Dean-Stark apparatus, — trap

A solution of 5.0 g of l-methyl-3-pyrrolidinol and 12.5 g of methyl phenyl-2-thienylglycolate in 200 ml of n-heptane is heated to reflux temperature, a trace of sodium methylate is added, and refluxing of the mixture is continued for 3 h. A Dean-Stark trap is incorporated in the reflux apparatus to separate and withdraw the methanol produced by the reaction. At the end of the reflux period, the reaction mixture is cooled and extracted two times with 100 ml portions of 2 N hydrochloric acid. The acid extracts are combined, basified with potassium carbonate, and extracted three times with 50 ml portions of benzene. The benzene extracts are combined, washed two times with 25 ml portions of water, and dried. The benzene is removed from the dried extract by evaporation at reduced pressure. The residue is l-methyl-3-pyrrolidylphenyl-2-thienylglycolate in the form of a clear liquid. 

Secondary amines react with ketones that contain an H atom in the a-position through an addition and subsequent El elimination to form enamines (Figure 9.29). In order for enamines to be formed at all in the way indicated, one must add an acid catalyst. In order for them to be formed completely, the released water must be removed (e.g. azeotropically). The method of choice for preparing enamines is therefore to heat a solution of the carbonyl compound, the amine, and a catalytic amount of toluenesulfonic acid in cyclohexane to reflux in an apparatus connected to a Dean-Stark trap. Did someone say Le Chateher ... 

A Dean-Stark trap is an apparatus used for removing water from a reaction mixture. To... 

Preparation of the reagent [70] A solution of PEG monomethyl ether 89 (MW = 750 5.88 g, 7.8 mmol) in benzene (20 mL) was dried azeotropically for 24 h in an apparatus fitted with a Dean-Stark trap and subsequently added dropwise to a solution of chlorosulfonyl isocyanate (88) (1.10 g, 7.8 mmol) in dry benzene (20 mL). The mixture was stirred at room temperature for 1 h, then concentrated to dryness. A solution of this residue in benzene (35 mL) was added dropwise to a solution of triethylamine (2.5 mL, 17.3 mmol) in benzene (15 mL). The mixture was stirred for 30 min at room temperature, then filtered, and the solid was dried to yield polymer-supported Burgess reagent 91 (6.2 g, 82%). 

A reaction apparatus with a Dean-Stark trap. The water is denser than the ester-benzene mixture, and collects in the side arm of the trap. 

After all the components have been thoroughly dried in an oven, the apparatus is assembled as shown. Dried xylene is added to the Morton flask and heated to reflux any traces of residual moisture are removed by distilling over several milliliters and removing any azeotrope that forms in the Dean-Stark trap. Anhydrous rerr-butyl alcohol is added to the flask, followed by potassium metal. The solution is stirred, and after all the potassium has reacted and the solution is boiling vigorously, slow addition of diethyl tetradecan-l,14-dicarboxylate from the Hershberg funnel is started. The solvent vapors, which condense and fall into the dilution chamber, dilute the diester and carry it into the Morton flask where the reaction occurs. An ethanol-xylene mixture is removed via the Dean-Stark trap at approximately the same rate as the solution is added from the dropping funnel. A slow continuous addition of the ester maximizes the probability of cyclization a typical reaction time is 24 hr. 

Fig. 1-14 High dilution apparatus (a) Morton flask (b) Dean-Stark trap ...

Pimelic acid (25) (10.0 g, 62.6 mmol) and allyl alcohol (12.8 mL, 187.8 mmol) were dissolved in toluene (30 mL) in a 100 mL round bottom flask equipped with a stirbar. p-Toluene sulfonic acid monohydrate (59 mg, 0.31 mmol) was added and a Dean-Stark apparatus was attached. The reaction mixture was heated to reflux until no further H2O was collected in the Dean-Stark trap (16 h). The reaction mixture was allowed to cool to room temperature and transferred to a separatory funnel where it was washed with saturated NaHCOs solution (3x5 mL), brine (20 mL) and dried over anhydrous Na2S04. The solvent was removed in vacuo to yield the product as a pale yellow oil (14.32 g, 95 %) without further purification. 

The dehydration of 34 to 29 is a reversible process that is driven to completion by removing the water from the reaction mixture. This is conveniently done by using toluene as the solvent for the reaction. Water and toluene form an azeotrope (Sec. 4.4), so azeotropic distillation allows the continuous separation of water as dehydration occurs. To minimize the amount of solvent that is required for distillations of this type, a Dean-Stark trap (Fig. 18.15) is commonly used. Because such traps are often not available in the undergraduate laboratory, an operational equivalent may be devised by assembling the apparatus in a way such that water, but not toluene, can be prevented from returning to the reaction flask (Fig. 18.16). 

This preparation is divided into three steps (1) the reaction of phosphorus (V) chloride with ammonium chloride in an inert solvent, (2) the rapid distillation from the solvent and from the nondistillable, rubber-forming higher polymers, and (3) the fractionation of the trimeric and tetra-meric compounds. The reaction apparatus consists of a 5-1. three-necked flask with standard-taper joints fitted with a thermometer and a motor-driven, heavy-duty stirrer, and heated by an electric mantle. For the preliminary removal of water from the solvent a Dean and Stark trap is used at a side joint in conjunction with a long water-jacketed condenser, the latter having a calcium chloride drying tube at its upper end. 

The microreador yield (up to 42%) is comparable to that of batch Stork enamine reactions using p-toluene sulfonic add in methanol under Dean and Stark conditions, that is, under water separation in a water trap (Dean-Stark apparatus). 

Figure 3. Modified Dean-Stark apparatus. The solvent (usually toluene) drips through the sample, dissolving the organic component and leaving the solids behind. The water, which codistills with the solvent, condenses and is trapped in the side arm and measured volumetrically. The solids and organic phases are determined gravimetrically after evaporating the solvent from the sample thimble and the solvent flask.

A mixture of 14.92 g /7-A,A -dimethylaminobenzaldehyde (0.1 mol), 4.45 g ethanol-amine, and 50 mL dry benzene in a Dean-Stark moisture determination apparatus was refluxed in an oil bath until the volume of water collected in the trap remained constant (2-3 h). The benzene was removed by distillation under reduced pressure, and the residual oil was poured onto an ice-water mixture. The solid crystalline mass was triturated with cold water, collected on a suction filter, and washed on the filter with several portions of cold water. After drying the crystals on the filter by use of a rubber dam followed by air drying, the crude material was dissolved in boiling petroleum ether (b.p. 30-60°C), treated with Norite A for 15 min, and filtered. The filtrate was cooled in an ice-water bath to induce crystallization. The crystals were collected on a suction filter and washed with several small portions of cold petroleum ether, in a yield of 57%, m.p. 103-104°C. 

Dean-Stark apparatus, -separator, - trap (s. a. Water entrainment, azeotropic)... 

Water Determination. The sample is refluxed with toluene and the resultant toluene—water a2eotrope is distilled iato a gradual water-trap receiver (Dean and Stark apparatus). Here the water and toluene separate iato two distinct layers, permitting the volume of water to be read and its percentage calculated. 

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.

Figure 5.1 Dean and Stark distillation apparatus with trap for use with heavy entraining...

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