- Application of Mechanochemical Catalysis to the Synthesis of Boric Acid Esters
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The syntheses of triisopropyl borate and other boric acid esters under conditions of mechanochemical activation (MCA) with the use of zeolite catalysts were presented. The proposed method showed short synthesis times, low energy consumption, higher yields of target products, and the absence of byproducts. The mechanism of the catalytic esterification of boric acid under conditions of MCA was described. The conversion was no > 30%. The introduction of zeolites into the reaction zone increased the degree of conversion because of water removal from the reaction medium. Lower conversions of 2-butanol were related to its high viscosity, as a result of which the intensity of MCA was considerably decreased.
- Molchanov,Goidin,Golovin,Zolotovskaya,Bogdanov,Volodin
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- Reaction of triethyl phosphite with boron tribromide
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Reaction of boron tribromide with triethyl phosphite led to the formation of triethyl tribromoborophosphate 1, a complex bearing a P→B bond.
- Lewkowski, Jaroslaw,Mortier, Jacques,Vaultier, Michel
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- Methyl camouflage in the ten-vertex: Closo -dicarbaborane(10) series. Isolation of closo -1,6-R2C2B8Me8 (R = H and Me) and their monosubstituted analogues
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Reported are procedures leading to the first types of methyl camouflaged dicarbadecaboranes with fewer than eleven vertices. The compounds contain the closo-1,6-C2B8 scaffolding inside the egg-shaped hepta-decamethyl sheath, which im
- Bakardjiev, Mario,Tok, Oleg L.,R??i?ka, Ale?,R??i?ková, Zdeňka,Holub, Josef,Hnyk, Drahomír,?palt, Zbyněk,Fanfrlík, Jind?ich,?tíbr, Bohumil
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- Low-Temperature Hypergolic Ignition of 1-Octene with Low Ignition Delay Time
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The attainment of the efficient ignition of traditional liquid hydrocarbons of scramjet combustors at low flight Mach numbers is a challenging task. In this study, a novel chemical strategy to improve the reliable ignition and efficient combustion of hydrocarbon fuels was proposed. A directional hydroboration reaction was used to convert hydrocarbon fuel into highly active alkylborane, thereby leading to changes in the combustion reaction pathway of hydrocarbon fuel. A directional reaction to achieve the hypergolic ignition of 1-octene was designed and developed by using Gaussian simulation. Borane dimethyl sulfide (BDMS), a high-energy additive, was allowed to react spontaneously with 1-octene to achieve the hypergolic ignition of liquid hydrocarbon fuel at -15 °C. Compared with the ignition delay time of pure 1-octene (565 °C), the ignition delay time of 1-octene/BDMS (9:1.2) decreased by 3850% at 50 °C. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry confirmed the directional reaction of the hypergolic ignition reaction pathway of 1-octene and BDMS. Moreover, optical measurements showed the development trend of hydroxyl radicals (OH·) in the lower temperature hypergolic ignition and combustion of 1-octene. Finally, this study indicates that the enhancement of the low-temperature ignition performance of 1-octene by hydroboration in the presence of BDMS is feasible and promising for jet propellant design with tremendous future applications.
- Sheng, Haoqiang,Huang, Xiaobin,Chen, Zhijia,Zhao, Zhengchuang,Liu, Hong
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p. 423 - 434
(2021/02/05)
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- Carboranes as Aryl Mimetics in Catalysis: A Highly Active Zwitterionic NHC-Precatalyst
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Modern catalysis takes advantage of aryl-based interactions to tune and control reactions. In the design of N-heterocyclic-carbene catalysts, both the electronic and steric nature of the nitrogen substituents play a crucial role. Although hydrocarbon-based systems and especially aryl residues have contributed considerably to overcome multifaceted catalytic challenges, the unique properties of carborane moieties, including delocalized charge, potential planar chirality, and well-known thermodynamic stability, offer unprecedented opportunities to develop new catalysts while being employed as aryl mimetics. We report a straightforward synthetic route to a novel zwitterionic triazolium-based N-heterocyclic carbene (NHC) precatalyst bearing a 7,8-dicarba-nido-undecaboranyl substituent. The catalyst's excellent activity and its broad applicability are demonstrated in a wide range of organocatalytic transformations. Comparison of the performance with known N-aryl NHC catalysts offers preliminary insights into the stereoelectronic nature of this nido-carboranyl substituent.
