Formaldehyde, formation, methanol synthesis

The carbon dioxide removed in synthesis gas preparation can be reacted with ammonia, to lonn urea CO(NH2)2- This is an excellent fertilizer, highly concentrated in nitrogen (46.6%) and also useful as an additive in animal feed to provide the nitrogen for formation of meat protein. Urea is also an important source of resins and plastics by reacting it with formaldehyde from methanol. 

In the methanol synthesis, a fast hydrogenation of the adsorbed formaldehyde would overcome arguments invoking any thermodynamic limitation to its formation. Formaldehyde adsorbed through both the oxygen and the carbon ends has been characterized in homogeneous catalysis (43), on oxide surfaces (44) and more recently on ruthenium metal (45). 

In CO2 hydrogenation over Cu/ZrOj based catalysts, the methanol formation activity could be correlated with copper dispersion. The reaction intermediates of methanol synthesis were carbonate, formate, formaldehyde and/or methoxy, and the rate determining step for methanol synthesis seems to be the conversion of formate into formaldehyde or methoxy. 

Enamines. In a synthesis of 19/3-norsteroids, Habermehl and Haaf1 found that the 19 -hydroxymethyl group of (1) is eliminated as formaldehyde on formation of the enamine (2). Thus, when (1) is heated to reflux with pyrrolidine in methanol, the enamine (2) separates within minutes. The enamine is hydrolyzed to the A4-3-ketone (3) by treatment with sodium acetate in acetic acid-methanol. Such an elimination had been observed previously by retroaldol... 

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. 

Similar IR experiments were performed to establish the reaction mechanism for methanol oxidation on unsupported and sihca-supported vanadia, which are more selective catalysts for formaldehyde synthesis than vanadia-titania. The formation of methoxy groups from methanol dissociative or condensative adsorption was determined while it was established that formaldehyde (directly adsorbed or produced by methoxy group oxidation) mainly adsorbs in the form of dioxymethylene species, stable only at relatively low temperatures. It was concluded that dioxymethylene can react with methanol at low conversion to give rise to dimethoxymethane while it preferentially desorbs as formaldehyde at higher conversions and temperatures. The weakness of the adsorption of formaldehyde was considered to be the key feature of catalysts allowing high selectivity in formaldehyde synthesis. 

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