Internal-reaction temperature

A. Ethyl 3-hydroxy-4-pentenoate. A dry, 2-L, two-necked, round-bottomed flask, capped with septa and equipped with a thermometer (Note 1), magnetic stirring bar, and an argon inlet is flushed with argon and charged with dry tetrahydrofuran (400 mL, Note 2) and diisopropylamine (30.8 mL, 220 mmol, Note 3). The solution Is cooled to -30°C and butyllithium (BuLi) (93.2 mL, 220 mmol, 2.36 M solution in hexanes, Note 4) is added. The reaction is stirred for 15 min and cooled to -76° to -78°C. Dry ethyl acetate (19.5 mL, 200 mmol, Note 5) is added dropwise so that the Internal reaction temperature remains below -66°C (addition time 10-15 min). When addition of the ethyl acetate is complete, the reaction Is stirred for 50 min at -70° to -78°C. A solutior of freshly distilled acrolein (13.4 mL, 200 mmol, Note 6) and 100 mL of dry... 

A Fluke 51 K/J digital thermometer with temperature probe is used to monitor internal reaction temperature. 

A. 1,1-Dibromo-2,2-bis(chloromethyl)cyclopropane (1). Into a 1-L, threenecked, round-bottomed flask, equipped with an efficient mechanical stirrer, a thermometer, and a condenser equipped with a potassium hydroxide drying tube, are placed 54.1 g (0.403 mol) of 3-chloro-2-(chloromethyl)propene (Note 1), 212 g (0.805 mol) of bromoform (Note 2), 1.70-2.00 g (14.4-16.9 mmol) of pinacol (Note 3), and 1.45 g (3.94 mmol) of dibenzo-18-crown-6 (Note 4). With very vigorous stirring (Note 5), 312 g of an aqueous 50% sodium hydroxide solution that has been cooled to 15°C is added in one portion. The reaction mixture turns orange, then brown, then black within 5 min, and the temperature of the reaction mixture begins to rise. Within 20 min, the internal reaction temperature is 49-50°C at which point the reaction flask is cooled with a room-temperature water bath, and the reaction temperature decreases to ca. 

A 500-ml flask equipped with a reflux condenser, stirrer, and a dropping funnel was treated with the step 4 product (0.027 mol) and 200 ml CH2C12. The solution was then treated with the dropwise addition of boron tribromide (0.135 mol) over 30 minutes at such a rate that the internal reaction temperature did not exceed 10°C. The mixture was then stirred at ambient temperature for 3 hours and then treated with water to stop the reaction. Posttreatment was carried out in the same manner as described in step 1 and 10.01 g of product isolated. 

Dimethoxyacetophenone (15 g, 83 mmol) was added over lh to coned HN03 (90 mL) with stirring, keeping the internal reaction temperature in the range 18-22 °C. After the addition was complete, the soln was stirred for an additional hour and then poured into H20 (1200 mL). After chilling, the product was collected and recrystallized from EtOH yield 8.4 g (45%) mp 130-132 °C. 

The submitters ran the reaction on a scale four times that described. The submitters also note that the reaction may be successfully carried out in a 2-L Erlenmeyer flask equipped with a thermometer to monitor the internal reaction temperature and a large magnetic stirring assembly. The gas delivery tube and rubber stopper, used in Figure 1, is placed in the mouth of the flask, and the HCI gas is forced into a base trap or disposed of through an aspirator. 

On larger scales (up to 50 grams of propiolic acid) the addition should still be complete within 1 min to allow the internal reaction temperature to rise to 100°C. 

It should be noted when carrying out reactions using cooling baths, that the reaction itself may not be at the same temperature as the bath due to exothermic processes taking place, so where possible the internal reaction temperature should also be monitored. A particularly convenient way of doing this is to use a digital low-temperature thermometer. These are commercially available, and most come with a hypodermic probe which can be inserted into the reaction flask through a sepmm (Fig. 9.21). 

To avoid reduction of the generated aldehyde that is more prone to reduction than the corresponding ester, the reducing agent should be added very slowly, avoiding any local temperature increase. The reaction mixture should be kept below -70°C. The checkers used a three-necked flask equipped with a low temperature thermometer to monitor the internal reaction temperature. 

The formation of a side product, N,N -dimethyl-N,N -diphenyl-1,4-phenylenediamine, was observed if the internal reaction temperature exceeded 65°C. 

An alternative would be the modification of the isothermal to an isoperibolic process with the side condition that the internal reaction temperature mtist not exceed a value of 383 K. The data given can be used to determine the initial temperature with the help of Equ.(4-157). The initial temperature is identical with the coolant temperature if this is kept constant during the process. As the thermal reaction number amounts to the relatively low value of 1.82, the correction fimction may be set to 1. 

The microwave irradiation was generated using a reactor setup that allowed accurate measurements of internal reaction temperature using fiber-optic probes. Experiments were carried out under at least two different power values, and also with simultaneous external cooling when a higher power of microwave radiation was applied. The same method of temperature measurement was also used in experiments with conventional heating. 

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