Extended additions

The synthetic scheme typically involves chain-extending addition of protected mononucleotides to a nucleoside bound covalentiy at the 3 -hydroxyl to an inert siUca-based soHd support, such as controlled pore glass (Fig. 11). The initial base-protected 5 -O-dimethoxytrityl (DMT) deoxynucleoside is linked to the soHd support via the reaction of a siUca-bound amino-silane and the -nitrophenylester of the 3 -succinylated nucleoside, yielding a 3 -terminal nucleoside attached to the soHd support (1) (Fig. 11). Chain elongation requites the removal of the 5 -DMT protecting group. 

For comparison, a conventional resol resin adhesive without lignin was prepared (24), and its gluability was examined. This resin was found to require a hot-pressing rate of at least 1.5 min per 1 mm plywood thickness before a satisfactory wet-bond adhesion strength was achieved at the low hot-pressing temperature of 120°C. This indicates that replacing a part of the phenol with lignin does not imply a mere extender addition, but that a positive role is achieved which enhances the reactivity of the adhesive. 

Fluorocarbon extender additive for water-repellent finishes. PROTE-SOIL 397 ... 

The zeolite-carbon adsorbents from mineral-carbon adsorbents group are novel and exhibit not quite well recognized properties with their unique, modified porous structure. The characteristic structures for zeolite, active carbon and intermediate structure exist in these materials. Such a structure results fi-om the modification of a surface of a mineral matrix by depositing carbon material. The efifectivity of enrichment of the structure of zeolite-carbon adsorbents (in relation to crystalline zeolite structure) in hydrophobic micropores (0.4 - 2 nm) and macropores (above 50 nm) is proportional to the fi action of carbon phase. Such combination of hydrophilic properties of mineral phase and hydrophobic properties of organic phase results in various sorptive properties of the material and the range of their application can be consequently extended. Additionally, the chemical resistance of these adsorbents for their exploitation in aggressive conditions takes place. 

Other factors should be considered when minimizing solvent charges. More concentrated reactions often mean shorter reaction times. However, too highly concentrated reactions can make stirring difficult, and lead to side reactions due to poor mixing and poor heat transfer. With more concentrated reactions there is less solvent available to help dissipate any exothermic reactions, making temperature control more difficult and extending addition times. 

FIGURE 5.10. Formation of an impurity in the chlorination of 27 with extended addition of POCl3. Reprinted with permission from Org. Process Res. Dev. 1997, 1,310. Copyright 1997 American... 

FIGURE 5.13. Minimizing polymerization of olefins through extended additions... 

An extended addition increases the effective mole ratio of reaction components, which can have a beneficial impact on reaction selectivity. This is particularly true for reactions using catalysts. In the dihydroxylations in Figure 8.7, olefin 13 was added over 6 hours in order to ensure high enantiomeric purity of the product [6], Excess olefin, which accumulates if the addition rate is faster than the reaction rate, is thought to coordinate with the catalyst in a fashion that leads to non-enantioselective dihydroxylation [6]. In the osmium-mediated dihydroxylation of... 

Extended additions effectively provide reaction conditions with greater concentrations of catalyst and can be important for reliable scale-up (see Figure 8.7). The mental concept of taking a snapshot can be useful in predicting the effect of an extended addition. In the asymmetric reduction of ketones using chiral... 

Continuous processes have recently been described in two patents for the preparation of cyclopropylamine, 10, (Figure 13.11), an intermediate for both the pharmaceutical and agricultural industries. In the earlier patent a two-reactor train was used in a CSTR approach [20]. To the first flask were charged simultaneously a solution of 8 in H20 and an aqueous solution of NaOCl.The overflow from this reactor was collected in a second reactor which was charged with 45% aqueous NaOH at temperatures below 30 °C. The extended addition allowed for temperature control of the very exothermic hydrolysis and decarboxylation. Subsequently the basic mixture was transferred to a distillation apparatus, and 10 was isolated by distillation in yields as high as 96%. 

Solvent occlusion is shown to be directly related to the ratio of nucleation rate over crystal growth rate. To minimize the occlusion, fine seed, extended addition time, and better mixing were found to be effective. 

Extend addition time until no further increase in mean particle size occurs (Chapters 9 and 10). 

Such final block copolymer products are described and used as compatibilised chain extender additives for the modification of melt viscosity of polyamides during compounding by reactive extmsion [10] (Fig. 6). 

There has been only one significant effort published so far to extend additivity to the level of component additivity, and it is worth examining in some detail. In their 1986 detailed survey of thermochemical data of organic compounds, Pedley, Naylor and Kirbydeveloped an elaborate scheme of component additivity relationships. In order to calculate enthalpies for the 64 linear alkanes for which experimental data were available, they found that they needed not all 65 components, but only 35. These components, with their contributions to enthalpy, are listed in Table 16. The numbers in parentheses designate the type of carbon ligand primary (1), secondary (2), tertiary (3) or quaternary (4). 

BASF AG [208] proposed glycidyl methacrylate copolymers as a chain extending additive. A particular version of this approach is Joncryl ADR 4368, a styrene-glycidyl methacrylate copolymer. This also appears to be the active ingredient in CESA-Extend , a masterbatch for chain extension of recycled polyesters jointly developed by Clariant and Johnson Polymer [181, 186]. 

A new chain-extender additive [185, 190] based on the cage-structured silanol derivative epoxycylohexyl polyhedral oligomeric silsesquioxane has been suggested to be a useful additive. 

Ecoflex, manufactured by BASF, is a random copolyester based on terephthalic acid (40-45%), adipic acid (55%), and 1,4-butanediol, plus chain-extending additives (Table 1). A modified poly(ethylene terephthalate) copolyester is manufactured by DuPont as Biomax (Table 1). 

Extended Additional functions beyond the minimal basis set are added typically more than one mathematical function is used to represent each AO, with each individual function receiving its own coefficient in the wavefunction. 

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