Reaction of tetrahydrofuran with sodium—cesium alloy: a model for lithium electrode surface reactions

Reaction of tetrahydrofuran with sodium—cesium alloy: a model for lithium electrode surface reactions

35, No 6 pi 1061-1063 1990 0 00134666,90 E300+000 1990 Pergamon Prm pk. REACTION OF TETRAHYDROFURAN WITH SODIUM-CESIUM ALLOY: A MODEL FOR LITHIUM ...

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35, No 6 pi

1061-1063

1990 0

00134666,90 E300+000 1990 Pergamon Prm pk.

REACTION OF TETRAHYDROFURAN WITH SODIUM-CESIUM ALLOY: A MODEL FOR LITHIUM ELECTRODE SURFACE REACTIONS MARK R BIELEFELD,~IOLET A CIPOLLA,CLARK T SAUNDERS ~~~JACQUELINEC SOLIS Department of Chemistry, The Umverslty of Dallas, Irvmg, TX 75062,U S A LEE ANN DAVIDSON,BRIAN HUGHES, SCOTT STEUBING,GREG WEST, JONI WEST and CLIFTON A YOUNG* Chemistry Department, Drury College 900 N Benton Avenue, [email protected],MO 65802, U S A (Recelued 7 August 1989) Abstract-Sochum-cesmm alloy was pernutted to react with tetrahydrofuran as a model for the htlnum electrode The products of tlus reactlon were treated with methyl bromide The NMR of the final products gves evidence that cleaved tetrahydrofuran reacts with more tetrahydrofuran to form denvatlves of Itself

Tetrahydrofuran and its methylated derlvatlves are of Interest as possible electrolyte solvents for secondary hthmm battenes[l+ It 1s known that hthtum reacts with tetrahydrofuran to a small extent formmg a surface coatmg on the hthmm Attempts have been made to ldentlfy the coatmg[5, 61 This ldentlficatlon 1s difficult because the amount of material that can be obtained 1s very small To get more material hthmm has been incubated with tetrahydrofuran at higher temperatures, different from actual battery storage condlttons We report here a closely related model system, the advantage of which 1s that we can get larger amounts of material under mild condltlons EXPERIMENTAL Mampulatlons were carried out m a boroslhcate glass vacuum system Materuzts

Cesmm was vacuum distilled to calibrated ampoules Tetrahydrofuran was drstllled under vacuum twice, first from calcium hydride and then from sodmm metal It was then vacuum distilled to cahbrated ampoules Reaction of tetrahydroforan wtth sodlum-cestum alloy

Quantltles are gven to show reactlon condrtlons No attempt was made to measure the amount of product 9 7 x 10M3mol (0 69 ml) of cesmm m a cahbrated ampoule and 1 55 x lo-’ mol (0 3558 g weighed m air) of sodium were vacuum dlstdled as completely as possible to a glass reaction container A calibrated breakseal ampoule contammg 0 147 mol (10 6 ml) of tetrahydrofuran had been sealed to that contamer The alloy formed from the sodium and cesmm remamed hqmd at room temperature The breakseal was broken and the tetrahydrofuran was

added to the alloy under, vacuum A deep blue color developed lmmedlately upon addition of the tetrahydrofuran to the alloy The mixture was permltted to react until no more blue solution would form on amtatlon and no liquid metal remained (approxlmately 34 months) Solid metal, however, did remam The reaction contamer was broken mto under vacuum by means of a previously attached breakseal The contents of the reaction contamer were permitted to react with methyl bromide untd all the sohd metal had apparently reacted to form metal bromides and ethane The reactmg methyl bromide gas was changed perlodlcally and discarded to remove the ethane Then all the volatde matenal was dlstdled off The proton NMR spectrum of the volatile matenal was Identical to that of tetrahydrofuran with an added smgle peak at 2 639 ppm which we attribute to dlssolved methyl bromide The reaction contamer was broken mto m air and the non-volatile reaction products were dissolved m water and carbon tetrachlorlde The water and carbon tetrachlorlde solutions were separated, and the solvents were vacuum dIstIlled from their respective extracts The dried water extract was m turn twice extracted wrth d&led tetrahydrofuran The tetrahydrofuran was vacuum dlstilled from thrs extract The tetrahydrofuran and carbon tetrachlorlde extracts were dissolved m a dlstdled dlethyl ether-water mixture and combmed The water and dlethyl ether solutions were separated The dlethyl ether was dIstIlled off under reduced pressure leaving behmd a yellow 011 Proton and 13CNMR spectra were taken of the yellow 011dissolved m deuterochloroform on an NT300 spectrometer (300 Mhz for proton and 75 5 Mhz for 13C) In both cases 5 mm sample tubes were used RESULTS AND DISCUSSION In thts model system we substitute other alkah metals or their alloys, which will react more readily with tetrahydrofuran, for hthmm

