Distillation of solvents

A violent explosion occurred during the distillation of solvents that had contained the peroxyacid. Although the solvents had been treated by addition of sodium sulfite to reduce the acid, dipropionyl peroxide (which is not reduced by sulfite, and which may have been produced by the sulfite treatment) remained in solution and subsequently decomposed on heating. If the solvent is added to the sulfite solution, the diacyl peroxide is not formed. 

Distillation of solvent chloroform from the preparation caused the residue to explode violently on 2 occasions. Previous publications had recommended use of solutions of the chloride, in preference to isolated material. 

In the preparation from lead(II) chloride and vinylmagnesium bromide in THF-hexane, violent explosions occurred during isolation of the product by distillation of solvent. This could be avoided by a procedure involving steam distillation of the tetravinyllead, no significant loss of yield by hydrolysis being noted. It is likely to be considerably more endothermic than tetraethyllead. 

Drinking water, waste water, natural water Direct distillation or distillation of solvent-cleaned sample (if necessary) at acidic pH, react with 4-amino-antipyrine and potassium Spectrophotometric 1 pg/L for 500-mL sample NG... 

The checkers used magnetic stirring with intermittent shaking as needed. Checkers used cannula filtration and vacuum distillation of solvent. 

An alternative procedure is used by the submitter from this point to the final distillation of solvent and ester The condenser is then set for downward distillation, and about 40 ml. of alcohol is distilled. Then 100 ml. of water is added, and an additional 100 ml. of alcohol and water is distilled. The cooled residue is diluted with 200 ml. of water and the solution freed of insoluble organic material by washing three times with 50 ml. of ether. After acidification with 40 ml. of concentrated hydrochloric acid, the organic layer is extracted with three 50-ml. portions of ether. The combined ether extracts are washed with water and dried over anhydrous magnesium sulfate. 

Figure 18.8 Glass storage container for volatile solvents. It is used for the storage and the vacuum distillation of solvents.

The molar mass of a newly synthesized organic compound was determined by the isothermal distillation method. In this procedure two solutions, each in an open calibrated vial, are placed side by side in a closed chamber. One of the solutions contained 9.3 mg of the new compound, the other 13.2mg of azobenzene (molar mass 182). Both were dissolved in portions of the same solvent. The experiment was untouched for three days, during which solvent distilled from one vial into the other until the same partial pressure of solvent was reached in both vials. After this, there was no further net distillation of solvent. Neither of the solutes distilled at all. The solution containing the new compound occupied 1.72mL and the azobenzene solution occupied 1.02mL. What is the molar mass of the new compound The mass of solvent in solution may be assumed to be proportional to the volume of the solution. 

Dimethoxyethane. Explosion resulted during addition of 1,2-dimethoxyethane to LiAlH4 caution is required during distillation of solvent from LiAlH4.7,8... 

The crystalline fractions are now systematically recrystallized from methanol. The head crop is recrystallized from about 600 cc. of this solvent, and the remaining crops are crystallized in order from the successive mother liquors. At each stage the volume of the solution is adjusted by addition or distillation of solvent so that from one-third to one-half of the salt crystallizes. A series of large Erlenmeyer flasks, fitted with a reflux condenser or distilling head as required, is convenient for the purpose. The recrystallization is continued, using fresh or recovered solvent, until the head fraction has [a]i> — 2.8° or less (c = 4, methanol). It is unnecessary to take rotation values until the crystalline appearance and solubility behavior of the head fraction become approximately constant. Usually five to seven recrystallizations are necessary for purification. When pure, the head fraction is removed from the series and the recrystallization of the remaining crops is continued as long as it appears profitable. The final mother liquor from each series is reserved. 

Vacuum distillation of solvents is frequently undertaken to reduce the temperature of the sofution, thereby reducing the risk of decomposition. Vacuum distiffation also speeds the removal of solvents. In a pilot plant, setting vacuum is usually generated through a great variety of sealed mechanical pumps, or, simply, using steam... 

Distillation of solvents may be extremely dangerous because many nonaqueous solvents are volatile and flammable. Hence, the distillation systems have to be explosion proof and equipped with a safety valve which can liberate pressure which develops in the system. It should be noted that ether solvents may contain peroxides that can cause an explosion upon heating. In fact, any ether solvent that is exposed to air is suspected of containing dangerous peroxides. 

Two basic types of solvent still are found in the lab. One is for distillation of solvents for routine use and the other is for distillation of ultra-dry solvents for carrying out reactions under dry conditions. 

There are two main types of solvent still that are commonly employed in organic research laboratories. One is the classical distillation set-up consisting of distillation pot, still-head, thermometer, condenser, receiver-adaptor, and collection vessel. This arrangement is described in more detail in Chapter 11, and is used for the distillation of solvents that are either required infrequently, or that can be stored without deterioration for long periods of time. The other is a continuous still set-up that consists of a distillation pot, collecting head, and condenser (see Fig. 5.1). 

By the use of a coil condenser (Fig. 27) the distillation of solvents is greatly facilitated. The free flame, if it be surrounded by a cylinder of wire gauze, may be employed in place of a water-bath. A piece of rubber tubing attached to the side tube of the receiver carries the vapours to a hood or below the surface of the table. 

Isolation of Volatiles. An aliquot of blended pulp (1.2 kg) was diluted with distilled water (700 mL) in a 3-L three-neck flask and vacuum distilled (25-30°C/l mm Hg). Distillation continued for 2.5 to 3 h yielding approximately 500 mL of distillate which was collected in two liquid nitrogen cooled traps. A total of 3.6 kg of fruit pulp was distilled in three batches. The distillates were combined and immediately frozen until use. The combined distillate was extracted in 250 mL batches for 20 h with 60 mL trichloro-fluoromethane (Freon 11, b p 23.8°C) using a continuous liquid-liquid extractor. The trichlorofluoromethane was distilled through a 120 x 1.3 cm glass distillation column, packed with Fenske helices, prior to use. Each extract was carefully concentrated to approximately 100 pL by distillation of solvent using a Vigreux column (16 cm), and a maximum pot temperature of 30°C. 

LSD laboratories will have specific equipment for the construction of molecules under an inert atmosphere (eg. gas tanks of nitrogen or argon) and distillation of solvents under reduced pressure (rotary/ flash evaporator, vacuum pump, dry ice trap). Although this equipment can be used in the preparation of LSD this equipment is also used by conscientious chemists so as not to contaminate the environment with solvents or those who are working with heat or air sensitive molecules. 

Dimethyl terephthalate + ethylene glycol Polyester resin Ediylene glycol Various 320-570 Distillation of solvent and recovery of the polymer as a melt... 

Safety. Distillation of solvents involves the safe handling of large amounts of vapour that may be toxic, explosive, flammable or strong-smeUing. Some plants may not be able to cope with such material satisfactorily and may have difficulty in getting a site licence. 

While steam distillation of solvents which are not water miscible produces a recovered solvent that is ready for reuse, or at worst only needs reinhibiting, the wet solvents resulting from steam distillation of alcohols, ketones and esters with boiling points up to about 120 °C are likely to need drying. Pervapora-tion is a technique particularly well suited to this problem, provided there are no glycol ethers in the... 

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