摘要:

AbstractHydrogenation of benzene and cyclohexene has been studied on Pt and four Pt‐Au alloys. The overall behaviour −‐ activity, selfpoisoning and regeneration was similar to that of Ni−Cu alloys. The surface of the two‐phase Pt−Au alloys had, according to the kinetic data a composition of the β‐alloy (Au‐rich phase). Hydrogenation of benzene was 103to 104times slower than the hydrogenation of cyclohexene. The most dilute alloys are active in cyclohexene hydrogenation but they are completely inactive in the low temperature hydrogenation of benzene. The main effect of alloying is the decrease in the pre‐exponential term of the rate. The effect is explained in geometric terms: activation of a benzene molecule for the low temperature hydrogenation requires larger ensembles than those for cyclohexene activation and the larger ensembles are missing on the surface of the

ISSN:0165-0513    

DOI:10.1002/recl.19760951102

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractThree series of novel crown ethers have been prepared in which polyether rings of various sizes are linked to a benzene ring through the 1,3‐ or 1,4‐positions or to a furan ring through the 2,5‐positions. They were synthesized from the corresponding α,γ‐ or α,δ‐bis(halomethyl)‐substituted aromatics by reaction with polyethylene glycol disalts or from the disalts of bis(hydroxymethyl)‐substituted aromatics by reaction with polyethylene glycol ditosylates. Both 1:1 (2−67 % yield) and 2:2 (6−30% yield) cyclic reaction products were formed.The fact that the above compounds, which may contain up to 31 ring atoms, are obtained in such high yields without operating at high dilution is connected with the relationship between the chain length of the polyethylene glycol and the diameter of the cation used in the synthe

ISSN:0165-0513    

DOI:10.1002/recl.19760951103

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractThiophene and its derivatives with R = H, alkyl or −SCH3group in the 2‐ and 5‐positions (1 and 4) undergo the following types of reaction with strong bases, depending upon the nature of the base and the solvent or solvent mixture: if R = H or alkyl: abstraction of the 2‐ and 5‐proton in relatively apolar media and ring opening to enynethiolates in strongly polar media (HMPT); if R = CH3S: substitution on S in the SCH3group by butyllithium in THF/HMPT, abstraction of a CH3S proton by butyllithium in THF (without HMPT) and ring opening in strongly polar media with L

ISSN:0165-0513    

DOI:10.1002/recl.19760951104

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19760951105

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractThe addition of HCl to 1,2,3‐pentatriene has been studied in 95 vol. % aqueous ethanol containing 4−10 mol/1 HCl. The reaction involves rate‐determining proton attack at the terminal methylene group with formation of 1,2‐ and 1,4‐adducts. Subsequently, the 1,2‐adduct is converted into a di‐adduct. The reaction shows pseudo‐first‐order kinetics. Logk1is linear inH0with a slope equal to −1.18 ± 0.01. The average value of the kinetic isotope effectkH/kDis 1.7. A change in nucleophile (ClO4−, SO24−, Br−) does not affect the rate. The addition of HCl is a two‐step process with a carbocation intermediate. In all probability, alcohol and water are not covalently present in the transition state

ISSN:0165-0513    

DOI:10.1002/recl.19760951106

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractPhenylcyclopropanone methyl hemiacetals1a−ccan be smoothly oxidised by a variety of oxidising agents, the nature of which exerts a strong influence on the product distribution. The common key‐intermediate in all these reactions is the ring‐opened phenyl stabilised β‐propionate radical3(Schemes 1 and 3). When the oxidation is carried out with cupric nitrate in pyridine the main product ismeso‐ and racemic dimethyl 3,4‐diphenyladipate4.With cupric or ferric chloride in acetonitrile or methanol, the intermediate radicals3a−ccombine with a halogen atom in a ligand transfer reaction and afford methyl 3‐chloro‐3‐phenylpropionates10a−c. Phenylcyclopropanone methyl hemiacetal la rapidly absorbs oxygen in the presence of a catalytic amount of cupric‐pyridine complex, giving methyl benzoylacetate15as the main product. Without this catalyst the absorption of one equivalent of oxygen is very sluggish and affords the methyl 3‐hydroperoxy‐3‐arylpropionate13a. The hydroperoxide formation is notably slower in benzene than in CCl4or CHCl3. In these chlorinated solvents, 2‐methyl‐2‐phenylcyclopropanone methyl hemiacetal1cgives the peroxylactone 5

ISSN:0165-0513    

DOI:10.1002/recl.19760951107

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractAs part of a structure‐activity relationship study of ribonuclease, focussing on the role of histidine‐12 in the active centre, the following polypeptides have been synthesized by the solid‐phase method and tested for S‐protein activating ability: bovine RNase S‐peptide 1−14, [Ile13]‐ S‐peptide 1−14 and the corresponding analogues in which histidine‐12 is replaced byL‐homohistidine. Whereas their binding tendency is considerably lower the [Hhi12] analogues show a remarkably high ability to generate enzymatic activity when combined with S‐protein in the presence of y

ISSN:0165-0513    

DOI:10.1002/recl.19760951108

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

摘要:

AbstractN‐Aminopyrimidinium salts,e.g. 4,6‐dimethylpyrimidinium (2a), 4,6‐diphenylpyrimidinium (2b) and 2,4,6‐trimethylpyrimidinium mesitylenesulfonates (2c), show a very divergent behaviour towards liquid ammonia at − 33°.1) Proton abstraction takes place from the amino group of2a, resulting in the formation of a 1,3‐dipolar intermediate, which under the reaction conditions dimerises.2) Adduct formation is observed on C(2) of2aor C(6) of2c, resulting in the formation of a pyrazole or a 1,2,4‐triazole ring.3) Deamination occurs with2band2c,viatwo pathways, namely, a nucleophilic attack of ammonia on the nitrogen atom of the amino group or by a ring opening/ring closure sequence. This last‐mentioned mechanism has been proved by use of15N

ISSN:0165-0513    

DOI:10.1002/recl.19760951109

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19760951101

出版商:WILEY‐VCH Verlag    

年代:1976

数据来源: WILEY