The X-ray crystal structures of the four stable phenylhydroxylamines (PhSOzNHOH, (PhS02)2NOH, PhS02NHOS02Ph, (PhS@)2NOSOZPh), and of PhS03'+H3NHNS02Ph are presented. The last of these is a by-product obtained during the isolation of PhS&NHOH (Piloty's Acid). The formation of and the bonding in these molecules are discussed.
Piloty's acid, PhS02NHOH, 1, was first prepared nearly one hundred years ago by the reaction of benzenesulfonyl chloride (PhS02Cl) with one equivalent of hydroxylamine hydrochloride in basic medium.' Perusal of the literature revealed that although the original synthesis has been repeated a number of times, no new synthetic approach has been described.* The many reported melting points of 1 lie between 120 and 129 'C?, but in our hands, the melting point was never greater than 109-10 'C regardless of the solvent used for recrystallization.4 This discrepancy led us to determine the structure of our material by X-ray crystallography, which confiied that it was indeed Piloty's acid.
During the recrystallization of 1, a hitherto unreported white solid was isolated and shown to be PhS03. +H3NNHS&Ph (5) by X-ray crystallography and elemental analysis. Another component of the mother liquor, PhSH, can be accounted for by the reduction of PhS02Cl by HONH2, &s however, we found no precedent for the formation of 5.
As in the case of 1, widely discrepant melting points have been reported for (PhS02)2NOH, (2)' The melting point problem for 1 and 2, coupled with the great difficulty in distinguishing the N-S from the O-S linkage spectroscopically, led us to undertake X-ray structure determinations of the entire set of phenylsulphonylhydroxylamines (cf. Figures 1234and Table 1).