Acrolein acetal formation

Reactions of vinyl halides with acrolein acetals and secondary amines lead to the formation of minor amounts of dienal acetals and major amounts of aminoenal acetals (equation 35).s3 The diene product retains the sterochemistry in the vinyl halide while the aminoenal acetal loses it through equilibration of the ir-allylpalladium intermediate. 

Acrolein acetals have also been prepared in high yields (66). The formation of the acetal requires the careful control of reaction conditions to avoid additions to the double bond. Table 5 lists a variety of acrolein acetals that have been prepared and their boiling points (68). 

The highest propene oxide yields were obtained with both the Ti-SBA-15- and the Ti-silica-supported catalysts, although a higher reaction temperature was needed in comparison to the titania-supported catalyst. The deactivation for these catalysts was also considerably less. At lower temperatures (up to 423 K), all catalysts had an inhibition period for both propene oxide and water formation, which is explained by product adsorption on the support. The side products produced by all catalysts were similar. Primarily, carbon dioxide and acetaldehyde were produced as side products and, in smaller quantities, also propanal, acrolein, acetic acid, and formaldehyde. Propanol (both 1- and 2- as well as propanediol), acetone, carbon monoxide, and methanol were only observed in trace amounts. 

Access to a 1,4-dicarbonyl substrate has been realised in several ways. Examples include alkylation of imines with 2-alkoxy-allyl halides (equivalents of 2-halo-ketones),addition of /3-ketoester anions to nitroalkenes, followed by Nef reaction,and rhodium-catalysed carbonylation of 2-substituted acrolein acetals. The dialdehyde (as a mono-acetal) necessary for a synthesis of diethyl furan-3,4-dicarboxylate was obtained by two successive Claisen condensations between diethyl succinate and ethyl formate, as shown in the sequence below. 

We have shown that the direct arylation of acrolein toward the synthesis of cinnamaldehyde derivatives was an efficient procedure. Using the palladacycle 1 as catalyst, substituted aldehydes 3 were prepared with up to 87% isolated yield from condensed aiyl bromides (Scheme 21.1, Route 1) that was extended successfully to heteroaiyl bromides, like bromoquinolines (6). Alternatively, the acrolein diethyl acetal was used as olefin and a selective formation of the saturated ester 4 was attained under the same reaction conditions (Scheme 21.1, Route 2). The expected aldehydes 3 were, however, obtained from most of the aiyl halides used under modified conditions. It was shown that the addition of n-Bu4NOAc in the medium... 

ETHYLENE GLYCOL ETHYL MERCAPTAN DIMETHYL SULPHIDE ETHYL AMINE DIMETHYL AMIDE MONOETHANOLAMINE ETHYLENEDIAMINE ACRYLONITRILE PROPADIENE METHYL ACETYLENE ACROLEIN ACRYLIC ACID VINYL FORMATE ALLYL CHLORIDE 1 2 3-TRICHLOROPROPANE PROPIONITRILE CYCLOPROPANE PROPYLENE 1 2-DICHLOROPROPANE ACETONE ALLYL ALCOHOL PROPIONALDEHYDE PROPYLENE OXIDE VINYL METHYL ETHER PROPIONIC ACID ETHYL FORMATE METHYL ACETATE PROPYL CHLORIDE ISOPROPYL CHLORIDE PROPANE... 

Several aspects of the reaction mechanism still need to be explained. For instance, nonnegligible amounts of C2 compounds (acetic acid, acrolein) are obtained, the formation of which is not satisfactorily explained by reaction mechanisms proposed in the literature. 

As a result of their accessibility, dihydropyrans provide a useful source of 4//-pyrans. Indeed one of the earliest syntheses of the parent compound involved the pyrolysis of 2-acetoxy-3,4-dihydropyran (165) (62JA2452). The concomitant formation of acrolein, vinyl acetate and acetic acid indicates that a reverse Diels-Alder reaction competes with the pyrolysis. 

