Pinacol Formation Research Articles

Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots.

We present an efficient and versatile visible light-driven methodology to transform aryl aldehydes and ketones chemoselectively either to alcohols or to pinacol products with CdSe/CdS core/shell quantum dots as photocatalysts. Thiophenols were used as proton and hydrogen atom donors and as hole traps for the excited quantum dots (QDs) in these reactions. The two products can be switched from one to the other simply by changing the amount of thiophenol in the reaction system. The core/shell QD catalysts are highly efficient with a turn over number (TON) larger than 4 × 104 and 4 × 105 for the reduction to alcohol and pinacol formation, respectively, and are very stable so that they can be recycled for at least 10 times in the reactions without significant loss of catalytic activity. The additional advantages of this method include good functional group tolerance, mild reaction conditions, the allowance of selectively reducing aldehydes in the presence of ketones, and easiness for large scale reactions. Reaction mechanisms were studied by quenching experiments and a radical capture experiment, and the reasons for the switchover of the reaction pathways upon the change of reaction conditions are provided.

Synthesis and properties of a novel poly(aryl ether sulfone) functionalized with pinacol phenylboronate pendants

A novel poly(arylene ether sulfone) (PAES) with pinacol phenylboronate pendants (PAES-B) was prepared by the borylation of brominated PAES (PAES-Br). The reaction was carried out under mild conditions in the presence of cuprous iodide and tri- n-butylphosphine in tetrahydrofuran solution. After heat treatment at 150°C for 132 h, the PAES-B exhibited an interesting solvent resistance. Fourier transform infrared spectroscopy (FTIR) and thermal analysis were performed to investigate the reason. FTIR spectra showed that heat treatment could facilitate losing of pinacol groups and formation of phenylboronic acid in the polymer. Meanwhile, differential scanning calorimetric (DSC) curves demonstrated that the polymer had cross-linking behaviors during heat treatment. In addition, the thermal oxidative stability of PAES-B was researched by the thermogravimetric analysis (TGA).

ChemInform Abstract: Praseodymium‐Induced Pinacol Formation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Praseodymium-Induced Pinacol Formation

In an attempt to regenerate Ti(0) from TiOx for possible application in a catalytic McMurry coupling reaction, a praseodymium-based pinacol reaction was uncovered. This reaction formed the two products 2,3-diphenyl-2,3-butanediol (3) and α,β-dimethyl-α-phenyl-β-[(trimethylsilyl)oxy]-benzene-ethanol (6) in a 1:3 ratio.

Pinacol Formation and Reduction of Aromatic Carbonyls with Magnesium—Methanol at Ambient Temperature.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Pinacol Formation and Reduction of Aromatic Carbonyls with Magnesium?Methanol at Ambient Temperature

A simple and inexpensive procedure for the pinacol formation of aromatic aldehydes and reduction of aromatic ketones to the corresponding alcohols with magnesium in dry methanol at ambient temperature is reported. The pinacol formation and reduction are proposed to be proceeding by SET from magnesium.

Direct Formation of Pinacols from Olefins over Various Titano–Silicates

The epoxidation and successive pinacol formation of tri- and tetraalkyl-substituted olefins using Ti-β/H2O2/H2O as the catalytic system has been investigated. Aluminum-free Ti-β exhibits better activity and pinacol selectivity than TS-1, TS-2, Ti–MCM-22, and mesoporous Ti–MCM-41. Pinacol (vic-diol) is obtained as the major product with small amounts of the side products pinacolone, alcohol (via hydration), and oligomers. The conversion and pinacol selectivity increase with an increase in reaction temperature and time. The change in product distribution with reaction time over Ti-β shows that the epoxide is the initial product which undergoes a secondary reaction to give pinacol as the major product. The conversion and H2O2 selectivity decrease with the bulkiness of the substituents at the CC bond but the selectivity of pinacol is not significantly affected. The reactivity of cyclic 1-methyl-1-cyclohexene is considerably lower than that of the corresponding open-chain analogue 2-methyl-2-butene. The symmetrical tetramethyl-substituted 2,3-dimethyl-2-butene led to the formation of small amount of dimers over medium-pore titanium silicates TS-1, TS-2, and Ti–MCM-22. The epoxidation of these substituted olefins proceeded more rapidly when using acetonitrile as a cosolvent than under triphase conditions. Mechanistically, the primary epoxide product undergoes acid-catalyzed nucleophilic ring opening by H2O molecules to give pinacol.

Photochemical reactions and on-line UV detection in microfabricated reactors.

This work presents an application of microfabricated reactors and detectors for photochemical reactions. Two fabrication schemes were demonstrated for the integration of the reaction and the detection modules: coupling individually packaged chips, and monolithic integration of the two functions. In the latter fabrication scheme, we have succeeded in bonding quartz wafers to patterned silicon wafers at low temperature using a Teflon-like polymer-CYTOP[trade mark sign]. Using quartz substrates allows reaction and detection with UV light of lower wavelengths than Pyrex substrates permit. The pinacol formation reaction of benzophenone in isopropanol was the model reaction to demonstrate the performance of the microreactors. The extent of reaction was controlled by varying the flow rate and therefore the on-chip residence time. Crystallization of the product inside the microreactors was avoided by the continuous-flow design. Instead, crystallization was observed in the effluent storage device. Off-chip analysis using HPLC confirms the results obtained from the on-line UV spectroscopy. The quantum yield estimated suggests that the reactor design is effective in improving the overall efficiency of the reactor unit.

