Methanol-acetic acid

The transformed variables describe the system composition with or without reaction and sum to unity as do Xi and yi. The condition for azeotropy becomes X, = Y,. Barbosa and Doherty have shown that phase and distillation diagrams constructed using the transformed composition coordinates have the same properties as phase and distillation region diagrams for nonreactive systems and similarly can be used to assist in design feasibility and operability studies [Chem Eng Sci, 43, 529, 1523, and 2377 (1988a,b,c)]. A residue curve map in transformed coordinates for the reactive system methanol-acetic acid-methyl acetate-water is shown in Fig. 13-76. Note that the nonreactive azeotrope between water and methyl acetate has disappeared, while the methyl acetate-methanol azeotrope remains intact. Only... 

FIG. 13-76 Residue curve map for the reactive system methanol-acetic acid-methyl acetate-water in chemical eqiiihhriiim. 

To a solution of the ester amide (160 mg, 0.26 mmol) in methanol (3 mL) and THF (3 mL) was added a 1 M solution of NaOMe in methanol (5 mL). The mixture was stirred at rt for 1.5 d then neutralized with methanolic acetic acid and concentrated in vacuo. The crude material was partitioned between water and CH2CI2. The organic phase was dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo to afford the bis(ester) 73 as a colorless solid, mp 154.4-155.5 C, [a] -17° (c = 0.3, MeOH). 

The solubility of the resulting product may dictate the choice of solvent. Reductive alkylation of norepinephrine with a series of keto acids proceeded smoothly over platinum oxide in methanol-acetic acid mixtures. However, when n = 4 or 5, the product tended to precipitate from solution, making catalyst separation difficult. The problem was circumvented by using glacial acetic acid as solvent 38). 

By selection of conditions and catalyst, the intermediate hydroxyimine (11) can be directed to either (he hydroxy ketone (10) or amino alcohol (12), Over platinum oxide in methanol-acetic acid-water the amino alcohol forms, whereas over alkali-free Ra-Ni in methanol-water or over 10% Pd-on-C in methanol-water containing boric acid, the hydroxy ketones form in excellent yield. Nitrile oxide cycloadditions have been applied to five-membered ring syntheses (.50). 

Electrostatic potential maps of the conjugate bases from methanol, acetic acid, and acetone are shown in Figure 2.4. As you might expect, all three show a substantial amount of negative charge (red) on oxygen. 

Analysis calculated for C1SH36N2O4S C, 57.41 H, 9.63 N, 7.43 S, 8.51. Found C, 57.60 H, 9.66 N, 7.37 S, 8.25. Thin-layer chromatograms (Note 10) run by the submitters showed a single spot for the product in each of three following solvent systems (solvents, volume ratio of solvents in the same order) chloroform-methanol-acetic acid, 85 10 5, Rf 0.60 1-butanol-acetic acid-water, 4 1 1, Rf 0.58 l-butanol acetic acid-pyridine-water, 15 3 10 12, Rf 0.71. 

Potential sources of carbon monoxide hazards include metal-refining processes, in which it is formed as a byproduct and used as a fuel (LEL 12.5%), and running vehicle engines (particularly petrol-driven) or gas-fired heaters in poorly ventilated confined spaces. It is also a feedstock in the manufacture of a variety of chemicals, e.g. methanol, acetic acid, phosgene and oxo-alcohols. 

Four different commercially available varieties of turmeric containing curcumin were isolated, separated by column chromatography, and identified by spectroscopy. The purity of the curcuminoids was analyzed by an improved HPLC method, performed on a Ci8 column using methanol, acetic acid, and acetonitrile and detection at 425 nm. The total percentages of curcuminoids in turmeric were between 2.34... 

Chloroform-methanol-acetic acid-formic acid-water (5 15 6 2 1)... 

Males et al. [103] used aqueous mobile phase with formic acid for the separation of flavonoids and phenolic acids in the extract of Sambuci flos. In a cited paper, authors listed ten mobile phases with addition of acids used by other investigators for chromatography of polyphenolic material. For micropreparative separation and isolation of antraquinone derivatives (aloine and aloeemodine) from the hardened sap of aloe (Liliaceae family), Wawrzynowicz et al. used 0.5-mm silica precoated plates and isopropanol-methanol-acetic acid as the mobile phase [104]. The addition of small amounts of acid to the mobile phase suppressed the dissociation of acidic groups (phenolic, carboxylic) and thus prevented band diffusions. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Fig. 5.5.3 ]H NMR spectrum obtained from a sample containing catalyst and reaction mixture (i.e., methanol, acetic acid, methyl acetate and water). Peaks A and B are the intra- and inter-particle ]H resonances, respectively, associated with the OH group. Peak C is the ]H resonance of the CH30 group associated with...

HPLC allows a quantitative determination with relatively simple extractions. In many cases, extraction only involves a heating of the commodity with water, followed by filtration and injection onto an HPLC column. In the determination of caffeine, theobromine, and theophylline in cocoa, coffee, or tea, as well as in other foods, there is scarcely a month that passes without a new paper on this assay. Kreiser and Martin provide typical conditions for analysis.28 In their studies, samples were extracted in boiling water and filtered prior to injection onto the HPLC column. The HPLC conditions used a Bondapak reversed phase column and a mobile phase of water methanol acetic acid (74 25 1) with detection at 280 nm. This method is accurate, precise, and conserves time. It has also been adopted by the AOAC as an official method for the determination of theobromine and caffeine in cocoa beans and chocolate products.29... 

