Column distillation Lewis method

A fractionating column is required to distill a liquid containing 25 per cent benzene and 75 per cent toluene by mass, to give a product of 90 per cent benzene. A reflux ratio of 3.5 is to be used, and the feed will enter at its boiling point. If the plates used are 100 per cent efficient, calculate by the Lewis-Sorel method the composition of liquid on the third plate, and estimate the number of plates required using the McCabe-Thiele method. 

While the Lewis acid-catalyzed reactions of imines with silyl enolates are one of the most efficient methods for the preparation of b-amino esters, many imines are hygroscopic, unstable at high temperatures, and difficult to purify by distillation or column chromatography. It is desirable from a synthetic point of view that imines, generated in situ from aldehydes and amines, immediately react with silyl enolates and provide b-amino esters in a one-pot reaction. However, most Lewis acids cannot be used in this reaction because they decompose or deactivate in the presence of the amines and water that exist during imine formation. Due to the unique properties of Ln(OTf)3, their use as catalysts for the above one-pot preparation of b-amino esters from aldehydes was planned. 

Although this method has not been described herein for solving problems in which a finite number of plates are used, it may be used for conventional distillation columns in conjunction with the 0 method of convergence as described by Holland.4 However, when more than one feed plate is involved, the procedure is subject to problems of roundoff error which appear to be unsolvable with today s computer capabilities. In spite of this difficulty, the Lewis and Matheson method is ideally suited for aid in the visualization of the characteristics of a column with infinitely many plates. 

The general methods of design for multicomponent distillation apply. Since in most cases all the components of the feed streams are found in the bottoms, the method of Lewis and Matheson can be used, starting at the bottom and computing to the top. There will be an optimum solvent-circulation rate small solvent rates require many trays, but the column diameters are small large ratios require fewer trays but larger column diameters and greater solvent-circulation costs. 

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