Syntlsis of Alkali Metal Telluridesfnd Ditell Rides in THF and Their Rela Ive

Vol.Indian30A, Jou,nal.l\uly1991, of Chemistrypp. 632-634

note anew facile synthesis of various alkali metal ditell rides in THF and their rela ive tellurides and ditellurides and their reactivities reac .vities towards alkyl bromides' A towards altyl bromides in THF. SyntlSiS of alkali metal telluridesfnd conve- ient synthesis of dialkyl tellu ides Experimental and dialkyl ditellurides Tetrahydrofuran was distilled under nitrogen -- from sodiumjbenzophenone ketyl before use. K Bhasin*, Vijay Gupta & R P Sharma Selenium (LOBA) and other organic bromides were Debartment of Chemistry, Panjab University, used as recieved without further purifications. Chandigarh 160014 Lithium, sodium and potassium were cut into chips Receivdd 3 December 1990; accepted 7 February 1991 before use. IH NMR spectra were recorded on a Varian EM Lithiu , sodium and potassium reduce s oothly 390 L spectrometer. Mass spectra wer,e recorded on a elemental tellurium to telluride (Te'!-) and dit lluride VG-70 S 11-250 J mass spectrometer. All the (Ter) ani ns in the tetrahydrofuran, THF, mediu in the manipulations were carried out strictly in an presence catalytic amounts of naphthalene. The elative reactivitie of these alkali metal tellurides towar s alkyl atmosphere of nitrogen to prevent the oxidation of bromides ave been investigated and a number 0 dialkyl oxygen sensitive intermediates. tellurides . nd dialkyl ditellurides prepared in ood to excellent yields. The compounds prepar dare Preparation of alkali metal tellurides and ditellurides characteri ed by elemental analysis, 1H NM R a d mass In a typical preparation, a dry, three-necked, spectral s udies. round bottom flask equipped with a condenser, magnetic stirrer and nitrogen inlet was charged with Organot llurium compounds have ecome tellurium powder (3.58 g, 0.028 mol), anhydrous increasin Iy imporfant reagents and intermed ates in THF (25 ml), alkali metal chips (01.056 mol) and organic ynthesis 1- 3. This has stimulated great naphthalene (0.72 g, 0.0056 mol). The mixture was interest i developing convenient methods f their refluxed for 3-5 hr during which time the reduction preparat n. Commercially available tellu 'um is was complete. Deep red colour in the case oflithium, known t exhibit a low chemical reactivity due to off-white colour in the case of sodium and light brown surface xidation4. Synthesis of alkali metal colour in the case of potassium were observed during telluride M2Ten(whereM = alkali metal an n = I the preparation of alkali metal tellurides in THF. or 2) is li ited to use ofliquid ammonia and pro tic Similarly, alkali metal ditellurides were prepared solventsS-6• by reacting alkali metal with tellurium powder in I: I DMF molar ratio, exactly in the manner described above, M+nE 'M E with increased refluxing periods. Brownish-red 110°C, 1 hr 2 n colour in the case oflithium, light brown in the case of (M=Na, K; E=Se, Te; n=I,2) sodium and brown in the case of potassium were observed for alkali metal ditelluride. Direct Ikali metal reduction of tellurium as not been carr ed out in less polar solvent like THF altho• Synthesis oldialkyl tellurides and dialkyl ditellurides ugh Sand an et al.7 were successful in prepari g sod• (i) Synthesis of' clialkyl tellurides ium and otassium tellurides and ditellurides n high A dry, three-necked, round bottom llask equipped boiling, rotic solvents such as N,N-dimeth Iform• with a condenser, a magnetic stirrer and nitrogen inlet amide (DMF), hexamethylphospho amide was charged with tellurium powder (1.79 g, 0.014 (HMP A) and N-methylpyrolidinone (NMP) Rece• mol), anhydrous THF (25 ml), alkali metal chips ntly, De and et al. 8 have successfully used ltraso• (0.028 mol) and naphthalene (0.18 g, 0.0028 mol). The und ind ced electrochemical synthesis to repare mixture was relluxed for 3-5 hr during which time the chalcoge ide anions of the type Te~ -, TeZ -, S ~- and reduction was complete as indicated by the complete Sez- in HF, acetonitrile and DMF. consumption of tellurium. The reaction flask was then cooled to ODC in an ice-salt bath and alkyl organoteIn con lunuminu.ation compounds9 of our work- II, onwe the report chem~stry1m thIs ~f bromide (0.028 mol) was added dropwise with

