Optimization-Based Approach to Process Synthesis for Process Intensification: Synthesis of Reaction-Separation Processes

Advancements in Optimization and Control Techniques for Intensifying Processes

Process Intensification (PI) is a vast and growing area in Chemical Engineering, which deals with the enhancement of current technology to enable improved efficiency; energy, cost, and environmental impact reduction; small size; and better integration with the other equipment. Since process intensification results in novel, but complex, systems, it is necessary to rely on optimization and control techniques that can cope with such new processes. Therefore, this review presents some advancements in the field of process intensification that are worthy of exploring in detail in the coming years. At the end, several important open questions that can be taken into consideration in the coming years are listed.

The Syntheses, Characterization and Crystal Structures of a Series of Heterocyclic β-Diketones and Their Isoxazole Compounds

BACKGROUND

In the field of coordination chemistry, the introduction of heterocyclic substituents into the structure of β-diketone enables ligand to produce multiple coordination sites. The adoption of small steric oxime group into the structure of heterocyclic β-diketone by Schiff-base condensation will further increase coordination sites and facilitate the generation of polynuclear structures.

OBJECTIVE

A series of β-diketones (2a-2c) containing different heterocycles such as pyridine, thiophene and furan and their corresponding isoxazole compounds (3a-3c) were synthesized.

MATERIALS AND METHODS

The Claisen condensations were investigated in a solvent-free rheological phase system at room temperature to obtain heterocyclic β-diketones 2a-2c, which further reacted with hydroxylamine hydrochloride to obtain heterocyclic isoxazoles 3a-3c. All these compounds were well characterized by EA, IR, 1H NMR and X-ray crystal diffraction to confirm the structures. Synthetic mechanisms of compounds and the effects of different heterocycles on reactivity were discussed deeply.

RESULTS

1H NMR indicated that these β-diketones do not exist as a total diketonic form but an equilibration between diketone and enol forms in CDCl3 solvent, in which the enol form accounts for 98.0% in 2a, 94.3% in 2b, 95.5% in 2c. While the crystal structures of 2a-2c showed that the reaction allows to isolate diketones in solid state. Crystal structures of 3a-3c showed that the neutral β-ketone oximes resonate and cyclize to form the target heterocyclic isoxazoles.

CONCLUSION

SN1 nucleophilic substitution mechanism of Claisen ketoester condensation was proposed for the syntheses of 2a-2c, and SN1 single molecule nucleophilic substitution reaction mechanism was put forward for 3a-3c.