摘要:

A synthesis of lamberlianic acid2astarting from podocarpic acid is described. The central intermediate, diester-ketone4b, is obtained by ozonolysis and hydrogenation, and the exocyclic methylene group in ring B generated via a Reformatsky reaction. The furan ring is attached by nucleophilic attack of 3-lithiofuran, for which an improved preparation is described, on either the acid chloride7bor the aldehyde16. The 12-oxygen atom is removed by mesylation of the alcohols12aandband Li–liquid ammonia reduction.

ISSN:0008-4042    

DOI:10.1139/v72-595

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Triphenyl-, diphenylmethyl-, and phenyldimethylsilyl-lithium react very rapidly with 9-phenylfluorene in tetrahydrofuran (THF) but the reaction can be followed spectroscopically using the stop-flow technique at low temperatures. The order of reaction, found from the dependence of the initial rate of reaction on the initial reactant concentrations, is unity in both 9-phenylfluorene and the relevant organosilyl-lithium reagent. The thermodynamic constants of activation for the reaction between 9-phenylfluorene and triphenylsilyl-lithium (Ph3SiLi), diphenylmethylsilyl-lithium (Ph2MeSiLi), and phenyldimethylsilyl-lithium (PhMe2SiLi), respectively, are: ΔH≠ = 4.5, 4.0, and 4.0 kcal mol−1; ΔG≠ = 13.0, 12.5, and 12.5 kcal mol−1; ΔS≠ = −34.9, −34.8, and −34.9 cal mol−1deg−1

ISSN:0008-4042    

DOI:10.1139/v72-596

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The rates of hydrolysis of 22 1-acyl-2-thiohydantoins in aqueous sulfuric acid to give 2-thiohydantoin and a carboxylic acid have been determined. In 0–90% sulfuric acid, hydrolysis takes place by an A-2 mechanism, and the rate reaches a maximum in about 70% acid. In acid more concentrated than about 90%, hydrolysis takes place by an A-1 mechanism, and the rate increases monotonically. Evidence for the two mechanisms comes from Yatesrand Bunnett-Olsenparameters; from entropies of activation; frompσ andpσ+relations; and from steric effects.

ISSN:0008-4042    

DOI:10.1139/v72-597

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

1-Acyl-2-thiohydantoins ionize in alkaline solution (pK ∼ 7). In solutions more alkaline than pH > 11 they are rapidly hydrolyzed to 2-thiohydantoin and a carboxylic acid, by attack of a hydroxide ion on the conjugate base of the 1-acyl-2-thiohydantoin. Possible mechanisms to accord with the entropy of activation, which is less negative than usual for base-catalyzed amide hydrolyses, are discussed. 1-Benzoyl-2-thiohydantoin hydrolyzes more rapidly than 1-acetyl-2-thiohydantoin, possibly because the ground state of the former molecule is destabilized by steric effects.

ISSN:0008-4042    

DOI:10.1139/v72-598

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Electrolytes studied in 100% trifluoroacetic acid exhibit a minimum in equivalent conductivity with increasing solute concentration. This behavior is accounted for by the formation of triple-ions at higher concentrations. Triple-ion dissociation constants,k, have been evaluated and, in general, they show the opposite trend with changing ion size to that of the ion-pair dissociation constants; that is the triple-ions of smaller ions are more dissociated. The experimentally observed trend is accounted for by using a partial ionic charge instead of unit charge for the ion-pair charges in the theoretical Fuoss expression fork.The excellent extrapolation of the triple-ion data to give a value of Λ0Kdfor the ion-pair, which agrees well with that determined from a Fuoss plot, permits an estimate of Λ0for LiO2CCF3from the triple-ion data.

ISSN:0008-4042    

DOI:10.1139/v72-599

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Molar enthalpies of mixing for the fiven-alkanes from pentane through nonane with carbon tetrachloride at 298.15 K have been measured. The maximum values are, with increasing chain length, 295, 315, 339, 373, and 417 J. Energies calculated from the enthalpies are compared with the lattice theory of mixtures. The comparison is also extended through hexadecane, using previously reported results.

