Methanol-formaldehyde reaction

Methanol undergoes reactions that are typical of alcohols as a chemical class (3). Dehydrogenation and oxidative dehydrogenation to formaldehyde over silver or molybdenum oxide catalysts are of particular industrial importance. 

Fig. 1. Examples of temperature dependence of the rate constant for the reactions in which the low-temperature rate-constant limit has been observed 1. hydrogen transfer in the excited singlet state of the molecule represented by (6.16) 2. molecular reorientation in methane crystal 3. internal rotation of CHj group in radical (6.25) 4. inversion of radical (6.40) 5. hydrogen transfer in halved molecule (6.16) 6. isomerization of molecule (6.17) in excited triplet state 7. tautomerization in the ground state of 7-azoindole dimer (6.1) 8. polymerization of formaldehyde in reaction (6.44) 9. limiting stage (6.45) of (a) chain hydrobromination, (b) chlorination and (c) bromination of ethylene 10. isomerization of radical (6.18) 11. abstraction of H atom by methyl radical from methanol matrix [reaction (6.19)] 12. radical pair isomerization in dimethylglyoxime crystals [Toriyama et al. 1977].

Reaction of (+)-sedridine (118) and a 37% aqueous solution of CH2O in MeOH at room temperature gave 3-methylperhydropyrido[l,2-c][l,3]oxa-zine (81) (97TA109). Similarly, reaction of andrachcinidine alkaloid, cis-2,6-H-2-(2-oxopropyl)-6-(2-hydroxypentyl)piperidine with 1.5% methanolic formaldehyde solution afforded cw-3,4n,9-H-9-(2-oxopropyl)-3-propylper-hydropyrido[l, 2-c][ 1,3]oxazine (00MI71). 

In this paper, the preparation, characterization and the catalytic performance of the Moo.esVoasWo.ioOx-mixed oxide as a partial oxidation catalyst for the methanol to formaldehyde reaction was studied. 

The calibrated m/z = 44 and m/z = 60 ion currents were converted into the respective partial reaction faradaic currents as described above, and are plotted in Fig. 13.3c as dashed (m/z = 44) and dash-dotted (m/z = 60) lines, using electron numbers of 6 electrons per CO2 molecule and 4 electrons per formic acid molecule formation. The calculated partial current for complete methanol oxidation to CO2 contributes only about one-half of the measured faradaic current. The partial current of methanol oxidation to formic acid is in the range of a few percent of the total methanol oxidation current. The remaining difference, after subtracting the PtO formation/reduction currents and pseudocapacitive contributions as described above, is plotted in Fig. 13.3c (top panel) as a dotted line. As mentioned above (see the beginning of Section 13.3.2), we attribute this current difference to the partial current of methanol oxidation to formaldehyde. This way, we were able to extract the partial currents of all three major products during methanol oxidation reaction, which are otherwise not accessible. 

This chapter compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It is proposed that with the basic catalyst, Mg/Fe/0, the tme alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacts with phenol to yield salicyl alcohol, which rapidly dehydrogenates to salicyladehyde. The latter was isolated in tests made by feeding directly a formalin/phenol aqueous solution. Salicylaldehyde then transforms to o-cresol, the main product of the basic-catalyzed methylation of phenol, likely by means of an intramolecular H-transfer with formaldehyde. With an acid catalyst, H-mordenite, the main products were anisole and cresols moreover, methanol was transformed to alkylaromatics. 

The results obtained indicate that in the reaction between phenol and methanol, formaldehyde is the trae methylating agent when basic catalysts are used. This indicates that the type of transformation occurring with methanol is the factor that mainly differentiates performances in phenol methylation when catalyzed by either basic or acid catalysts. The catalyst plays its role in the generation of the methylating species the nature of the latter then determines the type of phenolic products obtained. 

We have discussed these reactions previously in connection with equilibrium limitations on reactions, and we will discuss them again in Chapter 7, because both use catalysts. These reactions are very important in petrochemicals, because they are used to prepare industrial H2 and CO as well as methanol, formaldehyde, and acetic acid. As noted previously, these processes can be written as... 

Table II. The TON and selectivity to formaldehyde for the methanol oxidation reaction on various 1% supported vanadium oxide catalysts...

