Ohmic heating as a new efficient process for organic synthesis in water

Abstract

A new and efficient process for organic synthesis in aqueous media based on a direct ohmic heating reactor is described. Four representative organic transformations, a Diels-Alder cycloaddition, a nucleophilic substitution, an N-alkylation and a Suzuki cross-coupling reaction, were performed using this process. The results, when compared with those obtained under conventional external heating (oil bath) and microwave heating, showed that ohmic reactor allows faster and more uniform heating and an induced increase of dynamics/mobility of charged species leading in several cases to higher reaction yields and shorter reaction times. † Electronic supplementary information (ESI) available. See

Synthesis of Pyridyl and N‐Methylpyridinium Analogues of Rosamines: Relevance of Solvent and Charge on Their Photophysical Properties

“…The ohmic-heater reactor developed to perform chemical transformations [36] comprises the following elements:t he AC power supply; the signal generator; the heatingr eactor cell (50 mL glass vessel) containing one pair of stainless steel (316) rectangulare lectrodes (40 25 1mml ength/width/thickness) located at af ixed distance (23 mm);t emperature sensor (Ktype thermocouple);t he data logger system;P Cc omputer; data acquisition and control softwarep ackage;a nd it is identical to that previously described in the literature. [34,35] The AC voltage (VAC) rangesf rom 5t o1 00 VACa nd the typical working frequency is 25 kHz. The ohmic-heating system (reactor,i nstrumentation, data acquisition and control) is able to measure in real time, the temperature (8C), AC current intensity( IAC), AC voltage (VAC), workingf requency andt od erive the electric energy power( W), as wella st he electrical impedance of the reactor.T he experimentald ata was used to evaluate the efficiencyo famediumt ot ransfer the electric charge and used to define the VACv oltage applied in the setup (which was programmed/changeda long the experiment).…”

Influence of moderate electric fields on gelation of whey protein isolate

“…During heating phase and holding treatment, the MEF applied varied from 15 to 22 V cm -1 and 4 to 8 V cm -1 , respectively, whereas electrical frequency was of 25 kHz. At this high frequency, (25 kHz), electrochemical reactions at the electrode interface are reduced, thus minimizing potential corrosion and leakage of metals to the medium (Pataro et al, 2014;Pinto et al, 2013). Temperature measurement was performed as previously described for conventional heating.…”

Ohmic Heating: An Emerging Concept in Organic Synthesis

“…An electricalp rotection circuita voidsa ne lectrical short circuit, and includes am anual safety actuator that could be used to shut off the power input from the AC amplifiert ot he reactor and the reactor support is connectedt ot he ground ( Figure 5). [27,28] This ohmic heater is especially suitable for synthesis in aqueous media, where the reaction mediumi se lectrically conductive as in the case of aqueous solutionso fa cids, bases or salts. The application of this heating method to non-conductive media can be achievedb ya dding an adequate amount of as trong electrolyte such as NaCl.…”

“…[27] The ohmic heater developed to perform chemical transformations comprises all the elementsm entioned before:t he AC powers upply,t he signal generator, the heating cell containing the electrodes, the temperature sensor, the data loggers ystem and the computer (PC + software). [27,28] Some images of our www.chemeurj.org current prototypea re presented in Figure 5. One pairo fe lectrodes is fixed in ac over made of PEEK (polyether ether ketone), those shown in Figure 5w ere made of 316 stainless steel but we have others made of titanium.…”

“…To the best of our knowledge,t he first successful examples of the use of ohmic heatingi no rganic synthesis were reported by our group in 2013, [28] and in that field it can be considered as av ery recent and emergentr esearch topic. In order to test the ohmic heatera nd explore the benefits of this heatingp rocess, four representative reactions were selected:aDiels-Alder reaction, an ucleophilic substitution, an N-alkylation and aC ÀC cross-coupling reaction (Suzuki-Miyaura reaction) which were performed, in aqueous media, by using conventionalh eating (CH), microwavei rradiation( MW) and ohmic heating( WH), in the same scale and conditions, for comparison of the three heatingm ethods( Table 1).…”