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  Aug. 1, 2003  Vol.5 No.8 P.67 Copyright cij17logo.gif (917 bytes)

Synthesis, crystal structure and herbicidal activity of 1-benzoyl-3-(4,6- disubstitute - pyrimidine-2-yl)-thiourea derivatives

Xue Sijia, Duan Liping, Ke Shaoyong, Jia Liangbin 
(Department of chemistry, Shanghai Normal University, Shanghai,  200234, China)

Received June15, 2003; Supported by the Natural science of Shanghai (No. 2000D07)

Abstract This communication reports the synthesis, crystal structure and the herbicidal activity of 1-Benzoyl-3-(4,6-disubstitute-pyrimidine-2-yl)-thiourea. The structures of the five target compounds were determined by IR, 1H NMR and MS.
Keywords  crystal structure, herbicidal activity, 1-benzoyl-3-(4,6-disubstitute- pyrimidine-2-yl) -thiourea

Pesticides form a major proportion of the total agrochemicals production and usage. Approximately 4.5¡Á109 pounds of pesticides are used in a typical year only in USA[1]. Many acyl thiourea compounds have been widely studied for their insecticidal, antibacterial and pesticidal activities and promoting effect on plant growth[2-4]. These have attracted the attention of many investigators. A series of new 1-benzoyl-3-(4,6-disubstitute-pyrimidin-2-yl)-thioureas derivatives have been synthesized in this paper. Further, the crystal structure of Bdpt [1-Benzoyl-3-(4,6-dimethyl-pyrimidin-2-yl)-thiourea] were determined by X-ray and its herbicidal behavior were investigated.
    The synthesis route of these compounds is summarized by the equations below:

Target compound

a

b

c

d

e

X

CH3

CH3

CH3

Cl

Cl

Y

CH3

OCH3

OC2H5

OCH3

NC2H5

1. EXPERIMENTAL SECTION
1.1 Apparatus      
The structures of the synthesized compounds were characterized by IR, 1HNMR, MS. The IR spectra were recorded on a Jasco FT-IR spectrophotometer in the region 4000-400cm-1. The 1H NMR spectra were obtained on a Jeol FX-90Q spectrometer. All solids were dissolved in DMSO-d6 and TMS was taken as internal reference. MS spectra were performed on an HP-5988-A chromatograph-mass spectrometer. The melting points were determined on an XT4A melting point apparatus.
1.2 Reagents  
2-amino-4,6-disubstitute-pyrimidine was prepared by the literature method[5]. All other chemicals and solvents used were of AR grade.
1.3 Experimental Procedure 
Preparation of the Benzoyl isothiocyanate : A mixture of benzoyl chloride(2.81g,0.02mol), KSCN(1.96g,0.02mol) and 20ml of acetonitrile was refluxed with stirring for 1 hr, then filtered and the filtrate was not purified for the further reaction .During the course of reaction, the progress of reaction was controlled by TLC.
Preparation of the 1-Benzoyl-3-(4,6-dimethyl- pyrimidine-2-yl)-Thiourea : A solution of 2.2g(0.018mol) of 2-amino-4,6-dimethyl- pyrimidine in 20ml acetonitrile was added dropwise to the benzoyl isothiocyanate and stirred at ambient temperature. When the solution was added completely, the mixture was refluxed for 5 hr. The yellow precipitate (4.9g) was filtered off. And it is recrystallized from the mixed solvent of ethanol and chloroform (1:1). The yield of the product with m.p. 196-197oC is 85%.
Preparation of the single crystal of the target molecule : Its single crystal, suitable for X-ray analysis, grows from the mixed solvent of methanol and acetonitrile(1:2)by slow evaporation for 4 day.
1.4 Characterization Data for the Products               
Compound (a): Yield: 85%; m.p: 196-197oC; IR(cm-1):2900,3100(N-H),1710(C=O),1240(C=S),1600(C=N).1HNMR(d:ppm):2.40(s,6H,2CH3),6.72(s,1H,Py-5-H),7.42(m,5H,Ph-H). MS (m/z): 51(83), 77(97), 105(100), 149(89), 181(42), M+286(75).
Compound (b): Yield: 75%; m.p: 196-198oC; IR (cm-1): 2950,3150(N-H), 1720(C=O), 1240(C=S), 1600(C=N). 1HNMR(d:ppm):2.40(s,3H,CH3),3.92(s,3H,OCH3),6.28(s,1H,Py-5-H), 7.25(m,5H, Ph-H). MS (m/z): 51(74), 77(99), 105(100), 165(18), 197(5), M+302(7).
Compound (c): Yield: 87%; m.p: 182-183oC; IR (cm-1): 3000,3350(N-H), 1710(C=O), 1250(C=S), 1600(C=N).1HNMR(d:ppm):1.33(t,3H,OCH2CH3),2.52(s,3H,CH3),4.29(q,2H,OCH2CH3), 6.26 (s,1H,Py-5-H),7.49(m,5H, Ph-H). MS (m/z): 51(82), 77(100), 105(98), 181(26), 213(4), M+318(14).
Compound (d): Yield: 65%; m.p: 197-198oC; IR (cm-1): 3000,3150(N-H), 1720(C=O), 1230(C=S), 1600,1580(C=N). 1HNMR(d:ppm):4.10(s,3H,OCH3),6.64(s,1H,Py-5-H),7.50(m,5H, Ph-H). MS (m/z): 51(83), 77(99), 105(100), 185(11), 217(2), M+322(8), [M+2]+324(3)
Compound (e): Yield: 54%; m.p: 164-165oC; IR (cm-1): 2950,3150(N-H), 1710(C=O), 1240(C=S),1590(C=N).1HNMR(d:ppm):1.40(t,6H,N(CH2CH3)2),3.60(t,4H,N(CH2CH3)2),6.08(s,1H,Py-5-H),7.50(m,5H, Ph-H). MS (m/z): 51(81), 77(99), 105(100), 226(6), 258(2), M+363(4), [M+2]+365(1)