For formaldehyde reacting to give /cr/-buty I peroxy methanol, the reaction enthalpy is —66.5 kJmol-1 and for cyclohexanone reacting to give 1-tert-butylperoxycyclohexanol, the enthalpy of reaction is ca —45 kJ mol-1. The average of these is compatible with the value reported from Reference 28. By contrast, the gas phase formal reaction 11 to produce bis(hydroxymethyl) peroxide is calculated to be exothermic by some —218 kJ mol-1 for the case of formaldehyde. 

Direct Oxidation. Direct oxidation of petroleum hydrocarbons has been practiced on a small scale since 1926 methanol, formaldehyde, and acetaldehyde are produced. A much larger project (29) began operating in 1945. The main product of the latter operation is acetic acid, used for the manufacture of cellulose acetate rayon. The oxidation process consists of mixing air with a butane-propane mixture and passing the compressed mixture over a catalyst in a tubular reaction furnace. The product mixture includes acetaldehyde, formaldehyde, acetone, propyl and butyl alcohols, methyl ethyl ketone, and propylene oxide and glycols. The acetaldehyde is oxidized to acetic acid in a separate plant. Thus the products of this operation are the same as those (or their derivatives) produced by olefin hydration and other aliphatic syntheses. 

However, if the photochemical reaction is run in the presence of oxygen, then of course, the methyl radicals are oxidized, and one obtains instead methanol, formaldehyde, and their decomposition products. Now, if the vessel is pumped out after a photo-oxidation and once again a normal photolysis of acetone is run, the products in the first 10 or 15 minutes are still oxidation products rather than hydrocarbon products. It takes from 15 to 30 minutes to remove whatever it is that is attached to the wall before the normal photochemical decomposition of pure acetone products are produced. These results should remind us that oxidation system do produce species, some of which are not known or understood. 

The optimum residence times are to be 11-12 sec. for 400°C., 8-10 sec. for 430°C., 6-7 sec. for 450°C. and 4-6 sec. for 480°C. Carbon monoxide, methanol, formaldehyde, and acetone are decreased with the increase in reaction temperature. At 480°C. the yield of carbon monoxide is a little less and that of propylene oxide is more than those at the other temperatures because of the smaller content of oxygen in the feed gas. 

The methyl radicals produced in Reactions 2a, 15, and 16 could abstract hydrogen to produce the small amounts of methane found in the by-products or could be oxidized with oxygen and/or the metal ions in the 3+ oxidation state. Oxidation of alkyl radicals by metal ions has been studied extensively (11, 12). Also, the oxidation of the intermediates methanol, formaldehyde, and formic acid by cobalt (III) and manganese-(III) has been reported (2,13,15). 

The reaction is of importance, especially when as in (ii.) it is used for the production of phenolic methanols. Formaldehyde, when condensed with phenols in presence of acid or basic catalysts, yields resinous substances, which, when dehydrated under pressure, yield hard resinojds (Bakelite, Novolak). (See J. S. C. I. (C. I.), 1937,103). 

Tetrahydrofolate functions as a carrier of one-carbon units. There are numerous metabolic reactions that require either the addition or removal of a one-carbon unit of some specific oxidation state. THF binds one-carbon units of three oxidation levels the methanol, formaldehyde, and formate states. These are shown in Table 6.4 along with their origins and uses. The various one-carbon units are interconvertible, as shown in Figure 6.5. Nicotinamide coenzymes are involved. In addition, the one-carbon unit may be released as C02. The methanol-level THF-bound one-carbon unit 5-methyl-THF is the storage and transport form. Once formed, its main pathway of metabolism is to form methionine from homocysteine, a reaction that requires vitamin B12 in the form of methylcobalamin (see Figure 6.2 and Chapter 20) ... 

The photooxidation of alkyl iodides represents one of the early methods by which the oxidation of alkyl radicals was studied. Thus Bates and Spence,11 in 1931, found that the chief products in the photooxidation of methyl iodide were methanol, formaldehyde, water, and iodine. For these products they postulated the following reactions... 

Additional methanol is injected into the gas between the two reactors. The reactors contain many tubes filled with FK-2 catalyst, where methanol and oxygen react to make formaldehyde. Reaction heat is removed by a bath of boiling heat-transfer oil. Hot oil vapor is condensed in the waste-heat boiler (5), thus generating steam at up to 40 bar pressure. Before entering the absorber (7), the reacted gas is cooled in the after cooler (6) and reheats the circulating oil from the process-gas heater (2). 

