Abstract: A 3,5,5-trimethylhexanoic acid composition containing 3,5,5-trimethylhexanoic acid and t-butyl alcohol in which the t-butyl alcohol concentration in terms of toluene-d8 measured by gas chromatography-olfactometry/mass spectrometry after heating in an air atmosphere at 80° C. for four weeks under the conditions below exceeds 0 ppb by volume and is 400 ppb by volume or less is provided. The composition has low reproductive toxicity even after long-term storage: (Measurement Conditions) the 3,5,5-trimethylhexanoic acid composition is concentrated, and the concentrated sample is measured by gas chromatography-olfactometry using a column using dimethylpolysiloxane as a stationary phase, and the structure of a measured component is analyzed with a mass spectrometry detector.

Abstract: A method for producing 3,5,5-trimethylhexanal by allowing diisobutylene (DIB), carbon monoxide and hydrogen to react with one another in the presence of a cobalt-based catalyst, comprising: a step of allowing DIB to react with carbon monoxide and hydrogen in the presence of a cobalt-based catalyst until a convention of DIB reaches 50 to 85% (first stage reaction step); a step of separating unreacted DIB from a reaction product obtained in the first stage reaction step (unreacted DIB separation step); and a step of allowing the unreacted DIB separated to react with carbon monoxide and hydrogen in the presence of a cobalt-based catalyst (second stage reaction step).