Organometallic Chemistry sans Organometallic Reagents: Modulated Electron‐Transfer Reactions of Subvalent Early Transition Metal Salts

AbstractThe potential of low‐valent, early transition‐metal reagents as selective reductants in organic chemistry has been foreshadowed by intensive research on the ill‐defined and heterogeneous subvalent titanium intermediates generated in the McMurry reaction and its numerous variants. As part of the long‐term research effort to develop soluble, well‐defined transition‐metal reductants of modulated and selective activity toward organic substrates, the THF‐soluble reductant, titanium dichloride, has been throughly examined, as well as the analogous ZrCl2 and HfCl2 reagents, all of which are readily obtainable by the alkylative reduction of the Group tetrachloride by butyllithium in THF. Noteworthy is that such interactions of MCl4 with butyllithium in hydrocarbon media lead, in contrast, to M(III) or M(IV) halide hydrides. Analogous alkylative reductions in THF applied to VCl4, CrCl3, and MoCl5 have yielded reducing agents similar to those obtained from Mcl4 but gradated in their reactivity. Such reductants have proved capable of coupling carbonyl derivatives, benzylic halides, acetylenes and certain olefins in a manner consistent with an oxidative addition involving a two‐electron transfer (TET). Such a reaction pathway is consistent with the observed stereochemistry of pinacol formation from ketones and for the reductive dimerization of alkynes. In contrast of the reaction of CrCl3 with two equivalents of butyllithium, which leads to a CrCl intermediate, the interaction of CrCl3 in THF with four equivalents of butyllithium at –78°C yields a reagent of the empirical formulation, LiCrH4.2LiCl.2 THF, as supported by elemental and gasometric analysis of its protolysis. This hydridic reductant cleaves a wide gamut of s̀ carbon–heteroatom bonds (C–X, C–O, C–S and C–N), towards which the CrCl reductant is unreactive. The type of cleavage and/or coupled products resulting from the action of “LiCrH4” on these substrates in best understood as arising from single‐electron transfer (SET). In light of the aforementioned findings, the gradated reducing action noted among TiCl2, HfCl2 and CrCl, as well as the contrasting reducing behavior between CrCl and LiCrH4, there is no doubt that future research with early transition metals will continue to yield novel reductants of modulated and site‐selective reactivity.

Ketone Coupling on Reduced TiO2 (001) Surfaces: Evidence of Pinacol Formation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKetone Coupling on Reduced TiO2 (001) Surfaces: Evidence of Pinacol FormationKeith G. Pierce and Mark A. BarteauCite this: J. Org. Chem. 1995, 60, 8, 2405–2410Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/jo00113a021RIGHTS & PERMISSIONSArticle Views453Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (747 KB) Get e-Alerts Get e-Alerts

Production of tartrate and glycolate from the electrochemical reduction of glyoxylate

There has been considerable controversy about these reductions. Bewick and Greener [7, 8] claimed to have produced glycolic acid from CO2 on lead and malic acid from CO2 on mercury but they did not detect glyoxylic acid. Similar results were reported by Wolf and Rollin [9] but others were unable to repeat these results, or obtained different products [3]. A number of workers have studied the voltammetric reduction of glyoxylic acid [10, 11]. But there have been no direct preparative studies since Bauer [12] in 1931. Some preparative studies are presented here. It has been generally assumed that the electrochemical reduction of glyoxylate goes by a two electron process to give glycolate (perhaps explaining Bewick's results [7]). However another possibility exists: the formation of tartaric acid by a one-electron reduction followed by a dimerisation (pinacol formation). Further reduction of tartaric acid could lead to malic acid (as claimed by Bewick [8] and Wolf [9]). We observed an HPLC peak from the reduction products of the reduction of oxalic acid which could be attributable to malic acid [4].

ChemInform Abstract: Intramolecular Sm2+‐ and Sm3+‐Promoted Reaction of γ‐Oxy δ‐ Keto Aldehyde. Stereocontrolled Formation of Pinacol and Lactone.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Intramolecular Sm 2+ and Sm 3+ promoted reaction of γ-oxy-δ-ketoaldehyde; stereocontrolled formation of pinacol and lactone

Samarium promoted intramolecular pinacol coupling and Tishchenko oxidoreduction of γ-oxy-δ-ketoaldehyde proceeded stereospecifically. Newly forming hydroxy group is oriented anti to γ-silyoxy group in both reactions.

