Heterogeneous reaction mixture

Because the highest possible interfacial area is desired for the heterogeneous reaction mixture, advances have also been made in the techniques used for mixing the two reaction phases. Several jet impingement reactors have been developed that are especially suited for nitration reactions (14). The process boosts reaction rates and yields. It also reduces the formation of by-products such as mono-, di-, and trinitrophenol by 50%. First Chemical (Pascagoula, Mississippi) uses this process at its plant. Another technique is to atomize the reactant layers by pressure injection through an orifice nozzle into a reaction chamber (15). The technique uses pressures of typically 0.21—0.93 MPa (30—135 psi) and consistendy produces droplets less than 1 p.m in size. The process is economical to build and operate, is safe, and leads to a substantially pure product. 

In a 2-1. three-necked round-bottomed flask, fitted with an efficient sealed stirrer and a reflux condenser capped by a drying tube, are placed the dried anisyl chloride (Notes 2 and 3), 73.6 g. (1.5 moles) of finely powdered sodium cyanide, 10 g. of sodium iodide, and 500 ml. of dry acetone (Note 4). The heterogeneous reaction mixture is heated under reflux with -sngorous stirring for 16-20 hours, then cooled and filtered with suction. The solid on the filter is washed with 200 ml. of acetone and discarded (Note 5). The combined filtrates are distilled to remove the acetone. The residual oil is taken up in 300 ml. of benzene and washed with three 100-ml. portions of hot water. The benzene solution is dried over anhydrous sodium sulfate for about 15 minutes, and the solvent is removed by distillation at the reduced pressure of the water aspirator (Note 6). The residual -methoxyphenyl-acetonitrile is purified by distillation under reduced pressure through an 8-in. Vigreux column b.p. 94—97°/0.3 mm. 1.5285-1.5291. The yield is 109-119 g., or 74-81% based on anisyl alcohol (Notes 7 and 8). 

Reactions with Isocyanates. The reaction of alcohols with isocyanates to form carbamates is well known and similar reactions with poly(vinyl alcohol) would be expected. Until recently, the only available reaction conditions were to use a heterogeneous reaction mixture or to run the reaction in a poor solvent for poly(vinyl alcohol). The best poly(vinyl alcohol) solvents, water and formaide derivatives, react rapidly with isocyanates. Nevertheless, several such reactions have been run in the past and we will cite only a few of them. A potentially photosensitive polymer was made by the reaction of allyl isocyanate with poly(vinyl alcohol) (57) and several workers have crosslinked poly(vinyl alcohol) with hexamethylene diisocyanate (58.59). 

Typical procedure. Into a two-necked, 20 mL, round-bottomed flask containing PdClj (8.8 mg, 0.05 mmol), AgOAc (388 mg, 2.00 mmol) and di(/7-methoxyphenyl) teUuride (0.171 g, 0.50 mmol) were added dry methanol (10 mL), EtjN (0.202 g, 2.00 mmol) and styrene (0.104 g, 1.00 mmol). After the heterogeneous reaction mixture had been stirred at 25°C for 20 h, the sohd part was filtered. The filtrate was poured into brine (200 mL) and extracted with diethyl ether (3x50 mL). GLC determination of the ether extract with diphenyhnethane as an internal standard showed the presence of 0.99 mmol (99%) of (E)-p-methoxystilbene. 

The heterogeneous reaction mixture is stoppered tightly to avoid loss of cyclopentadiene. 

In water, the third-generation (16) and fourth-generation dendrimers (17) induced chirality toward the (S)-enantiomer (50% ee for 16 and 98% ee for 17). In THF high enantiomeric excess was achieved only with the third-generation dendrimer (99% (S) ee for 16 and 3% (S) ee for 17). Dendrimer 16 was recovered from the heterogeneous reaction mixture by nanofiltration on a Millipore microporous membrane system. After regeneration of the catalytic activity by treatment with... 

A 500-mL, three-necked, round-bottomed flask, equipped with a mechanical stirrer, condenser with Dean-Stark trap, nitrogen bubbler and a thermometer (Note 1), is charged with toluene (200 mL), (1 R,2S)-(-)-norephedrine (37.8 g, 0.25 mol), 1,4-dibromobutane (59.38 g, 0.275 mol) and sodium bicarbonate (46.2 g, 0.55 mol) (Note 2). The stirred heterogeneous reaction mixture is heated to reflux (105-118°C, Note 3) under a nitrogen atmosphere until completion of the reaction (Note 4). At the end of the reaction approximately 9 mL of water has collected in the Dean-Stark trap (Note 5). 

Gas-Solid Heterogeneous Reaction Mixtures. Gas-solid heterogeneous reaction mixtures may be advantageously irradiated in annular (immersion-type) photochemical reactors. Again, the content of solid particles is limiting the size and the productivity of the reactor system. This is of particular importance when the solid support is used to specifically adsorb substrates or products of the photochemical reaction the first to enhance specificity of radical substitution reactions [20], the latter to reach better photostability and to ensure optimal purity. 

The major drawback of CF processing, however, is the incompatibility with heterogeneous reaction mixtures and highly viscous liquids. Apart from the fact that obtaining a temperature measurement directly from a reaction mixture under flow can be complicated, the adaptation of conditions from small-scale batch reactions to a CF cell may be time-consuming. 

Add the alkylzinc bromide reagent dropwise to the cyclohexenone mixture over 20 min. Stir the heterogeneous reaction mixture for 3.5 h at -30°C. 

Add the 3-bromo-3,3-difluoropropene and THF (10 mL) to the addition funnel. Add the contents of the addition funnel dropwise to the stirred, heterogeneous reaction mixture. 

The reactor is characterized by no addition of reactant or removal of product during the reaction. Any reaction being carried out with this constraint, regardless of any other reactor characteristic, is considered batch. The assumptions for batch operation are (1) the contents of the tank are well mixed, (2) reaction does not occur to any appreciable degree until filling and startup procedures are complete, and (3) the reaction stops when quenched or emptied. The reactor can be operated with either a homogeneous or heterogeneous reaction mixture for almost any type of reaction. 

Hydrogenation catalysts are insoluble in common solvents, thus creating a heterogeneous reaction mixture. This insolubility has a practical advantage. These catalysts contain expensive metals, but they can be filtered away from the other reactants after the reaction is complete, and then reused. 

For homogeneous reaction systems at constant temperature, agitation is not normally necessary. However, most reactions involve heterogeneous reaction mixtures and so require some form of agitation to ensure efficient mixing of the reactants. The most commonly used methods of agitation are outlined in this section. 

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