Heterocyclic derivatives of purines. 3. Synthesis and mass spectrometric study of imidazo[1,2-]purine

A mixture containing 65% 1-methyl-2-phenyl-5,7-dichloro- and 35% 1-methyl-2-phenyl-3,5,7-trichloroimidazo [1,2-f] purine (the percentages of the components were established by means of Chromatographic mass-spectrometric analysis) was obtained by refluxing 1,8-dimethyl-2-phenylimidazo [1,2-f]xanthine in POCl₃ in the presence of excess PCl₅. Reduction of this mixture with concentrated HCl in the presence of red phosphorus leads to 1-methyl-2-phenylimidazo[1,2-f] purine, while heating with piperidine gives a mixture consisting of 55% 1-methyl-2-phenyl-6-piperidino-8-chloroimidazo [1,2-f] purine and 45% 1-methyl-2-phenyl-3, 8-dichloro-6-piperidino-imidazo [1,2-f] purine. The IR, PMR, and mass spectra of the compounds obtained are discussed.See [1] for communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1125–1129, August, 1980.     

Mechanisms of the reactions of chloromethanes with trimethylstannylsodium. Synthesis of tetrakis[trimethylstannyl]methane.

The reactions of CCl₄, CHCl₃, and CH₂Cl₂ with trimethylstannylsodium in tetraglyme have been examined. Tetrakis[trimethylst?annyl]methane can be obtained by reaction with CCl₄ in yields of about 40%. Among other products which have been characterized in varying degree are the following: trichloromethyltrimethylstannane, bis[trimethylstannyl]dichloromethane, tris[trimethylstannyl]methane, and hexamethyldistannane, The first step in the reaction leads to the formation of the trichloromethyl anion, and dichlorocarbene has been trapped with 2,3- dimethyl-2-butene. Dichlorobis[trimethylstannyl]methane reacts with Me₃SnNa to form tetrakis[trimethylstannyl]methane in 85% yield. When the reaction was carried out in the presence of $\text{t}$-butyl alcohol the only product formed was bis[trimethylstannyl]methane, indicating carbanionic intermediates. Chloroform yields tetrakis[trimethylstannyl]methane and bis[trimethylstannyl]methane, but no detectable tris[trimethylstannylmethane. Trapping experiemtns with 3-pentanol and 2,3-dimethyl-2-butene indicate the intermediacy of dichloromethyl anion and of dichlorocarbene. Methylene chloride yields bis[trimethylstannyl]methane. No intermediates could be trapped by added alcohol.     

A comparative,vapor-phase (G.L.C.-M.S.) study of various derivatives of prostaglandins A and B

The isomeric prostaglandins, A and B, can be readily distinguished by differences in the mass spectra of their derivatives. The mass spectra of the PGA₁- or PGA₂-methyl ester (ME)-trimethyl silyl (TMS) ether derivatives have a prominent ion at [M ? 71]⁺ or [M ? C₅H₁₁]⁺ while those of the PGB₁- or PGB₂-ME-TMS derivatives have a predominant ion at [M ? 99]⁺ or [M ? C₆H₁₁O]⁺ in addition to that at [M ? 71]⁺. Ions of similar origin characterize the spectra of the PGA₁- or PGA₂-TMS ether-TMS ester and PGB₁- or PGB₁-TMS-TMS derivatives, respectively. The fragmentation of other derivatives of PGA₁, PGA₂, PGB₁ and PGB₂ such as the ME-t-Bu-DMS (t-butyl-dimethylsilyl ether); ME-MO (methoxime)-TMS; ME-MO-Ac (acetate), and ME-Ac are also described comparatively. The composition of important ions was confirmed by deuterium labeling and/or high resolution mass spectroscopy, where appropriate. The potential advantages and limitations of the derivatives for quantitative analysis of prostaglandins by the specialized technique of multiple ion detection (MID) are described.     