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When tetrahydrofuran was added to pure cesmm metal under vacuum no reaction was observed Immediately on mlxmg tetrahydrofuran with cesmmsodium alloy the previously observed metal solution was formed[fl Solubdlty of the alloy facthtated the reaction A salt conslstmg of a posltlvely charged metal ion and a negatively charged ion reaction product of tetrahydrofuran was formed This negatively charged product was allowed to react with methyl bromide In this way we isolated macroscopic amounts of matenal which could be handled m air In prmclple the location of the methyl group should enable us to locate the negative charge on the ongmal product We believe that this kmd of procedure can be used to Identify possible constituents of surface coatmgs on hthmm m other solvents By substituting for lithium a more reactive, or hqmd, or soluble, form of alkali metal, reaction can take place under mild condltlons slmdar to actual battery storage conditions Furthermore smce the reaction may take place m the bulk or at a constantly refreshed and/or liquid metal surface Impunties on the surface of the metal will not affect the reactlon as much Tetrahydrofuran has been observed to react three different ways under highly reducmg condltlons Proton abstraction has been observed to form ethylene and the enolate of acetaldehyde[8] In the presence of a strong lewls acid hydndlc reductton formed butanol after hydrolysls[9] Butanol was also formed after hydrolysis of an aromatic amon mediated reduction of tetrahydrofuran at 66°C for 8 h[lO] Denvltlsatlon has been observed where a negatively charged reducmg spectes bonds to a carbon on tetrahydrofuran thus transfermg the negative charge to the oxygen atom This has been observed to take place m the presence of strong Lewis aclds[ll] and Cu(I)[12] Under our condltlons ethane and ethylene would not be detected It ts unhkely that methyl vinyl ether

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(from ractlon of methylbromlde with the enolate of acetaldehyde) would be detected We would expect to detect but did not detect butyl methyl ether or methyl pentyl ether m the proton nmr of the volatile material The proton NMR spectrum of the yellow oil and its mtegratton are gven m Fig 1 We attnbute the peaks gathered at 1 ppm to alkyl CH, and CH, protons The shoulder at 15 to 2 ppm we attnbute possibly to branchmg, CH, protons We assign the peaks at 34 ppm to O-CH, and O-CH, protons The small peaks at 5-6 ppm may indicate the presence of small amounts of unsaturated matenal An even smaller peak was noted at 0 5 ppm which may be attnbutable to aldehyde The 13C spectrum IS very complmated, but can be interpreted m the same manner These are spectra of the mixture of products of this reaction We beheve that the coatmg on the hthmm electrode may also be a mtxture We are trymg to charactenze a mixture, not obtain pure product We believe that when tetrahydroforan 1sreduced by an alkali metal the rmg 1sopened and either a dlamon, or a monoamon free radical, is formed In either case our evidence indicates that the carbamon or carbon radical attacks another tetrahydrofuran molecule to form a denvatlve m the manner suggested by Mdlon and Lmstrumelle[12] and by EIS et al [1 l] The negative charge 1s left on the oxygen atom The absence of methyl pentyl ether makes It unlikely that the unobservable ethylene and methyl vinyl ether were present Our results are not m conflict with those of Aurbach et al [S] as a dlalkoxlde would gve essentially the same lr as a butoxlde We have no explanation for our failure to isolate a butoxlde derivative m contrast to Koch[6] As he points out, however, lmpurlties in the tetrahydrofuran were very influential m his reactions Our model (using different metals), may, however, be mcomplete for the hthmm system Other recent work suggests that the hthmm-tetra-

