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The effects of a beta-nitrogen substituent on the keto-enol/enolate equilibria in the N-acetylamino-p-methylacetophenone system are investigated.

Research into the kinetics and reaction mechanisms of the quinone methide hydration reactions that form the basis of biological activity in living systems where water is the ubiquitous medium is presented. It was found that decay of the quinone methide is speeded up by acetic acid buffers through both acid- and base-catalyzed pathways.

Research has been conducted on the methyl mandelate. Results indicate that the flash dediazotization of methyl phenyldiazoacetate in aqueous solutions produces methyl mandelate through the O-H insertion reaction of the alpha-carbonylcarbene.

Research is presented describing the use of flash photolysis on 4-diazoisothiochroman-3-one in aqueous solution to produce 1,3-dihydrobenzo[c]thiophen-1-ylideneketene in a photo-Wolff reaction.

A study on keto-enol tautomerism of beta-ketoesters investigated the enol of 4,4,4-trifluoroactoacetic acid prepared by flash photolytic retro-(2+4)-cycloaddition of a suitable dioxinone and its analogues. Among other findings, trifluoromethyl was found to influence rates of enolization and ketonization. Results also confirm the electron-withdrawing nature of trifluoromethyl that reduces the electron density of the enolic vinyl group and renders it less susceptible to electrophilic attack by acids.

A rapid rise in absorbance of around lambda = 250 nm to 300 nm results from flash photolysis of aqueous solutions of 2-diazocyclohexane-1,3-dione. This is followed by a much slower decay. There are strong similarities between these absorbance changes and those seen in the production of acetoacetic acid by flash photolysis of 2,2,6-trimethyl-4H-1,3-dioxin-4-one. In aqueous solution, 2-ketocyclopentyl-ideneketene is produced from flash photolysis of 2-diazocyclohexane-1,3-dione. This hydrates to the enol of 2-oxocyclopentanecarboxylic acid, with the enol then isomerizing to the keto form of the acid.

Examination of the flash photolysis of phenyldiozoacetic acid and the methy, n-butyl and isobutyl esters of benzoylformic acid in aqueous solution shows that mandelic acid enol is generated by hydration of phenylcaboxycarbene. Isotopic trace studies and transient absorbance effects indicate that reaction paths are supported and described by acid-base catalysis and solvent isotope effects. Results indicate that the racemization of mandelic acid in neutral solution is catalyzed by the enzyme mandelate racemase.

Flash photolysis of 10-diazo-9(10H)-phenanthrenone in aqueous solution provided two successively formed transient species, producing fluorene-9-carboxylic acid. The transients were identified as fluorenylideneketene, produced from a photo-Wolff reaction. Bromine scavenging determined the rate of enolization of fluorene-0-carboxylic acid.

Rates of amide hydrolysis are measured for the substrate succinyl-Ala-Ala-Pro-Phe-p-nitroanilide catalyzed by subtilisin and its N155G mutant. These allow the solvent isotope effects, which show no differences between the wild-type and mutant enzymes, to be derived. The isotope effects also show that the curvature in the proton inventory of a reaction catalyzed by methyl chymotrypsin is not due to oxyanion hole interactions but can be accounted for by a medium effect. The presence of strong medium effects in subtilisin and its mutant is also observed.

Photodecarbonylation of phenylaminocyclopropenones give primary, secondary and tertiary ynamines in aqueous solution. In acid-catalyzed decay of the ynamines, protonation of the beta-carbon atoms leads to the keteniminium ions from which nitrogen-linked protons are eliminated to produce ketenimines. The ketenimines react with water to give phenylacetamides. Tertiary ynamine derived keteniminium ions lack nitrogen-linked protons and so are hydrated to form amide enols which ketonize to yield phenylacetamides. Only primary and secondary ynamines undergo base-catalyzed decay.

