Extraction with Aqueous Cupric Salt

To avoid the use of mineral acids, Kossel and Schmiedeberg (see Kossel, 1929, p. 19) devised the use of cupric chloride (or sulfate) to extract protamine from sperm heads. Dry sperm heads are treated with aqueous cupric chloride (or sulfate) for several days at room temperature. During the process, due to double decomposition, the protamine moiety is transferred into the aqueous phase in the form of hydrochloride (or sulfate) salt, while the nucleic acid moiety is converted to the insoluble cupric salt after removal of the insoluble salt, the protamine fraction is precipitated from the solution as picrate salt. 

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C 2-Bromo-4-methylbenzaldehyde A 3-1. three-necked flask is equipped with an efficient stirrer, a dropping funnel (Note 2), and a thermometer. The aqueous 10% formaldoxime prepared in step A is placed in the flask, and to it are added 6 5 g (0.026 mole) of hydrated cupric sulfate, 1.0 g. (0 0079 mole) of sodium sulfite, and a solution of 160 g of hydrated sodium acetate in 180 ml. of water The solution is maintained at 10-15° by means of a cold-water bath and stirred vigorously. The neutral diazonium salt solution prepared in step B is slowly introduced below the surface of the formaldoxime solution (Notes 3 and 4). After the addition of the diazonium salt solution is complete, the stirring is continued for an additional hour and then the mixture is treated with 230 ml. of concentrated hydrochloric acid. The stirrer and the dropping funnel are replaced by stoppers, and the mixture is gently heated under reflux for 2 hours The flask is set up for steam distillation, and the reaction product is steam-distilled. The distillate is saturated with sodium chloride, extracted with three 150-ml portions of ether, and the ethereal extracts are washed successively with three 20-ml portions of a saturated sodium chloride solution, three 20-ml. portions of an aqueous 10% sodium bicarbonate solution, and again with three 20-ml portions of a saturated sodium chloride solution. 

Early examples of enantioselective extractions are the resolution of a-aminoalco-hol salts, such as norephedrine, with lipophilic anions (hexafluorophosphate ion) [184-186] by partition between aqueous and lipophilic phases containing esters of tartaric acid [184-188]. Alkyl derivatives of proline and hydroxyproline with cupric ions showed chiral discrimination abilities for the resolution of neutral amino acid enantiomers in n-butanol/water systems [121, 178, 189-192]. On the other hand, chiral crown ethers are classical selectors utilized for enantioseparations, due to their interesting recognition abilities [171, 178]. However, the large number of steps often required for their synthesis [182] and, consequently, their cost as well as their limited loadability makes them not very suitable for preparative purposes. Examples of ligand-exchange [193] or anion-exchange selectors [183] able to discriminate amino acid derivatives have also been described. 

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