Zinc In Acid Research Articles

Synthesis of 3′,5′-dithiothymidine and related compounds

When 3′,5′-di-O-mesylthymidine 7 is heated first with triethylamine in ethanol solution and then with the sodium salt of 4-methoxyphenylmethanethiol 9 in N,N-dimethylacetamide (DMA) solution, the bis(sulfide) 11a is obtained in high yield; when the dimesyl ester 7 is treated with the same thiolate salt in hexamethylphosphoric triamide (HMPA) solution at room temperature, the threo-bis(sulfide) 12a is obtained stereospecifically. Treatment of the two bis(sulfides) 11a and 12a first with 2-nitrobenzenesulfenyl chloride 10 in acetic acid–dichloromethane (1:9 v/v) at 0 °C and then with zinc in hot acetic acid gives 3′,5′-dithiothymidine 5a and the cyclic disulfide 16, respectively, as crystalline solids in good overall yields. Although attempts to isolate the pure threo-dithio compoun 12b lead to the formation of the cyclic disulfide 16, when the crude material is treated with 2,2-dimethoxypropane in the presence of acid, its 3′,5′-S-isopropylidene derivative 17 is obtained and isolated as a crystalline solid in good overall yield.

Unprecedented ring expansion of [60]fullerene: incorporation of nitrogen at an open 6,6-ring juncture by regiospecific reduction of oxycarbonylaziridino-[2′,3′:1,2][60]fullerenes. Synthesis of 1a-aza-1(6a)-homo[60]fullerene, C60H2NH

Upon treatment with zinc in glacial acetic acid, N-oxycarbonylaziridino[2′,3′: 1,2][60]fullerenes 3 undergo a reversible reductive cleavage of the bridgehead C–C bond to provide the first examples of birdged fulleroids 4 having an open 6,6-ring juncture; deprotection of the N-tert-butoxycarbonyl derivative 4a allows the convenient synthesis of C60H2NH 5, the parent member of this new class of bridged fulleroids.

An Improved Method for the Separation of Paclitaxel and Cephalomannine

Treatment of a mixture of paclitaxel and cephalomannine with bromine under mild conditions yields a readily separable mixture of paclitaxel and 2‘‘,3‘‘-dibromocephalomannine. Cephalomannine can be regenerated by treating 2‘‘,3‘‘-dibromocephalomannine with zinc in acetic acid.

Imidazole Derivatives as Corrosion Inhibitors for Zinc in Hydrochloric Acid

Abstract The efficiency of various imidazole derivatives as zinc corrosion inhibitors in hydrochloric acid (HCl) was investigated using electrochemical and gravimetric methods. A difference in efficiency (z) was observed with the introduction of different substituents into a imidazole skeleton. It was established that substituents which increased the electron density at the reaction center improved the corrosion inhibiting properties of the heterocyclic compound. A linear correlation between reaction kinetic data and the sum of the polar substituent constants was obtained.

Synthesis of pyrrolo[2′,3′:4,5]furo[3,2-c]pyridines

The synthesis of pyrrolo[2′,3′:4,5]furo[3,2-c]pyridines (6a–6d) is described. Substituted pyridones (4a–4d) were prepared by thermic cyclization of the corresponding acyl azides (3a–3d), available from substituted propenoic acids (2a–2d)via a one pot reaction with ethyl chloroformate and sodium azide. Upon treatment with phosphorus oxychloride the pyridones (4a–4d) gave substituted chloropyridines (5a–5d) which were reduced with zinc in acetic acid to yield the title compounds (6a–6d).

Transformation and distribution of forms of zinc in acid, neutral and calcareous soils of China

The distribution of native zinc in 18 soils of China and the redistribution and transformations of added soluble zinc in 3 representive soils (acid, neutral and calcareous) were studied. Native Zn in 18 soils of China was mainly distributed over the residual fraction (60–99%) and the crystalline iron oxide fraction (5–30%). The percentages of the residual and exchangeable fractions were higher and the iron oxide fraction lower in acid soils than in calcareous soils. Soil pH is the most important factor of controlling the distribution of native and added Zn in soils. Zinc enrichment in the iron oxide fraction increased exponentially with increasing soil pH. The redistribution of added Zn in acid, neutral and calcareous soils occurred in the residual fraction, followed by the crystalline iron oxide fraction and the weakly bound to organic matter fraction at the lower loading level; and most of the zinc in the residual fraction and the weakly bound to organic matter fraction at the higher loading level of Zn. Zn in the amorphous iron oxide and crystalline iron oxide fractions was much higher in calcareous soils where Zn was added than in acid and neutral soils. Zn in the exchangeable, the weakly bound to organic matter, and to some extent, the carbonate fractions increased with increasing the treatment level of Zn. Transformations of the added Zn from the exchangeable, the weakly bound to organic matter and the amorphous iron oxide fractions into the strongly bound to organic matter and the crystalline iron oxide fractions were observed in soils. Much more complete transformations of these fractions occurred in calcareous soils than in acid and neutral soils. These transformations from the more active and available fractions into the more stable and less available fractions are important in controlling the availability and toxicity of Zn in soils to plants.

