Ethylene ketene acetal

One of the intrigMixig characteristics of the ethylene ketene acetal is its ability to copolymerize with a wide variety of coamon monomers, including styrene and methyl methacrylate. One should note that this process introduces an ester group into the backbone of an addition polymer. Although the copolymerization of oi gen would introduce a peroxide linkage into the backbone, this is the first time ttiat a relatively stable but yet hydrolizable functional group has been introduced into the backbone c an addition polymer (12). 

One of the intriguing characteristics of the ethylene ketene acetal is its ability to copolymerize with a wide variety of common monomers, including styrene and methyl... 

During this early period, a very ingenious free-radical route to polyesters was used to introduce weak linkages into the backbones of hydrocarbon polymers and render them susceptible to bio degradabihty (128—131). Copolymerization of ketene acetals with vinyl monomers incorporates an ester linkage into the polymer backbone by rearrangement of the ketene acetal radical as illustrated in equation 13. The ester is a potential site for biological attack. The chemistry has been demonstrated with ethylene (128—131), acryhc acid (132), and styrene (133). 

Pyrolysis of the ethylene acetal of bicyclo[4.2.0]octa-4,7-diene-2,3-dione yields a-(2-hydroxyphenyl)-y-butyrolactonc 11 a mechanism involving a phenyl ketene acetal is proposed. Tartrate reacts with methanediol (formaldehyde hydrate) in alkaline solution to give an acetal-type species (9) 12 the formation constant was measured as ca 0.15 by H-NMR. Hydroxyacetal (10a) exists mainly in a boat-chair conformation (boat cycloheptanol ling), whereas the methyl derivative (10b) is chair-boat,13 as shown by 1 H-NMR, supported by molecular mechanics calculations. 

From the diacetate ester (Figure 7.13), an ion-molecule complex consisting of the neutral ketene and the complementary alcoholate is formed. Either this complex dissociates to yield the ethylene glycol acetate anion A, which further fragments to yield the acetate anion E, or a proton transfer from the ketene to the alcoholate occurs in the complex, which after dissociation yields the ynolate ion G. 

Cyclic ketene acetals can also react with amines to give 1,1-enediamines with elimination of ethylene glycol76. Treatment of 2-[(methoxycarbonyl)cyanomethylene]-1,3-dioxolane (38) with 1,3-diaminopropane or with 4,5-dimethyl-1,2-phenylenediamine gives the hexahydropyrimidine and the benzimidazoline derivatives 39 and 40, respectively (equation 11). Similarly to the reaction of ketene dithioacetals with amines, the reaction between ketene acetals and amines proceeds via monoamino-substituted intermediates and ketene 7V,Oacetals can be isolated when one molar amine is used72. 

Since the report by Carboni and Lindsey in 1959 on the cycloaddition reaction of tetrazines to multiple bonded molecules as a route to pyridazines, such reactions have been extensively studied. In addition to acetylenes and ethylenes, enol ethers, ketene acetals, enol esters and enamines, and even aldehydes and ketones have been used as starting materials for pyridazines. A detailed investigation of various 1,2,4, 5-tetrazines in these syntheses revealed the following facts. In [4 + 2] cycloaddition reactions of 3,6-bis(methylthio)-l,2,4,5-tetrazine with dienophiles, which lead to pyridazines, the following order of reactivity was observed (in parenthesis the reaction temperature is given) ynamines (25°C) > enamines (25-60°C) > ketene acetals (45-100°C) > enamides (80-100°C) > trimethylsilyl or alkyl enol ethers (100-140°C) > enol... 

An unprecedented cyclopropanation reaction was observed during the reaction of ketene alkylsilyl acetals (191) with bromoform-diethylzinc. When monosubstituted acetals were used, cyclopropanecarboxylic esters (195) were formed by a novel C-H insertion. When disubstituted ketene acetals were used, byproducts such as a,)5-ethylenic esters (197) were also formed presumably via 196 (equation 49). This reaction provides a convenient method for the preparation of the bicyclo[3.1.0] hexane system and can be advantageously compared to the copper-catalysed intramolecular cyclization of unsaturated a-diazoketones . 

For example, the diene (192) reacts faster with ketene acetal (193a, R = R = OEt), an electron-rich dienophile, than with acrylonitrile (193c, R = CN, R = H), an electron-deficient dienophile.161 Since allyl alcohol (193b, R = CH2OH, R = H) probably has HOMO and LUMO energies very close to those of ethylene itself, and since it reacts at an intermediate rate,... 

