the benzimidazole nucleus is commonly present in a large number of natural products as well as pharmacologically active compounds .
it shows a wide spectrum of biological and pharmacological properties such as antifungal , antimicrobial , anthelmintic [ 4 , 5 ] , antiviral [ 6 , 7 ] , topoisomerase inhibition   and anticancer activities . some of their derivatives are marketed as antifungal drug ( carbendazim ) , anthelmintic drug ( mebendazole and thiabendazole ) , antipsychotic drug ( pimozide )   and antiulcer agent ( omeprazole ) . owing to their interesting pharmacological properties ,
the most common method is direct condensation of 1,2-phenylenediamine and carboxylic acids [ 14 , 15 ] or their derivatives , that require strong acidic conditions and sometimes need high temperature or the use of microwave .
the other synthetic route involves a two - step procedure that includes the cyclo - dehydrogenation of aniline schiff 's bases , which are often generated in situ from the condensation of 1,2-phenylenediamines and aldehydes , followed by oxidation with stoichiometric amount of oxidants , such as mno2 , oxone , nahso3 [ 21 , 22 ] , i2/ki / k2co3/h2o   or catalytic use of can   and aikit-5 . more recently ,
there are very few reports involving solid supported catalyzed reaction for synthesis of benzimidazole derivatives .
jacob et al .   synthesized 1,2-disubstituted benzimidazoles by silica supported zncl2 catalyst that was found to be of poor yield .
patil et al .   developed a method for synthesis of 2-alkyl benzimidazoles using silica supported hbf4 .
paul and basu   described the synthesis of 1,2-disubstituted benzimidazoles by using silica gel soaked with fe2(so4)3xh2o . recently , kumar et al .   reported silica supported hclo4 catalyzed synthesis of benzimidazoles .
periodic acid is an easily available hypervalent iodine reagent which is used in the oxidation of various functional groups [ 32 , 33 ] .
however , there are no reported efforts for the synthesis of benzimidazoles by using periodic acid . in this paper
, we report an efficient and facile synthesis of 2-aryl benzimidazoles by using silica supported periodic acid ( h5io6-sio2 ) as a catalyst ( scheme 1 ) .
further , all synthesized derivatives were screened for anticancer activity against two cancer cell lines , namely , mcf7 and hl60 .
herein , we used unprecedented silica supported periodic acid ( h5io6-sio2 ) as catalyst for synthesis of 2-aryl benzimidazole derivatives . in our initial experiments ,
we choose 1,2-phenylenediamine ( 1  mmol ) and m - nitrobenzaldehyde ( 1  mmol ) as a model reaction for optimization of catalyst and reaction conditions .
the use of 20  mol% of h5io6 catalyst supported on silica resulted in 95% of desired product , 5  g in 15  min at room temperature ( table 1 , entry 1 ) .
inferior yields were obtained on lowering the catalyst loading at room temperature ( table 1 , entries 2 and 3 ) . even , on increasing temperature , the yield was not improved ( table 1 , entries 6 to 8) . in control experiments ,
the poor yields were found in the absence of h5io6 ( table 1 , entries 5 and 10 ) at room temperature and 60c even after prolonged time ( 10  h ) .
further , the reactions were carried out with only h5io6 without silica support at room temperature and 60c ( table 1 , entries 4 and 9 ) where the yield was not found to be more than 35% .
these results confirmed that h5io6 supported on silica significantly increased the efficacy of catalysts which may be attributed to the increase in available surface area .
thus , we found optimized conditions as the 1,2-phenylenediamine ( 1  mmol ) , aldehyde ( 1  mmol ) and h5io6 ( 0.20  mmol supported on silica ) in acetonitrile ( acn ) at room temperature .
feasibility of the methodology was examined for a series of aryl / heteroaryl aldehydes bearing electron donating as well as electron withdrawing groups under the optimized reaction conditions and corresponding products were obtained in good to excellent yields ( table 2 ) .
presence of electron withdrawing group in aldehyde system fastened the reaction ( entries 5f5h ) while opposite effect was observed for electron donating substituents and hindered aldehydes ( entries 5b and 5h ) .
we have not observed any remarkable change in the reaction time for the different substituted diamines .
