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To the Editor:
We wish to comment on a useful addition to the experiment by R. E. Bozak and C. L. Hill, "Synthesis of Tetraphenylporphrin: A Convenient Undergraduate Organic Lahoratory Experiment," [J. CHEM,EDUC.,59,36 (1982)].The synthesis described in that paper is relatively simple and straightforward and, therefore, readily adaptable to various laboratory courses. However, the Bozak and Hill experiment may he made much more valuable through a simple addition to the original experiment. This addition, which does not take too much time, is tocarry the experiment a little further-to the synthesis of a metalloporphyrin. The addition is a modification of the work reported by Adler, e t al., [J. Inorg. Nucl. Chem., 32,2443 (1970)l. A solution is made by dissolving 1g of meso-tetrapbenylporphrin in 100 ml of N,N-dimethylformamide. T a k e c a r e not t o breathe t h e vapor o r to get t h e liquid reagent o n the skin. Dimethylformamide is a n irritant. This solution is heated to reflux. T o the refluxine solution a solid salt of a divalent metal is added (0.0016 moij in twoor three portions and heatinr cmtinued for an additional I5 min. The solution is then allowed to cool, first in air and then for 15 min in an ice hath. Next, 100 ml of cold water is added to the solution and it is filtered on a Biichner funnel (the filtration may need to be repeated). The solid is then washed with water and air dried. The yield is typically greater than 90%.The metal salts that we used were the hydrated acetates of zinc, copper, nickel, and cobalt; however, other salts such as the chlorides should also work. The effect of the metal upon the porphyrin can he easily examined in two ways. One change caused by the metal is the loss of the red fluorescence of the free porphyrin under longwave ultraviolet light. This phenomenon has been used to follow the metal insertion reaction described above (thereaction is complete when the fluorescence disappears). The second change occurs in the visible spectrum. The free porphyrin has a very intense hand (the "Soret" hand) a t 417 nm and four weaker bands at 514,551,591, and 648 nm. In the metalloporphyrins the Soret band is retained, but only two bands are observed in the longer wavelength region. M. S. Maitland University of Wisconsin-River Falls River Fails, Wi 54022 A. H. Langley Stephen F. Austin State University Nacogdoches, TX 75962
Simplest Formula for Copper Iodide To the Editor: I wish to comment on the paper, "Simplest Formula of Copper Iodide: A Stoichiometry Experiment," D. J. MacDonald, [J. CHEM.EDUC.,60,147 (1983)l. My views on this topic were expressed at some length in my 152, 367 (1975)l. In short, we own paper in the JOURNAL should no longer attempt to "prove" the Law of Definite Proportions with non-molecular inorganic solids, especially those which contain elements which exhibit multiple oxidation states. The results obtained by MacDonald's students for n in CuI, averaged 1.02, with a large standard deviation of 0.16. Assuming normal distribution, this means that 68% of the students reported formulae over the already very wide range 18 and that fully 32%reported even wider ranging CuIoSG-CuI~ results. Such results do indicate that the compound is closer to Cul than to C u b hut not a t all that CuI is stoichiometric. If we can assume that the students performed their work 566
Journal of Chemical Education
carefully, it would appear that it is more proper to interpret the results in terms of nonstoichiometry. In cases where n in CuI, is greater than 1 (and even the average formula is C U I ~ . some ~ ~ ) ,Cu2+may be presumed to he present, and this would be expected to make the material a semiconductor. Lawrence Suchow New Jersey Institute of Technolagy Newark College of Engineering 323 High Street Newark. NJ 07102 Solubility of Mercury To the Editoc In the article on "Mercury"in Chemical of the Month on p. 971 of the November 1982 issue of JOURNAL OF CHEMICAL EDUCATION, authors Kumar and Tate state that "mercury is soluble in both polar and non-polar liquids." This statement though true is misleading. Theoretically, any substance is soluble in any liquid. The question is "how soluble?" Cotton and Wilkinson state that mercurv is surorisinelv .. . soluble in both polar and non-polar solvents. However, they give as an exarnule the solubilitv of mercurv in water as 0.000U00639 e I-' which, though higker than some might expect, is still ver; low and hardly justifies the above statement by Kumar and Tate, particularly in the context of a secondary school audience. Incidentally, in view of the low melting point of mercury, what is so surprising about the fact that mercury is slightly more soluble in liquids than many other metals are? Harrv H. Sisler Distinguished Service PTofeSsOr of Chemistry University of Florida Gainesvilie. FL 32611 Possible Existence of Cesium Neonlde To the Editor: I was interested to read the article by Blake and Clack1 concerning the possible existence of cesium neonide. They are, however, wrong to suggest that there has been no consideration of the possible existence of compounds of the nohle gases with electropositive substances, as it is almost ten years since I published an article in the School Science Reuiew2 on the possible existence of anionic xenon. Interest had been aroused by a casual question from one of my students, and in a subsequent discussion we used a Born-Haher Cycle to estimate a value for AHre and for ACf' for cesium xenide. Electron affinities for the nohle gases were not a t that time available to me, and we used a figure based on a rather dubious extrapolation procedure. Moreover, because my students were in a secondarv school we used a rather less sophisticated aDproach to arrke at an estimate for the lattice energy of cesium xenide (by assuming it would he very similar to that of cesium iodide). Nevertheless, we came to very similar conclusions to Blake and Clack: that the experience was very motivating for the students concerned and the compound might in fact he stable. I subsequently incorporated some of the ideas in a small hook of questions which I p u b l i ~ h e d . ~ We did not, in a school, have the facilities to attempt to synthesize noble gas compounds, but I hope somebody will rise to the challenge.
' Blake, P. G. and Clack, D. W., J. CnEM. Eouc., 59,637 (1982).
Borrows, T. P., Sch. Sci. Rev.. 55,334 (December 1973). Borrows, T. P., "A Level Chemistry Structured Questions,"Blackie. Glasgow, 1978. T. P. Borrows Pimlico School London SWlV
LUPUSStreet 3AT. England
