Über kondensierte Heterocyclen aus β-Isothiocyanatoketonen und Aminoalkoholen bzw. Diaminen

2- and 3-aminoalcohols, o-aminobenzylalcohol, o-hydroxybenzylamine and o-amino(thio)-phenol react with 4-isothiocyanato-4-methyl-2-pentanone (1) to yield derivatives of condensed heterocycles (oxazolopyrimidines7, pyrimidooxazine8, pyrimidobenzoxazines9, 10, pyrimidobenzoxazole11 a and pyrimidobenzothiazole11 c respectively). Ethylenediamine or 1,3-diaminopropane react with1 to yield either imidazo-pyrimidine13 and pyrimidopyrimidine14 respectively or the 1,2-ethylene- and trimethylenebisdihydro-2(1H)-pyrimidinethione15 a, b respectively, according to the molar ratio of the reactants. o-Phenylenediamine gives pyrimidobenzimidazole11 d. 11a undergoes ring cleavage in boiling dimethylformamide followed by methylpyrimidine-pyridine rearrangement to dihydrohydroxyphenylamino-2(1H)-pyridinethione12, while15 a is converted into the bis-4-(ethanediimino)-pyridinthione16.     

Über 4-Alkylamino-bzw. 4-Arylamino-5,6-dihydro-2(1H)-pyridinthione

Heating 1-alkyl- or 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones5, 6 in an inert medium causes rearrangement to 4-alkylamino-(4-arylamino-)-5,6-dihydro-2(1H)-pyridinethiones11, 12, probably via the methylene form29, by thermal heterolysis of the N₁/C₂ bond and exchange of the alkylamino (arylamino) group 1 through the carbon atom of the methylene group 6. The aminodihydropyridinethiones11, which can be regarded as cyclic derivatives of 3-aminothiocrotonamide, react with bistrichlorophenylmalonate under diacylation, and with formaldehyde and primary amines to yield aminodialkylation products of the enamine system, tetrahydro-4-hydroxy-7,7-dimethyl-5-thioxopyrido[4,3-b]pyridine-2(1H)-ones13, 14 and hexahydro-7,7-dimethylpyrido[4,3-d]pyrimidine-5(6H)-thiones18, 19, 21 respectively. H₂O₂ converts11 to the corresponding 4-aminodihydro-2(1H)-pyridones22, which can be reconverted into11 with P₄S₁₀.11 reacts with alkyl halides to 2-alkylthiodihydropyridines23, 24, 25. The mechanism of the methylpyrimidine-pyridine rearrangement is discussed.     

Über 1-Alkyl-bzw. 1-Aryl-dihydro-6-methyl-2(1H)-pyrimidinthione

The title compounds7 are formed in a general reaction by heating β-isothiocyanoketones3 with primary amines in inert solvents, or by thermal elimination of water from tetrahydro-6-hydroxy-6-methyl-2(1H)-pyrimidinethiones5, also in inert solvents. The 1-alkyl compounds can also be prepared under similar conditions from α,β-unsaturated ketones by reaction with alkylammonium rhodanides. The NMR-spectra show that the 1-substituted dihydro-6-methyl-2(1H)-pyrimidinethiones are in tautomeric equilibrium with the tetrahydro-6-methylene-2(1H)-pyrimidinethiones13. The reactivity of 1-alkyl and 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones is similar to that of dihydro-4,4,6-trimethyl-2(1H)-pyrimidinethione7 j, although their ring stability is certainly less.     

