William E. McEwen

Structure of Antimony tris-(O,O-Diethyl Phosphorodithioate), a Passivation Agent for Contaminant Metals in the Catalytic Cracking of Crude Petroleum

Abstract The coordination polyhedron of the antimony atom in antimony tris-(O,O-diethyl phosphorodithioate) is a distorted capped octahedron with a stereochemically active lone pair in the capping position and approximately on a molecular pseudo triad axis which passes through the antimony atom.

MECHANISMS OF WITTIG REACTIONS; A NEW POSSIBILITY FOR SALT-FREE REACTIONS

Abstract Spin paired diradicals have been implicated as unstable intermediates in a wide variety of reaction mechanisms. A critical evaluation of the available sterochemical. kinetic and spectroscopic data is found to be consistent, for some Wittig reactions, with a mechanism that involves the intermediacy of a spin paired diradical. The proposed mechanism not only addresses the major stereochemical considerations around the phosphorus atom during the course of the Wittig reaction, but also provides a rational accounting of the observed cis olefin stereospecificity.

ROLE OF THROUGH-SPACE 2p–3d OVERLAP EFFECTS IN LITHIUM-ION CATALYZED WITTIG REACTIONS

Abstract The reactions of benzylidene-bis-(o-methoxyphenyl)methylphosphorane(17) with either banzaldehyde or trimethylacetaldehyde in the presence of lithium ion in tetrahydrofuran solution give higher ratios of cis: trans alkenes than do the corresponding reactions with benzylidenediphenylmethylphosphorane(16). However, when the intermediate oxaphosphetanes, 11 and 22 are produced by the action of lithium diphenylphosphide and lithium bis-(o-methoxyphenyl)phosphide (5), respectively, on trans-stilbene oxide (6), with subsequent addition of methyl iodide, the reactions are stereospecific, and only cis-stilbene is produced in each case. The results themselves and also attempted crossover experiments indicate that the oxephosphetanes do not revert to ylide plus aldehyde in the presence of lithium ion. The above observations, when combined with our knowledge of the preferred geometry of the through space 2p–3d overlap effect have enabled us to suggest a detailed mechanism for the lithium ion-catalyzed Wittig...

THE CRYSTAL AND MOLECULAR STRUCTURE OF BENZYL (2-METHOXYPHENYL)-DIPHENYLPHOSPHONIUM BROMIDE

Abstract The crystal structure of benzyl(2-methoxyphenyl)diphenylphosphonium bromide has been determined from three dimensional X-ray data collected on a three circle diffractometer using MoKα radiation. The salt crystallized in the orthorhombic space group Pbca with cell constants α=15.528 (7), b=16.892 (7), and c=17.921 (8) A. The observed and calculated densities for 8 molecules per unit cell are 1.308 (5) and 1.309 g · cm−3 respectively. The structure was refined by full matrix least squares to final residuals of R=0.089 and R w0.120 for the 1757 independent reflections in the range 2° > 2θ> 42° whose intensities were above background. The cation has near tetrahedral geometry with an average P-C bond distance of 1.819 (14) A and the configuration of the ion is such that the oxygen atom of the methoxy group is trans to the alkyl carbon atom of the benzyl group. The phosphorus-oxygen distance of 2.878 (12) A suggests a weak bonding interaction and qualitative support for this view is obtained from energ...

SOLVOLYSIS REACTIONS OF ANTIMONY (III) O,O-DISUBSTITUTED PHOSPHORODITHIOATES

Abstract Antimony (III) tris-(O,O-di-p-tolyl phosphorodithioate) (4) has been found to undergo solvolysis in ethanol to give antimony triethylate and O,O-di-p-tolyl phosphorodithioic acid (5). Both 4 and antimony (III) tris-(O,O-diethyl phosphorodithioate) (3) undergo solvolysis reactions with diethylamine to give the respective diethylammonium O,O-disubstituted phosphorodithioates and complex oxidation products. Compounds 3 and 4 are similar to passivation agents used in petroleum refining, and the results suggest that such compounds can undergo solvolysis at antimony with various components of crude petroleum prior to the ultimate pyrolysis reactions.

