Reflux conditions

Process Solvent Solvent additives and reflux conditions Operating tempera-ture, °C Contacting equipment Comments... 

Isobutyraldehyde reacts with aqueous ammonia at 0—10°C to give hexahydro-2,4,6-ttiisopropyl-r-ttiazine, (4) (18), whereas under refluxing conditions the enea2omethine [5339-41-3] (5), is formed (19). Isobutyraldehyde condenses with two mole equivalents of urea in the presence of an acid catalyst to give isobutyUdenediurea [2224-20-6] (IBDU), (6) a slow release fertiliser (20). 

The catalyst commonly used in this method is 5 wt % palladium supported on barium sulfate inhibited with quinoline—sulfur, thiourea, or thiophene to prevent reduction of the product aldehyde. A procedure is found in the Hterature (57). Suitable solvents are toluene, benzene, and xylene used under reflux conditions. Interestingly, it is now thought that Rosenmund s method (59) originally was successful because of the presence of sulfur compounds in the xylene used, since the need for an inhibitor to reduce catalyst activity was not described until three years later (60). 

From Table 13-31, a total of 394 time increments were necessary to distill all hut 22.08 Ih-mol of the initial charge of 99.74 Ih-mol following the establishment of total-reflux conditions. If this problem had to he solved by an explicit integrator, approximately 25,000 time increments would have been necessary. 

All the foregoing test programs involve distillation of well-defined mixtures under total reflux conditions. The primary value of the results is in the comparative data, but it should be emphasized that the design of each device was not necessarily optimized for the test conditions. 

The isoquinoline framwork is derived from the corresponding acyl derivatives of P-hydroxy-P phenylethylamines. Upon exposure to a dehydrating agent such as phosphorous pentaoxide, or phosphorous oxychloride, under reflux conditions and in an inert solvent such as decalin, isoquinoline frameworks are formed. 

Phenylphosphole with [Os3(CO)l2] and [Os3(CO)ll(AN)] under reflux conditions gives rise to 240 (R = H) and 241 as isolable products [91JOM(408)C18]. l-Phenyl-3,4-dimethylphosphole with [Os3(CO)l2] or [Os3(CO)j (AN)lo -J (x= 1, 2) yields 242 and 243. The latter, however, experiences subsequent oxidative addition to give 240 (R = Me). Species 242 and 240 (R = Me) mutually transform into each other, the direct process induced by light and the reverse occurring in dark [91JCS(D)3381],... 

To a solution of 142 g (1 mol) of trans-3,3 -trimethylcyclohexenol in 400 cc of anhydrous benzene heated to 70°C is added gradually 178 g (1 mol) of niacin chloride hydrochloride. Heating is carried out under reflux conditions for 3 hours, the solution is cooled, the ester hydrochloride is filtered off and then recrystallized in an ethanol-ethyl ether mixture to obtain 227 g (80% yield) of product melting at 155°C to 157°C. 

The effect of the partial condenser is indicated in Figure 8-13 and is otherwise represented by the relations for the rectifying and stripping sections as just given. The key point to note is that the product is a vapor that is in equilibrium with the reflux to the column top tray, and hence the partial condenser is actually serving as an external tray for the system and should be considered as the top tray when using the equations for total reflux conditions. This requires just a little care in step-wise ctdculation of the column performance. 

As the reflux ratio is decreased from infinity for the total reflux condition, more theoretical steps or trays are required to complete a given separation, until the limiting condition of Figure 8-23 is reached where the operating line touches the equilibrium line and the number of steps to go from the rectifying to stripping sections becomes infinite. 

Figure 8-23. Fractionation of binary mixture at minimum reflux condition.

At the minimum reflux condition all the 9 values are equal, and generally related ... 

Under reflux conditions, 5//-dibenz[c < lazepine (7) adds acetic anhydride across the imine bond to give 6-acetyl-6,7-dihydro-5//-dibenz[c,e]azepin-5-yl acetate (8).5... 

This untimely polymer formation is understood to be caused by the very rapid hydrolysis and aggregation of monomeric Pu(IV) species (at the region of condensate reentry into the hot plutonium solution) to produce hydrous polymers that are not readily depolymerized. At high temperatures such as found under reflux conditions, the polymer rapidly ages through the conversion of hydroxyl- to oxo-bridges ... 

If one takes the 4 or 6 M HNO3 data under reflux conditions and evaluates the increase in rates with increasing concentration of Pu(IV), he would find that the time to form observble polymer is inversely proportional to the first power (1.1 . 4) of the Pu(IV) concentration. At first glance this might seen to contradict earlier findings (7 ) that showed the... 

