Oct., 1944
COMMUNICATIONS TO THE EDITOR
A detailed description and correlation of the stereoisomers obtained in the synthesis of biotin will appear later.
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been interrupted temporarily, we hope to report on these investigations in detail a t a later date. CHEMICAL LABORATORIES
G. F. HENNION JAMESG. ANDERSON RALPHMOZINGO NOTREDAME,INDIANA RECEIVED SEPTEMBER 5, 1944 DONALD E. WOLF RESEARCH LABORATORY ANDREWN. WILSON GLENE. ARTH MERCK& Co., INC. RAXWAY, NEWJERSEY KARLFOLKERS POLAROGRAPHIC REDUCTION OF CARBON DIOXIDE RECEIVED AUGUST29, 1944 OF NOTRE DAME STANTON A. HARRIS UNIVERSITY
Sir: We have been engaged for some time in the study of the reduction of carbon dioxide at the BENZENES. PRELIMINARY REPORT dropping mercury cathode. On the basis of a Sir: large number of polarograms obtained by means In connection with studies on the alkylation of of a Heyrovsky Polarograph of the Sargent Co. benzene (and other aromatic nuclei), we have for with solutions of carbon dioxide in 0.1 molar some time been interested in developing new and tetramethylammonium chloride, we have arrived more generally useful derivatives of alkyl and a t the following definite conclusions: carbon dipolyalkylbenzenes. The polybromination of such oxide exhibits well-defined reduction waves with compounds h a s now been explored in a prelimi- a half-wave potential of remarkable constancy: nary manner and the rather surprising observa- -2.24 * 0.01 volt referred to the saturated calotion made that all secondary and tertiary alkyl mel electrode. This is the average of ten indegroups are replaced by bromine while primary pendent determinations with varying amounts groups are retained. In all cases the free posi- of carbon dioxide. When hydrogen is passed tions of the ring are filled a t the same time. For through the substituted ammonium salt solution example, when 1 g. of isopropylbenzene is added to before the dissolution of carbon dioxide, the waves 7 ml. of bromine and 0.2 g. of iron powder a t O', a are equally well defined, but the half-wave pogood yield of hexabromobenzene, m. p. 317', is ob- tential is somewhat less negative: -2.18 0.02 tained ; with n-propylbenzene the n-propyl group volt referred to the saturated calomel electrode. is apparently unaffected and the product appears This is the average of seven independent deterto be pentabromo-n-propylbenzene, m. p. 95'. minations, with varying amounts of hydrogen s-Butyl- and t-butylbenzene also afford hexa- and carbon dioxide. bromobenzene, while the n-butyl and i-butyl The slope dE/dul or id dE/dil a t the half-wave compounds give derivatives melting a t 78 and 7G0, ( E = cathodic potential] u = ratio of the current respectively, mixed m. p. 49-52'. Over thirty- i to the d8usion current id, u = 0.5 a t the halffive alkyl and polyalkylbenzenes having CI to wave) varies, according to the amount of carbon Cs alkyl substituents in various combinations dioxide, between rather wide limits : the lowest have been studied without encountering a single recorded slope is 0.359 v. and the highest is 0.614 exception to the rule cited above. As a matter of v. For an ordinary reduction involving one further interest, the procedure has been applied molecule, two electrons and two hydrogen ions, to a number of synthetic mixtures of isomeric in a medium of constant PH, this slope should be alkylbenzenes. Each component was found to 2 R T / F or 0.051 v. ( R = gas constant, T = abbehave normally, making it possible, for ex- solute temperature, F = 1 faraday).' ample, to detect readily 10%. or less of n-propylThe discussion of the various features of these benzene in isopropylbenzene. Obviously this polarographic waves, their detailed mathematical technique should have considerable diagnostic analysis, and our conclusions concerning the value in studying the fate of alkyl groups in mechanism of carbon dioxide reduction at the alkylation reactions and in the rearrangements of dropping mercury cathode will be presented in alkylbenzenes. subsequent communications. The various reaction products which have been DEPARTMENT OF CHEMISTRY accumulated are soon to be examined more fully UNIVERSITY PIERRE VANRYSSELBERGHE OF OREGON J . ALKIRE GEORGE as well as a number of the obvious applications EUGENE,OREGON RECEIVED AUGUST 28, 1944 of the general method, e. g., the study of products obtained in the aluminum chloride rearrangement (1) I . M. Kolthoff and J. J. Lingane, "Polarography," Interof dipropylbeazenes. Although this work has science Publishers, Inc., New York, N. Y.,1041, pp. 146, 194, etc. STUDIES ON THE POLYBROMINATION OF ALKYL-
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