auxiliaries has traditionally been in the academic and small-scale synthetic arenas. This, in part, has been a result of the infancy of chiral auxiliaries themselves in organic synthesis. Many of these chiral substrates have been developed only in the last 10-20 years, and their synthetic utility is only now being realized. Additionally, many chiral auxiliaries are difficult to prepare and handle at large scale. Only recently has their been considerable effort to produce large quantities of the auxiliaries. Another important consideration is the cost of the auxiliary compared to alternate methods, such as resolution. The experimental reaction conditions for some of the more common chiral auxiliaries often call for specialized equipment, extreme temperature conditions, or both. These factors, to date, have combined to limit the use of chiral auxiliaries on an industrial scale. 

Addition of a filler such as AKO s an alternate method to reduce creep. As shown in Table 3 this filler also increases mechanical strength as well as lowering the coefficient of thermal expansion. The latter aspect can be an important consideration when trying to match material coefficients of expansion in an encapsulating situation. It should also be noted that volume resistivity measurements of unfilled material (see Table 3) indicate these formulations provide satisfactory electrical insulation for encapsulating purposes. 

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