Ethylene elimination

Extensive studies on the Wacker process have been carried out in industrial laboratories. Also, many papers on mechanistic and kinetic studies have been published[17-22]. Several interesting observations have been made in the oxidation of ethylene. Most important, it has been established that no incorporation of deuterium takes place by the reaction carried out in D2O, indicating that the hydride shift takes place and vinyl alcohol is not an intermediate[l,17]. The reaction is explained by oxypailadation of ethylene, / -elimination to give the vinyl alcohol 6, which complexes to H-PdCl, reinsertion of the coordinated vinyl alcohol with opposite regiochemistry to give 7, and aldehyde formation by the elimination of Pd—H. 

Oxidative Carbonylation of Ethylene—Elimination of Alcohol from p-Alkoxypropionates. Spectacular progress in the 1970s led to the rapid development of organotransition-metal chemistry, particularly to catalyze olefin reactions (93,94). A number of patents have been issued (28,95—97) for the oxidative carbonylation of ethylene to provide acryUc acid and esters. The procedure is based on the palladium catalyzed carbonylation of ethylene in the Hquid phase at temperatures of 50—200°C. Esters are formed when alcohols are included. Anhydrous conditions are desirable to minimize the formation of by-products including acetaldehyde and carbon dioxide (see Acetaldehyde). 

Bowen, R.D. Derrick, P.J. The Mechanism of Ethylene Elimination From the Oxonium Ions [CH3CH2CH=0CH2CH3] and [(CH3)2C=0CH2CH3]7 J. Chem. Soc., Perkin Trans. 2 1992, 1033-1039. 

For example, the production of CF3-CFH2 (134a) from ethylene eliminates 10 moles of HCI for every mole of CF3-CFH2 (134a) as shown below. 

Diaminocarbene, H2N-C-NH2 (26), was prepared by collisional reduction of the corresponding cation-radical that was in turn generated by dissociative ionization of aminoguanidine [102]. Carbene 26 gives an abundant survivor ion in the +NR+ mass spectrum and is clearly distinguished from its more stable isomer formamidine. Amino(hydroxy)carbene, H2N-C-OH, has also been prepared by NRMS [103]. Hydroxy-thiohydroxy-carbene cation-radical, HO-C-SH+ (27+ ), is formed somewhat unexpectedly by ethylene elimination from ionized S-ethylthioformate and O-ethylthioformate instead of the expected thioformic acid. Carbene ion 27+ was characterized by a +NR+ mass spectrum that showed a dominant survivor ion of reionized carbene [104]. The energetics of neutral and ionic HO-C-SH have been addressed by ab initio calculations [105]. Di-(thiohydroxy)carbene, HS-C-SH, is also known [106]. 

These complexes are suitable for the ring-opening metathesis polymerization of functionalized norbomenes in water,148 as well as ring-closure reactions via ethylene elimination.149 The versatility of these catalysts has given rise to extensive applications in organic synthesis,150151 including, for example, amino acid derivatives.152... 

A new degenerate rearrangement process mixing all carbon atoms has been revealed by Franke et al. (1980, 1981) through studies of Cj-labelled [49]. Electron impact ionization (70 and 12 eV respectively) of [50], [51], [52] and [53] in the gas phase gave [M-Br]+ ions which unimolecularly yield ethylene with isotopic compositions indicating statistical distribution of the labels prior to ethylene elimination. All precursors gave the same distribution of labelled ethylenes. Various mechanisms (43) have been proposed in the litera-... 

More detailed studies of the behavior of benzotriazoles upon electron impact provided evidence for the exclusive presence of the l//-benzotriazole tautomer in the gas phase. The A/t of 2//-benzotriazole is generated from 2-ethylbenzotriazole (66) by ethylene elimination isomerization to the l//-tautomer precedes the fragmentation <730MS(7)1267). 

It seems that, under the conditions studied, the ethylene elimination occurs from the triplet state, and that free radicals are formed from both the excited singlet and the triplet molecules. The results, however, clearly indicate the importance of the extent of vibrational excitation in determining the mode of decomposition. (Note the different conclusions regarding the states responsible for primary process I in the direct and acetone-sensitized photolysis.) Since the vibrational levels involved in the two cases may differ considerably, we suggest this dissimilarity as a possible explanation for the different characteristics shown by the direct... 

It was shown by Wagner and Kemppainen that certain y substituents which increase the reactivity of alkyl phenyl ketones in type II photoelimination, actually reduce the overall quantum efficiency of the process. Baum et al. found that the quantum efficiency of ethylene elimination from butyrophenone and its para-... 

The molecular structure of the ethyl trichloro complex TiCl3(CH2CH3)(dmpe) has been redetermined by X-ray crystallography at low temperature, with results that are more precise but not significantly different from those previously reported. The extremely bent Ti-C-C chain as evidence for strong f3-agostic interaction was confirmed. Preliminary results on the decomposition reaction of this complex suggest a radical process, rather than (3-H transfer with ethylene elimination.231... 

The relative rates for intramolecular hydrogen migration and competing ethylene elimination allow just one exchange process. The decision whether the exchange processes are concerted reactions (proceeding via bicyclic transition states) or whether reactive intermediates come into existence (multistep reaction) is open to question. 

Complex hydrogen migrations precede also the ethylene elimination from aryl-and alkine substituted dimethylcarbenium ions136 -138). Investigations of 2H and l3C labelled compounds, 140, established that the carbon and hydrogen atoms of the side chain loose their positional identity before or during ethylene elimination. 

The decomposition maps obtained show that (after verification of basic decompositions) the [R-l-42] ion yields [R] by propene elimination (carbons 15, 16 and 17). This fragmentation is a general occurrence in the compounds studied the loss of CH3OH from [R -I- 42] and R] ions (m/z 125 and 83), as well as the formation of the m/z 59 ion [COOCHa], are characteristic of the presence of methyl esters and shed light on the structure of the side chain ethylene eliminations (such as C2H4, C3H6 and C4H3) indicate the presence of the hydrocarbon skeleton finally, the [M-R] + and [M-(R -I- 42)] ions obviously do not lead to R ions (Fig. 49). 

In dichloroethane and methylene chloride solutions, photoinduced two-center oxidative addition of chloroalkane takes place, leading to formation of the iridium(II) coordination compound. In the case of C2H4CI2, ethylene elimination takes place [scheme (6.141)]. 

As can be seen from Equation [10], the formation of m/z 58, 56, 55 and 57 requires 0, 1, 2 and 3 allylic 1,3-H/D shifts, respectively, which coincides with the shift of the maximum rate of the corresponding ethylene eliminations to longer times. 

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