the reaction underwent smoothly even with aldehyde bearing two functional groups ( entries 5c , 5h , 6c & 7c ) and afforded corresponding products in good yields ( entry 5h ) .
the reaction was carried out with substituted 1,2-phenylenediamine ( entries 6a6e and 7a7c ) and afforded 2,5-substituted benzimidazoles in moderate to good yields . using these reaction conditions exclusively formation of 2-substituted benzimidazoles
thus , table 2 illustrates generality and efficiency of this method for the synthesis of benzimidazoles .
we have also extended same methodology for the synthesis of bisbenzimidazole ( 8) derivative by using 1,2-phenylenediamine , aryl aldehyde ( 2  :  1 ) affording compound 8 in 80% yield ( scheme 2 ) . although the exact mechanism is not clear , a proposed mechanism for the formation of benzimidazole is shown in scheme 3 .
the actual oxidant is h5io6-sio2 and not sio2 as confirmed by our controlled experiments ( table 1 ) .
all the synthesized benzimidazoles were tested for their anticancer activity against two cell lines mcf7 ( human breast adenocarcinoma ) and hl60 ( human promyelocytic leukemia ) by mtt colorimetric assay using cisplatin as a standard anticancer drug .
the benzoyl substituted benzimidazole ( 7a7c ) showed the highest potency against two cell lines , while carboxyl substituted compounds ( 6a and 6b ) were moderately potent ( with the exception of 6c ) , as compared to unsubstituted benzimidazole ( 5a5c ) .
dichloro derivatives ( 5c and 6c ) exhibited more activity as compared to monochloro derivatives ( 5d and 6d ) against mcf7 and hl60 .
substitution of nitro group ( 5e5 g ) showed moderate and mostly similar effect for the given cell lines .
compound 5b with phenolic oh group ( ic50 27.63  m for mcf7 and 28.68  m for hl60 ) was comparable to 5h ( ic50 29.67  m for mcf7 and 26.52  m for hl60 ) which has additional methoxy group at p - position . replacing ring carbon of benzene ring with nitrogen atom as in 5i ( ic50 30.42  m ) showed better activity against mcf7 when compared with 5a ( ic50 35.67  m ) , but same compound did not show substantial difference in activity against hl60 .
bis - benzimidazole ( 8) was found to be more active for mcf7 ( ic50 17.45  m ) than hl60 ( ic50 30.69  m ) .
all the tested compounds are found to be more effective against both cell lines as compared to cisplatin .
we have developed a short and efficient method for the synthesis of 2-aryl benzimidazoles from 1,2-phenylenediamines and aryl aldehydes using h5io6-sio2 as catalyst .
the mild reaction condition , low cost , easy workup procedure and good to excellent yields as well as the scope for using wide substrates make our methodology a valuable contribution to the existing processes for synthesis of benzimidazole derivatives . among 18 derivatives , newly synthesized 5-substituted derivatives exhibited excellent activity against mcf7 and hl60 cell lines .
the current study provides better insight into the designing of more potent anticancer agents in the future .
thin - layer chromatography ( tlc ) was performed using 0.25  mm silica gel coated plates .
column chromatography was performed using the hexane : ethylacetate solvent and silica gel ( 60120  meshes ) .
h  nmr ( 300  mhz ) and c  nmr ( 75  mhz ) spectra were recorded on varian mercury instrument with dmso - d 6 or d2o as the solvents .
chemical shifts were reported in  unit ( ppm ) with reference to tms as an internal standard , and j values were given in hertz .
ir spectra were recorded on a shimadzu ftir 8400 spectrophotometer in kbr disc and expressed in cm .
elemental analysis was carried out with thermo - electron corporation chns analyzer flash - ea 1112 .
two cancer cell lines , mcf7 ( human breast adenocarcinoma ) and hl60 ( human promyelocytic leukemia ) , were obtained from national center for cell sciences , india .
mcf7 was cultured in dmem medium   while hl60 cells were cultured in a humidified atmosphere ( 37c , 5% co2 ) in rpmi1640 medium supplemented with 10% fetal bovine serum .
test compounds were evaluated for anticancer activity against two cancer cell lines using cisplatin as standard anticancer drug .
the compounds were evaluated in vitro at a concentration range of 10  m to 100  m .
