摘要:

AbstractThe occurrence of two consecutive cathodic waves, both with absolute rate control, in the case of the polarographic reduction of 2‐keto‐L‐gulonic acid in a buffer solution of malonic acid (pH between 4.8 and 6.3) is described. The theory of this case is based on the assumption that 2‐keto‐gulonic acid or its anion predominantly exists in the cyclic‐hemiacetal form, which is non‐reducible, but which produces the free keto‐acid or its anion by a very rapid reaction in the zone around the dropping mercury electrode. The latter substances are reducible, with different half wave potentials. Expressions in the relevant rate constants are derived for both the total current and the current of the first wave. This does not permit the calculation of all the rate constants involved. However, it could be shown that the wave heights are related to pH in the way predicted by the theory. Definite conclusions with respect to the relative magnitude of the rate constants could be drawn. The single wave in the lower pH range of 0.2 to 3.5 was also studied as a function of pH. The reaction mechanism is discussed on the basis of the relationships found and in connection with the expected influence of the ionization of the carboxyl group upon the reactivity of the catalytic species present. The process of ring closure or opening was shown to be second‐order,

ISSN:0165-0513    

DOI:10.1002/recl.19600790202

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractFor a number of pairs of isomeric α‐ and β‐monoglycerides with a carboxylic acid as component acid it is shown that these isomers mutually rearrange in ethanolic hydrogen chloride. At 25° the equilibrium mixture invariably contains about 88% of α‐ and consequently about 12% of β‐monoglyceride.From measurements of the migration rate of β‐monobenzoylglycerol in the said medium at 25° it appeared that the migration reaction shows kinetics of the first order and that the migration rate is directly proportional to the concentration of the catalyst. Addition of small quantities of water to the medium retards the migration reaction to a very great extent.The determination of α‐monoglyceride in mixtures of α‐ and β‐monoglyceride was effected by periodic‐acid oxidation, as described previously.The migration rate constant of a number of β‐monoglycerides was determined under identical experimental conditions. The nature of the acyl group has great influence on the migration rate, but not ‐ see above – on the position of the equilibrium.The mechanism of this intramolecular rearrangement of the monoglycerides is discussed and used for an explanation of the facts observed.Monoglycerides with a sulphonic acid as component acid do not show any tendency towards rearrangement unde

ISSN:0165-0513    

DOI:10.1002/recl.19600790203

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractDisodium ethylenebisdithiocarbamate and its products of oxidation by air (ethylenethiuram monosulphide, ethylenethiourea and sulphur) have been separated by ascending paper chromatographic techniques. Several commercial preparations derived from the dithiocarbamate have been analyzed for the presence of these oxidation products.

ISSN:0165-0513    

DOI:10.1002/recl.19600790204

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractThe photochemical conversion of isotachysterol2(in ether) has been studied; the effects of wave‐length and time of irradiation on the composition of the irradiation mixture are discussed. On chromatography of the crude irradiation product a compound was obtained in a pure, non‐crystalline form. The compound did not show antirachitic activity. The ultra‐violet and infra‐red absorption spectra, the iodine‐catalysed quantitative conversion to isotachysterol2, the behaviour on heating in solution and the very low reactivity towards maleic anhydride led to the conclusion that the compound is the Δ6,7‐cisisomer of isotachysterol2, i.e. 9,10‐secoergosta‐5(10),6‐cis, 8(14)

ISSN:0165-0513    

DOI:10.1002/recl.19600790205

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractA description is given of a cell used in taking ultraviolet spectra, especially at lower temperatures, and of a cryostat which can be kept constant within 0.02° down to −150°. Whilst the spectra are being taken, the concentration can be increased by means of a microburette, with exclusion of moisture and oxygen. Thus rates of formation and positions of equilibria of unstable systems can be determi

ISSN:0165-0513    

DOI:10.1002/recl.19600790206

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractA method for the preparation of acid amides by heating an equimolecular mixture of acid and thiourea, is described. The method has been successfully applied to aliphatic mono‐ and di‐basic acids, aryl‐aliphatic acids as well as benzoic acid. The yield has been found to be dependent upon the relative volatility of the acid employed for the reaction. Best yields have been obtained with aryl‐aliphatic acids. The mechanism of amide formation from acid and thiourea, based upon the intermediate addition of carboxylic acid to thiocyanic acid, the latter formed by the decomposition of thiourea, is suggested and an electronic representation of the mechanism i

ISSN:0165-0513    

DOI:10.1002/recl.19600790207

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractEs wurde festgestellt, dass das 2‐Chlor‐3,5‐dinitropyridin äusserst leicht kristallinische Derivate mit den wichtigsten aliphatischen Aminosäuren gibt. Auch mit einigen Polypeptiden und Eiweisstoffen wurden unlösliche gelbe Kondensationsprodukte erhalten.Es wird darauf hingewiesen, dass das 2‐Chlor‐3,5‐dinitropyridin vollwertig das Fluor‐2,4‐dinitrobenzen bei Eiweissuntersuchungen zu ersetzen vermag, und dabei manc

ISSN:0165-0513    

DOI:10.1002/recl.19600790208

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

AbstractThe experimental setups required for the cyclic potential‐step and cyclic current‐step methods are thoroughly discussed. Attention is paid to the following subjects: conditions for linear diffusion, reference electrode, potentiostatic conditions, time‐symmetry of the applied square wave and deviations from coulomb‐s

ISSN:0165-0513    

DOI:10.1002/recl.19600790209

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

摘要:

Partial reduction of prednisolone yields a mixture containing, besides the starting material, Cortisol, pregn‐1‐en‐11β, 17α, 21‐triol‐3,20‐dione and di‐hydrocortisol. The separation of these products is described. Using tritium gas, the same radioactive steroids with a high specific activity were prepared. The specific activity of cortisol‐1,2‐3H was 835 mc/mmole. The isotopic stability of the products has been examined and found satisfactory. Corticostérone‐1,2‐3H, cortisone‐1,2‐3H and androst‐4‐ène‐11β‐ol‐3,17‐dione of high specific activi

ISSN:0165-0513    

DOI:10.1002/recl.19600790210

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19600790201

出版商:WILEY‐VCH Verlag    

年代:1960

数据来源: WILEY