0-
3
-““-0330 HEAT
Figure 1. chamber
Molecular
uc
CLLII*T
distillation
of the joints is welded on opposite sides of the chamber. I n operation, the material in a solvent is transferred to the dish and the solvent is completely evaporated. The dish is placed on the steel grid in the chamber. The condenser is connected,
the trap and condenser are refrigerated with d r y ice and acetone, and the system is evacuated to a pressure 5 X 10-6 min. of mercury or lower. Initially the pressure measurements must be the same on both the McLeod and ionization gages. The ionization gage measures condensable as well as noncondensable gas pressures, while the NcLeod gage measures only the noncondensable gas pressures. This is important because the “base line,” or residual pressure, must be known so that the rise in pressure during distillation, as measured by the ionization gage, is the vapor pressure of the distilling substance at that temperature. The pressure measurement on the McLeod gage remains constant (base line) throughout the distillation. After the base line pressure has been attained (0.5-half to 1 hour), a definite amount of energy is supplied, as heat from the resistance heater. The energy is related to the voltage, which is controlled by B variable transformer. The temperature will, over a period of time, rise to a maximum. During this period the pressure \Til1 increase and then gradually drop back t o the base line pressure. The didillate collected during this cycle
is considered BS a fraction. The chamber is cooled with a blast of air, and the system is brought back to atmospheric prcssure. T h e condenser is removed, and the distillate is dissolved off the cold finger with a solvent, generally ether, and is ready for further examination by other means. The compound or compounds distilling for a given amount of energy are within limits of a definite molecular weight range. The next fraction will be a repeat of the cycle, but with a greater energy input. As the differences of the molecular weights in a mixture of compounds increase, the apparatus is able to perform sharper separation and greater purification of the compounds. The organic particulate matter froin air-borne pollutants n-ere distilled in the manner described above. The mixture was knon-n to contain aliphatic and polynuclear hydrocarbons. The distillates n ere characterized by ultraviolet spectra. From this mixture, distillates were obtained which, on the basis of ultraviolet absorption spectra, were benzpyrene and coronene in their pure states.
Sapphire-Windowed Spectrophotometer Absorption Cell for Use with Corrosive liquids Elliot Raisen,l Propellants Laboratory, Bell Aircraft Corp., Buffalo 5, N. Y. EAR-INFRARED
The assembled cell is shown in Figure
analysis for water in
N fuming nitric acid according t o the method of White and Barrett [ K h i t e
L., Jr., Barrett, Jv. s., A I ~ A LCHEhl. . 28, 1538 (1956)l has been used in the Bell Aircraft Propellants Laboratory for some time. Although not as accurate as titration, its relative speed and simplicity make it a very useful procedure. A change in analytical procedure was necessitated v h e n the practice of adding a corrosion inhibitor, hydrofluoric acid, was adopted. The hydrofluoric acid \\-as removed by reaction with soft glass beads, making it possible to continue to use a glass absorption cell. The procedure was impractical, because of the excessive amount of time required for the reaction with the glass beads, and the difficulty of obtaining a clear sample due to the presence of a precipitate of silicic acid. Therefore, a cell was designed which could be used in the presence of fuming nitric acid and hydrofluoric acid and n hich would not require any alteration of the Beckman DU spectrophotometer. The cell, howel-er, may also be used with other instruments that have similar cell carriers-e.g., Beckman DK, PerkinPresent address, Physical Chemistry Sertion, Armour Hece irch Foundation of Illinois Institute of Teciiriology, Chicago, Ill.
1. Construction details are given in Figure 2. T h e gaskets are placed be-
tween the windows and the spacer. The ground surfaces of the frames are placed against the n indow.
Figure 1.
Assembled cell
Elmer spectracords, and Cary spectrophotometers. The cell consists of a stopper, and sapphire windows. Although rather expensive, the sapphire FTindows are an excellent choice, because they are virtually impervious to attack by strong acids (including hydrofluoric), and strong bases, and have optical and physical properties which are slightly superior to those of quartz. If the cell is not subjected to strong alkali or hydrofluoric acid, quartz or glass windows can be used with a resultant saving in cost.