100  l of cell suspension ( 5  10  cells ) were plated in 96-well plates and allowed to attach for 24  h. the compounds were dissolved in 0.5% dmso .
cells were exposed in triplicate wells to these derivatives at various concentrations for 48  h. after 48  h , 20  l mtt ( 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide ) solution ( 5  mg / ml ) was added to each well . after 1  h of incubation , the solution was centrifuged for 5  min under 4000  rpm , and the medium was discarded carefully .
the formazan precipitate was dissolved in dmso ( 200  l ) , then shaken by oscillator .
the absorbance at 570  nm was determined on a microplate reader ( bio - rad model 3350 , japan ) .
the absorbance values were used to calculate % inhibition at various concentrations and ic50 values .
h5io6 ( 2.50  g , 10.96  mmol ) was dissolved in 15  ml of hot water ( 70c ) in a 50  ml round - bottomed flask .
to the hot solution was added silica gel ( 230400  meshes , 10  g ) with vigorous stirring .
the resultant h5io6 ( resultant mixture contains 20  wt% of h5io6 ) supported with silica gel was dried in oven at 100c for 12  h to obtain a white free flow powder .
a mixture of 1,2-phenylenediamine ( 108  mg , 1.0  mmol ) , m - nitrobenzaldehyde ( 151  mg , 1.0  mmol ) in acetonitrile ( 3.0  ml ) was taken , and h5io6 ( 45  mg , 20  mmol% supported on silica 210  mg ) was added at room temperature .
after completion of the reaction ( monitored by tlc ) , filter the reaction mixture over celite .
the filtrate was evaporated under vacuum and subsequently dried to afford crude product which was purified by column chromatography using hexane / ethylacetate as eluent to afford pure benzimidazole 5 g ( 227  mg , 95% ) .  
a mixture of 1,2-phenylenediamine ( 216  mg , 2.0  mmol ) , p - phthalaldehyde ( 134  mg , 1.0  mmol ) in acetonitrile ( 3.0  ml ) was taken , and h5io6 ( 90  mg , 40  mol% supported on silica 420  mg ) was added at room temperature .
after completion of the reaction ( monitored by tlc ) , the reaction mixture was filtered over celite .
the filtrate was evaporated under vacuum and subsequently dried to afford crude product which was purified by column chromatography using hexane / ethylacetate as eluent to afford pure benzimidazole 8 ( 250  mg , 80% ) .
white solid ; mp 291293c ; ( lit . [ 21 , 22 ] mp 290 - 291c ) ; ir ( cm , kbr ) : 3044 , 1622 , 1587 , 1537 , 1458 , 1439 , 1407 , 1312 , 1274 ; h nmr ( 300  mhz , dmso - d 6 ) :  12.91 ( brs , 1h ) , 8.15 ( d , j = 7.0  hz , 2h ) , 7.557.47 ( m , 5h ) , 7.19 ( brs , 2h ) ; c   nmr ( 75  mhz , dmso - d 6 ) :  151.2 , 143.7 , 134.9 , 130.1 , 129.8 , 128.9 , 126.4 , 122.4 , 121.6 , 118.8 , 111.3 ; ( found : c , 80.39 ; h , 5.18 ; n , 14.38 .
cal for c13h10n2 : c , 80.42 ; h , 5.19 ; n , 14.42% ) .
[ 21 , 22 ] mp 236 - 237c ) ; ir ( cm , kbr ) : 3327 , 3057 , 2332 , 1635 , 1280 , 1037 , 840 , 729 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.21 ( brs , 2h ) , 8.07 ( d , j = 7.7  hz , 1h ) , 7.67 ( brs , 2h ) , 7.287.40 ( m , 3h ) , 6.997.06 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  158.0 , 151.7 , 131.6 , 126.2 , 122.7 , 119.0 , 117.1 , 112.5 ; ( found : c , 74.25 ; h , 4.78 ; n , 13.31 .
mp 275 - 276c ) ; ir ( cm , kbr ) : 3368 , 3297 , 1558 , 1431 , 1369 , 1265 , 1132 , 735 ; h nmr ( 300  mhz , dmso - d 6 ) :  12.90 ( brs , 1h ) ,
7.537.71 ( m , 5h ) , 7.207.29 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  146.7 , 143.1 , 135.0 , 134.0 , 132.3 , 130.5 , 128.3 , 122.8 , 121.6 , 119.2 , 111.6 ; ( found : c , 59.33 ; h , 3.05 ; n , 10.62 .
cal for c13h8cl2n2 : c , 59.34 ; h , 3.06 ; n , 10.65% ) .