Reaction of 1,2-dimethylcyclohexene with the ethylene glycol acetal of acrolein in methylene chloride in the presence of 25 mol % of BF3.0Et2 at -78 to -10°C for 2 hours gives a 70% yield of the cycloadduct 1 in a formal 2k + 2% intermolecular cycloaddition. All of the evidence for this and related reactions, however, indicates a stepwise mechanism for the formation of 1. 

Chiral dienes have proved to be less popular in asymmetric Diels-Alder reactions than their chiral dienophile counterparts. This is primarily a result of the problem of designing a molecule that incorporates a chiral moiety, such as the formation of a chiral isoprenyl ether or vinyl ketene acetal.187-190 In addition, diastereoselectivities often are not high,54 191-199 as illustrated by the cycloaddition of the chiral butadiene 5 with acrolein (Scheme 26.4). Improved stereoselection is observed through the use of double asymmetric induction, although this is a somewhat wasteful protocol.35,54 177 200... 

Methyl formate, ethyl formate, carboxylic acids and derivatives, acetic acid CH3COOCH, acetic anhydride CH3COOCOCH3, formic acid HCOOH, oxalic acid HOOCCOOH, phthalic anhydride C3H4O3 Acetaldehyde CH3CHO, acrolein H2C=CHCHO, formaldehyde HCHO, furfural C5H4O2... 

Mo is the essential element of effective catalysts for propene oxidation to acrolein and acrolein oxidation to acrylic acid, while V is an essential element for effective catalysis of acrolein oxidation to acrylic acid. Mo-V-Nb oxide catalysts are capable of activating propane even at 573 K, but yields products of acetic acid, acetaldehyde, and carbon oxides. The addition of Te or Sb to Mo-V-Nb oxides induces certain structural changes leading to the formation of acrylic acid. ... 

Kubokawa et alP also studied by i.r. spectroscopy the oxidation, by both O2 and N2O, of acrolein and propanal on ZnO. An alkoxide species, produced by scission of the O—C(2>H bond of the epoxy ring and with electron donation to the surface, was formed initially from acrolein. With time, this species dehydrogenated to an enolate complex, CH3—CH—CH—O, which was oxidized in presence of O2 at 400 K to formate and acetate species. As with propene, only propionate species were produced by oxidation with N2O. An enol-type species on ZnO has also been reported for acetone, as deduced from studies of hydrogen redistribution between [ Hq]- and [ Hel-acetone. Propanal adsorbed by co-ordination with the carbonyl group. From this species both O2 and N2O produced principally propionate species, scission of C—C bonds occurring to a much smaller extent. The above differences in ease of C—C scission were concluded to be due to the enolate species from acrolein. 

Partial oxidation of propane was investigated in the presence of molybdenum oxide based catalysts. We have shown the existence of a synergetic effect between the two phases aNiMo04 and aMoOs. Indeed activity and selectivity towards acetic acid and acrylic acid were maximal with a ratio aMo03 / (aNiMo04 + aMoOj) close to 0.25. These results could be explained by an interaction and a mutual covering of the two phases. The addition of bismuth to these mixed systems led to a total or a partial inhibition in the production of acetic acid and an increase in the formation of acrolein and acrylic acid. 

The results of Table 6 showed that the addition of a very small amount of bismuth increases significantly the selectivity towards acrolein and acrylic acid with no change in the propane conversion. The propene formation and the acetic acid production decreased at the same time, which is quite an important result of the effect of bismuth on the reaction scheme. 

Like in the preceding example adding bismuth to the [Nio sMoO ] catalyst increases the selectivity towards acrolein and acrylic acid and decreases the formation of acetic acid and of propene (Table 7). 

Acetic acid formed via isopropanol and acetone could involve Mo " species. With the second way, acrolein and acrylic acid are obtained with the participation of Mo species. When the temperature increases the first way of the scheme is favored owing to a surface restructuration of the oxide Mo 03 which can contain pentacoordinated molybdenum species. The addition of bismuth to these phases decreases slightly the activity, the formation of acetic acid being supressed. When water is added to the reagent stream, the activity does not change, but the desorption of oxygenated compounds is favored and the selectivity towards acids enhanced. 

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