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1·'1 I I 'I 1·;111 NOTES

Table I-Reactions of alkali metal tellurides and ditellurides in THF Te Alkyl halide Conditions Product Yield compound (%) Na2Te CH3CH2CH2CH2Br O·C, 40 min, stir (CH3CH2CH2CH2h Te 80 Na2Te2 CH3CH2CH2CH2Br IO·C, I hr, stir (CH3CH2CH2CH2h Te2 85 Li2Te2 CH3CH2CH2CH2Br OT, 30 min, stir (CH3CH2CH2CH2h Te2 90 Na2Te C6HsCH2Br O·C, 2 hrs, stir (C6HsCH2h Te 75 Na2Te2 U C6HsCH2Br O·C, Ihr, stir (C6HsCH2)2 Te2 75 Li2Te· C6HsCH2Br O·C, 40 min, stir (C6HsCH2h Te 85 K2Te2 C6HsCH2Br reflux, 2 hrs (C6HsCH2)2Te2 55 Li2Te CH30CH2CH2Br O·C, I hr, stir (CH30CH2CH2h Te 65 Li2Te2 CH30CH2CH2Br O·C, 20 min, stir (CH30CH2CH2h Te2 60 K2Te CH30CH2CH2Br reflux, 3 hrs (CH30CH2CH2h Te 40 Na2Te CH3CH20CH2CH2Br O·C, 2 hr, stir (CH3CH20CH2CH2)2 Te 35 Na2Te2 CH3CH20CH2CH2Br O·C, Ihr, stir (CH3CH20CH2CH2h Te2 55 LhTe2 CH3CH20CH2CH2Br O·C, 50 min, stir (CH3CH20CH2CH2h Te2 75 K2Te CH3CH20CH2CH2Br reflux, 2 hr (CH3CH20CH2CH2h Te 20 stirring. The mixture was filtered and the filtrate metal tellurides viz., Li2Te and K2Te which are deep stripped of solvent. The residue was pistilled under red, off-white and light brown suspensions reduced pressure to obtain pure dialkyl tellurides. respectively. Similarly, alkali metals react with In the case of dibenzyl telluride the light yellow oily tellurium in 1:1 molar ratio to give ditellurides viz., residue was crystallised from petroleum ether when Li2Te2, Na2Te2 and K2Te2, which are brownish red, yellow needles of dibenzyl telluride were obtained, light brown and brown suspensions respectively in m.p.53De. THF.

(ii) Synthesis of dialkyl ditellurides Naphthalene: M2Ten 2M+ nTe lHF, reflux A dry, three-necked, round bottom flask equipped with a condenser, a magnetic stirrer arid nitrogen inlet (M=Li, Na, K; n= lor 2) was charged with tellurium powder (1.79 g, 0.014 mol), anhydrous THF (25 ml), alkali metal chips It was found that reduction of tellurium with (0.014 mol) and naphthalene (0.18 g, 0.0014 mol). The potassium was always faster than reduction with mixture was refluxed for 3-5 hr during which time all sodium which in turn was faster than reduction with the tellurium was consumed and the reduction was lithium. Potassium melts considerably in refluxing complete. After the completion of reaction, the THF and this phase change may be responsible for temperature was lowered to ODe in an ic~-salt bath enhanced rate of tellurium reduction. Sodium is and alkyl bromide (0.014 mol) was added dropwise nevertheless most convenient reducing agent with stirring. The reaction mixture was filtered and followed by potassium and lithium. the filtrate stripped of solvent. The oily residue was The relative reactivities of these alkali metal distilled under reduced pressure to obtain dialkyl tellurides formed in situ, towards various alkyl ditellurdes. bromides have been investigated. A considerable In case of dibenzyl ditelluride the yellow residue difference in reactivities is exhibited by them in was crystallised from petroleum ether when dibenzyl THF. ditelluride was obtained as brown plates, m.p. 80De. Addition of an alkylating agent to the above prepared suspension of alkali metal tellurides yields Results and discussion the corresponding dialkyl tellurides, indicating that a Elemental tellurium is not reduced by lithium, species chemically equivalent to Te2 - has been sodium or potassium even after prolonged refluxing formed. Of all the tellurides studied, Li2Te has been in THF. However, reduction of tellurium to telluride found to be the most reactive followed by Na2Te and (Te2-) and ditelluride (Ter) anions can be easily K2Te as is evidenced by the reaction time and the achieved in the presence of a small amount of subsequent yields (Table I). naphthalene. Alkali metals react with tellurium in 2: 1 Similarly, alkylation of the alkali metal ditellurides molar ratio in THF to give oxygen-sensitive alkali affords dialkyl ditellurides in excellent yields

