Lower-boiling distillates

Isomerization of cyclohexane in the presence of aluminum trichloride catalyst with continuous removal of the lower boiling methylcyclopentane by distillation results in a 96% yield of the latter (54). The activity of AlCl -HCl catalyst has been determined at several temperatures. At 100°C, the molar ratio of methylcyclopentane to cyclohexane is 0.51 (55). 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

The reaction is driven to completion by distilling the lower boiling alcohol. Metal methoxides are frequentiy insoluble and caimot be employed as starting materials in this reaction by the same token, they can be convenientiy prepared from solutions of higher alkoxides by precipitation with methanol. Alcoholysis also gives mixed metal alkoxides ... 

Fiaal purification of propylene oxide is accompHshed by a series of conventional and extractive distillations. Impurities ia the cmde product iaclude water, methyl formate, acetone, methanol, formaldehyde, acetaldehyde, propionaldehyde, and some heavier hydrocarbons. Conventional distillation ia one or two columns separates some of the lower boiling components overhead, while taking some of the higher boilers out the bottom of the column. The reduced level of impurities are then extractively distilled ia one or more columns to provide a purified propylene oxide product. The solvent used for extractive distillation is distilled ia a conventional column to remove the impurities and then recycled (155,156). A variety of extractive solvents have been demonstrated to be effective ia purifyiag propylene oxide, as shown ia Table 4. 

Evaporation and Distillation. Steam is used to supply heat to most evaporation (qv) and distillation (qv) processes, such as ia sugar-juice processiag and alcohol distillation. In evaporation, pure solvent is removed and a low volatiUty solute is concentrated. Distillation transfers lower boiling components from the Hquid to the vapor phase. The vapors are then condensed to recover the desired components. In steam distillation, the steam is admitted iato direct coatact with the solutioa to be evaporated and the flow of steam to the condenser is used to transport distillates of low volatiHty. In evaporation of concentrated solutions, there may be substantial boiling poiat elevation. For example, the boiling poiat of an 80% NaOH solution at atmospheric pressure is 226°C. 

Linalool can also be made from nerol and geraniol by the orthovanadate-catalyzed isomerization. Because linalool is lower boiling than nerol and geraniol, the isomerization can be mn under distillation conditions to remove the linalool overhead while continually adding nerol and geraniol to the distillation kettie for further isomerization (56). 

Similar ester carboxylate group containing polymeric titanate esters are obtained by the reaction of titanoxanes with carboxyUc acids (26), by reaction of a tetraalkyl titanate with a carboxyUc acid and 1—2 moles of water (27), or by reacting a polymeric metal acylate with a higher boiling carboxyUc acid and removing the lower boiling carboxyUc acid by distillation (28). 

The same reaction can be used to convert one alkoxide to another by distillation of a lower boiling ester ... 

The liberated alcohol must be lower boiling than any other species present so that it may be distilled at a convenient rate and drive the reaction to completion. It is possible to prepare esters of lower molecular weight from a higher member by usiag a large excess of alcohol and rapid iaefficient distillation, but the method is generally not practical. 

Esters of high volatility, such as methyl formate, methyl acetate, and ethyl formate, have lower boiling points than those of the corresponding alcohols, and therefore can be readily removed from the reaction mixture by distillation. 

The lighter (lower-boiling) components tend to concentrate in the vapor phase, while the heavier (higher-boihng) components tend toward the liquid phase. The result is a vapor phase that becomes richer in hght components as it passes up the column and a liquid phase that Becomes richer in heavy components as it cascades downward. The overall separation achieved between the distillate and the bottoms depends primarily on the r elative volatilities of the components, the number of contacting trays, and the ratio of the liquid-phase flow rate to the vapor-phase flow rate. 

The natural relative volatility of the system is enhanced when the ac tivity coefficient of the lower-boiling pure component is increased by the solvent addition (Yl/Yw increases and P IPh > 1). In this case, the lower-boiling pure component will be recovered in the distillate as expec ted. In order for the higher-boihng pure component to be recovered in the distillate, the addition of the solvent must decrease the ratio Yl/Yw such that the product of the Yl/Yw nd (i- -, ( l,h) in the... 

Use vacuum distillation to obtain lower boiling point of solvent to allow lower distillation temperature... 

In a fractional distillation, it is usual to reject the initial and final fractions, which are likely to be richer in the lower-boiling and higher-boiling impurities respectively. The centre fraction can be further purified by repeated fractional distillation. 

The 2-cyclohexenone obtained by an ordinary distillation at this point is contaminated with lower-boiling impurities (see Note 5), primarily ether and ethanol. 

The purity of the 2-cyclohexenone may be assayed by gas chromatography on an 8 mm. x 215 cm. column heated to 125° and packed with di-(2-ethylhexyl) sebacate suspended on ground firebrick. This method of analysis indicates that the 3-cyclo-hexenone in the product amounts to no more than 3%. The fore-run from this fractional distillation contains substantial amounts of 2-cyclohexenone accompanied by ether, ethanol, and minor amounts of other lower-boiling impurities. Additional quantities of pure 2-cyclohexenone can be recovered by redistillation of this fore-run. The preparation of 2-cyclohexenone has been run on twice the scale described with no loss in yield. The ultraviolet spectrum of an ethanol solution of the 2-cyclohexenone obtained has a maximum at 226 m/i (s = 10,400). 

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