Group Exchange Reactions Research Articles

Efficient synthesis of 2-methoxy- and 4-methoxy-estrogens

2-Methoxy- and 4-methoxy-estrogens are easily prepared from the corresponding 2-iodo or 4-bromo derivatives in high yields by a halogen–methoxy group exchange reaction using sodium methoxide–copper(II) chloride.

Electrical Conduction of Polypeptides as Related to Molecular Structure

The temperature dependence of electric conductivity, the frequency and temperature dependence of the dielectric constant, and the hydrogen–deuterium exchange reaction of the amide group were studied for solid poly(γ-methyl L-glutamate), poly(γ-benzyl L-glutamate), and poly(β-benzyl L-aspartate). A linear relation was found between the activation energy for conductivity and the reciprocal of the static dielectric constant, and was interpreted in terms of the carrier generation process. The conductivity at the glass-like transition temperature was about 3×10−18 ohm−1 cm−1. The generation of protons from the amide groups was concluded to be a source of the charge carriers in solid polypeptides.

Reaction of hydrogen atoms with diethyldisulfide and ethylmethyldisulfide

AbstractH atoms react with C2H5SSC2H5 to give C2H5SH as the sole retrievable product with ϕ = 2.32 at 25°C and 2.84 at 145°C. The primary reaction is postulated to be H + C2H5SSC2H5 ← C2H5SH + C2H5S with k1 = (4.73 ± 0.64) × 1013 exp [−(1710 ± 69)/RT] cm3/mol·s relative to the rate constant of the H + C2H4 ← C2H5 reaction. The high value of the entropy of activation suggests the presence of partial hydrogen bonding in diethyldisulfide which is broken in the transition state.Ethylmethyldisulfide reacts similarly: H + C2H5SSCH3 ← C2H5SH + CH3S or CH3SH + C2H5S. The thiyl radicals propagate a chain of radical exchange reactions forming the symmetrical disulfides with exposure‐time‐dependent quantum yields. The overall kinetics conform to a 16‐step mechanism from which the rate constants of the elementary reactions could be established by computer modeling. Thiyl radicals react considerably more slowly with disulfides than H atoms.

Oxygen-18 isotope effect in carbon-13 nuclear magnetic resonance spectroscopy. 4. Oxygen exchange of [1-13C,18O2]acetic acid in dilute acid

The /sup 18/O-iosotope shift in /sup 13/C NMR spectroscopy is shown to provide a widely applicable technique for studying the kinetics of oxygen exchange reactions in a nearly continuous assay mode. Here, the technique is used to study the acid-catalyzed medium carboxyl(oxygen)-water exchange reaction of (1-/sup 13/C, /sup 18/O/sub 2/)acetic acid at 32/sup 0/C. The /sup 18/O-isotope-induced shift fo the /sup 13/C NMR signal of the /sup 13/C-enriched carboxyl carbon in acetic acid permits a facile and direct measurement of the relative concentrations of the three (oxygen) isotopic species of acetic acid. The pseudo-first-order rate constant is evaluated as a function of pH and added salt for the salts sodium chloride and sodium perchlorate. The pH profile is typical of those observed for related acid-catalyzed oxygen exchange reactions of the carboxyl group. In the dilute-acid region the rate is approximately first order in hydrogen ion. The present results definitively establish the salt effect on the exchange reaction, resolving a conflict between earlier reports. The rate of the exchange reaction is decreased by increasing concentrations of the two salts. The magnitude of the rate decrease depends on he nature as well as the concentration of the salt. Possible interpretations of themore » results are discussed.« less

Complexation and exchange reactions of some dimethylamino-substituted group 4 compounds

