Reagents In Aqueous Solution Research Articles

43] 2-Bromoacetyl-SCoA

This chapter discusses the different aspects of preparation of 2-bromoacetyl-SCoA. The procedure involves the synthesis of 2-bromoacetylthiophenol, which is then expected to undergo reversible thiol exchange with CoASH to form 2-bromoacetyl-SCoA. The presence of alkylating moieties and reactive thiol groups in a basic environment presents the strong possibility of irreversible alkylation reactions occurring. The most direct procedure for the synthesis of 2-bromoacetyl-SCoA is to acylate CoASH using bromoacetyl bromide, but because of the extreme lability of this reagent in aqueous solution, the reaction must be carried out under anhydrous conditions. In order to dissolve CoASH in an appropriate organic solvent, it is necessary to convert it to the tri-n-octylamine salt. The acylation of CoASH dissolved in acetonitrile then proceeds quite readily. The synthesis of 2-bromoacetyl-SCoA can be followed by thin-layer cellulose chromatography using the isobutyrate solution as the developing solvent. It is found that owing to the electron withdrawing effect of the bromine, the thioester bond of 2-bromoacetyl-SCoA is extremely labile in aqueous solution at or above neutral pH values.

Chemical alkylation of lead (II) salts to tetraalkyllead (IV) in aqueous solution.

Methylation of lead in the environment would have serious consequences for water quality and for the well being of aquatic biota. As there is strong evidence that tetraalkylleads, the end products of lead alkylation, are considerably more toxic than lead (II) compounds, the elevated levels of inorganic lead now present in inland waterways and sediments as a result of industrial and motor vehicle emissions will pose a serious environmental hazard if mechanisms exist for the conversion to alkyllead (IV) species in aquatic systems. In the belief that the key to biological Pb(II) methylation lies in methyl transfer to Pb(II) from a carbonium ion donor (for example, S-adenosylmethionine), we recently initiated chemical and biological studies on the reactions of CH3+ donors with neutral and anionic Pb(II) compounds. We describe here the unequivocal synthesis of volatile tetramethyllead and other tetraalkylleads from Pb(II) salts and simple chemical reagents in aqueous solution. The known occurrence of methyl iodide in natural waters and our demonstration that Me4Pb is readily synthesized from this reagent and Pb(II) salts in aqueous solution could have far reaching significance not only for the chemical synthesis of toxic organoleads but also for possible mechanisms of microbiological methylation.

Phosphorylation of adenosine in aqueous solution by electric discharges

Dehydration reactions involving condensing reagents in aqueous solution have been studied as models of chemical evolution, and one such reagent has been found to be produced in the supposed primitive Earth conditions. We assumed that the dehydration condensation in aqueous solution could occur if the condensing reagents, which appear to be produced by electric discharges in the gas phase, could be carried to the aqueous solution through the recycling of water washing the wall of the vessel. We present here an experimental study of the dehydration condensation between phosphate and adenosine in aqueous solution using a new discharge apparatus (Fig. 1) which simulates prebiotic chemical evolution. The apparatus was designed so that water recycles in a vessel containing a solution at a relatively low temperature (approximately 30 degrees C), achieved by showering water at 18 degrees C from above the vessel. This is a simulation of the recycling system of water on the Earth, depending on a large difference in temperature between the ocean surface and the sky.

ChemInform Abstract: DEDIAZONIATION OF ARENEDIAZONIUM IONS IN HOMOGENEOUS SOLUTION. PART VIII. REACTION KINETICS AND PRODUCTS IN DIMETHYL SULFOXIDE

AbstractDie Dediazotierung des 4‐Nitrobenzoldiazoniumsalzes ergibt p‐Nitro‐phenol als Hauptprodukt.

Dediazoniation of arenediazonium ions in homogeneous solution. Part VIII. Reaction kinetics and products in dimethyl sulfoxide

Abstractp‐Nitrobenzenediazonium tetrafluoroborate dissolved in dimethylsulfoxide (DMSO) at 50° forms p‐nitrophenol in 88–90% yield. The phenolic oxygen atom originates exclusively from the oxygen atom of DMSO as demonstrated by the use of 18O‐labelled DMSO. The first‐order rate of dediazoniation is the same under N2 as it is in the presence of air. The rate is little influenced by the addition of benzene or iodobenzene. However, the products formed in the presence of these additives are significantly different. UV. spectra and the reactivity of diazonium salt solutions in DMSO when mixed with reagents in aqueous solution demonstrate that a relatively stable charge‐transfer complex is formed between the diazonium ion and DMSO. The product analyses and the kinetic and spectral results of dediazoniation in DMSO with and without additives are consistent with a mechanism in which the rate‐limiting step is the formation of a p‐nitrophenyl radical from the charge‐transfer complex. p‐Nitrophenol and the products with benzene and iodobenzene are formed in subsequent fast competition steps. In the presence of small amounts of pyridine the dediazoniation is much faster and follows a different kinetic law. Pyridine effectively competes with DMSO in the reaction with diazonium ions.

The acid stability constants of Alizarin Fluorine Blue

Two recent attempts to determine the dissociation constants of 3-aminomethylalizarin- N,N-diacetic acid are discussed and the results compared with values that can be predicted from earlier work on iminodiacetic acid derivatives and from the absorption spectra of the reagent at different pH values. Results of a potentiometric and spectrophotometric study to determine the stability constants of the various protonated species of the reagent in aqueous solution at ionic strengths 0·1 and 0·5 (potassium chloride) are: log K H HL = 12·1, log K H H 2L = 9·81, log K H H 3L = 5·47, log K H H 4L = 2·54, and log K H 2L H 5L 2 = 2·2 at ionic strength 0·5.

