Stoichiometric chemistry

Apart from new catalytic methods, cascade conversions require new process technologies, such as in situ product recovery, reactor design, and compartmental-ization. In the long term, part of the present-day stoichiometric chemistry as well as bio- and chemocatalytic conversions in multi-step syntheses will gradually be replaced by cascade catalysis in concert, and full fermentations by cell factory design, or combinations thereof (Fig. 13.17). 

Oxidative addition of organic halides to low-valent metal complexes generates reactive metal alkyls that can then be used in insertion, coupling, carbonylation-decar-bonylation and cyclization reactions for organic synthesis. These transformations can be made catalytic after development of the stoichiometric chemistry using the more stable metal alkyls. This section surveys the reactions of alkyl, aryl and acyl halides with transition metal complexes of the groups IIIA (lanthanides and actinides), IVA-VIII and IB. 

The exact mechanisms (a series intermediate reactions or steps) of oscillating reactions are elusive and difficult to obtain for all but the simplest reactions. The chemical equations and mechanisms commonplace to stoichiometric chemistry describe only the overall reactions, they do not specify the molecular transformations that place between colliding molecules. 

Of the methacrylics, methyl methacrylate (MMA) is by far the most important intermediate, with a production of approx. 2 X 10 t/a (1.6 X 10 t/a for Europe and USA [la]). It finds its main application in polymers as Plexiglass or Perspex, a crystal-clear artificial glass with high hardness, resistance to fracture, and chemical stability. About 80 % of the MMA is produced on the basis of the Acetone-Cyano//ydrin (ACH) process [lb]. This process involves stoichiometric chemistry and is characterized by an overall yield of MMA of about 80 % (based on acetone) with the stoichiometric production of about 2.4 t of ammonium bisul-fate/sulfuric acid waste per ton of MMA. This process is therefore faced with increasing environmental costs. As a consequence, several alternative catalytic processes for MMA production are - and have been - under development. 

In this context, the catalytic degradation of polymers as a possible new basic feedstock for organic chemicals seems worthy of reinforced efforts [15, 57i-l]. Catalytic activation of methane and other hydrocarbons remains of central interest in catalysis research in general [54]. To this end, any stoichiometric chemistry of this molecule has a signifieance of its own. 

Catalytic (non-stoichiometric) chemistry used None Hydrogenation... 

A series of methods to accelerate arene exchange have been developed. Irradiation can lead to displacement of the arene ligand. In addition, oxidation of the metal by I is commonly used to release an arene after it has been modified by stoichiometric chemistry this oxidation generates labile 17-electron complexes such as Cr(CO)3(arene) I. Catalysis of arene substitution by reductive electron-transfer is also known, as in the case of CpFe(aiene). ... 

Then in 1824 he published his System of Stoichiometric Chemistry The Theory of Definite Proportions, followed in 1826 by his four-volume "General Pharmacopeia. Nine years later, his List of Poisons and Their Antidotes appeared (1835). 

Catalytic chemistry is increasingly being adopted over stoichiometric chemistry, where possible. 

This stoichiometric chemistry has been revisited in the last few years [60,79-82] and, for instance, applied to the s)mthesis of a-methylene-y-hydroxy carboxylic acids and their derivatives (c/s-p.y-disubstituted a-methylene-y-lactones) by means of nickel-mediated sequential addition of carbon dioxide and aldehydes into terminal or internal allenes [80, 81], or exploited for the preparation of P-hydroxycarboxylic acid derivatives by 02-oxidation of the Ni-n -allyl species (5.8)... 

Described in this chapter is the stoichiometric chemistry of complexes in which a titanocene or zirconocene moiety is ri -bound to an alkene, alkyne, heteroalkene, or heteroalkyne. These complexes may be viewed as a metal-... 

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