Reaction in methanol

Tandem cyclization and 3-carboxylation has been done with o-(methanesulf-onamido)phenylacetylenes by conducting the reaction in methanol under a CO atmosphere[10]. 

These are diamagnetic 16 electron species (reaction in methanol or 2-meth-oxyethanol gives OsH(CO)Cl(PR3)2, presumably because the alcohol is oxidized to an aldehyde that can be a source of CO) (Figure 1.65). These... 

Broxton and Bunnett (1979) determined the products of the reaction of 4-chloro-3-nitrobenzenediazonium ions with ethoxide ion in ethanol, which is exactly analogous to the reaction in methanol discussed earlier in this section. These authors found 12.8% 4-chloro-3-nitrophenetole, 83% 2-chloronitrobenzene, and 0.8% 2-nitrophenetole. When the reaction was carried out in C2H5OD, the first- and second-mentioned products contained 99% D and 69% D respectively. Dediazoniation in basic ethanol therefore results in a higher yield of hydro-de-diazoniation with this diazonium salt compared with the reaction in methanol. This is probably due to the slightly higher basicity of the ethoxide ion and to the more facile formation of the radical CH3-CHOH (Packer and Richardson, 1975). Broxton and McLeish (1983 c) measured the rates of (Z) — (E) interconversion for some substituted 2-chlorophenylazo ethyl ethers in ethanol. 

The primary step is the absorption of a quantum, which results in an excitation of the Ti-orbital. This singlet orbital can undergo intersystem crossing with spin change to a triplet stage ((t, (t), which has been found in brominated arenes (ref. 29). The photolytic reaction in methanol is much slower compared to hexane (ref. 27). This is shown for 1,2,3,4-TBDD, for which the decay constants ha/e been determined in both solvents ... 

When utilizing microwave heating in sealed vessels, it is no longer necessary to use high-boiling solvents, as in a conventional reflux set-up, to achieve a high reaction temperature. With modern instrumentation, it is easily possible to carry out a reaction in methanol at 160 °C (see Fig. 2.8), or a transformation in dichlorometh-ane at 100 °C. 

The endo isomer was the major product, but the proportion of the endo isomer decreased with temperature, from approximately 90% at 0 °C to 85 % at 60 °C [69]. Ge-dye et al. [71] performed the reaction in methanol solution under MW heating in a closed Teflon container and found that the product contained 79% of the endo isomer at an estimated temperature of 110 °C. A plot of temperature versus percent endo isomer is effectively linear between 0 °C and 60 °C and assuming it remains linear to 110°C, the product should contain 80% endo isomer at this temperature. Thus it was concluded that the change in product composition was due to the change in temperature rather than to some special effect of MW. At higher temperatures there is an increase in the proportion of the exo isomer, which is thermodynamically more stable than the endo isomer. 

Reaction in methanol yields the substituted diether 13 whereas, in methylene chloride, intramolecular cyclization to an ether cation takes place and attack by the nucleophilic F from the electrolyte yields a fluorinated cyclic ether 14 (cf also Reference 197). 

The epoxidation of hex-l-ene catalyzed by Ti-beta samples synthesized in the conventional, basic medium (Ti-beta(OH)) is compared in Table X with that catalyzed by a sample synthesized in a fluoride-containing medium (Ti-beta(F)) (13). The latter was more hydrophobic. Results for the reaction catalyzed by TS-1 are also included in Table X. Ti-beta(F) is superior to TS-1 for reaction in acetonitrile solvent. The most significant difference between Ti-beta(F) and Ti-beta(OH) is in their selectivities. Although the selectivity to the epoxide for reaction in acetonitrile is always very high, regardless of the zeolite for reaction in methanol, Ti-beta(F) is more selective than Ti-beta(OH) (76.6 vi. 54.9%, Table X). Both Ti-beta samples are, however, less selective than TS-1 for reaction in methanol. 

Phelps, D. K., Weaver, M. J. and Ladanyi, B. M. Solvent dynamic effects in electron transfer molecular dynamics simulations of reactions in methanol, Chem. Phys., 176 (1993), 575-588... 