A different approach to quinoxalines and heterocycle-fused pyrazines has been described by the Lindsley group, based on the cyclocondensation of 1,2-diketones and aryl/heteroaryl 1,2-diamines (Scheme 6.260) [450]. Optimized reaction conditions involved heating an equimolar mixture of the diketone and diamine components for 5 min at 160 °C in a 9 1 methanol/acetic acid solvent mixture, which furnished the substituted quinoxalines in excellent yields. This approach could also be applied equally successfully to the synthesis of heteroaryl pyrazines, such as pyr-ido[2,3-b]pyrazines and thieno[3,4-b]pyrazines. The same group has employed 1,2-diketone building blocks for the preparation of other heterocyclic structures (see Schemes 6.198, 6.268, and 6.269). 

Gyclocondensation of diazomalonaldehyde 336 with 4-fluoroaniline carried out in methanol-acetic acid provides l-(4-fluorophenyl)-l,2,3-triazole-l-carbaldehyde 337 in 78% yield. Oxidation with MnOz in the presence of sodium cyanide in methanol converts aldehyde 337 into methyl ester 338 with 79% yield. Hydrazide 339 (84% yield) is obtained in a reaction of ester 338 with hydrazine. Product 339 reacts with various aromatic aldehydes to give hydrazones possessing interesting antiplatelet activity (Scheme 53) <2003BMC2051>. 

A thin-layer gas chromatographic system was devised by Pittman and Shekosky(39) for chicken tissue and feces. A TLC system of benzene methanol acetic acid (9 1 1) was used for prior separation the spots were then removed and esterified in 14% BF in methanol. A 4 ft. 3% OV-17 column at 240° was used. Retention times of about 7 minutes for nalidixic acid, 10 minutes for hydroxynalidixic acid and 17 minutes for the dicarboxylic acid were reported. 

A stock solution of lumefantrine was prepared in methanol-acetic acid (99.8 0.2 v/v). Standard working solutions were prepared by diluting the stock solution with acidic methanol. Calibration standards in plasma were prepared by spiking blank plasma (4900 fxL) with 100 jxL of working solution. 

Numerous chemical intermediates are oxygen rich. Methanol, acetic acid and ethylene glycol show a O/C atomic ratio of 1, as does biomass. Other major chemicals intermediates show a lower O/C ratio, typically between 1/3 and 2/3. This holds for instance for propene and butene glycols, ethanol, (meth)acrylic acids, adipic acid and many others. The presence of some oxygen atoms is required to confer the desired physical and chemicals properties to the product. Selective and partial deoxygenation of biomass may represent an attractive and competitive route compared with the selective and partial oxidation of hydrocarbon feedstock. 

The anthocyanin composition of flowers has also been frequently investigated by chromatographic methods. Acylated anthocyanins and flavonols have been extracted from the flowers of Dendrobium cv. Pompadour and separated by TLC and RP-HPLC techniques. Fresh flowers (approximately. 1 kg) were extracted with 101 of methanol-acetic acid-water (4 1 5, v/v), and the extract was concentrated and analysed by preparative and analytical RP-HPLC using ODS columns (150 X 19 mm i.d. and 250 X 4.6 mm i.d.) at 40°C. The gradient consisted of methanol-water-acetic acid in various volume ratios. Flow rates were 4 and 1 ml/min for preparative and analytical separations, respectively. Cyanidin 3- (6-malonylglucoside)-7,3 -di(6-synapilglucoside) and the demalonyl derivative were detected in the flowers [261],... 

The anthocyanin profile of the flowers of Vanda (Orchidaceae) was investigated with a similar technique. Flowers (2 kg) were extracted with 101 of methanol-acetic acid-water (9 l 10,v/v) at ambient temperature for 24 h. The extract was purified by column chromatography, paper chromatography, TLC and preparative RP-HPLC. Analytical HPLC was carried out in an ODS column (250 X 4.6 mm, i.d.) at 40°C. Gradient conditions were from 40 per cent to 85 per cent B in 30 min (solvent A 1.5 per cent H3P04 in water solvent B 1.5 per cent H3P04, 20 per cent acetic acid and 25 per cent ACN in water). The flow rate was 1 ml/min and analytes were detected at 530 nm. The chemical structures of acylated anthocyanins present in the flowers are compiled in Table 2.90. The relative concentrations of anthocyanins in the flower extracts are listed in Table 2.91. It can be concluded from the results that the complex separation and identification methods (TLC, HPLC, UV-vis and II NMR spectroscopy, FAB-MS) allow the separation, quantitative determination and identification of anthocyanins in orchid flowers [262],... 

Methanol-acetic acid (96 4 v/v) and various other conditions... 

Phosphorus, fatty acids, carbohydrates, glycerol, and amino acids were analyzed by the method described in our previous paper [8] and references cited therein. SDS-PAGE [8], TLC [9], HPLC [9], determination of phos-phomonoester [8], reducing sugar analysis [13], methylation analysis [14], and hexose analysis [15] were performed as described in the respective literature. Two dimensional TLC was performed on silica-gel plate (Merck Silicagel 60 F254 No. 5715) using the solvent systems, chloroform-methanol-acetic acid (65/10/1, v/v/v) for the first development and chloroform-methanol-25% ammonia solution (65/10/1) for the second. 

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