Crotonaldehyde selective reduction

Complex hydrides can be used for the selective reduction of the carbonyl group although some of them, especially lithium aluminum hydride, may reduce the a, -conjugated double bond as well. Crotonaldehyde was converted to crotyl alcohol by reduction with lithium aluminum hydride [55], magnesium aluminum hydride [577], lithium borohydride [750], sodium boro-hydride [751], sodium trimethoxyborohydride [99], diphenylstarmane [114] and 9-borabicyclo[3,3,l]nonane [764]. A dependable way to convert a, -un-saturated aldehydes to unsaturated alcohols is the Meerwein-Ponndorf reduction [765]. 

Selective reduction of the carbonyl group of a,/S-unsaturated aldehydes and ketones has been achieved by a vapor-phase hydrogen transfer reaction using saturated primary and secondary alcohols as hydrogen donors. The preferred catalyst for the reaction, which is reversible, is magnesium oxide. Application to the reduction of acrolein to allyl alcohol, methacrolein to methallyl alcohol, crotonaldehyde to crotyl alcohol, and methyl isopropenyl ketone to 3-methyl-3-buten-2-ol is described. 

The use of ethyl alcohol for the selective reduction of the carbonyl group in unsaturated aldehydes and ketones other than acrolein is illustrated in Table V. Here also, the data listed are the best obtained in a limited number of runs with each compound and do not necessarily represent optimum conditions. As previously stated, in the acrolein-allyl alcohol reaction a small amount of propyl alcohol is found in the products. This side reaction appears to be considerably more important with crotonaldehyde, since the C4 alcohol fraction here contained 27 % butyl alcohol. The relatively high conversion to saturated alcohol is believed to be due in part to unfavorable reaction conditions. With methacrolein and with methyl isopropenyl ketone the saturated alcohol amounted to 5 % of the imsaturated alcohol produced. 

Several water-soluble ruthenium complexes, with P = TPPMS, TPPTS, or PTA ligands (cf. Section 2.2.3.2), catalyze the selective reduction of crotonaldehyde, 3-methyl-2-butenal (prenal), and trans-cinnamaldehyde to the corresponding unsaturated alcohols (Scheme 2) [33—36]. Chemical yields are often close to quantitative in reasonable times and the selectivity toward the aUyhc alcohol is very high (> 95%). The selectivity of the reactions is critically influenced by the pH of the aqueous phase [11] as well as by the H2 pressure [37]. The hydrogenation of propionaldehyde, catalyzed by Ru(II)/TPPTS complexes, was dramatically accelerated by the addition of inorganic salts [38], too. In sharp contrast to the Ru(II)-based catalysts, in hydrogenation of unsaturated aldehydes rhodium(I) complexes preferentially promote the reaction of the C=C double bond, although with incomplete selectivity [33, 39]. 

It has been shown previously how water-soluble rhodium Rh-TPPTS catalysts allow for efficient aldehyde reduction, although chemoselectivity favors the olefmic bond in the case of unsaturated aldehydes [17]. The analogous ruthenium complex shows selectivity towards the unsaturated alcohol in the case of crotonaldehyde and cinnamaldehyde [31]. 

A method for the conversion of unsaturated aliphatic aldehydes to saturated aldehydes is a gentle catalytic hydrogenation. Palladium is more selective than nickel. Hydrogenation over sodium borohydride-reduced palladium in methanol at room temperature and 2 atm reduced crotonaldehyde to butyralde-hyde but did not hydrogenate butyraldehyde [57]. Nickel prepared by reduction with sodium borohydride was less selective it effected reduction of crotonaldehyde to butyraldehyde but also reduction of butyraldehyde to butyl alcohol, though at a slower rate [57]. Hydrogenation of 2,2,dimethyl-... 

