Homologization reaction

The reactivity of 2-methylselenazole toward carbonyl compounds is the same as its thiazoie homolog. Reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride as catalyst gives 4-methyl-2-styrylselenazoie [m.p. 74-75 C (19)] (Scheme 43). 

Activation volumes may be used to elucidate the mechanisms of classes of reactions involving the same functional groups, and changes in activation volumes can be used to characterize the point at which a change in reaction mechanism takes place in a series of homologous reactions. 

These various effects combine to result in different rate and equilibrium constants for homologous reactions. The substituents influence these parameters in part by displacements of electron density of the first two types and in part by geometric effects of the last type. When some of the possible complications are considered, it is not surprising that there is no generally useful method for correlating the Gyxn terms with satisfactory accuracy. However, there are a number of special cases in which useful correlations can be developed. This is particu-... 

It was an interesting idea to create the giant tube-like structures 46 capped with a Lewis acid center by the homologation reaction of 42 with dimethylsulfoxonium methylide and their deboronation to the three-armed star polymethylene polymers 47 incorporating a m, r-l,3,5-trisubstituted cyclohexane core (Scheme 12) <2003JA12179, 20010L3063>. 

Unusual Carbon Monoxide Activation, Reduction, and Homologation Reactions of 5/-Element Organometallics... 

In this paper we disclose the syngas homologation of carboxylic acids via ruthenium homogeneous catalysis. This novel homologation reaction involves treatment of lower MW carboxylic acids with synthesis gas (C0/H2) in the presence of soluble ruthenium species, e.g., Ru02, Ru3(C0)12, H4Ru4(C0)12, coupled with iodide-containing promoters such as HI or an alkyl iodide (1). 

Deuteration studies with acetic acid-d4 (99.5% atom D) as the carboxylic acid building block, ruthenium(IV) oxide plus methyl iodide-d3 as catalyst couple and 1/1 (C0/H2) syngas, were less definitive (see Table III). Typical samples of propionic and butyric acid products, isolated by distillation in vacuo and glc trapping, and analyzed by NMR, indicated considerable scrambling had occurred within the time frame of the acid homologation reaction. 

Co2(CO)g has been used to obtain encapsulated cobalt clusters in Y-faujasite, which have been used as model catalysts for methane homologation [152]. The gas phase adsorption of Co2(CO)8 under N2 rendered predominately encaged Co4(CO)i2 species whereas Co,s(CO)iis was obtained when the impregnation of Co2(CO)8 was carried out under a CO/H2 atmosphere [152, 155], Samples were oxidized at 80°C, subsequently reduced at 400 °C and then structurally characterized by EXAFS. Clusters of two and three cobalt atoms were formed from encaged Co4(CO)i2 and COis(CO)iis, respectively. Higher methane conversion and selectivity to C2+ products in the CH4 homologation reaction have been obtained for the two atoms-size cluster sample the results were discussed using a DFT model [152]. 

The homologation reaction was first reported nearly 40 years ago (2). The catalyst precursor was Co (CO). Subsequent workers utilized cobalt catalysts but also employed iodide promoters (, 4 ), a Ru co-catalyst ( ), and trivalent phosphines ( ) to increase the yield. The reaction is carried out at 180-200 °C and 4000-8000 psig. In the better cases, the ethanol rate and selectivity are 1-6 M/hr and 50-80 %. Unsatisfactory conversion, selectivity, and the required high operating pressure have prevented commercialization of the current homologation technology. Additionally, fermentation routes to ethanol have now... 

The homologation reaction proceeds via a similar mechanism except acetaldehyde is further reduced in situ to ethanol. 

In separate experiments, we have demonstrated that Reactions 5a and 5b take place with catalysts based only on Rh. Reaction 5b is also catalyzed by Ru. The reactions proceed particularly efficiently under homologation reaction conditions when promoters such as phosphines and pyridines are present. This observation is in line with examples described in a German patent application ( ). 

Reactions lla-e add up to Reaction 10. Reactions lla-b have been shown above to be catalyzed by Rh/CH3l. Reaction 11c, i.e. acid-catalysed pyrolysis of EDA to acetaldehyde and acetic anhydride, is well documented (9). Both reaction lid, hydrogenation of aldehyde, and Reaction lie, carbonylation of alcohols, are of course well known. The reaction sequence is in agreement with the fact that EDA and AH, especially in short-duration experiments, are detected as by-products. Acetaldehyde is also observed in small quantities, but no ethanol is found. Possibly, Reactions lid and He occur concertedly. We have separately demonstrated that both EDA and AH are suitable feeds to produce propionic acid under homologation reactions conditions. We thus demonstrated... 

Possible applications of ester-homologation reactions. The coproduction of acetic acid and ethyl acetate according to Reaction 4 may find some interesting applications ... 

The chemical and spectroscopic properties of the acid hydride HRu(C0) I and of the ion-pairs of the [Ru(C0) I ] anion are reported and their role in the catalytic carbonylation and homologation reactions on oxygenated substrates are discussed. 

Homologation reactions on alcohols-formic esters produce a mixture of oxygenates rich in acetates suitable for use in gasoline with interesting antiknock and combustion properties. 

The essential requirement for ruthenium catalysts to be active in homologation reactions of oxygenated substrates is the presence of an iodide promoter which may be I2, HI, an alkyl or metal iodide, or a quaternary ammonium or phosphonium iodide (3). With alkali iodides as promoters, ion-pairs of the [fac-Ru(CO)3l3] anion are formed in the catalytic solution of the homologation reactions starting from different precursors Ru(Acac>3, Ru3(CO)] 2> Ru(CO)4l2 etc. ( ). ... 

The carbonylation-homologation reaction may also be carried out on a mixture of alcohols and their formates. For instance, at a very high conversion of the reagents, methanol-methyl formate and i-butaiol -i-butyl formate produce a mixture of oxygenates particularly rich in acetates that are useful as octane improvers for gasoline (Fig. 3). 

The equivalence of sulfur and oxygen in this ring system carries over to NSAIDs as well. Preparation of the sulfur analogue of isoxepac (6-4) starts with the alkylation of thiophenol (27-1) with benzyl chloride (26-1). Cyclization of the intermediate thioether (27-2) then affords the homothioxanthone (27-3). The carboxyl side chain is then extended by means of the Amdt-Eistert homologation reaction. The acid is thus hrst converted to its acid chloride by means of thionyl chloride. Reaction with excess diazomethane leads to the diazoketone (27-4). Treatment of that intermediate with silver benzoate and triethylamine leads the ketone to rearrange to an acetic acid. There is thus obtained tiopinac (27-5) [28]. 

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