Arsenic compounds in terrestrial organisms. IV. Green plants and lichens from an old arsenic smelter site in Austria

Two lichens and 12 green plants growing at a former arsenic roasting facility in Austria were analyzed for total arsenic by ICP–MS, and for 12 arsenic compounds (arsenous acid, arsenic acid, dimethylarsinic acid, methylarsonic acid, arsenobetaine, arsenocholine, trimethylarsine oxide, the tetramethylarsonium cation and four arsenoriboses) by HPLC–ICP–MS. Total arsenic concentrations were in the range of 0.27 mg As (kg dry mass)⁻¹ (Vaccinium vitis idaea) to 8.45 mg As (kg dry mass)⁻¹ (Equisetum pratense). Arsenic compounds were extracted with two different extractants [water or methanol/water (9:1)]. Extraction yields achieved with water [7% (Alectoria ochroleuca) to 71% (Equisetum pratense)] were higher than those with methanol/water (9:1) [4% (Alectoria ochroleuca) to 22% (Deschampsia cespitosa)]. The differences were caused mainly by better extraction of inorganic arsenic (green plants) and an arsenoribose (lichens) by water. Inorganic arsenic was detected in all extracts. Dimethylarsinic acid was identified in nine green plants. One of the lichens (Alectoria ochroleuca) contained traces of methylarsonic acid, and this compound was also detected in nine of the green plants. Arsenobetaine was a major arsenic compound in extracts of the lichens, but except for traces in the grass Deschampsia cespitosa, it was not detected in the green plants. In contrast to arsenobetaine, trimethylarsine oxide was found in all samples. The tetramethylarsonium cation was identified in the lichen Alectoria ochroleuca and in four green plants. With the exception of the needles of the tree Larix decidua the arsenoribose (2′R)‐dimethyl[1‐O‐(2′,3′‐dihydroxypropyl)‐5‐deoxy‐β‐D ‐ribofuranos‐5‐yl]arsine oxide was identified at the low μg kg⁻¹ level or as a trace in all plants investigated. In the lichens an unknown arsenic compound, which did not match any of the standard compounds available, was also detected. Arsenocholine and three of the arsenoriboses were not detected in the samples. Copyright © 2000 John Wiley & Sons, Ltd.     

Demethylation of trimethylantimony species in aqueous solution during analysis by hydride generation/gas chromatography with AAS and ICP MS detection

The method of hydride generation for the speciation of antimony compounds was examined with respect to the problem of molecular "rearrangement'. Specifically, demethylation of trimethylstilbine during the analysis of trimethylantimony dichloride (Me₃SbCl₂) was studied. Previously published observations that enhanced demethylation takes place as a result of inadequate preconditioning of the analytical apparatus were found to be not reproducible. However, demethylation was enhanced as the pH decreased when using two different analytical methods: semi-continuous flow hydride generation–gas chromatography–atomic absorption spectrometry (HG– GC–AAS), and batch-type hydride generation– gas chromatography–inductively coupled plasma mass spectrometry (HG–GC–ICP MS). Applications of the hydride generation method to environmental samples revealed differences in analytical results at high and low pH, and enhanced demethylation taking place because of the matrix in a fungal extract sample. The authors recommend that researchers using the method of hydride generation for antimony compounds carefully test the reaction conditions with standard compounds and use the method of standard addition only. © 1998 John Wiley & Sons, Ltd.     

Stripping voltammetric determination of trace amounts of mercury using a carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone

A carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone was used for the voltammetric determination of mercury(II). Mercury was preconcentrated onto the surface of the modified electrode only by the complexing effect of the modifier without application of potential (i.e. in open-circuit conditions). After exchange of the medium, the accumulated amount of mercury(II) was determined by differential pulse anodic stripping voltammetry. The response depended on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 0.1 g 1^–1 Hg(II) for a preconcentration time of 15 min. Preconcentration for suitable times yielded a linear calibration graph from 0.5 to 6000 g 1^–1 Hg(II). For multiple determinations (5 runs), the relative standard deviation was 5% for a concentration of 100 g 1^–1 Hg(II). The proposed procedure was used to determine trace mercury in plant and sewage sludge samples with good results.On leave from Hainan University, Hainan Peoples Republic of China     