Impure plutonium oxide residues are dissolved in 12M HN03-0.1M HF under refluxing conditions, and then the plutonium is recovered and purified by anion exchange. Plutonium is leached from other residues, such as metal and glass, and is also purified by anion exchange. The purified plutonium eluate from the anion exchange process is precipitated with hydrogen peroxide. The plutonium peroxide is calcined to the oxide, and the plutonium oxide is fluorinated. The plutonium tetrafluoride is finally reduced to the metal with calcium. 

Independently, Caddick et al. reported microwave-assisted amination of aryl chlorides using a palladium-N-heterocyclic carbene complex as the catalyst (Scheme 99) [lOlj. Initial experiments in a domestic microwave oven (reflux conditions) revealed that the solvent is crucial for the reaction. The Pd source also proved very important, since Pd(OAc)2 at high power in DMF gave extensive catalyst decomposition and using it at medium and low power gave no reaction at all. Pd(dba)2/imidazohum salt (1 mol% catalyst loading) in DME with the addition of some DMF was found to be suitable. Oil bath experiments indicated that only thermal effects are governing the amination reactions. 

N-Arylpiperazin-2-ones, N-arylpiperazin-2,5-diones and N-aryl-3,4-dihydro-quinolin-2(lff)-ones have been synthesized via a microwave-enhanced Goldberg reaction [105]. N-arylation reactions with 4-benzylpiperazin-2-one and 4-benzylpiperazin-2,5-dione performed in the microwave (reflux conditions) were tremendously accelerated in comparison with the same transformations performed under classical heating at reflux (Schemes 103 and 104). The phenylation of 3,4-dihydroquinolin-2(lH)-one under microwave irradiation was also faster but less pronounced. 

In this way, the operational range of the Kolbe-Schmitt synthesis using resorcinol with water as solvent to give 2,4-dihydroxy benzoic acid was extended by about 120°C to 220°C, as compared to a standard batch protocol under reflux conditions (100°C) [18], The yields were at best close to 40% (160°C 40 bar 500 ml h 56 s) at full conversion, which approaches good practice in a laboratory-scale flask. Compared to the latter, the 120°C-higher microreactor operation results in a 130-fold decrease in reaction time and a 440-fold increase in space-time yield. The use of still higher temperatures, however, is limited by the increasing decarboxylation of the product, which was monitored at various residence times (t). 

When thiols with varying chain lengths, such as Cg-, Cio-, Ci2- and Ci6- are used, we observe very interesting trends [47]. First, all the colloids under reflux conditions display a strong reddish color. Nanoparticles, especially those of coinage metals like gold and silver, display striking colors... 

Methyl esterification When prohexadione was treated with methanolic HCl (3%, w/v) or sulfuric acid-methanol (1 %, v/v) under reflux at 75 °C for 60 min, or with BFs-methanol (14%, w/v) under reflux at 75 °C for 30 min, the yield of the methyl ester of prohexadione was 95,93 and 82%, respectively (prohexadione, 10 qg, volume 2 mL of methanolic HCl, 2 mL of sulfuric acid-methanol and 1 mL of BFs-methanol). A solution of 1% (v/v) sulfuric acid in methanol was chosen for ease of preparation. Even if prohexadione was treated with 1% sulfuric acid in methanol at room temperature for 12h, the yield of prohexadione methyl ester was not different from that under reflux conditions as described in Section 6.3. The conditions for methyl esteriflcation in Section 6.3 were chosen because of shortening of the analysis time and the reproducibility of the reaction yield in residue analysis samples which could contain large quantities of contaminants. 

The extraction rate of mepanipyrim with refluxing was higher than that with shaking (30 min) and sonication (Ultrasonic, 600 W, 28 kHz, 30 min). For the solvent system, acetone and acetonitrile showed almost similar extraction efficiencies. Methanol was found to be a less effective extraction solvent. Mepanipyrim was unstable in the acidic solution and alkaline solution under reflux conditions at 80 °C. The extraction rate of mepanipyrim under these conditions decreased to about 50% and 20%, respectively. Therefore, neutral solution was used as the extraction solvent in this method. 

The latest syntheses of novel four- and five-membered cyclic anions of the heavier group 14 elements (Si, Ge, Sn) provided a fresh look at the question of aromaticity (or nonaromaticity) of the heavier analogs of 6jt-electron aromatic systems. Thus, the story of the heavy analogs of cyclopentadienyl anion (Section 2.3.2.5) was continued by the preparation of the stannole dianion by Saito and co-workers. ° The stannole dianion 68 Li2 was prepared by the metalation of the bis(Ll-stannole) with an excess of Li in THF at elevated temperatures however, it can be better prepared by the lithiation of hexaphenylstannole with Li in THF under reflux conditions " (Scheme 2.65). 

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