M-Bromobenzotrifluoride

Figure 26.2 Heat profile and conversion of the benzophenone hydrazone and of the hexylamine for a competitive amination reaction involving 3-bromobenzotrifluoride (0.5 M), benzophenone hydrazone (0.25 M) and hexylamine (0.25 M). Temperature 90°C.

Further, we examined the Heck reaction between w-butyl acrylate and 4-bromobenzotrifluoride 5 in the presence of 2 mol% Pd clusters in a singlevessel monomode m/w oven fitted with an infrared thermometer. 100% conversion with quantitative yield to the cinnamate was obtained after 5 min irradiation at 75 W/240 °C. We then repeated the reaction under conventional heating at 240 °C. After 3.5 min a black tarry gel formed. Extraction followed by GC analysis showed only cinnamate, but the tarry material (probably acrylate polymers/oligomers) could not be analysed. These experiments show that when clusters are present different results are obtained depending whether m/w heating or conventional heating is used. In principle, this could be the result of hot spots created on the metal clusters. 

Heck coupling using conventional heating. 4-bromobenzotrifluoride (0.5 mL, 495 mM), -butylacrylate (0.5 mL, 1.0 M), KOAc (approx. 3 equiv), and nanocluster suspension (0.5 mL, 10 mM) were sealed in a 5 mL glass tube and heated (240 °C, 3.5 min) in a water-cooled oven. Workup and analysis was performed as above. 

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