Arylynolate and arylketenes are formed as short lived intermediates during the synthesis of arylacetic acid from arylhydroxycyclopropenones. The flash photolysis of kinetics of these arylylnolate and arylketenes shows that the related arylynols are strong acids having a pK(sub a) value of < 3. The rate of ketene hydration reactions reveal large steric effects. The photocarbonylation of hydroxycyclopropenones can be achieved in liquid solution at ambient temperature.

Flash photolytic production of phenylcyanoketene by a photo-Wolff reaction of alpha-cyano-alpha-diazoacetophenone after hydration of the ketene provided the enol of alpha-cyano-alpha-phenylatic acid as a short-lined transient species. Estimations of the rates of ketonisation of the enol in dilute hydrochloric acid solutions, acetic acid, biphosphate ion, tris(hydroxymethyl)methylamine and ammonia buffers provided a rate profile with turning points. The first and second acid ionization constants of the enol could be establish from this profile.

Two methods were used to determine the keto-enol equilibrium constants for the pyruvic acid system in both acidic and basic aqueous solution. The first method used the Meyer halogen titration while the second used the ratio of enolization to ketonization. The two methods produced consistent results but slight differences between values for acidic and basic solution were observed. Such differences can be explained by the fact that the pyruvic acid is an un-ionized carboxylic acid in acid solutions but becomes a pyruvate ion in basic solutions.

Research was conducted to determine whether alpha-carbonylcarbene intermediates are formed as ketene precursors in the photo-Wolff reaction of alpha-diazocarbonyl compounds. A comparison of pyridine scavenging of transients generated by laser flash photolysis of benzoyldiazomethane and 1-naphthoyldiazomethane with pyridine scavenging of transients formed by flash photolysis of the corresponding arylhydroxycyclopropenones was carried out. Results indicate that the species scavenged by pyridine after flash photolysis of benzoyldiazomethane and 1-naphthoyldiazomethane are ketenes and not alpha-carbonylcarbenes.

The generation of o-quinone alpha-phenylmethide as a short lived transient species in aqueous solution by flash photolysis of o-hydroxy-alpha-phenylbenzyl alcohol, and its rate of decay measured in HClO4 and NaOH solutions as well as in CH3CO2H, H2PO4-, and HCO3- buffers is detailed. It was observed that a preequilibrium exists in the acid-catalyzed reaction.

The enol of 2-hydroxy-2-cyano-N-methylacetamide in aqueous solution was studied using flash photolytic generation.

Kinetic studies of acid dissociation of N-(pentafluorophenyl)-2-phenylethynamine in aqueous solution reveal that the reaction has a pK(a) value of 10.28 and the acidifying effect is evaluated as 10 pK units. Flash photolysis of an aminocyclopropenone produces this ynamine and it undergoes isomerization to ketenimine in aqueous solutions. Kinetic isotopic studies help examine the isomerization reaction and determine rate constants for various steps.

A reexamination of the hydroxide ion-catalyzed enolization of acetone provided deuterium and tritium isotope effects having a Swain-Schaad exponent value of x = 1.49 +/- 0.07 that was consistent with theoretical results. The new procedure involved tritium nuclear magnetic resonance spectroscopy for determining tritium exchange in an acetone-water system. Bromine scavenging of the acetone enolate ion was performed to obtain protium and deuterium hydroxide ion catalytic coefficients which when combined with the experimental rate constants provided highly reliable isotope effects.