- Selg, Christoph,Neumann, Wilma,L?nnecke, Peter,Hey-Hawkins, Evamarie,Zeitler, Kirsten
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supporting information
p. 7932 - 7937
(2017/06/19)
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- Rehydrogenation of aminoboranes to amine-boranes using H2O: Reaction scope and mechanism
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Water has been successfully employed as a reagent with which to rehydrogenate aminoboranes (e.g., iPr2N=BH2, 2,2,6,6-Me4C5H6N=BH2, and also transient Me2N=BH2 derived from 1/2[Me2N-BH2]2) to amine-boranes (e.g., iPr2NH·BH3, 2,2,6,6-Me4C5H6NH·BH3, Me2NH·BH3) in approximately 30 yield. The conversion to amine-boranes from the corresponding aminoboranes using this method represents an example of a metal-free, single-step route for the hydrogenation of the B=N bond. Deuterium labeling studies indicated that the protic hydrogen (N-H) on the rehydrogenated amine-borane was derived from H2O, whereas the third hydridic hydrogen (B-H) on the amine-borane was generated from the formation of a postulated hydride-bridged intermediate H2B(μ-H)(μ-NR2)B(OH)H (R2 = Me2, iPr2, 2,2,6,6-Me4C5H6), which requires a second equivalent of the starting aminoborane, thus explaining the low yield. Formation of insoluble borates (BxOyHz) provides a driving force for the reaction. Significantly, the yield can be increased by adding a sacrificial source of BH3 (e.g., to ca. 53% for BH3·THF) or by adding a separate source of H- (e.g., to ca. 95% for LiBH4) to complement the H+ (from H2O) in a more atom-efficient reaction.
- Leitao, Erin M.,Manners, Ian
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p. 2199 - 2205
(2015/05/13)
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- Gold(I) complexes of tetrathiaheterohelicene phosphanes
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New tetrathia[7]helicene-based (7-TH-based) gold(I) complexes 6 and 7 have been readily prepared by reaction of the respective phosphine ligands 2 and 3 with Au(tht)Cl in a 1:1 and 1:2 molar ratio, respectively. These complexes have been fully characterized by analytical and spectroscopic techniques as well as quantum chemical calculations. The molecular structure of dinuclear complex 7 has been determined by single-crystal X-ray diffraction, showing a gold-gold interaction of 3.1825(3) A and a significant contraction of the 7-TH total dihedral angle. Au(I) complex 7 displays luminescence emission at room and low temperature in diluted solution and in the solid state. Quantum chemical calculations show that the luminescence emission at room temperature is primarily due to slightly perturbed fluorescence emission from purely ππ* excited states of the conjugated helicene scaffold. At 77 K phosphorescence emission is displayed as well. Preliminary studies on the use of 6 and 7 as catalysts in typical Au(I)-catalyzed cycloisomerizations have demonstrated the reactivity of these systems in the intramolecular allene hydroarylations and the hydroxycarboxylation of allene-carboxylates.
- Cauteruccio, Silvia,Loos, Annette,Bossi, Alberto,Blanco Jaimes, Maria Camila,Dova, Davide,Rominger, Frank,Prager, Stefan,Dreuw, Andreas,Licandro, Emanuela,Hashmi, A. Stephen K.
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p. 7995 - 8004
(2013/08/23)
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- Pronounced solvent effect on the hydrostannylation of propargylic alcohol derivatives with nBu3SnH/Et3B at room temperature
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The solvent is key: A general protocol is described for the hydrostannylation of propargyl alcohol derivatives at room temperature using Et3B/O2 as the promoter (see scheme). Rate and mechanistic studies point to a different autoxidation product of Et3B in THF than is observed in benzene, the typical solvent. Copyright
- Oderinde, Martins S.,Organ, Michael G.
