Conversion to aldehydes and

Both the conversion to aldehydes and the selectivity to normal aldehydes observed in the hydroformylation of 1-hexene by these complexes were markedly ligand dependent. A linear relationship between the electron density on the nitrogen atom and the normal/branched aldehyde ratio was found, indicating that for these aminophosphines the ratio is largely controlled by electronic factors.332... 

At the end of the reaction the autoclave was cooled and depressurised. Conversion to aldehydes and the regioselectivity of the reaction (2-phenylpro-panal/3-phenylpropanal) were determined without evaporation of the solvent. The reaction mixture was fractionally distilled under reduced pressure to give a mixture of regioisomers of aldehydes. The enantiomeric excess was determined... 

When precatalysts 4 and 7 were tested under different reaction conditions, for example, modification of solvent (toluene, dodecane), including reaction in ionic liquids ([BMIMJEF ) (BMIM = l-butyl-3-methylimidazolium), and variation of reaction time (3-16 h), similar results were observed [47]. When the syngas pressure was reduced by half, smaller amounts of aldehydes were produced. With complex 7, quantitative conversion to aldehydes and a TOF of >111 h were observed, which agree with other results in this series. 

Nitriles contain the —C=N functional group We have already discussed the two mam procedures by which they are prepared namely the nucleophilic substitution of alkyl halides by cyanide and the conversion of aldehydes and ketones to cyanohydrins Table 20 6 reviews aspects of these reactions Neither of the reactions m Table 20 6 is suitable for aryl nitriles (ArC=N) these compounds are readily prepared by a reaction to be dis cussed m Chapter 22... 

Okfm Syntheses. Conversion of aldehydes and ketones to olefins by the base-catalyzed decomposition of -toluenesulfonic (Ts) acid hydrazones (10) is known as the Bamford-Stevens reaction (54,55). 

If homolytic reaction conditions (heat and nonpolar solvents) can be avoided and if the reaction is conducted in the presence of a weak base, lead tetraacetate is an efficient oxidant for the conversion of primary and secondary alcohols to aldehydes and ketones. The yield of product is in many cases better than that obtained by oxidation with chromium trioxide. The reaction in pyridine is moderately slow the intial red pyridine complex turns to a yellow solution as the reaction progresses, the color change thus serving as an indicator. The method is surprisingly mild and free of side reactions. Thus 17a-ethinyl-17jS-hydroxy steroids are not attacked and 5a-hydroxy-3-ket-ones are not dehydrated. 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

The conversion of alkyl halides to aldehydes and ketones can also be accomplished indirectly (10-107). See also 12-30. 

The dilithio derivative of A-methanesulfinyl-p-toluidine (29) adds to aldehydes and ketones to give, after hydrolysis, the hydroxysulfinamides (30), which, upon heating, undergo stereospecifically syn eliminations to give alkenes. ° The reaction is thus a method for achieving the conversion RR CO — RR C=CH2 and represents an alternative to the Wittig reaction. ... 

Llewellyn, Green, and Cowley isolated the Co-H complex [CoH(CO)3(IMes)] 26, a relatively stable complex under inert conditions [31], The authors examined the hydroformylation activity of 1-octene with Co-hydride complex 26. With 8 atm of syngas (H /CO) at 50°C for 17 h and 1 mol% 26, the conversion to aldehyde products was 47% with a l b of 0.78. However, 83% of the product was the internal aldehyde 2-methyl-octanal, indicating isomerisation competed with hydroformylation and the rate of isomerisation occurred faster than hydroformylation. 

A mixture of 1,4-dioxane and water is often used as the solvent for the conversion of aldehydes and ketones by H2Se03 to a-dicarbonyl compounds in one step (Eq. 8.117).331 Dehydrogenation of carbonyl compounds with selenium dioxide generates the a, (i-unsaturated carbonyl compounds in aqueous acetic acid.332 Using water as the reaction medium, ketones can be transformed into a-iodo ketones upon treatment with sodium iodide, hydrogen peroxide, and an acid.333 Interestingly, a-iodo ketones can be also obtained from secondary alcohol through a metal-free tandem oxidation-iodination approach. 

By 1990, most of the catalytic reactions of TS-1 had been discovered. The wide scope of these reactions is shown in Fig. 6.1.35 Conversions include olefins and diolefins to epoxides,6,7 12 16 19 21 24 34 36 38 13 aromatic compounds to phenols,7,9 19 25 27 36 ketones to oximes,11 20 34 46 primary alcohols to aldehydes and then to acids, secondary alcohols to ketones,34-36 42 47-30 and alkanes to secondary and tertiary alcohols and ketones.6 34 43 31 52... 

Somewhat better results were obtained by the use of (Ph3P)2PtI2 in a polar solvent such as dimethylformamide (122). At 180°C and 250 atm H2/CO, an 89% conversion to aldehydes with an isomer ratio of 4.3 1 was obtained in 1 hour. Relatively high concentrations of catalyst (2500 ppm as Pt metal) were required. Palladium, as (Ph3P)2PdI2, was less effective and also produced considerable amounts of lactones. 

The low-temperature hydrocarbon oxidation mechanism discussed in the previous section is incomplete because the reactions leading to CO were not included. Water formation is primarily by reaction (3.56). The CO forms by the conversion of aldehydes and their acetyl (and formyl) radicals, RCO. The same type of conversion takes place at high temperatures thus, it is appropriate, prior to considering high-temperature hydrocarbon oxidation schemes, to develop an understanding of the aldehyde conversion process. 

The ejfect of water on the conversion and selectivity of cohalt-catalyzed hydroformylations has long been noticed in industry [7,85,86], A systematic study [87] of this effect in hydroformylation of 1-octene with [Co2(CO)s] with and without P Bu3 revealed that addition of water, and especially when it formed a separate aqueous phase, significantly inaeased the hydrogenation activity of the phosphine-modified catalyst Under the same reaction conditions (190 °C, 56 bar CO H2 1 1, P Co 3 1), approximately 40 % nonanols were formed instead of 5 % observed with water-free solutions. No clear explanation could be given for this phenomenon, although the possible participation of water itself in the hydroformylation reaction through the water gas shift was mentioned. It was also established, that the [Co2(CO)g]-catalyzed hydroformylation was severly retarded in the presence of water. Under the conditions above, 95 % conversion was observed in 15 hour with no added water, while only 10 % conversion to aldehydes (no alcohols) was found in an aqueous/organic biphasic reaction. 

A small number of examples is available for the synthesis of E and Z isomers of oximes. In many cases, E isomers were obtained either from the Z forms (by the hydrochloride method) or isolated by column chromatography. Often, the reagents that have been used for oximation of aldehydes and ketones also catalyze the interconversion of Z and E isomers. The rate of equilibration of a mixture of Z and E isomers and the position of the equilibrium is temperature-dependent ". In 2001, Sharghi and Sarvani reported a convenient method for controlling the stereochemistry of the reaction of hydroxylamine hydrochloride with aldehydes or ketones in the solid state. The highly stereoselective conversion of aldehydes and ketones to their corresponding oximes... 

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