Synthesis of Other Compounds

Acetaldehyde is a colorless liquid with a pungent odor. It is a reactive compound with no direct use except for the synthesis of other compounds. For example, it is oxidized to acetic acid and acetic anhydride. It is a reactant in the production of 2-ethylhexanol for the synthesis of plasticizers and also in the production of pentaerithritol, a polyhydric compound used in alkyd resins. 

Paraffins react with chlorine under the influence of light, heat, or catalysts to form chlorocarhons. The chlorocarhons are important in industry because of their own properties and because of their use as chemical intermediates in the synthesis of other compounds. Today, many of the chlorocarbons are regulated by federal and state agencies to limit their use because of detrimental effects on health and the environment. 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

The (n,n excited state of a ketone has electrophilic character, similar to that associated with alkoxy radicals, and it is not surprising that these excited states readily attack carbon-carbon multiple bonds. The overall reaction that normally ensues is a cycloaddition, giving a four-membered oxygen heterocycle—an oxetane from an alkene addend (4.62), or an oxete from an alkyne addend (4.63). Some oxetanes are of interest in their own right, but many are useful intermediates in the synthesis of other compounds. 

Benzoins are useful intermediates for the synthesis of other compounds because they can be oxidized to 1,2-diones and reduced in stages to various products, depending upon the reaction conditions. The 1,2-diketone known as benzil, which is obtained by nitric acid oxidation of benzoin, undergoes a base-... 

Small carbohydrates such as glucose, fructose, and pyruvate occupy key roles in energy metabolism and supply carbon skeletons for the synthesis of other compounds. Polymers in... 

Amino acid degradation serves three purposes (1) supplying energy, (2) supplying intermediates for the synthesis of other compounds, and (3) removing harmful excesses of certain amino acids. The number of steps in each pathway is indicated by a number alongside the conversion arrow. 

It is not only fatty acids that are modified (see section on Lipids ) in parasitic flatworms, but also cholesterol obtained from the host is not only used directly as a component of membranes in F. hepatica and 5. mansoni, but it is also used as a substrate for the synthesis of other compounds such as ecdysteroids (Foster etal., 1992). 

D-Mannitol has a diverse range of industrial applications. It is a nonhydroscopic, low-calorie, noncariogenic sweetener utilized by the food industry as well as a feedstock for the synthesis of other compounds. For example, mannitol can be oxidized at the 3 or 4 position to form two molecules of glyceraldehyde or glyceric acid, which can be used as building blocks for other compounds (Heinen et al., 2001 Makkee et al., 1985 van Bekkum and Verraest, 1996). Mannitol is formed from inulin via hydrolysis followed by catalytic hydrogenation. This yields mannitol and sorbitol from which the mannitol can be readily crystallized (Fuchs, 1987). Currently mannitol is primarily synthesized from starch. 

In Chapter 9 the competing reactions are examined in more detail. Then, in Chapter 10, applications of these reactions to the preparation or synthesis of other compounds are presented. 

Carbenes and carbenoids (carbene-like reagents) are useful both for the synthesis of other compounds and for the investigation of reaction mechanisms. The carbene intermediate is generated in the presence of its target compound, so that it can react immediately, and the concentration of the carbene is always low. Reactions using carbenes are discussed in Chapter 8. 

Rhenium displays an unusual array of oxidation states and coordination numbers that make it the subject of much current research. The following preparation, adapted from one developed by Chatt and coworkers, provides a convenient synthesis of trichlorooxobis(triphenylphosphine)rhenium(V)1 based on either rhenium(VII) oxide or perrhenate salts. The trichlorooxo compound is a versatile intermediate for the synthesis of other rhenium complexes such as wer-trichlorotris(dimethylphenylphosphine)rhenium-(III),2 as described below. The rhenium(III) complex, in turn, provides a starting point for synthesis of other compounds such as frans-tetrachloro-bis(dimethylphenylphosphine)rhenium(IV)3 and tris(dimethylphenylphos-phinepentahydrido)rhenium(V).4 An alternative synthesis of the trichloro-complex is described in the accompanying preparation by Douglas and Shaw.4... 

X (Disinfection by-product) tear gas fumigant gases reagent in the synthesis of other compounds 111,3512,354... 

While they form few complexes with simple amines, the pentavalent metals form important M(NR2)xX5 compounds. The M(NMe2)5 compounds, obtained by reaction of MC15 with LiNMe2, have been greatly studied and used for synthesis of other compounds. They are mononuclear in the gas phase with apparently square pyramidal geometry30 but in the solid Ta(NMe2)5 is tbp while Nb(NMe2)5 approaches an sp structure. Mixed species can be obtained by reactions such as... 

A further, equally relevant contribution of Mannich bases to oiganic chemistry is their use as intermediates in the synthesis of other compounds, as indicated in Fig. 80. This shows the variety of reactions that Mannich bases may provide, such as the formation of unsaturated derivatives, amino group replacement, cyclization, etc. Other reactions (reduction and oxidation, acylation, etc.), involving substrate or amine moiety, are also reported in the literature. The polymerization reaction, not included in the figure, is treated in Chapter 111., , ... 

Further related work including investigations of the reductive cleavage of C-S bonds for the synthesis of other compounds with the structure element "Li-CR2-El-CR2-Li" (El = element of group 14-16, partly with substituents R = H, alkyl, aryl) is in progress. 

About 25 years ago, most of the valence-bond isomers described in this review were beyond the dream of chemists but meanwhile these isomers have been synthesized. Some of them are expected to be used for the utilization of the solar energy. Most of these highly reactive compounds are very useful for the synthesis of other compounds. 

Although a large number of bromine compounds are known and described in the literature, they are used mainly in the synthesis of other compounds and have little commercial significance. In the Kirk-Othmer Encyclopedia (125) a chart is given of a number of bromine compounds, most of which have some industrial importance. This chart includes condensed information on preparations, methods, properties, and uses. 

The Knoevenagel reaction (Scheme 6.20) involves the reaction of aromatic aldehydes with a variety of molecules CH2XY. The groups X and Y may be the same or different, but are invariably electron withdrawing, so creating an activated methylene group from which the carbanion CHXY is produced. The reaction is usually carried out in pyridine solution, with piperidine as the basic catalyst. The reactions of benzaldehyde with propane-1,3-dinitrile [malononitrile, CH2(CN)2] and diethyl propane-1,3-dioate [diethyl malonate, CH.,(CO,Et)2] are illustrative. In both cases, manipulation of the CH=CX2 group in the product allows the synthesis of other compounds. 

The same thiazolium ylide (172) was utilized for the synthesis of other compounds (15) (Table 2) through 1,3-dipolar cycloaddition reactions exploiting assorted dipolarophiles (e.g., MeCOCHCHMe, MeCOCHCHPh, CH2CHC02Et) followed by silica gel-assisted cyclization <85T3537>. Other thiazolium ylides (172b) were also used for the preparation of this type of heterocycle. 

Aliphatic diazo compounds are often formed as short-lived intermediates in the synthesis of other compounds, e.g., of carbenes and carbenium ions, which are themselves transient intermediates for other products. In such cases, starting materials and methods are very often basically the same as for synthesis of diazo compounds as final products, but performed at higher temperature under irradiation or in other solvents. Such reactions will not be discussed here but in Chapter 7, which deals with dediazoniations of aliphatic diazo compounds. 

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