287289c ) ; ir ( cm , kbr ) 3433 , 3055 , 1427 , 1273 , 1091 , 829 , 744 ;
h nmr ( 300  mhz , dmso - d 6 , ) :  13.00 ( brs , 1h ) , 8.23 ( d , j = 8.2  hz , 2h ) , 7.63 ( d , j = 8.5  hz , 2h ) , 7.54 ( d , j = 5.9  hz , 2h ) , 7.21 ( brs , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  150.2 , 143.7 , 134.5 , 129.1 , 129.0 , 128.1 , 122.4 , 118.9 , 111.5 ; ( found : c , 68.27 ; h , 3.95 ; n , 12.21 .
cal for c13h9cln2 : c , 68.28 ; h , 3.97 ; n , 12.25% ) .
[ 21 , 22 ] mp 299301c ) ; ir ( cm , kbr ) : 3335 , 2912 , 1602 , 1514 , 1435 , 1340 , 1103 , 856 , 746 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.39 ( brs , 1h ) , 8.388.27 ( m , 4h ) , 7.61 ( s , 2h ) , 7.227.20 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  148.8 , 147.5 , 142.7 , 135.9 , 127.2 , 124.1 , 124.0 , 122.8 ; ( found : c , 65.25 ; h , 3.75 ; n , 17.52 .
cal for c13h9n3o2 : c , 65.27 ; h , 3.79 ; n , 17.56% ) .
208210c ) ; ir ( cm , kbr ) : 3410 , 3078 , 2686 , 1525 , 1348 , 1078 , 972 , 746 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.07 ( brs , 1h ) , 7.968.04 ( m , 2h ) , 7.837.89 ( m , 1h ) ,
7.727.78 ( m , 1h ) , 7.607.63 ( m , 2h ) , 7.237.26 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  148.9 , 147.2 , 132.5 , 131.4 , 130.8 , 130.8 , 128.6 , 124.2 , 122.4 , 119.1 , 111.5 ; ( found : c , 65.26 ; h , 3.74 ; n , 17.53 .
cal for c13h9n3o2 : c , 65.27 ; h , 3.79 ; n , 17.56% ) .
yellow solid ; mp 205207c ; ( lit . [ 21 , 22 ] mp 205 - 206c ) ; ir ( cm , kbr ) : 3371 , 3088 , 1587 , 1518 , 1473 , 1429 , 1346 , 1274 ; h nmr ( 300  mhz , dmso - d 6 )  13.29 ( s , 1h ) , 9.01 ( s , 1h ) , 8.60 ( d , j = 7.6  hz , 1h ) , 8.32 ( d , j = 7.9  hz , 1h ) , 7.84 ( t , j = 7.9  hz , 1h ) , 7.72 ( d , j = 7.3  hz , 1h ) , 7.58 ( d , j = 7.4  hz , 1h ) , 7.25 ( t , j = 6.7  hz , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  148.9 , 148.2 , 143.5 , 134.9 , 132.3 , 131.6 , 130.5 , 124.0 , 123.1 , 122.0 , 120.7 , 119.1 , 111.5 ; ( found : c , 66.26 ; h , 3.75 , n ; 17.55 . cal for c13h9n3o2 : c , 65.27 ; h , 3.79 ; n , 17.56% ) .
yellow solid ; mp : 218220c ; ir ( cm , kbr ) : 3273 , 2926 , 1500 , 1450 , 1265 , 1033 , 910 , 736 ; h nmr ( 300  mhz , dmso - d 6 ) :  12.65 ( s , 1h ) , 9.31 ( s , 1h ) , 7.527.63 ( m , 4h ) , 7.137.19 ( m , 2h ) , 7.05 ( d , j = 8.2  hz , 1h ) , 3.85 ( s , 3h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  151.5 , 149.3 , 146.6 , 139.9 , 122.8 , 121.6 , 117.9 , 114.4 , 113.7 , 112.0 , 55.6 ; ( found : c , 69.91 ; h , 4.99 ; n , 11.65 .
