Strong Protonic Acid Research Articles

Synthesis of cationic π-complexes of transition metals of groups VI–VIII by exchange of the carbonyl ligands in strong protonic acids

The review of the works of the author and coworkers reveals that metal carbonyl complexes may be successfully used as starting compounds in the synthesis of cationic π-complexes of transition metals of groups VI–VIII. The carbonyl ligands may be substituted be allyl, diene, propargyl, ethylene and arene ligands with the oxidation state of the metals being either increased or retained depending on the electronic requirements of the metal. Numerous examples demonstrate efficiency of this one-step synthesis making use of the combined action of strong protonic acid and UV irradiation.

Temperature-programmed desorption of aromatic hydrocarbons on silicalite-I and ZSM-5-type zeolites

Temperature-programmed desorption (t.p.d.) of benzene, toluene, p-xylene, o-xylene, m-xylene, and mesitylene on HZSM-5 in a helium stream from 353 to 673 K at different heating rates (2.5–25 K. mine −1) has been studied using a gas chromatographic technique and the heat of sorption of the hydrocarbons evaluated from the t.p.d. data. The influence of the Si Al ratio, degree of Na +-exchange, calcination temperature (or dehydroxylation), and poisoning of strong acid sites on the t.p.d. and heat of sorption of benzene on the zeolite has also been investigated. The decrease in the heat of sorption of benzene with the increase in the Si Al ratio, extent of dehydroxylation, and poisoning of the strong protonic acid sites with pyridine has indicated the involvement of surface hydroxyl groups responsible for protonic acidity in the sorption of HZSM-5. The increase in the heat of sorption of aromatic hydrocarbons with the decrease in their ionization potential (or with the increase in the number of CH 3 groups) has indicated the occurrence of strong interactions between the π-electrons of benzene nucleus and the hydroxyl groups. The higher heat of sorption of benzene in Na-containing ZSM-5 has revealed that the interaction of the benzene molecule with the Na + cation is much more stronger than that with the protonic acid site in HZSM-5. Further, the t.p.d. of benzene at different sorbate loadings has indicated site heterogeneity on HZSM-5.

Silica-Supported Heteropoly Acid Catalyst for Liquid-Phase Friedel–Crafts Reactions

Abstract Silica-supported Keggin-type heteropoly acids such as 12-tungstophosphoric, molybdophosphoric, and tungstosilicic acids efficiently catalyzed Friedel–Crafts alkylation and acylation reactions of aromatic hydrocarbons with 1-octene, benzyl chloride and benzoyl chloride in the liquid phase. The catalytic activity of heteropoly acid was generally enhanced when supported on silica. Silica-supported tungstosilicic acid worked as an insoluble heterogeneous catalyst even to the acylation of p-xylene with benzoyl chloride or benzoic anhydride, though deactivation was observed during repeated use. Considering that supported p-toluenesulfonic acid, an ordinarily used typical strong protonic acid, was far less active than the supported heteropoly acid, the high catalytic efficiency revealed by heteropoly acid appears to be due to a unique property of heteropoly anion which can stabilize alkyl and acyl cations as the reaction intermediates.

Synthesis of cationic allyl- and dienecarbonyl complexes of group VI-VIII metals in the presence of strong protonic acid

Cationic allylcarbonyl complexes of Cr, Mo, W, Mn, Re, Fe, Co, Rh and Ir are synthesized by reaction of a carbonyl-containing compound with allyl alcohol or conjugated diene in the presence of strong protonic acid. This reaction is promoted by an increase in basicity of the initial complex and an increae in acidity of the medium; the nature of the organic substrate is also important for synthesis of this type of carbonyl complex. Cationic diene complexes have been formed by the action of dienes and acid on compounds with a metal-metal bond or on neutral allyl complexes.

