Mechanisms of Formation of Hemiacetals: Intrinsic Reactivity Analysis

Abstract

The reaction mechanism of the hemiacetal formation from formaldehyde and methanol has been studied theoretically at the B3LYP/6-311++G(d,p) level. In addition to the study of the reaction between the isolated reactants, three different kinds of catalysis have been explored. The first one examines the use of assistants, especially bridging water molecules, in the proton transfer process. The second one attempts to increase the local electrophilicity of the carbon atom in formaldehyde with the presence of a Brønsted acid (H(+) or H(3)O(+)). The last one considers the combined effect of both catalytic strategies. The reaction force, the electronic chemical potential, and the reaction electronic flux have been characterized for the reaction path in each case. In general, it has been found that structural rearrangements represent an important energetic penalty during the activation process. The barriers for the reactions catalyzed by Brønsted acids show a high percentage of electronic reorganization contribution. The catalytic effects for the reactions assisted by water molecules are due to a reduction of the strain in the transition state structures. The reaction that includes both acid catalysis and proton assistance transfer shows the lowest energy barrier (25.0 kJ mol(-1)).

Catalytic (de)hydrogenation promoted by non-precious metals – Co, Fe and Mn: recent advances in an emerging field

“…This observation makes an important addition to the ADC and ester hydrogenation chemistry, as the non-catalysed hemiacetal formation or decomposition, often implied in the catalytic cycles throughout the field, is not necessarily a facile process that can be omitted. 180 The DFT-computed reaction pathway for Mn-promoted dehydrogenation (Scheme 19) features two steps that are energetically demanding. First one is the alcohol dehydrogenation sequence (Scheme 19, 1-EtOH -2-H, 17.9 kcal mol À1 ) leading to the aldehyde formation and generation of metal hydride aminopincer 2-H.…”

First Experimental and Theoretical Kinetic Study of the Reaction of 4‐Hydroxy‐4‐methyl 2‐pentanone as a Function of Temperature

“…Finally, the third phase, also the product phase between ξ 2 and ξ P , is associated with structural relaxation which leads to the products of the reaction . Note that ξ 1 < ξ TS < ξ 2 .…”

“…The second phase also known as the transition state phase involves chemical processes like bond cleavage and bond formation, largely associated with electronic reordering. Finally, the third phase, also the product phase between ξ 2 and ξ P , is associated with structural relaxation which leads to the products of the reaction [44,49,50]. Note that ξ 1 < ξ TS < ξ 2 [44].…”

“…The TS region (W 2 ) defines activation energy, which appears as a balance between structural and electronic effects. Besides, the structural and electronic processes can be determined from the relative weight of W 1 , W 2 in E # [44,51]. Table IV depicts the total activation energy E # and electronic partition energy (W) of each region.…”

A theoretical study of hemiacetal formation from the reaction of methanol with derivatives of CX3CHO (X = H, F, Cl, Br and I)

“…In the description of the mechanisms, the presence of a carbocation as intermediate was postulated. A study of the hemiacetal formation in the presence of Brønsted acids using conceptual density functional theory have been recently carried out in our group . The nucleophilic addition of ammonia to formaldehyde in the gas phase and in the complex with formic acid has been studied by Minyaev .…”