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.
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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.
