Process to prepare a trioxepane compound of the following formula (I) comprising less than 3.5 wt % of dialkyl peroxide based on the total amount of peroxides, said process comprising the steps of reacting a glycol compound of the formula R3CHOH—CH2—C(CH3)2OH with hydrogen peroxide in the presence of an acid to form a glycol hydroperoxide, purifying the glycol hydroperoxide, reacting the purified glycol hydroperoxide with a ketone or aldehyde of the formula R1R2CO in the presence of an acid to form the trioxepane compound, and purifying the trioxepane compound, wherein R1, R2, and R3 are independently selected from hydrogen and a substituted or unsubstituted hydrocarbyl group, with the proviso that if R1 and R2 are both methyl groups, R3 is not hydrogen. Initiator compositions comprising the so-prepared trioxepane compound are characterized by a high safe processing temperature in combination with a good crosslink efficiency.