Investigation of the stereochemistry of transition metal allyl cationic complexes

Stereochemistry of transition metal-allyl cationic complexes synthesized by reaction of the corresponding metal carbonyls with allyl alcohol or a conjugated diene in the presence of a strong protonic acid has been investigated by means of NMR and IR spectroscopy. The number of isomers, as well as the position of substituents in the allyl ligands of complexes of the group 6 and 7 metals and iron, is determined by the formation of η 2-diene complexes in the transoid conformation in which the diene is coordinated via a substituted or non-substituted double bond. The protonation products formed in the initial stage of the reactions of CpM(CO) 2 (where M = Co, Rh, Ir) with acids lead to the mixtures of syn- and anti-crotyl isomers in their subsequent reactions with butadiene, the anti-isomers being transformed into syn-complexes on heating. The study of conformational isomerism of the half-sandwich allyl complexes has shown that the Cr, Mo, W, Mn and Re compounds of [LM(CO) 2(allyl)] + BF 4 − (where L = arene, cyclopentadienyl) exist in the form of equilibrium mixtures of exo- and endo-conformers, the endo-conformer prevailing in the case of Mo, W and Re; for [CpM(CO)(allyl)] + BF 4 − (where M = Co, Rh, Ir), disappearance of the endo-isomer on heating has been observed.

Preparation of Poly(p-phenylene) by Electrooxidative Polymerization in Acidic Media

Abstract The electro-oxidative polymerization of benzene in the presence of strong acids yields poly(p-phenylene) efficiently. A strong protonic acid such as trifluoromethanesulfonic acid or Lewis acid such as an aluminum trichloride forms a complex with benzene and reduces the oxidation potential of benzene to 1.7 V, which brings about the high current efficiency. The acids act both as an electrolyte and as a catalyst in this polymerization of benzene.

The synthesis, using hexamethyldialuminium, and reactivity of new (1–5-η-cyclopentadienyl)methyl(nitrosyl)molybdenum complexes. Crystal structure of bromo(η5-cyclopentadienyl)methyl(nitrosyl)(triphenylphosphine)-molybdenum

Under appropriate conditions the reaction of [{Mo(η5-C5H5)(NO)X}2(µ-X)2][X = Cl (1), Br (2), or I (3)] with Al2Me6, gives the new (probably dimeric) methyl complexes [{MoMe(η5-C5H5)(NO)}2(µ-X)2](4)–(6) which react with an equimolar amount of different ligands to give the monomeric neutral complexes [MoMe(η5-C5H5)(NO)XL][L = tetrahydrothiophene (tht), X = Br (7); L = PPh3, X = Cl (8), Br (9), or I (10); L = OPPh3, X = Cl (11) or Br (12)] and the anionic complex [PPh4][MoMe (η5-C5H5)(NO)Br2](13). One of the routes to prepare complexes (7)–(12) gives instead of (12) a solid, (14), which contains a cation of variable composition and the same anion as in (13). The complexes (5) and (9) react with Tl(C5H5) to give the known [MoMe(ηn-C5H5)2(NO)](the value of n is unknown). The molybdenum–carbon bond in (9) suffers cleavage only by addition of highly concentrated solutions of strong protonic acids to give the neutral complex [Mo(η5-C5H5)(NO) Br2(PPh3)] with HBr, or the dicationic complex [Mo(η5-C5H5)(NO)(PPh3)2L]2+[L = Me2CO (15)] with HBF4. The same compound (9) reacts with LiR to give dialkyl complexes [MoMe(R)(η5-C5H5)(NO)(PPh3)][R = Me (16), C2Ph (17), or C6F5(18)]. The structure of complex (9) has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/a with a= 18.778(5), b= 14.713(5), c= 8.354(3)A, β= 102.77(2)°, and Z= 4. The structure has been solved from diffractomer data by Patterson and Fourier methods and refined by full-matrix least-squares methods to R= 0.036 for 2 532 observed reflections. The structure is of the ‘four-legged piano stool’ type with the PPh3 and Me ligands in trans positions. The Mo–N and N–O bond distances [1.814(6) and 1.115(8)A respectively] indicate considerable Mo–NO back-bonding. The Mo–N–O group is nearly linear [171.3(6)°].

Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. II. p‐vinylphenyl glycidyl ether: An epoxy‐functionalized styrene

Abstractp‐Vinylphenyl glycidyl ether (VPGE), a styrene derivative with an epoxy pendant, was polymerized by various cationic initiators, and its selective vinyl polymerization was investigated at low temperatures below −15°C. BF3OEt2 (a metal halide) and CF3SO3H (a strong protonic acid) polymerized both vinyl and epoxy groups of VPGE, and produced cross‐linked insoluble polymers. The HI/I2 initiating system and iodine, in contrast, polymerized its vinyl group in polar solvents (CH2Cl2 and nitroethane) highly selectively in the temperature range of −15 to −40°C to give soluble polymers with a polystyrene backbone and epoxy pendants; however, under these conditions, 10–15% of the epoxy groups of the polymers were consumed during the polymerization by the reaction with the growing species. The polymerization by HI/I2 in CH2CI2 involved a long‐lived propagating species, as indicated by a progressive increase in the molecular weight (M̄n) of the polymers with monomer conversion and their fairly narrow molecular weight distributions (M̄w/M̄n ∼ 1.6). The differences between the polymerizations of VPGE and p‐isopropenylphenyl glycidyl ether, an α‐methylstyrene‐type counterpart of VPGE, were also discussed with an emphasis on the effects of the α‐methyl group in the latter monomer.

Acidity and catalytic properties of H · Na-ZSM-8 zeolite: Effect of H + exchange, pretreatment condition, and poisoning of stronger acid sites

The influence of degree of H + exchange and calcination temperature of H · Na-ZSM-8 on its acidity distribution (measured by the chemisorption and stepwise thermal desorption of pyridine at 373–773 K) and catalytic properties for hydrocarbon conversion (viz., isomerization of o- and m-xylene and disproportionation of toluene) and methanol-to-aromatics conversion reactions have been investigated. Both the acidity and catalytic activity in these reactions increase with the decrease in Na + content and calcination temperature of the zeolite. The effect of poisoning of stronger acid sites with pyridine on the catalytic properties of the zeolite has also been studied. The catalytic activity and selectivity of the zeolite are strongly affected by this poisoning. The hydrocarbon conversion and aromatization reactions occur on strong protonic acid sites of the zeolite. Good correlations between catalytic activity and acidity (measured in terms of the chemisorption of pyridine at 673 K) have been obtained for these reactions. The increase in Na + content and calcination temperature and the poisoning have resulted in the increase in the shape selectivity of the zeolite in the formation of xylene isomers (i.e., the formation of p-xylene is increasingly favored) because of diffusion-reaction interactions. The physical, acidic, and catalytic properties, shape-selectivity behavior, and catalyst deactivation characteristics of ZSM-8 and ZSM-5 zeolites are compared.

Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. I. p‐isopropenylphenyl glycidyl ether: An epoxy‐functionalized α‐methylstyrene

Abstractp‐Isopropenylphenyl glycidyl ether (IPGE), a monomer of dual cationic functionality (isopropenyl and epoxy), was polymerized by a variety of initiators, and optimum conditions were established for its selective vinyl cationic polymerization. The hydrogen iodide/iodine (HI/I2) initiating system or iodine polymerized selectively the isopropenyl group in CH2Cl2 at a low temperature (−78°C), to produce soluble poly(IPGE) with epoxy pendants. Under these conditions, the number‐average molecular weight of the polymers was inversely proportional to the initial initiator concentration, indicating the formation of long‐lived propagating species. Soluble poly(IPGE) was also obtained at −15 and −40°C by HI/I2 or iodine. However, at these higher temperatures, transfer and/or termination reactions took place to give olefin‐terminated polymers, in which some of the pendant epoxy groups were consumed. BF3OEt2 (a metal halide) and CF3SO3H (a strong protonic acid) polymerized both epoxy and isopropenyl groups of IPGE and yielded crosslinked insoluble polymers.

