COKTRIBUTIONS TO T H E CHEMISTRY O F BERYLLIUM Beryllium 11.* Electrolysis of Beryllium Compounds in Organic Nitrogen Derivatives BY HAROLD
sImioNs
BOOTH ASD GILBERTA G. TORREP
Introduction Previous attempts to prepare metallic beryllium by electrolysis of solutions of it’ssalts have shown that no metal can be precipitated from a solution that contains water as such or the elements of water. Apparently the salts of beryllium all undergo hydrolysis unless every trace of water is eliminated. In order to prevent hydrolysis and yet secure the ionizing properties which make water so useful an electrolytic solvent, the closely analogous compound, ammonia, was considered as a solvent for beryllium salts. However, the inconvenience of working with anhydrous liquid ammonia encouraged the trial of substituted animonias. Since the behavior of these solutions is so similar this paper will deal only with the work done in the organic derivatives and will be followed by a paper concerning the results in inorganic nitrogen compounds. Choice of Solvents Kahlenberg’ prepared lithium by electrolyzing a solution of lithium chloride in pyridine. This method was tested by us and gave a closely adhering, smooth deposit of metallic lithium. Arguing from the close analogy usually observed between transition members of successive periodic groups it was thought that beryllium could be prepared in the same way. However, in all the electrolyses with pyridine a dark brown material was formed that obscured the electrodes and made the solution so opaque that’ no observation could be made of the evolution of gases. This brown material also behaved like a colloid and displayed cataphoresis so that the layer of hard, brown material would prevent any beryllium being deposited if liberated at the cathode. More stable solvents that would permit observation of the products of the electrolysis were then sought. Aniline was next tried with the expectation that it would be more stable on electrolysis. This, however, formed solutions of considerable resistance as compared with those in pyridine, and quinoline was selected as being more analogous to pyridine and yet possibly more stable toward the electric current. The solutions of quinoline were non-conducting so recourse was had to a less complex molecule containing nitrogen such as pyrrole. Although the conductivity of these solutions was satisfactory the troublesome brown material *For “Beryllium. I” see this Journal, 35, 246j (1931:. J. Phys. Chem., 3, 602 (1899).
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was still formed to some extent, nevcrtheless, metallic beryllium vas deposited. X saturated compound was next tried. Piperidine is merely pyridine with all the bonds saturated with hydrogen but this solvent formed solutions of such high resistance that only very small quantities of metal could be obtained after very long continued runs. Phenylhydrazine would not dissolve beryllium salts. The alkyl-substituted ammonias dissolved quantities of beryllium salts but apparently have no ionizing power as the solutions were absolutely non-conducting. Formamide was a good solvent but no metal was deposited from it. Preparation and Purification of Materials Pyridine was purified by letting it stand over solid potassium hydroxide, distilling it and collecting the fraction boiling between I 16'-I 17.5'C. -hiline was treated with sodium chloride, dissolved in ether and distilled. The fraction distilling at 182'c'. was collected for use. Quinoline was redistilled while the other solvents were used just as obtained in sealed containers fresh from the Eastman Iiodak Company. The container was opened, the solvent placed in the dried electrolyzing tube, beryllium salt added, and the tube quickly attached to the rest of the apparatus. A11 beryllium salts were prepared as described in a previous article. (See Beryllium I.) For the work in pyridine a series of solutions of all the available beryllium salts was prepared by allowing the solyent to stand over the solid salt until saturated. The behavior of the salts soon showed that only the chloride, acetylacetonate, and double fluoride of sodium and beryllium were useful as solutes. In the case of the other solvents as much beryllium salt was added as would dissolve quickly and no attempt was made to saturate the solvents completely. Apparatus The apparatus which was used for this work was similar to the one already described in an article on electrolysis in miscellaneous non-aqueous solvents. (See Beryllium I). The apparatus was never evacuated as these solutions do not readily absorb moisture and it was not essential to maintain a solvent atmosphere during the electrolysis. .Ilthough the tube which contained the solution was always oven dried the apparatus as a whole did not require special drying since the solvents do not vaporize to such an extent that they would become contaminated with moisture absorbed from the walls of the rest of the apparatus. Experimental I. Solutions i n P~ridi7ie. Sone of the beryllium salts showed a striking solubility in pyridine and their low solubility probably accounts for the small amount of current carried by these solutions. The pyridine was allowed t o stand over the solid salts for several days and the supernatant liquid poured directly into the electrolyzing vessel without filtering to prevent contamination by moisture of the air. S o quantitative determination was made of the solubility.
