Journal 01 Research 01 the Na tional Bu reau 01 Standards Vol. 47, No. I, July 1951 Research Paper 2224 Preparation and Purification of Hydrogen Deuteride

Abraham Fookson, Philip Pomerantz, and Edwin H. Rich

In an investigation of t he physical properties of hydr<;>gen isotopes it was n.ecessar.\:' t o prepare 10 liters of high-purity. hydro~en d ~ u.tend e. TI1JS was done ~y reactmg IJ t hlUm aluminum hydride with deutenum oXIde, g ly.;n ~ hy dro~e n deutende, ]I) .t wo ba tc h ~s, ?f 98.1- and 97.0-percent purity, respect ive!.\:' . .Ihls mater!ai was then fractIOnated at JtqUJd hydrogen t emperature in three batches, Yleldmg the desIred amoun t of hydrogen deutende in a purity of 99.8 percent.

I. Introduction figure 1, except for the method employed for adding deuterium oxide. This r eagent was added by m eans In connection with a projec t on th e measurem ent of a hypodermic sYTinge through a n eoprene septum of precise physical properties of hydrogen is? topes, held in a fitting attach ed to the taper ed joint, C. it was found n ecessary to prepare abou t 10 lIters of It was found that the sep tum could be punctured high-purity hydrogen d eut ~r i d e.. This substance several times without danger of admitting air to the had b een prepared for th e first tIme by Scott and system . This rendered it po sible to add the deu­ Brickwedde [2 , 6] l by passing a mixture of hydrogen terium oxide in several portions, ther eby diminish­ and deuterium over a h eated metal filamen t, fol­ ing th e vigor of th e r eaction. lowed by fractionation at liquid hydrogen tempera­ In addition to tb e m ethod for adding deuterium ture. The equilibrium mixture after conver~ lOn oxide, the apparatus of Dibeler was furth er modified contained about 50 mole per cent hydrogen deutende, by the inclusion of a magnetic sti.:rrer in th e flask, D; as would be anticipated from the equation this was operated by a rotating magn eti c field out­ sid e th e flask . The crude hyeh'ogen deuteride was di stilled in th e apparatus shown in figure 2. This is, wi th minor modificat.ion s, the apparatus used by Scott and Brick­ for which the equilibrium constant is about 4 [5]. wedde [2 , 6] in their work; this tecbnique has not MLxtures containing a high per centao-e of hyd!'o­ heretofore been publish ed.2 The still, A, consi ted gen deuteride have also b een prepm·?d by th e. actJOn of a jacketed boiler of abou t 5-ml capaci ty and monel of deuterium oxide or water on vanous hydrIdes or h elLx rectifying section, B, a r e-entrant portion, C, deuterides, r espectively . These method.s give, i.n wbich erved as a cold-finger depblegmating con­ general, higher yields of hydrogen deu tende th ~n IS denser , and a take-off tube, E , which was connected obtainable by equilibrating hy(irogen and deu ter-mID. to th e top of the still by means of a U-tube, D . The Thus, Norton [5] treated boron hydride, B 2H 6, with liquid was boiled by means of an electric h eater, F , deuterium gas to ob tain the deu tm:ated product, of constantan wire, the leads of which ran up the B 2D 6• The latter , wh en treated WIth 83-peJ'cent still and emerged through a vacuum-tight wax seal, sulfuric acid r eacted with th e water presen t to G. The still was immersed in a Dewar flask of liquid yield a mLxt~·e of hydrogen isotopes containing 85- hydrogen, th e level of which was maintained at percent hydrogen deu t erid ~.. . . abou t th e position illdica ted in th e drawing. This Similarly, lithium hydnde \ ~Ith deu tenum oXld e D ewar was in tUTn immersed in another D ewar con­ h as b een used to prepare ennch ed hydrogen deu­ taining liquid nitrogen (not shown in the ill·awing). teride [1] . With sodium hydride, 87-pel'?en t ~1J ?:ro­ The still was connected through a ground glass gen ~ eut erid e ~ s ob tainable [7l, an ~l WI th l ItIuum joint to a regulator valve, H , th e.nce t o a graduated alummum hydnde and d?uteI'lum oXlde at 0 C, 93- Toepler pump, J , of 500-ml capacIty. The regulator percen t hydrogen deutende h::s been prepared [fl . valve consisted of a len o-th of thin ell·ill rod brazed For the purpose at hand, whICh r eqUlres hydrogen to an iron core. The ill·ill rod fi t with little clearance deu teride containing no more than .several ten ths into a length of heavY-'walled capillary tubing, and per cent of impurities, the last-ment:oned r eactlO? was movable within this capillary by m eans of the suggested itself as the most appr?pnate . . In addI­ solenoid, K . By thereby varying the length of tion to furth er purify the materIal ob tamed from annular space between the ill'ill rod and tube wall, this'reaction, the fractionation technique of Scott the rate of flow of gas from the still to the Toepler and Brickwedde was employed. pump was easily controlled. The pressure in the still was indicated by a manometer ; by adjusting II. Apparatus thE' levels in the Toepler pump by means of the mer­ CUTY reservoir, M, to a preSSUTe less than that shown The " crude" hydrogen deuteride was prepared !n on the manometer, gas could be caused to flow from th e apparatus described by Dibeler [4], shown m 2 Clusius and Starke [3] bave recently described a similar procedure. Tbis t Figures in brackets indicate the li terature references at the end of tbis paper. was developed subsequent to, and independent of, Scott and Brickwedde. 31 VAC UUM