Photoreactions of aromatic compounds. Part XXI: Photoreaction of 4‐nitroanisole with cyanate ion: (Short Communication)

AbstractThe behaviour of photo‐excited 4‐nitroanisole toward nucleophilic reagents in aqueous solution is intriguing and only partially understood2,3,4. With hydroxide it yields 4‐nitrophenoxide and 4‐methoxy‐phenoxide5,6. On irradiation with alkylamines it gives N‐alkyl‐4‐nitro‐anilines7. A considerable amount of nitrite ion has been detected in the reaction with amines8, but it has as yet not been possible to isolate the corresponding substitution product.Letsinger and his coworkers5 demonstrated that 4‐nitroanisole on photoreaction with pyridine affords N‐(4‐methoxyphenyl)pyridinium nitrite. Interestingly, 4‐nitroanisole in its excited state undergoes substitution by cyanide ion exclusively at the position meta with respect to the nitro group, yielding 2‐cyano‐4‐nitroanisole9. This reaction is sensitive to oxygen: in solutions well purged with nitrogen, yields of 2‐cyano‐4‐nitroanisole are much lower than in air‐saturated solutions3.

Metal chelates of eriochrome black T in aqueous solutions

The elementary observations on the chelate formation of Eriochrome Black T have been described. The behavior of the reagent in aqueous solution and different conditions under which stable complexes are formed have been worked out for magnesium, zinc, cadmium, calcium, aluminium, gallium, indium, scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, thorium, uranium, chromium, iron, cobolt, nickel, molybdenum, and copper metals.

Substitution reactions of some bis(2,2'-bipyridine) and mixed 2,2'-bipyridine, 2,2',2'-terpyridine complexes of ruthenium(II). II. The kinetics of substitution of nitrite and other nucleophiles

The rates of substitution of the complex ions [Ru11(H2O)bipytrpy]2+ and [Ru11(H2O)2 bipy2]2+, where bipy = 2,2'-bipyridine and trpy = 2,2',2"-terpyridine, by a number of nucleophilic reagents in aqueous solution, have been determined as a function of temperature. The reactions were observed to be second order and rates fall in the sequence Ni > NO2 > SCN-> pyridine. The range of Arrhenius parameters is very large with some unusually low frequency factors. The diaquo complex appears to undergo substitution leading to disubstituted derivatives in a single step. In the case of substitution by nitrite, there is evidence that the final products are nitro complexes formed by rapid isomerization of intermediate nitrito complexes.

Investigation of the iron(II) complex of bis-3,3'-(5,6-dimethyl-1,2,4-triazine)

The reagent, bis-3,3'-(5,6-dimethyl-1,2,4-triazine) (BDMT), forms intensely colored complexes with selected transition metal ions. The reagent is water-soluble and easily prepared. An intense orange complex, Fe(BDMT) 3 2+;is formed on reaction of iron(II) with the reagent in aqueous solution at pH 4.0–7.0. Nuclear magnetic resonance data show that chelation occurs between the 2,2'-nitrogens of the reagent. The complex exhibits absorption maxima at 408 mμ, with molar absorptivities of 12,000 and 15,000 respectively. The perchlorate salt of the complex is readily extracted into nitrobenzene. A proposed spectrophotometric method for the determination of iron is both accurate and precis

A comparative study of some lanthanon chelates of alizarin complexan as reagents for fluoride

A study has been made of the comparative suitability of the cerium III, lanthanum and praseodymium chelates of alizarin complexan as reagents for the spectrophotometric determination of microgram amounts of fluoride. The cerium III reagent is most sensitive at pH < 4.5 and the lanthanum reagent at pH ⩾ 5.0. An enhancement of sensitivity may be obtained for both reagents at pH 4.3 by addition of acetone to 25 % v v , but the most sensitive means of determination is to use the lanthanum reagent in aqueous solution at pH 5.2 with measurement at 281 mμ. This procedure is 200% more sensitive than the standard method at 620 mμ.

The Colorimetric Determination of Various Antihistamine Compounds

Various antihistamine compounds react with ammonium reineckate reagent in aqueous solution producing precipitates which can be isolated, dissolved in acetone, and determined colorimetrically by measuring the transmittance at 525 mμ. A general method for antihistamines is given and a procedure for their extraction from tablets, capsules, and ointments, prior to determination. A procedure for the separation of methapyrilene hydrochloride from a mixture of acetylsalicylic acid, acetophenetidin, and caffeine is given. Determination on a number of commercial preparations gave results well within the tolerance limits for such preparations. Results were reproducible with variations generally within one per cent.

Assaying and Metallurgical Analysis for the use of Students, Chemists and Assayers

THE differences between assaying and chemical analysis in the ordinary usage of the terms are perhaps not very precise. An effort was made some years back in America to apply the word “assaying” only to the estimation of some or all of the elements in a substance by means of dry reagents and heat, and the word “analysis “to all estimations by the use of reagents in aqueous solution. These definitions, however, have not met with much favour, and have little to recommend them. It would be better to limit “assaying” to the estimation of the valuable constituent or constituents of an ore or other substance, and to use “analysis” for the estimation of the other constituents and for all qualitative determinations. According to this view, a gold ore would be assayed for gold and silver, and the sulphur, copper, iron, &c., would be determined by analysis, while a copper ore would be assayed for copper, the sulphur in iron pyrites would be determined by assay, and so on Messrs. Rhead and Sexton have in general followed this method, but there are difficulties in its adoption, and in any case an authoritative definition is required. Assaying and Metallurgical Analysis for the use of Students, Chemists and Assayers. By E. L. Rhead Prof. A. Humboldt Sexton Pp. x + 431. (London: Longmans, Green and Co.) Price 10s. 6d. net.