State of atoms and interatomic interactions in complex perovskite-like oxides: XXXI. Influence of magnesium concentration on chromium atoms state and interatomic interactions in lanthanum gallate doped with chromium and magnesium

Magnetic susceptibility of LaCr _x Ga_1−1.2x Mg_0.2x O_3−δ and LaCr _x Ga_1−1.5x Mg_0.5x O_3−δ solid solutions with the ratios [Cr]:[Mg] = 5:1 and 2:1 was studied. Fractions of clusters and single chromium atoms were calculated for the series of solid solutions with [Cr]:[Mg] = 5:1. The relation of the systems with [Cr]:[Mg] = 5:1 and [Cr]:[Sr]:[Mg] = 5:1:1 was revealed. For the system with [Cr]:[Mg] = 2:1 a temperature dependence of effective magnetic moment was found, which suggests that the exchange parameter is temperature dependent.     

Search for regular polypeptides possessing esterase properties. I. Polypeptides containing tyrosine and glutamic acid residues

An investigation has been made of the catalytic properties in relation to the hydrolysis of p-NPA of six polypeptides of regular structure: H-[Glu-Tyr]_n-OH (1), H-[Glu₂-Tyr]_n-OH (2), H-[Glu-Tyr₃]_n-OH (3), H-[Glu₃-Tyr]_n-OH (4), H-[Glu₃-Tyr]_n-OH (5), and H-[Glu-Tyr₂]_n]-OH (6). It has been shown that polypeptides (I), (III), and (IV) catalyze the hydrolysis of p-NPA (p-nitrophenyl acetate). An enzyme-like type of catalysis has been found. Some catalytic characteristics have been calculated and the dependence of the rate of hydrolysis on the pH of the medium, the temperature, and the concentration of p-NPA have been discussed. The structures of the catalytically active and catalytically inactive polypeptides have been studied by the circular dichroism method. It has been shown that under conditions in which the catalytic properties of polypeptides are shown to the maximum degree there is a structure of the random coil type. The catalytic activity falls or disappears completely when ordered fragments of the α-helix and β-structure types appear in the structure. It has been found that polypeptide (I) possesses the maximum catalytic activity. It exceeds the activity of a copolymer of the same amino acids by an order of magnitude.     

Novel Methods of Synthesis of Dibenzo[3n]crown-n and Their Cation Binding Studied by Fluorescence Spectroscopy. Part V

The dibenzo[3n]crown-n were synthesised starting from bis[2-(o-hydroxyphenoxy)ethyl]ether obtained from bis[2-(o-formylphenoxy)ethyl]ether via Baeyer-Villiger oxidation in H₂O₂/CH₃COOH in a good yield. The cyclic condensation ofbis[2-(o-hydroxyphenoxy)ethyl]etherwith tri- and tetraethylene glycol bisdichlorides andthe bisditosylate of pentaethylene glycol in DMF/Me₂CO₃ afforded the large cyclic ethers of dibenzo[21]crown-7, dibenzo[24]crown-8 and dibenzo[27]crown-9. The structures were analysed with IR, ¹H NMR, ¹³C NMR and low-resolution mass spectroscopy methods. The Na⁺, K⁺, Rb⁺ and Cs⁺ cations' recognition of the molecules were conducted withsteady-state fluorescence spectroscopy. The 1:1 association constants, K_a, in acetonitrile were estimated. Dibenzo[21]crown-7 was the best both for K⁺ and Rb⁺ binding but showed too small an effect on Cs⁺. Dibenzo[24]crown-8 exhibited the binding power in the order of Rb⁺ > K⁺ > Na⁺ > Cs⁺. However, dibenzo[27]crown-9 displayed marked binding with only K⁺ but not with Rb⁺ or with Cs⁺ cations probably due to the heavy atom effect of fluorescence quenching.     