The classical Meerwein-Ponndorf-Verley (MPV) process, named after the independent originators, can be illustrated by the reduction of crotonaldehyde (43) by aluminum isopropoxide (44) in isopropyl alcohol (equation 24). Aluminum isopropoxide transfers hydride reversibly to a carbonyl acceptor. Acetone is formed as a volatile side product, which can be removed during reaction. The reaction of equation (24) is forced even further to the right by the use of excess isopropyl alcohol. MPV reactions have been reviewed.In the Oppenauer variant of this reaction an alcohol is oxidized to a ketone, and acetone is used as hydride acceptor in the presence of a strong base like r-butoxide. This reaction was originally developed for the selective oxidation of sterols. The synthetic aspects of this procedure have also been reviewed. ... 

Borohydride reduced Pd is also a versatile hydrogenation catalyst that effects the partial reduction of multifunctional unsaturated compounds selectively. It can reduce the w-bond of C=C, N=N, N=0, but not the w-bond of C=N, C=0, nor the --bond of C— N, C—O. Allylic alcohols, allylic amines, allylic ethers, a-methylstyrene, acrylamide, 3-butene nitro, and also mesityl oxide, crotonaldehyde, and maleic anhydride are among the selectively reduced substrates. ... 

Formic acid and formates were among the most effective donors used for the reduction of olefins with [RuCl2(PPhj)j] or [RhCl(PPh3)3] catalysts in non-aqueous systems [239-241], No wonder, the water soluble analogues of these catalysts became widely used in aqueous solutions. In a series of investigations [242-245] with Ru/IPPMS and Rh/TPPMS catalysts olefins (such as 1-heptene) were hydrogenated in mixtures of HCOOH/HCOONa. Crotonaldehyde was selectively reduced to butyraldehyde by the [RhCl(TPPMS)3] catalyst [245], It was also established that (unfiltered) ultraviolet irradiation accelerated the reactions [245],... 

Figure 8.33. Comparison between experimental and calculated activity according to eq. 8.120 (K. Liberkova, R. Touroude, D. Yu. Murzin, Analysis of deactivation and selectivity pattern in catalytic reduction of a molecule with different functional groups Crotonaldehyde hydrogenation on Pt/Sn02, Chemical Engineering Science, 57 (2002) 2519).

The effect of the zinc content and the reduction temperature on the characteristics and catalytic properties of bimetallic Pt-Zn catalysts supported on zeolite NaX have been analyzed. Catalysts have been characterized by TPR, XRD and XPS. Their catalytic behavior in the vapor phase hydrogenation of crotonaldehyde (2-butenal) was studied after reduction a 632 and 773 K. The presence of zinc causes a drastic decrease in catalytic activity, although the selectivity towards the hydrogenation of the C=0 bond is improved. Higher reduction temperature also improves the catalytic selectivity. The formation of Pt-Zn alloyed phases upon reduction can explain this catalytic behavior, although the contribution of a steric effect due to constraints creation in the pores of the zeolite support can not be discarded. 

After screening several reductants in the aerobic epoxidation of olefins catalyzed by nickel(II) complexes, it was found that an aldehyde acts as an excellent reductant when treated under an atmospheric pressure of molecular oxygen at room temperature (Scheme 6). Similar reactions have been reported in the patents. Propylene was monooxygenated into propylene oxide with molecular oxygen in the coexistence of metal complexes and aldehyde such as acetaldehyde " or crotonaldehyde, but the conversion of olefin and the selectivity of epoxide were never reached satisfactory levels. Recently, praseodymium(III) acetate was also shown to be an effective catalyst for the aerobic epoxidation of olefins in the presence of aldehyde. ... 

The presence of zinc facilitated the reduction of surface ceria, thereby increasing the potential number of Ce -Pt metal interface sites, particularly in cases where small Pt particles were located in ceria-rich zones of the support. In the case of the vapor-phase hydrogenation of crotonaldehyde, the overall catalytic activity increased significantly after reduction at 500°C for the zinc-containing catalyst, and furthermore, the selectivity toward the hydrogenation of the carbonyl bond was improved (Table 13.12). 

Pt on mesostructured CeOg nanoparticles embedded within ultrathin layers of a highly structured SiOs binder had the highest activity with 80% selectivity for the chemoselective hydrogenation of crotonaldehyde.By increasing the reduction temperature, the... 

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