Flash photolysis of 2-diazocyclopentane-1,3-dione in aqueous solution produced 2-oxocyclobutylideneketene, which underwent hydration to the enol of 2-oxocyclobutanecarboxylic acid; the enol then isomerized to the keto form of this acid. Rates of the ketene and enol reactions were measured in acid, base, and buffer solutions across the acidity range [H+] = 10-1 -10-13 M, and analysis of these data, together with rates of enolization of the keto form of 2-oxocyclobutanecarboxylic acid determined by bromine scavenging, gave keto-enol equilibrium constants as well as acidity constants of the keto and enol forms. The keto-enol equilibrum constants proved to be 2 orders of magnitude less than those reported previously for the next higher homolog, 2-oxocyclopentanecarboxylic acid, reflecting the difficulty of inserting a carbon-carbon double bond into a small, strained carbocyclic ring. The acidity constant of the enol group of 2-oxocyclobutanecarboxylate ion, on the other hand, is greater, by 4 orders of magnitude, than that of the corresponding enol in the cyclopentyl system. This remarkable increase in acidity with diminishing ring size is consistent with the enhanced s character of the orbitals used to make the exocyclic bonds of the smaller cyclobutane ring. [ABSTRACT FROM AUTHOR]

Flash photolysis of diazophenylacetamide in aqueous solution produced phenylcarbamoylcarbene, whose hydration generated a transient species that was identified as the enol isomer of mandelamide. This assignment is based on product identification and the shape of the rate profile for decay of the enol transient, through ketonization to its carbonyl isomer, as well as by the form of acid-base catalysis of and solvent isotope effects on the decay reaction. Rates of enolization of mandelamide were also determined, by monitoring hydrogen exchange at its benzylic position, and these, in combination with the ketonization rate measurements, gave the keto-enol equilibrium constant pK[sub E] = 15.88, the acidity constant of the enol ionizing as an oxygen acid, pQ[sup E, sub a] = 8.40, and the acidity constant of the amide ionizing as a carbon acid PQ[sup K, sub a] = 24.29. (These acidity constants are concentration quotients applicable at ionic strength = 0.10 M.) These results show the enol content and carbon acid strength of mandelamide, like those of mandelic acid and methyl mandelate, to be orders of magnitude less than those of simple aldehydes and ketones; this difference can be attributed to resonance stabilization of the keto isomers of mandelic acid and its ester and amide derivatives, through electron delocalization into their carbonyl groups from the oxygen and nitrogen substituents adjacent to these groups. The enol of mandelamide, on the other hand, again like the enols of mandelic acid and methyl mandelate, is a substantially stronger acid than the enols of simple aldehydes and ketones. This difference can be attributed to the electronegative nature of the oxygen and nitrogen substituents geminal to the enol hydroxyl group in the enols of mandetic acid and its derivatives; in support of this, the acidity constants of these enols correlate well with field substituent constants of these geminal groups. [ABSTRACT FROM AUTHOR]

Examines the photolysis of p-quinone methide in aqueous solution. Heterolysis of the carbon-bromide bond in p-hydroxybenzyl bromide; Protonation of the quinone methide in the carbonyl carbon atom; Preequilibrium mechanisms of a p-hydroxybenzyl carbocation.

Focuses on the flash photolytic generation of o-quinone alpha-phenylmethide and o-quinone alpha-(p-Anisyl)methide in aqueous solution. Hydration of the quinone methide; Effects of acid-catalyzed reaction in the solvent isotope; Rate of decay of o-quinine apha-phenylmethide.

Examines the effect of beta-oxygen substituent to keto-enol/enolate equilibria in the isochroman-4-one system. Generation of enol from 1-tetralone; Measurement of ketonization rates in aqueous HClO[sub 4] and NaOH solutions; Hydrolysis of potassium salt and trimethylsilyl ether.

Examines the flash photolysis of cis-enol of N-acetylamino-p-methylacetophenone and the rates of ketonization in aqueous hypochlorite and sodium hydroxide solutions. Rates of enolization of N-acetylamino-p-methylacetophenone; Acid catalytic coefficients for rate-determining proton-transfer reactions.

Focuses on a study where flash photolysis of 2-(N-(pentafluorophenyl)amino)-3-phenylcyclopropenone, in aqueous solution was found to produce N-(pentafluorophenyl)phenylethynamine, by the expected photodecarbonylation reaction and also-2-phenyl-3-(N-(pentafluorophenyl)amino)acrylic acid, by an apparent unprecedented photochemical ring-opening process. Study methodology; Discussion of findings.