Linear and Cyclic Enkephalin Pseudopeptides. Use of RP-HPLC to Separate and Identify Diastereomers Formed during Synthesis

Abstract

During the course of synthesis of both a linear and a cyclic enkephal in pseudopeptide containing a ψ[CH₂S] amide bond replacement, two isomeric products were produced in each case in virtually equimolar quantities. RP-HPLC was used to: 1) isolate and characterize both pairs of products; 2) confirm their sulfide content by partial oxidation to their ψ[CH₂SO] equivalents, with two new pairs of diastereomeric sulfoxides formed in each case, and 3) confirm that the isomers were formed by epimerization of the C-terminal alpha carbon of the pseudopeptide, H-Tyr-D-Ala-Gly-Pheψ[CH₂S]Leu-OH and its cyclic counterpart in an early synthetic step. Both the presence and the absolute configurations of the new epimeric center were further established by RP-HPLC. This involved acid catalyzed hydrolysis and comparison of the resulting HPLC-isolated pseudodipeptides with authentic species of Pheψ[CH₂S]Leu and Pheψ[CH₂S]D-Leu prepared by controlled stereochemical routes.     

Metal Complexes with Macrocyclic Ligands. Part XL. Syntheses and silver(I) complexes of mono- and disubstituted dithiadiazamacrocycles

A series of N₂S₂-macrocycles with ring sizes varying between 12 and 16, as well as two 12-membered N₂S₂-rings with a pendant carboxylic and amino group, respectively, were synthesized. Their complexation properties towards Ag⁺ were studied by pH titrations and by potentiometry with a silver electrode. The observation that 1:1 ([AgLH₂]³⁺, [AgLH]²⁺, [AgL]⁺) and 1:2 species ([AgL₂H₂]³⁺, [AgL₂H]²⁺, [AgL₂]⁺) were formed is interpreted by postulating that Ag⁺ can bind either to the S-donors only, or to both the N- and S-atoms. The most stable complex [AgL]⁺ in the series of the nonfunctionalized macrocycles was found for the 12-membered N₂S₂-ring 3 . The stability of it increased when an additional donor group was introduced into the side chain. The highest formation constant (logβ₁₁₀ = 14.43(1)) was obtained with the 12-membered ring 12 carrying the ethanamine side chain. In view of a radiochemical application, all Ag⁺ complexes were tested in blood serum for their stability, but were not stable enough against transmetallation.     

Investigation of heterocycles containing nitrogen or sulfur. 48. Derivatives of 1-morpholinooxalyl-1,2-dihydrothiazolo-[5,4-b]pyridine,their structure,and reactions

The structures of the products of reactions of 1-N-morpholinooxahi-1,2-dihydrothiazolo-[5,4-b]pyridine have been studied by IR, NMR, UV, and mass spectroscopy. Geometric (cis-anti) and rotational (about the CO-N amide bond) isomers of 1-N-morpholinooxalyl-2-propionyi-5-chloro-1,2-dihydrothiazolo-[5,4-b]pyridine oxime have been observed and studied. Treatment of 1-N-morpholinooxalyl-2-propionyl-5-chloro-1,2-dihydrothiazolo[5,4-b]pyridine with ethanolic alkali gave 2-propionyl-5-chlorothiazolo-[5,4-b]pyridine, while treatment with concentrated H₂SO₄ gave 1,2-dioxo-ethylidene-7-chloroxazolidino[3,2-f]pyrido[2,3-b]1,4-thiazine.For Communication 47 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1133–1138, August, 1993.     

