Patent ID: 7553994

Claim:
A method for producing ditrimethylolpropane represented by the following formula 1: which has a melting point of 109° C., a phthalic acid resin color of 1.0, and a purity of 96 to 100%, the method comprising: a step of reacting n-butyl aldehyde and formaldehyde in the presence of a basic catalyst to obtain a reaction product solution; a step of extracting the reaction product solution with an organic extractant to obtain an extract; a step of distilling the extract to separate trimethylolpropane as a distillate and obtain a distillation still residue; and directly after said step of distilling, a step of adding an organic solvent to the distillation still residue in an amount of 0.6 to 10 times a weight of the distillation still residue, the organic solvent being at least one compound selected from the group consisting of acetone and methyl ethyl ketone, and a step of crystallizing said ditrimethylolpropane from the distillation still residue, in a single crystallization operation, which is only a single crystallization operation, at a crystallization temperature Y ° C. satisfying the following formula 3: 30≦ Y≦ 40 (3) for 1.5 to 2h, thereby crystallizing said ditrimethylolpropane having said melting point, said phthalic acid resin color and said purity, by only said single crystallization operation.