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supporting information
p. 2615 - 2618
(2013/03/14)
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- A mild and efficient rhenium-catalyzed transfer hydrogenation of terminal olefins using alcoholysis of amine-borane adducts as a reducing system
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[ReBr2(NO)(CH3CN)(PTA)2] (PTA = 1, 3, 5-triaza-7-phosphaadamantane) catalyzes the alcoholysis of ammonia-borane and amine-boranes and the catalytic transfer hydrogenations of various terminal olefins. Excellent yields were achieved at 70 °C in isopropanol using tBuOK as a co-catalyst affording TOF values up to 396 h-1.
- Dong, Hailin,Berke, Heinz
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experimental part
p. 1803 - 1808
(2011/06/19)
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- Triorganyl- and diorganyloxozirconium hydridoborates - Synthesis and structures
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The reactions of Zr(OBu)4 and Zr(OEt)4 with H 3B·THF in THF led to HB(OR)2 and B(OR)3, but no zirconium tetrahydroborate [(RO)4-nZr(BH4) n] could be isolated. On the contrary, the reactions of [tBu 3CO]4-nZrCln and [tBu3SiO] 4-nZrCln with LiBH4 generated the tetrahydroborates [(RO)3Zr(BH4)] and [(RO) 2Zr(BH4)2]. These can be used to produce by hydroborate exchange dihydridodiorganyl borates [(RO)4-nZr(H 2BC8H14)n] and byproducts. The structures of the new zirconium hydridoborates have been determined by X-ray crystallography. Compound [(tBu3CO)3Zr(H 2BC8H14)] shows site-disordered dihydroborate units with agostic Zr-H-C interactions, while [(tBu3SiO) 2Zr(H2BC8H14)2] is quite symmetric (C2/c). The corresponding tetrahydridoborates possess in most cases μ31-bonded ZrH3BH groups. Compounds of the type [(RO)4-nZr(BH4)n] were obtained from the reaction of(RO)4Zr (R = Bu, Et) with H 3B·THF or that of (RO)4-nZrCln(n = 1, 2; R = tBu3C, tBu3Si) with LiBH4. Boryl group exchange with H2BC8H14- leads to (RO)4Zr(H2BC8H14)n with agostic Zr-H-B bonding when n = 1, whereas a symmetric ZrH2B compound results when n = 2. Copyright
- Knizek, Joerg,Noeth, Heinrich,Schmidt-Amelunxen, Martin
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p. 5548 - 5557
(2012/02/04)
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- Catalyst-free alcoholysis of phosphane-boranes: a smooth, cheap, and efficient deprotection procedure
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Catalyst-free alcoholytic deprotection of borane-protected phosphorus compounds offers a smooth, efficient, and clean alternative to existing deprotection methods. In this paper we report our results on the general applicability of deprotecting phosphane-
- Van Overschelde, Michel,Vervecken, Elias,Modha, Sachin G.,Cogen, Simon,Van der Eycken, Erik,Van der Eycken, Johan
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experimental part
p. 6410 - 6415
(2009/12/09)
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- Practical and efficient procedure for the in situ preparation of B-alkoxyoxazaborolidines. Enantioselective reduction of prochiral ketones
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A new method for the in situ elaboration of B-alkoxyoxazaborolidines is presented. Their use in the enantioselective reduction of prochiral aromatic ketones provides excellent chemical and optical yields of chiral alcohols.
- Ponzo, Viviana L.,Kaufman, Teodoro S.
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p. 495 - 496
(2007/10/03)
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- Convergent synthesis of alpha -aryl- beta -ketonitriles
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The present invention relates to processes for the production of alpha -aryl- beta -ketonitriles, which serve as synthetic intermediates in the preparation of a series of biologically important molecules such as corticotropin releasing factor (CRF) receptor antagonists.