Since the monomer I would copolymerize with a wide variety of comonomers with the introduction of an ester group into the main chain, this appeared to make possible the preparation of biodegradable addition polymers. Copolymerization of ethylene and the ketene acetal I at 120°C produced a series of copolymers containing ester groups in the backbone of the copolymer, again with quantitative ring opening. 

More recently, Rousseau and Blanco reacted 3-methylbut-2-enoyl chloride with a number of silyl ketene acetals to produce -Yid-ethylenic P-keto esters, with yields in the range 62-80% neither but-2-enoyl chloride nor propenoyl chloride reacted under these conditions. They employed this reaction in a new synthesis of ( )-turmerone (6 Scheme 12). 

Dioxolan-2-ylium cations (7), derived from aldehyde ethylene acetals by hydride abstraction, react with silyl ketene acetals to give P-keto esters, selectively monoprotected at the ketone carbonyl (equation 14). 2... 

Conjugate addition of O-silyl ketene acetals to enones Addition of 1 -methoxy-1 -(r-butyldimcthylsilyloxy)ethylene to cyclohcxcnone proceeds in low yield when catalyzed by TiCI4 or TiCI4/Ti(0-/ -Pr)4, but is effected in 95% yield when catalyzed by 1.0 M LiCI04 in diethyl ether. 

Substitution of attylic alcohols by silyl ketene acetals. Allylic alcohols undergo substitution with l-methoxy-l-(r-butyldimethylsilyloxy)ethylene (1) in 3M LiCI04 in diethyl ether. 

A range of aliphatic and aromatic terminal alkenes reacted with silyl ketene acetals to produce esters 148 in moderate to quantitative yields. In particular, carbometallation of ethylene occurred at room temperature in 61 and 94% yields, respectively, at pressures of 1 and 10 atm, without polymerization of ethylene (Scheme 10.48, inset). A mechanistic rationalization for the formation of the alkylindium species 149 was proposed based on the crystallographic structure analysis ofa cyclic product of carboindation 149a suggesting an anti attack of the silyl ketene acetal nucleophilic species on the activated alkene substrate (Scheme 10.49). 

Although cyanoacrylate polymers are most commonly prepared by anionic polymerization, they may also be prepared by free-radical polymerization using conventional radical initiators (36-38), provided adequate amounts of anionic polymerization inhibitors are employed. Bulk photoanionic polymerization of cyanoacrylates has also been described by a number of workers (39-43). These systems rely on the in situ generation of an anionic initiator from a neutral species, following absorption of light of an appropriate wavelength. The zwitterionic and radical copolymerization of cyanoacrylates has also been reported for a number of comonomers including vinyl ethers (44), ketene acetals (45), furan (46), vinyl ketones (47), and ethylene (48). 

Ketene can be obtained by reaction of carbon oxides with ethylene (53). Because ketene combines readily with acetic acid, forming anhydride, this route may have practical appHcations. Litde is known about the engineering possibiHties of these reactions. 

The materials of constmction of the radiant coil are highly heat-resistant steel alloys, such as Sicromal containing 25% Cr, 20% Ni, and 2% Si. Triethyi phosphate [78-40-0] catalyst is injected into the acetic acid vapor. Ammonia [7664-41-7] is added to the gas mixture leaving the furnace to neutralize the catalyst and thus prevent ketene and water from recombining. The cmde ketene obtained from this process contains water, acetic acid, acetic anhydride, and 7 vol % other gases (mainly carbon monoxide [630-08-0][124-38-9] ethylene /74-< 3 -/7, and methane /74-< 2-<7/). The gas mixture is chilled to less than 100°C to remove water, unconverted acetic acid, and the acetic anhydride formed as a Hquid phase (52,53). 

Ketene [463-51-4] M 42.0, b 127-130 , d 1.093, n 1.441. Prepared by pyrolysis of acetic anhydride. Purified by passage through a trap at -75° and collected in a liquid-nitrogen-cooled trap. Ethylene was removed by evacuating the ethylene in an isopentane-liquid-nitrogen slush pack at -160°. Stored at room temperature in a suitable container in the dark. See diketene on p. 209. 

Figure 5.6 Alcohols, aldehydes, ketones and acids 15, ethylene glycol 16, vinyl alcohol 17, acetaldehyde 18, formaldehyde 19, glyoxal 20, propionaldehyde 21, propionaldehyde 22, acetone 23, ketene 24, formic acid 25, acetic acid 26, methyl formate. (Reproduced from Guillemin et at. 2004 by permission of Elsevier)...

The reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful. An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene. Nitroform is produced industrially via this method in a continuous process in 74 % yield. " The reaction of ethylene with 95-100 % nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane. Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. ... 

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