Microwave oven extraction

A solvent-free strategy for the synthesis of thiazoles involved mixing of thioamides with a-tosyloxy ketones in a clay-catalyzed reaction (Scheme 7). The typical procedure entailed mixing of thioamides and in situ produced a-tosyloxy ketones with montmorillonite K-10 clay in an open glass container. The reaction mixture was irradiated in a microwave oven for 2-5 min with intermittent irradiation and the product was extracted into ethyl acetate to afford 2-substituted thiazoles in 88-96% yields [8]. 

Applications Extraction is typically accomplished by refluxing the polymer in an appropriate solvent for l-48h [84,199]. In many cases, ultrasonic exposure reduces the extraction time [90,200], According to Table 3.5 there are several reports of US extraction from polymers. Ultrasonic extraction has been used for HDPE/(BHT, Irganox antioxidants, Isonox, Cyasorb, Am 340, MD 1024, Irgafos 168) [56], LDPE/Chimassorb 81 [201], SBR/tri(nonylphenyl) phosphite [200], HDPE/(Tinuvin 770, Chimassorb 944) [114], etc. Nielson [90] compared the recoveries obtained for a variety of analytes from PP, LDPE and HDPE with Soxhlet, ultrasonic bath and microwave oven. For all samples, the ultrasonic extraction could be achieved within 1 h. For LDPE and PP most compounds (except Irganox 1010) were extracted within 10 min. Further experiments by Nielson [56] on extraction from HDPE confirmed these results. Where phosphite antioxidants (such as Irgafos 168) are present the use of the solvent mixture DCM-cyclohexane was preferred as it prevented hydrolysis of the phosphite by extraction solvents such as alcohols [56]. Similarly, phosphite esters also undergo hydrolysis... 

Most average homes contain a microwave oven. Researchers have taken that same technology and applied it to sample extraction. Using microwave technology with acidic solutions has become a commonplace replacement for traditional acid digests. The sample is placed in a closed, chemical-resistant vessel and heated in a microwave. This process is much faster than hot-plate techniques and has become widely accepted by such agencies as the US EPA. 

A. Recipe for Salvia honey slurry Ingredients 5 grams of finely powdered dried Salvia leaf 1 tsp. McCormick Peppermint extract (80% alcohol) 4 tsp. honey that was first warmed in a microwave oven. Preparation the leaf powder is put into a teacup, add the peppermint extract, then the honey. Mix until a uniform slurry is formed. Use lie down... 

Figure 28-13 Extraction vessels in a microwave oven that processes up to 12 samples in under 30 min. Each 100-mL vessel has a vent tube that releases vapor if the pressure exceeds 14 bar. Vapors from the chamber are ultimately vented to a fume hood. The femperature inside each vessel can be monitored and used to control the microwave power. [Courtesy CEM Corp.. Matthews. NC.]...

Acetone absorbs microwaves, so it can be heated in a microwave oven. Hexane does not absorb microwaves. To perform an extraction with pure hexane, the liquid is placed in a fluoropolymer insert inside the Teflon vessel in Figure 28-8.18 The walls of the insert contain carbon black, which absorbs microwaves and heats the solvent. 

The catalytic reactions were performed either on the hydrated solids (equilibrated with the relative humidity -about 55%- of the atmosphere) or on the dehydrated catalysts (heated at 160°C, during 3 hours). An intimate mixture of the inorganic solid (100 mg) and the oxime in solid state (20 mg) was introduced in a Pyrex glass reactor. Thus, the reaction was carried out in "dry media" conditions, i.e. without any solvent. The mixtures were either activated with a microwave oven or heated at 100, 130 or 160°C in a conventional oven, during variable times (in the standard procedure 1 hour). The microwave oven used is a domestic (2450 MHz) Moulinex model FM 460, carrying out the experiments at 600 W of power and introducing a unic vessel in the oven in each experiment. The reaction products were extracted by treatment with a large excess (5 ml) of an appropriate solvent (methanol or chloroform), and the extracts were analyzed by GC. 