ChemInform Abstract: Correlation Between 119Sn Isomer Shifts and Quadrupole Coupling Constants for Dimethyltin(IV) Salts of Strong Protonic Acids and Superacids.

ChemInform Abstract: Correlation Between 119Sn Isomer Shifts and Quadrupole Coupling Constants for Dimethyltin(IV) Salts of Strong Protonic Acids and Superacids.

Valence Isomers of Compounds with Geminal Aryldiazene and Isocyanate Functions Stabilized by Protonation

Cyclic diazenium salts 2 are formed quantitatively upon treatment of compounds 1, containing the NNCNO structural unit, with strong protonic acids. Compounds 2, RMe, ArylPh, are characterized, in particular, by the very long CN bonds and the small angle between the five-membered ring and the phenyl group (only 17°).

Correlation between tin-119 isomer shifts and quadrupole coupling constants for dimethyltin(IV) salts of strong protonic acids and superacids

This communication identifies the structure and spectroscopic features of diethyltin(IV) salts, provides a rationale for the correlation between the /sup 119/Sn isomer shift (delta) and the quadrupole splitting (..delta..E/sub Q/) for the compounds, and suggests the use of the (CH/sub 3/)/sub 2/Sn group as an electronic probe in the estimation of anion basicities. The structural studies revealed essentially linear C-Sn-C groups with octahedral coordination for tin achieved by weakly coordinated, symmetrically bridging bidentate F or SO/sub 3/F anions. The /sup 119/Sn Moessbauer spectra indicated similar geometry in all dimethyltin(IV) salts. Quadrapole coupling constants for all compounds studied were well in excess of 4.12 mm s/sup -1/, and there was a gradual concomitant increase in delta with increasing ..delta..E/sub Q/. 20 references, 1 figure, 1 table.

Herstellung und Isomerisierung von 1-Alken-3-yl-acetaten und 2-Alken-1-yl-acetaten

Synthesis and Isomerization of 1-Alken-3-yl Acetates and 2-Alken-1-yl Acetates The allylic rearrangement of 1-alken-3-yl acetates in acetic acid containing sodium acetate proceeds at a slower rate but in higher yield than the rearrangement in the presence of strong proton acids. The predominant products are 2-alken-1-yl acetates. (E)-2-Hexen-1-yl acetate can be isomerized to the (Z)-isomer or rearranged to 1-hexen-3-yl acetate via the epoxide, depending upon the conditions of reduction of the epoxide.

Comparison of the cationic polymerization of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

AbstractSome features of the cationic polymerization of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) in methylene chloride in the presence of a strong protonic acid (CF3SO3H) were compared. The polymerizations of both these monomers show many similarities, which are taken as evidence for analogies in their mechanisms. In particular, in both cases the reaction is affected by the addition of a small amount of water. The role of water is interpreted in terms of its direct participation in some elementary reactions of the process. The addition of water affects also the state of hydrogen bonding association in the system. Some experimental results together with comments concerning the mechanism of ring formation in the polymerization system are included.

Some new compounds containing N(SO 2F) 2 group

Imidobis(sulfuryl fluoride), HN(SO 2F) 2, is a strong protonic acid. Like other strong protonic acids it forms adducts with carboxylic acids having composition RCOOH.HN(SO 2F) 2; R = CH 3, C 2H 5, n-C 3H 7, CF 3, CH 2Cl. The adducts are ionic, N(SO 2F) 2 is a potential pseudohalogen group. MN(SO 2F) 2, M = Co, Ni, Cu and SbCl 4N(SO 2F) 2 have been prepared and characterized. Compounds of the type A 2 [TiCl 4Y 2], A[FeCl 3Y], A 2[MCl 2Y 2], (A = Me 4N and/or S 4N 3; Y = N(SO 2F) 2; M = Mn, Fe, Co, Ni, Cu) will also be discussed.

