Acrolein complexes

Recently, Diels-Alder reactions between cyclopentadiene and menthoxyaluminum dichloride-acrolein complexes were investigated by means of combined AM1/AM3 calculations and the results were compared to full AMI results211. 

Ab initio calculations have been performed by Birney and Houk to define the transition state in Diels-Alder reactions catalyzed by boron derivatives [38]. As a model, the authors studied the reaction between butadiene and acrolein complexed with BH3. The preferred route is endo addition of the anti complex of s-cis acrolein. 

Several complexes of cuprous halides with acrylonitrile 69> and acrolein 70> have been investigated. The enthalpies of complexing have been found from vapour pressure measurements the enthalpy of formation of the complex from solid copper chloride and liquid acrylonitrile was -29.3 kJ mole-1, while with copper bromide this was -1.3 kJ mole-1. The corresponding value for the acrolein complex was -17.3 kJ mole-1 the enthalpy values for the formation from the gaseous olefinic compounds were -62.3, -34.3 and -49.2 kJ mole-1 respectively. 

OIL SAND Linseed oil and starch Heat - high Acrolein Complex organics Odour can be an issue as the core ovens are often extracted to air... 

The olefin complexes of these metals are often readily decomposed in aqueous solution and Cu(I)-olefin complexes are conveniently prepared by reduction of ethanolic solutions of copper(II) halides and the olefin with SO2 [73]. Distribution studies of olefins between carbon tetrachloride and aqueous solutions of silver and copper salts show that the Cu(I)-olefin complexes hav6 considerably higher stability constants than the analogous silver complexes [74]. Evidence for a relatively weak olefin-metal bond in the complexes of both metals comes from infrared and Raman spectra which show that usually the stretching frequency of the co-ordinated C=C is lowered by only 50-60 cm i compared with a lowering of > 120 cm i found for most olefin-platimun complexes. In the acrolein complex [(CHj=CHCHO)CuCflj the C=C stretch is lowered by 90 an [74fl]. 

Acrylonitrile seems to be a rather versatile ligand. As shown on p. 21 it may bond as a 77-ethylenic ligand. With molybdenum and tungsten, however, it forms complexes in which it bonds to fte metal by the nitrile group, e.g. CH2=CHCNMo(CO)s [88, 89] and thus behaves like CH3CN. It can also form the polymeric complex (acrylonitrile)2Mo(CO)2 [90], which may have a stmcture related to that proposed for the acrolein complex, 3.34. 

Benzaldehyde is easily oxidised by atmospheric oxygon giving, ultimately, benzoic acid. This auto-oxidation is considerably influenced by catalysts tiiose are considered to react with the unstable peroxide complexes which are the initial products of the oxidation. Catalysts which inhibit or retard auto-oxidation are termed anti-oxidants, and those that accelerate auto-oxidation are called pro-oxidants. Anti-oxidants find important applications in preserving many organic compounds, e.g., acrolein. For benzaldehyde, hydroquinone or catechol (considerably loss than U-1 per cent, is sufficient) are excellent anti-oxidants. 

Today the most efficient catalysts are complex mixed metal oxides that consist of Bi, Mo, Fe, Ni, and/or Co, K, and either P, B, W, or Sb. Many additional combinations of metals have been patented, along with specific catalyst preparation methods. Most catalysts used commercially today are extmded neat metal oxides as opposed to supported impregnated metal oxides. Propylene conversions are generally better than 93%. Acrolein selectivities of 80 to 90% are typical. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Propylene oxide is also produced in Hquid-phase homogeneous oxidation reactions using various molybdenum-containing catalysts (209,210), cuprous oxide (211), rhenium compounds (212), or an organomonovalent gold(I) complex (213). Whereas gas-phase oxidation of propylene on silver catalysts results primarily in propylene oxide, water, and carbon dioxide as products, the Hquid-phase oxidation of propylene results in an array of oxidation products, such as propylene oxide, acrolein, propylene glycol, acetone, acetaldehyde, and others. 

Ca.ta.lysts, A small amount of quinoline promotes the formation of rigid foams (qv) from diols and unsaturated dicarboxyhc acids (100). Acrolein and methacrolein 1,4-addition polymerisation is catalysed by lithium complexes of quinoline (101). Organic bases, including quinoline, promote the dehydrogenation of unbranched alkanes to unbranched alkenes using platinum on sodium mordenite (102). The peracetic acid epoxidation of a wide range of alkenes is catalysed by 8-hydroxyquinoline (103). Hydroformylation catalysts have been improved using 2-quinolone [59-31-4] (104) (see Catalysis). 

