Catalysis of Organic..

Zoeller and Barnette 393tributyl amine can be dried by azeotropic distillation and reused in producing thenext batch of methyl pivaloylacetate. (Bu 3 N forms a minimum boiling azeotropewith water.) The resultant effluent from the reactor is a stream representing 1.5 molof innocuous NaCl resulting from the neutralization.In summary, compared with earlier processes which utilize hazardous solventsand generate large waste streams, the carbonylation of chloropinacolone offers anenvironmentally and operationally advantaged process since it requires (i) very littleexcess amine or methanol, (ii) no extraneous reaction solvents, (iii) little or noextraction solvent, and (iv) the tributylamine coreactant and methanol componentsare readily recycled. This was accomplished while also demonstrating similar yields,shorter reaction times, and higher product concentrations which result in a significantreduction in the number of batches and time required to produce significantquantities of methyl pivaloylacetate.Experimental SectionScreening Reactions.The following general procedure is typical for the screening reactions.To a 300 mL Hastelloy-B autoclave was added 110 mL (87.0 g, 2.71 mol) ofmethanol, 30.0 mL (23.3 g, 126 mmol) of tributyl amine, 11.0 mL (11.3 g, 83.8mmol) of 1-chloropinacolone, and 0.1 mmol of catalyst. The autoclave was sealed,flushed with carbon monoxide, and pressurized to 30 psi with CO. The autoclavewas then heated to 105°C and the pressure was adjusted to 80 psi. The temperatureand pressure were maintained using a continuous carbon monoxide feed for 3 h. Themixture was then cooled and analyzed by gas chromatography. Phosphine effectsand additional comparison were conducted at 150 psi of CO as noted in the tables.Catalyst Optimization.The following procedure is typical for optimizing the catalyst utilizing low catalystand methanol concentrations.To a 300 mL Hastelloy-B autoclave was added 31.0 mL (24.5 g, 765 mmol)of methanol, 90.0 mL (70.0g, 378 mmol) of tributyl amine, 33.0 mL (33.8 g, 251mmol) of 1-chloropinacolone, 14.0 mg (0.019 mmol) of [(cyclohexyl) 3 P)] 2 PdCl 2 , and28.0 mg (0.1 mmol) of tricyclohexylphosphine. The autoclave was sealed, flushedwith carbon monoxide, and pressurized to 30 psi with CO. The autoclave was thenheated to 120°C and the pressure was adjusted to 150 psi. The temperature andpressure were maintained using a continuous carbon monoxide feed for 3 h. Themixture was then cooled to yield a two phase reaction product. The entire productmixture (both layers) was diluted with 50.0 mL (39.55 g) of methanol to generate ahomogeneous mixture and analyzed by gas chromatography. Variations in theprocedure regarding temperature, pressure, catalyst levels (phosphine and Pd) areindicated in the tables and text.