Sec-Butyl 3-methylheptanoate

A solution of 40 g. (0.2 mole) of sec-butyl 3-methylheptanoate in 100 ml. of ethanol containing 18.5 g. (0.3 mole) of potassium hydroxide and 20 ml. of water is heated under reflux for 30 minutes (Notes 7 and 8). The cooled solution is diluted with 200 ml. of water and acidified by the addition of 60 ml. of concentrated hydrochloric acid. The organic acid is extracted with three 100-ml. portions of 1 1 benzene-ether, and the combined benzene-ether extracts are washed with 50 ml. of saturated sodium chloride solution. The resulting solution is filtered by gravity through a bed of anhydrous magnesium sulfate. After removal of solvents by distillation, 26-27 g. (90-94%) of 3-methylheptanoic acid, b.p. 116-117710 mm., d 1.4242, is obtained by distillation in a modified Claisen flask (Note 9). 

Recent investigations4 by the submitter have shown that the yield of sec-butyl 3-methylheptanoate is improved to 80-85% if 1.4 g. (1.4 mole% with respect to the Grignard reagent) of cuprous chloride (commercial grade, analytically pure) is added in seven portions during the course of the addition of the ester. 

Under usual Grignard conditions, n-butylmagnesium bromide adds largely 1,4 to sec-butyl crotonate to give sec-butyl 3-methylheptanoate in the yield indicated. ... 

The yields of 1,4-addition products from sec-butyl crotonate and Grignard reagents are improved by CuCl-catalysis provided that the catalyst is added to the Grignard reagent in small portions concurrently with the ester soln.— E n-Butylmagnesium bromide from n-butyl bromide and Mg in ether treated at 0 with ethereal scc-butyl crotonate and simultaneously with 1.4 mole-% CuCl in small portions over a period of 3 hrs. scc-butyl 3-methylheptanoate. Y 80 to 85%. F. e. s. J. Munch-Petersen and V. K. Andersen, Acta Chem. Scand. 15, 271, 293 (1961) cf. Org. Synth. 41, 60 (1961). 

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