Harsh Thermal Conditions Research Articles

ChemInform Abstract: Benzo[b]fluorenes Formed in the Thermal Cyclization of 3-Ene-1,6-diynes.

A three-step preparation of the benzofluorene core is presented. The last step involves thermal cyclization of 3 -ene-1,6 -diyne (7) leading to the formation of four benzofluorene derivatives, one of which has been investigated by X-ray analysis. The harsh thermal conditions indicate that the cyclization of 7 might not proceed via a biradical intermediate as would be anticipated by a mechanistic proposal from Ueda.

Hydrothermal vent shrimps display low expression of the heat-inducible hsp70 gene in nature

The shrimp Rimicaris exoculata swarms over high-temperature chimneys at Mid- Atlantic Ridge hydrothermal sites, thriving in a mixture of hot vent fluid (350°C) and cold seawater (2°C). It may, therefore, be subjected to a thermal regime that is assumed to be stressful for animals. Evaluating the stress status of species in their natural environment is a key issue for understanding the thermal biology of metazoans. In the case of deep-sea species, attempts to quantify natural levels of stress proteins are obviously impaired by deleterious decompression effects during sampling. Here we quantified the heat shock protein (hsp70) mRNA expression of shrimps sampled at a depth of 2300 m and recovered at their native pressure. These shrimps were not heat-stressed, as witnessed by their very low level of heat-inducible hsp70, while an important response was evidenced after an experimental 30°C exposure. Our data also indicate that R. exoculata was nevertheless attracted by the temperature of fluid emission, and would deal with the harsh thermal conditions through micro- habitat selection close to its thermal preferendum (10 to 25°C).

On the Effect of Enhanced Mass Transfer on Side Reactions in Capillary Microreactors during High‐Temperature Synthesis of an Ionic Liquid

AbstractIn this work, the high‐temperature production of the imidazolium‐based ionic liquid 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) by means of micro reaction technology was investigated. This reaction is strongly exothermic and a two‐phase liquid/liquid system is formed. Heat and mass transfer limitations can, therefore, have a negative effect on product quality and reaction rate. Here we demonstrate that, even at harsh thermal conditions, the ionic liquid, [BMIM]Br, can be produced at high quality. Side product formation, which usually occurs at elevated temperatures, leading to strong discolorization, can be avoided by enhancing mass transfer in a capillary slug flow. This was done by adjusting the flow rate so that the reaction regime shifted from strongly mass transfer limited to kinetically controlled. Here, the Hatta‐number had been shown to be a suitable measure for defining the minimal flow rate. At 145 °C, [BMIM]Br could be produced continuously within a residence time of 1.3 min and at a space time yield of 1240 kg L–1day–1. This successful approach for continuous ionic liquid production with up to a thousand‐fold space time yield compared to batch processes could be easily transferred to other imidazolium‐based ionic liquids.

The Newman–Kwart Rearrangement of O‐Aryl Thiocarbamates: Substantial Reduction in Reaction Temperatures through Palladium Catalysis

Much cooler: The development of a catalyst for the Newman–Kwart rearrangement allows an escape from the harsh thermal conditions of the standard uncatalyzed reaction (see scheme). Mechanistic investigations, employing kinetic, isotopic labelling (2H, 18O, 34S) and DFT studies, suggest that the reaction proceeds through a five-centred Pd–S coordinated oxidative addition, with intermolecular exchange of aryl and thiocarbamate moieties through dimerization of the resting state.

Physiological tolerance to hyperthermia and hypoxia and effects on species richness and distribution of rockpool fishes of Loggerhead Key, Dry Tortugas National Park

Rockpools on Loggerhead Key in the Dry Tortugas National Park experience cyclic tidal changes in water quality and physical dimension resulting in ichthyofaunal assemblages that differ markedly from the adjacent coral reef. Within the beach rock formations and areas transitioning to the nearby reef, we observed 45 fish species; however, only four species – schoolmaster, Lutjanus apodus, French grunt, Haemulon flavolineatum, cocoa damsel, Pomacentrus variabilis, and frillfin goby, Bathygobius soporator – were found in all rockpools. All fishes were transient juveniles except for frillfin goby, which was a pool resident. High temperature tolerance, (Critical Thermal Maxima), and low oxygen tolerance, (Critical Oxygen Minima) for schoolmaster, French grunt, cocoa damsel, and frillfin goby were 40.9, 36.2, 37.6, 40.9 °C and 0.56, 0.77, 0.50, and 0.27 mg/L, respectively. All four species demonstrated thermal and hypoxia tolerance values similar to those published for species traditionally noted as abiotic specialists. Although fish distribution patterns in rockpools were likely influenced by structural complexity and spatial limitations, the relationship between pool morphology and species richness was weak, suggesting that physiological tolerance to high temperature and low oxygen among reef fishes may be more influential in determining which species inhabit the rockpools. Harsh thermal and oxic conditions that cannot be exploited by less tolerant species may be beneficial for some Loggerhead Key reef fishes in providing refuge from predators, foraging grounds, or potential nursery areas.

Benzo[b]fluorenes Formed in the Thermal Cyclization of 3-Ene-1,6-diynes

A three-step preparation of the benzofluorene core is presented. The last step involves thermal cyclization of 3 -ene-1,6 -diyne (7) leading to the formation of four benzofluorene derivatives, one of which has been investigated by X-ray analysis. The harsh thermal conditions indicate that the cyclization of 7 might not proceed via a biradical intermediate as would be anticipated by a mechanistic proposal from Ueda.