The PRECIPITATION of ALUMINUM, FERRIC, and CHROMIC IONS by HEXAMETHYLENE TETRAMINE LEO LEHRMAN
AND
ELVIN A. KABAT
The City College of the City of New York
H
E~AMETHYLENEtetramine has recently been used to effect separations in the analysis of the cations ( I ) , ( 2 ) . This reagent is a very weak base even in acid solution, precipitating certain metallic ions as hydroxides. However, i t has also been shown that compounds of metallic salts with hexamethylene tetramine exist (3), (4). Duff and Bills (4) state that zinc, ferric, chromic, and aluminum chlorides yield the corresponding hydroxides when boiled in aqueous solution with hexamethylene tetramine. They came to this conclusion by filtering off the precipitates obtained in the above reaction, washing them with water, and testing the residues for the presence of hexamethylene tetramine. No mention is made of the thoroughness of the washing to be sure of removing any excess of metallic chloride or of hexamethylene tetramine. The fact that the precipitates are gelatinous and therefore very difficult to wash free of adhering solutes led us to question the validity of their conclusion. Inasmuch as the purpose of this work is to determine the result of the reaction of metallic salt solutions with hexamethylene tetrimine, a method which removes any unreacted material, making specific tests to establish this fact, was used. Precipitates formed by the addition of excess hexamethylene tetramine solution, to separate boiling solutions of aluminum, ferric, and chromic chlorides, both in the absence and presence of ammonium salts were dialyzed until free of the reagent and the resultant gel was analyzed for organic matter, (CH2)6NI,and nitrogen. EXPERIMENTAL
About 1 g. of aluminum as AlCl3 in 100 ml. of solution was precipitated while boiling by adding 10% (CH2)sN4solution.* The suspension was then rapidly dialyzed in a simplified modification of the concentrating dialyzer (5), devised by F. E. Kendall (6) of the College of Physicians and Surgeons and Presbyterian Hospital, New York City, having an air trap attached (7), until only a very thick gel remained. This usually takes about two weeks. The process was stopped a t this point, distilled water was added to the
-
~
On standing for xvernl days the precipitate apparently dirsalves but actually is present in colloidal dispersion as shown by
its reappearance after dialyris.
gel inside the collodion bag, and the bag with its contents was suspended in a beaker of distilled water.? After one week the water inside and outside of the collodion bag was analyzed for (CH&N4. The test for (CH2)eNa was carried out by acidifying with dilute sulfuric acid, boiling for one minute, cooling, and testing for formaldehyde with Schiff's reagent. Both the water inside and outside gave negative tests, showing the complete removal of extraneous (CH2)aNa from the gel. Control tests on both the gel and the water surrounding the collodion bag, to which one drop of the (CHe)sNd solution had been added, gave distinctly positive results. The colorless gel is soluble in dilute mineral acids and bases on warming, with the exceptionof dilute (and concentrated) NHaOH. A small amount dissolved in dilute H2S04is reprecipitated by concentrated NH40H, insoluble in excess. When allowed to dry either by exposure to the air or in an oven a t 105"C., a horn-like substance, having a slightly yellowish color due to the presence of a trace of iron, is obtained. The dried material shows the same properties as the gel. A small amount of the gel heated in a test-tube showed no evidence of darkening or charring. Another portion, heated with concentrated HzSOa to the boiling point, dissolved without any darkening of the solution. A small amount of the gel was dissolved in dilute H,S04, boiled for one minute, cooled, and tested for formaldehyde with Schiff's reagent, giving a negative result. About 0.2 g. of the dried material was ground to a powder and tested for nitrogen by the metallic sodium fusion. The result showed the absence of nitrogen. All the above tests were repeated with the same material to which one drop of the (CH2)aNa solution had been added. In every case the results indicated the presence of the added reagent. The data thus show that the precipitate obtained by adding (CH&N4 solution to Al+++is AI(OH)3. One gram of aluminum as AlC13in 100 rnl. of solution, to which 2 g. of NHaNO3 had been added, was precipitated in boiling solution by adding excess 10% (CH&Na solution. It was dialyzed free of (CH2)sN4 and the same tests were carried out. The results again showed - that the precipitate is Al(0H)a. t Sobsequent experiments in which ( C H r ) ~ . ,solution was added to a portion of the gel showed that after 5 minutes the (CII&N, had begun to diRure through the collodion membrane.
For comparison some Al(OH)a,prepared by precipitating Al+++ with dilute NH40H, was dialyzed until free of the reagent and in the form of a thick gel. This material resembled the precipitates described except that in the dried condition it was more powdery and had a slightly lighter color. The same experiments and tests were repeated using FeC13 and CrCla solutions. The results showed that the precipitates obtained are the hydroxides of the metallic ions. SUMMARY
The precipitates obtained by adding (CH%)aN4solution to boiling solutions of Al+++,Fe+++,and Cr+++,
either in the absence or presence of ammonium salts, have been shown to be the hydroxides of the metallic ions. LITERATURE CITED
(1) RAY AND CHATTOPADAYA, Z. a ~ r g .allgem. C h . , 169, 99-112 (1928). (2) LEHRMAN,KABAT,AND WEISBERG,I. Am. Chem. Soc., 55, 3509 (1933). (3) RAY ANDSARKAR,I. C h . Soc., 119,390 (1921). (4) DUPEAND BILLS,ibid., 1929,4114. (5) SIWS,I. Ezpl. Med., 51,319 (1930). (6) RENDALL, personal communication. (7) L E ~ M AAND N KABAT,Ind. Eng. Chem., Analyt. Ed., 5, 358 (1933).