Fragmentation of the enolate ion of 2,3-butanedione. Characterization of the acetyl anion by charge inversion mass spectrometry

The unimolecular and collision-induced fragmentation reactions of the enolate ion of 2,3-butanedione, [CH₃COCOCH₂]^?, have been studied, Unimolecular fragmentation on the metastable ion time-scale forms [HCCO]^?, [C₂H₃O]^?, [C₃H₅O]^? and [CH₃CO₂]^?. Charge inversion mass spectrometry shows that the [C₂H₃O]^? ion is the acetyl anion while the [C₃H₅O]^? product is the acetone enolate ion; formation of the latter product involves a large release of kinetic energy (T _1/2 = 0.99 eV). The fragmentation reactions occurring following collisional activation have been determined for 8 keV collisions and over the range 1.5–30 eV center-of-mass collision energy. Formation of [HCCO]^? and [CH₃CO]^? are of the most important reactions following collisional activation and it is concluded that the two reactions have similar critical reaction energies even though formation of [HCCO]^? is favored thermochemically.     

Kinetic Analyis of TG Data XXXV. Spectroscopic and thermal studies of some cobalt(III) chelates with ethylenediamine

A number of 30 [Co(en)₃ ]Y₃ , [Co(en)₂ X₂ ]Y and [Co(en)₂ X(amine)]Y₂ type complexes (X =Cl, Br; Y =Cl, Br, I, NCO, NCS, NO₃ , ClO₄ , etc.; amine =aromatic and alkylamines) were obtained from trans-[Co(en)₂ Cl₂ ]Cl by double decomposition and by substitution reactions, respectively. The structure of the complexes was proved by means of far and middle FTIR spectra. The thermal decomposition was studied by TG, DTA and DSC measurements. Mass spectra were also recorded. In the case of [Co(en)₃ ]Y₃ complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently explosion like. The halides and thiocyanates seem to substitute an ethylenediamine ligand, yielding a rather unstable intermediate. The pyrolysis of [Co(en)₂ X₂ ]Y type derivatives yields no relatively stable intermediates, but the decomposition temperatures may be correlated with the nature of Y and with the cis or trans configuration of the compound. With the [Co(en)₂ X(amine)]Y₂ type complexes one observes the formation of [Co(en)₂ XY]Y as intermediate product. From the TG curves kinetic parameters were derived for some dehydration and deamination processes, by using the nomogram method. The validity of a non-linear kinetic compensation law was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Partially fluorinated heterocyclic compounds. Part 15 [1]. Further preparations of furan derivatives from pentafluorophenyl- and 1,3,4,5,6,7,8-heptafluoro-2-naphthyl prop-2-ynyl ethers. The isolation of the claisen rearrangement intermediate 1,3,4,5,6,7,8-heptafluoro-1-(propa-1,2-dienyl)-naphthalen-2-one

1,3,4,5,6,7,8-Heptafluoro-2-naphthyl prop-2-ynyl ether (5) and boiling isopropylbenzene gives 1,3,4,5,6,7,8-heptafluoro-1-(propa-1,2-dienyl)naphthalen-2-one (9) and two isomeric 2-(isopropylbenzyl)-4,5,6,7,8,9-hexafluoronaphtho [2,1-b]furans (11). Di-(4,5,6,7,8,9-hexafluoronaphtho [2,1-b]furan-2-ylmethyl) ether (17) and bis-(4,5,6,7,8,9-hexafluoronaphtho [2,1-b]furan-2-y1)methane (18) are formed from (5) in CF₂ClCFCl₂ at 137°. The solvolysis of 2-fluoromethyl-4,5,6,7,8,9-hexafluoronaphtho-[2,1-b]furan (10) in water at 145–156° yields (17) (2%), (18) (37%) and 4,5,6,7,8,9-hexafluoronaphtho[2,1-b]furan-2-ylmethyl alcohol (19) (13%). Pentafluorophenyl prop-2-ynyl ether (1) reacts in either C₆F₆ or CF₂ClCFCl₂ at 140° to give di-(4,5,6,7-tetrafluorobenzo [b] furan-2-ylmethyl) ether (15). The major product from the solvolysis of 2-fluoromethyl-4,5,6,7-tetra-fluorobenzo [b] furan (2) in water at 140–142° is 4,5,6,7-tetra-fluorobenzo [b] furan-2-ylmethyl alcohol (16) (87%) accompanied by (15) (2.5%).     

