Stille method

If the sample is an insulator there are still methods by which it can be studied in the instrument. The simplest approach is to coat it with a thin (10-nm) conducting film of carbon, gold, or some other metal. In following this approach, care must be taken to avoid artifacts and distortions that could be produced by nonuniform coatings or by agglomeration of the coating material. If an X-ray analysis is to be... 

Needless to mention, the exact capturing of time presents further challenges in the analysis. Fundamentally, a decision has to be made on how the time horizon has to be represented. Early methods relied on even discretization of the time horizon (Kondili et al., 1993), although there are still methods published to date that still employ this concept. The first drawback of even time discretization is that it inherently results in a very large number of binary variables, particularly when the granularity of the problem is too small compared to the time horizon of interest. The second drawback is that accurate representation of time might necessitate even smaller time intervals with more binary variables. Even discretization of time is depicted in Fig. 1.8a. 

The next phase focused on the goal of elaboration of the side chain in the desired sense. The primary alcohol function at C7 was unveiled by hydrogenolysis (Pd(OH)2/EtOAc-MeOH). Oxidation of the resultant compound 13 with chromic oxide pyridine afforded aldehyde 14, which was now to be elongated through some variation of a Homer-Emmons type of reaction. Shortly before tiiese investigations were launched. Still had demonstrated the use of phosphonate 15 as a device to achieve the two-carbon extension of an aldehyde to a Z-enoate (12). Happily, application of the Still method to compound 14 afforded the desired 16, mp 120-121° C, in 80% yield as a 20 1 mixture of Z E enoates. 

This protocol and the Pd-Cu-catalyzed direct cross-coupling with terminal acetylenes (Section 5.3.5) directly complement each other. The following examples, which cannot be applied to the latter, give normal coupling products only by Stille method [Eqs. 17-20] [28-31]. This method is especially useful for the cross-coupling reactions of organometallic complexes with cyclopentadienyl ligand that are sensitive to amines [Eq. 19] [30]. 

Later still, methods were discovered by which cellulose could be dissolved unchanged, and then reprecipitated as fiber or film by subsequent chemical treatment. This process yields viscose rayon fiber and cellophane film from the reconstituted cellulose and is still in use. These are much more useful products than were available from the early acetate rayon. 

The dynamic still method of obtaining vapor-liquid equilibrium data has several disadvantages. First, it is a slow and tedious process. Second, the compositions of the vapor and liquid must be analyzed (usually by gas chromatography), which is less precise and direct than measuring temperature, pressure, or weight. Consequently, alternative methods of measuring partial vapor-liquid equilibrium data have been developed that do not require chemical analysis.. ... 

The 2,5 -isomer (73) has been prepared by a Hantzsch synthesis (Scheme 28), by decarboxylation of the 5-carboxylic acid (50HCA1960), and by the Stille method (87S185). The 2-chloro derivative is also a minor byproduct in the diazotization of 2-aminothiazole [95 AX(C)72], whereas trisubstituted derivatives have been reported to be formed, in high yield, from reactions of a-haloketones with A,A -dimethyl-2,4-dithiobiuret (77CL1299). 

In principle it is necessary to measure only p and x ot p and y with the equilibrium still method. However, because of the practical difficulties in checking the correct operation of a still, it is advisable to measure p, x, and y as the results can then be checked by applying one of the various tests previously described. 

The reflectivity at stratified planar structures becomes more complicated if thin film structures are present. Still methods are available to make a straightforward calculation of the reflectivity. For thin film structures, a matrix method has been developed that still gives an analytical solution for the calculated reflectance (Azzam and Bashara 1977 Jackson 1998). 

Total alkaloids in tobacco are commonly determined spectrophotometrically. The Griffith Still Method (Griffith 1957) utilizes a steam distillation apparatus based on that of Willits et al. (1950) absorbance is measured at 236, 259, and 282 nm. Automated methods such as those of Harvey et al. (1969) and Davis (1976) are more commonly used today. Pyridyl moieties react with cyanogen bromide and aniline to form a chromophore measurable at 460 nm. 

Table 9.1 is a quick reference to the large number of side-chain functionalized PTs that have been synthesized to date. All of these have been covered throughout the chapter. The primary methods of synthesis used have been designated as Method A (McCullough), Method B (Rieke), Method C (GRIM), Method D (Stille), Method E (FeCl3), and Method F (derivatization). Please refer to the previous section for the general schemes of these synthesizes. 

Method A (McCullough), Method B (RIeke), Method C (GRIM), Method D (Stille), Method E (FeCIs), Method F (Suzuki) Method C (post-functionallzation) Method H (Ullmann). 

---