4844
given by S t r d o w and von Stackelberg for cadmium in this supporting electrolyte & / t ’ / & = 20.12
0.798t1/6
(4!
Figure 1 shows a plot of &/,!‘I* against t ‘ A for the two drops r e p ~ r t e dtogether ,~ with the straight line predicted by equation (4). Below t = 1 sec., the relatively high back pressure decreases m, and theref~rethe diffusion current calculated on the assumption that m is invariant with time. However, the experimental values are much too low to be accounted for by any reasonable modification of the theory. Above t = 1 see. the experimental values are too large by as much as S%, and the “theoretical” slope appears to be attained onlv as a limit with increasing drop age. It h a s been shown1-* that, under conditions similar to those psevailing in these experiments, the average current is, very closely, 0.89 times the maximum current instead of the 0.857 predicted by the IlkoviE equation. Equations (1) and (3) yield for the average and maximum currents the values 22.10 and 25.92 microamp., respectively, and the ratio of these figures is 0.853. From these considerations we conclude that the Strehlow-von Stackelberg equation does not provide a significantly more satisfactory representation than does the Ilkovir equation of the change of instantaneous current with drop age.8 Acknowledgment. -This work has been supported by Contract. Number &4T (30-1)-842 between the AltorriicEnergy Cornnlission and j7;ale University. 18) NOTEADDEDIN PUOOP.O n the basts of experiments with 1
mM cadmium in 0 5 &.potassium I chloride-0 01% gelatin, Airey and . 287 (1950)) recently concluded that the $ d t l / a Smales ( A n ~ l y d76, prediction of the Ilkovil: equation was obeyed to *26% at drop ages between 0.75 and 3 9 sec. Thew values show an ill-defined trend in accord with the experimental curve of Fig I, but they do not give sdlicient data t o allow comparison with the reqult= of Taylor. Smith and Cooter at very small values of I STERLING CHEMISTRT 12AI)ORATOKl
YALEUNIVERSIT’U NEW H A V E N , COSS
L O U I S hlEIrF3S ‘rHELMA M E I T E ~
RECEIVED AUGUST 9, 1950 -
Sir :
Val. 72
COMMUNICATIONS TO THE EDITOR
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SYNTHESIS OF P-CAROTBN8
Europe of the synthesis of @-caroteneprompted us to publish our own synthesis of this carotenoid. In our synthesis the ketone (I)2 was allowed to react, via the Grignard reaction, with two moles of the acetylene carbinol (11) prepared from the C14-aldehydea to form the tetrol (111). This tetrol was selectively hydrogenated with two moles of hydrogen in the presence of palladium deposited on calcium carbonate, and the resulting product dehydrated with four mole-equivalents of pyridine hydrobrornide in boiling pyridine. The crude deep red product was recovered and chromatographed through a calcium hydroxide column. Typical carotene zones were formed and from thew was isolated a product which upon
two crystallizations from a benzenemethanol mixture gave red hexagonal and rhombic plates A mixed typical of @-carotene,m. p. 179-181’. in. p. with an authentic sample of natural /?carotene gave no depression. No mixed chromatogram tests were carried out. Our synthetic $-carotene gives a deep blue color with antimony trichloride in chloroform and an absorption spectrum in benzene identical with that of the natural /?-carotene. It showed maxima (Beckman Model DU) at 428 (inflection), 154, and 484 mp, respectively. The principal maximum at 434 mp had an value of about 2000. This work is being actively continued and detailed results will he reported elsewhere. We are indebted to Research Corporation and to Foreign Student Summer Project for financial support of this investigd t’1on. DEPARTMENT OF CHEMISTRY MASSACHUSETTS INSTITUTE OF TECHNOLOGY CAMBRtDGE, MASSACHUSETIb
RECEIVED JULY
NICHOLAS A. MILAS
PAUtS DAVIS IGORBELIE DEAGUITN A. FLES 27, 1950
The recent preliminary announcements’ in (1) (a) Katfer and Eugsta, Coapt. rcrd., 8110, lPa0 (May 31, 1930); (b) Inhoffen, Bohlmann, Bartrsm and Pommer, ChrariAn. Pomprer and Bchlmanu %bid, 74, E?&, t&, 986 (1910); ( a ) Inhoffen, 309 (1960).
(2) This ketone was first synthssized in thir Laboratory by E E Mange, B S. Thesis, 31 I T I 1948 (3) Milas, e l al , THISJObRNAL,78, 1687 f 1048) 1 Mila- t i I I &bid 70 1597 , 1918)
