Methanol secondary formation

These results are presented here to emphasize the fact that selectivity and rates to various products can be subject to great variation as a result of secondary reactions. Any attempt to determine the fundamental responses of a catalytic system to changes in reaction variables must recognize the potential complications of such secondary reactions. Rathke and Feder have carried out calculations to determine the amounts of primary products actually produced by the cobalt system, assuming that these products are methanol, methyl formate, and ethylene glycol (38). The amounts of these primary products were estimated by the following relationships ... 

An interesting variation on the methanol formation is that in some cases higher oxygenates can be formed (e.g., ethanol, acetic acid or isobutanol), over mixed oxides (such as Zr02/Zn0/Mn0/K20/Pd) or promoted copper catalysts. These are probably secondary products derived from methanol and formate by more standard organic reactions. 

Further work by Schuster and his coworkers has shown that the dienone (257) yields, as well as the many products already reported in earlier publications, the new enone (258). The formation of this species arises from the intermediate (259). The cyclohexadienone (260) affords the bicyclic compound (261) on irradiation in methanol. This is formed by the trapping of a zwitterion by methanol. Secondary photolysis affords the cyclohexenone (262) by ring opening of the adduct (261). ... 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Oxidations usually proceed in the dark at or below room temperature in a variety of solvents ranging from aqueous bicarbonate to anhydrous benzene-pyridine. Base is quite commonly used to consume the hydrogen halide produced in the reaction, as this prevents the formation of high concentrations of bromine (or chlorine) by a secondary process. The reaction time varies from a few minutes to 24 hours or more depending on the nature of the reagent and the substrate. Thus one finds that NBS or NBA when used in aqueous acetone or dioxane are very mild, selective reagents. The rate of these oxidations is noticeably enhanced when Fbutyl alcohol is used as a solvent. In general, saturated, primary alcohols are inert and methanol is often used as a solvent. 

Enamines formed in this way may be distilled or used in situ. The ease of formation of the enamine depends on the structure of the secondary amine as well as the structure of the ketone. Thus pyrrolidine reacts faster than morpholine or piperidine, as expected from a rate-controlling transition state with imonium character. Six-membered ring ketones without a substituents form pyrrolidine enamines even at room temperature in methanol (20), and morpholine enamines are generated in cold acetic acid (21), but a-alkylcyclohexanones, cycloheptanone, and linear ketones react less readily. In such examples acid catalysis with p-toluenesulfonic acid or... 

X0 to hydroxy compounds. Lower temperatures favor ketone formation and sterically hindered carbonyls, such as 2-thienyl t-butyl ketone, are not reduced. The sensitivity of desulfurization to steric factors is evident by the failure to desulfurize 2,5-di-i-butyl-3-acetylthiophene. The carbonyl groups of both aldehydes and ketones can be protected by acetal formation, as particularly cyclic acetals are stable during desulfurization in methanol at room temperature. " The free aldehydes give primary alcohols on desulfurization. Another method to obtain only keto compounds is to oxidize the mixtures of ketone and secondary alcohol with CrOs after the desulfurization. - Through the desulfurization of 5,5 -diacetyl-2,2, 5, 2"-terthienyl (228), 2,15-hexadecandione (229) has been obtained, which... 

Intermolecular hydroalkoxylation of 1,1- and 1,3-di-substituted, tri-substituted and tetra-substituted allenes with a range of primary and secondary alcohols, methanol, phenol and propionic acid was catalysed by the system [AuCl(IPr)]/ AgOTf (1 1, 5 mol% each component) at room temperature in toluene, giving excellent conversions to the allylic ethers. Hydroalkoxylation of monosubstituted or trisubstituted allenes led to the selective addition of the alcohol to the less hindered allene terminus and the formation of allylic ethers. A plausible mechanism involves the reaction of the in situ formed cationic (IPr)Au" with the substituted allene to form the tt-allenyl complex 105, which after nucleophilic attack of the alcohol gives the o-alkenyl complex 106, which, in turn, is converted to the product by protonolysis and concomitant regeneration of the cationic active species (IPr)-Au" (Scheme 2.18) [86]. 

A particularly interesting Michael acceptor is dimethyl 2-hexen-4-ynedioate since it can react at either position of the double or triple bond to form 1,4- or 1,6-addition products. Winterfeldt and Preuss183 treated this substrate with several secondary amines and observed exclusive attack at C-5 with formation of the 1,6-addition products (equation 78). In contrast to this, sodium methanolate added at CM to give the 1,4-adduct as a mixture of E/Z isomers (equation 79) with increasing reaction time, the product distribution was shifted towards the thermodynamically more stable , -product184. Acheson and... 

A slightly modified view of the reaction of primary or secondary alcohols added to LAH (3 1 molar ratio) may be considered. The rapid consecutive reactions of alkoxyaluminum hydride species with a local excess of alcohol could lead to formation of the tetraalkoxy species, particularly under conditions of inefficient mixing. This result is summarized in eq. [4]. In the case of a simple unhindered primary alcohol such as methanol, a back reaction of the tetraalkoxy species with LAH leads to the trialkoxyaluminum hydride species (eq. [5]). The net result of the reaction of methanol with LAH (3 1 molar ratio) is... 

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

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