Search

25-oleum has proved to be an extremely useful solvent for recording the 31 P NMR spectra of a variety of compounds containing phosphonium ions. Not only have data in very good agreement with previous solid state and solution results been obtained, but the structures of some solids containing mixtures of phosphorus (V) species have been ascertained for the first time.

Halogen exchange reactions of phosphorus(V) halides and oxyhalides in strongly acidic solvents have been investigated by means of 31P spectroscopy. Neither PCl5 and PBr5, nor POCl3 and POBr3, undergo mutual exchange in an “inert” (non-exchanging) solvent such as 25 oleum at, or just above, room temperature. Exchange is observed when a suitable alkali metal halide is added to a solution of POBr3 in HSClO3 or HSFO3, but does not take place in the absence of the halide. The results confirm that exchange in these solvents does not involve direct reaction of the phosphorus(V) compound with the solvent, but occurs via an indirect mechanism.

SummaryInhibition studies, carried out using a partially purified L-asparaginase 2 preparation, have indicated that tobacco smoke and a number of reactive smoke components do not cause inhibition. Of the smoke components studied, only acrolein was inhibitory and this inhibition was found to be more marked at pH 8.4 than at pH 5.0. The -SH specific reagents, sodium arsenite and p-hydroxymercuribenzoate did not inhibit the enzyme.

Cigarette smoke has been shown to contain free radicals in both the vapour and particulate phases. The present investigation was undertaken to find out whether these radicals could initiate or promote the formation of radical peroxides which might in turn lead to lipid peroxidation. To investigate this, a system involving the coupled oxidation of b-carotene and linoleic acid was utilized. In this coupled reaction, b-carotene is destroyed through oxidation by free peroxy radicals. The system can therefore be used as a convenient detector of auto-oxidative mechanisms in which peroxide radicals participate, as well as provide an assay for antioxidants, since in their presence oxidative destruction of b-carotene is blocked. Our results show that smoke did not contribute to the oxidative destruction of b-carotene but rather behaved as an antioxidant. Both smoke vapour and particulate matter were found to be highly antioxidant. A number of pure vapour phase components were tested and the bulk of antioxidant activity was found to be due to HCN. Smoke condensates from different tobacco types were compared and differentiated according to their relative efficiencies of antioxidant activities. For comparison, units of antioxidant activity were expressed as rate of change of optical density with time. The highest antioxidant activities were obtained with air-, flue-cured (cut) and perique tobaccos. Pipe tobacco had the least activity while cigar and flue-cured (granulated), stem and sheet tobaccos had intermediate values. Tests done on smoke fractions derived from the fractionation of total condensate revealed that antioxidant activity resided largely in the neutral and water-insoluble acid fractions with virtually no activity in the basic fractions. The mode of antioxidant action of tobacco smoke is discussed in terms of free-radical mechanisms.

The compound PBr4Cl3 has been shown to have the ionic structure PBr+4Cl−− by means of 31P NMR and Raman spectroscopy. There was no evidence for the formation of mixed bromochlorophosphonium ions. It appears to be a member of a series of derivatives of the PBr−4 ion with trihalide or single halide counter-ions.

The reactions of PX3(X = Cl, Br, or I) with the strongly acidic solvents 100% H2SO4, 25 and 65 oleum, HSClO3 and HSFO3, have been investigated by means of 31P n.m.r. spectroscopy. The usual initial reaction is oxidation to [PX3(OH)]+, although HSClO3 also forms [PX3Cl]+. The reduction in acid strength which necessarily accompanies the redox reaction promotes solvolysis of P–X bonds, and halogen exchange in HSClO3 and HSFO3. Formation of [PBr4]+ from PBr3has also been observed in several solvents. Some interesting new species, notably phosphorus(V) cations containing P–I bonds, have been identified in solution, but not in 25 oleum. Condensation reactions involving elimination of HBr or HI may occur in 65 oleum. Possible mechanisms for the various reactions observed are proposed.

The reactions of PCl3O, PBr3O, [PCl4][PCl6], [NEt4][PCl6], and [PBr4] Br with the highly acidic solvents 100% H2SO4, HSClO3, HSFO3, 25 oleum, and 65 oleum have been investigated by means of 31P n.m.r. spectroscopy. The halide oxides undergo protonation at the phosphoryl oxygen, the extent of which depends on the acid strength of the solvent and the solute concentration. Solutions of PCl3O are stable, as are PBr3O solutions in the halogenosulphuric acids, but solvolysis of PBr3O occurs in 100% H2SO4 and 25 oleum and condensation in 65 oleum, probably via HBr elimination. The initial products from PCl5 are [PCl4]+, [PCl3(OH)]+, or both of these, depending on the solvent; further solvolysis is then observed, together with halogen exchange in HSFO3. Phosphorus(V) bromide forms [PBr4]+ initially, which may similarly undergo further reaction, but is stable in 65 oleum. The difference in behaviour between PCl5 and PBr5 is mainly due to the instability of the [PCl6]– ion in these solvents. Possible mechanisms for the observed reactions are proposed.

