Sulfonylhydrazones undergo facile deuterium exchange of their α-hydrogens, and such methods in conjunction with decomposition of sulfonylhydrazones via cationic, carbenic, and α-elimination processes should be valuable for synthesis of deuterated compounds. Lithium and sodium salts of aldehyde p-tosylhydrazones decompose efficiently at reduced pressures to pure primary diazoalkanes. Salts of p-tosylhydrazones of unbranched ketones decompose at higher temperatures than those of aldehydes, and the secondary diazo compounds formed do not survive (~5%) pyrolysis. It has now been found that (1) the decomposition temperatures of lithium salts of p-tosylhydrazones as solids, in suspension or in solution, are considerably lower than those of sodium salts, and (2) salts of p-tosylhydrazones of α-substituted ketones decompose at lower temperatures (30-40 °C) than do their unsubstituted analogs. It is now possible to convert lithium salts of p-tosylhydrazones of ketones such as 3-methyl-2-butanone and 3,3-dimethyl-2-butanone to 2-diazo-3-methylbutane and 2-diazo-3,3-dimethylbutane in 90-95% yields and >98% purity by vacuum pyrolysis. Highly unstable and involatile diazo compounds such as 2-diazo-1-phenylpropane and 2-diazo-1,3-diphenylpropane can now be prepared by the pyrolytic method at 80-120 °C. It is suggested that the lower decomposition temperatures of salts of p-tosylhydrazones of substituted ketones result primarily from cis strain release in conversion to products containing the linear diazo function. We wish to report the structure of a biologically active compound produced by a new strain of Streptomyces cinnamonensis. This compound, which has been named monensic acid, is a potent inhibitor of alkali metal cation transport into rat liver mitochondria and has broad-spectrum anticoccidial activity. Monensic acid (C36H62O11, mol wt 670) has mp 103-105 °C, νmax 3236 (OH) and 1695 cm⁻¹ (C=O), pKa' = 6.65 (66% DMF), and exhibits no ultraviolet absorption maximum above 210 nm. The 1695-cm⁻¹ band, attributed to the carboxyl group, moved to 1563 cm⁻¹ in the sodium salt. The nmr spectrum indicated the presence of a single methoxyl group at δ 3.37 ppm. The acid and its alkali metal salts are only slightly soluble in water (ca. 0.1 mg/ml), but are soluble in most organic solvents. The complete structure of monensic acid (III) was obtained by X-ray crystallographic analysis of its silver salt, showing the monensic acid ion wrapped around the cation and held in this conformation by two very strong hydrogen bonds between the carboxyl group and the two alcohol groups of the terminal six-membered ring, with a hydrocarbon-like exterior accounting for low water solubility. Recent interest in the stereochemistry of the addition of tetrachlorodiborane(4) to unsaturated organic compounds prompts us to report results obtained in this laboratory on the structure, isomerization, and cleavage reactions of the 1:1 addition product of B2Cl4 with acetylene. This compound was of interest in connection with a study of the relative reactivities of a series of unsaturated organometallic derivatives with B2Cl4, for which materials of known stereochemistry were required. The previously known 1:1 addition product (I) was obtained in 88% yield from the reaction of B2Cl4 with excess C2H2 at room temperature and an initial pressure of about 2 atm. Its proton magnetic resonance spectrum showed a broad single line at -6.57 ppm, narrowing with ¹¹B decoupling. Irradiation of I gave a new isomer (II) in 50% yield, confirmed by analysis. Results support that the reaction of B2Cl4 with acetylenic compounds is predominantly a cis addition.