Azeotropic dehydration

In typical processes, the gaseous effluent from the second-stage oxidation is cooled and fed to an absorber to isolate the MAA as a 20—40% aqueous solution. The MAA may then be concentrated by extraction into a suitable organic solvent such as butyl acetate, toluene, or dibutyl ketone. Azeotropic dehydration and solvent recovery, followed by fractional distillation, is used to obtain the pure product. Water, solvent, and low boiling by-products are removed in a first-stage column. The column bottoms are then fed to a second column where MAA is taken overhead. Esterification to MMA or other esters is readily achieved using acid catalysis. 

The trialkyltin alkoxides can often be prepared more conveniently by azeotropic dehydration of the appropriate bis(trialkyltin) oxide and alcohols, or by heating together the bis(trialkyltin) oxide and dialkyl carbonate (192). The latter reaction involves formation, and then decarboxylation, of the alkyl trialkyltin carbonate, e.g.,... 

Volkov (1994) has given a state-of-the-art review on pervaporation. A number of industrial plants exist for dehydration of ethanol-water and (.vwpropanol-water azeotropes, dehydration of ethyl acetate, etc. There is considerable potential in removing dissolved water from benzene by pervaporation. The recovery of dis.solved organics like CH2CI2, CHCI3, CCI4, etc. from aqueous waste streams also lends itself for pervaporation and pilot plants already exist. 

It is explosive, and distillation, even under reduced pressure as described, may be dangerous [1], A Hungarian patent describes a safe procedure for in-situ generation of the ester, azeotropic dehydration and subsequent metal-catalysed reaction with 1,3-dienes to give alkyl cyclopropanecarboxylates [2],... 

The acidity of terminal alkynes makes available routes to alkynylstannanes that do not apply to alkenylstannanes. Thus, alkynylstannanes can be made by the acidolysis of aminostannanes with alkynes, and the iV-stannylpyr-roles are recommended for this purpose as they can be readily prepared by azeotropic dehydration of the trialkyltin oxide and pyrrole, and the amine that is liberated is non-basic.242... 

Norman, W. S. Trans. Inst. Chem. Eng. 23 (1945) 66. The dehydration of ethanol by azeotropic distillation. Ibid. 89. Design calculations for azeotropic dehydration columns. 

PRATT, H. R. C. Trans. Inst. Chem. Eng. 25 (1947) 43. Continuous purification and azeotropic dehydration of acetonitrile produced by the catalytic acetic acid-ammonia reaction. 

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. 

For the azeotropic dehydration of aqueous ethanol mixtures approaching the constant boiling mixture, a brief comparison is shown for the entrainers, n-pentane, benzene, and diethyl ether. Since water is most non-ideal in n-pentane, the driest ethanol is expected to be produced if n-pentane is used. 

The first step in testing the material for suitability of the demulsify-ing, dehydrating process is to dilute the crude oil with a solvent which is used by itself or mixed with another in azeotropic dehydration of the emulsion. The minimum amount of solvent which is sufficient for the first step is that which cuts the viscosity of the crude enough to allow azeotropic distillation without excessive foaming. This may require about 40-60 volumes solvent per 100 volumes of crude, but this ratio of solvent, however, may not be sufficient to reduce the gravity of the crude below that of water to allow preliminary decantation of some of the water. 

Low boiling substances are removed from the chilled reactor product by distilling up to a cut point of 80 °C. These low boilers are gaseous dimethyl ether, methyl acetate, acetaldehyde, butyraldehyde, and ethyl acetate. The bottoms are flash-distilled to recover the rhodium catalyst. Flash distilled acid is azeotropically dehydrated. In the final distillation, glacial acid is obtained. Traces of iodine that may remain in the finished acid may be removed by fractional crystallization or by addition of a trace of methanol followed by distillation of the methyl iodide that forms. Somewhere in the carbonylation reaction, a minute amount of propionic acid seems to be made. It typically is found in the residues of the acetic acid finishing system and can be removed by purging the finishing column bottoms. 

It is possible to dispense with the extraction step if the oxidation section is operated at high propylene concentrations and low steam levels to give a concentrated absorber effluent. In dais case, the solvent recovery column operates at total organic reflux to effect azeotropic dehydration of the concentrated aqueous acrylic acid. Tliis results in a reduction of aqueous waste at the cost of somewhat higher eneigy usage. 

The bottoms from the solvent recovery (or azeotropic dehydration column) are fed to the foreruns column where acetic acid, some acrylic acid, and final traces of water are removed overhead The overhead mixture is sent to an acetic acid purification column where a technical grade of acetic acid suitable for ester manufacture is recovered as a by-product. The bottoms from the acetic acid recovery column are recycled to the reflux to the foreruns column. 

