Ketene dimers structure

The only stable 1,3,2-dioxathietanes known are fluorinated sulfate derivatives formed by addition of sulfur trioxide to bis(trifluoromethyl)ketene. These structures are fairly well characterized from spectral data and from reactions with nucleophiles. Hexafluoroisopropy-lidene-l,3,2-dioxathietane 2,2-dioxide acts as a sulfur trioxide transfer agent to alkenes and is in equilibrium with a dimeric form as indicated by 19F NMR (Scheme 138) (71KGS1645, 72KGS306, 73KGS178, 132l). 

Ketene looks pretty unlikely It is CH2=C=0 with two tt bonds (C=C and C=0) to the same carbon atom. The orbitals for these jt bonds must be orthogonal because the central carbon atom is sp hybridized with two linear o bonds and two p orbitals at right angles both to the o bonds and to each other. Can such a molecule exist When acetone vapour is heated to very high temperatures (700-750 °C) methane is given off and ketene is supposed to be the other product. What is isolated is a ketene dimer (C4H4O2) and even the structure of this is in doubt as two reasonable structures can be written. 

The history of the establiehmeat of thin structure U Mimmoiized in Table 10 which inoludee only a part of the work of C. D, Hwd and his school. We have also not mentioned some of the work of O. Sohroeter, of H. Staudingcr and of othera who have dlroumed the structure of the ketene dimer incidentally without furnishing any new evidence. 

Hie spontaneous dimerization of ketene, which was described as early as 191U, is only a particular case of this gen al reaction the jS-lactono structure of the ketene dimer, however, was not recognised until much later ... 

Most of the reactions of /3-lsctonee in the literature concern propiolactone itself. Since there is an undentandabie tendency to consider these reactions cf propiolactone as general reactions, one must bear in mind in working with substituted -lactones tiiat substituents can exert a profound influence, not only on the reaction rate, but sometimes even on the natiirc of the reactionB.m As the reactivity of the ketene dimers with a -lactone structure differs from that of the other lactones, they are treated separately in section Vn,... 

Ketene dimer (XXII), which is an analog of the 2-methylene-oxetane (XXI), will tndergo a higher extent of ring opening on polymerization to give copolymers with different structures depending on whether the reaction is run in a sealed tube or open to the air. 

The wettability of various wood fibres was studied in [173], including bleached and unbleached, and alkyl ketene dimer sized and non-sized fibres. An improvement of the wettability with an increase of the surfactant concentration, except nonionics, was observed for all types of fibres. It has been noted in [174] that the electrokinetic potential of fibres determines considerably the efficiency of their washing and dying. Alkali mercerisation of cotton influences not only the fine structure, morphology and conformation of cellulose molecules, but also the negative electrokinetic potential of the cotton fibres. Based on this, the selection of mercerisation conditions due to changes in the NaOH concentration will allow to... 

Figure 7.18. Chemical structures of (a) abietic acid, which is one of the more common constituents of rosin (b) alkyl ketene dimer (AKD), with R = C14-C18 (saturated or unsaturated) (c) alkenyl succinic anhydride (ASA) with R = C14-C18 (unsaturated)...

The tendency of ketene to undergo cyclodimerization reactions was noted as early as 1908 by Chick and Wilsmore , and by Staudinger and Klever . The unsymmetrical structure of the ketene dimer 3 was established by spectroscopical methods The mechanism of this cycloaddition reaction was studied recently and the chemistry of diketene was reviewed... 

It is important to emphasize that even if a measurable is not simply related to underlying physical properties, the measurable may still represent a valuable practical analytical tool for industrial purposes(114). Kaplan, et al. used DWS to study structure formation in alkyl ketene dimer emulsions(l 15). These systems are used in paper manufacture as sizing agents, but lead to technical difficulties if they gel, which they sometimes do. Within a few days, spectra of systems that were going to gel could readily be distinguished from spectra of systems that would remain stable. 