Reactions of CH2(NMe2)2, (1), SiMe2(NMe2)2, (2), [Ti(cp)(NMe2)3](cp =η-cyclopentadienyl), (3), and [Zr(cp)2(NMe2)2], (4), with covalent metal halides MCl4(M = Ti, Zr, Hf, Si, Ge, or Sn) and MCl3(M = Ti, V, or Cr) fall into two categories: (a)N-donor chelation leading to complex formation and (b) halide–NMe2 exchange. Compound (1) gives 1 : 1 complexes with MCl4(M = Ti or Sn) and a 2 : 1 complex with VCl3. Compound (2) provides 1 : 1 complexes with MCl4(M = Ti, Zr, Hf, or Sn). The decomposition of TiCl4·SiMe2(NMe2)2→[TiCl3(NMe2)] invariably occurs in both the solid state and solution. There is no reaction of (2) with metal(III) chlorides. With MCl4(M = Si or Ge)‘scrambling’ reactions involving halide–NMe2 exchange occur and these have been monitored by 1H n.m.r. spectroscopy. Reactions of (3) and (4) with MCl4(M = Si, Ge, Sn, Ti, Zr, or Hf) consistently feature halide–NMe2 exchange rather than adduct formation. All complexes have been characterised by analytical and spectroscopic (1H n.m.r. and i.r.) investigations.

Reactions of Me 2Al-i-Bu and Me 2AlCCMe with primary and secondary amines

The elimination reaction which takes place in complexes of dimethylisobutylaluminium or dimethylpropynylaluminium and N-methylaniline, di- n-butylamine or octylamine was investigated. The abilities of methyl, isobutyl and propynyl groups to take part in elimination reactions were different. A radical exchange reaction was observed.

Migration of hydrogen atoms from cyclopentadienyl rings to metal and hydrogen exchange reactions upon thermal decomposition of dicyclopentadienyl compounds of titanium and zirconium

Thermal decomposition of Cp 2MR 2- d 10 (M= Ti, Zr; R = CH 3, C 6H 5) has been studied. It has been shown that upon thermolysis of Cp 2MR 2 the migration of hydrogen atoms from Cp rings to the metal occurs which leads to destruction of the cyclopentadienyl group and hydrogen exchange reactions. Upon thermal decomposition of Cp 2Zr(CH 3) 2 exchange between the hydrogens of the Cp and R groups has been observed. The thermolysis of Cp 2MR 2 in the presence of Cp 2V-d 10 leads to the formation of RD and vanadocene of d 0– d 9 forms. Zirconium compounds are the most active ones in hydrogen exchange reactions. There is no hydrogen exchange upon thermal decomposition of Cp 2VR 2 (R = CH 3) in the presence of Cp 2V- d 10.

Synthesis, Reactions and Catalytic Properties of Stable Alkoxocopper, Phenoxocopper and Related Copper Complexes Containing Triphenylphosphine Ligands

Abstract A variety of new alkoxocopper and phenoxocopper(I) complexes containing triphenylphosphine ligands have been prepared by the reactions of methylbis(triphenylphosphine)copper(I) etherate (I) with the corresponding alcohols and phenols. The isolated complexes were characterized by elemental analysis, IR and NMR spectroscopy and chemical reactions. The reactions of the alkoxocopper and phenoxocopper complexes with alkyl halides and acyl halides or carboxylic anhydrides yield ethers and carboxylic esters, respectively. The stoichiometric exchange reactions of the alkoxo group in the alkoxocopper complexes with carboxylic esters proceed smoothly and the alkoxocopper complexes were found to act as excellent catalysts for the transesterifications between carboxylic esters and alcohols. The exchange reactions take place also between the alkoxocopper complexes and phenols or thiols producing phenoxocopper or alkylthiocopper complexes with the liberation of alcohols. Amides and nitromethane react with the alkoxocopper complexes releasing alcohols to give N-bonded amidocopper and O-bonded acinitrocopper complexes, respectively. The thermolysis of the alkoxocopper complexes in various solvents were studied and the mechanism and the factors influencing the course of thermolysis discussed.