Describes the flash photolysis of five diazonaphthoquinones in aqueous solution. Production of ketene and carboxylic enol intermediates preceding the ultimate indenecarboxylic acid reaction products; Catalysis of the decay of the two intermediates.

Examines the rates of hydration of acetylketene and ketonization of acetoacetic acid enol when acetylketene were produced by flash photolysis of 2,2,6-trimethyl-4H-1,3-dioxin-4one in aqueous solution. Acetylketene found to be a reactive substance; Information on ketene hydration; Results to show that the hydration of acetylketene if not acid-catalyzed up to an acidity of [H+]=0.10-...M.

Reports a study which investigated whether alpha-carbonylcarbene intermediates are formed as ketene precursors in the photo-Wolff reaction of alpha-diazocarbonyl compounds by comparing pyridine scavenging of transients generated by laser flash photolysis of benzoyldiazomethane. Experimental framework of the study; Results; Discussion of the results.

Reports on the production of the enol of the ester methyl fluorene-9-thionocarboxylate in aqueous solution. Keto-enol equilibrium constants; Acid dissociation constants of keto and enol forms; Acidity constants for the keto forms of a group of related esters.

The efficient separation of the 2,3-butanediol (2,3-BDO) intermediate from fermentation broth is an important issue in the production of biofuels from biomass-derived intermediates. Two zeolitic imidazolate frameworks ZIF-8 and ZIF-71 were investigated for the adsorption of 2,3-butanediol (2,3-BDO) from fermentation broth via liquid breakthrough adsorption measurements. While both ZIF materials initially show high separation performance, ZIF-71 retains robust separation performance even after aging in ethanol for two years, whereas the capacity of ZIF-8 decreases significantly. The robustness and stability of ZIF-71 are further confirmed with cyclic fixed bed adsorption measurements. The uptake of 2,3-BDO on ZIF-71 reaches >100 g/kg with negligible uptakes of sugars, organic acids, and other alcohols present in the fermentation broth. Excellent selectivity toward 2,3-BDO over water is also achieved. The 2,3-BDO-loaded ZIF-71 can be regenerated efficiently with ethanol as desorbent. These findings indicate that ZIF-71 shows considerable promise as an adsorbent to recover and purify diols from fermentation broths., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Fractals, mathematically defined as "self-similar subsets at different scales", are ubiquitous in nature despite their complexity in assembly and formulation. Fractal geometry formed by simple components has long been applied to many fields, from physics and chemistry to electronics and architecture. The Sierpiński carpet (SC), a fractal with a Hausdorff dimension of approximately 1.8933, has two-dimensional space-filling abilities and therefore provides many structural applications. However, few studies have investigated its mechanical properties and fracture behaviors. Here, utilizing the lattice spring model (LSM), we constructed SC composites with two base materials and simulated tensile tests to show how fractal iterations affect their mechanical properties and crack propagation. From observing the stress-strain responses, we find that, for either the soft-base or stiff-base SC composites, the second iteration has the optimal mechanical performance in the terms of stiffness, strength, and toughness compared to the composites with higher hierarchies. The reason behind this surprising result is that the largest stress intensities occur at the corners of the smallest squares in the middle zone, which consequently induces crack nucleation. We also find that the main crack tends to deflect locally in SC composites with a soft matrix, but in global main crack behavior, SC composites with a stiff matrix have a large equivalent crack deflection. Furthermore, considering the inherent anisotropy of SC composites, we rotated the samples by 45°. The results show that the tensile strength and toughness of rotated SC composites are inferior and the crack propagating behaviors are distinct from the standard SC composites. This finding infers advanced engineering for crack control and deflection by adjusting the orientation of SC composites. Overall, our study opens the door for future engineering applications in stretchable devices, seismic metamaterials, and structural materials with tunable properties and hierarchies.