In the study of the reaction of 2,4,6-trinitrotoluene with base (NaOMe, under first-order conditions), kinetic and equilibrium data for reaction in methanol-DMSO have been obtained. Since it has been found that plots of logarithms of rate and equilibrium constants versus the mole fraction of DMSO are linear, the value in pure methanol have been extrapolated (Kp = 12.4 lmol-1)213. 

The formation of the syn adducts has been explained by considering that carboxylic acids or BF3 catalyze the formation of the ionic intermediate by stabilizing the methoxy ion. This intermediate can then collapse directly to the cis product. Reactions in methanol give instead mainly the trans-1,2-adduct, the solvent collapse from the back-side being very rapid. Furthermore, the difference in syn selectivity, slightly larger for 1,4- than for 1,2-addition, has been attributed to a smaller steric hindrance for syn methoxy (methanol) attack at C(4) than at C(2). 

Cobaloxime(I), electrochemically regenerated from chloro(pyridine)-cobaloxime (III) (232), has been employed as a mediator in the reductive cleavage of the C—Br bond of 2-bromoalkyl 2-alkynyl ethers (253), giving (254) through radical trapping ofthe internal olefin (Scheme 95) [390]. An interesting feature of the radical cyclization (253) (254) is the reaction in methanol, unlike the trialkyltin hydride-promoted radical reactions that need an aprotic nonpolar solvent. An improved procedure for the electroreductive radical cyclization of (253) has been attained by the combined use of cobaloxime(III) (232) and a zinc plate as a sacrificial anode in an undivided cell [391]. The procedure is advantageous in terms of the turnover of the catalyst and the convenience of the operation. 

Table 9.4. Mixed Kolbe reactions in methanol. Yields for the mixed product are based on component 1, which is in deficiency. Acids are partially neutralised with sodium raethoxide.

Frensdorff (3) has determined log K values for the reaction in methanol of several cyclic polyethers of varying ring size and numbers of donor atoms with Na+, K+, and Cs+ (all chlorides). The log K values are plotted in Fig. 2 where several trends are evident. The relationship between ring size and cation size which has been referred to as the selectivity order changes from Na+>K+ for dicyclohexyl-14-crown-4 to Na+ K+>Cs+ for cyclohexyl-15-crown-5, to K+ >Cs+ Na+ for dibenzo-... 

Table 11. Log K values for reaction in methanol at 25° of Na+ and K+ with pentaglyme and 18-crown-6 (3)...

In connection with the synthesis of C-glycosyl compounds, Moffatt and coworkers182 developed the selective debenzoylation of 2,3,5-tri-0-benzoyl-/3-D-ribofuranosyl cyanide, which had been reported earlier163 reaction in methanolic ammonia-chloroform at 0° gave the crystalline 5 -0-benzoyl derivative in 83% yield, without recourse to chromatography. 

The relative reactivity of phenyl-substituted alkenes depends on the structure of the alkene and for reactions in methanol is as follows 10 1,1-diphcnylethene/triphenylethene/tetraphenyl-ethenc/9-benzylidcnefluorene 1.2 1 0.2 0.3. 

For the most reactive compounds in the series, i.e., 4,6-dinitro-benzofurazans and 4,6-dinitrobenzofuroxans, not only water222 but also methanol220 is found to be an effective neutral nucleophile in the appropriate pH range. The thermodynamic and kinetic analysis for the reactions in methanol similar to that described above for the reactions in water has been applied to the formation of 172 from 4,6-dinitro-7-methoxybenzofurazan (195) in the pH range from 2.2 to 14. The formation of 172 has been followed spectrophotometrically and found to be complete in methanol. The reaction scheme is as follows... 

The reaction in methanol or ethanol of S02 with hydrated Ni(BF4)2 in the presence of either... 

Treatment of quinoline with cyanogen bromide, the von Braun reaction, in methanol with sodium bicarbonate produces a high yield of l-cyano-2-methoxy-1,2-dihy droquinoline (3). 

Since nonpolar lipids (e.g., triacylglycerols) are generally not readily soluble in methanol, a solvent that can dissolve both neutral and polar lipids is necessary to facilitate the reaction in methanol. Toluene is chosen for this purpose because of its good solvent properties and relatively low toxicity. 

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