Patent ID: 8383664

Claim:
A process for preparing a solid fipronil comprising at least 85% by weight of the crystalline modification I fipronil being present in the monoclinic system having the centrosymmetric space group C2/c and showing, in an X-ray powder diffractogram at 25° C., at least 5 of the following reflexes: d= 7.45±0.1 Å (1) d= 6.07±0.07 Å (2) d= 5.57±0.05 Å (3) d= 4.84±0.05 Å (4) d= 3.76±0.05 Å (5) d= 3.67±0.05 Å (6) d= 3.23±0.05 Å (7) d= 3.01±0.05 Å (8) d= 2.77±0.05 Å (9). said process comprising: i) preparing a solution of a solid form of fipronil being different from the crystalline modification I in a solvent S wherein the solvent S comprises acetonitrile, dimethylsulfoxide, or at least one benzene derivative B1; ii) effecting crystallization of fipronil; and iii) isolating the resulting precipitate, wherein the benzene derivative B1 is selected from the group consisting of ethyl benzene, n-propyl benzene, isopropyl benzene, diisopropyl benzene, n-butyl benzene, tert-butyl benzene, s-butyl benzene, iso-butyl benzene, and mesitylene; and wherein, when the solvent S is pure acetonitrile, the crystallization step ii) is conducted at temperatures below 40° C. and when the solvent S is pure dimethylsulfoxide, the crystallization step ii) is conducted at temperatures below 80° C.