ヘテロ環化合物の研究(第42報)2-[α-Amino-β-(5-nitro-2-furyl)vinyl]furanの反応, および2-Furyl 5-Nitro-2-furfuryl Ketone類の合成について

Hydrolysis of 2-[α-amino-β-(5-nitro-2-furyl)vinyl] furan (I) gave 2-furyl 5-nitro-2-furfuryl ketone (II), and acetylation of I gave two kinds of compounds, mono- and diacetylamine. Results of other chemical reactions related to the amino group of I indicated that alkylation by propyl iodide, condensation with furfural, and amino group exchange reaction by morpholine were unsuccessful. Nine kinds of β-2-furoyl-β-(5-nitro-2-furyl)-vinyl derivatives and four kinds of 2-(2-furyl)-3-(5-nitro-2-furyl)-4, 5-disubstituted pyrrole derivatives were synthesized from II.

Tetraethylalumoxane—benzonitrile complex

Tetraethylalumoxane was found to form a complex with benzonitrile in the molar ratio 1 : 1. This complex is a monomer. The structure of the complex is proposed on the basis of molecular weight determinations, IR and PMR investigations, and the alkyl group exchange reaction with tetramethyllead. The acidities of tetraethylalumoxane and triethylaluminium are compared.

Purification and properties of 3-keto-5-aminohexanoate cleavage enzyme from a lysine-fermenting Clostridium.

The lysine-fermenting Clostridium SB4 is shown to contain a new type of beta-keto acid-degrading enzyme that converts 3-keto-5-aminohexanoate and acetyl-CoA reversibly to L-3-aminobutyryl-CoA and acetoacetate. Following the development of a sensitive radiochemical assay the enzyme was purified 175-fold to about 90% homogeneity in 44% yield. The specific activity of the purified enzyme is 44 IU/mg of protein at 30 degrees. The equilibrium constant for the forward reaction was found to be 0.68 at 30 degrees and pH 7.0, corresponding to a deltaG0' of 0.23 kcal/mol. The enzyme is highly substrate-specific. Of several substrate analogs tested in the forward and back reactions only beta-alanyl-CoA and D-3-aminobutyryl-CoA are utilized about 130% and 1.7% as fast as L-3-aminobutyryl-CoA, respectively. The product formed from beta-alanyl-CoA and acetoacetate is a neutral beta-keto acid, presumably 3-keto-5-aminopentanoic acid; its borohydride reduction product was partially characterized as a hydroxy-amino acid by various chromatographic and ion exchange methods. The activity of the purified enzyme is increased about 5-fold by addition of 0.1 mM Co2+ and to a lesser extent by Mn2+. Activity is inhibited by orthophosphate, thiol reagents, and EDTA; however, exposure of the enzyme to the latter compound prior to addition of Co2+ increases activity, presumably by removing competing divalent cations. Tracer experiments have shown that carbon atoms 1 and 2 of acetoacetate are derived from carbon atoms 1 and 2 of 3-keto-5-aminohexanoate whereas carbon atoms 3 and 4 are derived from acetyl-CoA. The amino acid moiety of 3-aminobutyryl-CoA is derived from carbon atoms 3 to 6 of 3-keto-5-aminohexanoate. Since no evidence for covalent enzyme-substrate intermediates could be obtained by the study of four possible group exchange reactions, a concerted reaction between 3-keto-5-aminohexanoate and acetyl-CoA is considered. The enzyme has a molecular weight of about 97,000 and probably contains four identical subunits. The relatively high specific activity of the enzyme in extracts of Clostridium SB4 indicates it functions in the main pathway of lysine degradation. This relatively stable enzyme provides a convenient and specific method for the quantitative estimation of nanomolar amounts of L- and D-3-aminobutyryl-CoA and beta-alanyl-CoA.