A new method for the analysis of arsenic species in urine by using HPLC-ICP-MS

Gas chromatographic (GC) and liquid chromatographic methods for the investigation of phenylarsenic compounds are presented. With gas chromatography using an electron capture detector (ECD), the chemical warfare agents PFIFFIKUS, CLARK I and CLARK II can be detected. After derivatization with mercaptans and dimercaptans the sum of diphenylarsenic compounds resp. phenylarsenic and phenylarsonic compounds can be detected as the mercapto resp. dimercapto derivatives. High performance liquid chromatography (HPLC) analysis may be used for the detection of triphenylarsenic compounds and ADAMSITE. Received: 17 July 1997 / Accepted: 9 October 1997     

Kondensierte Heterocyclen aus β-Isothiocyanatoketonen und Aminocarbonsäuren

On reaction of glycine, anthranilic acid and anthranilamide respectively with 4-isothiocyanato-4-methyl-2-pentanone (1), derivatives of condensed heterocycles (oxazolopyrimidine5, pyrimidobenzoxazine7 a, pyrimidobenzodiazine7 c) are formed. The same holds for the reaction of dithiocarbamates, prepared from glycine and CS₂ in aqueous NaOH, with 4-methyl-3-penten-2-one and cinnamaldehyde respectively (12 a, b). The reaction of hot dimethylformamide with7 a leads under initial aminolysis to pyrimidine-anthranildimethylamide2 i; this is subsequently transformed partly through methylpyrimidine-pyridine rearrangement into the N-4-pyridine-anthranil-N,N-dimethylamide10 d, partly under further aminolysis byDMF followed by rearrangement to the dimethylaminodihydro-2(1H)-pyridinethione10 c. 5 is converted to dihydro-4-methylamino-2(1H)-pyridinethione (10 a) in boiling hexanol and2 c to n-hexyl-3-(tetrahydrothioxo-pyridylamino)-propionate (10 b).     

Kondensierte Heterocyclen aus β-Isothiocyanatoketonen und Aminocarbons?uren

On reaction of glycine, anthranilic acid and anthranilamide respectively with 4-isothiocyanato-4-methyl-2-pentanone (1), derivatives of condensed heterocycles (oxazolopyrimidine5, pyrimidobenzoxazine7 a, pyrimidobenzodiazine7 c) are formed. The same holds for the reaction of dithiocarbamates, prepared from glycine and CS₂ in aqueous NaOH, with 4-methyl-3-penten-2-one and cinnamaldehyde respectively (12 a, b). The reaction of hot dimethylformamide with7 a leads under initial aminolysis to pyrimidine-anthranildimethylamide2 i; this is subsequently transformed partly through methylpyrimidine-pyridine rearrangement into the N-4-pyridine-anthranil-N,N-dimethylamide10 d, partly under further aminolysis byDMF followed by rearrangement to the dimethylaminodihydro-2(1H)-pyridinethione10 c. 5 is converted to dihydro-4-methylamino-2(1H)-pyridinethione (10 a) in boiling hexanol and2 c to n-hexyl-3-(tetrahydrothioxo-pyridylamino)-propionate (10 b).     

Reversed-phase ion-pair chromatographic separation of selenite and selenate with selenium-specific detection

Tetraalkylammonium salts [R₃RN]⁺X^– (R=R, XCH₃, Cl; C₂H₅, Br; C₃H₇, Br; C₄H₉, H₂PO₄; C₅H₁₁ Br; R, R, XCH₃, C₁₆H₃₃, Br) were investigated as ion-pairing reagents for the reversed-phase ion-pair chromatographic separation of selenite and selenate. Other chromatographic parameters such as composition and pH of the mobile phase and concentration of the ion-pairing reagent were also investigated. The compatibility of the proposed chromatographic procedures with various selenium-specific detectors is discussed. The absolute detection limits were found to be 31 ng Se for selenite and 51 ng Se for selenate (100 l injection) with a solution of 5 mM tetrabutylammonium dihydrogen phosphate in 5050 (v/v) methanol/water as mobile phase at a flow rate of 1 ml/min when a flame atomic absorption spectrometer was used as detector. The HPLC/FAAS system was employed for the determination of selenite in solutions serving as selenium supplement for animals.