Methanol, as solvent

There are two commercial solvent crystaUi2ation processes. The Emersol Process, patented in 1942 by Emery Industries, uses methanol as solvent and the Armour-Texaco Process, patented in 1948, uses acetone as solvent. The fatty acids to be separated are dissolved in the solvent and cooled, usually in a double-pipe chiller. Internal scrapers rotating at low rpm remove the crystals from the chilled surface. The slurry is then separated by means of a rotary vacuum filter. The filter cake is sprayed with cold solvent to remove free Hquid acids, and the solvents are removed by flash evaporation and steam stripping and recovered for reuse (10). 

Temperature-jump experiments showed an evident increase of the rate of transition by using methanol as solvent instead of water. According to Fig. 31, this is mainly caused by the increase of the fast kinetic phase at the expense of the following slow phase. 

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

Hydroxy-L-prolin is converted into a 2-methoxypyrrolidine. This can be used as a valuable chiral building block to prepare optically active 2-substituted pyrrolidines (2-allyl, 2-cyano, 2-phosphono) with different nucleophiles and employing TiQ as Lewis acid (Eq. 21) [286]. Using these latent A -acylimmonium cations (Eq. 22) [287] (Table 9, No. 31), 2-(pyrimidin-l-yl)-2-amino acids [288], and 5-fluorouracil derivatives [289] have been prepared. For the synthesis of p-lactams a 4-acetoxyazetidinone, prepared by non-Kolbe electrolysis of the corresponding 4-carboxy derivative (Eq. 23) [290], proved to be a valuable intermediate. 0-Benzoylated a-hydroxyacetic acids are decarboxylated in methanol to mixed acylals [291]. By reaction of the intermediate cation, with the carboxylic acid used as precursor, esters are obtained in acetonitrile (Eq. 24) [292] and surprisingly also in methanol as solvent (Table 9, No. 32). Hydroxy compounds are formed by decarboxylation in water or in dimethyl sulfoxide (Table 9, Nos. 34, 35). 

Carboxylic acids can be converted by anodic oxidation into radicals and/or carbo-cations. The procedure is simple, an undivided beaker-type cell to perform the reaction, current control, and usually methanol as solvent is sufficient. A scale up is fairly easy and the yields are generally good. The pathway towards either radicals or carbocations can be efficiently controlled by the reaction conditions (electrode material, solvent, additives) and the structure of the carboxylic acids. A broad variety of starting compounds is easily and inexpensively available from natural and petrochemical sources, or by highly developed procedures for the synthesis of carboxylic acids. 

These conclusions were supported by the results obtained in a study of the reactions of various types of acetylenes with TTN (94). Hydration of the C=C bond was found to occur to a very minor extent, if at all, with almost all of the compounds studied, and the nature of the products formed was dependent on the structure of the acetylene and the solvent employed. Oxidation of diarylacetylenes with two equivalents of TTN in either aqueous acidic glyme or methanol as solvent resulted in smooth high yield conversion into the corresponding benzils (Scheme 23). The mechanism of this oxidation in aqueous medium most probably involves oxythallation of the acetylene, ketonization of the initially formed adduct (XXXV) to give the monoalkylthallium(III) derivative (XXXVI), and conversion of this intermediate into a benzoin (XXXVII) by a Type 1 process. Oxidation of (XXXVII) to the benzil (XXXVIII) by the second equivalent of reagent would then proceed in exactly the same manner as described for the oxidation of chalcones, deoxybenzoins, and benzoins to benzils by TTN. The mechanism of oxidation in methanol solution is somewhat more complex and has not yet been fully elucidated. 

Using methanol as solvent, the conversions ranged from 12 to 42% at selectivities of 9-58% [38]. This corresponds to yields of 3-14%. Hence the performance of the direct fluorination in methanol is generally worse than that in acetonitrile. The highest yield was found for a liquid volume flow of 11.1 ml h using a 1.1 mol 1 toluene concentration at -17 °C. The fluorine/toluene molar ratio was 0.925. 

GL 1] [R 4] [P 2] Conversions from 17 to 95% were achieved using methanol as solvent (1.0-10.0 fluorine-to-toluene equivalents 0.1 M toluene room temperature 10 ml min gas flow 100 pi min methanol) [14]. The respective selectivities ranged from 37 to 10%. Taking into account also the difluorotoluenes and trifluorotoluenes gives a selectivity of about 45%. The yields passed through a maximum at 18%. 

Using methanol as solvent, the ratio is on average 5.5 1 2.4. Hence more products referring to an electrophilic substitution were formed [13]. 

GL 1] [R 4] [P 2] Variation of solvent affects also the substitution pattern to a certain extent [13], A ratio of ortho-, meta- and para-isomers for mono-fluorinated toluene amounting on average to 3.5 1 2 was found in the dual-channel micro reactor at room temperature, using acetonitrile as solvent [13]. Using methanol as solvent, the ratio was on average 5.5 1 2.4. Hence more products referring to an electrophilic substitution were formed [13]. 

