Synthesis technique

In order to begin practicing synthesis problems, it is absolutely essential that you master all of the individual reactions that we have seen so far. You must learn how to walk before you can start to run. Therefore, we will first focus on one-step synthesis problems. Once you feel comfortable with the individual reactions, then we can start stringing them together in various sequences to form synthesis problems. 

Until now, we have seen substitution reactions (SnI and Sn2), elimination reactions (El and E2), and five addition reactions. Let s quickly review what these reactions can accomplish. Substitution allows us to interconvert groups  

Addition reactions allow us to add two groups across a double bond. So far, we have seen the following five addition reactions  

Can you fill in the reagents necessary to accomplish each of these five transformations Try it.. . .  

EXERCISE 11.70 What reagents would you use to accomplish the following transformation  

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Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

D. Miller, J. H. Adair, W. Huebner, and R. E. Newnham, "A Comparative Assessment of Chemical Synthesis Techniques for Barium Titanate," Paper, 88th Annual Meeting of the American Ceramic Society, Pittsburgh, Pa., April 27—30, 1987. 

Heuristic. The heuristic approach is another early synthesis technique based on the appHcation of sets of rules to lead to a specific objective such as network cost. Unfortunately, heuristics caimot guarantee that the objective will be reached although they generally offer quick solutions. 

The eadiest use of heat-exchange network synthesis was in the analysis of cmde distillation (qv) units (1). The cmde stream entering a distillation unit is a convenient single stream to heat while the various side draws from the column are candidate streams to be cooled in a network. So-called pumparounds present additional opportunities for heating the cmde. The successful synthesis of cmde distillation units was accompHshed long before the development of modem network-synthesis techniques. However, the techniques now available ensure rapid and accurate development of good cmde unit heat-exchange networks. 

Nonpowder Synthesis. Many ceramic composites (qv) under iavestigation utilize reinforcing ceramic whiskers or fibers to achieve toughening (19). Whiskers (17,19,20) are produced by vapor-synthesis techniques. SiC whiskers can be produced by the rice hull or vapor—soHd (VS) method whereby rice hulls are pyrolyzed to produce a mixture of carbon, C, and Si02, and whiskers are produced by directional growth by vapor... 

Much of this chemistry is still at an early stage of research, and there are few, if any, commercial applications. However, the potential environmental and safety benefits of these and other innovative chemical synthesis techniques will encourage further research and development. 

In Chapters Three, Five, and Six, the MEN-synthesis techniques dealt with cases where the separation task was defined as part of the design task. Streams to be... 

Heretofore, the presented MEN/REAMEN synthesis techniques were applicable to the cases where mass-exchange temperatures are known ahead of the synthesis task. Mass-exchange equilibrium relations are dependent upon temperature and the selection of optimal mass-exchange temperatures is an important element of design. In selecting these temperatures, there is a tradeoff between cost of MSAs and cost of heating/cooling utilities. 

M. Ryle and A, Hewish (Cambridge) pioneering research in radioastrophysics Ryle for his observations and inventions, in particular of the aperture-synthesis technique, and Hewish for his decisive role in the discovery of pulsars. 

Both the metal-atom and matrix techniques have many applications (91) in the study of complexes having such classical, inorganic ligands as CO, N2, O2, or phosphines. From a metal-atom point of view, novel complexes have been synthesized that have not been readily accessible via normal, chemical-synthesis techniques. The entrapment of such species permits both a rationalization of their spectroscopic and chemical properties and an evaluation of their stability. 

Not only the preparation of so far unknown compounds, but also the development of new synthesis techniques such as the Schlenk technique and vacuum-line technique which allow the handling and manipulation of air- and moisture-sensitive, pyrophoric compounds, are the most striking breakthroughs of their fascinating work. 

We examined several approaches for synthesizing polyanhydrides, including melt polycondensation, dehydrochlorination, and dehydrative coupling. Extensive details of these new polymer synthesis techniques and numerous polymerization conditions for a wide variety of polyanhydrides were previously described (1). 

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