Elimination of carbon monoxide

Elimination of carbon monoxide accompanied by conversion of an acyl group to the corresponding alkyl moiety has been termed decarbonylation. The process is represented by Eq. (12) with L = CO. 

The elimination of carbon monoxide can occur by a concerted process in some cyclic ketones. The elimination of carbon monoxide from bicyclo[2.2.1]heptadien-7-ones is very facile. In fact, generation of bicyclo[2.2.1]heptadien-7-ones is usually accompanied by spontaneous decarbonylation. 

The elimination of carbon monoxide, ie. the (formal) reversal of cyclopropenone formation from divalent carbon species and alkynes, takes place when cyclopropenones are heated to higher temperatures (130—250 °C) or when subjected to photolysis or electron impact191 ... 

Another method to prepare allenyl ketones uses flash vacuum pyrolysis of the heterocycles 121 (Scheme 7.19) [163], This elimination of carbon monoxide is at least formally a cheletropic reaction. Highly reactive allenes such as esters and nitriles of type 124 or unsubstituted butadienal can be generated if retro-Diels-Alder reaction of 123 or similar precursors, respectively, is performed by flash vacuum pyrolysis [164]. 

Similarly, irradiation of 179 in the solid causes elimination of carbon monoxide and formation, almost exclusively, of cis-diphenylbenzocyclobutane, 180, in which configuration is retained. On the other hand, the major product from photoreaction in solution is the trans isomer, 181 (245). 

X-Ray analysis of the red-orange crystalline thioacrolein complex 272, which is derived from the dimeric thioacrolein derivative by way of thermal elimination of carbon monoxide (Scheme 17), has revealed a structure with an essentially square FejSs array. Analogous reactions with iron carbonyls have been carried out by McCaskie et who used thiete 1,1-dioxide instead of thiete (Scheme 18). 

Some homolytic fragmentation reactions are driven by formation of small, stable molecules. Alkyl acyloxyl radicals (RCOp decarboxylate rapidly (fe > 1 x 10 s ) to give alkyl radicals, and even aryl acyloxyl radicals (ArCOp decarboxylate to aryl radicals with rate constants in the 10 s range." Azo radicals produced in the homolysis of azo initiators eliminate nitrogen rapidly. Elimination of carbon monoxide from acyl radicals occurs but is slow enough (fe 10" -10 such that the acyl radical can be trapped in a bimolecular process,... 

Direct reaction of iron pentacarbonyl with trimethylsilyl isocyanide ( C=N—SiMe3) at 65°-75° yields an air-sensitive substitution product Me3Si—N=C Fe(CO)4 in 93% yield, with elimination of carbon monoxide (152). It was shown by infrared spectroscopy (38) that complex formation lowers the N=C bond order for Me3Si—N=C , whereas it raises the N=C bond order for Me3C—N=C , presumably as a result of interaction between dv orbitals of silicon with the metal d orbitals. 

Elimination of carbon monoxide from metal carbonyls and coordination of the organosilicon olefin has been reported for divinylsilanes (54, 108, 109) (the compounds obtained are air-sensitive) ... 

In a similar manner, UV irradiation of (triphenylsilyl)phenylacetylene with cyclopentadienylmanganese tricarbonyl 121) and cyclopentadienyl-niobium tetracarbonyl 122) results in elimination of carbon monoxide and formation of monodentate acetylene complexes (R = Ph) ... 

Thermolysis of indenone oxides (151) is an equally useful route to the betaines (150). Dimethyl acetylenedicarboxylate and compound 151 (R = R = Ph) at 175°C give adduct 153, and cyclohexanone at 150 C gives adduct 154. - Similarly, 1,3-dipolar adducts (e.g., 155) have been obtained using a wide variety of olefins—including cis- and [rans-, 2-dichloroethylene, dimethyl maleate, dimethyl fumarate, maleic anhydride, cis- and tran -stilbene, fran -dibenzoylethylene, tra .y-l,2-dicyanoethylene, A -phenylmaleimide, vinylene carbonate, acenaphthylene, and norbor-nadiene. With cis olefins the endo adduct (155) is usually the predominant isomer. Diphenylcyclopropenone gives compound 156 by spontaneous elimination of carbon monoxide from the initial adduct (157). Adduct 156... 

