COMMUNICATIONS TO THE EDITOR
Feb. 20, 1954
source of the &carbon atom of the 8-aminolevulinic acids2 It can be seen from Table I1 that the same CI4 distribution pattern was found in protoporphyrin synthesized from 8-aminolevulinic a ~ i d - 5 - C ' ~ and from glycine-2-C14; 50Y0 of the C 1 4 activity resides in the pyrrole rings and SOY0 in the methene bridges.
30
1205
38 42 46 50 Mass number, m / e . mass spectrum resulting from hydrolysis of pentaborane.
34
TABLE I1 Fig. 1.-Residual DISTRIBUTIOX OF Cl4 ACTIVITY IN PROTOPORPHYRIN SYNTHESIZED FROM &AMINOLEVULINIC ACID-5-cl4 AND FROM GLYCISE-2-C" was very small. The amount of hydrogen generMolar activity (Yo)in,fragments ated in the hydrolytic reaction increased with time. of porphyrin synthesized from 6-Aminolevulinic Glycine-2.~2'4 acid-c-C'4, % (ref. G ) , 70
Mass spectra taken immediately and a t short intervals after mixing pentaborane and water vapor Protoporphyrin 100 100 showed no residual pattern except for hydrogen. Pyrrole rings A B 23.5 24.6 The residual pattern given above is very similar (methylethylma1eimide)n to the mass spectrum of tetraborane3for which the Pyrrole rings C + D principal monoisotopic species is B4H6. We be25.2 25.3 (Hematinic acid)" lieve the first step in the hydrolysis of pentaborane PyrroleringsA + B + C + D 49.7 49 , 9 to be the removal of a borine by the "bound Methene bridge carbon atoms 50.3 .50 . 1 water" with subsequent generation of hydrogen. l a Obtained from protoporphyrin as previously de~cribed.~,' From a comparison of the models for pentaborane4 Our finding that 8-aniinolevulinic acid is an inter- and tetraborane5 the removal of any one of the four mediate in porphyrin synthesis has been confirmed basal borons of pentaborane would leave the tetraborane skeleton. in two recent c o m m u n i ~ a t i o n s . ~ ~ ~ T h a t the "bound water" in silica removes a (8) A. Neubergerand J. J. Scott, Naluve, 171, 1093 (1953). borine from pentaborane can also be demonstrated (9) E. I. R. Dresel a n d J. E. Falk, ibid., 171, 1185 (1953). by boron and hydrogen balances of what is retained DEPARTMENT OF BIOCHEMISTRY on the silica and what is recovered in the volatile COLLEGEOF PHYSICIANS AND SURGEONS DAVIDSHEMIN COLUMBIA UNIVERSITY TESSA ABRAMSKY portion of the products. By adding water to the SEW YORK32, N. Y. CHARLOTTE S. RUSSELL silica after all volatile material has been pumped off the solid, one can measure the amount of active RECEIVED JANUARY 22, 1954 hydrogen gasometrically and the amount of boron by titration with mannitol and standard base. FIRST STEP I N THE HYDROLYSIS OF PENTABORANE Silica must be filtered from the solution before Sir : titration of the boron. I n one experiment pentaNormally, the identification of intermediate borane from a carbon tetrachloride slush ( - 23') products resulting from the hydrolysis of boron was passed through a bed of silica a t room temhydrides is difficult to obtain because of the ease perature into a liquid nitrogen trap. The nonwith which they hydrolyze; however, by immobiliz- condensable gas (hydrogen) was compressed into a ing the water molecules we were able to obtain gasometer by means of a toepler pump. The evidence for the occurrence of such intermediates amount of hydrogen gas generated during the in the case of diborane.'I2 Now, by means of the pentaborane hydrolysis was approximately the mass spectrometer and with the technique of using same as that found after the addition of water to "bound water" in silica gel' we have succeeded in the silica. The ratio of active hydrogen to boron identifying the first step in hydrolysis pentaborane. in the silica was found to be slightly greater than Purified pentaborane gas was passed through a unity. Thus the over-all ratio of hydrogen (hyshallow bed of silica gel containing only bound dride) to boron accounted was ca. 2.3 instead of the water, and then led directly into a Consolidated expected value of 3.0 for borine. This difference Engineering model 21-103 mass spectrometer. can be attributed to errors of measurement because Mass spectra of the gaseous products were taken of the small amounts of material involved. The immediately and after intervals of 20, 40 and BO material caught in the liquid nitrogen trap was minutes exposure time of pentaborane to the silica found to be a mixture of pentaborane and an ungel. By stripping the mass spectrum for pure stable product which decomposed a t room temperapentaborane from these spectra, we obtained a ture over a period of hours to give hydrogen and a residual pattern whose peak heights as a function fibrous-looking solid boron hydride. of mass numbers (wz/e) is illustrated in Fig. 1. CHEMISTRY DIVISION The height of the residual peaks based upon a U. S. SAVAL ORDNANCE TESTSTATIOX I. SHAPIRO' H. G. WEISS" CALIFORNIA relative peak height of 100 a t m / e = 59 (highest PASADENA, RECEIVED JANUARY 22, 1Y54 peak height in pentaborane spectrum) was largest in the spectrum obtained after the 20 minutes (3) To be published. exposure time, and decreased with time. The (4) K. Hedberg, M . E. Jones and V. Schomaker, Puoc. A ' d A c d . residual pattern in the spectrum taken immediately Sci., 38, 679 (1952). ) M. E. Jones, K. Hedberg, and V. Schomaker, THIS JOURNAI after the pentaborane was exposed to the silica gel 75,( 54116 (1963); C. E. Nordman and W. N. Lipscomb, i b i d . , 76, 41lii Fragments of porphyrin
+
(1) I. Shapiro and H. G. Weiss. J . P h y s . C h e n z . , 5 7 , 219 (1953).
(2) H. G. Weiss and I. Shapiro, THISJ O U R S A L . 75, 1221 (1953)
(1053). (6) Research Dept., Mathieson Chemical Corp., Pasadena, Calif.
