The acid-catalyzed displacement by bases in 2-substituted tropones has been investigated. As an example, 2-iodotropone has been obtained from 2-chlorotropone, 2-bromotropone and tropolone p-toluenesulfonate by treatment with potassium iodide in acetic acid. The aromatization of 2-chlorotropoiie to benzoic acid 011 treatment with hydroxide ion also occurs with 2-bromo-and 2-iodotropone but riot with tropolone p-toluenesulfonnte which is reconverted to tropolone. \Vith phenyllithiiim no rrorrangenient is obsrrvrtl, tropoloiir, its nirthyl rthcr atid chlorotropone twiiig. converted to 2-phenyltropone.The recent uncovering by Doering and Knos? nf the rearrangement of chlorotropone (11 and the chloride exchange of tribroniotropolone has encouraged further investigation into the chemistry of the halotropones.The halide displacement reaction has been extended and studied in connection with the preparation of the bromo and iodo analogs. 2-Bromotropone (11) can be prepared conveniently from 2chlorotropone (I) by treatment with hydrogen bromide in boiling acetic acid. The extent of bromide exchange is determined analytically since mixtures of I and IT show no depression on melting and have not been separable by crystallization. 2-Todotropone (111) results from the action of potassium iodide in wet acetic acid on I or TI and from the action of tetraethylammonium iodide in dry acetic acid on I. The structural similarity of the three halotropones is suggested by the ultraviolet spectra (Fig. 11 in which ITT differs 4 0
2, jV. Y.The peroxy complexes of group IV, V, VI, and VII transition elements, formed in concentrated sulfuric acid media, were investigated for application to the analysis of niobia and tantala mixtures.(A number of correlations were made of the spectra of the peroxy complexes with their positions in the periodic table .) One result of this study was the discovery of a peroxy-tantalate whose absorption spectrum had its peak at 285 mg.
Polytechnic Institute of Brooklyn, Brooklyn, A'. Y.. i s the result of a study of the effects of absorptioii law deviations on the precision of colorimetric analyses, for absolute and relative concentration measurements, a simple method for estimating the maximum precision possible with any given absorber has been developed. In absolute measurements the precision is oaly slightly affected by absorption law deviations, but with relative measurements this effect may be considerable.X QU-4XTITATIVE colorimetry or spectrophotometry thc I precision of analysis may be materially improved if a relative rather than anabsolute concentration is determined. In this type of measurement a high absorbance standard is compared with a sample of similar but unknown concentration. The details of this general method have been extensively treated, as to both the theory involved (1, 6-8) and some direct analytical applications (2,d, 9, 12-f4). If a high absorbance reference standard is used, it becomes necessary to operate with an increased light intensity in order to achieve a photocurrent sufficient to set the transmittance scale at its normal value of 100%. With a monochromator of the type incorporated in the Beckman spectrophotometer, this is easily effected by opening the slits. A consequence of this manipulation is that the band of spectral energy passed by the instrument is broadened, causing absorption law dekiations which are particularly pronounced when the absorption band width is either narrower than, or comparable to, the pass band width. Such deviations lead to a loss of precision in colorimetric analysis.In this paper this problem is treated generally, not only for relative concentration measurements but for absolute ones as well. Techniques are described for selecting the reference standard concentration, so that maximum precision may be obtained in any given analysis. This study concludes with an examination of slit width effects when these high absorbance reference standards are employed. FORMULATION OF THE DEVIATION PROBLEMIn a previous paper (6) the effect of an absorption law deviation on the precision of a relative absorbance measurement was formulated in a preliminary fashion. It is now intended to develop that approach in a more explicit way, considering first the case of an absolute colorimetric measurement.For this purpose, suppose that the deviation case illustrated in Figure 1 is taken. In this instance the relation between the measured absorbance and the concentration (solid line) is linear a t low concentrations with a elope ( AA/Ac) equal to the absorptivity coefficient, a . At higher concentration values, however, the curve deviates considerably from a linear relation, so that a t some value c1, the absorbance hap a value given by A,. A tangent to the curve a t A1 will have a slope equal to an apparent absorptivity coefficient, a'. This absorptivity value obviously applies only for a very small concentration interval in the vicinity of c1. In this discussion b, the length of the light path in the absor...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.