Water Dean-Stark trap

Triethylenetetramine was purchased from Aldrich Chemical Company, Inc., as a hydrate. Anhydrous triethylenetetramine must be used in this procedure. The anhydrous tetraamine was obtained by azeotropic distillation of water (Dean-Stark trap, 3 days) from a solution of 125 g of the commercial hydrate in 150 mL of toluene. Analysis by 1H NMR verified the removal of water, and no further purification was necessary. 

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. 

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. 

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... 

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... 

Lithiimi iodide dihydrate is available from Fluka A.G., Buchs, S.G., Switzerland. The checkers used the trihydrate and, by means of a Dean Stark trap attached between the flask and the condenser, 1 mole, of water was removed via azeotropic distillation with collidine. 

Typically, the rate of nitrogen flow is ca. 200 bubbles/mln, as measured by a bubbler attached to the condenser outlet. Although a rapid flow of nitrogen is not essential, it facilitates the removal of water and formaldehyde from the reaction mixture this should amount to ca. 85 nt in the lower layer of the Dean-Stark trap. 

Incomplete removal of water and/or too slow removal of water can result in the formation of a significant amount of cyclic octamer, which is difficult to separate from the cyclic hexamer. It is important, therefore, to bring the reaction mixture to reflux (10-15 min) and to remove all the water. In addition to the ca. 85 ml of H2O/HCHO removed in the first phase of the reaction, an additional ca. 10 ml (as a cloudy, lower layer in the Dean-Stark trap) is removed in the second phase. 

Cyclic acetals are useful and common protecting groups for aldehydes and ketones, especially during the course of a total synthesis [8]. The successful synthesis of acetals frequently relies on the removal of water, a by-product of the reaction between the carbonyl compound and the corresponding diol. A Dean-Stark trap is often used for the removal of water as an azeotrope with benzene, but this method is not suitable for small-scale reactions. In addition, the highly carcinogenic nature of benzene makes it an undesirable solvent. Many of the reported catalysts for acetal synthesis such as p-toluenesulfonic acid and boron trifluoride etherate are toxic and corrosive. 

We developed a method for the synthesis of a variety of cyclic acetals that utilizes bismuth triflate as a catalyst and does not require the use of a Dean-Stark trap for removal of water [102]. In this method, an aldehyde or ketone is treated with 1,2-bis (trimethylsiloxy)ethane in the presence of bismuth triflate. A comparison study using o-chlorobenzaldehyde showed that with ethylene glycol a low conversion to the dioxolane was observed after 2 h whereas the use of the 1,2-bis(trimethylsiloxy) ethane afforded the corresponding dioxolane in good yields. (Scheme 9). 

C. l-d-2-Methylbutanal. A 1-1. three-necked round-bottomed flask is equipped with a dropping funnel, a gas inlet tube for steam, and a Dean-Stark trap to which is attached a condenser through which acetone cooled to —15° is circulated (Note 15). A solution of 50.4 g. (0.40 mole) of oxalic acid dihydrate in 200 ml. of water is added to the flask, and the solution is heated at reflux. Steam is introduced into the flask, and when some begins to condense,in the Dean-Stark trap, the distilled aldimine from part B is added dropwise from the funnel. The aldehyde and water collect in the trap, and the water layer is periodically removed. After the distillation of the aldehyde is complete, the product is drained from the trap, and the water layer is separated... 

In a system containing a Dean Stark trap arranged for azeotropic removal of water. 9.3 g (56 mmol) of (-)-(S)-a-(mcthoxymethyl)benzeneethanamine and 6.5 g (66 mmol) of cyclohexanone arc dissolved in 100 mL of benzene or toluene and heated to reflux until the theoretical amount of water is collected in the trap. Removal of the solvent and distillation of the oily residue gives a clear viscous oil yield 13.0 g (93 %) bp (Kugelrohr) 95-100°C/0.5 Torr [a]D —46.2 (c = 6.7, methanol). 

To a solution of 1.02 equiv of the carbonyl compound in benzene (70mL/50mmol), 1 equiv of SAMP is added. The reaction water is removed azeotropically using a Dean Stark trap. After the reaction is complete (TLC monitoring, up to 3 d), the benzene solution is dried over MgS04. concentrated under reduced pressure and distilled in vacuo. See Table 1 for physical data. 

A 250-mL round-bottomed flask equipped with a water collector (Dean-Stark trap), condenser, and magnetic stirrer is charged with p-H2N(C6H4)NH2 (36 g, 0.33 mol), formic acid (69 mL, 1.8 mol, 3 1 excess), and toluene (80 mL, reagent grade). The mixture is heated to reflux until the water is collected ( 3 h). The flask is cooled, and formamide is collected by hltration, and rinsed with copious amounts of ethanol and diethylether until formic acid is washed away. Color and percent yield of formamide ( 70%) is dependent on the purity of the amine. The reaction can be scaled up, depending on collector size. 

The benzylideneanilines of Table IX are prepared by refluxing a mixture of 0.010 mole each of the appropriate para-substituted benzaldehyde and aniline in 150 ml of benzene containing 0.1 gm of benzenesulfonic acid for 2-4 hr. A Dean-Stark trap is used to collect the water and then the solvent is removed under reduced pressure. The residue is recrystallized from hexane or other... 

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