Formaldehyde intermediate

Solutions of Ru3(CO)i2 in carboxylic acids are active catalysts for hydrogenation of carbon monoxide at low pressures (below 340 atm). Methanol is the major product (obtained as its ester), and smaller amounts of ethylene glycol diester are also formed. At 340 atm and 260°C a combined rate to these products of 8.3 x 10 3 turnovers s-1 was observed in acetic acid solvent. Similar rates to methanol are obtainable in other polar solvents, but ethylene glycol is not observed under these conditions except in the presence of carboxylic acids. Studies of this reaction, including infrared measurements under reaction conditions, were carried out to determine the nature of the catalyst and the mechanism of glycol formation. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor. 

Elliott and coworkers—carbonate, formate, and formaldehyde intermediates. 

The explanation of the key role played by acetic acid itself may be as proposed by Dombek (J ). In this, the presumed coordinated formaldehyde intermediate, as the primary product of CO reduction, is preferentially acylated to produce a carbon bound acyloxymethyl group leading to the sequence of reactions shown in the lower half of the reaction scheme ... 

The concept of a (bound) formaldehyde intermediate in CO hydrogenation is supported by the work of Feder and Rathke (36) and Fahey (43). Experiments under H2/CO pressure at 182-220°C showed that paraformaldehyde and trioxane (which depolymerize to formaldehyde at reaction temperatures) are converted by the cobalt catalyst to the same products as those formed from H2/CO alone. The rate of product formation is faster than in comparable H2/CO-only experiments, and product distributions are different, apparently because secondary reactions are now less competitive. However, Rathke and Feder note that the formate/alcohol ratio is similar to that found in H2/CO-only reactions (36). Roth and Orchin have reported that monomeric formaldehyde reacts with HCo(CO)4 under 1 atm of CO at 0°C to form glycolaldehyde, an ethylene glycol precursor (75). The postulated steps in this process are shown in (19)—(21), in which complexes not observed but... 

A very simplified possible scheme for subsequent reactions of a formaldehyde intermediate, modeled largely after one presented by Rathke and Feder (38), is the following ... 

Reactions of added formaldehyde may differ somewhat from those of a possible coordinated formaldehyde intermediate generated by CO hydrogenation. It may be unnecessary for an added formaldehyde molecule to be coordinated to the metal before reacting with its hydride ligand. Such an addition could take place by an ionic or even a radical process. However, the trends in selectivity appear to be consistent in those systems which both... 

In combustion systems it is generally desirable to minimize the concentration of intermediates, since it is important to obtain complete oxidation of the fuel. Figure 13.5 shows modeling predictions for oxidation of methane in a batch reactor maintained at constant temperature and pressure. After an induction time the rate of CH4 consumption increases as a radical pool develops. The formaldehyde intermediate builds up at reaction times below 100 ms, but then reaches a pseudo-steady state, where CH2O formed is rapidly oxidized further to CO. Carbon monoxide oxidation is slow as long as CH4 is still present in the reaction system once CH4 is depleted, CO (and the remaining CH2O) is rapidly oxidized to CO2. 

Relatively little basic information has been published regarding the kinetics of phenol-formaldehyde intermediates, especially of phenols, methylol phenols, benzyl alcohol and benzylic ethers with isocyanates. Due to the fact that a typical resole contains both phenolic and benzylic hydroxyl groups, it was of interest to determine their reactivity toward isocyanates in the presence of various catalysts, as well as the effect of substitution on their reactivity. This investigation describes the kinetics of model phenols and model benzyl alcohols with phenyl isocyanate catalyzed with either a tertiary amine (dimethylcyclo-hexylamine, DMCHA) or an organotin catalyst, dibutyltin dilaurate (DBTDL) in either dioxane or dimethylformamide solution. 

It is proposed that this reaction involves an acid-activated formaldehyde intermediate (i.e., in the form of hydroxymethyl carbonium ion ) that electrophilically attacks the olefinic double bond to form an oxetane oxonium or a three-member bridged... 

Comparatively the synthesis of long-chain oxygenated from methanol has attracted relatively low attention because very low selectivity was obtained in previous work, but more recent studies, using decomposed hydrotalcite (MgO/AlgOg mixed oxides) and ZnO promoted Cu as catalysts, concluded that a mixture of alcohols, ketones, aldehydes, esters and ethers, with two to nine carbon atoms (79% of the total oxygenates products) can be obtained. In addition, in this study it is proposed that the first C-C carbon bond formation goes via formyl and formaldehyde intermediates. 

Figure 7. CP-MAS C-NMR spectrum of the reaction product of pMDI with glutein protein hydrolysate-formaldehyde intermediate.

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