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- Molecular addition compounds. 15. Synthesis, hydroboration, and reduction studies of new, highly reactive tert-butyldialkylamine-borane adducts
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Two series of tert-butyldialkylamines have been prepared and examined for borane complexation. The complexing ability of each amine in the two series examined decreases in the order shown. First series: t- BuN(CH2CH2)2O 1a > t-BuNEt2 1b > t-BuNPr(n)21c > t-BuN(CH2CH2OMe)2 1d >> t-BuNBu(i)2 1e. Second series: t-BuNBu(i)Me 2a > t-BuNPr(i)Me 2b > t- BuNBu(i)Et 2c > t-BuNBu(i)Pr(n) 2d >>t-BuNPr(i)Et 2e. The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. The following amines form highly reactive liquid borane adducts hydroborating 1-octene in tetrahydrofuran at room temperature in less than 1 h: t- BuN(CH2CH2OMe)2, t-BuNBu(i)Et, and t-BuNPr(i)Me. The limit of borane complexation among the amines examined is reached for t-BuNBu(i)2 exchanging borane neither with BMS nor with BH3-THF. Among the various borane adducts prepared, the more promising borane adducts, t-Bu(CH3OCH2CH2)2N-BH3 (7), t-BuMePr(i)N-BH3 (8), and t-BuEtBu(i)N-BH3 (9), were selected for complete hydroboration and reduction studies. Hydroboration studies with the new, highly reactive trialkylamine-borane adducts 7-9 and representative olefins, such as 1-hexene, styrene, β-pinene, cyclopentene, norbornene, cyclohexene, 2-methyl-2-butene, α-pinene, and 2,3-dimethyl-2-butene, in tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane, and dichloromethane, at room temperature (22 ± 3°C) were carried out. The reactions are faster in dioxane, requiring 1-2 h for the hydroboration of simple, unhindered olefins to the trialkylborane stage. Moderately hindered olefins, such as cyclohexene and 2-methyl-2-butene, give the corresponding dialkylboranes rapidly, with further slow hydroboration. However, the more hindered olefins, α-pinene and 2,3-dimethyl-2-butene, give stable monoalkylboranes very rapidly, with further hydroboration proceeding relatively slowly. The hydroborations can also be carried out conveniently in other solvents, such as THF, tert-butyl methyl ether, and n-pentane. A significant rate retardation is observed in dichloromethane. Regioselectivity studies of 1-hexene and styrene using these amine-borane adducts show selectivities similar to that of BH3-THF. The rates and stoichiometry of the reaction of t-BuMePr(i)N-BH3 in tetrahydrofuran with selected organic compounds containing representative functional groups were also examined at room temperature. The reductions of esters, amides, and nitriles, which exhibit a sluggish reaction at room temperature, proceed readily under reflux conditions in tetrahydrofuran and dioxane and without solvent (at 85-90°C). The carrier amines can be recovered by simple acid-base manipulations in good yield and readily recycled to make the borane adducts.
- Brown, Herbert C.,Kanth, Josyula V. B.,Dalvi, Pramod V.,Zaidlewicz, Marek
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p. 6263 - 6274
(2007/10/03)
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- Metal Tetrahydridoborates and Tetrahydridoborato metalates, 18. Preparation and Molecular Structures of Tetrahydrofuran, Diethylene Diglycol Dimethyl Ether and 18-Crown-6 Complexes of Strontium and Barium Tetrahydridoborate
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The srontium and barium tetrahydridoborate complexes M(BH4)2 * 2 diglyme and M(BH4)2 * 18-crown-6 (M = Sr, Ba) have been prepared from the solvates M(BH4)2 * 2 THF by ligand displacement. 11B-NMR and IR data reveal strongly polar bonding of the BH4(-) groups to the metal centers, and X-ray structural analyses of the diglyme and crown ether compounds show molecular units in which the BH4(-) group is in contact via three H atoms with the metal center.In contrast, M(BH4)2 * 2 THF compounds are chain polymers in the solid state, and each metal center is surrounded by 2 THF molecules in trans position and four BH4(-) groups each of which forms bridges with two metal centers.Estimations of the effective radius for the BH4(-) group indicate a high polarity for the M-BH4 interaction. - Key Words: Strontium bis(tetrahydridoborate)-2 tetrahydrofuran, chain polymer of/ Strontium bis(tetrahydridoborate)-bis(diglyme) / Barium bis(tetrahydridoborate)-bis(diglyme) / Strontium bis(tetrahydridoborate)-1,4,7,13,16-hexaoxacyclooctadecane / Metal-hydrogen-boron briges
- Bremer, Mathias,Noeth, Heinrich,Thomann, Martina,Schmidt, Martin
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p. 455 - 460
(2007/10/02)
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- Preparation of phenylalkyl ethers and phenyl esters from benzenediazonium tetrafluoroborate with alkoxytrimethylsilanes and trimethylsilyl esters
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Sonication assisted reaction of benzenediazonium tetrafluoroborate with alkoxytrimethylsilanes and trimethylsilyl esters gives phenylalkyl ethers and phenyl esters, respectively, with trialkyl(aryl) borates as byproducts. The scope of the reaction, experimental conditions and proposed mechanism are discussed.