The dehydrogenation of ethanol in dilute aqueous solution photosensitised by benzophenones

The photochemical properties of a series of water-soluble benzophenones have been evaluated in dilute aqueous solution. The compounds possess lowest-energy singlet and triplet excited states demonstrating considerable n,π* character. As such, irradiation of the compounds in aqueous solution containing ethanol (2% v/v) results in pinacol formation via a triplet-state hydrogen-abstraction process. In the presence of a colloidal Pt catalyst, the intermediate ketyl and 1-hydroxyethyl radicals can be used to reduce water to H2. The rate of H2 formation and its total yield depend upon the nature of the substituent used to solubilise the benzophenone. The rate at which the ketyl radical transfers an electron to the Pt particles can be rationalised in terms of thermodynamic and electrostatic factors.

ChemInform Abstract: Enantioselectivity in Camphor Pinacolisation.

Abstract Total enantioselectivity has been observed in pinacol formation using Li/THF. (+) Camphor and (±) Camphor give the optically active and racemic form of a single pinacol whose stereochemistry has been established as endo:endo by X-ray analysis. An exo:endo pinacol is formed as the sole product if camphor is added to Li/NH 3 . Tentative mechanism is proposed.

Photoreduction of benzophenone by acetonitrile: correlation of rates of hydrogen abstraction from RH with the ionization potentials of the radicals R.cntdot.

Triplet benzophenone (/sup 4/K) abstracts a hydrogen from acetonitrile with a rate constant of 130 +/- 30 M/sup -1/ s/sup -1/. Despite this low rate constant acetonitrile is not really an inert solvent and at low light fluxes, where T-T annihilation is not a major fate of the triplet, a major decay path for /sup 4/K is hydrogen abstraction with resulting pinacol (K/sub 2/H/sub 2/) formation (phi/sub K/sub 2/H/sub 2/ approx. = 0.1 at t = 0). Both K/sub 2/H/sub 2/ formation and /sup 3/K lifetime rapidly decrease with irradiation due to the light absorbing transients (LAT's) which are formed along with K/sub 7/H/sub 2/ from ketyl radicals (KH). The rate constants per hydrogen (k/sub H/) for abstraction from R-H by the electrophilic /sup 3/K correlate well with the ionization potentials (IP) of the corresponding radicals (R).

Enantioselectivity in camphor pinacolisation

Total enantioselectivity has been observed in pinacol formation using Li/THF. (+) Camphor and (±) Camphor give the optically active and racemic form of a single pinacol whose stereochemistry has been established as endo:endo by X-ray analysis. An exo:endo pinacol is formed as the sole product if camphor is added to Li/NH 3. Tentative mechanism is proposed.

Liquid-phase photocatalytic dehydrogenation of 2-propanol with acetone- cis-[Rh 2Cl 2(Co) 2(dpm) 2] system

The photocatalytic system composed of acetone and cis-[Rh 2Cl 2(CO) 2-(dpm) 2] has been found quite effective for H 2 production from 2-propanol, with a turnover frequency of about three times that for methanol (high-pressure mercury lamp). The observed induction period is explained in terms of the large effect of acetone photosensitizer which accumulated autocatalytically. Long-wavelength irradiation (λ ⩾ 364 nm) gives H 2 and acetone solely, although the quantum efficiency is low (~10 −4). A unique character of photons around 338 nm was pointed out, where not only much more acetone is formed than at λ ⩾ 364 nm, but also pinacol formation is highly suppressed compared to at λ ⩽ 312 nm.

Radical addition to the carbonyl carbon of ketones promoted by aqueos titanium trichloride in acidic medium, one step synthesis of pinacols and lactones

Carbon centered radical 1 , generated by reduction of methyl phenyl-glyoxalate with Ti(III) ion, adds to the carbonyl carbon of ketones 2 to afford pinacols 3 . Yields of 3 are remarkably influenced by the structure of 2 , in that the reaction is very sensitive to steric factors. Many other functional groups present in 2 do not interfere with carbonyl addition, but lactonization of 3 occurs when the additional groups are COOH, COOC 2H 5, and OH. Alkyl radical addition to ketones is a reversible process, but the rapid reduction of the resulting alkoxy radical 8 by Ti(III) ion makes the whole process stpractically irreversible and accounts for pinacol formation.

Heterogeneous catalysis and electrosorption phenomena in the cathodic reduction of acetylpyridines: Part III. Preparative investigation of reduction of 2-, 4- and 3-acetylpyridine

On the basis of the predictions obtained from detailed electrode kinetic measurements in Part II [1]. electrosynthetic investigations were performed in order to confirm the general kinetics and the kinetics for optical induction in the cathodic reduction of 2-, 4- and 3-acetylpyridine. As predicted, reduction of 2-and 4-acetylpyridine at the DME at pH 2.5 in the absence of any surfactant results in pinacol formation. In the presence of adsorbed strychninium, the results of Kariv et al [2] could be verified and comparably high optical yields were obtained at lead cathodes. Optical induction in 3-acetylpyridine reduction which hitherto was believed to be impossible can be achieved by exchanging the weakly acidic strychnine with the stronger acidic surface-active camphoric acid (optical yield 7%). This confirms the importance of a high basicity of the intermediate ketyl radical for effective optical induction by adsorbed inductor acids.