Benzene azeotropes

For the process step involving handling of spent sulfuric acid, several patents have been issued in which improvements in this step were a main claim. The azeotropic nitration of benzene essentially eliminates the need to reconcentrate sulfuric acid (10,11). The nitration step is carried out at higher than usual temperatures (120—160°C). Because excess benzene is used, the higher temperature allows water to be removed as a water—benzene azeotrope. The water is separated and the benzene phase, containing approximately 8% nitrobenzene, is recycled back into the reactor. The dry sulfuric acid is then reused continuously. 

Draper and Pollard [Science 109 448 1949] added 12% water, 0.1% aluminium (can also use zinc), and 0.05% NaHC03 to phenol, and distd at atmospheric pressure until the azeotrope was removed. The phenol was then distd at 25mm. Phenol has also been dried by distn from the benzene soln to remove the water- benzene azeotrope and the excess benzene, followed by distn of the phenol at reduced pressure under nitrogen. Processes such as this are probably adequate for analytical grade phenol which has as its main impurity water. Phenol has also been crystd from pet ether/ benzene or pet ether (b 40-60°). Purified material is stored in a vacuum desiccator over P2O5 or CaS04. 

Ph2CHOH, cat. TsOH, benzene, azeotropic removal of water, 78-83% yield. ... 

D A solid insoluble in ethanol/ benzene azeotrope 25 Predominantly diaromatic and polynuclear perhaps combined through naphthenic bridges, with negligible aliphatic content. 

The product dries slowly, and several days in air or 24 hours in a vacuum desiccator is usually required. Considerable coloration will result if this is done in direct light. Drying in a heated oven or removing the water as a benzene azeotrope is not satisfactory because of some decarboxylation to skatole. The produc should be stored in a dark bottle away from direct sunlight. 

One of the checkers added both the dibromoethane and subsequently the ether solution of bis(trifluoro-methyl)bromobenzene via syringe through a rubber septum stopper in place of the addition funnel. Filtration of the benzene solution removes unreacted starting material and other soluble impurities. +The tan solid obtained after drying by the benzene azeotrope procedure is much less soluble in CH2CI2 than the oily solid present before. 

Azeotrope formers, generally polar compounds, have the ability to form, with hydrocarbons, nonideal mixtures having vapor pressures higher than either component in the mixture and therefore lower boiling points. Fortunately, different types of hydrocarbons show different degrees of nonideality with a given azeotrope former. For example, benzene and cyclohexane boil at about 176° F., while the methanol-cyclohexane azeotrope boils at 130° F., and the methanol-benzene azeotrope boils at 137° F., a difference of 7° F. Hence, fractionation of a mixture of benzene and cyclohexane in the presence of methanol effectively separates the two hydrocarbons. 

Another use for this set of curves is for estimating the azeotropic boiling point and composition at pressures other than atmospheric. Consider the azeotrope methanol-benzene. Since the vapor pressure curves of methanol and benzene are known, the difference in boiling point, A, can be obtained at any pressure. From this value of A and the C-A curve for methanol-hydrocarbons the azeotropic concentration C at that pressure can be determined. For example, the effect of pressure on the methanol-benzene azeotrope is shown in Table I. 

Commercial grades of DMF may be purified initially by azeotropic distillation with benzene (CAUTION). Distil a mixture of 1 litre of DMF and 100 ml of benzene at atmospheric pressure and collect the water benzene azeotrope which distils between 70 and 75 °C. Shake the residual solvent with powdered barium oxide or with activated alumina (Grade I), filter and distil under nitrogen at reduced pressure collect the fraction having b.p. 76°C/39mmHg or 40°C/10mmHg. The distillate is best stored over a Type 4A molecular sieve. 

A convenient purification procedure for an arylboronic acid is to convert it into the trimeric anhydride (4) by removal of water as a benzene azeotrope (see Expt 6.101, Note (3)). 

Tellurium Tetrabutoxide1 10 g (135 mmol) of butanol are added to 2.71 g (7.4 mmol) of tellurium tetraisopropoxide and the mixture is diluted with benzene. After the exothermic reaction has subsided, the mixture is heated under reflux for 2 h and then the isopropanol/benzene azeotrope is distilled from the mixture at 12°. Excess butanol and benzene arc distilled off, the residue is dried under reduced pressure at 20°, and the resultant colorless liquid is distilled yield 2.9 g (92%) b.p. 150°/ 0.8 torr. 

Diisopropoxy-4,5-dihydro-l,3,2-dioxatellurole2 To a flask fitted with a reflux condenser and protected from moisture is added a solution of 2.0 g (5.5 mmol) of tellurium tetraisopropoxide in anhydrous benzene, 0.34 g (5.5 mmol) of glycol are added, and the mixture is heated under reflux for 1 h. The isopropanol/benzene azeotrope is slowly distilled at 72°, excess benzene is distilled, and the residue is dried under reduced pressure. The remaining white solid product is insoluble in benzene and cannot be sublimed without decomposition to 1,4,6,9-tetraoxa-5-telluraspiro[4.4]nonane yield 1.63 g (82%). 

Lanthanides form complexes with Schiff bases or imines quite readily. The important ligands are obtained by the condensation of an amine with salicylaldehyde derivative or a /6-diketone. Schiff base complexes have been prepared by the reaction of ligand with a lanthanide 2-propanolate. The solvent medium is benzene and the liberated propanol during the complexation reaction is removed by distillation as alcohol-benzene azeotrope [57,58]. 

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