A commercially available monomer that is structurally related to 2-methylene-oxetane is ketene dimer. However, almost nothing has been reported concerning its polymerization by free radical procedures. When ketene dimer was heated with di-Jt-butyl peroxide at 130° in a sealed tube, a small pressure built up and the resulting polymer consisted of mostly 1,3-diketone units. When the pol3nneriza-tion was carried out in a solvent at atmospheric pressure, carbon monoxide was liberated and a copol3nner consisting of mainly monoketone units was obtained. 

Apparently the intermediate radical undergoes ring opening to give the carbonyl radical. In the sealed tube only a little decarbonylation takes place and the copol3mier contains mostly the g-diketone structure. When the reaction is carried out at atmospheric pressure, much more decarbonylation takes place and the copolymer consists of mostly the simple ketone units. Since ketene dimer is an article of commerce, this monomer appears to be an excellent start-x ing material for the introduction of keto groups into an addition polymer. 

Quinolone undergoes photochemical addition of tetramethylethylene to give (434) (70AHC(ii)50), l,3-oxazin-4-ones photocycloadd ketene acetals to give (435), and irradiation of 2,6-dimethylpyran-4-one yields the cage dimer (436). 2-Pyranones form [2 + 2] photodimers whose structure is similar to that of uracil dimers (432 or 433). 

Dimerization. A special case of the [2 + 2] cyclo additions is the dimerization of ketenes. Of the six possible isomeric structures, only the 1,3-cyclobutanediones and the 2-oxetanones (p-lactones) are usually formed. Ketene itself gives predominantly (80-90%) the lactone dimer, 4-methylene-2-oxetanone (3), called diketene [674-82-8]-, approximately 5% is converted to the symmetrical dimer, 1,3-cyclobutanedione [15506-53-3] (4) which undergoes enol-acetylation to so-called triketene [38425-52 1] (5) (44). 

Its structure as determined by an X-ray investigation is shown in Fig 21. It may be understood as a dimer of the assumed phosphathio-ketene intermediate. The cycloaddition of the phosphathioketene corresponds to the behavior of unsubstituted carbaketenes (146) and so is different from that of the phosphaketenes described earlier, while thioketenes dimerize to 1,3-dithietanes (147,148). An asymmetric retro ring cleavage can be initiated if l-thia-3-phosphetane is irradiated by a mercury lamp generating carbon disulfide and the 1,3-diphosphaallene [Eq. (78)] (117, p. 33). 

Much wphysical properties of the dimer of ketene which has the stnioture of the /3-lactone of 3-hydroxy-S-butenoio acid these values an given in Tables Tables 8 and 9 are concerned with the dimers of the substituted hetenes fcv whioh ft /8-lactone structure has been demonstrated. 

Bis-trifluoromethylmethylene)-1,2,4-thiadioxetane 1,1-dioxide (hexafluoro-isobutenylidene sulfate) (499) is a stable, colorless liquid obtained by treatment of bis(trifluoromethyl) ketene, 3,3,3-trifluoro-2-trifluoromethylpropanoic acid, or the anhydride of the latter with sulfur trioxide. It is said, on the basis of F nmr data, to be in equilibrium with a cyclic, eight-membered dimer (/Teq = 0.1321iter/mole at 34.5°C), analogous to the structure of the above-mentioned methylene sulfate . Hydrolysis of 499 gives 3,3,3-trifluoro-2-trifluoromethyl-propanoic acid. The cyclic sulfate is a powerful donor of sulfur trioxide, as exemplified by its reactions with fluoride, bromide, and iodide ions (but not chloride ions), triethylamine, dioxane, sulfolane, and alkenes (See... 

CO2. CHj, CO. H . propene. isobutene, dimethyl ketene. acrolein, diallyl ether, allyl methacrylate monomer and dimer, chain fragments including anhydnde structures from side-group cydization. and an aliphatic ketone in the vidnity of unsaturation CO , SO , phenol, bisphenol S, hydroquinone. fragments of backbone, benzene sulfonic acid... 

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