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IJCA 33A(12) 1110-1112.Pdf Indian Journal of Chemistry Vol. 33A, December 1994, pp. 1110-1112 Synthesis and characterization of In a typical preparation, a clean, dry, three alkyl-l-naphthyl selenides and tellurides necked round bottomed flask equipped with a condenser, a magnetic stirrer and a nitrogen inlet K K Bhasin", Vijay Gupta, S K Gupta, K Sanan & R P Sharma was charged with magnesium (0.72 g, 31.6 mmol) Department of Chemistry, Panjab University, taken in 25 ml of anhydrous THF. l-Bromonaph- Chandigarh 160014 thalene was added dropwise with stirring and ref- luxing was contianued till the completion of the Received 20 December 1993; revised 12 May 1994; accepted 20 July 1994 reaction as indicated by the disappearance of mag- nesium. To the Grignard's reagent so prepared Alkylation of l-naphthylseleno/ telluromagnesium was added powdered selenium or tellurium metal bromide, obtained by reacting I-naphthylmagnesium (31.6 mmol) in small amounts over a period of 30 bromide with elemental selenium or tellurium in 1HF min so as to maintain a gentle reflux. The reaction or diethyl ether, yields bivalent alkyl-I-naphthyl sele- mixture was further refluxed for 2 h and later nides/tellurides in excellent yields. The compounds pre- cooled to O'C, To this was added haloalkane (31.6 pared have been characterized by elemental analysis, mmol) dropwise with stirring over a period of 30 IR, IH, 13C NMR and mass spectral studies. min and stirring was continued for another Sh. The reaction mixture was then hydrolysed with an Diorganyl selenides and tellurides find widespread aqueous solution of ammonium chloride. applications in organic synthesis":', organic super- The organic layer was separated and the resi- conductors'v' and photographic imaging". Recent- due extracted with ether (3 x 25 ml), The combined ly, we have reported the preparation and charac- organic layers were washed twice with water (50 terization of a number of symmetrical and unsym- mI) and dried over anhydrous magnesium sulph- metrical diorganyl selenides and tellurides, as well ate. The solvent was distilled off on a rota-evapor- as their organoselenium/tellurium (IV) deriva- ator and the residue distilled under reduced pressure, rives"!", In continuation of our work on the chem- when alkyl-l-naphthyl selenides/tellurides were istry of organochalcogens", we report in this note obtained in excellent yields. the preparation and characterization of alkyl-l- Br MgBr EMgUl' naphthyl selenides and tellurides. OO~OO ii 000 Experimental All experiments were carried out in a dry, oxy- EMgBr ER gen-free nitrogen atmosphere. Iodomethane was freshly distilled. THF was distilled under nitrogen OO~OO from sodium benzophenone immediately before 30- • E=5. or T. use. All melting and boiling points are uncorrect- ed. E = Se; R = CH3CH2CH2, 3a, CH3CH2CH2CH2, The ]H NMR spectra were recorded in CDCI3 3b using TMS as an internal standard on a Varian E = Te; R = CH3, 3c, CH3CH2CH2CH2, 3d, 390L spectrometer. The infrared spectra were re- CH3CH2(CH3)CH,3e. corded as neat mulls between KBr plates in the range 4000-400 em -] on a Hitachi 250-H IR spec- Conditions: (i)Mg, Et20/THF, reflux 3h, (ii) E, reflux trophotometer. The mass spectra were obtained 2h. (iii) RBr, stir 5h.: on a VG-70S 11-250J mass spectrometer. Carbon ClOH7SeCH2CH2CH3 (3a): Yield 80%; b.pt. and hydrogen were estimated microanalytically on 104°C/6 torr; IR (KBr): vc.Se•c 58{) em-I; IH a Perkin-Elmer 2400 analyser. Selenium and tellu- NMR (CCVTMS) 0.92 (t, 2H), 1.64 (m, 2H); rium were estimated by standard methods". 2.80 (t, 3H); 7.10-8.45 (m, 7H). ClOH7SeCH'lCH2CH2CH3 (3b): Yield 65%; b.pt. Synthesis of Alkyl-I-naphthyl selenides and 125°C/4 torr; m (KBr): vc-se-c 584 em - 1; 1H tellurides NMR (CCVTMS) 0.78 (t, 2H); 1.45 (m, 4H); General Procedure 2.75 (1, 3H); 7.10-8.45 (m, 7H). NOTES 1111 ClOH7TeCH3 (3c): Yield 80%; b.pt. 84°C/4 torr; were good both in dry diethyl ether as well as in I IR (KBr): VC-Te-C 522 cm- ; 'H NMR (CCI4/TMS) dry THF. However, for alkyl-I-naphthyl tellurides, 2.15 (s, 3H); 7.20-8.30 (rn, 7H). dry tetrahydrofuran was found to be a better sol- ClOH7TeCH2CH2CH2CH3 (3d): Yield 70%; b.pt. vent as compared to diethyl ether, where substan- I 180°C/4 torr; IR (KBr): VC-Te-C 520 cm- ; IH tial amounts of symmetrical products were ob- NMR (CCVTMS) 0.79 (t, 2H); 1.55 (m, 4H); tained alongwith the desired products. In fact, in 2_82 (t, 3H); 7_07-8.40 (m, 7H). diethyl ether an equilibrium is set-up between CtoH7TeCH(CH3)CH2CH3 (3e): Yield 85%, l-naphthyltelluromagnisium bromide, dinaphthyl b.pt. 128°C/4 torr; IR (KBr): VC-Te-C 522 crn "; IH telluride and bis(bromomagnesium) tellurides, NMR (CCVTMS) 0.96 (t, 3H); 1.59 (5H); 3.40 Te(MgBr)2· (m, IH); 7.12-8.40 (m, 7H). 