Both chemical yield and enantioselechvity are strongly affected by the anionic part of the catalyst, and the trifluoroacetate anion is considered to play a key role in the catalysis. Excess benzoquinone is required for high yield of the product, and use of methanol as solvent is essential for the successful cyclizahon. 

As mentioned in Chapter 4, although this is a dynamic experiment where data are collected over time, we consider it as a simple algebraic equation model with two unknown parameters. The data were given for two different conditions (i) with 0.75 g and (ii) with 1.30 g of methanol as solvent. An initial guess of k =1.0 and k2=0.01 was used. The method converged in six and seven iterations respectively without the need for Marquardt s modification. Actually, if Mar-quardt s modification is used, the algorithm slows down somewhat. The estimated parameters are given in Table 16.1 In addition, the model-calculated values are... 

At room temperature in methanol as solvent, complex OsH(t 2-H2BH2)(CO) (P Pr3)2 decomposes to give the dihydride-dihydrogen compound OsH2(t 2-H2) (CO)(P Pr3)2. If the decomposition, however, is carried out under reflux the cis-dihydride-ds-dicarbonyl derivative OsH2(CO)2(P Pr3)2 is formed.13... 

The typical solution present in the capillary consists of a polar solvent in which electrolytes are soluble. As an example, we can use methanol as solvent and a simple salt like NaCl or BHC1, where B is an organic base, as the solute. Low electrolyte concentrations, 10-5-10 3 mol/L (M), are typically used in electrospray mass spectrometry (ESMS). For simplicity we will consider only the positive ion mode in the subsequent discussion. 

Grieco and coworkers have independently described the same type of Pictet-Spengler cyclization reactions involving tryptophan methyl ester and aldehydes, but using methanol as solvent and hydrochloric acid as a catalyst (microwave irradiation, 50 °C, 20-50 min) [416], Moderate to good product yields were obtained. 

A two-stage process for the hydroformylation of butadiene to give good yields of a desired product—1,6-hexanediol—has been described (100). The first stage employed [(C6H5)3P]2Rh(CO)Br and excess triphen-ylphosphine as catalyst and reaction conditions of I20°C and 200 atm of 1/1 H2/CO in methanol as solvent. The principal product was 3-penten-l-al dimethyl acetal. This was treated with 1,3-propanediol to form a cyclic acetal, then hydroformylated with Co2(CO)8 and dodecyl-9-phospha-9-bicyclononane at 170°C and 80-110 atm of 2/1 H2/CO. The product of... 

Liu et al. prepared palladium nanoparticles in water-dispersible poly(acrylic acid) (PAA)-lined channels of diblock copolymer microspheres [47]. The diblock microspheres (mean diameter 0.5 pm) were prepared using an oil-in-water emulsion process. The diblock used was poly(t-butylacrylate)-Wock-poly(2-cinna-moyloxyethyl) methacrylate (PtBA-b-PCEMA). Synthesis of the nanoparticles inside the PAA-lined channels of the microspheres was achieved using hydrazine for the reduction of PdCl2, and the nanoparticle formation was confirmed from TEM analysis and electron diffraction study (Fig. 9.1). The Pd-loaded microspheres catalyzed the hydrogenation of methylacrylate to methyl-propionate. The catalytic reactions were carried out in methanol as solvent under dihydro-... 

The first addition of nitroalkanes to glycals was recently described. It involved a radical mediated addition of nitromethane to tri-O-benzyl-D-glucal (48) in the presence of CAN and KOH and methanol as solvent, to give the diastereomeric mixture 49 + 50 (Scheme 18).42... 

Column III shows the effect of ultrasound upon the product ratio with methanol as solvent. As can be seen there is now 53 % bibenzyl, 32 % of methyl ether and 6% of methyl ester (with a total of 5 % of other products) suggesting a slight shift towards the two-electron products, but with an overall diminuition of solvent discharge (approx. 6% ester) and side-reactions (approx. 6%). This result confirms the fact the phenyl acetate electrooxidation favours the one-electron route (to bibenzyl) in a wide range of conditions [61], and is much less sensitive to mechanistic switches by manipulation of parameters (e. g. ultrasound) than is cyclohexane carboxylate electrooxidation [54]. 

In methanol as solvent, the results are comparable with respect to activity and enantioselectivity (Tab. 6.2, entry (1)) whereas in water the complex of the amphiphilic ligand shows a significant increase in activity and enantioselectivity compared with the BPPM complex (entry (2)). The values obtained for mixed micelles... 

Making a methyl glucopyranoside is relatively straightforward in that we can use the alcohol methanol as solvent, and, since it is thus present in large excess, this helps to disturb the equilibrium. The process is much less attractive for a... 

Scheme 2. . Steps in the electrochemical oxidation of cyclohexene using methanol as solvent.

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