UNIQUE DIALKYLSULFONIO-METHYLATION OF THE 7,8-C2B9H12(-) ION TO THE 9-R2S-CH2-7,8-C2B9H11 ZWITTERIONS BY FORMALDEHYDE AND DIALKYL SULFIDES - GENERAL-SYNTHESIS OF THE COMPOUNDS 10-R2E-7,8-C2B9H11 (E=O,S)

Dialkylsulfonio-methylation has been observed on the treatment of the 7,8-C2B9H12(-) ion with formaldehyde and dialkyl sulfides in aqueous a cidic medium. Four zwitterions of the type 9-R2S-CH2-7.8-C2B9H11 were formed with dimethyl and diethyl sulfide, tetrahydrothiophene and thio xane. In contrast, dialkyl ethers (diethyl ether, tetrahydrofuran, dio xane) afforded low amounts of the 10-R2O-7,8-C2B9H11 zwitterions, with the carborane 4,5-C2B7H13 being the principal product. Using acetalde hyde instead of formaldehyde, moderate yields of the 10-R2O- and high yields of the 10-R2S-7,8-C2B9H11 derivatives were obtained. With terti ary amines, only corresponding ammonium salts precipitated. Possible r eaction pathways for these transformations are discussed and compared with the specific degradation of the 7,8-C2B9H12(-) ion to the arachno -4,5-C2B7H13 carborane.