The Sulfonation of Aromatic Isocyanates: Sulfonated p‐Tolyl Isocyanate—An X‐Ray Structure Analysis

Abstract

isocyanate and sulfonic acid functions in one molecule are formed only in those cases in which the sulfo group enters the ortho position to the isocyanate group in the aromatic ring. We report here on the structure of sulfonation product 2d derived from p-tolyl isocyanate 2. Compound 2d was formed by reaction of 2 with gaseous sulfur trioxide or with chlorosulfuric acid in dichloroethane. 2d is a pale yellow powder which is practically insoluble in conventional inert organic solvents and is decomposed to the aminosulfonic acid 2c with evolution of C 0 2 on treatment with excess water. The IR spectrum of 2d shows a sharply resolved group of bands in the region 1200-1400 cm-' (sulfonic acid derivative) and one carbonyl band at 1780 cm -I . Chemically, 2d behaves like an isocyanatosulfonic acid, i.e. it gives the usual reactions of isocyanate and sulfo groups (urethane and urea formation, conversion into the isocyanatosulfonyl chloride or into the salt of the isocyanatosulfonic acid with a tertiary amine). ( L = P M e , P h , Scheme 1 P M e Phz) L L 4 , L = P M e 3 5 , L = onir ire), CNtBu) recently described by Stone et al., which are formed from Pt(q2-CH2=C5Ph4)C8HI2 and L, have an analogous structure['41.The I3C-NMR data are also consistent with the structure proposed for 4 and 5. The signals of the carbon atoms of the C=CH2 bond are each split into a doublet of doublets by coupling with two different 31P-nuclei, and the signal of C6 shows an additional triplet splitting in the off-resonance spectrum, due to CH coupling. The non-equivalence of the phosphane and phosphite ligands, respectively, is revealed in the "P-NMR spectrum by two doublets (4:We assume that the formation of 4 and 5 primarily involves the addition of a phosphane or phosphite molecule, respectively, to the metal accompanied by a do-rearrangement of the ally1 group in 3b, as has been demonstrated in the reaction of C5H5Pd(2-RC3H4) with PR3 and P(OR)31151. A subsequent hydride-shift leads to a fulvene(hydrido)palladium(~~) intermediate, from which, after elimination of 2,3,3-trimethyl-I-butene (detected 'H-NMR spectroscopically) and addition of a second molecule of L, the fulvene complexes are formed.That the formation of a 1,2,3,4-tetramethylfulvene ligand from CsMes is not restricted to palladium as metal atom has been shown by recent investigations on the synthesis of dinuclear (p-CSMe4-CH2) titanium complexes['61 as well as by NMR studies on the dynamics of Ti(CsMe5)2['71.