Reactions of bis(trifluoromethyl)nitroxyl with (CF 3) 3M (M=P, Sb) and properties of bis(trifluoromethyl)nitroxy derivatives of P, As and Sb

Bis(trifluoromethyl)nitroxyl gives an addition reaction with tris(trifluoromethyl)phosphine and radical exchange reactions with stibine. The mechanisms of the above reactions and the properties of bis(trifluoromethyl)nitroxy derivatives of phosphorus, arsenic and antimony are discussed.

CATALYTIC ACTIVITY OF ZrO2AND ThO2FOR H-D EXCHANGE REACTION BETWEEN METHYL GROUP OF ADSORBED ISOPROPYL ALCOHOL-d8AND SURFACE OH GROUP

The H-D exchange reaction of methyl group of adsorbed isopropyl alcohol-d8 with surface OH group was studied over several metal oxides by means of reflectance IR spectroscopy. Zirconium oxide and ThO2 showed a significant catalytic activity for the exchange reaction, though SiO2, Al2O3, TiO2, and SiO2–Al2O3 were all inactive.

Reaction zone thickness and formation of nitric oxide in turbulent diffusion flames

The Gibson-Libby [1] formula for the thickness of the reaction zone in a diffusion controlled-reaction is revised to account properly for the concentration gradients that occur in fully turbulent flow. The result is that the reaction zone is thickened considerably. When used to calculate reaction zone thickness in turbulent diffusion flames these are now found to be of the same order as the Kolmogoroff length scale. The presence of a relatively diffuse reaction zone allows the oxygen atom concentration to be above equilibrium over a significant proportion of the flow. For a hydrogen-air flame, O atom concentrations can be calculated from the assumption of equilibrium for the fast radical exchange reactions, with the hydrogen and oxygen molecule concentrations computed from the Kolmogoroff concentration fluctuation scale. With these assumptions nitric oxide formation rates show the Reynolds number dependence and “rich shift” found by Kent and Bilger [2] and Bilger and Beck [3].

Reactions of coordinated molecules : III. Alkoxy substituent exchange reactions on a cyclic ligand

The extraction of an ethoxide anion from a β-diethylacetal-acyl ligand of a neutral organometallic molybdenum complex affords a cationic complex having a cyclic ligand which is described best as a metal-stabilized oxonium ion. This ligand has an unusually reactive saturated carbon atom which reacts with a variety of alcohols and with ethanethiol via an alkoxy group exchange reaction affording a differently substituted cyclic ligand. The oxidization of the metal—ligand bond in the initial complex forms 4-ethoxy-γ-butyrolactone and, therefore, it is a precursor for the preparation of a variety of 4-substituted-γ-butyrolactones. The reaction of this complex with sodium methoxide and dimethyl sulfoxide is discussed, also.

The stabilisation of PVC: A study of the reaction of dry hydrogen chloride with white lead suspended in hot mineral oil

AbstractThe reaction of dry hydrogen chloride with a suspension of white lead in hot mineral oil (MO) has been studied by withdrawing samples and examining the solids by X‐ray powder diffraction (XRPD). The white lead basic lead carbonate was slowly converted into tribasic lead chloride, which itself reacted to form “basic lead chloride X”, and this was finally converted into normal lead chloride. Similarities between this reaction sequence and that observed when plumbonacrite (another basic lead carbonate) was used as a thermal stabiliser in an unplasticised polyvinyl chloride (PVC) blend indicate that this plumbonacrite behaved to a large extent as a scavenger for hydrogen chloride produced by thermal decomposition of the polymer. However, it is suggested that true stabilisation (by free radical exchange reactions which retard thermal decomposition of the polymer) may also take place to varying extents in rigid (unplasticised) PVC blends, depending on the formation and mobility of intermediate stabilising species (the most effective of which seem to be the lead compounds of organic acids). This behaviour is different from that in plasticised materials where true stabilisation seems to be the dominant reaction. XRPD data are tabulated for the uncharacterised “basic lead chloride X”.