2CIOH7TeMgbr s= (CIOH7hTe+ Te(MgBrh Results and discussion The precipitation of Te(MgBr)2 from the reac- A number of methods have been reported in tion mixture drives the equlibrium towards right in the literature for the preparation of unsymmetrical the above equation, giving higher yields of the selenides and tellurides. Most commonly used symmetrical products. However, this redistribution method involves the cleavage of diaryl diselenides reaction can be arrested substantially in THF and and ditellurides with alkali metals in THF and by lowering the reaction temperature. subsequent alkylation of the resulting aryl selenol- Invariably, it was found that the desired com- ate/telluroate anions, generated in situ, with a var- pounds were contaminated with the coupled pro- iety of alkylating agents 13-15. Employing the same ducts, which were removed by column chromatog- methodology, attempts to prepare unsymmetrical raphy on a small neutral alumina column eluted alkyl-l-naphthyl selenides and tellurides were not with n-hexane and/or benzene. met with success. It is because the complete clea- The compounds are viscous, high boiling oils vage of dinaphthyl diselenidel ditelluride could not be yellow in case of selenides and reddish yellow in achieved in THF/diethyl ether, even under rigo- case of tellurides, which are soluble in organic sol- rous conditions. Moreover, the starting material vents. These are stable for longer periods if kept dinaphthyl ditelluride which is obtained by the ae- in dark under dry nitrogen atmosphere. All the rial oxidation of l-naphthyltelluromagnesium bro- compounds were analysed by elemental analysis, mide afforded a poor yield. lR, IH NMR, J3C NMR- and mass spectral stud- ies. The infrared spectra of these compounds show a weak band - 580 em - I in case of selenides and ... (1) at '522-540 cm - I in the case of tellurides which has been assigned to E-Calky1 stretching frequency. The failure of the above approach led us to find All other bands show common features and are an alternative method for the preparation of the ti- consistent with the reported values for other tle compounds. Elemental selenium and tellurium organoselenidesl tellurides 16. has been found to react with I-naphthylmagne- The 'H NMR spectra revealed that the alkyl sium bromide, obtained by reacting magnesium protons in all these selenides and tellurides are with l-bromonaphthalene in diethyl ether or THF shifted to higher field and reflect the lesser desh- to give I-naphthylseleno/telluromagnsium bro- ielding effect of selenium! tellurium. mide, CtoH7EMgBr (E = Se/Te), which upon sub- The Be chemical shifts have been found to ref- sequent treatment with a suitable haloalkane gives lect total carbon atom electron density and are, unsymmetrical alkyl-J-naphthyl selenides/tellu- therefore, useful probes for the study of orga- rides. By using this sequence of reactions, we have nometallic compounds. Alkyl-l-naphthyl selenides been able to prepare a series of alkyl-l-naphthyl and tellurides follows the overall shift patterns si- selenides and tellurides in excellent yields. milar to that of monosubstituted naphthalenes and benzenes. The observed Be signals of the aromat- Conditions: (i) Mg, Et 0/THF, reflux 3h. (ii) E, 2 ic region can be quantitatively rationalized in reflux 2h. (ill) RBr, Stir 5h. terms of the influence of selenium/tellurium atom It was found that the choice of the solvent play- on the electron distribution within the ring. The ed an important role in the preparation of these com- tentative assignments were made with respect to pounds. The yields of alkyl-l-naphthyl selenides other closely related compounds. 1112 INDIAN J CHEM. SEe. A. DECEMBER 1994 An examination of the "C NMR spectral data Acknowledgement reveals that a large variation is found in the chem- One of us (VG) is thankful to the CSIR, New ical shifts of carbon atom C-1, to which seleniuml Delhi, for the award of a senior research fellow- tellurium atom is attached. The effect is more pro- ship. The financial support from DST, New Delhi, nounced in case of tellurium compounds 3c, 3d is gratefully acknowledged. and 3e compared to selenium compounds, prob- ably due to the difference in anisotropy, bond lengths and polarity of the Se - C and Te - C References bonds. Very large upfield effect for C-1 in tellu- 1 Goodman M M & Knapp F F, Organometallics, 2 (1983) 1106. rides namely 3c (1~5.78) and. 3d (115.58) and 3e 2 Petragnani N & Comasseto J V, Synthesis, (1986) 1; (1991) (116.0) as compared to 3d (132.19) and in 3b 793 & 897. (131.87), results from shielding of the more elec- 3 Engman L, Acc Chem Res, 18 (1985) 274. tropositive tellurium atom in comparison to seleni- 4 Williams J M, Beno M A, Wang H H, Leung P C, Emge um atom.
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