In these studies, various synthetic routes toward the mercaptoborane B12HuSH2~w ere investigated as was the chemistry of this anion. The most favorable synthesis involved nucleophilic attack of 7V-methylbenzothiazole-2-thione on B12H122f ollowed by basic hydrolysis. Other routes invariably resulted in considerable by-products, some of which were B12H10(SH)22™, B12HuOH2~, and polymeric boranes. Various oxidative reactions of B12HnSH2• were observed, and new products isolated include the mixed disulfides B!2HUSSR2" (R is an organic function) and the disulfide monoxide Bi2HnSOSB12Hn4".

The technique of boron neutron capture therapy in the treatment of cerebral gliomas depends upon the selective loading of the tumor with a 10B-enriched compound and subsequent irradiation of the brain with low-energy neutrons. The charged particles produced in the 10B (n,alpha) 7Li reaction have ranges in tissue of less than 10 mum so that the dose distribution closely follows the 10B distribution even to the cellular level. The effectiveness of this therapy procedure is dependent not only on the 10B compound but on the spectral characteristics of the neutron source as well. Hence, an optimization of these characteristics will increase the chances of therapeutic success. Transport calculations using a neutral particle transport code have been made to determine the dose-depth distributions within a simple head phantom for five different incident neutron beams. Comparison of these beams to determine their relative therapeutic efficacy was made by the use of a maximum useable depth criterion. In particular, with presently available compounds, the MIT reactor (MITR) therapy beam (a) is not inferior to a pure thermal neutron beam, (b) would be marginally improved if its gamma-ray contamination were eliminated, (c) is superior to a partially 10B-filtered MITR beam, and (d) produces a maximum useable depth which is strongly dependent upon the tumor-to-blood ratio of 10B concentrations and weakly dependent upon the absolute 10B concentration in tumor. A pure epithermal neutron beam with a mean energy of 37 eV is shown to have close to the optimal characteristics for boron neutron capture therapy. Futhermore, these optimal characteristics can be approximated by a judiciously D2O moderated and 10B-filtered 252Cf neutron source. This tailored 252Cf source would have at least a 1.5 cm greater maximum useable depth than the MITR therapy beam for realistic 10B concentrations. However, at least one gram of 252Cf would be needed to make this a practical therapy source. If the moderated 252Cf source is not 10B filtered, the resultant neutron beam has characteristics similar to those of the MITR beam with no gamma-ray contamination. For usch a beam, 100 mg of 252Cf would produce a flux of 2.4 X 10(8) neutrons/(cm2 sec), which is an intensity suitable for therapy applications.

Noteswhere p, the coefficient of vibronic mixing, assuming for simplicity that no quanta of vibration are present in the fundamental state, takes the form In this expression Az is the energy difference between 2A2/ and 2E'~ Expressions 5 and 6 for gll and g, have been obtained by means of standard methods of c a l c u l a t i~n ,~~ neglecting terms in C2/AZ2 and p2.

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borane, crystallized from water, and dehydrated a t 110 "C to give the anhydride, (PhBO),,l2 Dihydroxy-(n-butyZ)bora.lze. This was prepared according to the method of Snyder et aE.13Boronates. The cyclic derivatives were prepared by the azeotropic removal of water and toluene from a 3 : 1 molar mixture of the appropriate diol to anhydride. When the theoretical quantity of water was removed, the excess of toluene was removed under reduced pressure and the boronate was purified by vacuum distillation. The acyclic boronates, (EtO),BR (R = Ph and Bun) were prepared from the dihydroxyborane and alcohol according to Gerrard's procedure.14 3-Phenyl-2,4-dioxa-3-borabicyclo[3,2, 21nonane was purified by vacuum sublimation a t 70 "C and 0-05 mm. Hg. The yield of this last compound was only ca. 40% as commercial samples of cyclohexane-l,4-diol (quinitol) are an approximately equimolar mixture of the cis-and transforms. cis-Quinitol yields a cyclic product [equation (l)]