Dean and Stark method

Moisture levels as low as 200 ppm can easily be measured by the Karl Fischer method and in the handling of used solvent one should never use or specify the Dean and Stark method which is used in the fuel industry. 

Moisture. Determine by the Dean and Stark method, given in Appendix V (p. 803). 

Boronic acids are easily dehydrated to boroxines, the Dean and Stark method (distil off the water with benzene) being quite satisfactory except for the volatile methyl and ethyl compounds. 

Another test method that can be used, determination of the moisture content of moderately dry coal, can, in fact, be used for all coal samples that can be handled without appreciable loss of moisture. The principle of the method is that the coal is heated with an inert liquid that does not mix with water and which has a boiling point greater than that of water so that, on distillation, the water is carried over with the vapor from the liquid and, on condensation, separates from it in a graduated receiver. The Dean and Stark apparatus (Figure 3.1) or one of its many modifications can be used for this purpose. 

Although this method proved successful for 4-keto-L-proline methyl ester 48, it was decided to investigate the conventional azeotropic dehydration method. Derivative 48 and pyrrolidine (1.2 equiv) were heated under reflux in benzene, collecting the water produced using a Dean and Stark apparatus. A quantitative yield of the corresponding enamine 52 was obtained after only 30 min (Scheme 19). Again, full assignment of NMR spectra was complicated by the apparent presence of rotameric structures. 

Representative samples of the pre-treated material were analysed for water content for each herb using a Dean and Stark equipment and also for content of "oily" material (essential oils + natural oils + waxes) using the method of Bligh and Dyer (10). Samples were also subjected to a sieving procedure and examined microscopically to determine the range of sizes and shapes present. Samples of the residue material were analysed for water content. 

Dean and Stark distillation method for determination of water content (WHO/M/8.R1)... 

Water is a contaminant in gasoline and should be measured with the Karl Fischer method (ASTM E-203, ASTM D-1364, ASTM D-1744, ASTM D-4377, ASTM D-4928, ASTM D-6304), by distillation using a Dean and Stark condenser (ASTM D-4006) (Fig. 5.3), or by centrifuging (ASTM D-96) and excluded by relevant drying methods. 

Kerosene, because of its higher density and viscosity, tends to retain fine particulate matter and water droplets in suspension for a much longer time than gasoline. Free water in kerosene can be detected by the use of a Dean and Stark adaptor (ASTM D-4006, IP 358) (Fig. 7.3), by the Karl Fischer titration method (ASTM D-1744, ASTM D-6304), by the distillation method (ASTM D-95, IP 74), or by a series of alternate tests (ASTM D-4176, ASTM D-4860). The standard water reaction test method (ASTM D-1094, IP 289) can also be used. 

Thiazolines 58 One mole each of an aldimine and 2-mercapto-3-pentanone are boiled in benzene (300 ml) under a Dean and Stark apparatus until no more water appears in the separator. Then the solvent is evaporated and the residue is distilled in a vacuum or recrystallized. The 4-thiazolines recorded in the Table below were prepared by this method. 

Specification for Dean and Stark apparatus Methods for determination of BS 756... 

The total loss on evaporation by the method given above for the liniment, less the water found by a Dean and Stark distillation (p. 803), is a measure of the methyl salicylate. 

Another method is to determine the moisture by distillation with toluene or xylene in a Dean and Stark apparatus (p. 803), adding 10 g of lump resin, stearic acid, or anhydrous barium chloride to prevent frothing. 

For most purposes the following method using the apparatus originally due to Dean and Stark, and later modified by Bidwell and Sterling, is satisfactory ... 

Mix 5.5 g 3,4,5-trimethoxybenzaldehyde (or analog), 2.5 g NH4 Acetate, 25 ml nitroethane (or equimolar amount nitromethane for the analog), 25 ml benzene and reflux about twenty hours water being removed with a Dean-Stark tube. Cool and wash with 2X25 ml water, 2X25 ml saturated NaHS03 and 2X25 ml water and dry and evaporate in vacuum the benzene to get (I). Reduce the nitropropene (or nitrostyrene) by any method such as follows To a stirred suspension of 3 g lithium aluminum hydride in 50 ml tetrahydrofuran, add 4.4 g (I) in 50 ml tetrahydrofuran and reflux one hour. Cool in ice bath and treat slowly with wet tetrahydrofuran... 

The weak nucleophilic nature of polynitroaliphatic alcohols means that reactions often need to be catalyzed by Brpnsted acids or Lewis acids. The following methods are commonly used for the esterification of polynitroaliphatic alcohols (1) heating a solution of the alcohol and acid in the presence of sulfuric acid with Dean-Stark removal of water ° (2) using the acid chloride or anhydride in the presence of aluminium chloride " (3) reacting the acid and alcohol... 

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). 

A 10 gram sample was placed in a 200 ml round bottom flask and 100 ml of distilled water added. A Dean-Stark trap and condenser were used and the mixture was brought to a boil. The steam distilled oil was measured after four hours versus control mixtures. In order to measure surface oil on the spray-dried powders, the powder was first washed with a solvent (ethyl ether or hexane) then oil retentions were run by the steam distillation method illustrated above. Differences in oil volume for solvent washed versus non-washed were attributed to surface oil on the spray-dried powders. 

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. 

---