Acrolein reactivity

Donor substituents on the vinyl group further enhance reactivity towards electrophilic dienophiles. Equations 8.6 and 8.7 illustrate the use of such functionalized vinylpyrroles in indole synthesis[2,3]. In both of these examples, the use of acetyleneic dienophiles leads to fully aromatic products. Evidently this must occur as the result of oxidation by atmospheric oxygen. With vinylpyrrole 8.6A, adducts were also isolated from dienophiles such as methyl acrylate, dimethyl maleate, dimethyl fumarate, acrolein, acrylonitrile, maleic anhydride, W-methylmaleimide and naphthoquinone. These tetrahydroindole adducts could be aromatized with DDQ, although the overall yields were modest[3]. 

Acrolein (H2C=CHCH=0) reacts with sodium azide (NaNj) in aqueous acetic acid to form a compound C3H5N3O in 71% yield Propanal (CH3CH2CH=0) when subjected to the same reaction conditions is recovered unchanged Suggest a structure for the product formed from acrolein and offer an explanation for the difference in reactivity between acrolein and propanal... 

Acrolein is a highly toxic material with extreme lacrimatory properties. At room temperature acrolein is a Hquid with volatiUty and flammabiUty somewhat similar to acetone but unlike acetone, its solubiUty in water is limited. Commercially, acrolein is always stored with hydroquinone and acetic acid as inhibitors. Special care in handling is required because of the flammabiUty, reactivity, and toxicity of acrolein. 

Acrolein is a highly reactive compound because both the double bond and aldehydic moieties participate in a variety of reactions. 

Reactivity Acrolein is a highly reactive chemical, and contamination of all types must be avoided. Violent polymerization may occur by contamination with either alkaline materials or strong mineral acids. Contamination by low molecular weight amines and pyridines such as a-picoline is especially hazardous because there is an induction period that may conceal the onset of an incident and allow a contaminant to accumulate unnoticed. After the onset of polymeriza tion the temperature can rise precipitously within rninutes. 

There is a significant difference in the toxicological effects of saturated and unsaturated afiphatic aldehydes. As can be seen in Table 6, the presence of the double bond considerably enhances toxicity. The precautions for handling reactive unsaturated aldehydes such as acrolein, methacrolein [78-85-3] and crotonaldehyde should be the same as those for handling other highly active eye and pulmonary irritants, as, for example, phosgene. 

By substituting paraldehyde for glycerol, 2-methylquinoline [27601-00-9] may be synthesized. The Skraup synthesis is regarded as an example of the broader Doebner-von Miller synthesis. In the case of the Skraup synthesis, the glycerol undergoes an acid-catalyzed dehydration to provide a small concentration of acrolein that is the reactive species. If acrolein itself is used as a reactant, it would polymerize. Crotonaldehyde is the reactive intermediate in the Doebner-von Miller synthesis (28). 

By virtue of their unique combination of reactivity and basicity, the polyamines react with, or cataly2e the reaction of, many chemicals, sometimes rapidly and usually exothermically. Some reactions may produce derivatives that ate explosives (eg, ethylenedinitrarnine). The amines can cataly2e a mnaway reaction with other compounds (eg, maleic anhydride, ethylene oxide, acrolein, and acrylates), sometimes resulting in an explosion. 

The chemical reactivity of these two substituted ethylenes is in agreement with the ideas encompassed by both the MO and resonance descriptions. Enamines, as amino-substituted alkenes are called, are vety reactive toward electrophilic species, and it is the p carbon that is the site of attack. For example, enamines are protonated on the carbon. Acrolein is an electrophilic alkene, as predicted, and the nucleophile attacks the P carbon. 

Simple alkyl radicals such as methyl are considered to be nonnucleophilic. Methyl radicals are somewhat more reactive toward alkenes bearing electron-withdrawing substituents than towards those with electron-releasing substituents. However, much of this effect can be attributed to the stabilizing effect that these substiments have on the product radical. There is a strong correlation of reaction rate with the overall exothermicity of the reaction. Hydroxymethyl and 2-hydroxy-2-propyl radicals show nucleophilic character. The hydroxymethyl radical shows a slightly enhanced reactivity toward acrylonitrile and acrolein, but a sharply decreased reactivity toward ethyl vinyl ether. Table 12.9 gives some of the reactivity data. 

Several chemical compounds may cause inflammation or constriction of the blood vessel wall (vasoconstriction). Ergot alkaloids at high doses cause constriction and thickening of the vessel wall. Allylamine may also induce constriction of coronary arteries, thickening of their smooth muscle walls, and a disease state that corresponds to coronary heart disease. The culprit is a toxic reactive metabolite of allylamine, acrolein, that binds covalently to nucleophilic groups of proteins and nucleic acids in the cardiac myocytes. 

Polyfluoro-2-acylimmopropanes exhibit an interesting dichotomy of reactivity they react as dienophiles with cyclopentadiene but as heterodienes with acrolein [112] (equation 93)... 

