Formation of aldehydes

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(PhjP)4 as a catalyst[377]. Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetralluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et ,SiH or PH MS as the hydride source[379]. 

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Sodium me/aperiodate (NalO ) in cold aqueous solution readily oxidises 1,2-diols with splitting of the molecule and the consequent formation of aldehydes or ketones thus ethylene glycol gives formaldehyde and pinacol gives acetone. In the case of a 1,2,3-triol, the central carbon atom of the triol... 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

Garbonylation of Olefins. The carbonylation of olefins is a process of immense industrial importance. The process includes hydroformylation and hydrosdylation of an olefin. The hydroformylation reaction, or oxo process (qv), leads to the formation of aldehydes (qv) from olefins, carbon monoxide, hydrogen, and a transition-metal carbonyl. The hydro sdylation reaction involves addition of a sdane to an olefin (126,127). One of the most important processes in the carbonylation of olefins uses Co2(CO)g or its derivatives with phosphoms ligands as a catalyst. Propionaldehyde (128) and butyraldehyde (qv) (129) are synthesized industrially according to the following equation ... 

Acetaldehyde.—The formation of aldehyde from alcohol probably occtiis by the Liddition of oxygen and bubsetpiem ciimination of water,... 

It has been shown52 that under similar conditions reduction of the nitrile groups in cellulose ethyl cyanate and of those in the copolymer of vinylidene cyanide with vinyl acetate, proceed simultaneously in two directions with the formation of aldehyde and amine groups. g+ g ... 

The most popular reagent for the formation of aldehyde and ketone derivatives is 2,4-dinitrophenylhydrazine which forms hydrazones containing strong chromophores. 

Because 2-trimethylsilyloxy sulfides such as 1154 and 1157 are hemiphenyl thioacetals of aldehydes, they are readily hydrolyzed to aldehydes [8-12] or ketones [13]. Thus alkylation of the lithium salt 1162 with cyclohexyhnethylbromide 1163, gives in nearly quantitative yield, the sulfide 1164, which, after oxidation with m-chloroperbenzoic acid and hydrolysis, rearranges in 70% yield to cyclohexylacetal-dehyde 1165 [8] (Scheme 8.2). A more detailed discussion of the formation of aldehydes is given in Section 8.5. 

The transformations (1) lead to unstable alkyl nitrates, which can detonate very easily. The reactions (2) lead to more or less complete oxidations of the organic molecule. The formation of aldehydes is purely theoretical since they are more oxidisable than alcohols and therefore are not part of the oxidation process by nitric acid. On the other hand, a ketone can form with a secondary alcohol. With tertiary alcohols, carboxylic acid is the only possible outcome of the partial oxidation, which is caused by the breaking of C-C bonds. When the oxidation is out of control, it is likely to have a complete oxidation. Finally, with heavy metal... 

The reactions described so far do not require the involvement of the apo-B protein, neither would they necessarily result in a significant amount of protein modification. However, the peroxyl radical can attack the fatty acid to which it is attached to cause scission of the chain with the concomitant formation of aldehydes such as malondialdehyde and 4-hydroxynonenal (Esterbauer et al., 1991). Indeed, complex mixtures of aldehydes have been detected during the oxidation of LDL and it is clear that they are capable of reacting with lysine residues on the surface of the apo-B molecule to convert the molecule to a ligand for the scavenger receptor (Haberland etal., 1984 Steinbrecher et al., 1989). In addition, the lipid-derived radical may react directly with the protein to cause fragmentation and modification of amino acids. 

Poli, G., Cheeseman, K.H., Biasi, F., Chiarpotto, E., Dianzani, M.U., Esterbauer, H. and Slater, T.F. (1989a). Promethazine inhibits the formation of aldehydic products of the lipid peroxidation that is stimulated by carbon tetrachloride, but does not inhibit covalent binding of metabolites of carbon tetrachloride to microsomal lipid protein. Biochem. J. 264, 527-532. 

Motoda, S., Formation of aldehydes from amino acids by polyphenol oxidase, J. Ferment Technol., 57, 395, 1979. (CA92 17776e)... 

Together with the fast oxidation (at low temperatures) of NO to N02, the plasma causes the partial HC oxidation (using propylene, the formation of CO, C02, acetaldehyde and formaldehyde was observed). Both the effects cause a large promotion in activity of the downstream catalyst [86]. For example, a "/-alumina catalyst which is essentially inactive in the SCR of NO with propene at temperatures 200°C allows the conversion of NO of about 80% (in the presence of NTP). Formation of aldehydes follows the trend of NO concentration suggesting their role in the reaction mechanism. Metal oxides such as alumina, zirconia or metal-containing zeolites (Ba/Y, for example) have been used [84-87], but a systematic screening of the catalysts to be used together with NTP was not carried out. Therefore, considerable improvements may still be expected. 

Formation of aldehyde complexes from the zinc hydroxide complexes of tris(3-cumenyl-5-methylpyrazolyl)borate] was observed. The aldehyde ligands, such as pentafluorobenzaldehyde,... 

Mitch WA, Schreiber IM (2008) Degradation of tertiary alkylamines during chlorination/ chloramination implications for formation of aldehydes, nitriles, halonitroalkanes, and nitrosamines. Environ Sci Technol 42 4811-4817... 

The second rhodium-catalyzed route which is widely used in connection with domino processes is that of hydroformylation. This by itself is a very important industrial process for the formation of aldehydes using an alkene and carbon monoxide. Finally, rhodium catalysts have also been used in this respect. 

This simple strategy can be used to add amine residues to polysaccharide molecules after formation of aldehydes by periodate or enzymatic oxidation (Section 4.4, this chapter). Thus, glycoconjugates or carbohydrate polymers such as dextran may be derivatized to contain amines for further conjugation reactions. 

Figure 7.11 Oxidation of glycoproteins with periodate, such as glycosylated antibodies, results in the formation of aldehyde groups that can be used for conjugation to dendrimers containing amine groups. Reductive amination with sodium cyanoborohydride results in coupling via secondary (or tertiary) amine bonds.

In plant tissues, various enzymes convert the hydroperoxides produced by LOX to other products, some of which are important as flavor compounds. These enzymes include hydroperoxide lyase, which catalyzes the formation of aldehydes and oxo acids hydroperoxide-dependent peroxygenase and epoxygenase, which catalyze the formation of epoxy and hydroxy fatty acids, and hydroperoxide isomerase, which catalyzes the formation of epoxyhydroxy fatty acids and trihydroxy fatty acids. LOX produces flavor volatiles similar to those produced during autoxidation, although the relative proportions of the products may vary widely, depending on the specificity of the enzyme and the reaction conditions. 

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