Dean—Stark trap

Note 1). The mixture is heated with a mantle with stirring for 32 hr under a 50-cm fractionating column packed with 5-nm glass beads and topped by a Dean-Stark trap. The reaction mixture is then distilled through the packed column. The fraction which boils at 120 -126°C is collected. The yield is 86.0-87.3 g (77-78%) of 2,2-dimethyl-4-pentenal (1) as a clear, colorless oil, n 1.4216 (Note 2). 

In a 1-L rbf attached to a Dean-Stark trap, equipped with a reflux condenser is placed distilled aniline (1, 46.5 g, 45.5 mL, 0.5 mol), commercially available ethyl acetoacetate (5, 65 g, 63.5 mL, 0.5 mol), benzene (100 mL) and glacial AcOH (1 mL). The flask is heated at about 125 °C, and the water which distills out of the mixture with the refluxing benzene is removed at intervals. Refluxing is continued until no more water separates (9 mL collects in about 3 hrs) and then for an additional 30 min. The benzene is then distilled under reduced pressure, and the residue is transferred to a 125 mL modified Claisen flask with an insulated column. The flask is heated in an oil or metal bath maintained at a temperature not higher than 120 °C while the forerun of 1 and 5 is removed and at 140-160 °C the product distills giving 78-82 g, 76-80% yield of 6. 

It is occasionally necessary to carry out special operations in connection with a synthetic procedure. An example frequently encountered is the removal of water from a reaction mixture in order to alter equilibrium concentrations (for example, in the preparations of enamines). For this purpose, a Dean-Stark trap is employed as shown (Fig. A3.6). The reaction is carried out in a solvent that forms an azeotrope with water... 

Fig. A3.6. Dean-Stark trap for continuous removal of water.

Azeotropic drying of organic substances is also effective, providing the material is relatively nonvolatile. A benzene or toluene solution of the compound is distilled (in a Dean-Stark trap, if available) until the distillate is free of water droplets. The remaining solution is essentially dry. 

A mixture of 5,6-diamino-1,3-dimethylpyrimidine-2,4-(l//,3/f)-dione hydrate (5.0 g, 26.5 mmol), phthalic anhydride (7.9 g, 26.5 mmol) and A.A-dimethylaniline (60 mL) was heated tolux under N2 as H20 was removed using a Dean-Stark trap. After 1.5 h the mixture was cooled to rt and filtered. The resulting crude product was recrystallized from 95% F.tOH (800 mL) to give pale yellow needles yield 4.5 g (52%). An analytical sample was prepared by recrystallization (0.5 g in 300 mL of H20) as a hydrated solid mp > 250 C. 

A mixture of 4.2 g (40.7 niniol) of (S)-valinol, 4.4 g (41 mmol) of benzaldeliyde and 100 mL of benzene is refluxed for 3 h using a Dean-Stark trap. After concentrating under reduced pressure tlie residue is allowed to stand at r.t. to give crystals of 2a. Rccrystallization from pentane provides colorless prisms yield 6.8 g (89%) mp 71-72 C. 

S,5S)-5-(2-Alkeny/ideneamiuo)- or (4S,5S)-5-(2-Alkynylideneamino)-2,2-dimt lli)l-4-phenyl-l,3-clioxane 8 Equimolar amounts of an a,/f-unsaluraled aldehyde and (45,55 )-5-amino-2.2-dimethyl-4-phenyl-1,3-diox-ane 7 are mixed with cyclohexane and refluxed for 2 h using a Dean-Stark trap. Then the cyclohexane is removed, the residue is dissolved in Ei,0 and dried over MgSO . Evaporation of the solvent provides imine 8 yield. 90-98%. 

A mixture of 1 g (5.6 mmol) of (1 R,2S)-A -aminoephedrine and 0.67 g (5.6 mmol) of 4-mcthylbenzaldehyde in 100 mL of benzene is refluxed for 3 h using a Dean Stark trap. After removal of the solvent the residue is purified by column chromatography (silica gel, CH2C12) to provide the product yield 1.43 g (91%). (R)-a-Phcnylcthylamine Typical Procedure18 ... 

The aminal from 3.4-methylenedioxybenzaldehyde and morpholine (entry 5 in the table opposite) is prepared by dissolving the educts in toluene and refluxing. The water is removed by means of a Dean-Stark trap. 