The equivalent charge weight of TNT is calculated on the basis of the entire cloud content. FMRC recommends that a material-dependent yield factor be applied. Three types of material are distinguished Class I (relatively nonreactive materials such as propane, butane, and ordinary flammable liquids) Class II (moderately reactive materials such as ethylene, diethyl ether, and acrolein) and Class III (highly reactive materials such as acetylene). These classes were developed based on the work of Lewis (1980). Energy-based TNT equivalencies assigned to these classes are as follows ... 

The ratio of the two diastereomeric products 190 and 191 was found to depend on the reaction temperature and reaction time. The addition of acrolein or methyl vinyl ketone proceeded smoothly, but in the case of methylacrylate or acrylonitrile the reaction did not proceed under the same conditions (EtsN THF 30°C). An accompanying AMI calculation of these Q ,/3-unsaturated compounds [LUMOs for acrolein, -0.13877 for methyl vinyl ketone, -0.06805 (s-trans) for methyl acrylate, -0.01413 (s-tmns) for acrylonitrile, 0.04971] suggested the low reactivity of methyl acrylate and acrylonitrile toward the Michael reaction (99H1321). 

To overcome these problems with the first generation Brmsted acid-assisted chiral Lewis acid 7, Yamamoto and coworkers developed in 1996 a second-generation catalyst 8 containing the 3,5-bis-(trifluoromethyl)phenylboronic acid moiety [10b,d] (Scheme 1.15, 1.16, Table 1.4, 1.5). The catalyst was prepared from a chiral triol containing a chiral binaphthol moiety and 3,5-bis-(trifluoromethyl)phenylboronic acid, with removal of water. This is a practical Diels-Alder catalyst, effective in catalyzing the reaction not only of a-substituted a,/ -unsaturated aldehydes, but also of a-unsubstituted a,/ -unsaturated aldehydes. In each reaction, the adducts were formed in high yields and with excellent enantioselectivity. It also promotes the reaction with less reactive dienophiles such as crotonaldehyde. Less reactive dienes such as isoprene and cyclohexadiene can, moreover, also be successfully employed in reactions with bromoacrolein, methacrolein, and acrolein dienophiles. The chiral ligand was readily recovered (>90%). 

For the ordinary Diels-Alder reaction the dienophile preferentially is of the electron-poor type electron-withdrawing substituents have a rate enhancing effect. Ethylene and simple alkenes are less reactive. Substituent Z in 2 can be e.g. CHO, COR, COOH, COOR, CN, Ar, NO2, halogen, C=C. Good dienophiles are for example maleic anhydride, acrolein, acrylonitrile, dehydrobenzene, tetracya-noethylene (TCNE), acetylene dicarboxylic esters. The diene preferentially is of the electron-rich type thus it should not bear an electron-withdrawing substituent. 

For the Skraup synthesis, glycerol 2 is used as starting material in the presence of concentrated sulfuric acid (see scheme above) it is dehydrated to acrolein 6. Although it is assumed that the reactive carbonyl component in the Skraup reaction actually is acrolein, attempts to use acrolein directly, instead of glycerol, proved to be unsuccessful." ... 

Acrolein (2-propenal) is an unsaturated aldehyde with a disagreeable odor. When pure, it is a colorless liquid, that is highly reactive and polymerizes easily if not inhibited. 

Allylchromium reagents of similar reactivity may also be generated from allyl tosylates1, acrolein diethyl acetal13, and vinyloxiranes14. 

By using unactivated K-10 montmorillonite in the absence of solvent, the endo-exo selectivity of the cycloadditions of acrolein and methyl vinyl ketone with cyclopentadiene and cyclohexadiene is low [8] (Table 4.2, entry 3), while highly reactive dienophiles such as 1,4-benzoquinone and N-phenyl... 

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. 

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. 

The use of 2-vinyldioxolane, the ethylene glycol acetal of acrolein, as a dienophile illustrates application of the masked functionality concept in a different way. The acetal itself would not be expected to be a reactive dienophile, but in the presence of a catalytic amount of acid the acetal is in equilibrium with the electrophilic oxonium ion. 

An interesting observation was made when o-aminophenol (2-411) was employed in the reaction with carbethoxypiperidone 2-410 and acrolein (Scheme 2.98). In this case, the spirocydic scaffold 2-412 was exclusively formed in 67% yield. This result can be explained by invoking a stereoelectronic control due to the presence of the aromatic ring which prevents the formation of the corresponding fused tetracyclic isomer. Moreover, both reactive sites can simultaneously be functionalized using 2-amino-1,3-propanediol (2-413) as partner in the multicomponent reaction. This leads to the formation of three new cycles... 

Theoretical calculations have also permitted one to understand the simultaneous increase of reactivity and selectivity in Lewis acid catalyzed Diels-Alder reactions101-130. This has been traditionally interpreted by frontier orbital considerations through the destabilization of the dienophile s LUMO and the increase in the asymmetry of molecular orbital coefficients produced by the catalyst. Birney and Houk101 have correctly reproduced, at the RHF/3-21G level, the lowering of the energy barrier and the increase in the endo selectivity for the reaction between acrolein and butadiene catalyzed by BH3. They have shown that the catalytic effect leads to a more asynchronous mechanism, in which the transition state structure presents a large zwitterionic character. Similar results have been recently obtained, at several ab initio levels, for the reaction between sulfur dioxide and isoprene1. ... 

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