we would all agree that the answers to these two qnestions would add up to a comprehensive and rigorous course. For a group of students in a two-year health curriculum, on the other hand, the answers to these two questions would require something quite different. Here the content of the course would be determined by the needs of the students to learn enough about chemistry (including some topics from organic and biochemistrv) ". to enable them to make sense of the other courses in their crowded curriculum. Referring to such a course as "watered-down" obscures the problem and is an affront to the student.
Prediction of Periodic Acid Oxidation Products
To the Editor: Dr. Allen M. Schoffstall's note [J. CHEM.EDUC.,48, 736 (1971)] indicates that the products of periodic acid oxidation can be predicted using the rule that "the oxidation state of a carbon atom is increased by one for every carbon-carbon bond broken at that atom." An even simpler approach, which does not require calculation of oxidation states, is simply to retain in the products the number of hydrogen atoms originally bonded directly to each carbon atom in the reactant. After cleavage, each carbon atom is loaded up with as many singly-and doubly-bonded oxygen atoms as are required to form stable products. Comparison of this procedure with Dr. Schoffstall's, using his examples, reveals the same predicted product mixtures.
Modincation of TLC Analysis of APC
To the Editor: I n adopting the tlc experiment, "Analysis of APC Tablets" [J. CHEM.Educ. 48, 478 (1971)l for an engineering level general chemistry course we experienced a difficulty; our solution may he of interest to others. We inferred from the article that nearly any uv source can be used for the visualization of the separated components. In our case we borrowed a "hohbiest type" uv lamp which we discovered produces almost exclusively longwave uv (365 nm). Our students are using of a sheet of Eastman 6060 Silica Gel tlc plate clamped to a glass plate. On this surfacethe separated components are visible only under short wave uv (254 nm) light. I suspect that the lamp the author describes generates the shorter wavelengths although no statement is made about its frequency. In our case a borrowed short-wave uv light has produced easy visualization of an interesting experiment that demonstrates nicely the tlc separation technique.
Nitrenes
To the Editor: My recent review, "Nitrenes" (July, 1971) contains some overgeneralizations which could lead to incorrect or misleading conclusions about nitrene reactions (1) Of the three reactions shown in Figure 1, only path a is firmly established [LEWIS,F. D., AND SAUNDERS, W. H., JR; in "Nitrenes" (Editor: LWOWSKI, W.), Interscience, New York, 1970, p. 561. (2) In Figure 2, it should he noted that substitution processes are often important with aromatic substrates in addition to the additive ring expansion shown. (3) Several of the processes involving sulfonyluitrenes which are implied to occur have, to date, not been observed or only observed in special cases or occur by non-nitrene mechanisms, e.g., photolytic generation of sulfonylnitrenes from sulfonylazides, addition of sulfouylnitrenes to olefius, and reaction of sulfouylnitrenes with amines and alcohols. I wish to express my thanks to Dr. Evan P. Kyba for pointing out these overgeneralizations to me.
Lead Poisoning Danger in Pencils
To the Editor: An item which merits the attention of teachers and parents, particularly those of young children, appeared in the January 1972 "Special Education Newsletter" of the National Catholic Education Association. Lead paint poisoning, which the report states now affects 400,000 children per year, leaving 4000 with moderate to severe brain damage, has been found to be a threat to a larger segment of the population than previously supposed. Prior to the 1950's most interior paints contained leaded pigments and were a source of poisoning to young children fond of chewing on furniture and woodwork. Even now, when many household paints on the market no longer contain lead, the prohlem remains, particularly in older homes or in substandard dwellings where the years' accumulation of paint still flakes off in the thick chips. I n the past few years as a counter-measure many cities have introduced mass testing programs, especially in inner-city areas, to detect lead poisoning in children. Relatively unnoticed until the present, however, the paint on many brands of wooden pencils on the market contains lead in as high a concentration as 30y0! (Particularly suspect are yellow paints, in which lead chromate is a common pigment.) This report comes as the result of two studies recently undertaken by the Washington, D.C. Department of Public Health and the New York City Bureau of Lead Poisoning Control. Lead is a particularly nasty poison in that much of the amount taken into the body remains there to accumulate during the lifet.ime of an individual. (In this respect and in many of its effects lead behaves like mercury, which still is receiving the greater share of attention by the media.) Ordinarily more than 90% of the Volume 49, Number 5, May 1972
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body's burden of lead is concentrated in the bones; the substance is readily mobilized, however, during periods of high-calcium metabolism, such as during feverish illness. Relatively little lead transferred to the soft tissues, notably to the brain and nervous system, the blood, and the kidneys, can produce severe or even fatal damage. Children in the under-five age bracket are especially susceptible. Acute poisoning by lead is rather easily recognized by physicians. The more common chronic cases, however, can be marked by vague symptoms easily confused with common lethargy, learning difficulties, or simple nervous disorders. Vagueness, however, does not imply insignificance. The matter of lead-painted pencils is a most serious one. Anyone with even a casual familiarity with the classroom can attest to the high incidence of pencil chewing among young children. An official of HEW'S Maternal and Child Health Services has stated that children three years of age or under should ingest no more than 300 pg of lead per day. (The air we breathe and the food we eat contribute to this daily total.) A child eating just one milligram of paint, an amount equal in weight to about one thousandth of an aspirin tablet, would receive 300 pg, if the paint contained 30% lead. Further information concerning the basic medical and environmental aspects of lead poisoning may be found in the current issue of Environmental Science and Technology in an article by Stephen K. Hall.
