LETTERS To the Editor: A program for the computation of the roots of a HMO secular determinant and the coefficients of the corresponding eigenfunctions has been written for the smaller IBM computer such as the 1620 and the 1401. The nature of the Fortran used is such that the source deck could he processed with little or no modification on any suitable computer. The maximum size of the molecular system which can be handled depends upon the available internal storage, and one dimension card in the program specified this. I n the case of a 20k 1620, the maximum is 12. The program is ideally suited for classroom use in the teaching of HMO theory. The input follows directly from the secular determinant written in standard form and the output eigenfunctions are numbered according to the input numbering scheme. Problems may be run consecutively with each having an identifying heading. A report with the above title containing a program listing and an input-output description is available; it may be obtained by writing Rev. George C. McGregor, O.P., Director, Computing Laboratory, this college. E. R. BOYKO and G. A. WHITTAKER COLLEGE PROVIDENCE PROVIDENCE. RAODE ISLAND To the Editor: Two recent comments on the limitation of the Hinsberg method for primary amines by P. E. Fanta and C. S. Wang [THISJOURNAL 41, 280 (1964)l and W. C. Stickler [THIS JOURNAL 41, 515 (1964)l appear to place unwarranted emphasis on a n alleged error in modern texts. Perhaps, in regard to the Hinsherg technique, the error is one of omission rather than a bold misstatement of fact. If the sole criterion for a positive Hinsberg test for a primary amine is complete solubility of the sulfonamide in dilute alkali, then the method is substantially limited in scope. Triethyl* mine, benzenesulfonyl chloride, and dilute alkali eventually give a clear solution due to the solubility of the amine and the sulfonyl chloride, not because of any sulfonamide formation. However, even partial solubility should be suggestive of a primary amine, and the simple expedient of acidifying the filtrate of the reaction mixture to precipitate the sulfonamide would indicate a positive test. Again, even this simple suggestion is fraught with danger, especially with the student in a first year course. Too many times have we seen a precipitate of sodium chloride mistaken as a sulfonamide of a primary amine. The student should always be cautioned to dilute the result of any oeutralization reaction to obviate the presence of an inorganic salt precipitated by common ion effect. Even the modification of the Hinsberg test suggested 48
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by F. 0. Ritter [THIS JOURNAL 29, 506 (1952)j can give erroneous results. The use of a large excess of amine does minimize the formation of disulfonyl derivatives of primary amines but also minimizes the sulfonylation of all amino functions in a poly-amine. Ethylenediamine fails to give a positive test for primary amine by this method due to the solubility of the monobenzenesulfonamide in the hydrochloric acid used to remove excess amiue from the reaction mixture. Fanta and Wang report the insolubility of the benzenesulfonamide of cyclohexylamine in dilute sodium hydroxide but we have found just the reverse. Since solubility is a relative phenomenon, no doubt the ratio of solute to solvent (not mentioned in their paper) is to be considered. I n the same vein many textbooks offer the insolubility of the phenylalkylamine sulfonamides as a limitation of the method. We have had the opportunity to prepare a few of these compounds up to a five-carbon side chain and have found all to give a positive Hinsberg test (partial solubility of the sulfonamide, as evidenced by regeneration of the sulfonamide on acidification of the alkaline filtrate). I n fact, whereas the sulfonamides of benzylamine and phenethylamine are purported to be insoluble in dilute alkali we have found just the opposite to be true and they are completely soluble in 5% alkali. I would suggest that the textbook author not be chastised too severely for omitting some or all of the limitations of a chemical test for a particular functional group. To even attempt to include all of the possible traps, modifications, limitations, and adaptations would no doubt generate a volume equal in size to the original text. Because there are so many exceptions to a functional group test, this should emphasize the fallacy of depending upon one test to establish clearly the presence or absence of a functional group. It behooves the reader of the text and the teacher to realize there is no simple, all-inclusive functional group test. A. R. GENNARO PHILADELPHIA COLLEGE OF PHARMACY AND SCIENCE PHILADELPHIA, PENNSYLVANIA
To the Editors: Your readers may be interested in learning of a simple method by which the effectiveness of magnetic stirring bars may be greatly improved in solutions which contain an undissolved solid soch as sand or which must he stirred a t a constant rate (as in polarized electrode titrations). The tendency of Teflon or glass covered magnetic stirring bars to jump or rock back and forth in the above cases results in irregular stirring rates. This irregularity can be avoided simply by drilling a hole in. smaller than the diameter of the covered stirring bar in the center of a short piece of Teflon rod '/% in. in diameter. Slicing off '/la in. of the drilled-out rod yields a small Teflon ring. If two such rings are forced onto a covered stirring bar, about in. from each end, a stirring bar "on wheels" results, which produces a constant rate of stirring even when the bottom of the beaker is nearly covered with coarse crystalline solids. CURTISE. UEBELE UNIVERSITY OF KANSAS KANSAS LAWRENCE,
