Hydroxide Ion Initiated Reactions Under Phase Transfer Catalysis Conditions: Mechanism and Implications. New Synthetic Methods (62)

Abstract

The development of Phase Transfer Catalysis (PTC) represents a major step forward in the employment of many organic reactions and renders them very convenient and useful processes. These reactions involve the application of nucleophiles in general, anions and bases in particular, in reactions carried out in a water‐organic solvent system. They can be performed both in the laboratory and on an industrial scale. The ease of application of PTC processes is the main reason for their increasing utilization in industry. An outstanding achievement of this technique is the employment of aqueous bases in reactions which traditionally would otherwise require a strong base in a nonaqueous medium. The classical procedures that require severe anhydrous conditions, expensive solvents and dangerous bases such as metal hydrides and organometallic reagents are now replaced by aqueous solutions of, e.g., sodium or potassium hydroxides (PTC/OH processes). In contrast to the extensive synthetic applications of PTC/OH systems, the detailed mechanisms of these processes have been the subject of a great deal of controversy and various mechanisms have been suggested. However, it would seem that our knowledge concerning the mechanistic aspects of such reactions has now reached the stage where it can be used to advantage in synthesis planning. A better understanding of the various factors which influence the reaction would undoubtedly help to optimize PTC/OH processes such as to enable higher yields in shorter reaction times at lower temperatures. The importance of, inter alia, the catalyst will be pointed out and it is highly recommended that such catalysts be always available in the laboratory, for the range of organic reactions that they can efficiently, conveniently and safely catalyze is vast indeed.

Quantification of phenolic metabolites of environmental chemicals in human urine using gas chromatography–tandem mass spectrometry and isotope dilution quantification

“…The quaternary salt, TBAHSO 4 , was used as the catalyst in a basic media (3N NaOH), which increases the rate of the phase transfer as previously reported by Rabinovitz et al [10] and fully observed in our results [6,7]. Also, we evaluated the efficiencies of the derivatization reactions at two temperatures (60 • C and 70 • C) and different reaction times from 30 min to 4 h. The optimal derivatization condition for most of the analytes was incubation for 1-h reaction at 60 • C. After derivatization, the reaction mixtures were cleaned using sorbent-immobilized liquid extraction instead of using formal liquid-liquid extraction coupled with silica gel cleanup, which enabled us to significantly reduce the amount of time required for the analysis.…”

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase-Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

“…PTC reactions that use aqueous bases to generate carbanions are termed hydroxide-initiated PTC. 30 The mechanism of hydroxide-initiated PTC reactions is an intensely investigated subject that has been thoroughly reviewed from both a chemical 31 and engineering 32 perspective. Pioneering studies by Makosza 33 and Starks 34 led to two distinct mechanistic descriptions, later termed the interfacial (Makosza) and extraction (Starks) mechanisms.…”

Ultrasound Methodology for the Synthesis of 2-(4-nitrophenyl)-phenylacetonitrile with Phase-Transfer Catalysis Condition ? A Kinetic Study

“…The free catalyst can, again, undergo the ion exchange at the interface. Rabinovitz et al [47] reviewed the interfacial mechanism of hydroxide ion initiated alkylation in presence of PTC. In view of the early results and observation, the mechanism for C-arylation of phenylacetonitrle with 1-chloro-4-nitrobenzene under liquid-liquid biphase condition involves the following steps: 1) The organic phase substrate phenyl acetonitrle is deprotonated at the interface by the aqueous phase NaOH and forming an ion-pair [Na …”