Main-group derivatives of the highly electronegative OIF 4O-group

The oxygen-bonded derivatives FXeOIOF 4 and Xe(OIOF 4) 2, including all isomers derived from cis-trans isomerism associated with the OIF 4O-group, have been observed as the reaction products in IO 2F 3/XeF 2 solution mixtures by 19F and 129Xe NMR spectroscopy. The 129Xe chemical shifts have been used to establish that the OIF 4O-group is the most electronegative group known next to fluorine. In addition, the Xe(IV) derivative F 3XeOIOF 4, has also been characterized in solution. Generally, the isolation of OIF 4O-derivatives may not be accomplished by routes analogous to those used in the syntheses of -OTeF 5 derivatives. For example, direct reaction of HOIOF 4 and XeF 2 may lead to violent detonations which arise from the formation of the shock-sensitive hypofluorite, FOIOF 4. The formation of FOIOF 4 is circumvented by avoiding the use of fluoride precursors. Thus, it is possible to synthesize and isolate cis,cis- Xe(OIOF 4) 2 by displacement of volatile HOTeF 5 from Xe(OTeF 5) 2 by reaction with a stoichiometric amount of the strong protonic acid HOIOF 4. The solid state low-temperature Raman spectrum as well as the 19F and 129Xe NMR spectra are consistent with the proposed cis,cis-structure.

Catalysis by heteropoly compounds: IX. Role of water in catalytic dehydration of 2-propanol over copper salts of H 3PW 12O 40

The catalytic and acidic properties of copper salts of 12-tungstophosphoric acid have been studied. An induction period was observed in the dehydration of 2-propanol and it became longer as the water content decreased. In addition the catalytic activity was enhanced by the addition of water to the feed gas. This catalytic behavior has been explained on the basis of the “pseudo-liquid phase” model as follows. The absorption of 2-propanol into the bulk of the copper salts was accelerated by the presence of water. Thus, the increase of the rate is ascribed to the expansion of the effective reaction zone caused by water-promoted absorption of 2-propanol. Infrared spectroscopy of adsorbed pyridine revealed that the copper salts were strong protonic acids, and the amounts of proton were about one-third that of the acid form. Based on the infrared data of absorbed pyridine and electron spin resonance of Cu 2+, the mechanism for the generation of acidity is discussed.

Organometallic nitrosyl chemistry. 18. Electrophile-induced reduction of coordinated nitrogen monoxide. Sequential conversion of a .mu.3-nitrosyl group to .mu.3-hydroxylimido and .mu.3-imido ligands by protonic acids

The principal impetus for the investigation of the reactivity of coordinated nitrogen monoxide derives from the widespread occurrence of nitrogen oxides as atmospheric pollutants. Initial studies in this regard were focused primarily on the behavior of nucleophiles or electrophiles toward linear or bent M-NO linkages, respectively. More recent research has begun to examine the analogous reactivity patterns of transition-metal complexes containing doubly bridging NO groups. However, maximum reduction of the N-O bond order (and hence optimum activation of the bond NO) should occur in M/sub 3/(..mu../sub 3/-NO) systems. Accordingly, we have investigated the reactions of one such system with strong protonic acids and now report unprecedented, sequential transformations where M = (n/sup 5/C/sub 5/H/sub 4/Me)Mn(NO) which involve an overall formal reduction of the ..mu../sub 3/-NO ligand.

ChemInform Abstract: CATALYSIS BY HETEROPOLY COMPOUNDS. III. THE STRUCTURE AND PROPERTIES OF 12‐HETEROPOLYACIDS OF MOLYBDENUM AND TUNGSTEN (H3PMO12‐XWXO40) AND THEIR SALTS PERTINENT TO HETEROGENEOUS CATALYSIS

AbstractDie grundlegenden Eigenschaften von 12‐Heteropolysäuren des Mo und W, wie Struktur, Oberfläche, Acidität und Redoxmechanismus im festen Zustand werden im Hinblick auf die heterogene Katalyse untersucht.