Merck's 99.5% 2-methylpropanal (I), 200 g, was aldol-condensed (0.3-2 h, 40-125degreesC) over 0.01-0.08 mol calalyst/mol I (Table 1); the catalyst was aq. 15, 30, or 50% NaOH, or methanolic 20% CH3ONa, or 20% 2-MePrONa in 2-MePrOH. The condensates of 11 statistically designed syntheses were chromatographed on a FID-equipped Perkin-Elmer 9000 with an OV-17-impregnated 100/120-mesh Chromosorb WHP 1.8 m/3 mm column and the data (Table 2) were step-regressed on to show I to yield optimally 3-hydroxy-2,2,4-trimethylpentyl 2-methylpropionate (II) at 0.04 mol aq. 15% NaOH catalyst/mol I, 60degreesC, and 120 min; the yield and selectivity of II were 71% and 91% resp. Crude II was distilled to remove I. Physical property data on pure II were very close to those of a commercial product.