Application To produce aqueous formaldehyde (AF) or urea formaldehyde precondensate (UFC) from methanol using Haldor Tbpspe A/S FK-Series iron/molybdenum-oxide catalysts. Description The process is carried out in a recirculation loop at low pressure (0 to 6 psig) (1 to 1.5 bar abs). Vaporized methanol is mixed with air and recycle gas that were boosted by the blower (1). The mixture may be preheated to about 480°F (250°C) in the optional heat exchanger (2) or it may be sent directly to the reactor (3). In the reactor, methanol and oxygen react in the catalyst-filled tubes to make formaldehyde. Reaction heat is removed by an oil heat transfer medium (HTM). The reacted gas exits the reactor at approximately 540°F (290°C) and is cooled in the LP steam boiler (4) to 260°F (130°C) before entering the absorber (5). In the absorber, the formaldehyde is absorbed in water or urea solution. Heat is removed by one or two cooling circuits (6, 7). From the lower circuit (6)... 

The metabolism of folic acid involves reduction of the pterin ting to different forms of tetrahydrofolylglutamate. The reduction is catalyzed by dihydtofolate reductase and NADPH functions as a hydrogen donor. The metabolic roles of the folate coenzymes are to serve as acceptors or donors of one-carbon units in a variety of reactions. These one-carbon units exist in different oxidation states and include methanol, formaldehyde, and formate. The resulting tetrahydrofolylglutamate is an enzyme cofactor in amino acid metabolism and in the biosynthesis of purine and pyrimidines (10,96). The one-carbon unit is attached at either the N-5 or N-10 position. The activated one-carbon unit of 5,10-methylene-H folate (5) is a substrate of T-synthase, an important enzyme of growing cells. 5-10-Methylene-H folate (5) is reduced to 5-methyl-H,j folate (4) and is used in methionine biosynthesis. Alternatively, it can be oxidized to 10-formyl-H folate (7) for use in the purine biosynthetic pathway. 

To promote both the conversion of reactants and the selectivity to partial oxidation products, many kinds of metal compounds are used to create catalytically active sites in different oxidation reaction processes [4]. The most well-known oxidation of lower alkanes is the selective oxidation of n-butane to maleic anhydride, which has been successfully demonstrated using crystalline V-P-O complex oxide catalysts [5] and the process has been commercialized. The selective conversions of methane to methanol, formaldehyde, and higher hydrocarbons (by oxidative coupling of methane [OCM]) are also widely investigated [6-8]. The oxidative dehydrogenation of ethane has also received attention [9,10],... 

Carbon atoms have several oxidation states. Those of biological interest are found in methanol, formaldehyde, and formate. Table 14.2 lists the equivalent one-carbon groups that are actually involved in synthetic reactions. 

Unsupported two-component oxide systems were used by Stroud in 1975 [169]. In their composition, the first component was preferably molybdenum oxide and the second cupric oxide (i.e., Mo03- CuO). The reaction conditions were 20 bar and 485°C, and the yield was 490 g/kg-cat/hr of oxygenated products, including methanol, formaldehyde, ethanol, and acetaldehyde. The work by Stroud used oxygen as the oxidant. Liu et al. [170] used nitrous oxide as the oxidant at 1 bar over the 1.7% Mo/Si02 catalyst. A combined selectivity of 84.6% towards methanol and formaldehyde was obtained with a conversion of 8.1%. They also used a different catalytic system of 1.7% Mo03 supported on Cab-O-SilM-5 silica. Their kinetic study obtained a power law rate expression of the Arrhenius plot for CH4 concentration was... 

In trying to confirm their theory in regard to the intermediate formation of oxygenated products during combustion, Bone 9 and his co-workers carried out extensive researches and from their work has come the present hydroxylation theory. According to Bone the oxidation of methane takes place in steps, methanol, formaldehyde, formic acid, and carbonic acid being formed in the order named. These various steps are indicated below. The double arrows point out the mam course of reaction, while the single arrows show how the intermediate compounds may decompose. 

A great number of catalysts have been tried in the oxidation of methane at atmospheric pressure with the hope of obtaining intermediate products of oxidation. It appears, however, that catalysts tend to carry the reaction to equilibrium, at which state methanol, formaldehyde and formic acid are present in only extremely minute traces. This is well illustrated by the work of Wheeler and Blair," who studied the influence of catalysts in connection with their work on the mechanism of combustion. When methane was oxidized in the presence of metallic and metallic oxide catalysts, no formaldehyde could be detected even at very short times of contact. The formaldehyde produced in the circulation experiments was in a concentration much greater than that required for equilibrium in the reaction ... 

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