Über Chalkogenolate. LIII. Untersuchungen über Thioameisensäuren 1. Darstellung und Eigenschaften von Monothioformiaten und Monothioameisensäure

Na[HCOS] or [KHCOS] were prepared by hydrolysis of phenyl formate with NaHS or KHS. The monomeric monothioformic acid is formed on treatment of Na[HCOS] with 18% HCl and it can be distilled from the solution in a vakuum at ?5°C. The pale yellowish acid exists in the thiol form HCOSH and polymerizes even at 30°C. The S-methyl ester HCO(SCH₃) is formed on reaction of Na[HCOS] with methyl iodide, and the O-methyl ester HCS(OCH₃) on reaction of methyl orthoformate and H₂S in the presence of ZnCl₂ and hydroquinone. The prepared compounds were characterised by different methods.     

The Photorearrangements of a Naphthobarrelene-like System. Dependence on excited-state spin multiplicity and electronic configuration,and evidence for biradical intermediates. Preliminary communication

8-Benzoyl-9-deuterio-naphtho [de-2.3.4]bicyclo [3.2.2]nona-2,6,8-triene ( 1 ) rearranged quantitatively in a photochemical di-π-methane-type process to 2-, 6-, and 9-deuteriated 1-benzoyl-naphtho [de-2.3.4]tricyclo [4.3.0.0^2,9]nona-2, 6-diene ( 8a–c ). The phenylhydroxymethyl analogue 2 underwent a similar regioselective rearrangement to 9a–c . The rearrangement 1 → 8a–c is proposed to proceed along three reaction paths evolving from two primary photochemical processes of naphthylvinyl and vinyl-vinyl bonding ( 1 → 3 + 6 ). Evidence for a competition between several paths and involvement of biradical intermediates derives from changes in the isotopomeric composition with temperature, and from laser flash detection (λ_exc 353 nm) of a transient. The dependence of the quantum yield for product formation from 1 on excitation wavelength and sensitizer triplet energy leads to the conclusion that reaction to the primary biradicals occurs directly from the S₁ (n, π*) and T₂ (n, π* ) states, and that reaction from T₁ (π, π*) and from S₂ (π, π*) proceed either directly or via T₂.     

Photoactive cryptands. Synthesis of the sodium cryptates of macrobicyclic ligands containing bipyridine and phenoanthroline groups

The NaBr cryptates of five macrobicyclic ligands containing bipyridine (bpy) and phenanthroline (phen) groups, i.e, of [bpy.bpy.bpy] 1 [bpy.bpy.phen] 2 [phen.phen.-phen] 3 [2.1.phen] 4 and [2.2.phen] 5 , have been prepared. 1, 2, 4 and 5 have been obtained in high yield by condensation of bis(bromomethyl)bipyridine 6 or -phenanthroline 9 with the corresponding macrocyclic diamines in presence of Na₂CO₃. Direct access to the NaBr complexes of th symmetrical cryptands 1 and 3 was achieved by a one-step macrobicyclisation procedure. The metal-ion complexes of ligands 1-5 have the attractive feature of combining the cation inclusion, nature of cryptates with the photoactivity of bipyridine and phenanthroline groups; they may thus be expected to posses a variety of interesting physical and chemical properties.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 5. The4 N-cyclohexyl derivative