The acid stability of zeolitic imidazolate frameworks (ZIFs) is an important issue hindering their application. Acid-gas damage of ZIFs has been considered irreversible. However, we demonstrate a methodology called solvent-assisted crystal redemption (SACRed) to reverse acid-gas damage to ZIFs with a high degree of structural and functional recovery. For example, post-SACRed ZIF-8 is shown to be structurally and chemically near-identical with the original pristine ZIF-8 that suffered a large loss of surface area, porosity, and crystallinity during acid-gas exposure. We also provide mechanistic insight into the recovery process using deuterium-labeled linkers and 2 H NMR spectroscopy. SACRed treatments could allow large extensions in the lifetime of ZIF-based membranes and adsorbents that degrade over time.

Nanoparticle LiFePO4, the basis for an entire class of high power Li-ion batteries, has recently been shown to exist in binary lithiated/delithiated states at intermediate states of charge. The Mn-bearing version, LiMn(y)Fe(1-y)PO4, exhibits even higher rate capability as a lithium battery cathode than LiFePO4 of comparable particle size. To gain insight into the cause(s) of this desirable performance, the electrochemically driven phase transformation during battery charge and discharge of nanoscale LiMn0.4Fe0.6PO4 of three different average particle sizes, 52, 106, and 152 nm, is investigated by operando synchrotron radiation powder X-ray diffraction. In stark contrast to the binary lithiation states of pure LiFePO4 revealed in recent investigations, the formations of metastable solid solutions covering a remarkable wide compositional range, including while in two-phase coexistence, are observed. Detailed analysis correlates this behavior with small elastic misfits between phases compared to either pure LiFePO4 or LiMnPO4. On the basis of time- and state-of-charge dependence of the olivine structure parameters, we propose a coherent transformation mechanism. These findings illustrate a second, completely different phase transformation mode for pure well-ordered nanoscale olivines compared to the well-studied case of LiFePO4.

o-Thioquinone methide, 2, was generated in aqueous solution by flash photolysis of benzothiete, 1, and rates of hydration of this quinone methide to o-mercaptobenzyl alcohol, 3, were measured in perchloric acid solutions, using H2O and D2O as the solvent, and also in acetic acid and tris(hydroxymethyl)methylammonium ion buffers, using H2O as the solvent. The rate profiles constructed from these data show hydronium-ion-catalyzed and uncatalyzed hydration reaction regions, just like the rate profiles based on literature data for hydration of the oxygen analogue, o-quinone methide, of the presently examined substrate. Solvent isotope effects on hydronium-ion catalysis of hydration for the two substrates, however, are quite different: k(H)/k(D) = 0.42 for the oxygen quinone methide, whereas k(H)/k(D) = 1.66 for the sulfur substrate. The inverse nature (k(H)/k(D) < 1) of the isotope effect in the oxygen system indicates that this reaction occurs by a preequilibrium proton-transfer reaction mechanism, with protonation of the substrate on its oxygen atom being fast and reversible and capture of the benzyl-type carbocationic intermediate so formed being rate-determining. The normal direction (k(H)/k(D) > 1) of the isotope effect in the sulfur system, on the other hand, suggests that protonation of the substrate on its sulfur atom is in this case rate-determining, with carbocation capture a fast following step. A semiquantitative argument supporting this hypothesis is presented.

In previous work (Can. J. Chem. 1987, 65, 1719-1723 and J. Am. Chem. Soc. 1995, 117, 9165-9171), flash photolysis of diazoacetophenone or phenylhydroxycyclopropenone in aqueous solution was found to produce phenylketene as a short-lived transient species with absorbance at lambda congruent with 260 nm, which decayed with single-exponential kinetics. It has now been discovered that, in the acidity region [H(+)] = 0.000 01 to 0.06 M, this decay is preceded by a faster absorbance rise, and that the overall change conforms well to a double exponential rate law. Analysis of the new data produces rate profiles whose general shapes, as well as the numerical values of their constituent rate constants, plus the form of buffer catalysis, indicate that this newly discovered absorbance rise represents ketonization of phenylacetic acid enol, and that the subsequent absorbance decay represents addition of water to phenylketene. The chemistry of the system, however, requires ketene hydration to precede enol ketonization in a time sequence opposite from that of the absorbance changes. This seemingly counter-intuitive result is nevertheless consistent with the rate law that governs the time evolution of the central species in a two-step rise and decay, such as that observed here.

