Supports crotonaldehyde

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

As was for example seen with Pd and Pt (Section 2.6.1, crotonaldehyde), dense (111) metal faces are not favorable to C=C coordination. Accordingly, greater participation of this face in the catalyst surface, with large faceted particles or by support epitaxy, can favor the unsaturated alcohol [159]. 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

Bailie et al. were the first to mention alcohol formation from aldehydes by supported gold-catalyzed selective hydrogenation. The reaction of the formation of crotyl alcohol from crotonaldehyde showed high selectivity (up to 81%) at conversions of 5-10%, with preferential hydrogenation of C=0 rather than the C=C bond [216]. The addition of thiophene promoted this selective hydrogenation. This promotional effect was also observed in similar situations for Cu and Ag, but it was not very common for gold. 

The hydrogenation of 3-methyl crotonaldehyde was investigated over Ru supported on NaY and KY zeolites in both liquid- and gas-phase reactions. Significant effects of the nature of the support on the product selectivity were observed. It was suggested that increased basicity of the zeolite resulted in increased selectivity towards the unsaturated alcohol product. 

Nagase et al. studied the hydrogenation of crotonaldehyde over a Ag-Mn catalyst supported on A1203-5A1P04 in hexane at 5 MPa H2.68 The high activity and selectivity to crotyl alcohol was obtained over Ag-Mn catalysts with >1.5 Mn/Ag atom ratio at 180°C (72.0% selectivity at 98% conversion, compared to 43.2% selectivity at 84.3% conversion over the catalyst without Mn). 

While alcohol oxidations have been the most common metal promoted reactions involving molecular oxygen, a number of other metal catalyzed oxidations of potential synthetic interest have been reported. Supported palladium catalysts are comparable to many soluble palladium catalysts in promoting the selective oxidations of alkenes and aromatics. 2-Butene was oxidized primarily to crotonic acid over Pd/C in water but methyl vinyl ketone and crotonaldehyde were also formed in significant amounts. When this oxidation was run in acetic acid the allyl acetates were the major products, particularly when a Pd/Al203 catalyst... 

Results from these studies are important for the ongoing debates on the existence and utility of Sn/Pt alloy phases in bimetallic Pt-Sn supported catalysts. For example, our observation of dramatically decreased carbon buildup on the alloy surfaces from acetylene (a coke-precursor), and the enhanced yield of aromatics and alkenes from alkane dehydrogenation mimics important aspects of the chemistry of commercial Pt-Sn supported catalysts used for reforming. On the contrary, it seems unlikely that Sn/Pt alloy phases are solely responsible for the high selectivity observed in crotonaldehyde hydrogenation using Pt-Sn bimetallic catalysts. 

This hypothesis was supported by the difference NOE measurement of the CAB-complexed methacrolein and crotonaldehyde in CD2CI2 at -95 -75 "C. Irradiation of uniformly resulted in a strong NOE to and no NOE to H and and irradiation of led to a strong NOE to fT, indicating that the complex of methacrolein with CAB is primarily in the s-trans conformation independently of the boron substituent (Table 1-6). However, all the NOE data results for crotonaldehyde in Table 1-7 clearly reveal that (1) uncomplexed crotonaldehyde is primarily in the s-trans conformation, (2) the crotonaldehyde complexes with CAB... 

A new method of synthesis of selective platinum catalysts for the hydrogenation of unsaturated carbonyl compounds is presented. Platinum was deposited on the supports tailored with the monolayer of transition metal oxide. Selectivity of these catalysts strongly depended on the type of inorganic support as well as on the type of transition metal in the monolayer. Catalysts were tested in the hydrogenation of furfural, crotonaldehyde and cinnamaldehyde. Selectivity of the synthesis of the appropriate unsaturated alcohols was enhanced when compared with the reactions performed over classical Pt-metal oxide catalysts. 

When a compound contains both a C=C double bond as well as a 0=0 double bond, the thermodynamics of the system favours the reduction of the former. For example, for crotonaldehyde (CH3CH=CHCH=0) hydrogenation, the free energy change for conversion to butyraldehyde (C3H7CHO), crotyl alcohol (CH3CH=CHCH20H) and -n-butanol at 273 K are —71, —31 and —105 kJ mol-1 respectively. Therefore, crotonaldehyde conversion over non-modified supported metal catalysts usually yields saturated butyraldehyde as the initial product, with butanol as either a primary or secondary product. 

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