The rubber septum-retaining device was fitted to the flask, at 0, and the latter attached to the con­ denser, E. The reaction mixture was frozen by means of a VACUUM liquid nitrogen bath, the system evacuated, and the reaction mixture heated until it boiled under its own vapor pressure. After 1% hours, the flask was again cooled with liquid nitrogen, and the system re-evacu­ ated. By means of a hypodermic syringe, 5 ml of deuterium oxide (99.5-percent purity) was added to the solid reaction mixture. The latter was per­ mitted to melt, and the gas evolved as a consequence of the ensuing reaction was eollected in two 5-li tel' collecting bulbs attached to a manifold at I. During this operation, the mixture was being stirred continu­ ously. Due to its low temperature, the outside of the flask quickly accumulated a layer of frost. Whenever this began to melt, the liquid nitrogen bath was applied; in this manner, the reaction temperature was kept at 0° C or lower . o During the course of the reaction, deuterium oxide was added two more times, to make a total of 18 ml of this reagent added. This quantity was about FIGURE 1. Apparatus used in prepamtion of hydrogen 150 percent excess over that required to make 10 deuteride. liters of gas as calculated from the above equation. This drawing is identical with t bat rel)roduccd in V. H . Dibeler's paper [4] . It was found desirable to use this excesss in order to the still to the Toepler pump at a rate determined preven t the reaction from becoming too sluggish as by the pressure difference and the setting of the the reagents were consumed. regulator valve. After each run was eompleted, a sample was with­ The Toepler pump was connected to a manifold, drawn from the collecting bulb by means of the N, and from there to a mercury diffusion pump. Toepler pump, and added to an evaeuated sample The manifold was fitted with a number of ground tube. These samples were subsequently analyzed glass joints, to which sample tubes, receiver bulbs, or mass spectrographicall y t.o determine purity of the bulbs containing charging stock could be attached. hydrogen deuteride. This was found to be 98 .1 The general pract.ice was to use the charging bulbs and 97.0 percent, respectively, for the two batches as receivers, after the material they contained had prepared. been added to the still and the residual gas removed by the vacuum pump. IV. Distillation of Hydrogen Deuteride III. Preparation of Hydrogen Deuteride Since about 935 ml of hydrogen deuteride gas at Since 10 liters of high-purity hydrogen deuteride 20° C is equivalent to 1 ml of liquid at the boiling were required, this could readily be obtained by point of hydrogf'n, 20. 34° K , one 5-liter bulbfull distillation from 15 liters of crude prepared by the of the crude as prepared was used as a convenient m ethod of Wender, Friedel, and Or chin [7] (lithium charge for each distillation. The entire 15 li ters aluminum hydride and deuterium oxide at 0° C). was therefore distilled in three batches, of which only Generous allowance could then be made for losses one will be described in detail. incurred during handling and distillation. The collecting bulb, S (letters in this section refer Accordingly, 15 liters of hydrogen deutride were to fig. 2) containing the charge at atmospheric prepared in two runs, of 5 and 10 liters, respectively, pressure was attached to the manifold, as shown, and of 98 .1- and 97.0 percent purity. Since both batch es the entire system evacuated by means of a mercury were prepared in the same manner, only one will be diffusion pump. The Dewar flasks sUlTounding the described. still were filled with liquid hydrogen and liquid Into the Claisen flask, D (letters in this section nitrogen, stopcock R was closed, and stopcocks refer to fig. 1), there was distilled about 150 mlof U, 0, P , and Q opened; the regulator valve, H , was n-butyl ether, which had been previously dried and also opened wide by means of solenoid K. The distilled from sodium. This was followed by 5.75 g contents of S were thereby permitted 0 flow into of lithium aluminum hydride, the addition of this the still, where condensation occurred on the con­ reagent being carried out in a nitrogen atmosphere. denser surface, O. After about 1 hour, the jacketed This quantity of lithium aluminum hydride was 40 portions of the still had cooled sufficiently to permit percent in excess of that required to prepare 10 liquid to begin accumulating in the boiler. The liters of gas, as calculated from the equation Toepler pump was then used to withdraw the remain- 32 G "" 700 I E Q E 600 w- E a: ~ 500 if) w D a: ~ 400 S --' >= if) 300 0 1000 2000 3000 4000 VOLUME DISTILLED, CORRECTED TO 760 mm Hg