- Olah,Wu
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p. 204 - 206
(2007/10/02)
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- Organosubstituted 2,5-Dihydro-1,2,5-oxoniasilaboratoles - Characterization and Reactivity
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The potassium salt of the anions , prepared from the organosubstituted cis-2-boryl-1-silylalkenes 1a-d and KOH, react with the electrophiles R1Hal IV: ClElIV(CH3)3, ElIV = Si, Ge, Sn, Pb> to give the neutral five-membered ring compounds .On heating of 3H or 3Sn either ethyl migration occurs to yield the saturated diasteromers , or elimination of ethane takes place to give the unsaturated compounds .The reaction of 2 with ClPb(CH3)3 leads to 3Pb (11B-NMR), which exclusively form 5 with elimination of C2H5Pb(CH3)3.
- Koester, Roland,Seidel, Guenter,Wrackmeyer, Bernd
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p. 1003 - 1016
(2007/10/02)
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- Addition compounds of alkali-metal hydrides. 24. A general method for preparation of potassium trialkoxyborohydrides. A new class of reducing agents
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The generality of the synthesis of potassium triisopropoxyborohydride, stabilized toward disproportionation by storing over excess potassium hydride, was examined with seven additional organoborates of varying steric requirements. The reaction of trimethoxy- and triethoxyborane with potassium hydride proceeded readily at room temperature, but the products could not be stabilized by the presence of excess potassium hydride. Triphenoxyborane reacted readily, even at -10°C, and stabilization was achieved. Tri-sec-butoxy- and tricyclopentoxyborane required refluxing in THF for 12-24 h, and the products were stabilized over potassium hydride. Finally, the reactions of tris(2-methylcyclohexoxy)- and tri-tert-butoxyborane were even slower, requiring a number of days for completion. Both products were stabilized toward disproportionation over potassium hydride. Indeed, potassium tri-tert-butoxyborohydride was quite stable toward disproportionation without excess potassium hydride. The stereoselectivities of these reagents in the reduction of representative cyclic ketones were examined. The stereoselectivities varied in an erratic manner with the steric requirements of the alkoxy group and did not approach the stereoselectivities previously achieved with lithium tri-sec-butylborohydride and lithium trisiamylborohydride.
- Brown, Herbert C.,Cha, Jin Soon,Nazer, Behrooz
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p. 2929 - 2931
(2008/10/08)
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- Metall-Bor-Verbindungen, 13. Zur Synthese und Reaktivitaet einiger (Trimethylstannyl)borane
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The preparation of some amino(trimethylstannyl)boranes and their chemical properties are described.With Me3SnLi (Me = CH3) as a reagent only the synthesis of Me3SnB(NR2)2 (1a, b), Me3SnBCl(NR2) (2a, b), and (Me3Sn)2BNR2 (3b) was achieved.The stannylboranes Me3SnB(NR2)2 show astonishing thermal stability.Their Sn - B bonds are broken by hydrogen, the halogens, and chalcogens as well as by alcohols.HCl cleaves the B - N bond.
- Noeth, Heinrich,Schwerthoeffer, Ruediger
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p. 3056 - 3062
(2007/10/02)
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- Process for preparing aldehydes from oxirane compounds
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Aldehydes are prepared by reacting an oxirane compound with hydrogen peroxide in the presence of a boron compound.
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