ISSN:0008-4042    

DOI:10.1139/v72-600

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

A variety of methods of synthesis of hitherto unknown isomericcis-8-oxabicyclo[4.3.0]nonan-3-ols were studied, and the best method for obtainingcis-8-oxabicyclo[4.3.0]nonan-3β-ol (2) was hydroboration ofcis-8-oxabicyclo[4.3.0]non-3-ene (1).cis-8-Oxabicyclo[4.3.0]nonan-3α-ol (3) could be obtained highly stereoselectively by the hydrogenation ofcis-8-oxabicyclo[4.3.0]nonan-3-one (4) over platinum oxide in an acidic medium. The configurations of2and3were deduced mainly from the chemical and spectral similarity with the knowncis-bicyclo[4.3.0]nonan-3-ols. The preferred conformations of the two isomeric alcohols were discussed in terms of i.r. as well as n.m.r. spectroscopy using paramagnetic shift reagents. There is almost no difference in the coordination abilities of europium ions with the alcoholic and ethereal oxygen atoms in these compounds.

ISSN:0008-4042    

DOI:10.1139/v72-601

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Methane can be converted into C2hydrocarbons and hydrogen in a triboelectric discharge arising from the intermittent contacting of mercury with a glass surface. The discharge is a result of the accumulation of high densities of static charge at the interface by the transfer of electrons from the mercury to the glass. Excited species with energies up to 20 eV above their ground states have been detected by spectroscopic examination of the discharge. The effects of physical parameters such as surface area and surface nature on the triboelectrification process have been examined. Both the area and nature of the solid surface influence the extent of breakdown and discharge. The rates of conversion are virtually invariant with pressure from 760 to 200 Torr, but at 200 Torr they increase sharply before gradually falling off again as the pressure is further reduced. This behavior is explained in terms of the opposite effects of pressure on the electrical breakdown of the gas and on the rates of the chemical reactions accompanying the discharge. The pressure at which the rise in yield occurs has been used to estimate the production of an average static charge density of 2 e.s.u. cm−2by contact electrification at a mercury/glass interface. The effects of inert gases and oxygen have also been studied and the results of these experiments together with a comparison of the products formed in other decomposition processes suggest that CH2and CH3are important intermediates in the triboprocess occurring in methane.

ISSN:0008-4042    

DOI:10.1139/v72-602

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The polarographic behavior of the lead ion in the presence of excess DTPA was studied over the pHrange 2–10. Three different polarographic waves can be distinguished. The wave occurring at the most negative potentials and highest pHvalues is assigned to an irreversible reduction of PbHA2−. The kinetic current treatment gives the resultsThe wave occurring at intermediate potentials and pHvalues is also assigned to an irreversible reduction of PbHA2−. The kinetic current treatment gives the resultsProtonation is assumed to occur at different coordination sites. In the former case it occurs at the center carboxyl group; in the latter case it occurs at a terminal nitrogen atom. The reversible wave occurring at the most positive potentials and lowest pHvalues can be interpreted in either of two waysFor the stability constant we obtained logKpbA = 19.1. All values above were obtained at 25° and an ionic strength of 0.2.

ISSN:0008-4042    

DOI:10.1139/v72-603

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The normal-mode approach to the solution of the vibration–dissociation coupling problem for a dilute diatomic gas, which was described in Part III of this series, has been extended to the treatment of recombination in a steady supersonic nozzle expansion. This method of solution did not suffer from the familiar instabilities associated with parasitic eigenvalues which have so far impeded solution of this problem. We report a calculation on H + H + M → H2 + M (withoutV–V coupling) yielding simultaneously the temperature, density, velocity, and the populations ofeachindividualvibrational level from 3900–1500 °K which was completed with acceptable accuracy along the zero-streamline in a few minutes of computer time.In the absence of V–V coupling effects, although grossly distorted vibrational population distributions were found, the populations were always monotonic with vibrational quantum number; however, it was possible to generate absolute overpopulations of one vibrational state with respect to another by simulating vibrational coupling effects.The main conclusions of the calculation are that under these conditions (i) the rate constant for recombination is the normal phenomenological recombination rate constant; (ii) the vibrational relaxation time τvibappears to vary over several orders of magnitude depending on the approximation used to define the vibrational energy content, but if a proper measure of the vibrational energy is used, τvibcan be correlated with the second eigenvalue of the relaxation matrix, and is therefore the same as that which would have been found in a shock-tube measurement.

ISSN:0008-4042    

DOI:10.1139/v72-604

出版商:NRC Research Press    

年代:1972

数据来源: NRC