Synthesis and isomerization of 19-hydroxy-5β,19-cyclosteroids

Synthesis of 19(R/S)-hydroxy-5β,19-cycloandrostane-3,17-dione by reductive cyclization of the steroid 4-en-3-one 19-aldehyde with zinc in aqueous acetic acid is reported. On either acid or base treatment the R-isomer is converted to the S-isomer through an intermediate 3-hydroxy-3,5-cyclosteroid.

Metal-Directed Synthesis of Macrocyclic Tetraamines With Pendant Nitro or Amine Groups, Based on trans-Cyclohexane-1,2-diamine

Reaction of R,R:S,S-, R,R:R,R(or S,S:S,S)- bis (trans-cyclohexane-1,2-diamine)copper(II) with formaldehyde and nitroethane in aqueous base yields the macrocyclic molecular cation (4,15-dimethyl-4,15-dimethyl-4,15-dinitro-2,6,13,17-tetraazatricyclo[16.4.0.07,12] docosane )copper(II) with two -NH-CH2-C(Me)(NO2)-CH2-NH-links completing the macrocycle, as well as the molecular cation [N,N′- bis (2-aminocyclohexyl)-2-methyl-2-nitropropane-1,3-diamine]copper(II) with a single such link inserted. The rigid polycylic macrocycle , based on a 14-membered tetraazacycloalkane ( cyclam ) frame, may exist as a number of isomers. Spectroscopic and chiroptical properties of the isolated complexes are reported. Reduction of the nitro groups with zinc in aqueous acid produces the corresponding molecules with primary amine (or ammonium) pendants in good yield, as metal-free hydrochloride salts.

Selective recovery of mercury(II) from industrial wastewaters I. Use of a chelating ion exchanger regenerated with brine

An iminodiacetic acid chelating ion exchanger is able to remove mercury(II) selectively from solutions containing iron, zinc, cadmium and lead in sulfuric acid at pH 1.5. At an initial Hg concentration of 10–12 mg/l, mercury leakage is below 50 μ/l over at least 200 bed volumes. Leakages are higher in the presence of chloride because of complexation; a combination of chloride and fluoride results in even higher leakages. Mercury is only partly eluted from the resin with nitric acid, but is readily eluted with sodium chloride solution and can be recovered in pure form by reduction to Hg(I) or Hg(0). The extent of desorption depends on NaCl concentration, pH and flow rate. At 3 M and pH 7, desorption of mercury in the first cycle averages 70–80% in ten bed volumes of eluate. Recovery of mercury taken up in subsequent cycles is close to 100% provided that the resin was loaded to more than 10% of its capacity.

Synthesis of aromatic amines from electron-rich arenes and bis(2,2,2-trichloroethyl) azodicarboxylate

Electron-rich arenes react with bis(2,2,2-trichloroethyl) azodicarboxylate in 3 M lithium perchlorate-diethylether or acetone solution to produce para-substituted aryl hydrazides in high yields. The corresponding aromatic amines are readily obtained by reducing the hydrazides with zinc in acetic acid.

A mild two-step hydrolysis of γ,δ-unsaturated anilides

Iodolactonization of γ,δ-unsaturated anilides 2 in the presence of water and subsequent reduction of the resultant iodolactones 3 using zinc in acetic acid yield the carboxylic acids 4 without significant epimerization α to the carbonyl group. The diastereoselectivity inherent in iodolactonizations of anilides 2 resembles the kinetic stereoselection found for the corresponding transformations of related carboxylic acids.

Unusual macromolecular architectures: the convergent growth approach to dendritic polyesters and novel block copolymers

A versatile approach to dendritic polyesters and their use in the preparation of two different types of novel macromolecular architectures represent dendritic block copolymers is described. The chemistry developed for the synthesis of dendritic polyesters involves generation growth through an esterification step using dicyclohexylcarbodiimide (DCC) and 4-(dimethylamino)pyridinium p-toluenesulfonate (DPTS) followed by activation of the focal point through removal of its trichloroethyl ester group with zinc in acetic acid. Unusual globular block architectures are then obtained by the controlled placement of different ether and ester chemistries in radial or concentric fashion around a central polyfunctional core. Therefore, a dendritic segment-block copolymer is obtained through the attachment of radially alternating dendritic segments incorporating polyester and polyether chemistry to the polyfunctional core. Similarly, a dendritic layer-block is obtained by the concentric alternation of etherand ester-linked layers in the preparation of the dendritic fragments that are finally coupled to the core moiety. The monomer unit used for the preparation of ether-linked fragments was 3,5-dihydroxybenzyl alcohol, while 2,2,2-trichloroethyl 3,5-dihydroxybenzoate was used for the ester-linked fragments. Analysis of the new block copolymers by NMR spectrometry and size-exclusion chromatography suggests that they are pure and monodispersed. In the absence of large differences in the nature of their chain ends, the glass transition temperatures for the various block copolymers appear to be controlled only by the relative proportion of the ether and ester building blocks rather than by the exact geometry.

