SECTION 5 Organic Reactions

In 1983, the Rare Earth Society of Japan published a literature guide to the organic chemistry of rare earth elements that included the section Organic Reactions and Syntheses by Using Rare Earth Elements as Reagents and Catalysts (Uemura, 1983). Covering more than 60 years of research, this compilation is notable for several reasons ... 

In this section, the basic concepts of reaction retrieval are explained. The first example is concerned with finding an efficient way to reduce a 3-methy]cydohex-2-cnonc derivative to the corresponding 3-mcthylcyclohcx-2-cnol compound (see Figure 5-24). As this is a conventional organic reaction, the CIRX database should contain valuable information on how to syntbesi2e this product easily. 

In this way the student s knowledge of the organic reactions is consolidated as he proceeds through the sections, his experience of the general method of identification steadily increases, and the investigation of the unknown compounds forms a welcome break from the systematic pursuit of the sectional work. 

The exchange resins 6nd application in (i) the purification of water (cation-exchange resin to remove salts, followed by anion-exchange resin to remove free mineral acids and carbonic acid), (ii) removal of inorganic impurities from organic substances, (iii) in the partial separation of amino acids, and (iv) as catalysts in organic reactions (e.g., esterification. Section 111,102, and cyanoethylation. Section VI,22). 

Several Pd(0) complexes are effective catalysts of a variety of reactions, and these catalytic reactions are particularly useful because they are catalytic without adding other oxidants and proceed with catalytic amounts of expensive Pd compounds. These reactions are treated in this chapter. Among many substrates used for the catalytic reactions, organic halides and allylic esters are two of the most widely used, and they undergo facile oxidative additions to Pd(0) to form complexes which have o-Pd—C bonds. These intermediate complexes undergo several different transformations. Regeneration of Pd(0) species in the final step makes the reaction catalytic. These reactions of organic halides except allylic halides are treated in Section 1 and the reactions of various allylic compounds are surveyed in Section 2. Catalytic reactions of dienes, alkynes. and alkenes are treated in other sections. These reactions offer unique methods for carbon-carbon bond formation, which are impossible by other means. 

Most of these theoretical aspects are discussed in the following sections, pointing out the particuliar suitability of the very dissymmetrical molecular frame of thiazole for quantitative study, on the same species, of a large variety of fundamental organic reactions. 

Section 16 7 Dialkyl ethers are useful solvents for organic reactions but must be used cautiously due to their tendency to form explosive hydroperoxides by air oxidation in opened bottles... 

The conversion of alcohols to esters by O-acylation and of amines to amides by N-acylation are fundamental organic reactions. These reactions are the reverse of the hydrolytic procedures discussed in the preceding sections. Section 3.4 in Part B discusses these reactions from the point of view of synthetic applications and methods. 

Electrophilic aromatic substitution reactions are important for synthetic purposes and also are one of the most thoroughly studied classes of organic reactions from a mechanistic point of view. The synthetic aspects of these reactions are discussed in Chapter 11 of Part B. The discussion here will emphasize the mechanisms of several of the most completely studied reactions. These mechanistic ideas are the foundation for the structure-reactivity relationships in aromatic electrophilic substitution which will be discussed in Section 10.2... 

Most of the free-radical mechanisms discussed thus far have involved some combination of homolytic bond dissociation, atom abstraction, and addition steps. In this section, we will discuss reactions that include discrete electron-transfer steps. Addition to or removal of one electron fi om a diamagnetic organic molecule generates a radical. Organic reactions that involve electron-transfer steps are often mediated by transition-metal ions. Many transition-metal ions have two or more relatively stable oxidation states differing by one electron. Transition-metal ions therefore firequently participate in electron-transfer processes. 

The second use of activation parameters is as criteria for mechanistic interpretation. In this application the activation parameters of a single reaction are, by themselves, of little use such quantities acquire meaning primarily by comparison with other values. Thus, the trend of activation parameters in a reaction series may be suggestive. For example, many linear correlations have been reported between AT/ and A5 within a reaction series such behavior is called an isokinetic relationship, and its significance is discussed in Chapter 7. In Section 5.3 we commented on the use of AS to determine the molecularity of a reaction. Carpenter has described examples of mechanistic deductions from activation parameters of organic reactions. 

One needs to interpret product data from preparative organic reactions with a great deal of reservation (cf. Section III,B,1 and... 

Activation energy (Section 5.9) The difference in energy between ground state and transition state In a reaction. The amount of activation energy determines the rate at which the reaction proceeds. Most organic reactions have activation energies of 40-100 kj/mol. 

Chapter 5, An Overview of Organic Reactions—A new Section 5.11 comparing biological reactions and laboratory reactions has been added. 

Volume 6 Volume 7 Reactions of Non-metallic Inorganic Compounds Reactions of Metallic Salts and Complexes, and Organometallic Compounds Section 4. ORGANIC REACTIONS (6 volumes)... 

Among the organic reactions that have been investigated in aqueous medium, the Diels-Alder cycloaddition has been the most studied owing to its great importance from the synthetic and theoretical point of view [7a, bj. In this section Diels-Alder reactions carried out in water under conventional conditions of temperature and pressure will be illustrated. The use of water at supercritical or near-supercritical conditions will be discussed in Section 6.4. 

A part of the chemical consequences of the cyclic orbital interactions in the cyclic conjngation is well known as the Hueckel rule for aromaticity and the Woodward-Hoffmann rule for the stereoselection of organic reactions [14]. In this section, we describe the basis for the rnles very briefly and other rules derived from or related to the orbital phase theory. The rules include kinetic stability (electron-donating and accepting abilities) of cyclic conjugate molecules (Sect. 2.2.2) and discontinnity of cyclic conjngation or inapplicability of the Hueckel rule to a certain class of conjngate molecnles (Sect. 2.2.3). Further applications are described in Sect. 4. 

In this section, redox reactions between NADH in an aqueous solution (W) and Q in an organic solution (O) at the W/O interface are investigated as a function of potential differences between W and O, w/o- The ion transfer at the W/O interface coupled with the redox reaction is also discussed. 

I. Fleming in Frontier Molecular Orbitals and Organic Reactions , Wiley, Chichester, 1978, ch. 6, section 6.3.1-6.3.3. 

A list of examples in this section is not exhaustive rather, they have been chosen to illustrate the different approaches used for immobilization of the catalysts for important classes of organic reactions, namely hydrogenation, oxidation, and coupling reactions. Due to the major industrial importance of olefin polymerization (see Chapter 9.1), and although the objectives of immobilization of polymerization catalysts are rather different from the other examples, some references to this will also be given here. 

Although the discussion to this point has been concerned with the explanation of the behavior of Bronsted acids as catalysts, there is an enormous range of reactions in which catalysis by acids and bases occurs. Many of the important types of organic reactions involve catalysis by acids or bases. In this section, several reactions will be mentioned, but the mechanistic details will not be presented in this book on inorganic chemistry. The discussion is intended to show the scope of catalysis by acids and bases. 

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