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Reactlon of THF with Na-Cs alloy hydrofuran system 1s very complex Stupak et al Cl33 have observed that specially punfied hthmm metal dissolves m tetrahydrofuran to form a hght blue solution This means that during electrodeposltlon both electromc conduction with solvated electrons and negative metal Ion conduction can lead to electrochemically Isolated metal deposits as has been observed[14] This latter problem may have serious lmphcatlons for other solvents of interest m alkah metal secondary battenes as these metal solutions appear to be ublqmtous[7,13,15,16] These and other solvents stable under reducmg condltlons could conceivable be of interest to hthmm battery chemists Furthermore Edwards has observed solutions of alkah metals m 1-methyl-2-pyrrohdmone and l-ethyl2-pyrrohdmone[ 171 Usmg techniques reported prevlously[lYj we have also observed fleeting blue solutions of sodmm m both of the above solvents and fleetmg dark blue solutions of sodium- potassium alloy m the second of the above solvents We have also observed fleetmg dark blue solutions of sodmmpotassium alloy m 1,3-drmethyl-3,4,5,6-tetrahydro-2pyrlmldmone and 1,3 dlmethyl-2-lmldazohdmone In conclusion we feel that m studymg alkah metal electrodes m various solvents allowance should be made for the posslblhty of different processes takmg place simultaneously m film forming reactions and m electrodeposltlon

REFERENCES

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Acknowledgements-We thank the John B O’Hara Chemical Sciences Institute of the Umverslty of Dallas and the Petroleum Research Fund of the American Chemical Society of financial support We thank Dr Hanna Gran, Dr Steve Pickup and Dr Tuck C Wong of the Umverslty of Mlssoun (Columbia) for valuable dIscussIons and for takmg the NMR spectra

K M Abraham and S B Brummer, m Lzthlum Battertes (Edlted by J P Gabano), p 391, Academic Press, New York (1983) S B Brummer, m L&mm Battery Technology (Edited by H V Venkatasetty), p lS9, John Wdey, New York (1984) V R Koch, .I Pr Sources 6,357 (1981) K M Abraham, m Ldwm (Edlted by R 0 Bach), p 155, John Wdey, New York (1985) D Aurbach, M L Daroux, P W Faguy and E Yeager, J electrochem Sot 135, 1863 (1988) V R Koch, J electrochem Sot 126, 181 (1979) J L Down, J Lewis, B Moore and G Wdkmson, .I them Sot, 3761(1959) R B Bates, L M Kroposkl and D E Potter, J org Chem 37, 560 (1972) W J Badey and F, Marktscheffel, .I org Chem 25,1797 (1960) J J Elsch, J org Chem 28, 707 (1963) M J EIS, J E Wrobel and B Ganen. J Am them Sot 106.3693 (1984) J Mdlon and G Lmstrumelle, Tetrahedron Lett , 1095 (1976) C M Stupak,T R Tuttleand S Golden,.! phys Chem 88,3804 (1984) V R Koch and J H Young, J electrochem Sot 125, 1371 (1978) C A Young and R R Dewald, .I them Sot, them commun, 188 (1977), C A Young, Ph D Thesis, Tufts University (1977) J C Thompson m The Chemtstry of Non-Aqueous Solvents, Vol 2 (EdIted by J J Lagowskl), p 265, Academic Press, New York (1967) P P Edwards, Umverslty of Cambndge, personal commumcatIon (1989), also J R Langan, K J Lm, G A Salmon, P P Edwards, A Ellaboundy and D M Holton, Proc R Sot (London) A421,169 (1989), A A H Kadhum, J R Langan, G A Salamon and P P Edwards, J radIoanal nucl Chem 101,319 (1986), A F Sowmsky and G M Whltestdes J org Chem 44, 2369 (1979)