Dean Stark apparatus

Of the alkyl esters, methyl esters are the most useful because of their rapid hydrolysis. The acid is refluxed with one or two equivalents of methanol in excess alcohol-free chloroform (or dichloromethane) containing about O.lg of p-toluenesulfonic acid (as catalyst), using a Dean-Stark apparatus. (The water formed by the... 

Aldehyde 22 and aminoacetaldehyde dimethyl acetal 23 (3eq.) were heated to reflux in toluene (Dean-Stark apparatus) until all of the starting material was consumed. The crystalline product was collected and washed with solvent to yield imine 24, which was used without further purification. 

By heating 2-benzyloxycyclohexanone 208 and (R)-l-phenylethylamine in refluxing toluene for 4 days in a Dean-Stark apparatus, the imine 209 was formed, then a rearrangement occurred to give first the a-aminocyclohexanone derivative 210 and finally the Q, o -disubstituted imine 211 with moderate diastereoselectivity. Reduction of this imine with sodium borohydride gave a mixture of two trans diamines (S,S)-212 and (R,R)-212, which were separated by chromatography. The enantiomers of 1-benzyl-1,2-diaminocyclohexanes 213 were then obtained by hydrogenolysis [99] (Scheme 31). 

Instead of using the Dean-Stark apparatus, the reaction can be carried out at reflux using MeNH3Cl/AcOK/MeOH with HC(OMe)3 as a water scavenger. A wide variety of nitroalkenes can be prepared in good yields by this method (Eq. 3.35).59... 

Application of ultrasound62 or microwave irradiation63 greatly assists these condensation reactions as shown in Eqs. 3.37 and 3.38, respectively, rendering the use of a Dean-Stark apparatus unnecessary. 

The preparation of imines, enamines, nitroalkenes and N-sulfonylimines proceeds via the azeotropic removal of water from the intermediate in reactions that are normally catalyzed by p-toluenesulfonic acid, titanium(IV) chloride, or montmorillonite K 10 clay. A Dean-Stark apparatus is traditionally used which requires a large excess of aromatic hydrocarbons such as benzene or toluene for azeotropic water elimination. 

R,5)-lbuprofen acid (20 g, 96.9 mmol), p-toluenesulfonic acid (0.44 g, 2.27 mmol) and 2-ethoxyethanol (21.9 mL, 224 mmol) were dissolved in the organic solvent, isooctane (180 mL). The boiling chips were added into the reaction flask as anti-bumping agent. Then the reaction mixtures were refluxed for 8—9 h using a Dean-Stark apparatus. 

Use of Heptane Azeotrope in a Dean-Stark Apparatus (Z. Liu and A. Taylor, Unpublished Results)... 

The reaction from an enamine is initiated by the addition of a trace of a strong acid, e.g. /7-toluenesulfonic acid (TsOH, 4-methylbenzene-sulfonic acid), to the ketone and pyrrolidine in a solvent such as toluene. When the mixture is at reflux in a Dean-Stark apparatus, water is liberated and is removed through azeotropic distillation, leaving the enamine in the reaction vessel. After a follow-up reaction between the enamine and a suitable electrophile, an iminium salt is produced that liberates both the a-substituted ketone and pyrrolidine when it is treated with aqueous acid (Scheme 6.20). 

On a commercial scale, furan is obtained from 2-formylfuran (furfural, furan-2-carbaldehyde) (see Section 6.2.7) by gas-phase decarbonylation, but in the laboratory, furans can be formed by the cyclodehydration of 1,4-dicarbonyl compounds. Heating in boiling benzene with a trace of /7-toluenesulfonic acid as a catalyst in a Dean-Stark apparatus is often effective (Scheme 6.30a). 

Sodium 4-hydroxybenzenesulfonate dihydrate (2.37 g, 0.01 mol) was dehydrated by distillation with benzene using Dean-Stark apparatus and then dissolved in 20 mL of acetone in a lOOmL round-bottomed flask with a reflux condenser. Ethyl bromoacetate (2.04 g, 0.012 mol), potassium carbonate (2.79 g, 0.02 mol) and dibenzo-18-crown-6 (74 mg, 0.2 mmol) were added, and the mixture was heated at reflux for 48 h. After cooling to room temperature, the crystals were collected on a Buchner funnel, washed with acetone (2 x 60 mL), and dried under reduced pressure to yield 2 as a white powder (2.68 g, 95 %). m.p. > 300 °C. 