B. 3-(4,4,5,5-Tetramethyl-[l,3,2]dioxaborolan-2-yl)pyridine. A 250-mL, one-necked, round-bottomed flask equipped with a magnetic stirbar and a Dean-Stark trap fitted with a condenser capped with a nitrogen inlet adaptor is charged with tris(3-pyridyl)boroxin-0.85 H20 (3.0 g, 9.1 mmol), pinacol (4.07 g, 34.4 mmol) (Note 6), and 120 mL of toluene. The solution is heated at reflux for 2.5 hr in a 120°C oil bath. The reaction is complete when the mixture changes from cloudy-white to clear. The solution is then concentrated under reduced pressure on a rotary evaporator to afford a solid residue. This solid is suspended in 15 mL of cyclohexane (Note 7) and the slurry is heated to 85°C, stirred at this temperature for 30 min, and then allowed to cool slowly to room temperature. The slurry is filtered, rinsed twice using the mother liquors, washed with 3 mL of cyclohexane, and dried under vacuum to afford 4.59 g (82%) of 3-pyridylboronic acid pinacol ester as a white solid (Note 8). 

Toluene (99.8% anhydrous, water <0.001%, evaporation residue <0.005%) was purchased from Aldrich Chemical Company and used as received. The capacity of the receiver in the Dean-Stark trap was 28 mL. The initial amount of toluene placed in the flask was 88 mL. Upon heating to reflux, 28 mL of toluene was distilled from the flask and collected in the receiver. The remaining volume of toluene in the reaction flask was ca. 60 mL, corresponding to an approximately 0.50M concentration of the reactants. 

Synthesis of Unsaturated Polyester A. The unsaturated polyester oligomer A was prepared in a 500 milliliter 4-neck flask fitted with a variable speed stirrer, a heating mantle, a gas inlet tube, a thermometer, a Dean-Starke trap and a condenser. The flask was charged with 147.0 g (1.5 mol) of maleic anhydride (Amoco), 195 g (1.88 mol) of 1,5-pentane diol (BASF), about 35 ml of xylene and 0.3 g of Fascat 4100. Then heated slowly under a nitrogen blanket to 175° C while the water of condensation was removed... 

Bromomethyl acetyl sulfide (26.8 g, 0.16 mol) and triethyl phosphite (28.4 g, 0.17 mol) were combined in a flask fitted with a Dean-Stark trap. The mixture was stirred at 130°C for 2.5 h, during which time ethyl bromide collected in the Dean-Stark trap. The reaction mixture was vacuum distilled to give the pure (diethyl phosphonomethyl) acetyl sulfide (23.5 g, 65%) as a clear oil of bp 105 to 106°C/0.03 torr, which exhibited NMR spectra in accord with the proposed structure. 

A mixture of (triisopropyl phosphito)copper(I) bromide (17.6 g, 0.05 mol) and l-bromo-2,2-diphenylethylene (9.1 g, 0.035 mol) was heated at 200°C for 1 h under a nitrogen atmosphere in a flask equipped with a Vigreaux column topped by a Dean-Stark trap. The alkyl halide produced in the reaction was collected in the trap. After cooling, the reaction mixture was poured into toluene (60 ml), and ethylenedi-amine was added (5 ml). After filtering and washing the precipitate with toluene, the combined toluene solutions were washed with 10% hydrochloric acid (10 ml) and water (10 ml), dried over magnesium... 

Mix 0.25M substituted benzaldehyde, 0.3M nitroethane, 50 ml dry toluene and 5 ml n-butylamine (or other amine), and reflux 3 hours with a Dean-Stark trap (or prepare the nitro-propene as described elsewhere here). Add 50 g iron powder and 1 g FeCl3 optional) and reflux while adding 90 ml concentrated HCI over 3 hours. Reflux 1 hour more, add 2 liters of water and extract 3 times with ether, then dry and evaporate in vacuum (or steam distill until about 3.5 liters of distillate is obtained extract the distillate 3 times with toluene wash the toluene layers with 7 g NaHS03 in 225 ml of water, then 3 times with water and dry, evaporate in vacuum) to get the ketone. Mix 0.13M ketone, 28 g formamide (or dimethyl-formamide if the N.N-dimethylamine is desired) and 3 ml formic acid and heat at 160°. Add 3 more ml formic acid and heat 16 hours at 170-180° adding formic acid from time to time to keep the pH acid. Distill off the water formed (about 16 ml), cool and extract with 3X70 ml benzene. Distill off the benzene and reflux the residue 7 hours with 30 ml concentrated HCI. Chill, basify with 10% NaOH and extract with 3X70 ml ether. Dry and evaporate the ether in... 

A three-necked 250 mL round-bottom flask, was equipped with a magnetic stir bar, reflux condenser, Dean-Stark trap, and a gas inlet/outlet adapter. The following mixture was added ... 

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