It seems like the distillation of asarone glycol (and possibly also the distillaion of the epoxide, if water is present) forms a crystalline by-product, which is a glycol dimer, and not solely 2,4,5-trimethoxyphenyl-2-propanone.
Asarone 1,2-glycol
Distillation of asarone 1,2-glycol (an oil) at 170-230°C/4 mmHg gives a red oil, which solidifies on standing. Through crushing the crystals under ether, a solid was left undissolved, which after recrystallization from alcohol melted at at 204-205°C, and had the molecular formula C24H32O8 [Could possibly be the 2,5-dimethyl-3,6-(2,4,5-trimethoxyphenyl)-1,4-dioxane cyclic ether]. Evaporation of the ether from which the dimer was separated gave an oil which partly crystallized, and after purification through its semicarbazone (mp 157-158°C), 2,4,5-trimethoxyphenyl-2-propanone (mp 47-48°C) was obtained. On heating asarone 1,2-glycol with acetic anhydride, the dimeric compound is formed in quantitative yield.
Asarone dibromide
To 5g beta-asarone in 20ml dry ether cooled to -20°C, there was added 4g Br2 in 6ml CS2 [Use another solvent, like ether or DCM]. Removal of the solvent gave 0.4 g of a crystalline dibromide (mp 82-83°C), while the main product remained as an oil. The same procedure on alpha-(trans)-asarone gave 7g of a solid dibromide (mp 82-83°C).
Reference: J. Chem. Soc. 1338 (1937)