Dean-Stark head

When a mixture of toluene and water boils, the vapour produced is a constant ratio mixture of toluene vapour and water vapour known as an azeotrope. If this mixture is condensed, the liquid toluene and water, being immiscible, separate out into two layers with the water below. By using a Dean Stark apparatus, or Dean Stark head, the toluene layer can be returned to the reaction mixture while the water is removed. Reactions requiring removal of water by distillation are therefore often carried out in refluxing toluene or benzene under a Dean Stark head. 

Synthesis of polymer-supported Pd catalyst [44] For the synthesis of polymer 41, see refs. [46-48]. All solvents vs ere degassed by ultrasonication and argon purging prior to use. To a -well-stirred solution of 44 (0.36 mmol in phosphine) in THF (72 mb) was added a solution of 45 (0.12 mmol) in H2O (30 mb) and the mixture was again degassed. After the mixture had been stirred for 62 h at room temperature, a yellow precipitate formed. Water (30 mb) was added to the suspension, and THF was removed at 80 °C by distillation for 4 h in an apparatus fitted with a Dean-Stark head to leave a reddish precipitate. This precipitate was stirred at 100 °C, first in H2O (100 mb) for 12 h, then in THF (100 mb) for 3 h, and finally in further H2O (100 mb) for 12 h to wash away the unreacted palladium species and polymers. After drying in vacuo (ca. 0.1 mmHg), 41 was obtained as a dark-red solid in almost quantitative yield. 

A solution of 500 g of (-)-camphorquinone in 2.4 L of benzene is heated under reflux with 22 g of 4-methylbenzenesulfonic acid and 375 g of 1,2-ethanediol, using a Dean - Stark head, for 17 h, after which time 98 mL has collected in the aqueous phase. (On occasions, up to 48 h is required for this quantity to collect.) The solution is washed with dil NaOH and HzO, dried over Na2S04, and evaporated. The residue gives the ketal (317 g) as prisms, mp 88 C (EtOH). A second crop is obtained by dilution of the mother liquors with H20 total yield 337.5 g (53%) [a],2,5 +74 (r = 1, EtOH). (lR,4S)-2-exo-Hydroxy-3-bomanone (e.vo-31)31 ... 

A suspension of 2 - [1 - (2 - amino - 5 - chlorophenyl) -1 - phenylmethylamino] acetic acid in xylene refluxed with stirring under a Dean-Stark head until after 6 hrs. no more water separates 7-chloro-l,3,4,5-tetrahydro-5-phenyl-2H-l,4-benzo-diazepin-2-one (startg. m. f. 372). Y 81%. R. I. Fryer et al., J. Org. Ghem. 30, 1308 (1965) S,N-heterocyclics s. M. Uskokovi6 et al., J. Org. Ghem. 30, 3111. 

Azeotropic water entrainment. A mixture of ethyl acetonylcyanoacetate, ethylene glycol, benzenesulfonic acid, and benzene refluxed ca. 4 hrs. under a Dean-Stark head until water evolution ceases ethyl a-cyano-a-(2-methyl-1,3-di-oxolan-2-ylmethyl) acetate. Y 87%. J. Davoll, Soc. 1960, 131. 

A mixture of 63.1 g. (0.5 mole) of 2-methyl-l,3-cydohexane-dione (Note 1), 52.6 g. (0.75 mole) of methyl vinyl ketone (Note 2), about 0.25 g. (3 pellets) of potassium hydroxide, and 250 ml. of absolute methanol is placed in a 500-ml. round-bottomed flask fitted with a reflux condenser and a drying tube (Note 3). The mixture is heated under reflux for 3 hours, and the dione gradually goes into solution. At the end of this period, methanol and the excess methyl vinyl ketone are removed by distillation under reduced pressure (Notes 4 and 5). The residual liquid is dissolved in 250 ml. of benzene, a Dean-Stark phase-separating head is attached, and 20 ml. of solvent is removed by distillation at atmospheric pressure to remove traces of water and methanol. The solution is cooled well below the boiling point, 3 ml. of... 

A 250-niL round-bottomed flask equipped with a Dean-Stark trap and reflux condenser was charged with the ketone (5.2 g, 33.3 mmol) and pyrrolidine (2.4 mL, 33.3 mmol) in anhydrous benzene (200 mL). The solution was refluxed for 8 h until no more HiO was collected in the Dean-Stark trap. The Dean-Stark trap was removed and replaced with a distillation head, and the benzene was removed by distillation. The product was distilled (0.2 torr, 105 °C) to give the enamine (4.78 g, 69%) as a yellow viscous oil, which was used immediately to avoid decomposition. 

A mixture of 2-methyl-l,3-cyclohexanedione, methyl vinyl ketone, a few KOH-pellets, and abs. methanol refluxed 3 hrs., methanol and excess methyl vinyl ketone removed by distillation, the residual 2-niethyl-2-(3 -oxobutyl)-1,3-cyclo-hexanedione (Y 85% when isolated) dissolved in benzene, a Dean-Stark phase-separating head attached, traces of water and methanol removed by azeotropic distillation, cooled well below the boiling point, pyrrolidine added, refluxed until separation of water ceases after ca. 30 min., and refluxing continued for 15 min. l,6-dioxo-8a-methyl-l,2,3,4,6,7,8,8a-octahydronaphthalene. Y 63-65% based on dione. S. Ramachandran and M. S. Newman, Org. Synth. 4 1, 38 (1961) ring closure with an increased amount of pyrrolidine s. W. L. Meyer and A. S. Levinson, J. Org. Ghem. 28, 2184 (1963) Michael addition with NaOH instead of KOH s. T. A. Spences, K. K. Schmiegel, and K. L. Williamson, Am. Soc. 85, 3785 (1963). 

Place a mixture of 53 g. of A.R. lactic acid (85-88 per cent, acid), 75 g. (85-5 ml.) of commercial anhydrous isopropyl alcohol, 300 ml. of benzene and 20 g. of Zeo-Karb 225/H (1) in a 700 ml. bolt-head flask, equipped with an automatic water separator (e.g., a large modified Dean and Stark apparatus with a stopcock at the lower end, see Fig. Ill, 126, 1) carrying an efficient reflux condenser at its upper end, and a mercury-sealed stirrer (alternatively, the hquid-sealed stirrer shown in Fig. 11,7,11, c. may be used). Reflux the mixture, with stirring, on a steam bath for 5 hours or until water no longer collects in appreciable amount in the water separator run off the water from time to time. Filter off the resin at the pump and wash it with two 25 ml. portions of benzene. Shake the combined filtrate and washings with about 5 g. of precipit-ated calcium... 

Figure 8.2 Different apparatus used for steu distillation. A aodified Gaman steam distillation apparatus A, steam generation flask B, sample chamber C, splash head D, condenser B, delivery tube F, separatory funnel. B = micro steam distillation apparatus A, boiling flask B, collection bulb C, water return arm D, Condenser. C - steam distillation apparatus using a Dean and Stark type trap. D = Nielsen-Kryger steam distillation apparatus.

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