A rapid preseparation technique was developed for the extraction of SAL from various chicken tissues using the irradiation of the sample in EtOH-2-PrOH for 9 s in a common household microwave oven. The extract was analyzed without further cleanup and detected via postcolumn reaction with DMABA at 86°C. Recoveries ranged between 87% and 100% (105). 

The synthetic procedure developed by Usyatinsky involves pre-absorbing the mixture of acidic support and ammonium acetate (ammonia source) with an ether solution of the starting materials, evaporating the solvent and heating the solid residue in a domestic microwave oven for 20 min (Scheme 5.21). After irradiation, the reaction mixture was allowed to cool to room temperature and was then washed with a mixture of acetone and triethylamine to extract the product from the solid support. No yields were quoted but the purities of the products were quoted to be 75-85%. 

Freshly prepared NaBH4-alumina (1.13 g, 3.0 mmol of NaBH4) is thoroughly mixed with neat acetophenone Id (0.36 g, 3.0 mmol) in a test tube and placed in an alumina bath inside the microwave oven and irradiated (30 s). Upon completion of the reaction, monitored on TLC (hexane-EtOAc, 8 2, v/v), the product is extracted into ethylene chloride (2x15 mL). Removal of solvent under reduced pressure essentially provides pure sec-phene thy 1 alcohol 2d in 87% yield. No side product formation is observed in any of the reactions investigated and no reaction takes place in the absence of alumina. 

In a typical experiment, benzaldehyde (106 mg, 1 mmol) was added to the finely powdered paraformaldehyde (60 mg, 2 mmol). To this mixture, powdered barium hydroxide octahydrate (631 mg, 2 mmol) was added in a glass test tube and the reaction mixture was placed in an alumina bath (neutral alumina 125 g, mesh 150, Aldrich bath 5.7 cm diameter) inside a household microwave oven and irradiated for the specified time at its full power of 900 W intermittently or heated in an oil bath at 100-110 °C. On completion of the reaction, as indicated by TLC (hexane-EtOAc, 4 1, v/v), the reaction mixture was neutralized with dilute HC1 and the product extracted into ethyl acetate. The combined organic extracts were dried over anhydrous sodium sulfate and the solvent removed under reduced pressure. The pure benzyl alcohol (99 mg, 91%), however, is obtained by extracting the reaction mixture with ethyl acetate prior to neutralization and subsequent removal of the solvent under reduced pressure. 

A mixture of benzaldehyde la (0.53 g, 5 mmol), paraformaldehyde (1 g, 30 mmol) and solid sodium hydroxide (0.16 g, 4 mmol) were taken in an Erlen-meyer flask and placed in a commercial microwave oven operating at 2450 MHz frequency. After irradiation of the mixture for 25 s (monitored by TLC), it was cooled to room temperature, extracted with chloroform and dried over anhydrous sodium sulfate. Then the solvent was evaporated to give the corresponding ben-zylalcohol 2a in 90% yield exclusively without the formation of any side products. Preparative column chromatography with silica gel was used for further purification of the alcohols, eluting with petroleum ether (60/80)-CHCl3 (1 1). 

M11O2 doped silica (1.25 g, 5 mmol of M11O2 on silica gel, Selecto Scientific, 230-400 mesh with large surface area of 600 m2 g ) is thoroughly mixed with benzyl alcohol la (108 mg, 1 mmol) and the material is placed in an alumina bath inside the microwave oven and irradiated for 20 s. Upon completion of the reaction, monitored on TLC (hexane-AcOEt, 10 1), the product is extracted into methylene chloride, solvent removed and the residue passed through a bed of silica gel (4 cm) to afford exclusively benzaldehyde 2a. The overoxidation to carboxylic acid is not observed. The same reaction could be completed in 2 h at a comparable temperature of 55 °C in an oil bath. 