Light-induced deazotization of 3-diazo-3H-benzofuran-2-one (1) in solution is accompanied by facile (CO)-O bond cleavage yielding 6-(oxoethenylidene)-2,4-cyclohexadien-1-one (3), which appears with a rise time of 28 ps. The expected Wolff-rearrangement product, 7-oxabicyclo[4.2.0]octa-1,3,5-trien-8-ylidenemethanone (4), is not formed. The efficient light-induced formation of the quinonoid cumulenone 3 opens the way to determine the reactivity of a cumulenone in solution. The reaction kinetics of 3 were monitored by nanosecond flash photolysis with optical (lambda(max) approximately 460 nm) as well as Raman (1526 cm(-1)) and IR detection (2050 cm(-)(1)). Remarkably, the reactivity of 3 is that expected from its valence isomer, the cyclic carbene 3H-benzofuran-2-one-3-ylidene, 2. In aqueous solution, acid-catalyzed addition of water forms the lactone 3-hydroxy-3H-benzofuran-2-one (5). The reaction is initiated by protonation of the cumulenone on its beta-carbon atom. In hexane, cumulenone 3 dimerizes to isoxindigo ((E)-[3,3']bibenzofuranylidene-2,2'-dione, 7), coumestan (6H-benzofuro[3,2-c][1]benzopyran-6-one, 8), and a small amount of dibenzonaphthyrone ([1]benzopyrano[4,3-][1]benzopyran-5,11-dione, 9) at a nearly diffusion-controlled rate. Ab initio calculations (G3) are consistent with the observed data. Carbene 2 is predicted to have a singlet ground state, which undergoes very facile, strongly exothermic (irreversible) ring opening to the cumulenone 3. The calculated barrier to formation of 4 (Wolff-rearrangement) is prohibitive. DFT calculations indicate that protonation of 3 on the beta-carbon is accompanied by cyclization to the protonated carbene 2H(+), and that dimerization of 3 to 7 and 9 takes place in a single step with negligible activation energy.

A series of 3-[[(aryloxy)alkyl]piperidinyl]-1,2-benzisoxazoles was synthesized and evaluated as potential antipsychotic D2/5-HT2 antagonists. Most of these compounds showed potent antipsychotic-like activity in an apomorphine-induced climbing mouse paradigm, with many also showing preferential mesolimbic activity, as indicated by their weaker effects in an apomorphine-induced stereotypy model. In receptor binding assays, many displayed a moderate affinity for the D2 receptor coupled with a significantly greater affinity for the 5-HT2 receptor: a property that has been suggested as necessary for atypicality. From this series, compound 45, 1-[4-[3-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1- piperidinyl]propoxy]-3-methoxyphenyl]ethanone (iloperidone, HP 873), was further evaluated in a battery of in vivo and in vitro assays. This compound showed a 300-fold greater potency in inhibition of climbing than in inhibition of stereotypy or induction of catalepsy, and when evaluated chronically in an electrophysiological model, 45 caused a depolarization blockade of dopamine neurons in the A10 area of the rat brain but not in the A9 area. Additionally, it showed positive activity in a social interaction paradigm, suggesting potential efficacy against asociality, a component of the negative symptoms of schizophrenia. In chronic ex vivo studies, 45, similar to clozapine, caused a down regulation of 5-HT2 receptors but had no effect on the number of D2 receptors. Compound 45 is currently undergoing clinical evaluation.