摘要:

Ultraviolet spectral and kinetic measurements are reported for the transformations in aqueous solution undergone by the cyclic iminium ion, the 2-aryl-1-methyl-1-pyrrolinium ion I+. In solutions with pH < 9.5 this ion equilibrates with a ring-opened hydrated form, the protonated 4-methylaminobutyrophenone SH+. The concentration of the latter at equilibrium is small, but it can be observed using nuclear magnetic resonance spectroscopy. A kinetic analysis provides a measure of theequilibrium constant. Values range from 0.06 for 4-methoxyphenyl to 0.17 for 3-chlorophenyl. In acid solutions (pH < 5) the equilibration is slow (half-life ≈ 20 min for phenyl) and pH independent. Above pH 5 this process becomes first order in hydroxide ion. In strongly basic solutions a neutral species is formed in equilibrium with these two cations, with pK(app) for the transformation cations  neutral + H+ranging from 11.8 to 11.3. Spectral arguments imply that the base species is the ring-opened 4-methylaminobutyrophenone S, with less than ten percent of the pseudobase of I+presen

ISSN:0008-4042    

DOI:10.1139/v87-283

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Reaction of tetrahydro-2,2,5,5-tetramethyl-3(2H)-furanone (1) with 96 or ca. 100% sulfuric acid or hot polyphosphoric acid followed by aqueous quenching gave the following products: 2-hydroxy-2,5-dimethyl-4-hexen-3-one (3), 2,4,4-trimethyl-2-cyclopenten-1-one (7), 3,5,5-trimethyl-2-cyclopenten-1-one (8), tetrahydro-3,4,5,5-tetramethylfuran-2,3-diol (11), 2,5-dihydro-3,5,5-trimethyl-2-methylenefuran (17) and its dimer20, 2,5-dihydro-2,3,5,5-tetramethyl-2-furanol (18), 4-hydroxy-2,4-dimethyl-2-pentenoic acid γ-lactone (22), 2,3,5-trimethyl-2-cyclopenten-1-one (23), and tetramethylfuran (25). In 96% sulfuric acid the products arise by ring opening, ring opening followed by reclosure to carbocyclic products, methyl migration from C-2 to C-3 to give rearranged furan derivatives, and oxidation. In ca. 100% sulfuric acid or hot polyphosphoric acid further methyl migrations can occur to give23and25.

ISSN:0008-4042    

DOI:10.1139/v87-284

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Hydrolysis of 5-neopentoxy-1,3-diiminoisoindoline gave 5-neopentoxy-1H-isoindole-1,3(2H)-dione (4-neopentoxyphthalimide), which, on treatment with Lawesson's reagent, yielded the thiophthalimides, 5-neopentoxy-1H-isoindole-1,3(2H)-dithione, 2,3-dihydro-6-neopentoxy-3-thioxo-1H-isoindol-1-one, and 2,3-dihydro-5-neopentoxy-3-thioxo-1H-isoindol-1-one. Attempted S-alkylations of the thiophthalimides resulted in the formation of β-isoindigos and N-alkylation products. In a new phthalocyanine synthesis crossed condensations of 1,3-diiminoisoindoline with 5-neopentoxy-1H-isoindole-1,3(2H)-dithione yielded mixtures of phthalocyanines from which 2-neopentoxyphthalocyanine and 2,16-dineopentoxyphthalocyanine could be purified in part from other phthalocyanines.

ISSN:0008-4042    

DOI:10.1139/v87-285

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Benzo-4-bromo-2,5-cyclohexadienone (5) has been observed in the aqueous bromination of 1-naphthol and the kinetics of its enolization to 4-bromo-1-naphthol have been studied in the pH range 0–7. This process is catalyzed by the proton, hydroxide ion, water, buffer acids, and by buffer bases. For catalysis by general bases the Brønsted β = 0.59 whereas catalysis by general acids has a value of α ~ 0. These findings are very similar to those obtained previously for the 4-bromo-2,5-cyclohexadienone2b, formed during the aqueous bromination of 2,6-dimethylphenol. The mechanistic implications of the results are discussed. The enolization of the related dienone8, formed from bromine and 1-naphthol-2-carboxylic acid, was also studied. At acidic pHs the dienone8is much more reactive than5, with the 2-COOH behaving as an internal catalyst having an "effective molarity" of about 110 M. The enolization of8is also catalyzed by buffer bases.