This is not the case in most fires where some oi the intermediate produces, formed when large, complex molecules are broken up, persist. Examples are hydrogen cyanide from wool and silk, acrolein from vegetable oils, acetic acid from timber or paper, and carbon or carbon monoxide from the incomplete combustion of carbonaceous materials. As the fire develops and becomes hotter, many of these intermediates, which are often toxic, are destroyed—for example, hydrogen cyanide is decomposed at about 538°C (1000°F). 

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

Both experimental [7] and theoretical [8] investigations have shown that the anti complexes of acrolein and boranes are the most stable and the transition states were located only for these four anti complexes. The most stable transition-state structure was calculated (RHF/3-21G) to be NC, while XT is the least stable of the four located. The activation energy has been calculated to be 21.6 kcal mol for the catalyzed reaction, which is substantially above the experimental value of 10.4 1.9 kcal mol for the AlCl3-catalyzed addition of methyl acrylate to butadiene [4a]. The transition-state structure NC is shown in Fig. 8.5. 

The mechanism of the carbo-Diels-Alder reaction has been a subject of controversy with respect to synchronicity or asynchronicity. With acrolein as the dieno-phile complexed to a Lewis acid, one would not expect a synchronous reaction. The C1-C6 and C4—C5 bond lengths in the NC-transition-state structure for the BF3-catalyzed reaction of acrolein with butadiene are calculated to be 2.96 A and 1.932 A, respectively [6]. The asynchronicity of the BF3-catalyzed carbo-Diels-Alder reaction is also apparent from the pyramidalization of the reacting centers C4 and C5 of NC (the short C-C bond) is pyramidalized by 11°, while Cl and C6 (the long C-C bond) are nearly planar. The lowest energy transition-state structure (NC) has the most pronounced asynchronicity, while the highest energy transition-state structure (XT) is more synchronous. 

Nafion-H (144), a perfluorinated resin-sulfonic acid, is an efficient Bronsted-acid catalyst which has two advantages it requires only catalytic amounts since it forms reversible complexes, and it avoids the destruction and separation of the catalyst upon completion of the reaction [94], Thus in the presence of Nafion-H, 1,4-benzoquinone and isoprene give the Diels-Alder adduct in 80% yield at 25 °C, and 1,3-cyclohexadiene reacts with acrolein at 25 °C affording 88 % of cycloadduct after 40 h, while the uncatalyzed reactions give very low yields after boiling for 1 h or at 100 °C for 3.5 h respectively [95], Other examples are given in Table 4.24. In the acid-catalyzed reactions that use highly reactive dienes such as isoprene and 2,3-dimethylbutadiene, polymerization of alkenes usually occurs with Nafion-H, no polymerization was observed. 

Hersh et al. found that the cationic complex [CpFe(CO)2(THF)]BF4 (23) can accelerate the [4 + 2] cycloaddition of acrolein and cyclopentadiene [32]. However, the catalytic activity was higher than expected from rate constants determined in stoichiometric experiments, indicating that a Brpnsted or Lewis acid impurity might accelerate this process and generating doubts about the role of 23. 

In 1999, Kiindig and Bruin reported a closely related catalyst system 29a, in which a more readily accessible ligand has been employed [37]. Catalytic activity and stability are strongly dependent upon the nature of the neutral ligand L. While the acetonitrile complex 29b is stable, yet catalytically inactive, complex 29a with L = acrolein is stable only in the solid state, but decomposes as a solution in DCM... 

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. 

Enantioselective D-A reactions of acrolein are also catalyzed by 3-(2-hydroxyphenyl) derivatives of BINOL in the presence of an aromatic boronic acid. The optimum boronic acid is 3,5-di-(trifluoromethyl)benzeneboronic acid, with which more than 95% e.e. can be achieved. The TS is believed to involve Lewis acid complexation of the boronic acid at the carbonyl oxygen and hydrogen bonding with the hydroxy substituent. In this TS tt-tt interactions between the dienophile and the hydroxybiphenyl substituent can also help to align the dienophile.114... 

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