To become familiar n-ith the assembly procedure, and to avoid breakage of the expensive sapphire TT indows by excessive tightening of the screws, the cell should first be assembled using glass nindows. The glass n-indows can be readily cut from a microscope slide. Tighten the screws evenly to a finger-tight pressure. Then fill the cell with acetone to check for leakage. If the seal leaks, remove acetone, loosen the s c r e m slightly, dry with air or nitrogen, retighten the screws, and test again. Repeat this procedure until the tension of the screns is sufficient to form a leakproof seal. Because of the low surface tension and viscosity of acetone (and of fuming nitric acid) the screws must be fairly tight. With other solvents-e.g., n-ater, methanol, etc.-the cell can usually be made leakproof on the first attempt. Primarily because of minor nonuniformity of the sapphire, the cellr should be calibrated against a standard. The calibration should be checked after reassembling a cell. A medicine dropper with a long, thin tip is used to fill and empty the cell. Because nitric acid attacks rubber, and VOL. 31,
NO. 3, MARCH 1959
485
hydrofluoric acid attacks glass, a polyethylene pipet with a Tygon bulb was fsbricated. A piece of polyethylene tubing I/* inch in internal diameter and 1/16-inchwall was heated in a flame and drawn down to form a tip approximately 1 mm. in diameter and 5 inches long. The tubing must be held under slight tension until it cools. The large end of the tubing was flared by heating and pressing against a flat surface. The bulb was made b y heating the center portion of a 5il6-inch internal diameter, l/la-inch wall piece of Tygon tubing 3 inches long and holding it clamped until it cooled. The sealed portion was then cut to form two bulbs. Each bulb was pressed onto the flared end of a pipet. Blthough the use of nitric and hydrofluoric acids presents a severe corrosion problem, two of these cells have been in continuous use in this laboratory for approximately 3 years and have rendered excellent service with no noticeable corrosion. Four more cells h a w since been fabricated. ACKNOWLEDGMENT
The work described was supported by a USAF contract. Thanks are due to William L. Clark, Henry Heubusch, Leon Olender, Thomas F. Reinhardt, Robert Schnitzer, William Sheridan, and John C. Tynan of Bell Aircraft Corp. for their aid, and to the Armour Research Foundation for providing the time to prepare the manuscript.
flf:j+ I
500
T p00-d
i
.
820
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039
4
n - v
Figure 2.
250C
Construction details
A.
Frame, holes threaded with a 4-48 National fine thread Spacer, determines length of light path. Screw holes are 0.1 25 inch in outside diameter. Filling hole is 0.125 inch in outside diameter, tapered to 7/64 inch. The wide depression in the top acts as a reservoir to prevent spillage of the corrosive samples C. Frame, holes are 0.1 25 inch outside diameter, countersunk on outside surface D. Teflon gaskets, cut with a razor and straightedge from a 0.005-inch sheet of Teflon. Whenever the cell is disassembled new gaskets should be used E. Sapphire windows, obtained from Linde Air Products to the dimensions shown, polished on both sides, and flat to within 0.0003 inch F. Teflon stopper, formed on a lathe from a Teflon rod l/, inch outside diameter. Tapered to fit the filling hole in B G. Screws, four flathead No. 4-48 National Fine 2B screws made of 347 stainless steel are required A, B, and C are mode of 347 stainless steel. Both surfaces of B, and the inside surface of A and C are ground flat to within 0.0003 inch. In addition, the faces of B are parallel with each other within 0.001 total indicator reading. This degree of flotnesr is required to form a seal, and to prevent breakage of the windows when the screws are tightened.
B.
Detection of the Ferrocene Nucleus in a Complex Reaction Mixture Stanley I. Goldberg, Materials Laboratory, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio
I
n the preparation of ferrocene or dicyclopentadienyl iron(I1) derivatives from substituted cyclopentadienyl intermediates, indication of the presence of a ferrocene compound in the crude reaction mixture is desirable before undertaking a work-up procedure. Although all ferrocene derivatives are colored, color is not necessarily indicative of the presence of a ferrocene compound, for a complex reaction mixture is itself usually colored. A simple, fast, diagnostic test depends on detection of iron(II1) on a paper chromatogram by appearance of the characteristic red iron(II1) thiocyanate complex. A sample of the crude reaction mixture is spotted on a paper strip and dried as in the preparation of a paper chromatogram. Any filter paper and any method of development (ascending, descending, or circular) is applicable. The chromatogram is developed with benzene in a closed chamber, and the 486
ANALYTICAL CHEMISTRY
solvent is allowed to proceed about 10 cm. along the strip. The developed chromatogram is dried, sprayed with a fresh solution of hydrogen peroxide, and redried in a stream of air. Treatment with hydrogen peroxide destroys the ferrocene nucleus through oxidation of iron(I1) to iron(111). An aqueous solution of sodium thiocyanate is applied to the dried paper strip as a fine spray; the appearance of a deep-red spot or band, due to the formation of the iron(II1) thiocyanate complex, indicates the presence of the ferrocene nucleus in the original reaction mixture. A deep-red spot a t or near the originof the chromatogram is not to be taken as a positive test, for it may have originated from the carryover of iron(I1) and/or iron(II1) salts present in the crude reaction mixture. This test has proved very useful in this laboratory, particularly when a desired ferrocene product is present in very small yield. It is, however, limited t o reaction mixtures in which a
ferrocene nucleus is to be formed, and where ferrocene or substituted ferrocenes are not used as starting materials. The paper chromatography system described is adequate for detecting a ferrocene compound, but not for paper chromatography in which R, values are t o be measured. Ferrocene compounds, when chromatographed on untreated paper with a single solvent such as benzene, usually flow with the solvent front or give rise to high R/ valuesgreater than 0.9. This procedure, therefore, is not recommended for measnrement of RI values or separation of ferrocene derivatives. It is useful only for detection of the presence of the ferrocene nucleus. ACKNOWLEDGMENT
The aiithor thanks Gunter Zmeig, University of California, whose helpful suggestions gave rise to the development of this diagnostic test.