The step 1 product (0.004 mol) and potassium r-butoxide (0.008 mol) were heated to 110°C in a solvent mixture of 25 ml DMAc and 10 ml hexane overnight in a flask containing a Dean-Stark apparatus. After hexane was removed, the mixture was cooled to ambient temperature and treated with trans-l,4-dibromo-2-butene (0.004 mol) and then stirred at ambient temperature for 48 hours. The mixture was then poured into 800 ml of water and a white solid isolated that was air dried and the product isolated in 91% yield. 

Macrolides. Steliou, Hanessian, and co-workers- have prepared lactones and lactams in moderate to excellent yield by treatment of ro-hydroxy or ru-amino carboxylic acids with catalytic amounts of di-r -butyltin oxide in refluxing mesitylcne or xylene in a Dean-Stark apparatus for 12 24 hours. The method has the advantage of high dilution, since the tin reagent is regenerated continuously. As expected, yields arc low for medium-sized rings. 

A soln of acylamidrazone 62 (0.113 g, 0.28 mmol) in xylenes (mixture of isomers) was heated in an oil bath at 190 °C for 5h using a Dean-Stark apparatus. The soln was concentrated and the residue chromatographed (silica gel, EtOAc/pentane 3 2) to afford 63 yield 24 mg (22%). 

SYNTHESIS In 50 mL of benzene there was dissolved 31.6 g 2,5-dimethoxy-4-methylbenzaldehyde (see recipe for 2C-D for its preparation), 20.2 mL 1-nitropropane, and 6 mL cyclohexylamine. This solution was held at reflux in a Dean Stark apparatus for 24 h, effectively removing the water of reaction. Upon cooling, there was deposited 19.6 g of 1 -(2,5-dimethoxy-4-methylphenyl)-2-nitro-1 -butene as brilliant orange crystals. The mp, after recrystallization from MeOH, was 114-115 °C and a second recrystallization increased the mp another 2 °C. Anal. 

A. 2-( Bromomethyl)- .-( ehloromethyD-1, -dioxane. A 100-mL, round-bottomed flask is equipped with a 10-mL Dean-Stark apparatus and a condenser. The flask is charged with 30.0 g (0.138 mol) of l-bromo-3-chloro-2,2-dimethoxypropane (Note 1), 10.0 mL (0.138 mol) of 1,3-propanediol (Note 2), and 3 drops of concentrated sulfuric acid. The resulting solution is heated (bath temperature 140°C) for 8 hr (Note 3) with distillative removal of methanol (ca. 11 mL). The mixture is allowed to cool to room temperature and the crude product is partitioned in 150 mL of pentane and 40 mL of water. The... 

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). 

It may also help to distil out the water that is formed in the reaction diethyl adipate (the diethyl ester of hexanedioic add) can be made in toluene solution using a sixfold excess of ethanol, concentrated H2SO4 as catalyst, distilling out the water using a Dean Stark apparatus. You can tell from the yield that the equilibrium is very favourable. 

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. 

A solution of the Step 3 product (0.071 mol) in a mixture of 93 ml pyridine, 30 ml acetic acid, and 560 ml toluene was refluxed with a Dean-Stark apparatus for 5 hours, then concentrated. The residue was purified by chromatography using hexane/EtOAc, 1 1, and the product isolated in 78% after recrystallization in acetonitrile as a white solid, mp = 209-210°C. 

A mixture of the Step 1 product (17.9g) and 1,3-dichloroacetone (14.8 g) dissolved in 83 ml toluene was refluxed 9 hours using the Dean-Stark apparatus. After cooling, the mixture was diluted with water, then extracted with EtOAc, washed with brine, dried, and concentrated. The residue was purified by chromatography using silica gel with hexane/EtOAc, 6 1-5 1, and 15.1 g product isolated as colorless needle crystals. 

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