摘要:

Potentiometric measurements carried out in a 50-50 (v/v) H2O-Me2SO mixture together with1H and13C NMR studies carried out in pure Me2SO-d6reveal that 3-aminothiophene (4a), 3-N-(methylamino)thiophene (4b), and 3-N,N-dimethylaminothiophene (4c) undergo protonation exclusively at the amino groups in dilute acid solutions. The pKavalues of4a,4b, and4care equal to 3.38, 3.65, and 3.53, respectively, at 25°C, comparing well with those for related anilines in the same aqueous Me2SO mixtures. However, despite this similarity of the nitrogen basicities, compounds4a,4b,and4care found to behave differently from anilines upon treatment with super-electrophilic 4,6-dinitrobenzofuroxan (DNBF). While anilines react to give first an N-bonded sigma -adduct that subsequently decomposes to afford the thermodynamically more stable C-bonded adduct, the 3-aminothiophenes react only as carbon nucleophiles, giving rise directly to the corresponding C-adducts. Based on1H and13C NMR data as well as measurements of the rate constants (k1DNBF) for DNBF addition to4a,4b,and4c, it is demonstrated that 3-aminothiophenes possess such high negative charge density at C-2 that they can be regarded as strongly enaminic in nature. Estimates of the pKavalues for protonation at C-2 of4a,4b, and4ccould be made: pKa4aapprox -0.4; pKa4bapprox 0.2; pKa4capprox 0.8. Thus, these compounds are more susceptible to electrophilic addition at this position than most of the five-membered ring heterocycles studied so far. Altogether, the results demonstrate the importance of the hyper-orthorelationship in the thiophene systems, accounting for the ease of both electrophilic and nucleophilic reactivity of 3-X-thiophenes in &sgr; -complex formation processes.Key words: aminothiophenes, enamines, superelectrophiles, dinitrobenzofuroxan, hyper-orthorelationship.

ISSN:0008-4042    

DOI:10.1139/v98-079

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Reactions of OH-and F-withp-nitrophenyl diphenyl phosphate (pNPDPP) are inhibited by very dilute dodecyl (10) and (23) polyoxyethylene glycol (C12E10and C12E23, respectively), but rate constants become independent of surfactant concentrations at concentrations above the critical micelle concentration. Low charge density anions, e.g., ClO4-, inhibit and low charge density cations, e.g., (n-C7H15)4N+, accelerate reactions, probably by controlling concentrations of nucleophiles in the palisade layer. Diphenyl phosphorofluoridate, generated by attack of F-, is not detected but is rapidly hydrolyzed to phenyl phosphorofluoridate or diphenyl phosphate ion with loss of phenol or F-. The products are different in DMSO containing modest amounts (<15 vol%) of water and no surfactant and are phenyl phosphorofluoridate and difluorophosphate ions generated by attack of F-on the initial phosphorofluoridate. These differences are consistent with the micellar palisade layer being water-rich. Although the nonionic surfactants do not intervene nucleophilically in reactions of pNPDPP, considerable amounts of ether are formed in the reaction of 2,4-dinitrochlorobenzene (DNCB), in C12E10and C12E23at high pH by attack of alkoxide ion with the relatively hydrophilic DNCB located close to the micellar surface. The differences in the chemistries of reactions of pNPDPP and DNCB appear to be associated largely with differences in locations of these substrates in the nonionic micelles.Key words: fluoridates,p-nitrophenyl diphenyl phosphate, 2,4-dinitrochlorobenzene, nonionic micelles, palisade layer.

ISSN:0008-4042    

DOI:10.1139/v98-093

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Fe(II) phthalocyanine topologically anchored on NaA zeolite has been prepared. The catalytic activity of zeolite-supported Fe(II) phthalocyanine has been studied in the liquid-phase hydroxylation of benzene by H2O2. The main product of the reaction at room temperature is phenol. By refluxing, the reaction proceeds to give the products of subsequent oxidation, i.e., hydroquinone andp-benzoquinone, in low yields.Key words: topologically anchored Fe(II) phthalocyanine, catalysis, oxidation, benzene, phenol.

ISSN:0008-4042    

DOI:10.1139/v98-091

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The hydrolysis of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) was studied in 10% v/v aqueous ethanol at 25°C and &mgr; = 0.1 (KCl). The water-catalyzed hydrolysis showed that, as forp-nitrobenzyl cellulose xanthate, it occurs through two parallel reactions with rate constantsk'H2O= 4.40 x 10-3s-1for the fast hydrolysis, andk''H2O= 6.90 x 10-5s-1for the slow hydrolysis. The entropy of activation of the fast hydrolysis was 0.7 ± 1.8 cal K-1mol-1. External nucleophiles such as hydroxide and simple amines show simple first-order kinetics. The spontaneous hydrolysis of CelXDNP in acetone-water mixtures indicates that the fast reaction does not occur through water polymers and that for water molarity higher than 30 M there are no acetone molecules (or very few) in the highly ordered cybotactic region of cellulose. The spontaneous hydrolysis of methyl 4,6-O-benzylidene- &agr; -D-glucopyranoside 3-(S-p-nitrobenzyl-xanthate) although is faster than the 6-isomer, it is slower than the fast hydrolysis ofp-nitrobenzyl cellulose xanthate (CelXNB). Also &Dgr;Sdouble daggeris highly negative (-41.0 cal K-1mol-1), as it is for alkyl and sugar analogues. Only for the fast hydrolyses of CelXDNP and CelXNB is the entropy of activation almost zero. It is concluded that there is no neighbouring OH effect on the fast hydrolysis of cellulose xanthate esters.Key words: hydrolysis, water catalysis, cellulose xanthate esters, methyl glucose, xanthate esters, neighbouring OH effect.

ISSN:0008-4042    

DOI:10.1139/v98-046

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Superoxide anion is generated from aromatic radical anions produced in nucleophilic aromatic photosubstitutions when the reactions are carried out in non-deoxygenated solutions of polar aprotic solvents. Superoxide anion thus generated displaces cyanide anion from acetonitrile and benzyl cyanide, ethoxide anion from ethyl acetate, and methanesulfenate anion from dimethyl sulfoxide. Hence, non-deoxygenated polar aprotic solvents should be avoided in nucleophilic aromatic photosubstitution reactions.Key words: superoxide, fluoride, nucleophilic aromatic photosubstitution.

ISSN:0008-4042    

DOI:10.1139/v98-044

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Halo(acyl)rhenate complexescis-[Rf(CO)Re(CO)4Hal]Na (Hal = Cl, Br; Rf= C6F5,trans-(CF3)3CCF== CF) are the primary products of the reactions of [Re(CO)5]Na with the corresponding aryl or vinyl halides RfHal.Key words: pentacarbonylrhenate anion, carbonylmetallates, halogen-metal exchange, nucleophilic aromatic substitution, nucleophilic vinylic substitution.

ISSN:0008-4042    

DOI:10.1139/v98-051

出版商:NRC Research Press    

年代:1998

数据来源: NRC