Phase-transfer catalysts Methyltrioctylammonium chloride

As we have seen earlier in this chapter, metal catalysts may be made soluble in water by careful design of the ligands around them. Metal catalysed reactions may also be conducted under phase transfer conditions. Here, by contrast, the metal catalyst usually resides in the organic phase and not the aqueous phase. The use of a phase transfer catalyst in these systems may be to transfer a water-soluble metal catalyst into the organic layer, or else to ensure a supply of water-soluble substrate or reagent to a catalyst already resident in the organic phase. An example of the former is the use of methyltrioctylammonium chloride to extract aqueous RhCL... 

Synthesis of aldehydes and ketones.1 The carbanion of 1 can be generated by aqueous NaOH and can be alkylated with use of methyltrioctylammonium chloride as phase-transfer catalyst. A second alkylation is possible using NaH in DMF as base. The dialkylated product (3) can be hydrolyzed to a ketone by HC1 or H2S04 in CH3OH (equation I). 

When methyltrioctylammonium chloride is used as the phase-transfer catalyst, formation of 2-c/iZorohexane as a by-product is possible. Why would contamination of the desired 2-bromohexane by the chloro compound be a minor concern in this experimental procedure ... 

Arylselenocyclopropanes 6 were prepared from aryl chloromethyl selenides and alkenes in a solid-liquid phase-transfer catalytic system, under sonication. The best results were obtained using solid potassium hydroxide as the base, methyltrioctylammonium chloride as catalyst and the alkene as solvent ( 10 fold excess in respect to carbene precursor). 

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