5508
~OMMUNICATIONSTO THE EDITOR
Pentacarbanilino-D-glucose Diethyl Mercaptal T o a solution of 3.0 g. (10.5 millimoles) of D-glucose diethyl mercaptal (m.p. 125") in 75 ml. of dry pyridine, maintained a t looo, was added all a t once 11.4 ml. (105 millimoles) of phenyl isocyanate. The mixture was stirred a t 100' for 6.5 hours, cooled, and added t o 300 ml. of absolute ethanol. This clear solution on dilution with an equal volume of water gave 9.1 g. (98.5% of the theoretical amount) of crude pentacarbanilino-D-g~ucose diethyl mercaptal. Two recrystallizations from hot n-butanol in the proportion of 50 ml. of solvent per gram of crude compound gave an analytically pure material melting a t 207-210°, [ a I z 6 D +41.8' (c 0.9, pyridine). Recovery of purified
Vol. 73
material was approximately 83% a t each recrystallizatioii step. Anal. Calcd. for C~&IUN~O,&:C, 61.3; H, 5.3; N, 7.9; S, 7.3. Found: C, 61.3; H, 5.5; N, 7.7; S , 7.3. J. E. Hodge prepared the &glucose diethyl mercaptal and C. I-I. Van Etten performed the microanalyses. NORTHERN REGIONAL RESEARCH LABORATORY BUREAU OF AGRICULTURAL AND INDUSTRIAL CHEMISIRY AGRICULTURAL RESEARCH ADMINISTRATION LT.S. DEPARTMENT OF AGRICULTURE I. A. WOLPP PEORIA, ILLINOIS P. R. WATSON JULY 30, 1951 RECEIVED
C O M M U N I C A T I O N S 3'0 T H E E D I T O R -
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RETENTION OF B e IN COMPLEX BROMIDES, FOLLOWING ISOMERIC TRANSITION' Sir :
with either complex was negligible in the ca. two hours time involved (in the dark). Evidently, disruption of the bromopentamrnineThe 18 minute bromine nascent from the iso- cobaltate(II1) ion occurred upon every isomeric meric transition decay of Br*BOis known to possess transition, and without recombination of fragments a high chemical reactivity. Disruption of the par- or any re-entry of bromine into another molecule of ent molecule appears always to occur, in the case of complex. Recombination of primary fragments to aqueous bromate ion and of various organic bro- give the original complex might be expected to be mides, although in pure condensed systems some improbable since the complex ion is unstable in recombination of the primary fragments has been solution and aquates slowly; the process might be postulated. This reactivity is due to the high posi- responsible for the small retention in the solid. Retive charge on the bromine which results from the entry of the "hot" 18 minute bromine into a difAuger ionization that follows internal conversion.2 ferent molecule of complex would be unlikely in It seemed possible that a bromine-containing Wer- solution because of the low concentration of the ner complex might more easily tolerate such a posi- complex. tive increment in charge, especially if the complex The high retention by aqueous bromoplatiion were negative in sign to begin with. Results nate(1V) ion cannot be due to re-entry, by the same axe here reported for Co(NHs)sBr+2and PtBrs-2. argument as above, and also in view of the lack of The general procedure was to prepare a solution dependence of the effect upon concentration and of the complex, labelled with 4.4 hour Brxo(in equi- upon added free bromide ion. Furthermore, i t librium,with the 18 minute daughter), and then to seems unlikely that the retention was due to a reprecipitate the complex as brornopentaiiitnineco- combination of primary fragments, again because the baltate(II1) nitrate or as ainnioniurn bromoplati- complex ion is unstable toward aquation. Internate(1V). Sodium bromide, if not already pres- estingly, the same high retention was observed ent, was added before the separation. The degree when free bromide ion was initially present, indiof retention of the 18 minute isomer was deter- cating that isomeric transition did not so activate mined from the growth curve of the precipitated the complex as to permit exchange. complex. Retention in the solid state was deterThese results suggest that the degree of reactivmined by dissolving the solid complex, adding so- ity induced by isomeric transition is strongly dedium bromide, and immediately reprecipitating pendent upon the charge of the parent molecule, the complex. Ordinary exchange of bromide ion but the two complex ions studied are too dissimilar for this conclusion to be more than tentative. FurTABLE I ther work on this and related systems is in progress. Complex
Co( NHa)sBr+2 [eo(NH&Br]( NO& PtBrs-3
Concn. of complex, JI
0.01 (solid) 0.00166 0 0005 0.0005 with 0.003 11.1 NaBr (NH&PtBre (solid) Possibly some photocatalyzed exchange.
% :etention
0 14 52 52 70" 53 54 100
(1) This work was carried out under contract N6onr23809 between the University of Southern California and the Office of Naval Research. (2) For R recent bibliography see S.Coldhaber. R . S. H. Chiang and J. E.Willard. THISJOURNAL.^^. 2271 (19313.
DEPARTMENT OF CHEMISTRY UNIVERSITY OF SOUTHERN CALIFORNIA ARTHUR W. ADAMSOX JEAN M. GRUNLAND Los ANGELES 7, CALIFORNIA RECEIVED AUGUST28, 1951
STERIC INHIBITION OF HYPERCONJUGATION
Sir : For p-dkylbenzhydryl chlorides, the first order rates of solvolysis decrease in the order CH3 > CH3CH2 > (CH&CH > (CH&C. Stabilization
