COMPLEXATION IN ACETONITRILE OF TETRAMETHYLGUANIDINIUM (BH+) SULFATE WITH BISULFATE BHSO4- AND BH+ IONS

From the data obtained from conductance, differential vapor pressure, and solubility measurements in acetonitrile as solvent, it has been concluded that the tetramethylguanidinium ion (BH+) forms a host of complex salts and ions with sulfate. The normal sulfate is present in solution as a stable dimer, {(BH)2SO4}2, which dissociates into [formula-omitted] and [formula-omitted] ions, the ionic dissociation constant, Kd, being about 7 × 10-5, while its solubility product Ksp = 3.5 × 10-7. In mixtures with a molar ratio of B:H2SO4 of 1.5 the solutions contain (BH)2SO4·BHHSO4 which dissociates into [formula-omitted] and [formula-omitted]. This compares with a Kd of HHSO4 of 5 × 103. Part of the complex is present as the dimer, {(BH)2SO4 BHHSO4}2, the dimerization constant being of the order of 1.5 × 101. In mixtures with a molar ratio of B:H2SO4 of 1.67 a large fraction of sulfate is present as the complex {(BH)2SO4}2BHHSO4 which dissociates into [formula-omitted] with Kd~10-3. This has been substantiated by solubility measurements of {(BH)2SO4}2 in dilute sulfuric acid. In a mixture of tetraethylammonium bisulfate (Kd~ 3 × 10-2) with excess of B the reaction [formula-omitted] occurs. The bisulfate also forms with {(BH)2SO4}2 the complexes Et4N(BH)2SO4·HSO4 and Et4N(BH)2SO4·BHSO4 which are fairly strong electrolytes. Two complexes are formed between {(BH)2SO4}2 and BHPi (picrate) :(BH)2SO4BHPi and {(BH)2SO4}2BHPi, the latter yielding the · ion. Conductometric and potentiometric titrations of sulfuric acid and of tetraethylammonium bisulfate with tetramethylguanidine in the absence and presence of the hydrogen-bond donor p-bromophenol are reported and interpreted. © 1969, American Chemical Society. All rights reserved.