Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.

[reaction: see text] Receptor-mediated imaging and therapy of diseased tissue is rapidly gaining favor in the medical community. The synthesis and facile aqueous/organic coupling of a peripheral-type benzodiazepine receptor ligand to a cyclen-based fluorophore is described herein. The contrast agent QM-CTMC-PK11195, when chelated with lanthanides, produces bright luminescence and good MRI contrast and can potentially serve as an imaging and demarcation agent for certain types of cancers.

No abstract

Phenoxathiin cation radical perchlorate (PO.+ClO4(-)) added stereospecifically to cyclopentene, cyclohexene, cycloheptene, and 1,5-cyclooctadiene to give 1,2-bis(5-phenoxathiiniumyl)cycloalkane diperchlorates (4-7) in good yield. The diaxial configuration of the PO+ groups was confirmed with X-ray crystallography. Unlike additions of thianthrene cation radical perchlorate (Th.+ClO4(-)) to these cycloalkenes, no evidence for formation of monoadducts was found in the reactions of PO.+ClO4(-). This difference is discussed. Addition of Th.+ClO4(-) to five trans alkenes (2-butene, 2-pentene, 4-methyl-2-pentene, 3-octene, 5-decene) and four cis alkenes (2-pentene, 2-hexene, 2-heptene, 5-decene) gave in each case a mixture of mono- and bisadducts in which the configuration of the alkene was retained. Thus, cis alkenes gave erythro monoadducts and threo bisadducts, whereas trans alkenes gave threo monoadducts and erythro bisadducts. In these additions to alkenes, cis alkenes gave predominantly bisadducts, while trans alkenes (except for trans-2-butene) gave predominantly monoadducts. This difference is explained. 1,2-Bis(5-phenoxathiiniumyl)cycloalkanes (4-7) and 1,2-bis(5-thianthreniumyl)cycloalkanes underwent fast elimination reactions on activated alumina forming, respectively, 1-(5-phenoxathiiniumyl)cycloalkenes (8-11) and 1-(5-thianthreniumyl)cycloalkenes (12-16). Among adducts of Th.+ClO4(-) and alkenes, monoadducts underwent fast ring opening on alumina to give (5-thianthreniumyl)alkenes, while bisadducts underwent fast eliminations of H+ and thianthrene (Th) to give (5-thianthreniumyl)alkenes also. Ring opening of monoadducts was a stereospecific reaction in which the configuration of the original alkene was retained. Thus, erythro monoadducts (from cis alkenes) gave (E)-(5-thianthreniumyl)alkenes and threo monoadducts (from trans alkenes) gave (Z)-(5-thianthreniumyl)alkenes. Among bisadducts, elimination of a proton and Th occurred and was more complex, giving both (E)- and (Z)-(5-thianthreniumyl)alkenes. These results are explained. Configurations of adducts and (5-thianthreniumyl)alkenes were deduced with the aid of X-ray crystallography and (1)H and (13)C NMR spectroscopy. In the NMR spectra of (E)- and (Z)-(5-thianthreniumyl)alkenes, the alkenyl proton of Z isomers always appeared at a lower field (0.8-1.0 ppm) than that of E isomers.

Total syntheses for four acorane sesquiterpenes, 0-acoradiene (4), -acoradiene (5), and the enantiomers (27 and 28) of acorone (1) and isoacorone (2), are described. The synthetic route involves conversion of (fi)-pulegone (11) into 3-methyl-2-carbethoxycyclopentanone (8) by improvement of literature procedures, then conversion of this into (fi)-3-methyl-2-methylenecyclopentanone (17) by the sequence ketalization, reduction, deketalization, and dehydration, A Diels-Alder reaction between 17 and isoprene gave four adducts 18-21. The para:meta ratio in this reaction was improved from 2:1 to 24:1 by the use of SnCl4 catalysis, which gave a ratio of products of 69: 27:3:1. Structures were assigned to the various isomers on the basis of the known steric and electronic requirements in the Diels-Alder reaction. The major ketones 18 and 19 were purified by preparative high-pressure liquid chromatography. Treatment of 18 with isopropyllithium and then SOCI2 gave -acoradiene (4) and its endocyclic isomer 23, whereas 19 led to -acoradiene (5) and its isomer 25. Hydroboration of 25 followed by Jones oxidation gave an equilibrium mixture of (-)-acorone ( 27), the enantiomer of natural acorone (1), and (+)-isoacorone ( 28), the enantiomer of natural isoacorone (2).Acorone (1), isolated from the oil of Sweet Flag, Acorus calamus L., is the best known member of a small group of spirocyclic sesquiterpenes having the acorane skeleton.3 Other members include isoacorone (2), cryptoacorone (3), and acorenone from the same source,3 as well as acorenone B from Bothriochoa intermedia,4, two unnamed dienes from Vetiveria zizanoides,4 5 and -acorenol, /3-acorenol, aacoradiene, /3-acoradiene, -acoradiene (4), and -acoradiene (5) from Juniperus rígida.5 -Alaskene, isolated from alaska cedar, Chamecyparis nootkatensis, was shown to be identical with -acoradiene, but /3-alaskene from the same source was shown to be enantiomeric to -acoradiene.6 4 5

The monoadducts (4a-d) of thianthrene cation radical perchlorate (1a) and isobutene, 2-methylbutene, 2-methyl-2-butene, and 2-methylpentene decompose spontaneously in acetonitrile (MeCN) solution, with the formation of thianthrene (Th). Decomposition of 4a (1,2-(5,10-thianthreniumdiyl)-2-methylpropane diperchlorate) and 4a', the corresponding dihexafluorophosphate, was studied in depth and extensively with (1)H and (13)C NMR spectroscopy. Decomposition of 4a was found to involve the solvent itself as well as water in the solvent, remaining from incomplete drying, and gave, apart from Th, successively, the perchlorate salts of 2,4,4-trimethyl-2-oxazoline (6) and 2-amino-2-methylpropyl acetate (7). These salts, 6-HClO(4) and 7-HClO(4), respectively, were prepared and used in understanding the reactions of 4a as well as the relationships among 6, 7, and 2-(acetylamino)-2-methyl propanol (8) in acidified MeCN solution. Decompositions of 4a-d in MeCN and other nitriles (RCN) containing an added alcohol (R'OH) led to new products, 5-[(1-alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates (5a-u). These compounds were identified with (1)H and (13)C NMR spectroscopy and, in part, with X-ray crystallography and elemental analysis. The mechanisms of formation of 5-7 are discussed.

The rearrangement, in trifluoroacetic acid at 38.5°, of two series of 4,4-disubstituted cyclohexadienones to give 3,4-disubstituted phenols has been studied. In the first series, a carbethoxy group is placed in intramolecular migratory competition with other common substituents (Me, Et, Ph, z'-Pr, Bz). The carbethoxy group is found to migrate in preference to Me, Et, or Ph with relative rates of 1:0.45:135. In the case of the z'-Pr and Bz substituted compounds, fragmentation occurs instead of rearrangement to give 4-carbethoxyphenol and the z'-Pr and Bz carbonium ions, respectively. In the second series, intermolecular kinetic comparisons of a series of compounds in which the substituents migrate in a methyl-substituted framework allows one to assess the migration tendency, as defined by Stiles and Mayer, of the substituents in the dienone system. The order found is Me < COOEt < Et < Ph

No abstract