2. X-RAY CRYSTAL STRUCTURE DETERMINATION
A pale-yellow crystal of Compound (a) with dimensions of 0.507¡Á0.321¡Á0.220mm was mounted in a glass capillary and data were collected at 293K with a Bruker SMART platform ccd diffractometer crystal .Four different sets of frames were collected using 0.30 steps in w range from 2.15 to 28.26.The exposure time was 35 per frames and the detector to crystal distance was about 4.5 cm .The resolution of the data set was 0.84Å. The structure was solved with direct methods .All the non ¨Chydrogen atoms were refined anisotropically. The hydrogen atoms were placed in idealized positions and refined by using a riding method.

Figure 1 The crystal structure of 1-Benzoyl-3-(4,6-dimethyl-pyrimidine-2-yl)-thiourea

Crystallographic data: C14H14N4OS, Mr=286.35, triclinic, space group P¨©, a=8.2155(11), b=9.5026(12), c=9.9417(13), Z=2, V=697.21(16), Dc=1.364g/cm3, a=74.995(2)o b=76.774(2)o g=70.305(2)o £¬F(000)=300, R=0.0457, wR=0.0965. The crystal structure of 1-Benzoyl-3-(4,6-dimethyl-pyrimidine-2-yl)-thiourea is shown in Figure 1. The torsin angle C(2)-N(1)-C(1)-C(9), C(1)-N(1)-C(2)-N(2),C(3)-N(1)-C(2)-N(2) are near 180o,the deviations from this value are between ¨C3o and ¨C1o.The torsin angles C(1)-N(1)-C(2)-N(2)and O(1)-C(1)-C(9)-C(10) are near 0 o, the deviations are between ¨C7o and 3o .The data showed that the molecule is in a plane.

Figure 2 The packing crystal cell of target molecula

Data Figure2 demonstrates that the molecular structures form dimer compounds through intermolecular hydrogen bond .The bond carbonyl group C(2)=S form intramolecular hydrogen bond with N(2), whereas atom N(1) interacts with N(4) of the pyrimidine ring by intramolecular hydrogen . It should be stressed that these hydrogen bonds might possibly suggest the relation with herbicide activities by binding the site which block the transfer of electrons from the electron donor to the electron carriers.

3. HERBICIDAL EFFICIENCY
The preliminary biological tests showed that the Bdpt has excellent inhibitory activities against broad leaf (such as Amaranthus retroflexus L), meanwhile, it has part selectivity on monoctyledon plant(such as Echinochloa Crusgauis(L)).

Table 1. The Inhibition Percentage of Bdpt to kinds of weeds

Concentration
(gAIha-1)

species

Digitaria sanguinalis(L)Scop

Chenopodium Serotinum l

Chenopodium Serotinum l

Amaranthus retroflexus L

50

24.6

83.8

7.8

100

75

70.8

86.5

9.1

100

120

86.2

100

10.0

100

Acknowledgements  
The X-Ray measurements were undertaken by Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. The herbicidal efficacy was carried out by Institute of Plant Protection ,Shanghai Academy of Agricultural Science.

REFERENCES
[1] Laspelin A. Document 733-R-002, United States Environmental Protection Agency,1997.
[2] Noguchi T, Ohkuma K, Kosaka S. Proceeding of the 2nd International IUPAC Congress of Pesticide Chemistry, New York, 1972, 5, 263.
[3] Ramadas K, Svinivasan N. Synth. Commun, 1995, 25 (2D): 338.
[4] Lieb F, Philip U C. Chem. Plant Prot, 1994, 10: 189 (C.A.1995,122:153983k)
[5] Jin Shan Zhou, Si Jia Xue. J.Central China Norm.Univ.(Nat.Sci), 1999, 33(1): 233-237.

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