Kinetics and Mechanisms of Dehydration of Secondary Alcohols Under Hydrothermal Conditions

Abstract

Alcohol dehydration by elimination of water is central to a series of functional group interconversions that have been proposed as a reaction pathway that connects hydrocarbons and carboxylic acids under geochemically relevant hydrothermal conditions such as in sedimentary basins. Hydrothermal dehydration of alcohols is an example of an organic reaction that is quite different from the corresponding chemistry under ambient laboratory conditions. In hydrothermal dehydration, water acts as the solvent and provides the catalyst, and no additional reagents are required. This stands in contrast to the same reaction at ambient conditions, where concentrated strong acids are required. Hydrothermal dehydration is thus of potential interest in the context of green chemistry. We investigated the mechanism of hydrothermal alcohol dehydration for a series of secondary alcohols using studies of kinetics and stereoelectronic effects to establish reaction mechanisms. The E1 elimination mechanism dominates over the corresponding E2 mechanism, with the E2 mechanism being competitive with E1 only for the most favorable stereoelectronically restricted alcohols included in the present study. These results are relevant to understanding the kinetics and product distributions of alcohol dehydration reactions in natural geologic systems and can guide the development of organic chemical reactions that mimic geologic organic reactions under laboratory green chemistry conditions.

Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering

“…For example, 100% conversion of n -butanol-1 was observed only at 330 °C and the products were propion and butyr aldehydes, butane and butyl butyrate [ 14 ]. This can be probably explained by the different alcohol polarization and, therefore, different sorption mechanism [ 59 ].…”

Lignin Cellulose Nanofibrils as an Electrochemically Functional Component for High‐Performance and Flexible Supercapacitor Electrodes

“…Under hydrothermal conditions, hydroxy, carbonyl, epoxy, and other oxygen‐containing moieties are removed from the surface of the GO nanosheets to obtain water‐dispersible rGO nanosheets. The mechanism of reduction is believed to be analogous to the H + ‐catalyzed dehydration reaction of alcohols to form alk(a)ene [50] . Briefly, superheated water acted as a source of H + , which reacted with −OH and other oxygen‐containing moieties at the edges and in the basal plane of the nanosheets [51] …”

“…LCNF and CNF (as a comparison) were prepared following previously reported protocols [30,32,50] . Red cedar bark was extracted with 1 % NaOH solution at 90 °C for 2 h. The wet bark residues were washed with excess hot water and 2 wt% of the residues were soaked in distilled water for 48 h. The residues were then fibrillated using a super mass colloider (MKZA10‐15J, Masuko Sangyo Co., Ltd., Japan) at 1500 rpm for 20 passes to obtain LCNF.…”

“…The weight concentration of LCNFs suspended in distilled water was determined by the gravimetric method. For the preparation of CNF, lignin was first removed via a chlorite treatment on the extracted and dried bark residues before undergoing the fibrillation step [50] . Briefly, 100 g of the bark residues was placed in distilled water (3200 mL), glacial acetic acid (10 mL), and reagent‐grade sodium chlorite (30 g).…”

Earth as Organic Chemist

“…When reaction (14.9) occurs in hydrothermal solution, it most likely follows a bimolecular elimination (E2) mechanism involving the alcohol and a molecule of H 2 O as shown in the lower panel, which is common for primary alcohols. In contrast, secondary and tertiary alcohols are likely to dehydrate in aqueous solution by unimolecular elimination (E1) mechanisms triggered by protonation of the hydroxyl group in the alcohol (Bockisch et al, 2018). Note that alkene products of dehydration differ depending on the structure of the parent alcohol.…”