Similar to other ot-oxo acids, 2-oxopentanedioic acid reacts with sulfur tetrafluoride with elimination of carbon monoxide cyclization is, however, the main reaction pathway. 2,2.5,5-Tetrafluorotetrahydrofuran (26) is formed as the major product together with 1,1,1,4,4,4-hexa-fluorobutane.117... 

This reaction also involves the elimination of carbon monoxide and the formation of a mixture of hydrocarbons, principally ethane and methane. It is homogeneous and conveniently measurable between 450° and 600° C. The decomposition is kinetically unimolecular over a considerable range of pressure, but at pressures below about 80 mm. Hg the velocity constant falls appreciably, in the manner which would be expected if Lindemann s theory were correct. In the region of pressure where the reaction is unimolecular the velocity constants (sec-1) are given by... 

The reaction mechanism was explained on the theory that the oxidative attack was through the methyl group, n-octane being converted to n-octaldehyde and this in turn to the next lower aldehyde, with the elimination of carbon monoxide. The degradative action was believed to be repeated step by step, through a nonstop run, to formaldehyde as the final product. n-Heptaldehyde and n-butvraldehyde gave essentially the same products. It was believed the luminescence was due to the chain reaction by which each aldehyde was converted to the next lower aldehyde with the elimination of carbon monoxide. 

The elimination of carbon monoxide from nonfluonnated acyl fluorides, however, does not result in a fluorine compound Although it was claimed earlier that benzoyl fluoride can be converted into fluorobenzene by using tns(triphenyl-phosphine)rhodium chloride, recent studies proved that the product is benzene and not fluorobenzene [91]... 

Saturated ketones undergo a large number of photochemical reactions which include photoreduction, elimination of a-heterosubstituents, a-cleavage, 7-hydrogen transfer, and elimination of carbon monoxide. In this chapter only photochemical rearrangements of saturated ketones will be considered. 

R = H) and 1,3,5-heptatriene (Formula 377) (R = Me), respectively (62,161). The 3,5-cycloheptadienes cannot have the diene system planar and consequently show anomalous ultraviolet absorption (161). The excitation for the elimination of carbon monoxide involves the carbonyl group not the diene system (see Sec. IIC) (161). 

A wavelength-dependent photoreaction has been described in thecarbonyl-containing thiiran (131)113 irradiation at X = 254 nm gave the alkene (132), whereas irradiation at X > 280 nm gave products 133 and 134 arising by Type I cleavage, followed either by elimination of carbon monoxide or by cyclization to the oxacarbene. 

In theory, pyrolysis of carbonyl-based heteronuclear cluster compounds should, by analogy with homonuclear carbonyl cluster chemistry, cause elimination of carbon monoxide followed by cluster aggregation. In practice it is difficult to predict the course of these reactions, which can involve simple loss of ligand, cluster aggregation, or degradation, and reactions are often complex and result in low yields. A few... 

Peterson, J.E., and R.D.Stewart. 1970. Absorption and elimination of carbon monoxide by inactive men. Arch. Environ. Health 21 (2) 165—171. 

A great variety of transformations of (N//-enamino)carbene complexes (Z)-97 become possible because of the presence of hydrogen at the nitrogen atom, which is readily replaced by other functional groups. C-Amino-methylenation of [2-(/V//-amino)ethenyl]carbene complexes (CO)5M = C(OEt) — CH = C(NHR)Ph (Z)-97 (M = Cr, W) with formamides HCO — NR2 (NR2 = NMe2, pyrrolidine, morpholine) in the presence of benzoyl chloride and triethylamine affords [2-amino-l-(iminoacyl)ethe-nyl]carbene complexes (CO)5M=C(OEt) - C[C(Ph)=NPh]=CHNR2 (E)-107 in 61-83% yield (Scheme 40). By elimination of carbon monoxide,... 

During their attempts to synthesize disaccharides, Freudenberg and WolP discovered that the pyrolysis of bis(2,3 5,6-di-O-isopropylidene-D-mannofuranosyl) oxalate afforded a low yield of bis(2,3 5,6-di-0-isopro-pylidene-D-mannofuranosyl) carbonate, with the elimination of carbon monoxide. 

The photodecomposition of l,3-dichloro-l,l,3,3-tetrafluoroacetone (5) gives, with elimination of carbon monoxide, 1.2-dichloro-l,1.2.2-tetr ifluorocthane and dichlorodifluoromclhane. ... 

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