cal for c14h12n2o2 : c , 69.99 ; h , 5.03 ; n , 11.66% ) .
yellow solid ; mp 218220c ; ir ( cm , kbr ) : 3057 , 2667 , 1595 , 1444 , 1315 , 1280 , 1122 , 850 , 744 , 615 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.11 ( brs , 1h ) , 8.72 ( d , j = 4.8  hz , 1h ) , 8.33 ( d , j = 8.1  hz , 1h ) , 8.02 ( t , j = 7.7  hz , 1h ) , 7.497.69 ( m , 3h ) , 7.217.24 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  151.2 , 150.1 , 148.3 , 138.3 , 125.6 , 123.6 , 122.0 , 116.2 ; ( found : c , 78.80 ; h , 4.60 ; n ,
21.51 . cal for c12h9n3 : c , 78.83 ; h , 4.65 ; n , 21.52% ) .
white solid ; mp 301303c ; ir ( cm , kbr ) : 3405 , 1680 , 1621 , 1450 , 981 , 770 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.18 ( brs , 1h ) , 12.79 ( brs , 1h ) , 8.19 ( m , 3h ) , 7 .
84 ( d , j = 8.5  hz , 1h ) , 7.63 ( d , j = 15.2  hz , 1h ) , 7.587.48 ( m , 3h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  193.2 , 167.8 , 153.5 , 134.5 , 130.4 , 129.5 , 129.2 , 129.0 , 128.5 , 126.7 , 124.6 , 123.6 , 117.1 , 114.6 ; ( found : c , 70.55 ; h , 4.24 ; n , 11.72 .
cal for c14h10n2o2 : c , 70.58 ; h , 4.23 ; n , 11.76% ) .
white solid ; mp 301303c ; ir ( cm , kbr ) : 3319 , 3059 , 1681 , 1633 , 1491 , 1261 , 1130 , 748 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.43 ( brs , 1h ) , 12.84 ( brs , 2h ) , 8.27 ( brs , 1h ) , 8.10 ( d , j = 7.2  hz , 1h ) , 7.90 ( brs , 1h ) , 7.72 ( brs , 1h ) , 7.43 ( t , j = 7.4  hz , 1h ) , 7.07 ( d , j = 8.6  hz , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  168.3 , 158.0 , 153.9 , 132.9 , 132.0 , 129.1 , 127.3 , 125.5 , 124.6 , 120.1 , 117.6 , 112.8 ; ( found : c , 66.16 ; h , 3.93 ; n , 10.09 .
cal for c14h10n2o3 : c , 66.14 ; h , 3.96 ; n , 11.02% ) .
white solid ; mp 304306c ; ir ( cm , kbr ) : 3171 , 1915 , 1668 , 1622 , 1433 , 1315 , 779 ; h nmr ( 300  mhz , dmso - d 6 ) : 13.12 ( brs , 1h ) , 12.64 ( brs , 1h ) , 8.288.17 ( m , 1h ) , 7.88 ( d , j = 7.6  hz , 1h ) , 7.727.57 ( m , 4h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  167.7 , 167.3 , 134.9 , 134.6 , 132.6 , 132.3 , 130.0 , 129.7 , 128.4 , 128.1 ; ( found : c , 54.71 ; h , 2.59 ; n , 9.14 .
cal for c14h8cl2n2o2 : c , 54.75 ; h , 2.63 ; n , 9.12% ) .
white solid ; mp 194196c ; ir ( cm , kbr ) : 3090 , 2821 , 1907 , 1676 , 1624 , 1425 , 1319 , 1026 , 947 , 835 , 731 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.30 ( brs , 1h ) , 12.77 ( brs , 1h ) , 8.19 ( m , 3h ) , 7.84 ( brs , 1h ) , 7.65 ( m , 3h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  167.8 , 152.4 , 135.0 , 129.1 , 128.4 , 128.4 , 124.7 , 123.8 , 122.4 , 119.9 ; ( found : c , 61.65 ; h , 3.31 ; n , 10.25 .
cal for c14h9cln2o2 : c , 61.66 ; h , 3.33 ; n , 10.27% ) .
