Thin Layer Chromatographic Analysis of Some Mercaptoacetamides

J. llldlu ae... Soc., VoL LX, Jauua..,. 1983, pp. 47-48 Thin Layer Chromatographic Analysis of Some Mercaptoacetamides K. K. JAIN, S. BATBJA and C. S. BHANDARI Department of Chemistry, University of Rajasthan, J'a.ipur-802 004 Manusonpt rsCBt'IJBa16 May1980, acuptstl 28 Septembw 1982 ~:>CH(O) Thin layer chromatographic stndies or N·aryl substituted·2-mercapto acetamides bare been made using dlll'erent solvent systems. R1 values increases regularly with the increase In dielectric constant or the solvent in the order CHCI,> CH,COCH 1 > > CH 1 0H. C HROMATOGRAPHIC studies of N-phenyl-2-mercaptoacetamide and its analogous have not been reported in literature. The present paper reports a method for the separation and detection of N-aryl mono substituted-2-mercaptoacetamides in microgram quantities on thin layer silica gel G using non-aqueous solvent systems. Experimental Apparatus and reagent : Standard Biochem TLC kit, supplied by Universal Biochemicals, Madurai, was used in running the chromatograms. All chemicals used were of analytical grade or purified by distillation as such or under reduced pressure. Preparation : N-Aryl mono substituted mercaptoacetamides were prepared by the method Their disulphides, (C 8 described ear1ier 1 ' 1 • H1NHCOCH11S)11, were prepared by the oxidation of corresponding mercaptoacetamides with iodine in aqueous-alcoholic solution. 2RSH+I 1 ~RS+2HI where R=C 8' H,( -p-X; where X=H or Cl)NHCOCH11. The crude was filtered and purified by crystallisation. Chromatographic procedure : Five plates (200 x 200 mm) coated uniformly with silica gel G (30 gjfO ml water ; thickness of the layer 250 mp) were air dried, activated by heating in an oven at 120• for 1 hr and cooled to room temperature (30•) before use. Alcoholic solution of the compounds (1-10 pg/ml) was used in spotting the spots on the plates with a micropipette. The spots were 10 mm apart and the size of a single spot was less than 3 mm in diam. These plates were placed in a developing tank saturated with the solvent and developed by ascending method until the solvent front bad travelled 100-150 mm. After marking the solvent front the plates were allowed to dry. The spots were identified in brown colour on exposing the plates to iodine vapour. The mean R, value for N-phenyl-2-mercaptoacetamide (compound 1 ; Table 1), taken as reference or standard, was obtained from three plates with six spots each. This mean value was regarded as fixed. The mean R 1 values of all compounds were obtained from three plates with six spots each. N-Phenyl-2-mercaptoacetamide was included on all plates as a standard. Relative R, values were thus obtained and corrected in terms of fixed value of the standard. Rr values were reproducible within ±0.02 R, unit. Results and Discussion Out of the various solvent combination studied the following were found to be most suitable : (A) benzene, chloroform and glacial acetic acid (85 : 10: S), (B) benzene, acetone and glacial acetic acid (85 : 10 : S), (C) benzene, isopropanol and glacial acetic acid (85 : 10 : S), and (D) benzene, methanol and glacial acetic acid (85 : 10: 5). Solvent systems without acetic acid did not yield good separation either due to trailing of the spots in some cases or to low R 1 values. The disulpbides (compounds No. 1 and 2 ; Table 2) had lower Rr values in comparison to the corresponding mercaptoacetamides (Table 1). This is possibly due to the fact that disulphide molecules are bulkier than simple mercaptoacetamides molecules. It was noticed that by changing the solvent in which mercaptoacetamides were soluble, the Rr values increased regularly with the increase in the dielectric constant of the solvent in the order chloroform ) acetone ) isopropanol methanol. > EQect of substitution on R1 values : Substitution of an electron withdrawing group in para or meta position of the phenyl ring, such as N0 1 decreases the Rr values. Conversely, an electron releasing 47 J. INDIAN CHBM. SOC,, VOL. LX, JANUARY 1983 Tnr.ll 1-TaiN La.YJUt CaJt.OMA~GliUBI Sl. No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. DA~ IIOR IvitRCA'PO:S~.MDJl (R-NHOOOH.SH) Oompcmnd R System A hRr hRs, System B hR,, hRr System 0 hRr hRst o.H. c.H.(p-F) c.H(p-CI~ C1 H 4 (p-Br CeH.(p-I) c.H,(p-NO.) C.H.(p-CH 1 ) o.H.(m-CI) C 0 H 4 ~m-N0 1) C1 H 4 m-CH,) C.H 4 (o-Cl) c.H,(o-CH 1 ) C1 H 4 (o-CCH 1 ) Solvent system A Solvent system B Solvent system C Solvent system D 30 27 30 33 35 21 31 33 23 30 40 52 52 49 52.5 51 47 100 100 94 101 98 90 104 100 92 98 135 92 119 100 102 93 107 100 90 104 104 93 102 127 95 115 55 56 100 51 57 110 55 117 49 70 57 103 54 57 110 52 77 48 51 100 51 56 133 70 70 48 52 38 127 62 63 Benzene, chloroform a.nd gla.cia.l acetic a.cid (85 : 10 : 5) Benzene, acetone a.nd gla.cia.l a.cetic acid (85 : 10: 5) Benzene, isopropanol and glacial a.cetic acid (85 : 10 : 5) Benzene, methanol and glacial acetic acid (85 : 10 : 5) 100 90 TABLB 2-THUI LAYBR Compound 1. (C.H.NHCOCH,S), 2. (0 6 H 4 (p-Cl) -NHCOCH,S], System A* hRr hR,, 13 -!3 13 43 C!IROMA~GJ.'B DA~ System D hRi - hR,, 64 63 62 62 60 57 66 65 58 63 76 61 74 100 98 97 97 94 89 103 102 91. 98 119 95 116 POll DISULPBIDJt!! System B hRr hR,, svtem c hRr hRst System D hRr hRst 14 15 14 15 16 18 27 29 26 27 25 28 *Solvent systems are the sa.me a.s in Table 1. group such as CH 8 , causes an increase in Rr values. Effect of halogen substitution is not clearly understood in terms of electromeric effect. However, Rr values increase in the order F ) Cl ) Br ) I in solvent A system (Table 1). The substitution of Cl, OCH 8 or CH 9 group in ortho position of the phenyl ring causes an increase in R, value in comparison to compound 1 possibly due to +M effect of Cl or OCH 11 group. Acknowledgement The authors are thankful to the Head of the Chemistry Department for facilities. (S. B.) and 4S (K. K. ·J.) are also thankful to C. S. I. R., New Delhi and University of Rajasthan, Jaipur, respectively for Research Fellowships. References 1. C. S. BBANDAJli, U. S. !.ABNO~ Prakt. Ohem., 1971, 313, 849. and N. C. SOGANI, J. 2. 8. BA'I'ltJA, (Miss) BATBY VllRMA, C. S. BKANDA:R.I and N. C, SoGANI,J. Prakt. Chem.,l979, 321,134,