Summary Metal ion complexes of the thiosemicarbazone,⁴ N-cyclohexyl-2-[1-(2-pyridinyl)ethylidene]hydrazinecarbothioamide (HL4CH), have been prepared and spectrally characterised. Both the size of the cyclohexyl-group attached at⁴N as well as the⁴N hydrogen affect the stoichiometry and stereochemistry of the isolated complexes. The large cyclohexyl-group evidently causes the isolation of [Fe(HL4CH) (L4CH)H₂O](ClO₄) instead of the expected [Fe(L4CH)₂]ClO₄[Co(L4CH)Br] instead of [Co(HL4CH)Br₂], and [Ni(L4CH)Br] instead of [Ni(HL4CH)₂Br₂]. The presence of the hydrogen at⁴N presumably hinders the deprotonation of HL4CH on complex formation since [Cu(HL4CH)Cl₂] was isolated rather than [CuLCl], which occurs when the thiosemicarbazone has⁴N with two alkyl groups or incorporated in a ring. Further, although we prepared [Ni(L4CH)Br], complexes of this stoichiometry are planar and diamagnetle when⁴N does not have a hydrogen(s) attached to it rather than tetrahedral and paramagnetic as has been found for the present complex.     

Conformational Analysis of Endoperoxides Grafted onto Bicyclo[2.2.n]alkanes as a Test of the Rigidity of the Bicyclic Skeleton. Photo-oxidation of [2.2.2] Hericene and 2,3,5,6-Tetramethylidenebicyclo[2.2.n]alkanes

The photo-oxidation of [2.2.2]hericene ( 6 ) gave successively the endoperoxides 11 (9,10,11,12-tetramethylidene-4,5-dioxatricyclo[6.2.2.0^2,7]dodec-2(7)-ene), the bis-endoperoxide 16 (15,16-dimethylidene-4,5,11,12-tetraoxatetracyclo[6.6.2.0^2,7.o^9,14]hexadeca-2(7),9(14)-diene), and the tris-endoperoxide 19 (4,5,11,12,17,18-hexaoxapentacyclo[6.6.6.0^2,7.0^9,14.0^15,20]icosa-2(7),9(14),15(20)-triene). The endoperoxides 11, 16 , and 19 were formed in the presence or in the absence of a dye sensitizer. The sensitized photo-oxidations of 2,3,5,6-tetramethylidenebicyclo[2.2.2]octane ( 4 ), 5,6,7,8-tetramethylidenebicyclo[2.2.2]oct-2-ene ( 5 ), 2,3,5,6-tetramethylidenebicyclo[2.2.1]-heptane ( 7 ), and 2,3,5,6-tetramethylidene-7-oxabicyclo[2.2.1]heptane ( 8 ) gave successively the corresponding mono-endoperoxides 9, 10, 12 , and 13 and the bis-endoperoxides 14, 15, 17 , and 18 , respectively. Low-temperature NMR spectra of the bis-endoperoxides 14 and 16 indicated that their C₂ and C_s conformers have the same stability. Similarly, there was no difference in the enthalpy of the D₃ and C₂ conformers of the tris-endoperoxide 19 . The following reactivity sequence was observed for the sensitized photo-oxidations of 6–8 and 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene ( 23 ): 6 + ¹O₂→ 11 > 7 + ¹O₂→ 12 > 8 + ¹O₂→ 13 > 23 + ¹O₂→ 24 , a trend parallel with that reported for the ethylenetetracarbonitrile (TCNE) cycloadditions to the same polyenes. The rate-constant ratios k₁/k₂ and k₂/k₃ for the three successive photo-oxidations of [2.2.2]hericene ( 6 ) did not differ significantly from unity, in contrast with the Diels-Alder additions of 6 . Similarly, the rate-constant ratios k₁/k₂ for the two successive photo-oxidations of tetraenes 7 and 8 were significantly smaller than those reported for the successive TCNE cycloadditions to 7 to 8 . The endoperoxide formations are not sensitive to the change in the exothermicity of the reactions but they are sensitive to the electronic properties (IP's) of the polyenes.     

