Molecular distillation partial reflux

A,A,A, A -Tetramethylethylenediamine (TMEDA, TEMED) [110-18-9] M 116.2, m -55", b 122", 04 1.175, Up 1.4153, pK 5.90, pK 9.14. Dry TMEDA partially with molecular sieves (Linde type 4A), then distil it in a vacuum from butyl lithium. This treatment removes aU traces of primary ani secondary amines and water. [Hay et al. J Chem Soc, Faraday Trans 7 68 1 7 972.] Or dry it with KOH pellets, reflux for 2hours with one-sixth its weight of n-butyric anhydride (to remove primary and secondary amines) and fractionally distil it. Reflux it with fresh KOH, and distil it under nitrogen. [Cram Wilson J Am Chem Soc 85 1245 1963.] It was also distilled from Na. Store it sealed under N2. The dipicrate has m 263°(dec). [Beilstein 4 H 250, 4 1 415, 4 II 690, 4 III 512, 4 IV 1172.]... 

Hydrochloric acid [7647-01-0], which is formed as by-product from unreacted chloroacetic acid, is fed into an absorption column. After the addition of acid and alcohol is complete, the mixture is heated at reflux for 6—8 h, whereby the intermediate malonic acid ester monoamide is hydroly2ed to a dialkyl malonate. The pure ester is obtained from the mixture of cmde esters by extraction with ben2ene [71-43-2], toluene [108-88-3], or xylene [1330-20-7]. The organic phase is washed with dilute sodium hydroxide [1310-73-2] to remove small amounts of the monoester. The diester is then separated from solvent by distillation at atmospheric pressure, and the malonic ester obtained by redistillation under vacuum as a colorless Hquid with a minimum assay of 99%. The aqueous phase contains considerable amounts of mineral acid and salts and must be treated before being fed to the waste treatment plant. The process is suitable for both the dimethyl and diethyl esters. The yield based on sodium chloroacetate is 75—85%. Various low molecular mass hydrocarbons, some of them partially chlorinated, are formed as by-products. Although a relatively simple plant is sufficient for the reaction itself, a si2eable investment is required for treatment of the wastewater and exhaust gas. 

UK. = Light key component in volatile mixture L/V = Internal reflux ratio L/D = Actual external reflux ratio (L/D) ,in = Minimum external reflux ratio M = Molecular weight of compound Mg = Total mols steam required m = Number of sidestreams above feed, n N = Number of theoretical trays in distillation tower (not including reboiler) at operating finite reflux. For partial condenser system N includes condenser or number theoretical trays or transfer units for a packed tower (VOC calculations) Nb = Number of trays from tray, m, to bottom tray, but not including still or reboiler Nrain = Minimum number of theoretical trays in distillation tower (not including reboiler) at total or infinite reflux. For partial condenser system,... 

When the inside temperature reaches 140°, boiling commences and water plus a very little phenol begins to distil. The distillation is allowed to continue until 60 cc. (one molecular equivalent) of water has been collected this usually requires one hour, and the inside temperature rises to 146°. The downward condenser is then replaced by a reflux condenser (Note 1) and the reaction is allowed to continue until a total of four hours has elapsed from the time the contents of the flask first reached 140°. After the return condenser has been attached, the inside temperature declines slowly to 1410 or 142° and the reaction mixture becomes thicker and somewhat tarry. After the contents of the flask have been partially cooled, they are... 

The acetal (b 82.5 ) is removed during fractional distillation. Traces of benzene, if present, can be removed as the benzene/MeOH azeotrope by distillation in the presence of MeOH. Distillation from LiAlH4 removes aldehydes, peroxides and water. Dioxane can be dried using Linde type 4X molecular sieves. Other purification procedures include distillation from excess C2H5MgBr, refluxing with Pb02 to remove peroxides, fractional crystallisation by partial freezing and the addition of KI to dioxane acidified with aqueous HCl. Dioxane should be stored out of contact with air, preferably under N2. 

This type of unit features the main steps encountered in partial condensation. The available gas mixture, previously dried on molecular sieves, is cooled to around — 120 C by heat exchange in a series of piaicexchangers operating in countercurrent flow on the cold purified products, and is then introduced at the bottom of a tray column with a downflow of liquid methane. The operation takes place at a pressure of abont 1.6.10 Pa absolute. It yields hydrogen with a purity better than 98.5 per cent volume, and which contains less than 10 ppm of CO. After expansion and partial vaporization, the extract feeds a distillation colnmn operating at 0.2. 10 Pa absolute, which separates the carbon monoxide at the top with a yield of at least 80 per cent at a purity over 99 per cent volume, and liquid methane at the bottom. This methane provides reflux to the scrubbing column and partly to the feed cooling uuiL... 

To prepare a suitable resin for adhesive applications, urea is dissolved in formalin (initially neutralized to pH 7.5) to give the desired U/F molar ratio. After boiling under reflux for about 15 min to give demethylol urea and other low-molecular products, the resin is acidified, conveniently with formic acid, to pH 4, and reacted for a further period of 5-20 min. The resulting water-soluble resin with approximately 50% solids content is stabilized by neutralizing to a pH 7.5 with alkali. For use as an aqueous solution, as is normally the case, the resin is then partially dehydrated by vacuum distillation to give a 70% solids content. 

This solvent is employed widely in analytical and coordination chemistry. At its boiling point it undergoes partial decomposition to yield dimethylamine and carbon monoxide. The decomposition is catalyzed by various substances, particularly those with acidic or basic properties this must be taken into consideration in the selection of the material used for drying. Under no circumstances may this solvent be refluxed with, for example, potassium hydroxide, sodium hydroxide or calcium hydride. Dimethylformamide can be dehydrated most advantageously with a molecular sieve of pore size 0.4 nm however, calcium sulphate, magnesium sulphate or silica gel may also be employed. After dehydration, the solvent may be purified by vacuum distillation. 

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