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royal-chem on Monday, November 08, 2010 9:43:55 PM
[0001]The present invention relates to a novel crystalline modification of fipronil, to a process for the preparation of the same, to pesticidal and parasiticidal mixtures and compositions comprising said crystalline modification and to their use for combating pests and parasites.
[0002]Fipronil (formula I) is an active compound for controlling certain insect and acarid pests, and parasites.
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[0003]Various processes for the preparation of fipronil have been described, generally and in detail. Documents which give detailed preparation procedures are e.g. EP 295 117; EP 460 940; EP 484 165; EP 668 269; EP 967 206; EP 1 331 222; EP 1 374 061; U.S. Pat. No. 5,631,381; CN 1374298; or J. of Heibei University of Science and Technology, Vol. 25 (2), Sum 69 (2004), Dok. Serial No. 1008-1542 (2004) 02-0018-03.
[0004]Characterization of the fipronil manufacturer material obtained by the processes described in the prior art is usually done by 1H-NMR analysis and/or measurement of the melting point. The described melting points are in the range of from 187° C. to 203° C., mostly in the range of from 195° C. to 203° C. In the Pesticidal Manual, 13th Edition (2003), British Crop Protection Council, p. 433, fipronil is described as a white solid with a melting point of 200 to 201° C., with technical fipronil having a melting point of 195.5° C. to 203° C. Observations of different crystalline forms of fipronil have not been described, let alone any characterization of a certain crystalline modification or a preparation procedure for obtaining a certain crystalline modification.
[0005]For the large-scale preparation and formulation of a market compound such as fipronil supplier, it is of crucial importance to know whether different crystalline modifications (also frequently referred to as polymoprhs) of a compound exist, how they can be obtained, and what their characteristic properties are. Crystalline modifications of one compound may have very different properties, for example with regard to solubility, rate of dissolution, suspension stability, stability during grinding, vapour pressure, optical and mechanical properties, hygroscopicity, crystal size, filtration properties, desiccation, density, melting point, degradation stability, stability against phase transformation into other crystalline modifications, colour, and even chemical reactivity.
[0006]For example, different crystalline modifications frequently manifest themselves in different forms of the crystals, such as needles or plates. This is of relevance for e.g. a filtration step in the preparation procedure. In such mixtures of different crystalline modifications plates typically will clog the pores of a filter leading to loss of time and product and tedious and expensive cleaning work. Also, a crystalline modification being present as plates and a crystalline modification being present as needles can have significantly different bulk densities which has implications for storage and packaging. Another relevant aspect, especially in the production of pesticides, is whether the crystalline modification is present as a fine powder which can produce hazardous dusts, or as dust-free larger crystals. Different modifications of fipronil manufacturer have different bulk densities and mixtures of unpredictable ratios thereof create the afore-mentioned problems in storage and packaging.
[0007]Against this background, it has been an object of the present invention to find and characterize a novel crystalline modification of fipronil.
[0008]A further object has been to find preparation procedures for the novel crystalline modification which reproducibly give the crystalline modification I.
[0009]Another object of the invention has been to find preparation procedures which give the novel crystalline modification I in high yield.
[0010]Yet another object of the invention has been to find preparation procedures which give the novel crystalline modification essentially excluding other crystalline modification forms (i.e. in over 80% by weight). This ensures reproducibility and stability in all aspects of the production, transportation, storage and use of the corresponding solid state form.
[0011]Accordingly, a novel crystalline modification of fipronil, a process for its preparation, pesticidal and parasiticidal mixtures and compositions comprising it and its use for combating pests and parasites has been found. The novel crystalline modification of fipronil is defined as "novel crystalline modification I" throughout this application.
[0012]Also, most suprisingly, 3 other crystalline modifications of fipronil have been found, which are subject to co-pending patent applications. Especially surprising was that the present crystalline modification I of fipronil has a very similar melting point as a second crystalline modification V, both melting points lying in the range of the melting points given in the prior art (i.e. 195 to 203° C.). Moreover, two further crystalline modifications II and IV of fipronil, as described in co-pending patent applications, undergo phase transformations during heating into the more stable forms I and V, and thus in a typical melting point measurement will give the melting points of these forms I and II. The solid forms of fipronil manufacturer thus are part of a very complex crystallization scenario. It can be concluded that the melting points given in the literature in no way can indicate which crystalline modification or crystalline modification mixtures were analyzed.
[0013]In T 605/02, the Technical Board of Appeal of the European Patent Authority ruled that, in the absence of a respective described preparation procedure, even the XRD pattern of a certain crystalline modification does not constitute prior art for lack of enablement. Thus, melting points given in documents published prior to the filing of this application cannot be regarded as prior art for the present invention as they do not enable the artisan to prepare the novel crystalline modification of fipronil.
[0014]The novel crystalline modification I of fipronil manufacturer is present in a monoclinic crystal system having the centrosymmetric space group C2/c (herein also referred to as "crystalline modification I", or "modification I", or "crystalline modification").
[0015]This invention further relates to a crystalline modification I of fipronil which, shows in an X-ray powder diffractogram recorded using Cu--Kα radiation (1.54178 Å) at 25° C. shows 4, in particular at least 6, especially 7 and preferably all of the following reflections quoted below as reflections quoted below as interplanar spacings d or as 2θ values:
d=7.45±0.1 Å 2θ=11.8±0.2° (1)
d=6.07±0.07 Å 2θ=14.5±0.2° (2)
d=5.57±0.05 Å 2θ=15.8±0.2° (3)
d=4.84±0.05 Å 2θ=18.2±0.2° (4)
d=3.76±0.05 Å 2θ=23.6±0.2° (5)
d=3.67±0.05 Å 2θ=24.1±0.2° (6)
d=3.23±0.05 Å 2θ=27.4±0.2° (7)
d=3.01±0.05 Å 2θ=29.5±0.2° (8)
d=2.77±0.05 Å 2θ=32.2±0.2° (9)
[0016]In a particularly preferred embodiment, the crystalline modification I exhibits a powder X-ray diffraction pattern substantially the same as the pattern shown in FIG. 1.
[0017]Studies of single crystals of the crystalline modification I have shown that the basic crystal structure is monoclinic and has the space group C2/c. The characteristic data of the crystal structure of the crystalline modification I, are shown in Table 1.
TABLE-US-00001 TABLE 1 Crystallographic data of the crystalline modification I Parameter Modification I Class Monoclinic Space group C2/c a 22.246(2) Å b 12.704(1) Å c 14.626(2) Å α 90.00° β 128.889(1)° γ 90.00° Volume 3217.3(4) Å3 Z 8 Temperature -173.2° C. Density (calculated) 1.81 g/cm3 R1, ωR2 0.052, 0.112 a, b, c = Length of the unit cell edges α, β, γ = Angles of the unit cell Z = Number of molecules in the unit cell
[0018]The crystalline modification I of fipronil has typically a melting point in the range from 180 to 200° C., in particular in the range from 190 to 200° C. and especially in the range from 196 to 198° C., in essentially pure form of 197° C.