633 INDIANIJ CHEM, SEC A, JULY 1991

•• Ms Compounds" m.p. CC) or yield IH NMR CCI4/TMS in ppm ., b.p. CCjm Hg)b (%) 378 (M+)244248374188 54/10 85 1.63 (t, 6H); 2.63 (g, 4H) 406443276318313 Table 2:--Physical97-98/11 and analY~iral data of dialkyl90 tellurides0.96 (t, 6H); and dialkyl 1.20-1.92 ditellurides (m, 8H); 2.66 (t, 4H) 53 607590858070 3.98 (s, 4H); 7.20 (br, s, 10H) 93/0.576-78/6101/4 2.74 (t, 4H); 3.38 (s, 6H); 86/990-92/480126-128/4 3.73 (t, 4H) 1.18 (t, 6H); 2.77 (t, 4H); 3.52 (g, 4H); 3.72 (t, 4H) 1.63 (t, 6H); 3.03 (q, 4H) 0.93 (t, 6H); 1.15-1.92 (m, 8H); 3.16 (t, 4H) 4.23 (s, 4H); 7.22 (br, s, 101-;1); 3.24 (t, 4H); 3.43 (s, 6H); 3.73 (t, 4H) 1.17 (t, 6H); 3.33 (t, 4H); 3.55 (g, 4H); 3.76 (t, 4H)

a.b. Satisfa4toryUncorrlected analysis obtained.

studies of these alkali metal tellurides and ditellurides wing reactivity orders were obse ved for in situ in THF. ges the and formation tellurides ofTe3- towards anions alkyl in br Stlution. mides: Acknowldegement One of the authors (V Gupta) is thankful to the Li2Te2 Na2Te2 > K2Te2, and Li2Te > UGC, New Delhi, for financial assistance. K2Te. References This convenient preparation of alkal metal I The chemistry o{organic selenium and tellurium compounds. tellurid and ditellurides in the presence of atalytic Edited by S Patai and Z Rappoport (John Wiley & Sons, New amount of naphthalene, which acts as a soluble York), Vol I (1986) and Vol II (1987).· chargt: t ansfer agent, constitutes a novel me hod for 2 Irgolic K J, J organomet Chern, 203 (1980) 367. the pre ration of a variety of dialkyl tellur des and 3 Petragnani N & Comasseto J V, Synthesis, (1986) 1. 4 Chiang L V, Shu P, Holt D& Cowan D, )orgChem, 48(1983) dialkyl itellurides. Using the above meth dology, 4713 .. we have en able to prepare a number ofkn wn and 5 Klayman D L & Griffin T S, J Am.chern Soc, 95 (1973) 197. unkno , relatively stable, dialkyl telluri es and 6 Engman L, Organometallics. 5 (1986) 427. ditelluri es. The compounds prepared possess 7 Sandman D L, Stark J C. Acampora L A & Gagne P, disagre able smell. These were characte ised by Organometallics, 2 (1983) 549. 8 Gautheron B, Tainturier G & Degrand C, JAm ehem Soc, 107 element I analysis, IH NMR and mass pectral (1985) 5579. studies Table 2). 9 Bhasin K K & Gautam A, Phosphorus and Sulphur, 38 (1988) 211. 10 Sandhu A, Singh S, Bhasin K K & Verma R D, J.fluorine Chern, and hig purity of the products indicate it to be a 47 (1990) 249. _ useful ethod for such preparations, and to the best II Bhasin K K, Sharma R P, Gautam A, Khajuria R, Sandhu A &. ofThe our ~sek owledge, of experimental the present work paper up, reportsexcellett the yields first Verma R D, Proc Ind Naill Sci Acad, :55 (1989) 470.

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