Divalent sulfur can also react as a soft Lewis acid and as a general Usanovic acid allowing it to be readily reacted with bases of many sorts. The reactions of thiocompounds with hydrides, trivalent phosphorus compounds, and Raney nickel are examples in this category. One important synthetic example not mentioned by Block is the conversion of oxathiolanes to carbonyl compounds by Raney nickel. The availability of d orbitals for reaction can be used to rationalize not only octet expansion reactions but also the stability of anions alpha to sulfur and reactions which probably proceed through triplct states such as the dimerization of thiophosgene and other thiocarbonyl compounds to 1,3-dithiacyclobutanes, other irradiation promoted reactions and the easy oxidation by molecular oxygen of many sulfur compounds. The possible application of thiocompounds in any synthesis deserves serious consideration as these compounds have acid base characteristics markedly different from their oxygen analogs, as well as octet expansion capabilities and relatively low-lying triplet states which allow redox reactions to take place which are impossible with the oxo-analogs. Two almost unknown publications which might be of value to other workers in the area of organic sulfur chemistry are 0. C. Dermer, "Copolymers of Olefin Sulfides," W.A.D.C. Technical Report, 55-447, Wright Air Development Center, June 1956, which contains information on oxathiolanes which is otherwise unavailable; and a dissertation, "Thermal Decomposition of 1,3-Dioxan-2-ones and 1,3-Dioxan-2-thiones with Comments on the Structure of the Thiocarbonyl Group," Microfilm Abstracts Order No. 67-9151, 158 pp., $7.40 by Xerography, which contains infrared and pmr data and synthetic methods for thiocarbonyl compounds which are not available elsewhere.
Organic Sulfur Compounds in Synthesis
To the Editor: The excellent review by Eric Block on "Organic Sulfur Compounds in Organic Synthesis" [J.CHEM.EDUC., 48, 815 (1971)], does not explicitly state some broad summary generalizations which are useful in considering the use of organic sulfur compounds in synthetic work. These particular generalizations complement rather than contradict Block's discussion. Divalent sulfur is an excellent nucleophile in displacement reactions and a soft base which reacts readily with soft acids such as heavy metal cations and positive halogen compounds, while reacting much less readily, if at all, with relatively hard acids such as boron trifluoride. Two reactions which deserve to be better known illustrate these ideas. One is the reaction of mercaptans, mercaptide salts, and carbon tetrachloride to form disulfides and trithioformates. RSH
+ 4RSNa + CC4
+ RSSR
+ HC(SR), + 4NaCI
This reaction probably has as one transient intermediate an analog of C1,-. The reaction of thiqacids, boron trifluoride, and nmercaptans to form dithioesters is predicated specifically on the great difference in reactivity and bond stability of divalent oxygen and divalent sulfur with respect to boron trifluoride. An example is 380
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DEANL. SINCLAIR
Scientitlc Writing Course Survey
To the Editor: The Council of Biology Editors (CBE) has long sought to improve the quality of scientific writing, especially in professional journals. Now, through its Committee on Training in Scientific Writing, CBE is attempting to identify all those governmental and industrial institutions that offer to their scientists formal courses in scientificwriting. A s a related matter, CBE would like to know of courses in scientific writing that are being taught in undergraduate, graduate, and professional schools.