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a. Beryllium nitrate. Beryllium nitrate tetrahydrate gave a solution of fair conductivity taking five amperes/sq. dm. with 6.15 volts potential across the cell terminals. On continued electrolysis the resistance of the solution increased and sufficient heating occurred to distill away the pyridine unless a cooling bath was used. The solution became brown, hydrogen and oxygen were evolved, but no metal was deposited; this was to be expected on account of the presence of water. b. Anhydrous beryllium chloride dissolved in pyridine carried only 1.8 amperes/sq. dm. with 9.1 volts potential. Considerable amounts of gas were evolved a t the anode but no apparent deposit of metal was produced at the cathode. c. Anhydrous beryllium sulfate gave a solution of high resistance carrying .I ampere/sq. dm. with 10.22 volts potential. A white, spongy precipitate was produced in the solution. This was doubtless beryllium hydroxide due to traces of water which are very difficult to remove completely from this salt. Both electrodes were coated with a soft, brown, gelatinous material. No metal was deposited. d. The sodium-beryllium fluoride solution carried .I ampere/sq. dm. a t 4.5 volts potential. A curve of decomposition voltages was run and the break observed a t 3.75 volts. Although on breaking the circuit a back E.M.F. of .2 volts was always observed no metal was ever permanently deposited whether electrolysis was conducted on the I O volt or I I O volt circuits. The E.M.F. might be due to traces of gas on the electrode although no evolution of gas was ever observed. e. Beryllium acetylacetonate gave an even more resistant solution than the fluoride taking only .07 ampere/sq. dm. a t 9.15volts, but a n adherent, finely divided, black precipitate was produced on the cathode. The black material was soluble in concentrated hydrochloric acid giving a gas and tiny white crystals that rapidly deliquesced. A black E.M.F. of .37 and .49 volts was observed in two trials. The black deposit was metallic beryllium but in such small amounts as not to encourage further study. Pyridine was also added to beryllium basic acetate, beryllium basic carbonate and beryllium orthophosphate but the supernatant liquid was nonconducting in all cases probably due to the insolubility of these salts. 2. Solutions in Aniline. A series of solutions of beryllium salts similar to that in pyridine was prepared in aniline with the oxide added and the nitrate omitted. These solutions possessed a much greater internal resistance than the solutions in pyridine. A IOO volt potential was necessary to force even traces of current through the solutions. The solution of beryllium sulfate was absolutely non-conducting. The solutions of the phosphate and the sodium-beryllium fluoride carried .OOI ampere/sq. dm. and the oxide .ooj ampere a t g j volts potential. The basic carbonate and the acetylacetonate carried respectively .OI5 and .I 5 amperes/ sq. dm. but with no result save a brown coloration of the solution. Due to the large proportion of the elements of water and the probably complex character of the beryllium basic acetate it was not considered a likely
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source of metallic beryllium. The solution of this salt was very resistant carrying .o j aniperes/sq. dm. at 98 volts potential. However, a solid material of delicate violet color was deposited on the cathode. This material was treated with concentrated hydrochloric acid giving a white solid which rapidly dissolved on exposure to air due to its hygroscopicity. The small amount of solid obtained by electrolysis made it impossible to test more than the solubility in hydrochloric acid but it mas doubtlcss metallic beryllium. 3 . Solutions in Quinoline. The low Conductivity of the solution in aniline indicated that a compound in which the nitrogen atom was directly in t,he ring was more satisfactory than one in which the nitrogen was in the side chain. The brown compound that was forincd in the pyridine solutions was believed due to polymerization so a more stable compound was sought in which the nitrogen would be similarly placed. Quinoline was selected. A sample of pure quinoline was placed in the electrolyzing apparatus over anhydrous beryllium chloride and connected in series with a source of current giving 1 2 0 volts potential. S o conductivity was observed. A trace of pure sodium chloride was added giving a very slightly conducting solution. X deep red color spread through the solution from the anode but no gases or other electrode products were observed. 4. Solutl'ons in Pyrrole. The failure of the quinoline to produce conducting solutions suggested that the less complex compounds formed solutions of better conductivity probably due to greater solubility of the salts. a. Beryllium acetylacetonate was found to dissolve in considerable quantities in pyrrole. Five cubic centimeters of the solvent readily dissolved .z9 gram and w v : ~not then saturated. The conductivity was very low, ,04j ampere:'sq. dm. on a 15 volt circuit, but an adherent black deposit was formed on the cathode. The electrode was washed with alcohol and examined under the microscope. The black deposit ~ w crystalline s and metallic in appearance. With hyc!rochloric acid a gzs was evolved. There was formed in the solution a black material of the same gelatinous nature as in former csperiinents with the other solvents but which did not cling t o the electrodes. The current was reversed and a black deposit, also soluble in acid with evolution of gas, was obtained showing that the deposit could only be formed on the cathode. Tests indicated that it was metallic beryllium. b. A solution of similar conductivity was obtained by dissolving beryllium chloride in pyrrole and gave the same, black metallic deposit on the cathode. The conductivity was . I ampere/.sq. dm., but sloivly dropped to a constant value of .06 amperes on running for some time. The solution of acet'placetonate in pyrrole also gave the same final value for the conductivity on being allowed to run f o r some time. j. Solutions i 7 z Piperidine. Since all the unsaturated nitrogen compounds had given the troublesome brown, gelatinous material in varying amounts it was thought that a compound in which the nitrogen was similarly placed but completely saturated might prevent the formation of the colloidal material. In piperidine the arrangement is exactly the same as in pyridine but the nitrogen is saturated with hydrogen in place of the double bond to