Apparent absence of reversal of oxaphosphetane formation in some Wittig reactions

Reversal of oxaphosphetane formation in the reaction of benzaldehyde with benzylidene(2-N,N-dimethylaminophenyl)diphenylphosphorane (1) and benzylidine(4-N,N-dlmethylamlnophenyl)diphenylphosphorane (2), respectively, is found not to occur in tetrahydrofuran solution. The reason for this is that the rates of dissociation of the oxaphosphetanes to stilbenes and the corresponding triarylphosphine oxide are faster than reversal to the reagents.

A General Hypothesis for the Mechanism of the Wittig Reaction

Abstract Arguments are presented that an ionic mechanism is operative in the Wittig reaction when a metal ion is a part of the transition state leading to oxaphosphetane formation but that formation of a spin paired diradical precedes oxaphosphetane formation in other cases.

Acid generation in the thermal decomposition of diaryliodonium salts

Diphenyliodonium tetrafluoroborate and diphenyliodonium hexafluorophosphate have been found to generate up to two equivalents of hydrogen fluoride per equivalent of the iodonium salt by pyrolysis at 239°C in the neat state and at 150°C in the presence of anisole or nitrobenzene. The formation of hydrogen fluoride is presumed to arise by dissociation of hydrogen tetrafluoroborate or hydrogen hexafluorophosphate initially formed, due to the high temperatures, thus giving rise also to the Lewis acids boron trifluoride and phosphorus pentafluoride, respectively. A detailed analysis of the volatile organic products of the decomposition of the diphenyliodonium salts was also carried out. Many products were identified in all of the cases studied. For example, the neat decomposition of diphenyliodonium tetrafluoroborate afforded benzene, fluorobenzene, iodobenzene, the three isomeric iodobiphenyls, biphenyl, three isomeric terphenyls, and one or more of the diiodobiphenyls, iodoterphenyls, and polyaromatics. Among the iodobiphenyls, the ortho and para isomers were found to predominate over the meta isomer. The terphenyl isomers did not exhibit this ortho, para selectivity. It was significant that decomposition of the diaryliodonium salts in anisole suspension did not afford methoxybiphenyls or iodomethoxybiphenyls. An interpretation of these results is presented.

THE ROLE OF O2p-P(IV), N2p-P(IV) AND SIMILAR INTERACTIONS IN HETEROATOM CHEMISTRY

Abstract Phosphines having o-methoxyphenyl or o-(N,N-dimethylaminophenyl) groups bonded to the phosphorus atom exhibit moderate anchimeric assistance effects, attributable to through space O2p-P(IV) or N2p-P(IV) interactions, in reactions with alkyl halides. These SN2 reactions have early transition states, and that is why the anchimeric assistance effects are only moderate. Quaternary phosphonium salts having o-methoxyphenyl groups bonded to phosphorus undergo slow alkaline decomposition reactions as expected because of O2p-P(IV) interactions, but unusual effects are operative when o-(N,N-dimethylaminophenyl) groups are bonded to the phosphorus atom. Spectra of these types of compounds also show unusual characteristics. This review article provides rationalizations of these unusual data partly in terms of through space O2p-P(IV) and N2p-P(IV) interactions

REDOX REACTIONS OF ANTIMONY(III) O,O-DISUBSTITUTED PHOSPHORODITHIOATES WITH FERRIC CHLORIDE

Abstract The reaction of antimony(III) tris-(O,O-diethylphosphorodithioate) with three equivalents of ferric chloride in ether solution has been found to give ferrous chloride, bis-(O,O-diethylthiophosphoryl) disulfide and dichloroantimony O,O-diethyl phosphorodithioate as the major products. However, a relatively low yield of bis-(O,O-diethylthiophosphoryl) trisulfide was also obtained. The structures of these products were established by independent syntheses. Several additional antimony(III) tris-(O,O-disubstituted phosphorodithioates) were prepared, and the major organic product obtained by reaction of each of these compounds with three equivalents of ferric chloride was the corresponding bis-(O,O-disubstituted thiophosphoryl) disulfide. A mechanism for this reaction has been suggested, and evidence in support of the mechanism has been presented. The various antimony(III) tris-(O,O-dialkyl phosphorodithioates) are passivating agents used in petroleum refining. The results reported in this and in our p...