Methylene dichloride, purification

Neat amino alcohols la-e (10 mmol) were placed in a Pyrex open flask allowing the removal of furan. After microwave irradiation or conventional heating, the products were removed with methylene dichloride and analyzed by ll NMR spectroscopy. Unsaturated amino alcohols 2 obtained under microwaves were highly pure and did not need further purification. 

A recommended method of TXN purification involves recrystallization from water, diethyl ether or methylene dichloride, vacuum sublimation or distillation 44). TXN is inert towards alkalies thus, basic drying agents may be used to remove water. On the large scale TXN is conveniently dried by distillation of the crude trimer with solvent which forms ternary azeotropes with high water content (e.g. n-heptane)45). 

Methylene dichloride is prepared by chlorination of methane and thus contains chloroform and carbon tetrachloride as impurities. Water can be removed by drying over sodium sulfate, calcium chloride, potassium carbonate, or phosphoric oxide. Further purification can be achieved by prior washing with, successively, water, concentrated sulfuric acid, water, sodium hydroxide solution, and again water. 

Chloroform is also prepared by chlorination of methane but also by treatment of ethanol with bleaching powder. Because of its tendency to decompose, chloroform contains phosgene, hydrogen chloride, and chlorine as well as other chlorination products of methane it is usually stabilized by addition of 0.5-1.0% of ethanol. The impurities formed by decomposition are removed by washing with water or dilute potassium hydroxide solution. Further purification, which is usually superfluous, can be effected as for methylene dichloride. The same drying agents as in that case may be used of these, calcium chloride and phosphoric oxide are most efficient in removing also the ethanol. 

Carbon tetrachloride is prepared by chlorinating methane or carbon disulfide. In the latter case the solvent always contains traces of disulfur dichloride or carbon disulfide as impurity it cannot be freed from these contaminants by distillation, but they are removed by vigorous shaking with dilute sodium hydroxide solution.4 Further purification, if necessary, can be effected as for methylene dichloride. All higher chloroalkanes can be purified by essentially the above methods. 

Synthesis of block copolymers The A-B-A block copolymers were prepared by reacting the middle block with the N-carboxy anhydride of Y benzyl-L-glutamate, yethyl-L-gluta-mate, c-N-carbobenzyloxy-L-lysine, Y niethyl-L-glutamate, or Y-methyl-D,L-glutamate. The polymerization was carried out in the absence of moisture at room temperature in dioxane-methylene dichloride mixture at 3 % total concentration of amino acid-NCA and the middle block. The polymerization was followed by infrared spectroscopy. After the pol3nneri-zation was terminated, the copolymer was precipitated in methanol for purification and then dried in vacuo. 

The pre-purification of barbiturates to be isolated from urine can likewise be carried out by acid ether extraction [43, 56, 166]. Methylene dichloride has been employed also [34]. Acidification with hydrochloric acid is preferable since, if this is performed with weaker, organic acids, amphoteric medicinal components like sulphonamides, are extracted at the same time [166]. After drying the organic phase with sodium sulphate, further purification on a charcoal or alumina column can be carried out [43, 166]. Urine colouring materials can be removed by shaking the ethereal solution with 5% lead acetate solution [56]. After purification, the... 

All 4 chlorocompounds, namely methyl chloride, methylene dichloride, chloroform and carbon tetrachloride, are of commercial importance they are produced by successive chlorination of methane, followed by separation and purification of the halomethanes mixture [40]. 

Organic halides are often excellent solvents and are particularly useful for recrystaUization and extraction. Methylene chloride (bp 41°) has solvent characteristics similar to those of ether and is heavier than water. The commercial material is satisfactory for most purposes, and if purification is desired, it may be washed with concentrated sulfuric acid and with water and then dried and distilled. Ethylene dichloride (bp 84°) is similar to methylene chloride in its solvent properties and may be purified in the same fashion. 

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