Structure of Manasse's dimer fromendo-2-hydroxyepicamphor by NOE difference spectroscopy

Reduction of (1R)-(+)-camphorquinone by zinc in acetic acid yields a mixture of endo-2-hydroxyepicamphor and 3-hydroxycamphor. The former undergoes reaction in anhydrous methanol with HCl gas to furnish a stable crystalline solid, first reported in 1902. High-resolution electron impact mass spectrometry showed the solid to be a dimer of formula C22H36O4. The 13C{1H} spectrum showed 11 discrete environments, in keeping with a symmetrical dimer. High-field 1H NOE difference experiments were used to determine not only the connectivity but also the stereochemistry of the system. All of the NOE experiments are consistent with only one structure, that of the symmetrical dimer. In addition, 2D carbon-proton correlation experiments (HETCOR) were used to assign unambiguously its 13C{1H} spectrum.

1,4,4a,10b-Tetrahydro-N,N-dimethyl-4-phenanthridinamines and 1,4,4a,5,6,10b-hexahydro-N,N-dimethyl-4-phenanthridinamines

Synthetic procedures to prepare the title compounds are described. Diels-Alder cycloaddition of β-nitrostyrene derivatives 5 to N,N-dimethyl-1,3-butadien-1-amine, 6, gave 5-aryl-N,N-dimethyl-6-nitro-2-cyclohexen-1-amines 7. Reduction of 7 with zinc in acetic acid gave the diamino derivatives 8. Schotten-Baumann acylation of 8 gave amides 9. Treatment of 8 with alkyl isocyanates gave the aminourea derivatives 10. Bischler-Napieralski cyclodehydration procudure of 9 and 10 gave 1,4,4a,10b-tetrahydrophenanthridinamines 3 and N6-alkyl-1,4,4a,10b-tetrahydro-N4,N4-dimethyl-4,6-phenanthridinediamines 11, respectively. Condensation of diamines 8 with aryl aldehydes under azeotropic conditions gave imines 12 which on treatment with acids yielded 6-aryl-1,4,4a,5,6,10b-hexahydro-N,N-dimethyl-4-phenanthridinamines 4. The stereochemistry of these materials is assigned from the proton magnetic resonance studies.

Quinquedentate co-ordination of amino-substituted tetraazacycloalkanes to cobalt(III). Part 3. Synthesis of an unsymmetric ligand and crystal structure of its cis-chlorocobalt(III) complex

The unsymmetric pendant-arm macrocycle 9-methyl-9-nitro-1,4,7,11-tetraazacyclotetradecane (L1) was prepared by a copper(II)-directed condensation of 3,6-diazanonane-1,9-diamine with nitroethane and formaldehyde. Reduction of the copper(II) complex of L1 with zinc in aqueous acid produced the new potentially quinquedentate polyamine 9-methyl-1,4,7,11-tetraazacyclotetradecan-9-amine (L2). Reaction of L2 in water with cobalt(II) ion and air, followed by aqueous hydrochloric acid and equilibration with activated charcoal, yielded exclusively cis-[CoL2(Cl)][ClO4]2, which crystallized in the monoclinic space group P21/c, with a= 12.745(5), b= 11.438(5), c= 14.414(8) and β= 104.80(3)°. The pendant primary amine and two adjacent secondary amines necessarily occupy an octahedral face, with the chloro ligand cis to the primary amine, and secondary amines adopt RRSS stereochemistries. The average Co–N distance is 1.960Å, and the Co–Cl distance is 2.252(1)Å. Stereoretentive base hydrolysis (kOH 9100 dm3 mol–1 s–1) and other structural and physical properties are compared with those of the symmetric analogue 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine.