The compound PBr4Cl3 has been shown to have the ionic structure PBr+4Cl−− by means of 31P NMR and Raman spectroscopy. There was no evidence for the formation of mixed bromochlorophosphonium ions. It appears to be a member of a series of derivatives of the PBr−4 ion with trihalide or single halide counter-ions.

The reaction of Ph2P(O)OH, Ph2P(O)Cl, Ph3PO, Ph3PS, and MeP(O)Cl2, with the strongly acidic solvents 100% H2SO4, HSClO3, 25 and (in most cases) 65 oleum have been investigated by 31P n.m.r. spectroscopy. The initial reaction is protonation of the phosphoryl oxygen for phosphoryl compounds, although Ph3PS appears not to protonate. Further reactions including sulphonation of the aromatic rings, and/or solvolysis of phosphorus–chlorine bonds, have also been observed in many instances. The relative basicities of these and other phosphorus(V) compounds are discussed on the basis of the results.

The reactions of PCl3O, PBr3O, [PCl4][PCl6], [NEt4][PCl6], and [PBr4] Br with the highly acidic solvents 100% H2SO4, HSClO3, HSFO3, 25 oleum, and 65 oleum have been investigated by means of 31P n.m.r. spectroscopy. The halide oxides undergo protonation at the phosphoryl oxygen, the extent of which depends on the acid strength of the solvent and the solute concentration. Solutions of PCl3O are stable, as are PBr3O solutions in the halogenosulphuric acids, but solvolysis of PBr3O occurs in 100% H2SO4 and 25 oleum and condensation in 65 oleum, probably via HBr elimination. The initial products from PCl5 are [PCl4]+, [PCl3(OH)]+, or both of these, depending on the solvent; further solvolysis is then observed, together with halogen exchange in HSFO3. Phosphorus(V) bromide forms [PBr4]+ initially, which may similarly undergo further reaction, but is stable in 65 oleum. The difference in behaviour between PCl5 and PBr5 is mainly due to the instability of the [PCl6]– ion in these solvents. Possible mechanisms for the observed reactions are proposed.

The reactions of PPhO(OH)2 and PPhCl2O with the strongly acidic solvents 100% H2SO4, 25 and 65 oleum, and HSClO3 have been investigated by means of 31P n.m.r. spectroscopy. Initial protonation of the phosphoryl oxygen, the extent of which varies with solute and solvent, is followed in most instances by sulphonation of the aromatic group (except in H2SO4), and/or condensation [PPhO(OH)2] or solvolysis (PPhCl2O). Slow chlorination of PPhO(OH)2 was also observed in HSClO3. Attempts to prepare the intermediate compound PPhClO(OH) did not yield pure products, but reaction of two of the mixtures thus obtained with 100% H2SO4 and HSClO3 confirmed its participation in some of the above systems.

The reactions of PX3(X = Cl, Br, or I) with the strongly acidic solvents 100% H2SO4, 25 and 65 oleum, HSClO3 and HSFO3, have been investigated by means of 31P n.m.r. spectroscopy. The usual initial reaction is oxidation to [PX3(OH)]+, although HSClO3 also forms [PX3Cl]+. The reduction in acid strength which necessarily accompanies the redox reaction promotes solvolysis of P–X bonds, and halogen exchange in HSClO3 and HSFO3. Formation of [PBr4]+ from PBr3has also been observed in several solvents. Some interesting new species, notably phosphorus(V) cations containing P–I bonds, have been identified in solution, but not in 25 oleum. Condensation reactions involving elimination of HBr or HI may occur in 65 oleum. Possible mechanisms for the various reactions observed are proposed.

The reactions of some phosphorus(III) halides with halogens in the strongly acidic solvents 25 oleum, HSFO3, and 100% H2SO4 have been investigated by means of 31P n.m.r. spectroscopy. The compound PCl3 and Br2, and PBr3and Cl2, react to give complex mixtures of products containing tetrahalogenophosphonium ions [PBr4–nCln]+, together with solvolysed species [PBr3–nCln(OH)]+(25 oleum) or PF3O(HSFO3). No evidence has been found for halogenophosphonium ions [PXnY4–n]+ derived from PI3, although the partially solvolysed species [PlnX3–n(OH)]+(X = Cl or Br) have been identified in solution.

A procedure is outlined for identification of polyhydric alcohols by thin-layer chromatography. Those with similar RF values are identified by their specific colour reactions with 2-thiobarbituric acid.