Methanol acceleration

Dimethyl sulphoxide (amounting to slightly more than equimolar with azide and less than 1% overall concentration in solution in methanol) accelerates the copper-catalyzed decomposition and the only product formed (97%) is the sulphoximine (21). Even in the absence of copper, DMSO and benzenesulphonyl azide were found to undergo a slow reaction in boiling methanol to give 21 (< 40%). It was suggested33) that the sulphonyl azide itself (slow) or the copper complex 24 (fast)... 

As significant amounts of hydrogen are formed, it has long been assumed that formaldehyde is essentially formed by dehydrogenation of methanol, accelerated by the combustion of a large part of the liberated hydrogen. Recently, however, several authors explain the kinetics on the basis of direct interaction of methanol with oxygen. 

Ring expansion. In early work3 the ring expansion of cyclohexanone to 2-methylcycloheptanone by reaction with ethereal diazoethane was found to proceed slowly and in poor yield. The results were confirmed by Marshall and Partridge.4 These chemists noted, however, that Mosettig5 had observed that methanol accelerates the reaction of cyclohexanone with diazomethane. They then carried out the ring expansion of cyclohexanone (1) with diazoethane in 20% ethanol in diethyl ether as solvent. The reaction was complete within 2 hours and gave a 9 1 mixture of 2-methylcycloheptanone (2) and the oxide (3) in over 90% yield. They also carried out the reaction on a number of 4-substituted cyclohexanones. 

The mechanism in Figure 9.5 also provides a rationalization for some observations of solvent effects in bromine addition reactions. The major product of the reaction of bromine with cyclohexene in methanol is trans-2-bromo-l-methoxycyclohexane. traMS-l,2-Dibromocyclohexane is observed if Br is added to the solution, but the yield of the dibromo adduct approaches 0% as [Br ] approaches 0 M. This result stands in contrast to the 27% of 1,2-dibromo adduct obtained from the corresponding reaction in acetic acid. It appears that the greater polarity of methanol accelerates the dissociation of IIP to DI, and the greater nucleophiliciW of methanol enhances the reaction of solvent with IIP, SSIP, DI, and SSIP. ... 

Addition of a relatively small amount (< ca. 3 mol/1) of methanol, a good solvent for polj NMMAm), led to similar results. However, the presence of larger amounts of methanol accelerates bimolecular termination between polymer radicals, and hence causes a decrease of and of the polymer molecular weight. Consequently, maxima in R and of the polymer were observed when the methanol concentration was changed (Fig. 9). N,N-Dimethylformamide, a good solvent for poly(AN), shows a similar behavior in the AN polymerization in benzene... 

HalicteSCC of Ti-811 in methanol accelerates with halo-gen/halide additions. Water additions have an in-hibitive effect, and numerous species have been found that inhibit transgrantilar (Stage II) stress cracking in methanol depending on halide level. These include nitrate and sulfate ions, NaF, and O.IM concentrations of Al, Zr" ", Cd , and Sn" " metallic ions Corrosion, Vol 27,1971, p 46-48). Investigators have also demonstrated that titanium alloy SCC in neutral methanol/halide solutions can be fully arrested by appHed cathodic potentials of—1.0 to —1.5 V (SCE). 

Neverov AA, Liu CT, Bunn SE, Edwards D, White CJ, Melnychuk SA, et al. A simple DNAse model system comprbing a dinuclear Zn(II) complex in methanol accelerates the cleavage of a series of methyl aryl phosphate diestets by 10"-10. J Am Chem Soc. 2008 130 6639-6649. 

Since an enzyme is a biological catalyst and therefore merely accelerates a reaction, it cannot alter the position of equilibrium in a reversible reaction. The hydrolysis of p-methylglucoside is reversible and emulsin should therefore be capable also of synthesising this compound frc n glucose and methanol. This synthesis can actually be carried out by the action of the enzyme on glucose dissolved in an excess of methanol, the excess of the alcohol throwing the equilibrium over to the left. Owing to experimental difficulties, this reaction is not here described. 

Eig. 7. EuU-throtde acceleration for diesel and methanol-powered GM RTS coaches having simulated full-seated passenger loads of 43 passengers. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

The reactions of trialkylboranes with bromine and iodine are gready accelerated by bases. The use of sodium methoxide in methanol gives good yields of the corresponding alkyl bromides or iodides. AH three primary alkyl groups are utilized in the bromination reaction and only two in the iodination reaction. Secondary groups are less reactive and the yields are lower. Both Br and I reactions proceed with predominant inversion of configuration thus, for example, tri( X(9-2-norbomyl)borane yields >75% endo product (237,238). In contrast, the dark reaction of bromine with tri( X(9-2-norbomyl)borane yields cleanly X(9-2-norbomyl bromide (239). Consequentiy, the dark bromination complements the base-induced bromination. 

MonofluoToalkanes and vicinal difluoroalkanes are dehydrofluonnated if strong enough bases are applied [10 12] In 5-fluorononane and fluorocyclodo-decane, elimination by means of sodium methoxide in methanol gives cis- and trans allcenes in respective yields of 8 and 21% and in ratios of 1 2 2 2 4, however, the bulky lithium diisopropyl amide m tetrahydrofuran produces trdns-isomers almost exclusively The strength of the base does not have much effect on the rate of elimination, but the lithium cation causes considerable acceleration [10] (equation 10)... 

By a more detailed study of the reaction of 5-azauracil with diazo-methane it was found that this reaction is considerably accelerated by the presence of a small amount of water, methanol, or dimethyl-formamide. It does not proceed appreciably in absolute ether. By... 

Nucleophilic displacement reactions One of the most common reactions in organic synthesis is the nucleophilic displacement reaction. The first attempt at a nucleophilic substitution reaction in a molten salt was carried out by Ford and co-workers [47, 48, 49]. FFere, the rates of reaction between halide ion (in the form of its tri-ethylammonium salt) and methyl tosylate in the molten salt triethylhexylammoni-um triethylhexylborate were studied (Scheme 5.1-20) and compared with similar reactions in dimethylformamide (DMF) and methanol. The reaction rates in the molten salt appeared to be intermediate in rate between methanol and DMF (a dipolar aprotic solvent loiown to accelerate Sn2 substitution reactions). 

In this oxidative degradation, MTO decomposes into catalytically inert perrhenate and methanol. The decomposition reaction is accelerated at higher pH, presumably through the reaction between the more potent nucleophile H02- and MTO. The decomposition of MTO under basic conditions is rather problematic, since the selectivity for epoxide formation certainly profits from the use of nonacidic conditions. 

Table 5 shows the rate ratios between ethylenes differing by an increase by two in number of alkyl substituents. It can be observed that in solvents as different as methanol, ethanol, and acetic acid, the rate ratio is always around 10, that is of the same order of magnitude of the increase in Kf. This indicates that substituent effects are not much more influential on the kinetic constants that on Kf. A possible rationalization of the lower accelerating effects by alkyl substituents on the bromination rate, relative to what could be expected for an AdgCl mechanism on... 

Anchimeric assistance in the solvolysis of /3-arylthiovinyl sulfonates was demonstrated by means of kinetic studies on model compounds (182). In a variety of solvents ranging from nitromethane and methanol to acetic acid, the /3-arylthiovinyl sulfonate 216 was shown to react 20 to 33 times faster than the triphenylvinyl sulfonate 217. Different accelerating factors were... 

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