Synthesis of a new potentially sexidentate pendant-arm macrocyclic polyamino acid and co-ordination to cobalt(III)

From reaction of bis(ethane-1,2-diamine)copper(II) with formaldehyde and diethyl malonate then formaldehyde and nitroethane in turn the pendant-arm macrocyclic complex ion (hydrogen 13-methyl-13-nitro-1,4,8,11-tetraazacyclotetradecane-6-carboxylate)copper(II) was prepared. Reduction with zinc in aqueous acid yields the free pendant-arm β-polyamino acid macrocycle hydrogen 13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylate (L3) as the hydrochloride salt. Co-ordination to cobalt(III) was achieved following reaction with cobalt(II) ion and air, yielding the chloro(hydrogen 13-amino-13-methyl-1,4,8,11-tetraazacyclotetradecane-6-carboxylate)cobalt(III) ion, as well as its aqua analogue. The chlorocobalt(III) complex crystallized as the perchlorate salt in the space group Pbca, a= 10.256(4), b= 12.689(5), c= 33.08(2)Å, Z= 8, with the co-ordinated chloride in a cis disposition relative to the pendant amine, the four secondary amines co-ordinated in a folded geometry with uncommon RRRR stereochemistry, and the pendant carboxylic acid group not co-ordinated. Equilibration of the reaction mixture from this synthesis at pH 8 over activated carbon yielded almost exclusively the complex with the ligand bound as a sexidentate ligand where the pendant amine and carboxylate groups occupy trans sites. This complex crystallized as the perchlorate salt in the space group P21/n with a= 10.939(2), b= 13.355(2), c= 14.596(2)Å, β= 102.17(1)° and Z= 4. Metal–donor distances [Co-O 1.899(2), Co–N(pendant) 1.956(2), average Co–N(secondary) 1.951Å] are at the short end of the range for saturated polydentate amino acid ligands, presumably influenced by the sterically efficient ligand.

N‐demethylation of (±)‐6β‐acetoxy‐3‐tropinone. Synthesis of (±)‐6β‐acetoxynortropane

AbstractNortropinone 5, prepared from 3 by N‐demethylation with trichloroethyl chloroformate, followed by deprotection of carbamate 4 with zinc in acetic acid, served as a starting material to prepare the N‐protected 6‐acetoxy ketones 7 and 9–12, and alcohols 6 and 8. Nortropane 16 was prepared from 3 by decarbonylation via dithioketal 13 followed by N‐demethylation, and from 10 by decarbonylation via dithioketal 14. When ethanol was used in the desulfurization of 14 instead of tetrahydrofuran, substantial amounts of the N‐ethylated amine 17 were produced.

1,2,4 Benzothiadiazine 1,1-dioxide. V: 1 synthesis of built-in hydroxuguanidine tricycles as potential anticancer agents

Two representative built in hydroxyguanidine tricycles, 10- N-hydroxy-2,3-dihydroimidazol [1,2- b ][1,2,4]benzothiadiazine 5,5-dioxide ( l a) and 11- N-hydroxy-2,3-dihydro-4 H-pyrimido-[l,2- c] [l,2,4]benzothiadiazine 6,6-dioxide ( l b), were obtained in 78% and 30% yields, respectively by a treatment of 1-(2-nitrobenzenesulfonyl)-2-benzylthio-2-imidazolidine and -4,5-dihydro-6 H-pyrimidine with zinc in acetic acid under ice-cooling for 30 min.

Synthesis of 3β,14-dihydroxy-5β,14β-pregnan-20-one C-3 derivatives: ozonolysis of digitoxin and digitoxigenin and their derivatives followed by zinc–acetic acid reduction to the C-21 methyl ketone

Ozonolysis of digitoxin, digitoxin tetraacetate, digitoxin tetrakis-(2,2,2-trichloroethyl carbonate), digitoxigenin, digitoxigenin acetate, digitoxigenin hemisuccinate and digitoxigenin 2,2,2-trichloroethyl carbonate followed by treatment with excess of zinc in acetic acid gave either the corresponding 21-hydroxy ester after 5 min or the 21-methyl ketone after 20 h. This procedure is more efficient than methods previously reported for the conversion of the α,β-unsaturated γ-lactone into an acetyl group and is applicable to the cardiac glycosides directly to give 14β-hydroxypregnan-20-one derivatives. Acidic hydrolysis of 14,21-dihydroxy-and 14-hydroxy-3β-tris(digitoxosyloxy)-5β,14β-pregnan-20-one is reported. Structures are based on 1H and 12C NMR assignments.

Thermal generation of 2-alkyl-3-carbethoxy-cyclopentadienones from angularly alkylated tricyclo[5.2.1.0 2,6]Decadienones. Their use in the synthesis of cyclopentenoids and dihydrosarkomycins

Angularly alkylated 2-carboethoxy-tricyclo[5.2.1.0 2,6]tricyclodecadienones 2 exhibit a facile and efficient thermal [4+2]-cycloreversion reaction in DMF at 155 °C to produce 2-alkyl-3-carboethoxy-cyclopentadienones 9 . Trapping of these relatively stable cyclopentadienones with cyclopentadiene gives the novel tricyclodecadienone esters 10 in excellent yields. Regio- and stereospecific enone reduction in 10 with zinc in acetic acid, followed by Flash Vacuum Thermolysis (FVT) leads to cyclopentenoids ( 20 and 25 ) which upon catalytic hydrogenation afford dihydrosarkomycins ( 22 and 30 ) in high overall yields.