yellow solid ; mp 272274c ; ir ( cm , kbr ) : 3338 , 2949 , 1699 , 1604 , 1514 , 1348 , 1213 , 853 , 774 ; h nmr ( 300  mhz , dmso - d 6 , ) :  13.38 ( s , 2h ) , 8.39 ( s , 4h ) , 8.20 ( s , 1h ) , 7.86 ( d , j = 8.1  hz , 1h ) , 7.69 ( d , j = 8.1  hz , 1h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  168.0 , 151.5 , 148.4 , 142.3 , 139.5 , 135.4 , 131.8 , 128.9 , 128.0 , 125.6 , 124.5 , 117.9 , 115.3 ; ( found : c , 59.32 ; h , 3.15 ; n , 14.81 .
cal for c14h9n3o4 : c , 59.37 ; h , 3.20 ; n , 14.84% ) .
yellow solid ; mp 221 - 222c ; ir ( cm , kbr ) : 3375 , 3061 , 1645 , 1572 , 1321 , 902 , 707 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.30 ( s , 1h ) , 8.20 ( d , j = 6.2  hz , 2h ) , 7.94 ( brs , 1h ) , 7.767.54 ( m , 10h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  195.5 , 138.0 , 132.0 , 130.9 , 130.4 , 129.4 , 129.0 , 128.3 , 126.6 , 124.2 ; ( found : c , 80.43 ; h , 4.65 ; n , 9.31 .
cal for c20h14n2o : c , 80.52 ; h , 4.73 ; n , 9.39% ) .
light yellow solid ; mp 227229c ; ir ( cm , kbr ) : 3298 , 3057 , 1919 , 1726 , 1614 , 1450 , 1294 , 981 , 786 ; h nmr ( 300  mhz , dmso - d 6 ) :  12.91 ( brs , 2h ) , 8.10 ( d , j = 8.1  hz , 1h ) , 8.08 ( brs , 1h ) , 7.817.75 ( m , 4h ) , 7.69 ( m , 1h ) , 7.58 ( m , 2h ) , 7.42 ( m , 1h ) , 7.087.02 ( m , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  196.5 , 158.0 , 154.3 , 138.3 , 133.0 , 132.8 , 131.9 , 130.0 , 129.0 , 127.4 , 135.3 , 120.2 , 117.7 , 113.0 ; ( found : c , 76.41 ; h , 4.42 ; n , 8.88 .
cal for c20h14n2o2 : c , 76.42 ; h , 4.49 ; n , 8.91% ) .
white solid ; mp 164166c ; ir ( cm , kbr ) : 3059 , 1734 , 1651 , 1431 , 1317 , 970,788 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.29 ( brs , 1h ) , 8.05 ( brs , 1h ) , 7.74 ( m , 3h ) , 7.707.64 ( m , 5h ) , 7.58 ( t , j = 7.6  hz , 2h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  195.7 , 148.9 , 137.8 , 134.8 , 132.6 , 132.0 , 129.9 , 129.4 , 128.3 , 120.0 ; ( found : c , 65.38 ; h , 3.25 ; n , 7.70 .
cal for c20h12cl2n2o : c , 65.41 ; h , 3.29 ; n , 7.63% ) .
white solid ; mp 245247c ; ir ( cm , kbr ) : 3061 , 1626 , 1440 , 1317 , 1118 , 966 , 846 , 740 ; h nmr ( 300  mhz , dmso - d 6 ) :  13.01 ( brs , 2h ) , 8.33 ( s , 4h ) , 7.61 ( s , 4h ) , 7.23 - 7.20 ( m , 4h ) ; c nmr ( 75  mhz , dmso - d 6 ) :  150.3 , 138.9 , 130.7 , 127.0 , 122.6 , 115.1 ; ( found : c , 77.31 ; h , 4.54 ; n , 17.98 .
cal for c20h14n4 : c , 77.40 ; h , 4.55 ; n , 18.05% ) .
 a new , efficient method for the synthesis of 2-aryl substituted benzimidazole by using silica supported periodic acid ( h5io6-sio2 ) as a catalyst has been developed . 
 the salient feature of the present method includes mild reaction condition , short reaction time , high yield and easy workup procedure . 
 the synthesized benzimidazoles exhibited potent anticancer activity against mcf7 and hl60 cell lines . 