Azocalixarenes. 6: Synthesis, complexation, extraction and thermal behaviour of four new azocalix[4]arenes

Four new azocalix[4]arenes {5,11,17,23-tetrakis[(2-hydroxy-5-tert-butylphenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (1), 5,11,17,23-tetrakis[(2-hydroxy-5-nitro phenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (2), 5,11,17,23-tetrakis[(2-amino-5-carboxylphenylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (3) and 5,11,17,23-tetrakis[(1-amino-2-hydroxy-4-sulfonicacidnapthylazo)]-25,26,27,28-tetrahydroxycalix[4]arene (4)} have been synthesized from p-tert-butylphenol, p-nitrophenol, p-aminobenzoic acid and 1-amino-2-hydroxy-4-sulphonic acid by diazo coupling reaction with p-aminocalix[4]arene. The resulting ligands (1–4) were treated with three transition metal salts (e.g., CuCl₂·2H₂O, NiCl₂·6H₂O or CoCl₂·6H₂O). Cu(II), Ni(II) and Co(II) complexes of the azocalix[4]arene derivatives were obtained and characterized by UV-vis, IR, ¹H-NMR spectroscopic techniques and elemental analysis. All the complexes have a metal:ligand ratio of 2:1. The Cu(II) and Ni(II) complexes of azocalix[4]arenes are square-planar, while the Co(II) complexes of azocalix[4]arenes are octahedral with water molecules as axial ligands. The solvent extraction of various transition metal cations from the aqueous phase to the organic phase was carried out by using azocalix[4]arenes (1–4). It was found that, azocalix[4]arenes 1, 2 and 3 examined selectivity for transition metal cations such as Ag⁺, Hg⁺ and Hg²⁺. In addition, the thermal stability of metal:azocalix[4]arene complexes were also reported. Dedicated to Prof. Dr. Mustafa Yılmaz on the occasion of his 50th birthday     

Bivalent 3d-metal complexes of malonyl- and succinyldihydrazide based macrocyclic ligands. Synthesis and characterization

Summary The macrocycles 2,10-dimethyl-3,4,8,9,15-pentaazabicyclo-[9.3.1]-pentadeca-1 (15),2,9,11,13-penta-ene-5,7-dione (L) and 2,11-dimethyl-3,4,8,9,10,16-pentaazabicyclo[10.3.1]-hexadeca-1 (16),2,10,12,14-penta-ene-5,8-dione (L) were prepared and characterized by elemental, i.r. and mass spectral data. The macrocycles react with various metal(II) chlorides to yield complexes of the types [MLCl₂H₂O] (M = Mn, Co, Ni, Cu or Zn), [MLCl₂H₂O] (M = Mn, Ni, Cu or Zn) and [Co₃L₂Cl₄]Cl₂. The complexes were characterized by physico-chemical and spectroscopic methods.     

Kinetics and mechanism of chromic acid oxidation of oxalic acid in absence and presence of different acid media. A kinetic study

Kinetics and mechanism of the reaction of Cr(VI) with oxalic acid have been studied in presence and absence of H₂SO₄, HClO₄, and CH₃COOH by monitoring the formation of Cr(III)-oxalic acid complex at 560 nm. The effect of total [oxalic acid], [Cr(VI)], [H₂SO₄], [HClO₄], and [CH₃COOH] on the reaction rate was determined at 30°C. Formation of carbon dioxide was also confirmed. The oxidation rate increases with [oxalic acid] and [CH₃COOH] while it decreases with [H₂SO₄], [HClO₄], and pH. The rate law governing the oxidation of oxalic acid over a wide range of conditions is rate=k₁ K_es1 [oxalic acid]_T [Cr(VI)]_T 1+K_es1 [oxalic acid]_T, where only undissociated oxalic acid is kinetically active. Kinetic evidence for the formation of a Cr(VI)(SINGLEBOND)oxalic acid 1:1 complex has been obtained and the equilibrium constant for their formation has been determined. The 1:1 complex exists most likely in an open chain form. The rate-limiting step of the oxidation reaction involves the breaking of the C(SINGLEBOND)C bond in the 1:2 complex. Oxidizing ability of Cr(VI) species have been discussed. Mechanism with the associated reaction kinetics is assigned. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 335–340, 1998