The orbital description of the potential energy curves and properties of the lower excited states of the BH molecule

The electronic wavefunctions for the ground (X 1 Σ +) and the low-lying excited states (a 3Π, A 1Π, 3Σ +) of the BH molecule have been calculated as a function of internuclear distance using the ab initio generalized valence bond method (GVB) with optimization of spin coupling (SOGI). The potential curve of the A 1Π state in the zero rotational level is found to have a hump of 0.150 eV at R = 3.8 9 a o (experimentally a hump of unknown size is found at 3.9 ± 0.4 a 0); a smaller hump at larger R (0.02 eV at R = 4.9 2 a 0) is also found for the calculated a 3Π state. The presence of such humps is found to result from the recoupling of orbitals that must occur as R is decreased from ∞ to R e and is comparable in origin to the activation barrier in a radical exchange reaction (e.g., H 2 + D ⇌ HD + H). The calculated binding energies of the BH states are 3.272 eV (X 1 Σ +), 2.216 eV (a 3 Π), and 0.502 eV (A 1 Π). The 3Σ + state is unbound although it does exhibit a small unbound minimum. The dipole moment, quadrupole moment, and electric field gradient are calculated as a funtion of R. The shapes of the potential curves and the properties are interpreted in terms of simple qualitative considerations of the GVB orbitals.

Electron transfer reactions involving cobalt(II) and organometallic cobalt(III) Schieff-base complexes

Group exchange reactions have been studied between organocobalt(III) derivatives containing Schiff-base ligands and related cobalt(II) complexes. Reactions are fast in DMSO for cobalt(III) alkyls but very slow for fluoroalkyl and aryl derivatives. Measurably slow reactions occur with CF 3CH 2 substituents. A mechanism is proposed involving nucleophilic attack of a cobalt(II) species on the carbon atom attached to cobalt(III).

Methyl group exchange reactions of trimethylaluminium dimer

Variable temperature susceptibility measurements have been made on a number of bis(N,N-dialkylmonothiocarbamato)nickel(II) complexes. The results are characteristic of ferromagnetically coupled NiII clusters. Within the range 300-80 K the susceptibilities can be fitted extremely well to a number of possible cluster models and it is not possible to distinguish the exact molecularity. ��� Measurements on one of the complexes down to liquid helium temperatures confirm the ferromagnetic behaviour and demonstrate inter- cluster interaction at very low temperatures. The magnetic behaviour of these complexes contrasts with the diamagnetism of the square planar bis(N,N-dialkyldithiocarbamato) analogues.

Photoreactions of Nitroso Compounds in Solution. XXI. Stereochemical Course of Photoaddition of Nitrosamines to some Cyclic Olefins and Conformational Isomers Generated by A1,3-Interaction

The results of the photoadditions of N-nitrosopiperidine and N-nitrosodimethylamine to three substituted cyclohexenes are discussed in terms of an "electrophilic" free radical attack of the aminium radicals generated from the photolysis of the nitrosamines. The photoaddition to 4-t-butylcyclohexene gave all four possible oximes; the axial approach of the aminium radical was preferred over the equatorial approach. The photoadditions to 3-methylcyclohexene are highly stereoselective giving oxime pairs 1–2 and 4–5. Both oximes in each pair have 2-amino and 6-methyl substituents in trans-relation; but locked in the alternative conformations through A1.3 interaction of the oximino group. In this addition the aminium radical almost exclusively approaches the C-1 carbon of the most stable conformer from the axial side. The steric hindrance to all possible axial and equatorial approaches to conformers of olefins have been compared. Piperidinium radicals, however, abstract an allylic hydrogen from Δ9,10-octaline since the steric hindrance in the addition process is too great to overcome. The hydrogen abstraction process leads to an intermolecular hydrogen–nitroso group exchange reaction which is similar to that in the photolysis of nitrosamides. A pathway is suggested to account for the generation, insitu, of the heteroannular diene 28 from which oxime 17 could be derived by photoaddition in 1,4-mode.