An official website of the United States government
Abstract Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high‐temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron‐demand dehydro‐Diels–Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations.
more »
« less
Microwave-specific acceleration of a retro-Diels–Alder reaction
A high-temperature retro-Diels–Alder reaction is accelerated by microwave (MW) heating to rates higher than expected based on Arrhenius kinetics and the measured temperature of the reaction mixture. Observations are consistent with selective MW heating of the polar reactant relative to other, less polar components of the reaction mixture.
more »
« less
- Award ID(s):
- 1665029
- PAR ID:
- 10198163
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 56
- Issue:
- 76
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 11247 to 11250
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Macroscopically homogeneous mixtures of p -nitroanisole ( p NA) and mesitylene (MES) can be selectively heated using microwave (MW) energy. The p NA solutes agglomerate into distinct phase domains on the attoliter-scale (1 aL = 10 −18 L), and these agglomerates can be MW-heated selectively to temperatures that far exceed the boiling point of the surrounding MES solvent. Here, a 1 : 20 mixture of p NA : MES is used as a mixed solvent for aryl Claisen rearrangement of allyl naphthyl ether (ANE). ANE itself does not heat effectively in the MW, but selective MW heating of p NA allows for transfer of thermal energy to ANE to accelerate rearrangement kinetics above what would be expected based on Arrhenius kinetics and the measured bulk solution temperature. This focused study builds on prior work and highlights 1 : 20 p NA : MES as a mixed solvent system to consider for strategically exploiting MW-specific thermal effects.more » « less
-
Abstract The coordinated, cooperative use of microwave heating with conventional heating can provide advantages in chemical synthesis. Here, heterogeneous mixtures comprising ionic, highly microwave‐absorbing organic reagents and nearly microwave‐transparent arene solvents are heated conventionally and/or with microwaves, resulting in faster and, in some cases, higher yielding reactions when the two heating methods are applied cooperatively as compared to either method independently. Control experiments in more polar arene solvents show no advantage of cooperative heating, consistent with selective microwave heating phenomena. The experiments are facilitated by reactor technology that regulates internal reaction temperature and coordinates the application of conventional and microwave heating. The positive outcomes in this initial exploratory system suggest that cooperative heating can offer benefits in other systems designed for selective microwave heating.more » « less
-
Reactions between tungsten alkylidyne [tBuOCO]W≡CtBu(THF)2 1 and sulfur containing small molecules are reported. Complex 1 reacts with CS2 to produce intermediate η2 bound CS2 complex [O2C(tBuC═)W(η2-(S,C)-CS2)(THF)] 8. Heating complex 8 provides a mixture of a monomeric tungsten sulfido complex 9 and a dimeric complex 10 in a 4:1 ratio, respectively. Heating the mixture does not perturb the ratio. Addition of excess THF in a solution of 9 and 10 (4:1) converts 10 to 9 (>96%) with concomitant loss of (CS)x. Both 9 and 10 can be selectively crystallized from the mixture. An alternative synthesis of exclusively monomeric 9 involves the reaction between 1 and PhNCS. Demonstrating ring expansion metathesis polymerization (REMP), tethered tungsten alkylidene 8 polymerizes norbornene to produce cis-selective syndiotactic cyclic polynorbornene (c-poly(NBE)).more » « less
-
Soy protein processing impacts the ice recrystallization inhibition activity of protein hydrolysatesAbstract Soy protein hydrolysates have demonstrated moderate ice recrystallization inhibition (IRI) activity, but the properties of the unhydrolyzed protein contributing to this activity are not well known. The objective of this research was to identify the main protein processing factors important to the varying IRI activities observed. Three possible modification reactions were applied to soy protein isolate (SPI): the Maillard reaction that can occur in soy flour before protein isolation, heat denaturation of the fully defatted protein, and heat denaturation of the protein with the presence of residual lipid, mainly polar phospholipids. These modified proteins were hydrolyzed by Alcalase protease (for 2 min) to produce hydrolysates, which were characterized by HPLC and FTIR to investigate how molecular weight (MW) and changes in secondary structure relate to IRI activity. A multilinear regression with the parameters of modification type, surface hydrophobicity, secondary structure profile, and average MW of the hydrolysates was used to investigate their roles in reducing ice crystal size. It was discovered that polar lipids present in the soy hydrolysate samples and MW were the only significant factors (p < 0.05) for IRI activity of SPI hydrolysates which had an ice crystal size reduction from 22.0% to 36.7%. This study demonstrates for the first time a protein hydrolysate‐phospholipid interaction can produce IRI active molecules.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0cc04584e
