32461-97-5Relevant academic research and scientific papers
Effect of alkyl group size on the mechanism of acid hydrolyses of benzaldehyde acetals
Belarmino, Alexanders T. N.,Froehner, Sandro,Zanette, Dino,Farah, Joao P. S.,Bunton, Clifford A.,Romsted, Laurence S.
, p. 706 - 717 (2003)
Hydrolyses of benzaldehyde acetals, PhCH(OR)2, are specific hydrogen-ion catalyzed when R = methyl, n-butyl, but with secondary and tertiary alkyl derivatives, R = i-propyl, s-butyl, t-butyl, t-amyl, hydrolyses are general-acid catalyzed. The Broonsted α values for both secondary and tertiary alkyl groups are in the range: α = 0.57-0.61. A simple iterative procedure was developed to estimate the individual rate constants for general-acid catalysis by the diacid and monoacid forms of succinic acid buffer. Plots of log kobs (at [buffer] = 0 M) against pH are linear for the secondary and tertiary acetals, and plots of log kH for the H3O+-catalyzed reaction, 13C and 1H chemical shifts, and 1JCH coupling constants against the Charton steric parameter, v, for alkoxy groups are linear. The second-order rate constant, kH, increases about 100-fold on going from R = Me to R = t-amyl, indicating the significant role of steric effects on reactivity. Steric effects upon 13C NMR chemical shifts and coupling constants indicate that increasing the bulk of the alkoxy moiety increases the electron density at the carbon reaction center, which accelerates hydrolysis. Analysis of the Jencks-More-O'Ferrall free energy diagram for the reaction provides support for concerted proton transfer and C-O bond breaking in the transition state for hydrolyses of benzaldehyde acetals with secondary and tertiary alkyl groups in contrast to specific hydrogen catalysis with R = Me and n-Bu. All our results are consistent with rate-determining acid hydrolysis of benzaldehyde dialkyl acetals to hemiacetal intermediates that breakdown rapidly to benzaldehyde.
Method for synthesizing bis-ether compound by catalyzing benzaldehyde through mixed type heteropoly acid
-
Paragraph 0015; 0016, (2017/05/18)
The invention discloses a method for synthesizing a bis-ether compound by catalyzing benzaldehyde through mixed type heteropoly acid. Benzaldehyde and an alcohol compound are used as raw materials and mixed type heteropoly acid is used as a catalyst, so as to conduct reaction to prepare the bis-ether compound, wherein the alcohol compound is methanol, n-butanol or ethylene glycol, the molecular formula of mixed type heteropoly acid is H20[P8W60Ta12(H2O)4(OH)8O236].125H2O, and mixed type heteropoly acid is formed by one tetrameric Ta/W mixed type heteropoly anion, 20 protons and 125 crystal water molecules. Prepared mixed type heteropoly acid has the strongest acidity in heteropoly acid known at present, and has higher acid catalytic activity due to the strong acidity.
A Ta/W mixed addenda heteropolyacid with excellent acid catalytic activity and proton-conducting property
Li, Shujun,Peng, Qingpo,Chen, Xuenian,Wang, Ruoya,Zhai, Jianxin,Hu, Weihua,Ma, Fengji,Zhang, Jie,Liu, Shuxia
, p. 1 - 7 (2016/08/12)
A new HPAs H20[P8W60Ta12(H2O)4(OH)8O236]·125H2O (H-1) which comprises a Ta/W mixed addenda heteropolyanion, 20 protons, and 125 crystalline water molecules has been prepared through ion-exchange method. The structure and properties of H-1 have been explored in detail. AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10?3?S?cm?1 (25?°C, 30% RH). Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite. Hammett acidity constant H0 of H-1 in CH3CN is ?2.91, which is the strongest among the present known HPAs. Relatively, H-1 exhibits excellent catalytic activities toward acetal reaction.
The gas phase 1,2-Wittig rearrangement is an anion reaction. A joint experimental and theoretical study
Sheldon, John C.,Taylor, Mark S.,Bowie, John H.,Dua, Suresh,Chia, C.S. Brian,Eichinger, Peter C. H.
, p. 333 - 340 (2007/10/03)
The migratory aptitudes of alkyl groups in the gas phase 1,2-Wittig rearrangement have been determined experimentally as follows. An anion Ph- -C(OR1)(OR2), on collisional activation, competitively rearranges to the two 1,2-Wittig ions PhC(R1)(OR2)(O-) and PhC(R2)(OR1)(O-)[R1 and R2 = alkyl and R1 2]. These two ions respectively eliminate R2OH and R1OH. The smaller alkanol is eliminated preferentially, indicating that R2 (the larger alkyl group) is migrating preferentially (observed tert-Bu > iso-Pr > Et > Me): a trend generally taken to indicate a radical reaction. However, a Hammett investigation of the relative losses of MeOH from R-C6H4--C(OMe)2 shows this loss decreases markedly as R becomes more electron withdrawing, an observation not consistent with a radical reaction. Ab initio calculations [at the CISD/6-311 + + G**//RHF (and UHF)/6-311 + + G** levels of theory] have been used to construct potential surface maps for the model 1,2-Wittig systems -CH2OMe→ EtO-, and -CH2OEt→PrO-. Each of these exothermic reactions involves migration of an alkyl anion. There are no discrete intermediates in the reaction pathways. There is no indication of a radical pathway for either rearrangement. It is proposed that the gas phase 1,2-Wittig rearrangement involves an anionic migration, and that it is not the barrier to the early saddle point but the Arrhenius A factor (or the frequency factor of the QET), which controls the rate of the rearrangement. Weak H-bonding between the alkyl anion and the oxygen of the neutral carbonyl species acts as a pivot in holding the molecular complex together during the migration process. This electrostatic interaction increases with an increase in the number of hydrogens able to H-bond to oxygen and with the number of equivalent ways this H-bonding can occur. The relative migratory aptitude of alkyl anions bound within these molecular complexes is tert-Bu- > iso-Pr- > Et- ? Me-, an order quite different from the migratory aptitudes of anions expected from thermodynamic considerations. This conclusion indicates that great care must be exercised in utilising thermodynamically derived migratory aptitudes to explain the course of a kinetically controlled reaction in the gas phase.
