摘要:

Maghemite, prepared in the usual way (but with exclusion of silica, e.g., from glassware) by precipitation of non-stoichiometric magnetite Fe3−xO4−xin aqueous MOH (M = Na, K) followed by air oxidation, picks up moisture from the air to reach the limiting composition MδH1−δFe5O8, where δ ~ 0.02–0.03 for fresh material, but changes under hydrothermal conditions because of ion exchange. Despite the role of absorbed moisture in stabilizing maghemite, formation of the latter from Fe3−xO4−xis markedly retarded, and its decomposition to α-Fe2O3greatly accelerated, under hydrothermal conditions relative to the rates of the corresponding reactions of the dry solids. The rate of hydrothermal decomposition of maghemite is strongly retarded by silica. Over the range 160–187 °C at least, silica-free maghemite decomposes in water according to the empirical equation −ln (1 − α) = (kt)n, where α is the fractional extent of decomposition, andn ~ 2.5 for neutral water (withk = 1.3 × 10−5 s−1at 160 °C and 3.1 × 10−5 s−1at 175 °C) but approaches unity, without major effects on the overall time-scale of reaction, at high [MOH]. The mechanistic significance of these and previous results are considered; the hydrothermal conversion of maghemite to hematite evidently proceeds by a dissolution–reprecipitation sequence.

ISSN:0008-4042    

DOI:10.1139/v80-279

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The reaction of (OHP)3Fe(II) (OHP = 4,7-dihydroxy-1,10-phenanthroline) with oxygen in aqueous 0.1 NNaOH solution takes place according to the stoichiometry:This stoichiometry holds whether (OHP)3Fe(II) or O2is in excess. The rate law over a wide range of (OHP)3Fe(II) and O2concentrations at 0.1 NNaOH has the form:A notable feature of this oxidation is thatfreeHO2−is not produced as an intermediate. A plausible mechanism involvingboundsuperoxide or peroxide as intermediates is proposed. Due to the redox nature of the OHP ligand and the low potenial of the (OHP)3Fe(II) complex, a 4 electron transfer from one (OHP)3Fe(II) to one O2to give a Fe(IV) species with an oxidized ligand is a distinct possibility. The rate–pH profile is consistent with the protonation of (OHP)3Fe(II) (pKa ≈ 9.4) to give a more reactive specie

ISSN:0008-4042    

DOI:10.1139/v80-280

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

An expression for the amplitude of the ultrasonic relaxation arising from the exchange of amphiphiles between micelles and surrounding solution has been derived on the basis of the same assumptions as used by Aniansson and Wall to obtain the expression of the relaxation time for this process. The derived expression somewhat extends the range of investigation of micellar systems which can be performed by means of the ultrasonic relaxation method. It has been used for the quantitative interpretation of ultrasonic absorption measurements concerning the effect of ionic strength on the dynamics of the exchange process in micellar solutions of potassium decanoate.

ISSN:0008-4042    

DOI:10.1139/v80-281

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The 1-methoxy-, 1-methoxy-3-rnethyl-, and 1-methoxy-2,3-dimethylallyl cations,2,5, and9, were prepared by treatment of the dimethyl acetals of acrolein, crotonaldehyde, and tiglaldehyde, respectively, with FSO3H. Each of these ions was capable of existing in various stereoisomeric forms. The thermodynamically preferred conformation of2,5, and9all had a C1—O,Econfiguration and5and9anEconfiguration about the C2—C3 bonds. Irradiation of FSO3H solutions of these ions at −70 °C using 254 nm light caused them to be converted to the other stereoisomers. Relatively efficient photoisomerism about both the C1—O and C2—C3 bonds was observed. The rates of the reverse thermal conversion of the photoproducts to2,5, and9were measured and on the basis of medium and substituent effects it was concluded that thermal isomerism about the C1—O bond takes place by an inversion process while stereomutation about the C2—C3 bond involves the addition of base to C3.

ISSN:0008-4042    

DOI:10.1139/v80-282

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Partial molal volumes have been determined for the nickel(II) complexes of ethylenediaminetetraacetic acid (monocomplex) and methyliminodiacetic acid (biscomplex). The formation of these is accompanied by appreciable increases in volume, greater in the case of the second ligand. The observations are discussed in terms of reduced electrostriction of water by the complexes, and the different volume increases are accounted for by structural features of the complexes which are partially confirmed by spectral measurements.

ISSN:0008-4042    

DOI:10.1139/v80-283

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A stereospecific total synthesis of the title compound,37, starting from diacetone glucose (9), is described. Key intermediates in the synthesis are 3-deoxy-5,6-anhydro-1,2-O-isopropylidene-glucofuranose (15), obtained in 55% yield from9, and methyl 8-tert-butyldiphenylsilyl-9,11-O-isopropylidene-8R,9S,11R-trihydroxy-12-oxo-dodeca-5Z-enoate (33), an important intermediate in the synthesis of other oxidation products of arachidonic acid.

ISSN:0008-4042    

DOI:10.1139/v80-284

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Pictet discovered 90 years ago that quinoline andp-toluidine were formed on heatingN-methylacetanilide with zinc chloride. It has now been shown that 6-methylquinoline is also produced in this reaction. It was established by means of13C nmr that [1-13C-acetyl]-N-methylacetanilide affords quinoline and its 6-methyl derivative enriched at C-4. [N-methyl-13C]-N-Methylacetanilide yielded [2-13C]quinoline and [2,6-methyl-13C2]-6-methylquinoline.N-Methylpropionanilide afforded 3-methylquinoline. These results are in accord with a new mechanism for the formation of quinoline, different from the one previously proposed.

ISSN:0008-4042    

DOI:10.1139/v80-285

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Ease of methylation of hydrogenated 2H-inden-2-ones depends on the presence of a double bond in the cyclohexane ring, and occurs readily with compound20but not with10. Differences of reactivity are also noted in Wittig reactions. Most reactions of the system are highly stereoselective, and the stereochemistry of hydrogenated indenes is discussed.

ISSN:0008-4042    

DOI:10.1139/v80-286

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Ethyl-3-amino-2-benzoyl-2-butenoate crystallizes from pentane as either theE(mp 82–84 °C) or theZ-isomer (mp 95.5–96.5 °C). TheEisomer is less stable, and changes spontaneously into theZ, which bas been identified by X-ray crystallography. The structure is characterised by an N–H/ester CO hydrogen bond and a very long C2—C3 bond (1.39 Å). Nuclear magnetic resonance methods have been used to measure the rate ofisomerization at several temperatures, leading to the estimate that the free energy of activation at 268 K is 56 ± 8 kJ.

ISSN:0008-4042    

DOI:10.1139/v80-287

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The reactions of perivinol (27) with voacangine (3), and of perivinol with catharanthine (29), yield in each case two bisindole alkaloids of the voacamine type.1H and13C nmr data are used to assign structures to these compounds and the general utility of these techniques for determining the position of attachment of the 2-acylindole unit to the Iboga unit in such compounds is discussed. The reaction of dregaminol (28) with catharanthine is also reported.

ISSN:0008-4042    

DOI:10.1139/v80-288

出版商:NRC Research Press    

年代:1980

数据来源: NRC