F I G URE 3. Distillation CUTve oJ hydrogen deuleride. '[ TO MERCURY B RESERVOIR concern; what was of interest during the disLillation was its variation. As can be seen from figure 3, the pressure-volume distilled curve for this distilla­ FIG L' RE 2. Appamtus used for pW'ification of hydrogen tion, the bulk of the distjll ate was removed at 478 to deuteride by fmctional distillation. 480 mm. The press ure at any time was influenced by the level, E, of liquid hydrogen, the take-off rate at that moment, the ambient temperature, and Lhe ing gas from S and to force it in to the still ; this last rate of boiling. operation was continued until the preSS lU"e in the During the co urse of the distillation it was neces­ bulb as read on the manometer (s topcock Q closed), sary to adjust the reg ulator valve several times and was 50 mm. It was not consider ed practical, with to determine the proper pressure in the Toepler regard to the amount pumped for the time con­ pump, in order to achieve the desired refilL,( r atio. sumed, to attempt to reduce the press ure any lower. The heat of vaporization of hydrogen deuteride is Stopcock P was then closed, and a current of 71 257 cal mole- I at its boiling point, 22.54° Ie [8] . ma permitted to flow through the heater, F. This Since the heat input was 0.033 cal sec-I, the boil-up current was controlled by means of a variable rate was 185 ml min - \ at 20 ° C and 760 mm. The transformer ; since the heater had a resistance of take-off rate was observed by noting the amoun t 27 ohms, it was equivalent to a heat inpu t of 0.136 withdrawn in the Toepler pump, and the time taken watt, or 0.033 cal/see. The charge was thus caused to withdraw it. From these figures, the reflux ratio to boil under total r eflux, and, as the hydrogen was calculated. Because of the nature of the adj ust­ present in the still was concentrated in the head as a ments necessary to the operation of the still (as the consequence of fractionation, the pressure indicated mercury level in J fell, th e leveling bulb, M , had to on the manometer rose from an ini tial value of be periodically lowered to maintain approximately 447 to 531 mm. This rise occ urred in about 45 min the same head), the reflux ratio was variable. Dur­ and did not increase thereafter . (Had there been ing the withdrawal of the pure hydrogen deuteride sufficient hydrogen in the charge, the press ure at fraction , this quantity ranged from 9.3 :1 to 26.5 :1, equilibrium shou ld have been about atmospher ic, with an average of 13.7:l. or somewhat greater due to the fact that heat was In the distillation described above, the charge was being introduced.) equivalent to 4,600 ml of gas, at 20° and 1 atm. During t hi s time, stopcocks R, U, and 0 were open, There was distilled 3,580 ml, of which 390 ml was evacuating the Toeple!' pump and the bulb, S, forerun, 2,850 ml pure hydrogen deuteride, and the for use as a receiver. Other, smaller, bulbs were also rest holdup. The volumes of the fractions were on the manifold, to be used as forerun and residue obtained by summing the volumes of gas discharged receivers; these are not shown in figure 2. from the Toepler pump and correcting to 20 ° C and When equilibrium had beell reached, as indicated 1 atm; these values arc plotted on the distillation by co nstancy of pressure, the r eg ulator valve was cmve, figure 3. Upon completion of the distillatio'l, adj usted to about half-open, stopcock 0 was closed, the pressure in the bulb containing the pure hydrogen and stopcock P opened. The merclU"Y levels in J and deuteride was measured on the manometer. The M were adjusted so" that the pressure in the Toepler corrected volume as calculated from this figure was pump was about 160 mm less than that in the still. 3,080 ml. It is believed that this value is more Take-off of distillate was thereby begun. reliable than that obtained by summing the Toepler Each time the bulb J filled, stopcock P was closed, pump fractions, sin ce the latter undoubtedly contain stopcock 0 was opened, and the contents of the cumulative errors. Toepler pump were discharged into the appropriate The distillation was continued until the boiler rece iver . The points at which fractions were to be and the lower coils of the fractionating section were cut were determined by the pressure indicated on dry. This left a holdup of about 1 liter of gas, since the manometer. This pressure was approximately with such a small amount of material fractionation the equilibrium pressure of the distillate at the con­ was impossible in this still. The forerun and holdup denser temperature. Its absolute value was of little of the distillation were discarded.