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carbon. Piperidine dissolved beryllium acetylacetonate very readily. About .4 gram was added to five cubic centimeters of piperidine without saturating it. The resulting solution carried only a few hundredths of an ampere on a I 15 volt circuit but gave a closely adherent deposit similar t'o that obtained on the cathode in previous experiments with pyrrole. Apparently these solutions give metallic beryllium but the amount is very small due to the low conductivity and it would require extremely long runs to produce a sufficient amount for the careful study of the metal obtained. The same brown, gelatinous material was obtained in this experiment but did not coat the electrodes. Since all the aryl derivatives of ammonia gave polymerization products it seemed advisable to try the alkyl derivatives which might be more stable. Amines in which one, two or all of the hydrogens of ammonia were replaced were tried. 6. Solutions i n n-Propylamine. Beryllium acetylacetonate dissolved very readily in this solvent. About .3 gram was dissolved but the solution was absolutely non-conducting on either I O volt or I I O volt circuits. On standing several months in a sealed tube this mixture went to a solid, transparent gel. 7 . Solutions in Di-ethyl amine. This solvent was selected as having two of the hydrogens replaced by alkyl and by analogy of structure should have behaved the same as piperidine in which two hydrogens are replaced by aryl linkages. a. Beryllium acetylacetonate dissolved very slowly in this solvent, ten cubic centimeters of solvent requiring several hours to dissolve .z gram. No conductivity was observed on eit,her I O volt or I I O volt circuits. b. A small amount of beryllium chloride was added to a portion of the solvent but showed no tendency to solution and the supernatant liquid was non-conducting. 8. Solutions i n Tri-ethylamine. a. Beryllium acetylacetonate dissolved in this solvent slowly. About . I gram was taken up by ten cubic centimeters of solvent but the solution was absolutely non-conducting. b. Beryllium chloride showed no apparent solubility in this solvent and the supernatant liquid was non-conducting. g Solutions i n Phenylhydrazine. Apparently the most satisfactory compounds of nitrogen are those in which there is no double bond to nitrogen and in which one hydrogen has been left unsubstituted. In phenylhydrazine nitrogen is linked to aryl group, to hydrogen by one bond and the third bond is satisfied by linkage to nitrogen again. However, neither beryllium acetylacetonate or beryllium chloride showed any solubility in this solvent and the supernatant liquid was non-conducting. On standing some reaction seemed to have taken place as the salts had swollen and formed new types of crystals. Probably the phenylhydrazine had formed addition products with t,hese salts as it is known t,o do with other metallic salts.
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IO. Formamide. The fact that the presence of an amino group seemed to favor the formation of conducting solutions of beryllium salts suggested the use of formamide and acetamide as electrolytic solvents. a. Beryllium chloride in formamide. A small amount of anhydrous beryllium chloride was dissolved in pure formamide. The solution carried 1.0 h per sq. dm. at 2 . 7 volts potential across the cell. Strong gassing occurred a t t,he anode and small amounts of gas a t the cathode but' no metal was deposited. In a saturated solution of beryllium chloride a drop in potential of 8.1 V. at C.D. of I j ampereslsq. dm. likewise gave no metal. The voltage was increased to 14.5volts without depositing beryllium. b. Beryllium acetylacetonate in formamide. Beryllium acetylacetonate was found to be quite soluble in formamide and at a C.D. of 15 amperes,' sq. dm. showed a drop in potential across the cell of 7 . 2 volts. Considerably more gassing was obtained a t the anode than a t the cathode but no metal was deposited. Increasing the voltage failed to cause deposition of beryllium. c. Beryllium basic acetate. This salt was quite soluble in formamide but on electrolysis a t a current density of I j amperelsq. dm. with drop in potential of 7 volts no metal was deposited. Increasing the voltage did not cause deposition of metal. Recently Tntema and Audrieth' have found that zinc, cadmium, lead, tin, cobalt, and nickel were deposited electrolytically from solutions of their salts in formamide, although they were unable to deposit metals higher than zinc in the electromotive series.
Conclusion Solutions of various beryllium salts in organic derivatives of ammonia have been elect,rolyzed. Some of the solutions are abRolutely nun-conducting while others carry a small current and produce metallic beryllium in small quantity, particularly solutions in piperidine and pyrrole. In general the solutions form gelatinous, colloidal substances which render the practical separation of metallic beryllium from these solvents problematical. .lforley Chemical Laboratory, Tl'estern Reserve ~ ~ n a o e i s z t y , Clei eland, Ohio. W
Tntema and .ludrieth: ,J. Am. Chem. SOC., 52, 2693 (1930;.