Simple organotin alkoxides or phenoxides are available from the halides on reaction with MOR or MOAr, as well as from the oxides and the alcohol or phenol on azeotropic dehydration. These compounds are generally sensitive to H2O and to CO2. Cyclic alkoxides, e.g. (51) and (52), and cyclic diaUcoxides from diols, e.g. (53), can also be prepared. These complexes are usually oligomeric. 

The compound is only slightly soluble in water, but dissolves in methanol and ethanol, from which it can be recrystallized. A saturated chloroform solution at 25° is ca. 0.02 M. It is only very slightly soluble in cold carbon tetrachloride and benzene. In hot chloroform, carbon tetrachloride, and benzene, it is azeotropically dehydrated, giving solutions of anhydrous bis(2,4-pentanedionato)cobalt(II) vide infra). 

Stannametalloxanes containing the unit SnOM, where M is a metal or an organometallic group, can generally be prepared by the reaction of MOLi or MONa with a tin halide, or by the azeotropic dehydration of MOH and a tin oxide or hydroxide,141 or by the cohydrolysis of MCI and an organotin halide. 

Simple stannasiloxanes such as Me3SiOSnPh3 or (Ph3SiO)2SnMe2 can be prepared by azeotropic dehydration of the appropriate silanol and distannoxane141 and disiloxydi-stannoxanes such as Me3SiOMe2SnOSnMe2OSiMe3 by the cohydrolysis of the appropriate chlorosilane and dichlorostannane.149... 

The first group of reactions (13-1-13-3) can be carried out by mixing aliquots of the tin oxide or hydroxide and acid in a solvent such as methanol (e.g. equation 13-7).3 The water can often be conveniently removed by azeotropic dehydration in benzene or toluene, but with aryltin compounds it may be better to use molecular sieves, to avoid the risk of cleaving the aryl-tin bonds.4... 

The butyltin oxycarboxylates, BuSn(0)0C0R, which are formed by azeotropic dehydration of a 1 1 mixture of butanestannonic acid and the acids R C02H (R = Pr1 or Bu1), have been shown to be hexamers with a drum-shaped structure, as described in Section 12.3.9... 

Organotin esters of the oxy- and thio-acids of phosphorus can be prepared inter alia by azeotropic dehydration of a mixture of the organotin hydroxide or oxide and the acid, or by treating a tin alkoxide or tin amide with the acids, or an organotin halide with a salt of the phosphorus acid. By using different molecular ratios of the reactants, products of different compositions can be obtained. Attempts to prepare phosphites may result in an Arbuzov rearrangement to a phosphorus(V) compound (e.g. equation 13-11).47... 

The sodium halide which is formed in these reactions is very finely divided, and may be difficult to filter off.2 A more convenient way of preparing the triorganotin alkoxides and phenoxides is by the azeotropic dehydration of a mixture of the bis(trialkyltin) oxide and alcohol or phenol in a solvent such as benzene or toluene.4... 

Less work has been carried out on the cyclic monoalkyltin glycollates. Azeotropic dehydration of a mixture of butylstannonic acid and ethane-1,2-diol gives products which are believed to have the structures 14-15, and 14-16 or 14-17."... 

Borane is an effective reducing agent for organotin alkoxides and amides,11 and this has been exploited in the preparation of diorganotin dihydrides from the dioxastan-nolanes which can readily be obtained by azeotropic dehydration of a mixture of diorganotin oxide and 1,2-diol (e.g. equation 15-9).12... 

Whereas alkoxystannanes can be prepared by azeotropic dehydration of a mixture of bis(tributyltin) oxide and an alcohol (pKa ca. 16), aminotin compounds cannot normally be prepared from the oxide and an amine (pKa ca. 35). The important exception to this rule is pyrrole which is a stronger acid (pKa 15), and iV-tributylstannylpyrrole can readily be prepared by the azeotropic dehydration of bis(tributyltin) oxide and pyrrole, or by heating together tributyltin methoxide and pyrrole.3... 

Sulfonamides, like carboxamides, can be (V-stannylated by azeotropic dehydration in the presence of bis(tributyltin) oxide in a solvent such as benzene or toluene, and the products can usually be purified by distillation.58... 

The tri-n-butyltin phenoxides can be easily prepared by azeotropic dehydration of a mixture of phenol and bis(tri-n-butyltin) oxide (TBTO) in toluene. In experiments reported by Kinart the tin phenoxides and DEAD were added to a 4 M solution of LiC104 in diethyl ether at 23 °C. For measuring the half-lives of the reactions, the concentrations of the reagents were 0.0254 M and the absorbance of DEAD at 410 nm was monitored. On a preparative scale, the reaction was followed by TEC or NMR and the products were isolated by chromatography, which also served to remove the n-BusSn group. Table 6.3.7... 

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