The oxidation of benzyl alcohol la to benzaldehyde 2a is representative of the general procedure employed. Benzyl alcohol la (0.108 g, 1 mmol) and IBD (0.355 g, 1.1 mmol) doped on neutral alumina (1 g) are mixed thoroughly on a vortex mixer. The reaction mixture is placed in an alumina bath inside an unmodified household microwave oven and irradiated for a period of 1 min. On completion of the reaction, followed by TLC examination (hexane-AcOEt, 9 1, v/v), the product is extracted into dichloromethane and is neutralized with aqueous sodium bicarbonate solution. The dichloromethane layer is separated, dried over magnesium sulfate, filtered, and the crude product thus obtained is purified by column chromatography to afford pure benzaldehyde 2a in 94% yield. Alternatively, the crude products are charged on a silica gel column that provides io-dobenzene on elution with hexane followed by pure carbonyl compounds in solvent system (hexane-ethyl acetate, 9 1, v/v). 

Montmorillonite K-10 supported bis(trimethylsilyl)chromate (0.93 g, equivalent to 1.5 mmol) was thoroughly mixed with 0.192 g benzyltetrahydropyranyl ether (1 mmol), and the material was placed in a beaker inside the microwave oven (900 W) for 20 s. After completion of the reaction as monitored by TLC (hex-ane-AcOEt, 8 2) the product was extracted into CH2CI2, the solvent was removed, and the residue was chromatographed on a silica gel column using hexane-AcOEt (8 2) to afford 92% benzaldehyde. 

The sulfide 1 (0.75 mmol) is dissolved in dichloromethane (2-3 mL) and adsorbed over silica supported sodium periodate (20%, 1.36 g, 1.28 mmol) that is wetted with 0.3 mL of water by thoroughly mixing on a vortex mixture. The adsorbed powdered material is transferred to a glass test tube and is inserted in an alumina bath (alumina 100 g, mesh 65-325, Fisher scientific bath 5.7 cm diameter) inside the microwave oven. The compound is irradiated for the time specified in the table and the completion of the reaction is monitored by TLC examination. After completion of the reaction, the product is extracted into ethyl acetate (2x15 mL). The removal of solvent at reduced pressure affords crude sulfoxide 2 that contains less than 5% sulfone. The final purification is achieved by column chromatography over silica gel column or a simple crystallization. 

Clayfen (1.0 g) is thoroughly mixed with the sulfide (2 mmol) in a test tube. The reaction mixture is placed in an alumina bath inside the microwave oven and is irradiated for the stipulated time. On completion of the reaction, monitored by TLC, the products were extracted with CH2C12 (3x10 mL). The solvent was removed on a rotary evaporator and the crude product, thus obtained, was charged on a silica gel column. The fractions eluted by chloroform-hexane (1 1) provided sulfone and final elution in chloroform afforded pure sulfoxide. 

Barbituric acid 1 (5 mol), aldehyde 2 (6 mmol) and montmorillonite KSF (1 g) were ground with solid aldehyde or were mixed with liquid aldehyde. The mixture placed in an open Pyrex Erlenmeyer flask (25 mL) was irradiated with a microwave oven. After cooling the product was extracted with DMF (15 mL) and the solvent was evaporated in vacuo. The resulting solid was ground and washed with ether (30 mL), filtered and dried. 

Salicylaldehyde 3 (0.122 mg, 1 mmol), KF-alumina (0.620 g, 2 mmol of KF) and a-tosyloxyketone 2 (1 mmol) were placed in a glass tube and mixed thoroughly on a vortex mixer. The glass tube was then placed in an alumina bath inside the microwave oven and irradiated (intermittently at 1.5-min intervals 130 °C) for a specified time. On completion of the reaction, followed by TLC examination (hexane-EtOAc, 9 1), the product was extracted into methylene chloride (3xl0mL). The solvent was then removed under reduced pressure and the residue was crystallized from ethanol to afford a nearly quantitative yield of 2-ar-oylbenzo[/ ]furans 4a-h. 

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