Heating oil baths

N,N Dimethylcyclohexanecarboxamide A 500-ml three-necked flask is equipped with a reflux condenser (drying tube), a pressure-equalizing dropping funnel, and a magnetic stirrer. The flask is charged with 32 g (0.25 mole) of cyclohexanecarboxylic acid and thionyl chloride (45 g, 0.375 mole) is added over 5 minutes to the stirred acid. The flask is heated (oil bath) at a temperature of 150° for 1 hour. The reflux condenser is... 

Cyclopropyltriphenylphosphonium Bromide (5). The lactone salt is pyrolyzed by placing it in a round-bottom flask fitted with an adaptor attached to a vacuum source (aspirator is sufficient). The flask is heated (oil bath) to 180-190° for 48 hours. The residue is a virtual quantitative yield of the tan product, which may be crystallized from ethyl acetate giving cream crystals, mp 189-190°. An alternate setup is convenient if a drying pistol (Abderhalden) is available. The compound is placed in the pistol, which is then evacuated. Decalin (bp approx. 187°) is refluxed over the pistol to provide the heating source. The work-up is the same. 

C) Preparation of 6-Allyl-7-Hydroxy-4,8-Dimethylcoumarin 7-Allyloxy-4,8-dimethyl-coumarin (195.0 g, 0.84 mol) was heated (oil bath) to 215 4°C (reaction mixture temperature) for 3 hours and was then poured into absolute alcohol (ca 1.5 liters). Activated carbon (Norite) (19.5 g) was added, and the solution was heated to boiling, filtered, and diluted with excess water (ca 12 liters). The product was collected by filtration and partially dried at 70°C for 6 hours. 6-Allyl-7-hydroxy-4,8-dimethylcoumarin was obtained as pale yellow microcrystalline prisms, MP 166° to 168°C, by two recrystallizations from aqueous ethanol of a portion of the partially dried solid. The remaining partially dried solid was used in the next step. 

One of the first published microwave-assisted synthesis of benzothiazoles is the condensation of a dinucleophile such as 2-aminothiophenol, with an ortho-ester (neat) in the presence of KSF clay in a mono-mode microwave reactor operating at 60 W under a nitrogene atmosphere [ 12] (Scheme 12). Traditional heating (oil bath, toluene as solvent and KSF clay) gave the expected products in similar yields compared to the microwave experiments but more than 12 h were required for completion. Solvent-free microwave-assisted syntheses of benzothiazoles was also described by attack of the dinucleophiles cited above on benzaldehydes and benzaldoximines [13] (Scheme 12). This methodology was performed in a dedicated monomode microwave reactor... 

Manganese(III)-promoted radical cyclization of arylthioformanilides and a-benzoylthio-formanilides is a recently described microwave-assisted example for the synthesis of 2-arylbenzothiazoles and 2-benzoylbenzothiazoles. In this study, manganese triacetate is introduced as a new reagent to replace potassium ferricyanide or bromide. The 2-substituted benzothiazoles are generated in 6 min at 110°C imder microwave irradiation (300 W) in a domestic oven with no real control of the temperature (reflux of acetic acid) (Scheme 15). Conventional heating (oil bath) of the reaction at 110 °C for 6 h gave similar yields [16]. 

The same Suzuki couplings could also be performed under microwave-heated open-vessel reflux conditions (110 °C, 10 min) on a ten-fold larger scale, giving nearly identical yields to the closed-vessel runs [33, 35], Importantly, nearly the same yields were obtained when the Suzuki reactions were carried out in a pre-heated oil bath (150 °C) instead of using microwave heating, clearly indicating the absence of any specific or non-thermal microwave effects [34],... 

N-Ethylaniline was alkylated by reaction with benzyl chloride under liquid-liquid PTC conditions in the presence of 30% sodium hydroxide solution and CTAB as a catalyst. Microwave irradiation (25 min) of the reaction mixture in a sealed vessel afforded N-benzyl-N-ethylaniline in 90% yield, compared with 16 h of conventional heating (oil bath) (Eq. 30) [24]. 

MW monomode reactor Ultrasound (cleaning bath) Conventional heating (oil bath)... 

It is interesting to point out that under the action of microwave irradiation the formation of ionic liquid 72 could be monitored visibly in the reaction - when it turns from a clear solution to opaque and finally clear. After the first irradiation for 30 s at 240 W (bulk temperature -70-100 °C) the homogeneity of the reaction mixture changes because of the formation of a small amount of ionic liquid 72. Additional irradiation was then repeated for 15 s until the formation of a clear, single-phase ionic liquid product. A series of ionic liquids 72 was prepared by microwave heating and the procedure was then compared with conventional heating (oil bath at 80 °C) using the same preparation (Tab. 8.5). 

At first some bumping may. occur if the heating is too vigorous mechanical stirring may reduce this, but does not improve the yield. The submitters found an electrically heated oil bath or a steam bath to be satisfactory, but not a heating mantle. 

Diacetoxylation of 1,3-butadiene (typical procedure) To a mixture of TeOj (0.80 g, 5 mmol), LiBr (2.17 g, 25 mmol), AcOH (18 mL) and AC2O (2 mL) in a glass pressure bottle, chilled at -20°C, is added chilled 1,3-butadiene (1.35 g, 25 mmol). The resulting suspension is heated (oil bath) at 120-130°C for 20 h under magnetic stirring, producing a... 

A. 1-Butyl-3-methyiimidazolium chioride. A 2-L, three-necked, round-bottomed flask is equipped with a heating oil bath, a nitrogen inlet adapter, an internal thermometer adapter, an overhead mechanical stiner, eind a reflux condenser. The flask is flushed with... 

Instead of a steam bath or a water bath, an electrically heated oil bath is suitable. This permits easy regulation of the rate of distillation. However, the temperature of the bath should not exceed 95-100° when isopropyl alcohol is the solvent if possible dehydration of a sensitive alcohol is to be avoided. For this same reason, a burner, hot plate, or sand bath is not recommended for heating. Especially at the end of the reduction, superheating of the concentrated alkoxide solution may bring about dehydration or other decomposition of the product. 

The specific microwave effects were presumably responsible for the observed 40-fold acceleration in microwave-assisted synthesis of 1,3,5-triazines 107 compared to conventional thermal conditions. Thus, microwave heating of benzonitrile and dicyandiamide 106 in an ionic liquid ([bmim]PF6) in the presence of powdered KOH at 130 °C for just 12 min afforded 2,4-diaminotriazine 107 in 87% yield. Under otherwise identical conditions the reaction in a pre-heated oil-bath (130 °C temperature) took 8 hours to afford the target heterocycle 107 in 79% yield [140] (Scheme 57). 

Figure 3 shows a schematic view of a flow reactor. It is similar to the photochemical reactor previously described in [5] but the UV photolysis cell has been replaced by a 1 m. stainless steel coil in a heated oil bath. As before, FTIR is used to monitor the conversion and optimise the conversion of reactant to product. Using such a system (C5Me5)Mn(CO)2(C2H4) can be obtained in a high yield as in Scheme 1. We are now scaling up this miniature reactor to a technical scale, ultimately with the aim of carrying out solvent-free reactions on a kilogramme scale.

An electrically heated oil bath is used to maintain a constant bath temperature of 130-140°. 

VIII F. The thin (2 25 mm.) layer of liquid (2) was between two copper plates (1) and (3), the upper one in contact with an electrically heated oil bath at a temperature ti, and the lower one at a temperature tz with a coppered block of... 

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