9:~88G I - H- :; 33 A sample of the main fraction was analyzed by V. References means of the mass spectrometer, and was shown to have a purity of 99 .S-percent hydrogen cleuteride, [1] H. Beutler, G. Brauer, and H. C. Junger, Naturwissen­ disregarding a small percentage of nitrogen. The schaften, 2!l, 347 (1936). [2] F. G. Brickwedde and R. B. Scott, Phys. Rev. 55, 672 remainder of the crude hydrogen deutericle was (1939). distilled in the manner described herein, and yielded [3] K. Cl, and K. Starke, Z. Naturfol'sch !la, 549 (1949). material of about the same purity. [4] V. H . Dibeler, J. Research NBS H, 363 (1950) RP 2083. [5] F. J . Norton, Science 111,202 (1950). [6] R. B. Scott and F. G. Brickwedde, Phys. Rev. 48, 483 The authors express their appreciation to V. H. (1935) . Dibeler, whose apparatus was used in the preparation [7] 1. Wender, R. A. Friedel, and :'11. Ol'chin, J . Am. Chem. of the crude hydrogen deutel'ide, and who performed Soc. 71, 1140 (1949) . the mass spectrographic analyses reported in this [8] H. W. Woolley, R. B. Scott, and F. G. Brickwedde, work. Thanks are also due R. B. Scott and W. E. J. Research NBS 41, 379 (1948) RP 1732. Gifford, who assisted in the distillation described in this paper. WASHINGTON, November 29, 1950.

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