Alcohols secondary, dehydrogenation

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

In the presence of reduced nickel, acetone is reduced to isopropyl alcohol at 210° to 220° C. At 200° to 230° C. isopropyl alcohol is dehydrogenated in the presence of nickel and also begins to decompose into saturated hydrocarbons. Under pressure an equilibrium between these two reactions is established. At 250° C. the approach to equilibrium is very slow and is accompanied by decomposition of both acetone and isopropyl alcohol into gaseous hydrocarbons.98 For normal secondary butyl alcohol the corresponding temperatures are somewhat higher, being about 250° to 300° C. in the presence of reduced nickel. The higher... 

The experiments of Wibaut and Diekmann were perhaps the earliest to indicate the reversibility of the dehydration of ethanol to ethylene and water vapor. These workers found that when a mixture of water vapor and ethylene was passed over aluminum oxide or sulfate at 300° to 400° C., the reaction product contained 0.2 to 0.4 per cent of acetaldehyde. This was not the result of oxidation of ethylene as was shown by passing ethylene and air over the same catalysts at 360° C. From this they concluded that hydrolysis to alcohol had taken place as the primary reaction and that secondary dehydrogenation had formed acetaldehyde. 

Using a commercially available AC ( 50wt%), various secondary benzylic alcohols were dehydrogenated aerobically to the corresponding ketones [62, 63]. 

Second, 1,4-diols undergo intermolecular hydrogen transfer, giving lactones efficiently in acetone containing Cp Ru(P-N) catalysts the TOF of this reaction at 30 C exceeds 1,000 h (Fig. 21) [67]. The catalytic oxidative lactonization of diols is characterized by its unique chemo- and regioselectivity. The significant rate difference between primary and secondary alcohols in dehydrogenation, and the rate difference between 1,4-diols and 1,5- or 1,6-diols enable unique oxidative lactonization of triols. 

Scheme 41.35 Kinetic resolution of secondary alcohols by dehydrogenative coupling with recyclable silicon-steieogenic silanes.

The reaction between perfluoraarylmagnesium halides and esters of dicar-boxyltc acids gives, besides the expected keto esters, secondary alcohols as reduction products [29, 30, 31] (equation 10) Such a reduction is enhanced by higher temperature The hydrogen necessary for reduction comes from the solvent, diethyl ether, which is dehydrogenated to ethyl vinyl ether, which has been identified as a by-product in a similar reaction of perfluoroalkyllithium compound [52]... 

A hypothesis for the oxidation of purines in the presence of this enzyme has been elaborated by Bergmann and his colleagues. It postulates that the purine, often in one of its less prevalent tautomeric forms, is adsorbed on the protein, or the riboflavin coenzyme, of the enzyme then hydration occurs under the influence of the electronic field of the enz5rme, and this must involve a group that is not sterically blocked by the enzyme but which is accessible to the electron-transport pathway of the riboflavin moiety. Finally, the secondary alcohol is assumed to be dehydrogenated in this pathway to give a doubly... 

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. 

Dehydrogenation of alcohols.1 Ally lie or secondary alcohols can be oxidized to the ketones by reaction with 1 catalyzed by RuH2[P(C6H5) ,]4 in benzene. The... 

Dehydrogenation of primary alcohols gives aldehydes, but in only moderate yield, but primary allylic alcohols are oxidized in high yield (80-95%). Secondary alcohols are also oxidized in high yield. The method, being neutral, is recommended for oxidation of substrates containing acid- or base-sensitive groups. 

Dehydrogenation often occurred for the reactions of Cu+ and the formation of the ketone complex was common for the reaction of secondary alcohols with Ag+. Many of these ions react with alcohol to form a two-coordinate complex [M(ke-tone)(alcohol)]+. 

Specific dehydrogenation of secondary benzylic alcohols (Table 10.39)... 

The formation of another metabolite, l-hydroxybut-3-ene-2-one (10.109), postulated to arise by dehydrogenation of the secondary alcoholic group, could be demonstrated only indirectly. l-Hydroxybut-3-ene-2-one is believed to react with glutathione and other endogenous nucleophiles, to be oxidized to 2-oxobut-3-enoic acid (10.110), and to break down to form unidentified products. 

Some information about structure effects on the rate of dehydrogenation of alcohols to aldehydes and ketones on metals is found in the older literature 129-132) from which it follows that secondary alcohols react more easily than the primary alcohols 129) and that the reactivity decreases with the length of the carbon chain 131). Some series can be correlated by the Taft equation using a constants (Ref. 131, series 103, Cu-Cr203 catalyst, 350°C, four points, slope 18 Ref 132, series 104, Cu catalyst, four points, slope 22). Linear relationships have been used in a systematic way by... 

The oxidative dehydrogenation of secondary alcohols to ketones on iridium at 130°C has been measured by Le Nhu Thanh and Kraus (i-Zi), and the rates have been correlated by the Taft equation [series 112, four reactants of the structure R CH(OH)CH3, slope 4.7]. 

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