ISSN:0008-4042    

DOI:10.1139/v87-286

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The ketenesn-BuCH=C=O, PhCH=C=O, and Ph2C=C=O have been generated by flash photolysis and their reactivities toward water, including acid and base catalysis, have been measured in wholly aqueous media by ultraviolet spectrophotometry. The phenyl group electronically enhances the reactivity of ketenes relative ton-butyl toward water and hydroxide, but retards reaction with protic acids. The presence of bulky groups, including phenyls, on each side in the ketene plane sterically retards nucleophilic attack. The reactions are interpreted as involving in-plane attack by nucleophilic water or hydroxide in the neutral and base-induced reactions, and electrophilic protonation perpendicular to the ketene plane for the acid-catalyzed reaction.

ISSN:0008-4042    

DOI:10.1139/v87-287

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Native cellulose samples having a wide range of crystallinity and crystallite size were mercerized by treatment with sodium hydroxide. The resultant cellulose II samples showed only a narrow range of crystallinity and an essentially constant crystallite size. For the low-crystallinity samples, crystallinity and crystallite size actually increased on mercerization. These results are in line with the proposal that mercerization involves the mingling of chains from adjacent and antiparallel cellulose Imicrofibrilsto form cellulose II crystals of antiparallel chains.

ISSN:0008-4042    

DOI:10.1139/v87-288

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

We have made electrochemical measurements with a glass electrode that have yielded pKvalues atT = 298.15 K for monothanolamine (MEA), triethanolamine (TEA), diisopropanolamine (DIPA), and methyldiethanolamine (MDEA) relative to the already well-known pKfor diethanolamine (DEA), with all pKvalues referring to equilibria of the type AmH+(aq) = Am(aq) + H+(aq) in which Am(aq) represents an alkanolamine in aqueous solution and AmH+(aq) represents the corresponding protonated alkanolamine. We have also made calorimetric measurements leading to ΔH0values for dissociation of the protonated species of all five of these alkanolamines in aqueous solution atT = 298.15 K. These pKand ΔH0values have led to ΔG0and ΔS0values for the corresponding dissociation reactions of all five AmH+(aq) species.

ISSN:0008-4042    

DOI:10.1139/v87-289

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Thermodynamic pK1and pK2values of 36 arylphosphonic acids have been determined. The pKvalues of themetaandparacompounds are correlated well by the σnparameter, suggesting that there is little conjugation between the phosphonic group and the aromatic ring; the ρ values of the first and second dissociations are 0.923 and 1.140, respectively. The —PO3H−group itself appears to be electron donating, contrary to earlier literature reports. The effect oforthogroups has been examined using multivariate analysis; the steric component of the proximity effect is acid weakening and has a larger effect on the second dissociation than on the first, presumably because a greater change in degree of solvation accompanies the second dissociation than the first.

ISSN:0008-4042    

DOI:10.1139/v87-290

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

We have measured the rate constants for the enolization of acetone catalyzed by 29 arylphosphonate dianions (ArPO32−) and by 20 arylphosphonic acids (ArPO3H2). An excellent Brønsted correlation is found for the former reaction, with mostorthosubstituted compounds falling on the line drawn for themetaandparacompounds (β = 0.72). The largest deviation is found foro-iodo, whose small positive deviation is ascribed to a polarizability effect in the transition state. The arylphosphonic acids give a fairly good Brønsted plot (α = 0.37) but here theorthosubstituents tend to react slightly faster than would be expected on the basis of their equilibrium acid strengths. Catalysis by the monoanion ArPO3H−is difficult to detect; such ions appear to be acting as general acids, not general bases, and do not appear to act as bifunctional catalysts; it is shown that protonating acetone is 3.4 × 104times as effective as deprotonating ArPO3H−. The Brønsted coefficients (β) for the rate-controlling steps for the enolization of acetone by the principal routes are shown to be inversely related to the magnitude of the rate constants.

ISSN:0008-4042    

DOI:10.1139/v87-291

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Interactions between beef lung heparin and Mg2+and La3+counterions, in the presence of sodium ions, have been investigated by13C-nmr spectroscopy. The chemical shift displacements observed for the carbons of the main disaccharide unit of heparin, when analysed on the basis of counterion condensation theory, indicate that the association between the heparin polyanion and Mg2+is a delocalized process. This is analogous to the Ca2+/Na+/heparin system, despite the fact that the binding affinity of heparin for Ca2+is stronger than that for Mg2+. By contrast, the interaction with La3+is in excess of the theoretical predicted, which suggests that there is at least a partial site-binding of this counterion. In Ca2+/M+/heparin systems in which M+ = Na+or K+, the selective binding preference of heparin for the univalent cations may be related to the order of their crystallographic ionic radii. A critical assessment is offered of the validity of this nmr spectroscopic approach to the study of counterion binding to heparin.

ISSN:0008-4042    

DOI:10.1139/v87-292

出版商:NRC Research Press    

年代:1987

数据来源: NRC